Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Cellulose nanocrystals aqueous suspensions as water-based lubricants Shariatzadeh, MohammadJavad 2018

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
24-ubc_2018_september_shariatzadeh_mohammadjavad.pdf [ 3.05MB ]
Metadata
JSON: 24-1.0371189.json
JSON-LD: 24-1.0371189-ld.json
RDF/XML (Pretty): 24-1.0371189-rdf.xml
RDF/JSON: 24-1.0371189-rdf.json
Turtle: 24-1.0371189-turtle.txt
N-Triples: 24-1.0371189-rdf-ntriples.txt
Original Record: 24-1.0371189-source.json
Full Text
24-1.0371189-fulltext.txt
Citation
24-1.0371189.ris

Full Text

Cellulose Nanocrystals aqueous suspensions as water-based lubricants   by MohammadJavad Shariatzadeh  BSc, Sharif University of Technology, 2016   A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF APPLIED SCIENCE In THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES   (Mechanical Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August 2018 © MohammadJavad Shariatzadeh, 2018 ii  The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis/dissertation entitled:  Cellulose Nanocrystals aqueous suspensions as water-based lubricants   submitted by MohammadJavad Shariatzadeh in partial fulfillment of the requirements for the degree of Master of Applied Science in Mechanical Engineering   Examining Committee: Dana Grecov Supervisor  Jasmin Jelovica Supervisory Committee Member  Anasavarapu Srikantha Phani Supervisory Committee Member iii  Abstract Lubrication is an effective means of controlling wear and reducing friction. Friction and wear are the major cause of material wastage and loss of mechanical performance. To reduce the friction, most of the mechanical devices are lubricated by oils or in some cases by water. To enhance the properties of lubricants a chemical component or blend is added to improve their performance.  In this research, we have used Cellulose Nanocrystals (CNC) as additives in water-based lubricants. CNC is synthesized from native cellulose which is one of the most abundant biopolymer resource available. It has many advantages such as renewable, biodegradable and non-toxic. Tribological tests were performed on a pin on cylinder tribometer to investigate the application of CNC as water-based lubricants additives. The coefficient of friction and wear between a stainless-steel shaft and a chrome steel ball were measured in the presence of the CNC lubricant with different concentrations.  One of the applications were water is used as a lubricant is in gland sealed slurry pumps. Gland seals prevent pumped fluid from leaking into the environment. The gland seal packing material is tested with CNC lubricant to study the behavior of the new lubricant as a possible alternative of water in industrial applications. Effect of normal force, rotational speed and shaft diameter on the coefficient of friction and wear were studied as well. It was found that adding 2 wt.% of CNC in water improved lubrication and provided a very low friction coefficient of approximately 0.09. It reduces the wear depth and width by more than 50%. The improvement of the coefficient of friction and wear is mainly due to the high strength of CNC rods and alignment of CNC nanoparticles. iv  Lay Summary It is estimated that one-third of the world's energy resources in present use are needed to overcome friction in one form or another. Hence, any reduction in friction and wear can result in energy savings. Currently, water is used as a lubricant for some applications like lubrication of gland sealed pumps. It is environment-friendly, inexpensive, readily available, non-flammable and has high thermal conductivity. However, due to its low viscosity, corrosive properties, low boiling point, and high freezing point, it is unacceptable for most tribological applications. Additives are used to reduce the shortcomings and improve the water properties. In this work, the effect of adding Cellulose Nanocrystals (CNC) as additives to water is investigated. Tribology tests show that adding CNC particles to water can greatly improve the coefficient of friction and reduce wear.  v  Preface Dr. Dana Grecov performed the identification and design of this research project.  For all chapters, I completed all research, experimental work, and analysis. Part of the results in chapter 4, which are related to gland seal packing material was published as a conference paper at the 20th International Conference on Tribology Technology held in Toronto, Canada in June 2018:  MohammadJavad Shariatzadeh, Dana Grecov, “Cellulose Nanocrystals Suspensions as Water-Based Lubricants for Slurry Pump Gland Seals” at 20th International Conference on Tribology Technology, June 21-22, 2018, Toronto, Canada. In addition, a journal paper is submitted to the journal of Cellulose, based on results of chapter 4, with a title of: Tribological properties of Cellulose Nanocrystals aqueous suspensions as water-based lubricants. vi  Table of Contents  Abstract ......................................................................................................................................... iii Lay Summary ............................................................................................................................... iv Preface .............................................................................................................................................v Table of Contents ......................................................................................................................... vi List of Tables ..................................................................................................................................x List of Figures ............................................................................................................................... xi List of Symbols ........................................................................................................................... xiv Acknowledgements .................................................................................................................... xvi Dedication .................................................................................................................................. xvii Chapter 1: Introduction ................................................................................................................1 1.1 Motivation ....................................................................................................................... 1 1.2 Objectives ....................................................................................................................... 3 1.3 Organization .................................................................................................................... 4 Chapter 2: Background .................................................................................................................5 2.1 Tribometry ...................................................................................................................... 5 vii  2.1.1 Tribology principles .................................................................................................... 5 2.2 Cylindrical Tribometers .................................................................................................. 7 2.3 Wear characterization ..................................................................................................... 8 2.3.1 Wear mechanisms ....................................................................................................... 8 2.3.2 White light interferometry principle ........................................................................... 9 2.4 Rheometry ..................................................................................................................... 10 2.4.1 Rheometry principles ................................................................................................ 10 2.4.2 Rheological instruments............................................................................................ 11 2.4.3 Working equations .................................................................................................... 12 2.5 Lubrication .................................................................................................................... 13 2.5.1 Lubricant regimes ..................................................................................................... 14 2.5.2 Water-based lubricants.............................................................................................. 15 2.6 Slurry pump gland seals ................................................................................................ 17 2.7 Liquid Crystals .............................................................................................................. 18 2.8 Polarized Optical Microscopy ....................................................................................... 19 2.9 Cellulose nanocrystals .................................................................................................. 21 Chapter 3: Experimental Method...............................................................................................26 viii  3.1 Preparation of cellulose nanocrystals suspensions ....................................................... 26 3.2 Tribometer..................................................................................................................... 26 3.2.1 Non-abrasive tests ..................................................................................................... 32 3.2.2 Abrasive tests ............................................................................................................ 32 3.2.3 Petroff’s Equation ..................................................................................................... 34 3.3 White light interferometer ............................................................................................. 36 3.4 Rheological measurements ........................................................................................... 37 3.5 Transmission electron microscopy (TEM) ................................................................... 37 3.6 Polarized optical microscopy (POM) ............................................................................ 38 3.7 Scanning electron microscopy ...................................................................................... 38 Chapter 4: Results and Discussion .............................................................................................39 4.1 Measuring particle sizes ................................................................................................ 39 4.2 Non-abrasive tests ......................................................................................................... 40 4.2.1 Tribology tests .......................................................................................................... 40 4.2.2 Wear characterization ............................................................................................... 43 4.2.3 Contact pressure ........................................................................................................ 46 4.3 Abrasive test.................................................................................................................. 49 ix  4.3.1 Tribology tests .......................................................................................................... 50 4.3.2 Wear characterization ............................................................................................... 51 4.4 Rheology tests ............................................................................................................... 53 4.5 Structure visualization .................................................................................................. 57 Chapter 5: Conclusion .................................................................................................................60 5.1 Summary ....................................................................................................................... 60 5.2 Contribution .................................................................................................................. 62 5.3 Future directions ........................................................................................................... 62 Bibliography .................................................................................................................................64 Appendices ....................................................................................................................................75 Appendix A ............................................................................................................................... 75  x  List of Tables Table 1 Hertzian pressure between a 6 mm chrome steel ball and different stainless steel shafts 48  xi  List of Figures Figure 2-1 Schematic of a typical a) Pin on disk b) linear reciprocating test apparatus ................. 6 Figure 2-2 Cone and plate rheometer............................................................................................ 13 Figure 2-3 Stribeck curve and lubrication regimes ....................................................................... 14 Figure 2-4 Slurry pump sealing using gland seal packing material .............................................. 17 Figure 2-5 Schematic illustration of a variety of liquid crystal structures (Adapted from reference [60])............................................................................................................................................... 20 Figure 2-6 Concept of polarized optical microscopes (adapted from [64]) .................................. 21 Figure 2-7 Schematic illustration of isotropic and chiral nematic phases of CNC (Adapted from reference [77]) ............................................................................................................................... 24 Figure 3-1 3D model of the designed tribometer .......................................................................... 27 Figure 3-2 Load cell calibration curve .......................................................................................... 27 Figure 3-3 Dead weight mechanism to calibrate the lidar ............................................................ 29 Figure 3-4 Lidar calibration curve ................................................................................................ 30 Figure 3-5 Designed tribometer for measuring the coefficient of friction of round shafts........... 30 Figure 3-6 Coefficient of friction between stainless steel and chrome steel ball in presence of water as a lubricant with a normal force of 50N applied to 25.4 mm shaft rotated at 130rpm .... 31 Figure 3-7 Vulcan Type VG4 graphite gland packing.................................................................. 33 xii  Figure 3-8 Experimental setup with packing material and sands ................................................. 33 Figure 3-9 Petroff’s journal bearing consist of a shaft and a bushing .......................................... 35 Figure 4-1 TEM images of CNC suspensions with a concentration of 0.005 wt. % sonicated at 1000 J/g CNC ................................................................................................................................ 39 Figure 4-2 The coefficient of friction between the stainless steel shaft and the chrome steel ball in the presence of different lubricants with a normal force of 50 N applied to 25.4 mm shaft rotated at 130 rpm ......................................................................................................................... 40 Figure 4-3 The coefficient of friction between the stainless steel shaft and the chrome steel ball with different test variables. D is the shaft diameter, F is the normal force and w is the rotational speed of the shaft. ......................................................................................................................... 42 Figure 4-4 Sample wear profiles of lubricated surfaces with a) Water, (b) CNC 1 wt.%, (c) CNC 2 wt.% and (d) CNC 3 wt.% for friction test with a normal force of 50 N applied to a 25.4 mm shaft rotated at 130 rpm ................................................................................................................ 44 Figure 4-5 Output of WYKO Vision Software for wear cross-section profile ............................. 44 Figure 4-6 Wear depth on a surface lubricated with different concentrations of CNC with different test variables. D is the shaft diameter, F is the normal force and w is the rotational speed of the shaft..................................................................................................................................... 45 Figure 4-7 Wear width on a surface lubricated with different concentrations of CNC with different test variables. D is the shaft diameter, F is the normal force and w is the rotational speed of the shaft..................................................................................................................................... 45 xiii  Figure 4-8 The contact region between a sphere and a cylinder ................................................... 46 Figure 4-9 The coefficients of friction between the stainless steel shaft and the chrome steel ball in the presence of CNC 2 wt.% with different normal forces applied to 25.4 mm shaft rotated at 130 rpm ......................................................................................................................................... 49 Figure 4-10 The coefficients of friction between the stainless steel shaft and the packing material in the presence of different lubricants with a normal force of 50 N applied to a 25.4 mm shaft rotated at 130 rpm ......................................................................................................................... 50 Figure 4-11 The wear profiles of stainless steel shaft lubricated with (a) water, (b) CNC 1wt.%, (c) CNC 2wt.%, (d) CNC 3wt.%. ................................................................................................. 52 Figure 4-12 The steady-state viscosities of CNC suspensions versus the shear rate .................... 54 Figure 4-13 The steady-state viscosities of CNC shows power law behavior at high shear rates 55 Figure 4-14 Tribology test of CNC 4wt.% shows that particles trap in high viscous lubricants.. 55 Figure 4-15 SEM images of the ball surfaces after a 1-hour friction test with a normal force of 50 N and a rotational speed of 130 rpm. (a) lubricated with pure water. (b) lubricated with CNC 2 wt.% .............................................................................................................................................. 57 Figure 4-16 The  patterns obtained from a) CNC 1 wt.%, b) CNC 2 wt.%, c) CNC 3 wt.%, d) CNC 4 wt.% as observed by a Polarized Optical Microscope at rest ........................................... 59  xiv  List of Symbols 𝜏  shear stress  𝑅  radius  𝑀 applied torque  𝛾̇  shear rate  𝜔  angular speed  𝛼  cone angle μ  shear viscosity η Kinematic viscosity u  velocity of the moving part ?̅?  mean pressure in the fluid film p Cholesteric liquid crystal pitch    xv  Abbreviations CNC  Cellulose Nanocrystal  TEM Transmission electron microscopy SEM Scanning electron microscopy POM  Polarized optical microscopy xvi  Acknowledgements I must express my very profound gratitude to my parents and to my sister for providing me with unfailing support and continuous encouragement throughout my years of study and through the process of researching and writing this thesis.  I would like to say a very big thank you to my supervisor Dr. Dana Grecov for all the support and encouragement she gave me. Without her guidance and constant feedback, this research would not have been achievable.  Many thanks to my friends and colleagues at Industrial and Biological Multiphysics Laboratory. Special thanks to Miayan Yeremi, Somesh Bhatia, and Ali Pourzahedi for their help, support, and the constructive discussions we have had during the last two years.  I am indebted to the University of British Columbia for providing me the opportunity to perform my research in a remarkable human and scientific environment. I would like to thank Markus Fengler for his comments and helps to design and build my experimental setup. This project had been funded by Mitacs program and Kamloops Precision Machining Ltd. which are highly appreciated.   xvii  Dedication This dissertation is dedicated to my parents and my sister. For their endless love, support and belief in me. 1  Chapter 1: Introduction 1.1 Motivation Lubrication is an effective means of controlling wear and reducing friction. Friction and wear are the major cause of material wastage and loss of mechanical performance. It is estimated that one-third of the world's energy resources in present use are needed to overcome friction in one form or another. Hence, any reduction in friction and wear can result in considerable energy savings. To reduce the friction, mineral or synthetic oils are used to lubricate most of the mechanical devices. The base oils usually contain toxic substances such as polycyclic aromatic hydrocarbons or additives like cadmium, zinc, phosphorus, lead, and chlorine.  In some applications, water is used as a lubricant. It is environmentally friendly, inexpensive, readily available, and non-flammable and has high thermal conductivity. However, due to its low viscosity, corrosive properties, low boiling point and high freezing point, it is unacceptable for most tribological applications.  Kamloops Precision Machining Ltd was established in 1991 as a complete repair and manufacturing facility. They make slurry pumps for mineral processing application and also repair and service them. One of the biggest problem that they have currently is the cost of repairing and overhauling the pump. Pump’s seal is worn rapidly due to the inefficient lubricant that is used in slurry pumps. Slurry pumps use water as a lubricant. The friction on circular shafts is an important concern for slurry pumps. Slurry pump gland seals are particularly used in mineral processing pumps to 2  prevent the pumped fluid (slurry) from leaking to the external environment. The slurry particles entrained in the gap of a gland seal create a lubricated abrasive wear contact mechanism and is analogous to the wear of plain bearing journals. If the slurry is hazardous, the seal failure may create an unsafe workplace. To reduce the seal failure rate, a high-performance lubricant is needed, which in addition to reduce the friction and remove wear particles, is free of harmful additives or chemicals.  To enhance the properties of lubricants a chemical component or blend is added to improve the fluid performance. Additives can be soluble in oil-based, water-based or both lubricants. With the development of nano-lubricating technology and the deepening understanding of the particularity of functional nano-materials, nanoparticles used as additives show unique physical and chemical properties and have a broad application prospect in lubrication. The drawbacks are that these lubricant additives are typically difficult to synthesize. Metal materials such as Cu, Fe, and Co were reported to significantly reduce the coefficient of friction but metallic nanoparticles are difficult to disperse in water. One of the nanoparticles, which is soluble in water, environmental friendly and very abundant in nature is cellulose nanocrystal (CNC).  Cellulose nanocrystals can be synthesized from native cellulosic source materials by various means, for example, acid hydrolysis, enzymatic hydrolysis, and mechanical treatment [1]. CNC possesses many advantages, such as nanoscale dimension, high modulus of elasticity, high surface area, unique optical properties, renewable, biodegradable, non-toxic [2]. Another salient feature of CNC is the formation of liquid crystalline networks. Their mechanical properties are determined by different factors, including the orientational order.  3  1.2 Objectives The first objective of this work was to develop a custom-made pin on cylinder tribometer for measuring the coefficient of friction on the surface of cylindrical shafts. The second objective was using the designed tribometer to study the lubrication performance of different lubricants. In this work, we studied the lubrication performance of Cellulose nanocrystals as a water-based lubricant additive. For this purpose, we have studied different properties of lubricant and metal surfaces. The work plan for this study is described in the following steps. 1- A custom-made pin on cylinder tribometer for cylindrical shafts is used to investigate the effects of CNC concentration, shaft rotational speed, normal force and shaft diameter on the friction reduction ability of cellulose nanocrystals as water-based lubricant additives. 2- Wear on metal surfaces are visualized and dimensions were measured on a white light interferometer microscope. To visualize more details about scars and find the evidence of wear reduction, a scanning electron microscope is used. 3- Viscosity of cellulose nanocrystals aqueous suspensions as a key parameter in lubrication are studied in a wide range of shear rates. 4- Microstructures of cellulose nanocrystals aqueous suspensions is visualized by a polarized optical microscope to see the liquid crystal orientation of particles. Also, dimensions of CNC rods are measured with a transmission electron microscope. 4  1.3 Organization Chapter 2 provides a background of lubrication and the tests that we have used in this study. In addition, a description of some phenomena such as liquid crystals properties is provided. A short description of water-based lubricants and cellulose nanocrystals are provided as well. Chapter 3 explains different tests and experimental setups for each test such as tribology, rheology, interferometry, polarized light microscopy, transmission electron microscopy, and scanning electron microscopy.  Chapter 4 describes the results of different tests, which are described in chapter 3, and discussions about the results and outcomes of this study. Chapter 5 presents the overall conclusions of this thesis, as well as some recommendations for potential future work. 5  Chapter 2: Background In this chapter, a background about the different tests and measurements that we have done in this study is provided. In addition, the principles and presentation of previous studies on liquid crystals, water-based lubricants, and cellulose nanocrystals are reviewed. 2.1 Tribometry 2.1.1 Tribology principles The investigation of the wear and friction properties of materials, known as tribology, is often conducted using a device known as tribometer, which creates a relative motion between two contacting test samples. The nature of the friction and material removal induced is quantified and used to predict the behavior of the materials in real-world applications. The accuracy with which the laboratory test results may be applied to actual applications depends greatly upon the ability to replicate the conditions of the actual application during the test. Wear properties are highly dependent upon kinematic conditions, such as the path of travel, normal force at the material interface, and relative velocity of the surfaces, as well as environmental factors, such as temperature and humidity. These parameters must be closely monitored and controlled to produce meaningful results.  Tribological tests have generally been limited to relatively simple test configurations, such as a linear reciprocating motion of a pin on a flat plate, or a stationary pin on a rotating disk. However, the wear properties for such simplified flat paths could be different from material behavior under the more complicated conditions experienced in actual applications. 6  In the American Society for Testing and Materials (ASTM) standards, there are two methods for finding friction of flat surfaces. The first method is Pin-on-disk method [3] which a spherically-tipped pin revolves about the center of another sample in the form of a disk as shown in Figure 2-1(a). The pin is held at a constant radius on the disk, such that the worn path is a circle, with the pin traveling through the same track during each revolution.  The second method is linear reciprocating method [4] in which a sample with a spherically-shaped tip slides back and forth along a linear path along a flat plate sample as shown in Figure 2-1(b).  Figure 2-1 Schematic of a typical a) Pin on disk b) linear reciprocating test apparatus However, the wear properties for such simplified flat paths could be different from material behavior under the more complicated conditions experienced in actual applications. One example is friction and wear on the surface of circular shafts, which is one of the most common mechanical parts in the industry. 7  2.2 Cylindrical Tribometers Currently, there are some cylindrical tribometers to measure friction on curved surfaces. Trauth et al [5] built a pin on cylinder tribometer for which had an axial feed to study the effect of surface roughness in friction. The revolution path changes continuously and the pin does not pass the same point during the test. Their device mounts on a lathe and a hydraulic system is used to apply the normal force. Although their design is very robust, they cannot use the tribometer on other lathes and they have a very expensive mechanism for applying the force. Another cylindrical tribometer is the Falex lubricant testing machine, which has become one of the industry’s standard test devices. It consists of the loading of two self-aligning v-blocks on a rotating pin. This arrangement produces pure sliding for a cylinder-on-flat configuration with four line contacts [6]. The Falex device is a laboratory device and it is good for measuring friction on cylindrical pins not industrial shafts. The coefficient of friction depends on the shaft diameter.  El-Tayeb et al [7] designed a pin on cylinder tribometer to perform a dry abrasion test. Their device used dead weight mechanism to apply the normal force that is not a reliable mechanism in dynamic situations due to vibration. Clearly, a suitable tribometer for cylindrical shafts, which has an easy and reliable mechanism, portable, inexpensive, useful for both laboratory and industrial applications is lacking.   8  2.3 Wear characterization 2.3.1 Wear mechanisms The Committee of the Institution of Mechanical Engineers has defined wear as ‘the progressive loss of substance from the surface of a body brought about by mechanical action [8]. Wear includes six principal, quite distinct phenomena that have only one thing in common: the removal of solid material from rubbing surfaces [9]. These are (1) adhesive; (2) abrasive; (3) fatigue; (4) impact by erosion and percussion; (5) chemical (or corrosive), and (6) electrical-arc-induced wear. According to some estimates, two-thirds of all the wear encountered in industrial situations occur because of the adhesive- and abrasive-wear mechanisms. Wear by all mechanisms, except by fatigue mechanism, occurs by the gradual removal of material [10]. The adhesive wear occurs when film failure impairs the relative movement between solid bodies and inevitably causes severe damage to the contacting surfaces. The consequence of film failure is the severe wear. The wear in these circumstances is the result of the strong adhesion at the contact interface [11].  On the other hand, if the surfaces are in contact with a flow which consists of hard particles such as slurry particles or merely flows against one body without providing support against another body then a form of wear, which sometimes can be very rapid, known as abrasive wear occurs. This kind of wear results in micro-machining, wear grooves, tearing, plowing, scratching and surface cracking. The wear debris produced usually takes the shape of fine chips or flecks, similar to those produced during machining [12]. 9  The most commonly used techniques to evaluate wear are weighing and measurement of changes in dimensions. Weighing may often be difficult if the worn volume is small compared to the weight of the component. Further, weighing gives no information about the distribution of the wear over the worn surface [13]. With the introduction of high-resolution instruments such as the scanning electron microscopy (SEM) [14], atomic force microscope (AFM) [15], and optical interferometry [16], techniques capable of determining height differences in the sub-nanometer range and storing the obtained topographical data digitally. The wear measurement system used in this study was light interferometry.  2.3.2 White light interferometry principle White light interferometry is a non-contact, optical technique for measuring surface height and shape with great speed and accuracy [17].  In an optical profiler, white light is emitted by a conventional light source and is split into two beams by beam splitter housed inside the double beam interferometer objective. The reference beam is directed to a mirror located in the objective, which serves as the reference surface. Conversely, the sample-beam travels directly to the sample surface [18]. When the light reflected from these two surfaces recombines, a pattern of interference fringes forms. Maximum fringe contrast occurs at the best focus position for each given point on the sample. A short-coherence-length white light source is used, producing interference fringes only over a very shallow depth on the surface. Either the test surface or measurement head is scanned vertically such that each point on the surface passes through focus [19]. At evenly spaced intervals during the scan, frames of 10  interference data imaged by a video camera are captured and processed. The system uses a series of advanced computer algorithms to record the exact vertical position for each point on the surface with a sub-nanometer resolution [20]. The longitudinal uncertainty with which the profile can be measured is related to the surface roughness and is independent of the magnification used, allowing the use of low magnifications to study wider area with high resolution [21]. 2.4 Rheometry 2.4.1 Rheometry principles Rheology describes the deformation of solids or liquids under the influence of stresses. Ideal solids deform elastically. The energy required for the deformation is fully recovered when the stresses are removed. Ideal fluids deform irreversibly. The energy required for the deformation is dissipated within the fluid in the form of heat and cannot be recovered simply by removing the stresses [22]. There are some materials, which show both elastic and viscous characters. When these materials are loaded in shear, extension or combination of shear and extension, an instantaneous deformation, as expected for an elastic solid is followed by a continuous deformation. When the load is removed, part of the deformation recovers instantly, more recovered with time, and in some materials, there is a permanent set [23]. The motivation for any rheometrical study is that the observed behavior in the industrial situation can be correlated with some easily measured rheometrical function. Rheometry is therefore of potential importance in quality control and process control. It is also of potential importance in assessing the usefulness of any proposed constitutive model for the test material [24]. 11  Rheometers can be used to measure one or more of the rheometrical functions such as complex modulus, shear viscosity, first and second normal stress coefficients [23]. Among these rheometrical functions, the shear viscosity is a parameter that plays a fundamental role in lubrication. Viscosity changes with temperature, pressure and for some fluids with shear rate. The relation between these parameters influences the pressure development, the temperature distribution, and the film thickness between the rolling or sliding surfaces [25]. Therefore, at first glance, it appears that the more viscous lubricants would give better performance since the generated films would be thicker and a better separation of the two surfaces in contact would be achieved. This, unfortunately is not always the case since lubricants that are more viscous require higher power to flow. Consequently, the power losses are higher and more heat is generated resulting in a substantial increase in the temperature of the contacting surfaces, which may lead to the failure of the component [26].  2.4.2 Rheological instruments To measure the viscosity, we must design an experiment to produce shear, and then we must measure the stress components needed and calculate the viscosity. Fundamental rheological properties are independent of the instrument on which they are measured so different instruments will yield the same results [27]. Common instruments, capable of measuring fundamental rheological properties of fluids may be placed into two general categories: rotational type and tube type [28]. Rotational instruments may be operated in the steady shear or oscillatory mode. The most common geometries are parallel plates, cone and plate, concentric cylinders and mixer types. In such 12  devices, the material is placed between two surfaces, one of which rotates with respect to the other. Because of the onset of flow instabilities, rotational rheometers are not able to access high shear rates and are thus limited in their ability to probe nonlinear behavior [29].  Tube type or capillary rheometers are used to determine material viscosity at high shear rates. When pressure drives a fluid through a pipe, the velocity is maximum at the center and the velocity gradient or shear rate is maximum at the wall and zero in the center of the flow. The flow is therefore non-homogeneous and capillary viscometers are restricted to measuring steady shear viscosity [30]. 2.4.3 Working equations In this study, the cone and plate geometry is used to measure the viscosity of the lubricant. Schematic of the experiment is shown in Figure 2-2. The working equations under rotational shear tests using the cone and plate measuring system are as follows [31]: 𝝉 =𝟑𝑴𝟐𝝅𝑹𝟑      (2-1) 𝜸 =𝝎𝐭𝐚𝐧𝜶      (2-2) 𝝁 =𝝉𝜸 =𝟑𝑴 𝐭𝐚𝐧𝜶𝟐𝝅𝑹𝟑     (2-3) Where  • 𝜏 is the shear stress  • 𝑅 is the radius of the plate  • 𝑀 is the applied torque  • 𝛾̇ is the shear rate  13  • 𝜔 is the angular speed  • 𝛼 is the cone angle  • μ is the shear viscosity   Figure 2-2 Cone and plate rheometer 2.5 Lubrication The most important function of lubricants is the reduction of friction and wear. In times when saving energy and resources, and cutting emissions have become central environmental matters, lubricants are increasingly attracting public awareness. Scientific research has shown that 0.4% of the gross domestic product could be saved in terms of energy in Western industrialized countries if current tribological knowledge, i.e. the science of friction, wear, and lubrication, was just applied to lubricated processes [32]. 14  2.5.1 Lubricant regimes Pertaining to lubricant film thickness between surfaces in relative motion, four regimes can be identified: hydrodynamic, boundary, mixed, and elastohydrodynamic. The parameter usually used for characterizing these regimes is the ratio of the minimal film thickness to the asperity height. A commonly accepted illustration of the regimes is the Stribeck curve (Figure 2-3) which represents the dependence of the friction coefficient on the bearing parameter 𝜂𝑢?̅? where η is the kinematic viscosity, u the velocity of the moving part, and ?̅? the mean pressure in the fluid film [33].  Figure 2-3 Stribeck curve and lubrication regimes Lubricated tribological systems, operating under conditions of high load and low speed, frequently run in the boundary lubrication regime. Tribological systems under boundary lubrication are controlled by the tribochemical processes which take place at the interface [34]. Under these conditions, the chemistry occurring within a few nanometers of the surface becomes a critical factor determining friction, wear and stick-slip. The molecular structure and composition of the lubricant and the additives present in its formulation determine the tribological performance of the 15  system [35]. The molecules either adsorb onto the sliding surfaces or react with the surfaces under severe conditions such as high load and low speed giving rise to protective tribolayers of low shear modulus [36]. The hydrodynamic lubrication regime occurs when the lubricant completely separates the surfaces. It is mostly associated with film thicknesses near or more than one μm. Friction losses under hydrodynamic lubrication are very small. Elastohydrodynamic lubrication can be defined as a form of hydrodynamic lubrication where the significant elastic deformation of the surfaces takes place and it considerably alters the shape and thickness of the separating lubricant film. Such contacts occur in, for example, rolling bearings, cam-tappet systems, gears, flexible seals, and human synovial joints [37]. Most sliding contacts of practical importance, e.g., high-speed gearing, are not lubricated by either purely hydrodynamic or by classical adsorption lubrication. In this situation, neither the lubricant film nor the asperity contacts can be ignored, and both share the total load [38]. The lubrication regime where several mechanisms act simultaneously is termed mixed lubrication. 2.5.2 Water-based lubricants To reduce the friction, mineral or synthetic oils lubricate most of the mechanical devices. The base oils usually contain toxic substances such as polycyclic aromatic hydrocarbons or additives like cadmium, zinc, phosphorus, lead, and chlorine [39]. Water is used as a lubricant for some applications like lubrication of gland sealed pumps [40]. It is environmentally friendly, inexpensive, readily available, non-flammable, and has high thermal conductivity. However, due 16  to its low viscosity, corrosive properties, low boiling point and high freezing point, it is unacceptable for most tribological applications [41]. To enhance the properties of lubricants a chemical component or blend is added to improve the fluid performance. Additives can be soluble in oil-based, water-based or both lubricants [42]. Recently, many investigations have been conducted on  nanoparticles to use them as additives in lubricants to improve their tribological properties [43]. For instance, TiO2 [44], Cu/SiO2 [45], Cu [46], SiO2 [37,38], Al2O3 [49], multi-walled  carbon nanotube (MWCN) [50], Graphene Oxide [51], diamond nanoparticles [52], and fullerene (C60) [53] have been used as water-based lubricant additives and possess excellent tribological performances in terms of friction and wear reduction.  For instance, the solution of TiO2 nanoparticles in water with 0.8 wt.% can reduce the coefficient of friction between steel surfaces to 0.2. Al2O3 suspension with 2 wt.% can reduce the coefficient of friction between steel surfaces to 0.2 as well. Multi-walled carbon nanotubes (MWCN) have an excellent effect on friction reduction. While the suspension of MWCN in water with a concentration of 0.2 wt.% can reduce the coefficient of friction to 0.04. Although nanoparticle additives exhibit excellent lubrication performance for tribological applications, they usually lead to environmental pollution and there is a problem with recycling them. Another problem is that synthesizing nanoparticles additives are usually very expensive. These all mean that the development of an environmentally friendly water-based lubricant with superior lubrication performance and relatively inexpensive synthesize process becomes a trend in the field of lubrication [54]. 17  2.6 Slurry pump gland seals The friction on circular shafts is an important concern for slurry pumps. As shown in Figure 2-4 Slurry pump gland seals are particularly used in mineral processing pumps to prevent the pumped fluid (slurry) from leaking to the external environment [40]. The slurry particles entrained in the gap of a gland seal create a lubricated abrasive wear contact mechanism and is analogous to the wear of plain bearing journals.  Modern packing is manufactured from a mix of synthetic fibers which are woven into a braid for improved mechanical strength and typically lubricated either with a PTFE (polytetrafluoroethylene) boundary lubricant or graphite [55]. Under ideal operating and maintenance conditions, the useful life of the seal may be in the order of couple thousand hours necessitating several replacements of the packing. However, if a deviation in the seal conditions occurs, the useful life may be reduced significantly, typically to the order of hundreds of hours. If the slurry is hazardous, the seal failure may create an unsafe workplace. To reduce the seal failure rate, a high-performance lubricant is needed, which in addition to reduce the friction and remove wear particles, is free of harmful additives or chemicals [56].  Figure 2-4 Slurry pump sealing using gland seal packing material 18  The underlying wear mechanisms inside a gland seal are complex. Research in this area is sparse, and design is mainly guided by experience, and expensive trial and error experimentation. Realistic models of the gland seal wear rates must consider many factors such as pressure, temperature, abrasive concentrations, abrasive particle size and hardness, motor rpm, packing material, gland lubricant, gland geometry, shaft sleeve coating, friction between shaft sleeve coating and packing material, and more. The physics of an operating gland seal enter the domain of multi-physics, where many coupled partial differential equations must be solved (i.e. equations range from heat conduction, fluid dynamics, the theory of elasticity, tribology, and more). In addition, the problem is made even more difficult, because of the problems spatial scale range from microscopic to macroscopic scales. Experimentation is also difficult due to the large set of factors affecting wear rates, and the long time it takes to run a gland seal to fail. New experimental equipment and techniques must be employed to produce results in an accelerated fashion. 2.7 Liquid Crystals Liquid crystals are a state of matter intermediate between that of a crystalline solid and an isotropic liquid. They possess many of the mechanical properties of a liquid such as high fluidity, inability to support shear, formation, and coalescence of droplets. At the same time, they are similar to crystals that possess order and exhibit anisotropy in their optical, electrical, and magnetic properties [57]. Liquid crystals are of two types, thermotropic and lyotropic, according to whether the temperature or the concentration drives molecules towards orientational order, respectively. For thermotropic liquid crystals, the order of its components is determined or changed by temperature. 19  Correspondingly, for lyotropic liquid crystals, there is a critical value of the concentration above which the disorder-to-order transition takes place [58]. Liquid crystals may display various organized structures. The nematics are elongated cylinders or plates which have one directional order and lie more or less parallel to one another. Smectic liquid crystals are characterized by a layered structure, and thus they have both positional and orientational ordering. Different types of smectic liquid crystals are classified depending on the order within the layer and interlayer correlation. In the smectic A phase the long axis of the molecule is on the average perpendicular to the layer plane while in the smectic C phase it is tilted. Cholesterics are considered a special case of the nematic structure where the nematic planes are twisted from one layer to the next forming a helical structure, characterized by its pitch. The pitch (p) of the helix is defined as the distance required for the particle direction to make one full rotation about the cholesteric axis [59]. Figure 2-5 shows the schematic illustration of liquid crystals organized structures. It is noted that in cholesteric crystals the molecular orientation is repeated at a distance equal to the period p/2. 2.8 Polarized Optical Microscopy The use of polarized light on the optical microscope allows us to determine the optical properties of liquid crystals. A polarizer is a filter that only permits the light oriented in a specific direction with its polarizing direction to pass through. There are two polarizers in a polarizing optical microscope (POM) and they are designed to be oriented at a right angle to each other, which is termed as cross polar. The polarizing direction of the first polarizer is oriented vertically to the incident beam, so only the waves with vertical direction can pass through it. The second polarizer 20  subsequently blocks the past wave, since this polarizer is oriented horizontally to the incident wave [61].  Figure 2-5 Schematic illustration of a variety of liquid crystal structures (Adapted from reference [60])  Liquid crystal is birefringent, meaning that it possesses two different indices of refraction. One index of refraction corresponds to light polarized along the director of the liquid crystal, and the other is for light polarized perpendicular to the director. Chiral nematic liquid crystal is birefringent in a different way. Supposing that the helical structure is aligned with the direction of propagation of the light, circularly polarized light will travel through the crystal at different speeds depending on whether it is right-circularly polarized or left-circularly polarized (referring to the direction the polarization rotates around the axis of propagation). This is called circular birefringence, and it is 21  exhibited in the chiral nematic liquid crystal because of the helical structure formed by the molecules. The circular birefringence is highly wavelength dependent, so light of different colors gets modified in different amounts [62]. The concept of a polarized optical microscope is shown in Figure 2-6. 2.9 Cellulose nanocrystals Cellulose is one of the most abundant biopolymer resource available which exists in plant-based material and also synthesized by algae, tunicates, and some bacteria [63].  Cellulose nanocrystals (CNC) can be synthesized from native cellulosic source materials by various means, for example, acid hydrolysis, enzymatic hydrolysis, and mechanical treatment [1]. CNC possesses many advantages, such as nanoscale dimension, high modulus of elasticity (150GPa), high surface area, unique optical properties, renewable, biodegradable, non-toxic [2].  Figure 2-6 Concept of polarized optical microscopes (adapted from [64]) 22  Due to the natural properties of CNC such as high surface area, unique morphology, low density, and mechanical strength, these materials have broad applications in the nanocomposites field [65]. There are also potential applications in barrier films, antimicrobial films, transparent films, flexible displays, biomedical implants, pharmaceuticals, drug delivery, fibers and textiles, templates for electronic components, separation membranes, batteries, supercapacitors, electroactive polymers, and many others [66]. CNCs are considered as an effective rheological modifier to improve the rheological performance of water-based drilling fluids [67]. Parallel stacking of multiple cellulose chains within a single crystal is believed to be promoted by van der Waals and intermolecular hydrogen bonds. Typically, individual cellulose molecules form larger units known as elementary fibrils or protofibrils, which are packed into larger units called “microfibrils” and assembled into the familiar cellulose fibers [68]. Within an individual cellulose elementary fibril, cellulose molecular chains are hierarchically organized in crystalline and amorphous regions. The cellulose chains are firmly held in the fibril’s crystalline region by a hydrogen bond network formed between surface hydrogen and oxygen molecules, intra and intermolecularly. This hydrogen bond network is also believed to be responsible for the anisotropy of the elastic properties of cellulose, where the Young’s modulus and Poisson’s ratio show crystallographic dependence [69]. Based on the density functional theory with semi-empirical correction for van der Waals’ interactions, the largest Young’s modulus (206 GPa) was found to be aligned with the axis where covalent bonds dominated the mechanical response of the cellulose crystal.  The second greatest value (98 GPa) for Young’s modulus was associated with the direction perpendicular to the cellulose chain axis, and the lowest value (19 GPa) was computed along the 23  direction perpendicular to the previous two where weak van der Waals’ interactions dominate the mechanical response [70]. Suspensions of stiff and rod-like CNCs, derived from natural cellulose sources, can form a stable chiral nematic liquid crystalline phase [71]. The chiral nematic also called cholesteric phase is characterized by long-range orientational order of the nanorods combined with a helical modulation of the direction in which they align [72]. As shown in Figure 2-7, at low concentration, CNC particles are randomly oriented in aqueous suspension as an isotropic phase, and when the concentration reaches a critical value, they form anisotropic chiral nematic liquid crystalline phase [71]. As the concentration increased further, aqueous CNC suspensions showed a shear birefringence phenomenon. The critical concentration for sulphated CNC typically ranges between 1 and 10% (w/w), which is a function of the aspect ratio of CNC, charge density and osmolarity [73]. CNCs hydrolyzed in sulfuric or phosphoric acid can easily form a chiral nematic phase, whereas those hydrolyzed using hydrochloric acid cannot [74]. The transformation from isotropic to fully lyotropic liquid crystal in the case of CNCs has been difficult to study, but critical understanding may come from the structure of tactoids, which are key components in the evolution of liquid crystallinity in CNCs. Tactoids are spherical, ellipsoidal or spindle-shaped anisotropic droplets nucleated with sharp edges in isotropic dispersions. They have been observed in many liquid crystalline substances, including polypeptides [75]. As these tactoids with short-range ordered structures are the intermediate state that bridges the isotropic phase and the macroscopic liquid crystalline phase with long-range anisotropy [74], great efforts 24  have been made in the past 50 years to explain their origin, shape, and structure. These studies were based on polarized optical microscopy (POM), X-ray diffraction and scanning electron microscopy.  Electron microscopy results show that the tactoids themselves have chiral nematic structure and they are already well organized [76]. These organized tactoids form the layered, iridescent chiral nematic structure that is familiar for films of CNCs.   Figure 2-7 Schematic illustration of isotropic and chiral nematic phases of CNC (Adapted from reference [77]) The stability of these suspensions depends on the dimensions of the crystallites, size polydispersity, and surface charge. CNCs prepared by sulfuric acid hydrolysis can form more stable suspensions than those obtained from hydrochloric acid hydrolysis because the former 25  produces negatively charged crystallites through the sulfate esters introduced during hydrolysis [78]. 26  Chapter 3: Experimental Method In this chapter, a description of experimental setups and conditions are reviewed. 3.1 Preparation of cellulose nanocrystals suspensions Sulfuric acid hydrolyzed CNC powder was purchased from CelluForce Inc. with the particle size of 1-50 μm and sulfur content of 0.86-0.89%. CNC powder was added to water in order to make aqueous suspensions with concentrations of 1 wt. %, 2 wt. %, 3 wt. %, and 4 wt. %. To prepare the CNC aqueous suspensions, Ultrasonic processor model VCX-130 (Sonics & Materials Inc.) with a 6 mm probe was used to apply 1000 Joules ultrasound energy per gram of CNC to the suspensions in order to disperse the CNC particles homogeneous. This amount of energy is the minimum energy which breaks the aggregates with a minimum loss of viscosity [79]. 3.2 Tribometer Because commercial tribometers cannot measure the friction and wear between circular shafts and a counterpart in presence of a lubricant, we designed and built a tribometer that measure friction of shafts. To predict material behaviors in the real situation, the tribometers must capable to work with different lubricants, high normal forces, and different rotational speeds. The 3D model of the tribometer is shown in Figure 3-1, which was designed in Solidworks software.  The tribometer concept is based on the bending of a cantilever beam. The circular shaft is rotating by a lathe at different rotational speeds. The friction between the shaft surface and the pin enforces a beam to bend. An S-type load cell stretch due to beam bending and produce a voltage. By calibrating the output voltage and force on the tip of the pin we can measure the friction force. The 27  load cell accuracy is 0.01N. Dead weight method was used to calibrate the load cell. Standard weights hanged from the tribometer tip and the load cell output was measured. The calibration curve for the load cell is shown in Figure 3-2.  Figure 3-1 3D model of the designed tribometer  Figure 3-2 Load cell calibration curve 28  The circular shaft is placed between the lathe chuck and is rotated at different speeds. The radial and axial positions of the tribometer are controlled by the lathe carriage with a precision of 0.001 mm in the radial direction and 0.01 mm in the axial direction. The normal force is produced by a stiff compression spring with 4" length, 2.187" outer diameter and 0.207" wire diameter, which can exert the maximum normal force of 800 N before reaching the dead length. The spring’s back plate is attached to the lathe cross slide. Therefore, by rotating the cross-feed hand wheel the spring compressed and normal force applies to the shaft. There is a linear relation between normal force and spring’s length. To measure the distance between two parallel plates where the spring is mounted, an Adafruit VL6180X Time of Flight Micro-LIDAR Distance Sensor is used. The sensor contains a very tiny laser source and a matching sensor. The VL6180X can detect the time of flight, or how long the laser light has taken to bounce back to the sensor. Since it uses a very narrow light source, it is good for determining the distance of surfaces directly in front of it. Unlike IR distance sensors that try to measure the amount of light bounced, the VL6180X is much more precise and does not have linearity problems or double imaging where you cannot tell if an object is very far or very close. Communicating to the sensor is done over I2C with some simple commands. Most of the work is handled inside the sensor itself and the sensor output is sent to the computer one bit at a time, sequentially as a serial communication. To measure the normal force, we should calibrate the lidar output. Therefore, dead weight was used to apply normal force on spring and the lidar output was monitored in real time (Figure 3-3). The calibration curve for lidar is shown in Figure 3-4. The horizontal axis in Figure 3-4 is the output of lidar which is a dimensionless number and must be calibrated with the normal force. 29  Data from the load cell and lidar are collected by an Arduino Uno board and transferred to the computer as serial data. Real-time curves of normal force (lidar data), friction force (load cell data) and coefficient of friction which is the ratio of friction force to normal force, are plotted by a developed GUI with MATLAB.  Figure 3-3 Dead weight mechanism to calibrate the lidar The tribometer body is made from precipitation-hardened aluminum alloy grade 6061. The metallic body and fasteners reduce errors due to vibration and movements due to the flexibility of parts. In addition, the device is portable and works with any lathe as a measurement tool. It has a simple mechanism for applying a constant force, which can be calibrated easily. The experimental setup is shown in Figure 3-5. 30   Figure 3-4 Lidar calibration curve  Figure 3-5 Designed tribometer for measuring the coefficient of friction of round shafts 31  Before using the tribometer as a laboratory device, the results of the coefficient of friction obtained from the tribometer must be checked with published results. Wu et al [54] measured the coefficient of friction between a low carbon steel disk and a 9 mm chrome steel ball in presence of water as a lubricant with a pin on disk tribometer and 50N normal force. They measured the steady state coefficient of friction of 0.34. Results of friction test with our cylindrical tribometer for friction between a low carbon steel shaft with a diameter of 25.4 mm and a 6mm chrome steel ball in presence of water as a lubricant and 50N normal force are shown in Figure 3-6.   Figure 3-6 Coefficient of friction between stainless steel and chrome steel ball in presence of water as a lubricant with a normal force of 50N applied to 25.4 mm shaft rotated at 130rpm 32  As it can be seen from Figure 3-6, the coefficient of friction reaches to the steady value of 0.33 that is in good agreement with the results presented in the literature.  3.2.1 Non-abrasive tests Tribological tests are performed using the designed tribometer. To find the effect of independent variables, the rotational speed of 130 rpm and 300 rpm, and stainless steel shaft diameter of 25.4 mm and 50.8 mm with different normal forces are used. The counterpart is a 6 mm diameter chrome steel ball. CNC suspensions with different concentrations are used as lubricants during experiments with the flow rate of 1.25 ml per minute. This is the minimum flow rate that a stable film of lubricant forms between two surfaces and metal contact noise is not heard. 3.2.2 Abrasive tests In the real situation, slurry particles enter the gap between shaft and gland seal packing and produce a complex tribological environment, which causes friction increasing, heat generation, lubricant loss and raise of wear rate. The particle size distribution strongly depends on the transported mineral type. Generally, the specific wear rate increases with the particle size [80]. Gland sealing is the standard form of sealing adopted for many slurry pump applications due to its relative robustness, gradual failure mode and ease of maintenance. The Vulcan Type VG4 graphite gland packing with a square cross section and width of 1cm was used as the packing material (Figure 3-7). The experimental particle distribution size included more than 80% particles from 400-600 microns. Washed and dried silica sands were used as slurry particles and purchased from VWR 33  ANALYTICAL Company. Particles were added to the experiment at the rate of 0.6 gram per minute as shown in Figure 3-8. The particles rate is chosen based on try and error to find the best value where particle rate is not too low that the packing material and shaft surface are not worn after 1 hr friction test and is not too much that particles do not have enough time to mix with lubricant and insert the gap. So, 0.6 grams/min is a value in between where we can see scars on the shaft surface after friction test and also particles have enough time to mix with CNC.  Figure 3-7 Vulcan Type VG4 graphite gland packing  Figure 3-8 Experimental setup with packing material and sands 34  3.2.3 Petroff’s Equation To choose the experimental parameters correctly and get a same result as the real situation, we should find an analogy between gland seal lubrication in real slurry pumps and our experimental setup. As mentioned before, the theoretical and numerical models of gland seal lubrication are very complicated due to change in many parameters. To run the experiments and measure the coefficient of friction between 25.4 mm stainless steel shaft and 1 cm width gland seal packing material we need to apply a normal force. To find the appropriate force we imagine that the lubrication mechanism is same as lubrication mechanism in journal bearings. Therefore, we use the Petroff’s method and calculate the normal force as we have the same coefficient of friction in the real situation.  Petroff first explained the phenomenon of bearing friction with the assumption that the shaft is concentric with its bushing. Though we shall seldom make use of Petroff’s method of analysis in the material to follow, it is important because it defines groups of dimensionless parameters and because the coefficient of friction predicted by this law turns out to be quite good even when the shaft is not concentric [81].  We consider a shaft rotating in a guide bearing. It is assumed that the bearing carries a load and the clearance space is completely filled with lubricant (Figure 3-9). We denote the radius of the shaft by r, the radial clearance by c, and the length of the bearing by l. If the shaft rotates at N rev/s, then its surface velocity is 𝑈 = 2𝜋𝑟 𝑁. Since the shearing stress in the lubricant is equal to the velocity gradient times the viscosity, we have 𝜏 = 𝜂𝑈∆𝑟=2𝜋𝑟𝜂𝑁𝑐                                                                                                                        (3-1) 35   Figure 3-9 Petroff’s journal bearing consist of a shaft and a bushing The force required to shear the film is the stress times the area. The torque is the force times the lever arm r. Thus, 𝑇 = (𝜏𝐴)𝑟 =4𝜋2𝑟3𝑙𝜂𝑁𝑐                                                                                                                (3-2) If we now designate a force on the bearing by W, then the pressure P, is 𝑃 = 𝑊/2𝑟𝑙. The frictional force is f W, where f is the coefficient of friction, and so the frictional torque is 𝑇 = 𝑓𝑊𝑟 = 2𝑟2𝑓𝑙𝑃                                                                                                                   (3-3) Substituting the value of the torque from (3-3) in (3-2) and solving for the coefficient of friction, we find 𝑓 = 2𝜋2𝜂𝑁𝑃𝑟𝑐                                                                                                                               (3-4) Equation (3-4) is called Petroff’s equation and was first published in 1883 [82]. 36  Therefore, if we want to have the same result for the coefficient of friction as in the real situation we must have the same coefficient of friction for both conditions. Data for slurry pumps made in Kamloops Precision Machine Ltd indicates that 16-inch stainless steel shaft rotates at 575rpm and packed by gland seals with a pressure of about 60 psi (413 kPa) and use water with the viscosity of about 9 × 10−4 𝑃𝑎. 𝑠. The coefficient of friction for both cases must be the same. Hence, 2𝜋29×10−4×575413000(16 𝑖𝑛𝑐ℎ𝑐) = 2𝜋2𝜂𝑁𝑊2∗𝑟𝑙𝑟𝑐                                                                                        (3-5) Where l is the packing material width. The CNC suspension has a Non-Newtonian viscosity model as measured with rheometers and results are presented in next chapter. As an estimation, we assume the viscosity of 10−2𝑃𝑎. 𝑠 for our calculations. If we assume that the shaft clearance for both cases is approximately the same, from Equation we can find the normal force 𝑊 = 51 𝑁.  We should note that this value is an approximate value for the normal force we must apply on the packing material during tribology experiments.  3.3 White light interferometer A Wyko NT1100 Optical Profiling System with a vertical resolution of < 0.1𝑛𝑚 was used to measure the depth and width of wear and surface roughness.  The interferometer is able to take measurements via optical Phase Shifting (PSI) and white light Vertical Scanning (VSI). Outputs are sent to the WYKO Vision Software for analysis and characterizing the wear dimensions. In VSI mode, the white light source filtered with a neutral density filter, which preserves the short coherence length of the white light, and the system 37  measures the degree of fringe modulation, or coherence, instead of the phase of the interference fringes. 3.4 Rheological measurements The rheological measurements for low shear rates (0.1-800 𝑠−1) were performed on a Kinexus Rheometer (Malvern Instruments Ltd., UK) using a cone and plate geometry (2° cone angle, 60 mm diameter). Cone and plate fixtures have the advantage that the shear rate is very nearly uniform throughout the sample, and this is essential for tests such as large-strain stress relaxation and start-up of steady shear and for measuring viscosity and normal stress differences [83] For high shear rates (800 to 7000 𝑠−1) the measurements were performed on a microfluidic capillary rheometer with a niddle radius of 0.545 mm and length of 320 mm. The rheometer is designed and developed by one of the research students in our research lab. All experiments were conducted at the temperature of 25℃. 3.5 Transmission electron microscopy (TEM) TEM images of the CNC crystallites were obtained using an FEI Tecnai G2 200 kV. To image the individual CNC crystallites, a 1mL drop of very dilute (~0.005 wt.%) CNC suspension was deposited on a TEM grid immediately after sonication and dried under ambient conditions. Image J software has been used to measure the physical dimensions of CNC particles. 38  3.6 Polarized optical microscopy (POM) To visualize the microstructure and particles orientation of CNC solution an Olympus-BX41 microscope with 40x lens was used. A 1 mL drop of CNC with different concentrations was visualized immediately after sonication. 3.7 Scanning electron microscopy To visualize the scar on the ball surface and investigate the chemical composition on the contact region, balls were washed with ultrasonic cleaning in ethanol after friction test. A Hitachi S3000N variable pressure scanning electron microscope was used to obtain images of ball surface at contact region. 39  Chapter 4: Results and Discussion In this chapter, results of different tests, which are described in previous chapters, are presented. Results of each set of tests are shown in separate sections followed by a discussion about results.  4.1 Measuring particle sizes Transmission electron microscopy (TEM) images of dried suspensions revealed that the lubricant contains needle shape crystal with a length of about 200 nm and high aspect ratio (Figure 4-1). Image J software has been used to measure the physical dimensions of CNC particles.   Figure 4-1 TEM images of CNC suspensions with a concentration of 0.005 wt. % sonicated at 1000 J/g CNC  40  4.2 Non-abrasive tests 4.2.1 Tribology tests For each CNC concentration, four sets of tests have been done. In each test, the effect of one variable was investigated. Test variables include the normal force, the rotational speed, and the shaft diameter. Water is used as the lubricating fluid for comparison. Figure 4-2 shows the variation of coefficient of friction versus time for the different concentration of CNC and water when the normal force of 50N applied to 25.4 mm shaft rotated at 130 rpm.   Each tribology test was repeated three times and the steady-state value of the coefficient of friction had a standard deviation of less than 3%.  Figure 4-2 The coefficient of friction between the stainless steel shaft and the chrome steel ball in the presence of different lubricants with a normal force of 50 N applied to 25.4 mm shaft rotated at 130 rpm 41  As it can be seen from Figure 4-2, the coefficient of friction curves starts with a pick, which is the static friction region. Static friction primarily caused by interlocking asperities. After some revolution of the shaft against the pin, asperities have been destructed and a stable film of lubricant was formed between the two surfaces. In this situation, the friction caused by chemical bonding between the surfaces is called the kinematic friction region and the coefficient of friction reached a steady state value. After passing the static friction region and experiencing high friction force, the coefficient of friction decreased until it reached a steady state. The steady state coefficient of friction for water, CNC 1 wt.%, CNC 2 wt.%, CNC 3 wt.% and, CNC 4 wt.% is 0.33, 0.17, 0.11, 0.14, and 0.19 respectively which shows that compared to lubrication with water, CNC 2 wt.% can reduce the friction by a factor of 3. Figure 4-3 shows the coefficient of friction for different tests and CNC concentrations. Compared to the first set of experiments where the normal force of 50 N applied to a 25.4 mm shaft rotated at 130 rpm, for the second, third and fourth set of experiments, normal force decreased to 25 N, rotational speed increased to 300 rpm and shaft diameter increased to 50.8 mm, respectively. As it can be seen from Figure 4-3, the minimum coefficient of friction obtained from the tribology experiments is about 0.09, which occurred when a normal force of 50 N is applied to 25.4 mm stainless steel shaft rotated at 300 rpm and lubricated with CNC 2 wt.%. Figure 4-3 shows the results of four friction test wherein each test one parameter is changed. The blue columns show results of friction test for 25.4 mm shaft under 50 N normal force and 130 rpm rotational speed while the red columns are results of the same experiment with 25 N normal force. 42  By comparing the blue columns with red columns, we can conclude that the coefficient of friction decreases when normal force decreases.  Figure 4-3 The coefficient of friction between the stainless steel shaft and the chrome steel ball with different test variables. D is the shaft diameter, F is the normal force and w is the rotational speed of the shaft. Comparing blue columns with grey columns, which have the same experimental parameters except different rotational speeds, shows that increasing rotational speed decreases the coefficient of friction. The friction reduction due to increasing rotational speed for water, CNC 1 wt.% and CNC 2 wt.% are more effective than decreasing force. Although, for CNC 3 wt.% they have the same result and for CNC 4wt.% decreasing the normal force causes lower friction. Here, the difference in results is due to changing viscosity. However, viscosity changes not only with the CNC concentration but also due to changing temperature and non-Newtonian properties of CNC suspensions, viscosity changes with rotational speed. Therefore, viscosity has more complex effects on friction and we will postpone the discussion to rheology section. 43  Comparing blue columns with yellow columns, which have the same experimental parameters except different shaft diameter, shows that increasing shaft diameter causes the coefficient of friction to increase.  4.2.2 Wear characterization The surface profiles were captured by the interferometer microscope on 10 different regions of the surfaces. Depth and width measurements were done on an area of each picture, which had the best resolution. Sample profiles for the friction test with a normal force of 50 N applied to a 25.4 mm shaft rotated at 130 rpm are shown in Figure 4-4. In these pictures there are some black areas which due to the partially light reflection of surface the signal to noise ratio is low and the device could not find the right distance, so there is no data for these regions. The low reflection could be due to CNC particles attached to the surface during the tribology test. The WYKO Vision Software output could be a two-dimensional groove profile as shown in Figure 4-5 and the groove height and width can be measured from the picture.   Average and uncertainty of 10 measurements for the scar depth and width were plotted in Figure 4-6 and Figure 4-7. As it can be seen from these figures, the wear depth and width have the minimum value for the lubricated surface with CNC 2 wt. % for the set of experiments with a normal force of 25 N. 44   Figure 4-4 Sample wear profiles of lubricated surfaces with a) Water, (b) CNC 1 wt.%, (c) CNC 2 wt.% and (d) CNC 3 wt.% for friction test with a normal force of 50 N applied to a 25.4 mm shaft rotated at 130 rpm  Figure 4-5 Output of WYKO Vision Software for wear cross-section profile 45   Figure 4-6 Wear depth on a surface lubricated with different concentrations of CNC with different test variables. D is the shaft diameter, F is the normal force and w is the rotational speed of the shaft.  Figure 4-7 Wear width on a surface lubricated with different concentrations of CNC with different test variables. D is the shaft diameter, F is the normal force and w is the rotational speed of the shaft.  46  4.2.3 Contact pressure When a sphere is in contact with a cylinder, the entire force is applied into a theoretical point. Due to the elastic properties of the materials, this point will deform to a contact area. The stress field created by the contact stresses was first introduced by Hendrick Hertz in 1881 [84]. Here we assume that the surfaces in contact are perfectly smooth, the elastic limits of the materials are not exceeded, the materials are homogeneous, and there are no frictional forces within the contact area. Although the friction forces within the contact region are not zero, this parameter is important when the elastic modulus of two materials are different [85]. In our experiment, both materials are steel alloy and have very close elastic modulus. For a spherical contact, like a ball and socket or ball on a flat plate, the pressure distribution is circular and extends out as shown in the contact area region from Figure 4-8. The size of this region depends on the elastic properties and the geometries of the parts in contact.  Figure 4-8 The contact region between a sphere and a cylinder  47  In general, the maximum pressure in the contact region Pmax, can be calculated as 𝑷𝒎𝒂𝒙 =𝟑𝑭𝟐𝝅𝒂𝟐                                                                                                                              (4-1)                                                                                                                                        Where F is applied force and a is the radius of contact region as shown in Figure 4-8.                                                                                                                                               To calculate the radius of the contact region, Puttock et al [86] developed equation (4-2) for different geometry and materials.  𝒂𝟑 = 𝟑𝑨𝑭(𝟏−𝝂𝟏𝟐𝝅𝑬𝟏+𝟏−𝝂𝟐𝟐𝝅𝑬𝟐)𝟏𝑹𝟏+𝟏𝑹𝟐                                                                                                                   (4-2)                                                                                      Where E1 and E2 are the moduli of elasticity for sphere and cylinder, ν1 and ν2 are the Poisson’s ratios, and R1 and R2 are the radiuses, respectively. A is a constant, which is a function of radius ratio (c).  𝒄 =𝟏𝑹𝟏𝟏𝑹𝟏+𝟏𝑹𝟐                                                                                                                                      (4-3) We should use table 3 in reference [86] and find A based on the calculated radius ratio. This table is provided in the appendix section. In this study, we used E52100 chrome steel balls with the elastic modulus of 210 GPa and the Poisson’s ratio of 0.3 versus AISI type 304 stainless steel shaft with the elastic modulus of 195 GPa and the Poisson’s ratio of 0.29. For a 25.4 mm cylinder, the radius ratio is 0.81, therefore from Appendix 1, A= 0.8710. The Hertzian pressure for a 50 N normal force is 2.5 GPa, for a 25 N normal force it becomes 2.0 GPa. For the 50.8 mm stainless steel cylinder, the radius ratio is 0.89 so A= 0.8297. For 50 N normal force, the Hertzian pressure becomes 2.45 GPa.  48  Table 1 Hertzian pressure between a 6 mm chrome steel ball and different stainless steel shafts Shaft Diameter (mm) Normal force (N) Radius ratio A Hertzian pressure (GPa) 25.4 50 0.81 0.8710 2.5 25.4 25 0.81 0.8710 2.0 50.8 50 0.89 0.8297 2.45  The Stribeck curve has been proven to be useful for identifying the lubrication regime [87] which represents the dependence of the friction coefficient on the bearing ratio 𝜂𝑢?̅?, where η is the kinematic viscosity, u the velocity of the moving part, and ?̅? the mean pressure in the fluid film. To predict the lubricant regime, one of the mentioned parameters should be changed and the difference in the coefficient of friction should be investigated. The CNC suspension is a shear thinning non-Newtonian material. Therefore, by changing the velocity of the moving part the shear rate changes and viscosity changes. Also, changing the viscosity by varying concentration is not suitable because changing the concentration is similar to changing the lubricant while the Stribeck curve classifies the lubricant regime for one lubricant.  To change the bearing ratio we can change the mean pressure by changing the normal force. In Figure 4-9 the coefficient of friction versus time is plotted for 25.4 mm stainless steel shaft lubricated with CNC 2 wt.% and the rotational speed of 130 rpm with different normal forces of 50 N, 38 N and 25 N. As it can be seen, the difference between the steady coefficients of friction is less than 3%, which is our device error; 49  therefore we can conclude that the coefficient of friction is independent of the normal force. Based on the Stribeck curve, the coefficient of friction does not change with changing the normal force in boundary lubrication regime. Therefore, the bulk fluid viscosity of the lubricant has little or no effect on the friction and the wear. In this situation, the lubrication regime is controlled by additives present in the lubricant[88].  Figure 4-9 The coefficients of friction between the stainless steel shaft and the chrome steel ball in the presence of CNC 2 wt.% with different normal forces applied to 25.4 mm shaft rotated at 130 rpm 4.3 Abrasive test In the slurry pumps, slurry particles enter the gap between the shaft and the gland seal packing and produce a complex tribological environment that causes friction increasing, heat generation, 50  lubricant loss and raise of wear rate. Therefore, by adding washed sand to the experiment to mimic the slurry particles and using a packing material as a counterpart of tribology test, we expect to see a higher coefficient of friction.  4.3.1 Tribology tests For each lubricant, three sets of experiments were performed, and the following results are average of all the sets. The coefficient of frictions versus time between the stainless-steel shaft and the packing material is shown in Figure 4-10. The steady-state coefficients of friction for water, CNC2 wt.%, CNC 3 wt.% and, CNC 4 wt.% are 0.36, 0.30, 0.27, and 0.31 respectively.     Figure 4-10 The coefficients of friction between the stainless steel shaft and the packing material in the presence of different lubricants with a normal force of 50 N applied to a 25.4 mm shaft rotated at 130 rpm Elastohydrodynamic lubrication (EHL) occurred in the friction tests because the elastic deformation of the packing material played a fundamental role. As it can be seen from Figure 4-10, 51  the coefficient of friction does not change significantly, because the deformation of the packing material and the presence of the abrasive sands did not allow the lubricant to make a thick film in the contact region to support the load and pulls the surfaces apart. A 25% friction reduction was obtained for CNC 3 wt.% compared to water. 4.3.2 Wear characterization The surface roughness after experiments was changed because of abrasive wear caused by sands. The surface profiles were captured by the interferometer microscope on 10 different regions of the surfaces. A sample profile for each case is shown in Figure 4-11. There are some gaps through the curves, where interferometer could not measure the height of that point because of poor light reflection from that regions. As it can be seen from Figure 4-11, after adding sands as slurry particles to the experimental setup, the surface roughness completely changes because each sand act like a pin and make a scar on the surface. There is no single scar on the surface for depth and width measurement. Therefore, we measured the surface roughness by the interferometer microscope and calculated the root mean square (RMS) roughness from the following equation 𝑹𝑴𝑺 = √∑ (𝒀𝒊−𝒀)𝟐𝑵𝒊=𝟏𝑵−𝟏                                                                                                                       (4-4)                                                                                                     Where, Y is the height of each point on the surface from a default level defined for the device. N is the number of the points on the surface with the heights measured by the interferometer microscope. In our experiments, N was 640. The average surface roughness for water, CNC 2 52  wt.%, CNC 3 wt.% and, CNC 4 wt.% are 1.45 μm, 0.61 μm, 0.19 μm, and 0.68 μm respectively with a maximum error of 3%.   Figure 4-11 The wear profiles of stainless steel shaft lubricated with (a) water, (b) CNC 1wt.%, (c) CNC 2wt.%, (d) CNC 3wt.%.  The wear rate reduced significantly for CNC. The surface roughness in the case of lubrication with CNC 3 wt.% was reduced more than 7.5 times compared to the lubrication with water which could lead to an important increase in the shaft life cycle.    53  4.4 Rheology tests Steady-state viscosities as functions of the shear rate of CNC suspensions with concentrations of 1, 2, 3, and 4 wt.% are shown in Figure 4-12.  As shown in Figure 4-12, by increasing the concentration, viscosity of suspensions increases due to the growth in the collision possibility of CNCs [89].  The viscosity decreases as the shear rate increases over the whole investigated shear rate ranges. The power-law or Ostwald–de Waele model describes viscosity with a function that is proportional to a power of the shear rate 𝛾̇ . 𝜇 = 𝑚𝛾̇ 𝑛                                                                                                                                    (4-6) The power-law equation has two parameters that must be fit to experimental data. One parameter is the exponent of 𝛾̇ , n (power law coefficient), which is the slope of 𝑙𝑜𝑔 𝜇 versus 𝑙𝑜𝑔 𝛾̇ . The second parameter is m, which is called the consistency index.  Rotational rheometers cannot apply very high shear rates. In this study, we have used a micro niddle to apply very high shear rates of up to 7000 𝑠−1 which is not investigated in the literature. Results of viscosity for shear rates of 1000𝑠−1 to 7000 𝑠−1 are plotted in Figure 4-13 and shows that the samples exhibit shear thinning power law behavior at very high shear rates. However, we couldn’t measure the viscosity for higher shear rates to predict the viscosity during the friction test which has shear rates of around 105 𝑠−1. 54   Figure 4-12 The steady-state viscosities of CNC suspensions versus the shear rate While the viscosity of CNC increases with concentration, results show that the lubricant with the highest viscosity does not have the best friction reduction ability. The wear particles are trapped into the lubricant at higher concentration due to the higher viscosity, increase the friction, and wear rate by the abrasive mechanism. As shown in Figure 4-14, for a high viscous suspension of CNC 4wt.%, wear particles removed from stainless steel and trap inside lubricant and change the lubricant color. 55   Figure 4-13 The steady-state viscosities of CNC shows power law behavior at high shear rates  Figure 4-14 Tribology test of CNC 4wt.% shows that particles trap in high viscous lubricants 56  The temperature characteristics are important in the selection of a lubricant because of its effect on viscosity. In addition, the temperature range over which the lubricant can be used is of extreme importance. Rheology tests allow us to test the lubricants at high temperatures and measure the viscosity. Viscosity measurements of CNC 3 wt. % and 4 wt. % shows that even at 80 ℃ its viscosity is higher than the water viscosity (Water viscosity is 8.90 ×  10−4 𝑃𝑎. 𝑠) [90]. The thermal stability of CNC particles depends on the synthesis process. Espinosa et al [91] used thermogravimetric analysis to investigate the thermal instability of CNCs synthesized with three different acids of hydrochloric acid, phosphoric acid, and sulfuric acid. CNC synthesized with HCl showed the highest thermal stability. This material started to decompose at about 220°C, but the process sets in slowly, as indicated by the fact that the 5% weight loss mark and the maximum decomposition temperature are at 305°C and 350°C, respectively. The thermal stability of synthesized CNC with phosphoric acid has the same trace as synthesized CNC with HCl and reveal only a minor reduction in thermal stability. Here decomposition sets in at the same temperature as for H-CNCs (220°C), but the 5% weight loss mark (290°C) and the maximum decomposition temperature (325°C) are recorded at temperatures that are 15−25°C lower than those of synthesized CNC with HCl. While synthesized CNC with sulfuric acid shows lower thermal stability. For synthesized CNC with sulfuric acid, decomposition starts at around 150°C [91]. 57  4.5 Structure visualization The improvement of the coefficient of friction and wear by adding CNC to water could be due to two main reasons: the high strength CNC particle and the alignment of CNC particles. Images obtained from scanning electron microscopy of the ball surface shows that the surface composition at the contact region differs for balls lubricated with CNC 2 wt.% and pure water Figure 4-15, respectively. The backscattered electron imaging mode in Figure 4-15 shows that the lighter areas in the SEM image have different chemical composition from the background material. It is likely that the notable friction reduction observed in this study was achieved by adsorption of the high strength CNC rods to the surfaces of the sliding parts, which acted as protective coatings.   Figure 4-15 SEM images of the ball surfaces after a 1-hour friction test with a normal force of 50 N and a rotational speed of 130 rpm. (a) lubricated with pure water. (b) lubricated with CNC 2 wt.% The bending strength and elastic modulus of the synthesized cellulose nanoparticles with sulfuric acid measured by Raman spectroscopy are about 10GPa and 150GPa respectively [92]. Therefore, this high strength material adheres to both surfaces and act as a protective coating.  58  The second reason that CNC acts as a powerful lubricant is the alignment of the CNC particles under flow. The rod-like shape and negative surface charge of CNC particles give rise to electrostatically stable colloidal suspensions which phase separate into an upper random phase and a lower ordered phase, at CNC concentrations above a critical value [77]. This self-organization phenomenon was revealed by the appearance of the fingerprint patterns obtained from the suspensions observed by a Polarized Optical Microscope, indicative of a chiral-nematic ordering [93]. For the low concentration of CNC, nanoparticles are mainly dispersed randomly. However, as it can be seen in Figure 4-16-a,b pictures are not entirely dark which means there are some areas in which particles have the same orientation. The critical concentration occurs for CNC 3 wt.% where there is a two-phase system in which one of the phases is isotropic and the other is an anisotropic mesophase Figure 4-16-b. The mesophase is interspersed in the isotropic phase in the form of spheroids or ovaloids droplets which are called tactoids [76]. As discussed in the previous chapters, tactoids are a transition state between isotropic and macroscopic liquid crystalline phases. By increasing the CNC concentration, tactoids coalesce to form an anisotropic phase where CNC rods have a unidirectional self-organized structure. Above the critical concentration of CNCs, the suspensions turn into a chiral nematic ordered phase displaying the signature of the cholesteric liquid crystals as shown in Figure 4-16-c.   59   Figure 4-16 The  patterns obtained from a) CNC 1 wt.%, b) CNC 2 wt.%, c) CNC 3 wt.%, d) CNC 4 wt.% as observed by a Polarized Optical Microscope at rest 60  Chapter 5: Conclusion In this chapter, an overall description of the experiments performed, the contribution of the study and some suggestions for possible future research will be reviewed. 5.1 Summary In this research, we have designed and built a new pin on cylinder tribometer to measure the coefficient of friction on the surface of shafts and test performance of different lubricants. The tribometer has the capability of testing gland seal packing materials with different slurry particles as well. We used the designed tribometer to measure the coefficient of friction between stainless steel shaft and chrome steel ball in presence of cellulose nanocrystal suspensions as water-based lubricants. After measuring the coefficient of friction, depth and width of the scar on the shaft surface were measured with an interferometer. In case of using washed sands as slurry particles, the surface roughness was measured instead of scar depth and width.  The viscosity of cellulose nanocrystals suspensions was measured with a rotational rheometer using a cone and plate geometry for low shear rates and with capillary rheometer for high shear rates.  The structure of CNC was visualized utilizing a polarized optical microscope. Moreover, scanning electron microscopy was used to visualize the CNC particles on the metal surfaces. . Following are the highlights of this study. 61  1. The friction coefficient between a stainless steel shaft and chrome steel ball in presence of CNC with 2 wt.% can be as low as 0.09 which is approximately 1/4 of the friction coefficient of water. In addition to the friction reduction, CNC reduced the wear depth and width by more than 50%. 2. The CNC suspension can be used as a lubricant in slurry pumps gland seal. CNC with 3 wt.% showed the best coefficient of friction in the presence of the abrasive sands. The surface roughness in the case of the lubrication with CNC 3 wt.% was reduced by more than 7.5 times compared to the lubrication with water which can increase the life cycle of shaft and gland seal packing material. To have a steady lubricant film between metal surfaces in presence of slurry particles, we need a lubricant with higher viscosity. Therefore, CNC 2 wt.% is a proper lubricant for normal situations but CNC 3 wt.%, which has a higher viscosity is needed when the slurry particles and the packing material exist. 3. In all experiments, due to the high Hertzian pressure between surfaces, boundary lubrication occurred and the fluid viscosity had little or no effect on the friction and wear reduction. The beneficial properties of CNC suspensions were mainly due to the orientation and alignment of the high strength nanoparticles. The nanoparticles oriented along the shear direction in the contact region between the two sliding surfaces, hence decreasing the friction coefficient and the wear between the sliding surfaces.  These results suggest a good potential for the application of CNC as a water-based lubricating additive to reduce friction and surface wear. 62  5.2 Contribution The main contributions of the present work are: 1.  The development of a new pin on cylinder tribometer for measuring the coefficient of friction of cylindrical surfaces with different normal forces in presence of different lubricants. The tribometer has a capability of mounting on different lathes and work as an experimental or industrial device.  2. Cellulose nanocrystals as an environmentally friendly water-based lubricant additive.  5.3 Future directions • We have designed and built a pin on cylinder tribometer with a capability to mount on different lathes and use different lubricants. Another feature which we can add to the tribometer for future is temperature control. Therefore, we can test lubricant performance at high or low temperatures. • In this study, we use cellulose nanocrystals suspension in water. However, the CNC particles are solvable in other organic polar solvents such as Glycerol [94], Dimethylformamide [95], and Dimethylsulfoxide [96] which may work as a lubricant. In addition, the application of CNC as an oil-based lubricant additive can be investigated in future.  • Cellulose nanocrystals suspension with concentrations of more than 3 wt.% exhibit liquid crystal fingerprints and one of the reasons that CNC is a good lubricant is the organized structure of its particle. While there are many other environmental friendly liquid crystals such as Graphene oxide or Triphenylene which can be tested as lubricant additives to make water based or oil based lubricants.  63  • Currently, water is used as a lubricant in the slurry pump gland seals and one of the issues with water is the high freezing point. In the cold regions, especially in many regions in Canada during the winter the temperature is far below water freezing point. The idea of adding antifreeze to cellulose nanocrystals suspension is tested but the CNC is not solvable in ethylene glycol based antifreeze which is commercially available. Also, adding antifreeze doesn’t reduce the coefficient of friction or wear rate. Therefore, finding a new antifreeze which is compatible with CNC and also improve the lubricant properties of CNC suspension would be one of future directions.  64  Bibliography [1] Y. C. Ching et al., “Rheological properties of cellulose nanocrystal-embedded polymer composites: a review,” Cellulose, vol. 23, no. 2. pp. 1011–1030, 12-Apr-2016. [2] L. Du, J. Wang, Y. Zhang, C. Qi, M. Wolcott, and Z. Yu, “Preparation and Characterization of Cellulose Nanocrystals from the Bio-ethanol Residuals,” Nanomaterials, vol. 7, no. 3, p. 51, 2017. [3] A. Standard, “G99, Standard test method for wear testing with a pin-on-disk apparatus,” ASTM Int. West Conshohocken, PA, 2006. [4] A. International, “Standard Test Method for Linearly Reciprocating Ball-on-Flat Sliding Wear,” ASTM Standard G-133–95,” Annu. B. Stand., vol. 3, pp. 521–528, 1996. [5] D. Trauth et al., “Evaluation of the shear stresses on surface structured workpieces in dry forming using a novel pin-on-cylinder tribometer with axial feed,” Int. J. Mater. Form., vol. 10, no. 4, pp. 557–565, 2017. [6] B. A. Baldwin and J. E. Lee, “An automated laboratory lubricant test to simulate valve train wear,” Wear, vol. 84, no. 2, pp. 139–150, 1983. [7] N. S. M. El-Tayeb and R. M. Nasir, “Effect of soft carbon black on tribology of deproteinised and polyisoprene rubbers,” Wear, vol. 262, no. 3–4, pp. 350–361, 2007. [8] A. W. J. de Gee and G. W. Rowe, “Glossary of Terms and Definitions in the Field of Friction, Wear and Lubrication Tribology,” Organ. Econ. Co-operation Dev. Paris, 1969. 65  [9] B. Bhushan, Principles and applications of tribology. John Wiley & Sons, 2013. [10] B. Bhushan, Introduction to tribology. John Wiley & Sons, 2013. [11] B. Bhushan, Modern tribology handbook, two volume set. CRC press, 2000. [12] A. Abdelbary, Wear of polymers and composites. Woodhead Publishing, 2015. [13] P. J. Blau, ASM Handbook, Volume 18-Friction, Lubrication, and Wear Technology. ASM international, 1992. [14] B. Bhushan, “Nano-to microscale wear and mechanical characterization using scanning probe microscopy,” Wear, vol. 251, no. 1–12, pp. 1105–1123, 2001. [15] L.-Y. Lin, D.-E. Kim, W.-K. Kim, and S.-C. Jun, “Friction and wear characteristics of multi-layer graphene films investigated by atomic force microscopy,” Surf. Coatings Technol., vol. 205, no. 20, pp. 4864–4869, 2011. [16] A. F. Fercher, “Arrangement for spectral interferometric optical tomography and surface profile measurement.” Google Patents, 23-Apr-2002. [17] K. Creath, “V phase-measurement interferometry techniques,” in Progress in optics, vol. 26, Elsevier, 1988, pp. 349–393. [18] I. Koyuncu, J. Brant, A. Lüttge, and M. R. Wiesner, “A comparison of vertical scanning interferometry (VSI) and atomic force microscopy (AFM) for characterizing membrane surface topography,” J. Memb. Sci., vol. 278, no. 1–2, pp. 410–417, 2006. [19] A. Devillez, S. Lesko, and W. Mozer, “Cutting tool crater wear measurement with white 66  light interferometry,” Wear, vol. 256, no. 1–2, pp. 56–65, 2004. [20] K. G. Larkin, D. J. Bone, and M. A. Oldfield, “Natural demodulation of two-dimensional fringe patterns. I. General background of the spiral phase quadrature transform,” JOSA A, vol. 18, no. 8, pp. 1862–1870, 2001. [21] P. Pavliček and J. Soubusta, “Theoretical measurement uncertainty of white-light interferometry on rough surfaces,” Appl. Opt., vol. 42, no. 10, pp. 1809–1813, 2003. [22] G. Schramm, A practical approach to rheology and rheometry. Haake Karlsruhe, 1994. [23] C. W. Macosko, Rheology: principles, measurements, and applications. Wiley-vch, 1994. [24] H. A. Barnes, J. F. Hutton, and K. Walters, An introduction to rheology, vol. 3. Elsevier, 1989. [25] W. J. Bartz and J. Ehlert, “Influence of pressure viscosity of lubrication oils on pressure, temperature, and film thickness in elastohydrodynamic rolling contacts,” J. Lubr. Technol., vol. 98, no. 4, pp. 500–507, 1976. [26] G. Stachowiak and A. W. Batchelor, Engineering tribology. Butterworth-Heinemann, 2013. [27] F. A. Morrison, “Understanding Rheology. 2001,” Ox. Un. Press. ISBN, pp. 970–978. [28] J. F. Steffe, Rheological methods in food process engineering. Freeman press, 1996. [29] R. G. Larson, “Instabilities in viscoelastic flows,” Rheol. Acta, vol. 31, no. 3, pp. 213–263, 1992. 67  [30] R. P. Chhabra and J. F. Richardson, Non-Newtonian flow and applied rheology: engineering applications. Butterworth-Heinemann, 2011. [31] T. G. Mezger, The rheology handbook: for users of rotational and oscillatory rheometers. Vincentz Network GmbH & Co KG, 2006. [32] W. Dresel, Lubricants and lubrication. John Wiley & Sons, 2007. [33] P. J. Davim, Tribology for engineers: A practical guide. 2011. [34] C. McFadden, C. Soto, and N. D. Spencer, “Adsorption and surface chemistry in tribology,” Tribol. Int., vol. 30, no. 12, pp. 881–888, Dec. 1997. [35] G. A. Somorjai, “Progress in our understanding of structure bonding and reactivity of metal surfaces and adsorbed monolayers at the molecular level: A 25 year perspective,” Prog. Surf. Sci., vol. 50, no. 1–4, pp. 3–29, Sep. 1995. [36] Y. K. Cho, L. Cai, and S. Granick, “Molecular tribology of lubricants and additives,” Tribol. Int., vol. 30, no. 12, pp. 889–894, Dec. 1997. [37] P. M. Lugt and G. E. Morales-Espejel, “A review of elasto-hydrodynamic lubrication theory,” Tribol. Trans., vol. 54, no. 3, pp. 470–496, 2011. [38] Y.-Z. Hu and D. Zhu, “A full numerical solution to the mixed lubrication in point contacts,” J. Tribol., vol. 122, no. 1, pp. 1–9, 2000. [39] M. W. Sulek and T. Wasilewski, “Tribological properties of aqueous solutions of alkyl polyglucosides,” Wear, vol. 260, no. 1–2, pp. 193–204, 2006. 68  [40] N. Ridgway, C. B. Colby, and B. K. O’Neill, “Slurry pump gland seal wear,” Tribol. Int., vol. 42, no. 11–12, pp. 1715–1721, 2009. [41] H. J. Song and N. Li, “Frictional behavior of oxide graphene nanosheets as water-base lubricant additive,” Appl. Phys. A Mater. Sci. Process., vol. 105, no. 4, pp. 827–832, Dec. 2011. [42] B. R. M. Gresham, “The mysterious world of MWF additives,” Tribol. Lubr. Technol., vol. 62, no. 9, pp. 30–32, 2006. [43] Y. Y. Wu, W. C. Tsui, and T. C. Liu, “Experimental analysis of tribological properties of lubricating oils with nanoparticle additives[sherif] (6),” Wear, vol. 262, no. 7–8, pp. 819–825, 2007. [44] J. Sun, Y. Li, P. Xu, and Z. Zhu, “Study on the Lubricating Performance of Nano-TiO 2 in Water-Based Cold Rolling Fluid,” Mater. Sci. Forum, vol. 817, pp. 3989–3993, Apr. 2015. [45] C. Zhang, S. Zhang, L. Yu, Z. Zhang, Z. Wu, and P. Zhang, “Applied Surface Science Preparation and tribological properties of water-soluble copper / silica nanocomposite as a water-based lubricant additive,” Appl. Surf. Sci., vol. 259, pp. 824–830, 2012. [46] C. Zhang et al., “Preparation and tribological properties of surface-capped copper nanoparticle as a water-based lubricant additive,” Tribol. Lett., vol. 54, no. 1, pp. 25–33, Apr. 2014. [47] W. Jian, S. Min, L. I. Jin, and W. Xiao, “The Preparation and Tribological Properties of 69  Water - soluble Nano - silica Particales,” en.cnki.com.cn, no. September 2010, 2011. [48] H. Xie, B. Jiang, X. Hu, C. Peng, H. Guo, and F. Pan, “Synergistic Effect of MoS2 and SiO2 Nanoparticles as Lubricant Additives for Magnesium Alloy–Steel Contacts,” Nanomaterials, vol. 7, no. 7, p. 154, 2017. [49] S. Radice and S. Mischler, “Effect of electrochemical and mechanical parameters on the lubrication behaviour of Al2O3 nanoparticles in aqueous suspensions,” Wear, vol. 261, no. 9, pp. 1032–1041, 2006. [50] H. J. Pei X, Hua L, Liu W, “Synthesis of water-soluble carbon nanotubes via surface initiatedredox polymerization and their tribologicalproperties as water-based lubricant additive,” EurPolym J, vol. 44, p. 2458–2464., 2008. [51] H. Kinoshita, Y. Nishina, A. A. Alias, and M. Fujii, “Tribological properties of monolayer graphene oxide sheets as water-based lubricant additives,” Elsevier, vol. 66, pp. 720–723, 2014. [52] Y. Liu, X. Wang, G. Pan, and J. Luo, “A comparative study between graphene oxide and diamond nanoparticles as water-based lubricating additives,” Sci. China Technol. Sci., vol. 56, no. 1, pp. 152–157, Jan. 2013. [53] H. Lei, W. Guan, and J. Luo, “Tribological behavior of fullerene – styrene sulfonic acid copolymer as water-based lubricant additive,” Elsevier, vol. 252, pp. 345–350, 2002. [54] H. Wu et al., “A study of the tribological behaviour of TiO2 nano-additive water-based lubricants,” Tribol. Int., vol. 109, no. October 2016, pp. 398–408, 2017. 70  [55] N. I. Ridgway, “Slurry pump gland seal three body wear and the influence of particle properties including hardness, size, fracture toughness and shape.” 2010. [56] B. A. Khorramian, G. R. Iyer, S. Kodali, P. Natarajan, and R. Tupil, “Review of antiwear additives for crankcase oils,” Wear, vol. 169, no. 1, pp. 87–95, 1993. [57] M. J. Stephen and J. P. Straley, “Physics of liquid crystals,” Rev. Mod. Phys., vol. 46, no. 4, p. 617, 1974. [58] A. M. Sonnet and E. G. Virga, Dissipative ordered fluids: theories for liquid crystals. Springer Science & Business Media, 2012. [59] G. Biresaw, Tribology and the liquid-crystalline state. American Chemical Society, 1990. [60] A. G. Dumanli and T. Savin, “Recent advances in the biomimicry of structural colours,” Chem. Soc. Rev., vol. 45, no. 24, pp. 6698–6724, 2016. [61] C. Xiang and A. R. Barron, “The analysis of liquid crystal phases using polarized optical microscopy,” Creat. Commons Attrib. Licens. Modul. m38343, 2011. [62] S. Agamanolis, “Liquid crystal displays: Past, present, and future,” Massachusetts Inst. Technol., 1995. [63] M. Moniri et al., “Production and Status of Bacterial Cellulose in Biomedical Engineering,” Nanomaterials, vol. 7, no. 9, p. 257, 2017. [64] T. J. Fellers and M. W. Davidson, “Polarized Illumination.” [Online]. Available: https://www.olympus-lifescience.com/pt/microscope-resource/micd/anatomy/micdpolarized/. 71  [65] Y. Habibi, L. A. Lucia, and O. J. Rojas, “Cellulose nanocrystals: Chemistry, self-assembly, and applications,” Chem. Rev., vol. 110, no. 6, pp. 3479–3500, Jun. 2010. [66] R. J. Moon, A. Martini, J. Nairn, J. Simonsen, and J. Youngblood, Cellulose nanomaterials review: structure, properties and nanocomposites, vol. 40, no. 7. 2011. [67] M. C. Li et al., “Cellulose Nanocrystals and Polyanionic Cellulose as Additives in Bentonite Water-Based Drilling Fluids: Rheological Modeling and Filtration Mechanisms,” Ind. Eng. Chem. Res., vol. 55, no. 1, pp. 133–143, Jan. 2016. [68] Y. Nishiyama, G. P. Johnson, A. D. French, V. T. Forsyth, and P. Langan, “Neutron crystallography, molecular dynamics, and quantum mechanics studies of the nature of hydrogen bonding in cellulose Iβ,” Biomacromolecules, vol. 9, no. 11, pp. 3133–3140, Nov. 2008. [69] F. L. Dri, L. G. Hector, R. J. Moon, and P. D. Zavattieri, “Anisotropy of the elastic properties of crystalline cellulose Iβ from first principles density functional theory with Van der Waals interactions,” Cellulose, vol. 20, no. 6, pp. 2703–2718, 2013. [70] W. Y. Hamad, Cellulose nanocrystals: properties, production and applications. John Wiley & Sons, 2017. [71] J. Revol, H. Bradford, … J. G.-I. journal of, and  undefined 1992, “Helicoidal self-ordering of cellulose microfibrils in aqueous suspension,” Elsevier. [72] P.-G. de Gennes and J. Prost, “The physics of liquid crystals (international series of monographs on physics),” Oxford Univ. Press. USA, vol. 2, p. 4, 1995. 72  [73] B. L. Peng, N. Dhar, H. L. Liu, and K. C. Tam, “Chemistry and applications of nanocrystalline cellulose and its derivatives: A nanotechnology perspective,” Canadian Journal of Chemical Engineering, vol. 89, no. 5. pp. 1191–1206, Oct-2011. [74] J.-F. Revol, L. Godbout, and D. G. Gray, “Solid self-assembled films of cellulose with chiral nematic order and optically variable properties,” J. Pulp Pap. Sci., vol. 24, no. 5, pp. 146–149, May 1998. [75] F. C. Bawden, N. W. Pirie, J. D. Bernal, and I. Fankuchen, “Liquid crystalline substances from virus-infected plants,” Nature, vol. 138, no. 3503, p. 1051, 1936. [76] P.-X. Wang, W. Y. Hamad, and M. J. MacLachlan, “Structure and transformation of tactoids in cellulose nanocrystal suspensions,” Nat. Commun., vol. 7, p. 11515, 2016. [77] S. Beck, J. Bouchard, G. Chauve, and R. Berry, “Controlled production of patterns in iridescent solid films of cellulose nanocrystals,” Cellulose, vol. 20, no. 3, pp. 1401–1411, Jun. 2013. [78] J. Araki, M. Wada, S. Kuga, and T. Okano, “Flow properties of microcrystalline cellulose suspension prepared by acid treatment of native cellulose,” Colloids Surfaces A Physicochem. Eng. Asp., vol. 142, no. 1, pp. 75–82, Nov. 1998. [79] S. Shafiei-Sabet, W. Y. Hamad, and S. G. Hatzikiriakos, “Rheology of nanocrystalline cellulose aqueous suspensions,” Langmuir, vol. 28, no. 49, pp. 17124–17133, Dec. 2012. [80] A. Misra and I. Finnie, “On the size effect in abrasive and erosive wear,” Wear, vol. 65, no. 3, pp. 359–373, Jan. 1981. 73  [81] J. E. Shigley, Shigley’s mechanical engineering design. Tata McGraw-Hill Education, 2011. [82] E. Sakurai and J. F. Hamilton, “The prediction of frictional losses in variable-speed rotary compressors,” 1984. [83] J. M. Dealy and K. F. Wissbrun, Melt rheology and its role in plastics processing: theory and applications. Springer Science & Business Media, 2012. [84] N. LeCain, “Tutorial of Hertzian Contact Stress Analysis,” Coll. Opt. Sci. Univ. Arizona, Tucson, pp-1 to, vol. 6, no. 3, 2011. [85] K. L. Johnson, “Contact mechanics, 1985.” Cambridge University Press, Cambridge, 1974. [86] M. J. Puttock and E. G. Thwaite, Elastic compression of spheres and cylinders at point and line contact. Commonwealth Scientific and Industrial Research Organization Melbourne, Australia, 1969. [87] X. Lu, M. M. Khonsari, and E. R. M. Gelinck, “The Stribeck Curve: Experimental Results and Theoretical Prediction,” J. Tribol., vol. 128, no. 4, p. 789, 2006. [88] S. M. Hsu and R. S. Gates, “Boundary lubricating films: formation and lubrication mechanism,” Tribol. Int., vol. 38, no. 3, pp. 305–312, 2005. [89] M. C. Li, Q. Wu, K. Song, S. Lee, Y. Qing, and Y. Wu, “Cellulose Nanoparticles: Structure-Morphology-Rheology Relationships,” ACS Sustain. Chem. Eng., vol. 3, no. 5, pp. 821–832, May 2015. 74  [90] S. S. Sabet, “Shear Rheology of Cellulose Nanocrystal ( CNC ) Aqueous Suspensions A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF,” 2013. [91] S. Camarero Espinosa, T. Kuhnt, E. J. Foster, and C. Weder, “Isolation of thermally stable cellulose nanocrystals by phosphoric acid hydrolysis,” Biomacromolecules, vol. 14, no. 4, pp. 1223–1230, 2013. [92] A. Šturcová, G. R. Davies, and S. J. Eichhorn, “Elastic modulus and stress-transfer properties of tunicate cellulose whiskers,” Biomacromolecules, vol. 6, no. 2, pp. 1055–1061, 2005. [93] J. Yi, Q. Xu, X. Zhang, and H. Zhang, “Chiral-nematic self-ordering of rodlike cellulose nanocrystals grafted with poly (styrene) in both thermotropic and lyotropic states,” Polymer (Guildf)., vol. 49, no. 20, pp. 4406–4412, 2008. [94] A. Dorris and D. G. Gray, “Gelation of cellulose nanocrystal suspensions in glycerol,” Cellulose, vol. 19, no. 3, pp. 687–694, 2012. [95] H. Dong, K. E. Strawhecker, J. F. Snyder, J. A. Orlicki, R. S. Reiner, and A. W. Rudie, “Cellulose nanocrystals as a reinforcing material for electrospun poly (methyl methacrylate) fibers: Formation, properties and nanomechanical characterization,” Carbohydr. Polym., vol. 87, no. 4, pp. 2488–2495, 2012. [96] D. Viet, S. Beck-Candanedo, and D. G. Gray, “Dispersion of cellulose nanocrystals in polar organic solvents,” Cellulose, vol. 14, no. 2, pp. 109–113, 2007. 75   Appendices Appendix A   76   

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.24.1-0371189/manifest

Comment

Related Items