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Enhanced barrier performance of cellulosic wood fiber/filler network Feng, Xianzhong 2016

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  Enhanced Barrier Performance of Cellulosic Wood Fiber/Filler Network    by     Xianzhong Feng  B.Eng., Zhejiang University, China, 2014       A THESIS SUBMITED IN PARTIAL FULFILLMENT OF  THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF APPLIED SCIENCE  in   THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Chemical and Biological Engineering)    The University of British Columbia (Vancouver)     July 2016   © Xianzhong Feng, 2016   	 ii	ABSTRACT Cellulose is an abundant material, which is widely used in papermaking. It is both a biodegradable and sustainable material. However, its hydrophilic nature may limit its applications in specific and novel areas such as waterproof packaging and paper based microfluidics. In this thesis, three different routes are followed to render the surface of the paper superhydrophobic. First, chemical vapor-phase silanization is done on handsheets made from wood pulp with untreated kaolin clay and precipitated calcium carbonate (PCC) as fillers. The effect of fiber length, filler’s type, size, and concentration on the barrier performance of handsheets is shown. Secondly, mircofibrillated cellulose (MFC), which serves as reinforcement agent in paper, is employed as an additive to change the hydrophilic property of paper. MFC is silanized to obtain hydrophobicity before being dispersed into the pulp suspension. Then the resulting paper undergoes an additional silanization (post-treatment). The third approach involves depositing Janus clay particles on untreated paper. A Janus particle has a hydrophobic and a hydrophilic surface. Because clay particles are hydrophilic, they are treated to obtain hydrophobicity on one side, while the other side remains hydrophilic. An efficient method to obtain these types of particles is the formation of a Pickering emulsion. The study here, focuses on the determining the barrier properties of the prepared superhydrophobic or hydrophobic papers: wettability, water vapor transmission rate (WVTR), and air permeability. The handsheets with shorter fiber length, precipitated calcium carbonate, smaller filler size and lower filler content, were found to exhibit lower WVTR values. The water contact angle of handsheets loaded with fillers, Janus clay particles and hydrophobic MFC, was found to be 120~130º, 141º and 134~144º respectively.  	 iii	PREFACE This dissertation is original, unpublished, independent work by the author, Xianzhong Feng.   	 iv	TABLE OF CONTENTS ABSTRACT ....................................................................................................................... ii PREFACE ......................................................................................................................... iii TABLE OF CONTENTS ................................................................................................ iv LIST OF TABLES ........................................................................................................... vi LIST OF FIGURES ........................................................................................................ vii ACKNOWLEDGMENTS ............................................................................................. viii CHAPTER1. INTRODUCTION ..................................................................................... 1 1.1 Motivation of the Study ....................................................................................................... 1 1.2 Cellulosic Wood Fiber and Paper ....................................................................................... 1 1.3 Fillers and Additives ............................................................................................................ 3 1.3.1 Kaolin Clay ..................................................................................................................... 5 1.3.2 Calcium Carbonate ......................................................................................................... 5 1.3.3 Microfibrillated Cellulose ............................................................................................... 7 1.4 Janus Particles ...................................................................................................................... 8 1.5 Pickering Emulsion .............................................................................................................. 9 1.6 Silanization .......................................................................................................................... 12 1.7 Criteria for Superhydrophobic Surface ........................................................................... 13 1.8 Wettability .......................................................................................................................... 15 1.9 Applications in Packaging and Fundamental Device ..................................................... 17 CHAPTER 2: THESIS OBJECTIVES ......................................................................... 18 CHAPTER 3: MATERIALS AND METHODS .......................................................... 19 3.1 Materials and Experimental Apparatus .......................................................................... 19 3.2 Preparation of Handsheets Loaded with Fillers .............................................................. 21 3.3 Silanization on Handsheets ................................................................................................ 23 3.4 Preparation of Handsheets with Hydrophobic MFC ...................................................... 24 3.5 Pickering Emulsion Stabilized by Fillers ......................................................................... 25 3.6 Fabrication of Janus Kaolin Clay Particles ..................................................................... 25 3.7 Incorporation of Janus Clay Particle Coating on Handsheet ........................................ 26 3.8 Handsheet Properties Characterization ........................................................................... 27 3.8.1 Weight of Handsheets ................................................................................................... 27 3.8.2 Thickness (L&W Micrometer) ..................................................................................... 27 3.8.3 Air Resistance (Gurley Method) ................................................................................... 27 3.8.4 Water Vapor Transmission Rate (WVTR) ................................................................... 27 3.8.5 Water Contact Angle Measurement .............................................................................. 28 CHAPTER 4: RESULTS AND DISCUSSION ............................................................ 29 	 v	4.1 Thickness and Density of Handsheets .............................................................................. 29 4.2 Water Vapor Transmission Rate (WVTR) of Handsheet .............................................. 31 4.2.1 Effect of Fiber Size on WVTR of Paper ....................................................................... 33 4.2.2 Effect of Filler Type on WVTR of Paper ..................................................................... 34 4.2.3 Effect of Filler Content on WVTR of Paper ................................................................. 35 4.2.4 Effect of Filler Size on WVTR of Paper ....................................................................... 36 4.2.5 Effect of Silanization on WVTR of Paper .................................................................... 37 4.3 Air Permeability of Handsheets ........................................................................................ 37 4.4 Wettability of Handsheets after Silanization ................................................................... 38 4.4.1 Effect of Fiber Size on Water Contact Angle ............................................................... 40 4.4.2 Effect of Filler Type on Water Contact Angle ............................................................. 40 4.4.3 The Influence of Other Factors on Water Contact Angle ............................................. 41 4.5 Wettability of Handsheets Loaded with Hydrophobic MFC ......................................... 41 4.6 The Stability of Pickering Emulsions ............................................................................... 42 4.7 Wettability of Handsheets Coated with Janus Clay Particle ......................................... 46 CHAPTER 5: CONCLUSION AND RECOMMENDATION ................................... 47 BIBLIOGRAPHY ........................................................................................................... 48   	 vi	LIST OF TABLES Table 3.1: Pulp and fiber specifications ........................................................................... 19 Table 3.2: The specifications of fillers ............................................................................. 19 Table 3.3: Pulp Suspension Concentrations ..................................................................... 22 Table 4.1: The thickness and density of handsheets with KU ......................................... 29 Table 4.2: The thickness and density of handsheets with KR1 ........................................ 29 Table 4.3: The thickness and density of handsheets with KU+KR1 ................................ 30 Table 4.4: The thickness and density of handsheets with KU+KR2 ................................ 30 Table 4.5: The WVTR values of handsheets with KU (g/(m2·day)) ................................ 31 Table 4.6: The WVTR values of handsheets with KR1 (g/(m2·day)) ............................... 31 Table 4.7: The WVTR values of handsheets with 50%-50% KU + KR1 (g/(m2·day)) .... 31 Table 4.8: The WVTR values of handsheets with 50%-50% KU + KR2 (g/(m2·day)) .... 31 Table 4.9: The WVTR values of handsheets before and after silanization ...................... 32 Table 4.10: The errors of WVTR values of handsheets ................................................... 32 Table 4.11: Air Permeability of KU+KR2 handsheets (s/100cc) ..................................... 37 Table 4.12: Water contact angle (WCA) of KU handsheets ............................................ 38 Table 4.13: Water contact angle (WCA) of KR1 handsheets ........................................... 39 Table 4.14: Water contact angle (WCA) of KU+KR1 handsheets ................................... 39 Table 4.15: Water contact angle (WCA) of KU+KR2 handsheets ................................... 39 Table 4.16: Water contact angle of silanized KU handsheets with hydrophobic MFC ... 42 Table 4.17: The stability of Pickering emulsion stabilized by Kaolin clay ..................... 43 Table 4.18: The formula of Pickering emulsion stabilized by other fillers ..................... 43   	 vii	LIST OF FIGURES Figure 1.1: Structure of cellulose ....................................................................................... 2 Figure 1.2: A schematic of the modern papermaking process ........................................... 3 Figure 1.3: Filler used in paper products by grade in 2008 ............................................... 4 Figure 1.4: Delamination of kaolin stacks ......................................................................... 5 Figure 1.5: Structure of microfibrillated cellulose ............................................................. 8 Figure 1.6: Schematic of silanization on hydrophilic surface by DCDMS ..................... 13 Figure 1.7: Wetting models (Left) at a smooth surface; (Middle) in Wenzel state; (Right) in Cassie-Baxter state ........................................................................................................ 16 Figure 3.1: Schematic of customized handsheet former .................................................. 22 Figure 3.2: Schematic of silanization equipment ............................................................. 23 Figure 4.1: The WVTR values of handsheets with different fiber sizes .......................... 33 Figure 4.2: The WVTR values of handsheets loaded with different fillers ..................... 34 Figure 4.3: The WVTR values of handsheets loaded with Calcined clay (upper) and PCC (below) at different filler content ...................................................................................... 35 Figure 4.4: The WVTR values of KR1 handsheets with different filler size ................... 36 Figure 4.6: The water contact angle of handsheets without filler .................................... 40 Figure 4.7: SEM images of colloidosome (a, b) Kaolin clay, (c) calcined clay, (d) Nano-clay, (e) PCC, (f) Nano-PCC ............................................................................................ 45 Figure 4.8: Static water contact angle on handsheets coated with Janus clay particle .... 46 	  	 viii	ACKNOWLEDGMENTS First and foremost, I would love to express my sincere appreciation and gratitude to my supervisor Dr. Peter Englezos for his continuous supports in the past two years. He opened the door to academic research for me and offered great help on the path to master degree. Without his guidance, patience, and encouragement, the study would not be successfully completed. Dr. Englezos is always concerned about the progress of project and enthusiastic to answer the questions. My interest of research is inspired by his academic knowledge and perspective a lot. It is an invaluable experience to be a student under his supervision. I appreciate Dr. Savvas Hatzikiriakos and Dr. Mark Martinez as my committee members. It is very helpful to have their comments on my research. I am really grateful to our research group members for their ideas and help. Special thanks to my colleague Mehrnegar Mirvakili for kindly helping me with the study and training of the experiment. It is a wonderful opportunity to work with her. I am grateful to my friends in here for their company and encouragement, making my graduate life an impressive learning experience. Last but most importantly, I would like to express my deepest love to my family for their countless supports and encouragement. They are always there when I grow up and pursue my dreams. It means a lot to accomplish my master education in UBC. And I could not reach the goals without them. The happiest thing is to have them in my life.  	 1	CHAPTER1. INTRODUCTION In this chapter the motivation of the study is presented as well as a brief introduction to the main materials used in this work. 1.1 Motivation of the Study The interest on cellulose-based materials research is growing due to the fact that these materials exhibit biodegradation and renewability and thus are environment-friendly. There is a growing demand for such sustainable industrial and consumer products (Ljungberg, 2007). Cellulose may be obtained from plants, food crops and even bacteria. Cellulose is a fundamental material for paper manufacture. Its application is limited to tissue, printing, food containers and packaging, in part because of the hydrophilic nature of cellulosic fibers. This research aims at rendering the cellulosic paper hydrophobic and or superhydrophobic through functionalization of filler/additives, such as kaolin clay, precipitated calcium carbonate and microfibrillated cellulose (MFC), with the aid of chemical vapor-phase silanization. The addition of these filler/additives makes a remarkable difference on the microstructure and surface properties of paper, such as porosity, density, and roughness. Combined with the effect of low-surface-energy chemical, dichlorodimethylsilane (DCDMS), the barrier performance can be improved by affecting wettability and permeability of water and air molecules. The effects of fiber size and filler’s type, particle size, content on the barrier properties of paper are also investigated in this study. The papers with improved barrier property have a strong potential in special applications such as waterproof and self-cleaning packages, microfluidic devices and detection of gas and liquid. 1.2 Cellulosic Wood Fiber and Paper Cellulose is one of the most important natural materials in the world, which derives from wood, plants and bacteria. Wood consisting of cellulose, hemicellulose, lignin and extractives, is the major source of cellulose. The repeating molecular unit of cellulose is β-D-glucopyranose, which forms a linear chain through acetal function between C-1 and C-4 carbon atoms (Figure 1.1) (Figueiredo et al. 2010). There are a large amount of hydroxyl groups existing along the polymeric chain. Thus, cellulose is hydrophilic in nature and capable for chemical modification. Cellulosic molecular chains bound 	 2	together through intermolecular hydrogen bonding. Cellulose fibers have crystallographic and amorphous domains. In the crystalline domain, the cellulose chains orient in a parallel form, and behave impermeable to water (Figueiredo et al. 2010). In contrast, the cellulose molecules in the amorphous domain are more dispersible in water and have higher reactivity.  Figure 1.1: Structure of cellulose (Adapted from Figueiredo, 2010) Cellulose plays an essential role in both people’s daily life and in manufacturing. In comparison with fossil derivative materials, cellulose-based materials are biodegradable, renewable and recyclable. It is the main component in paper, textile, membranes, etc. (Cerruti et al. 2008). Paper and paperboard products consume most of cellulose-based materials all over the world.  It is widely recognized that the original papermaking process was developed in China by Cai Lun around 105 AD. In the modern papermaking industry (Figure 1.2), wood is transformed into pulp after chemical (e.g. Kraft process, sulfite process) and mechanical (e.g. thermomechanical process (TMP), groundwood process (GW)) pulping. Then, the pulp is fed into a papermaking machine and undergoes pressing and drying to form paper sheets. In finishing processes, the obtained paper is modified to alter its chemical and or physical properties to meet the demand of applications. Paper is made into packaging and food containers, printing and writing papers, and sanitary and household papers (McCarthy & Urmanbetova 2011).  	 3	 Figure 1.2: A schematic of the modern papermaking process (Adapted from www.paperonline.org) 1.3 Fillers and Additives Except for cellulosic fibers, mineral fillers constitute the second largest component in paper. The most widely used fillers include kaolin clay, calcium carbonate, titanium dioxides, and Talc (Figure 1.3). Conventionally, fillers are added into pulp suspension in the wet end. The addition of fillers lowers the cost of paper manufacturing. The regular price of pulp is around $400-800/ton, while the filler cost of clay and PCC is around $100-200/ton. Besides the cost, the fillers can also help improve the optical properties of paper, such as brightness and printing quality by providing ink adsorption. The water drainage rate will increase as well. However, there are several adverse effects accompanying the addition of fillers. First of all, the paper suffers a loss in strength, since the fillers interfere with the intermolecular hydrogen bonding between fibers. During the wet-end operation, fillers may cause abrasive problems to the machines, and dust hazardous in factory as well. 	 4	 Figure 1.3: Filler used in paper products by grade in 2008 (Adapted from Finnish Forest Industries, 2009) Although it is cost effective to use more fillers in paper, usually the filler content is up to 50% in paper. In order to retain the fillers when draining water, some polymers are used as additives, such as cationic polyacrylamide (cPAM), and starch (Shen et al. 2009b). With the aid of these polymers, preflocculation of fillers and polymer coating on the surface of fillers happen (Chauhan & Bhardwaj 2014). Thus, the fillers are fixed onto the fibers.	 Applying fillers only at the surface of paper via a size press is an alternative to conventional wet-end addition (Shen & Qian 2012). In this process, the fillers are placed onto paper surface and inserted into the existing pores of matrix. Since fillers don’t penetrate into the bulk, the decrease of paper strength is alleviated. In recent years, there is interest on biodegradable, environmental friendly and recyclable materials, which points to a new demand for filler development. Also, fillers play an essential role in the creation of papers with unique properties. How to efficiently modify the fillers is an ongoing research topic (Shen et al. 2009b). Filler modification brings important properties, such as hydrophobic, magnetic, photocatalytic, flame retardant and deodorizing ability to paper (Shen et al. 2011). Kaolin 38% 11.4Mt Talc, TiO2 and others 7% 2.1Mt Ground Calcium carbonate (GCC) 38.5% 11.5Mt Precipitated Calcium Carbonate (PCC) 16.5% 11.5Mt 	 5	1.3.1 Kaolin Clay Clay is the second largest filler used in paper (after calcium carbonate). It consists of sodium and potassium silicates with metal oxides (e.g. alumina, magnesium oxide) and hydroxide. Tetrahedral and octahedral sheets are two basic crystal structures of clay. Different ratio of these two crystal structures constitutes various types of clay minerals, such as kaolinite (1:1), montmorillonite and illite.  The term “Kaolin” is derived from a hill, named as “Kauling” in China, meaning high ridge. The clay at that location has been mined for ceramics centuries ago (Prasad et al. 1991). The chemical formula of Kaolin clay can be represented as Al2O3∙2SiO2·2H2O. Kaolin clay has a plate-like shape (Figure 1.4) with positive charge at the edge and negative charge on the surface.  Figure 1.4: Delamination of kaolin stacks (Adapted from Murray & Kogel, 2005) Kaolin clay is one of the most versatile raw materials, and can be used in numerous applications, such as paper, coatings, fire proof-materials, ceramics and rubber (Liu et al. 2013),. The papermaking industry consumes the largest amount of Kaolin clay for paper coating and filling in US (Prasad et al. 1991). With the aid of Kaolin clay, the smoothness, brightness, printability, fire resistance are improved as well as significant cost savings are realized in the operation (filler is cheaper than fibres). 1.3.2 Calcium Carbonate Calcium carbonate is considered as dominant mineral filler in the papermaking industry. With the addition of CaCO3, the paper exhibits enhanced brightness, opacity, and printability. There are two main types of CaCO3: ground calcium carbonate (GCC) 	 6	and precipitated calcium carbonate (PCC). GCC is generally obtained by grinding limestone and chalk from shells of marine life. Its most common crystal structure is rhombohedral. PCC is manufactured by chemical reaction of calcium quicklime slurry and carbon dioxides (as shown below), and performs higher brightness. By controlling the reaction conditions, the characteristics of PCC, such as particle size, particle shape, surface area, and crystal structure can be well designed to meet the demand of a specific application. CaO+CO2→CaCO3                                                                               (1-1) Ca(OH)2+CO2→CaCO3+H2O                                           (1-2) PCCs with different crystal structures perform different behavior in paper. When colloidal PCC is applied into pulp suspension, it agglomerates into an ellipsoidal shape and mostly deposits at the end of fibers. In contrast, rhombohedral and scalenohedral type of PCC forms a spider-web structure with fibers (Subramaniana et al. 2007). Thus, the papers loaded with different type of PCCs exhibit significant differences on filler retention, dewatering, density and tensile strength. However, the chemical nature of PCC limits its use under acidic conditions. Calcium carbonate dissolves in an acidic environment. Precipitated calcium carbonate fillers become acid-resistant, when modified by a treatment with phosphoric acid and sodium hexametaphosphate (Shen et al. 2009a). Compared with unmodified filler, these acid-tolerant fillers can considerably increase the brightness, air permeability of paper, and the retention of filler. Calcium carbonate is hydrophilic in nature, with a water contact angle close to 0, which results to its poor compatibility with polymer matrix. In order to make hydrophobic CaCO3 and broaden its applications, surface modification is needed. Generally, polymer grafting, surfactant, and stearic acid are adopted to modify the hydrophilic character of CaCO3. In a modification process, polymer grafting is performed on calcium carbonate particles surface (Wu & Lu 2003). During this process, mechanical energy, provided by stirring, is applied to promote the reaction by producing active sites on the particle surface, the carbonate ions. As a result, the polymer grafting needs less initiating 	 7	reactants and the overall reaction time is decreased. In addition, multi-layered grafted polymer on calcium carbonate is achieved. So it offers a fascinating view upon surface modification. Cationic and anionic surfactants are common chemicals to change the surface charge of fillers. CTAB (hexadecyltetramethylammonium bromide) and sodium oleate can be used to modify calcium carbonate nanoparticles (NPCC) via the wet carbonation technique (Dufresne et al. 2014). After the paper is coated with these cationic or anionic NPCC, several key properties of paper change. The water contact angle increases to 112° for CTAB-NPCC coated paper, while that of ground calcium carbonate-coated paper and oleate-NPCC paper is 104° and 42°, respectively. Calcium carbonate nanoparticles (NPCC) are hydrophilic in nature. In order to render the surface of these particles hydrophobic, dodecanoic acid (DA) is employed. Ca2+ reacts with DA and forms hydrophobic Ca(C12H23O2)2, which covers the surface of hydrophilic CaCO3. By increasing the dosage of DA, the water contact angle of NPCC dramatically increased to 120°	(complete coverage) (Chen et al. 2010).  1.3.3 Microfibrillated Cellulose Microbibrillated cellulose (MFC) is a branch of the cellulose family, described as micro or nano level fibers. MFC may serve as reinforcement additive in papermaking. MFC has a large surface area with hydroxyl groups and can be well dispersed into a pulp suspension. The hydroxyl groups provide possibilities for modification of MFC. If it is reacted with some polymers or organic molecules by proper methods, the hydrophilic property of MFC can be changed to hydrophobicity. A literature gave a comprehensive review of microfibrillated cellulose (MFC) and provided the definition of microfibrillated cellulose, such that distinguish it from cellulose and nanocellulose (Lavoine et al. 2012). MFC consists of aggregates of 10-50 cellulose microfibrils with a diameter in the range 20-60 nm and a length of several micrometers. This paper also discussed the mechanical and chemical treatment for MFC. The intrinsic properties of MFC are also reported, including morphology, crystallinity and surface chemistry. And the barrier properties, such as water vapor transfer, oxygen 	 8	barrier and hydrophilicity, are emphasized in certain applications, like MFC nanocomposites.  Figure 1.5: Structure of microfibrillated cellulose (Adapted from Lavoine et al. 2012) Due to the MFC’s hydrophilic nature, a number of nanocomposites can be made through dispersing MFC into hydrophilic matrices uniformly. To extend its application in fabrication of new nanocomposites, various chemical modifications have been explored to change the hydrophilicity of MFC to hydrophobicity (Siro & Plackett 2010). The resulting materials can be well applied into hydrophobic polymers serving as a reinforcement agent. This article also presented many types of cellulose-based nanocomposites and the corresponding fabrication methods. Cellulose nanocrystals and microfibrillated cellulose have great potential applications in four areas: aerogels, emulsions, templated materials, and stimuli-responsive nanodevices (Tingaut et al. 2012). The characteristics of cellulose-based materials in these fields are also demonstrated. Furthermore, based on the microstructure and performance of the nanocellulose, many functionalization methods are developed to modify its surface, in order to open up new possibilities for application. 1.4 Janus Particles A Janus particle has two sides of different chemistry or polarity. It is named after a god of the Roman religion. Janus particles of various shapes are divided into three categories: polymeric, inorganic, and polymeric-inorganic. Fabrication methods for these particles include Pickering emulsion interfacial synthesis, self-assembly of block copolymer and phase separation (Liang et al. 2014; Walther et al., 2008). The special structure of Janus particles opens up a door to the applications in fields such as water-	 9	repellent coating, stabilizer, drug delivery and catalysis (Hu et al. 2012; Kumar et al. 2013; Walther and Miller, 2008).  According to the Pickering emulsion route to fabricate Janus particles, untreated particles adsorb at a wax/water interface, and their exposed surfaces towards a continuous phase are chemically modified. Subsequently, the prepared particles are detached from the wax droplets and the inner surfaces undergo further chemical treatment. The chemical modification is done in either liquid or vapor phase (Hong 2006; Jiang et al. 2008). The geometry (Janus balance) of the particles can be controlled by adjustment of the surfactant concentration (Jiang & Granick 2008). Kalia et al. (2014) studied the surface modification of nanofibrillated cellulose, which shares similar structure with microfibrillated cellulose, despite the difference in length. After modification, the hydrophilic character of nanofibrillated cellulose is changed to hydrophobicity and the compatibility with polymer is enhanced (Kalia et al. 2014). The study demonstrated that nanofibrillated cellulose could be used as reinforcement additive in polymer matrices. Amphiphilic Janus particles can be applied onto a textile with the hydrophobic side pointing outwards. Larger particles  of micrometer size fill in the space between fibers, and smaller particles (submicrometer size) deposit right on the surface of a fiber bundle. The synergistic effect of hydrophobicity and dual roughness contributes to the water-repellent textile (Synytska et al. 2011). 1.5 Pickering Emulsion Pickering emulsion was first proposed by Pickering in 1907 (Pickering, 1907). By employing mechanical forces, such as agitation, oil can be dispersed into water but without stabilizers, the dispersed oil phase (oil droplets) will soon coalesce and phase separation occurs. However, if solid particles (e.g. silica) are added into the emulsions, a thermodynamically stable emulsion can be obtained. The mechanism behind this phenomenon is that, the oil droplets are covered by solid particles, which play a similar role as a surfactant. The optimum condition to form a Pickering emulsion is that the contact angle of particles is approximately 90°. The energy equation for stabilization is given below: 	 10	∆𝐸 = 𝜋𝑟!𝛾!" 1− cos𝜃!" !                                      (1-3) where ΔΕ is the change of energy when particles adsorb at the oil/water interface, r is the particle radius, γow is the interfacial tension between water and oil, and θow is the contact angle (Aveyard et al. 2003). The wetting behavior of solid particles at the oil/water interface is governed by the surface energies of all components in the emulsion system (Binks & Clint 2002). For example, the three phase contact angles of calcium carbonate and hydrophilic silica at the interface of dodecane/water are around 40° (Aveyard et al. 2003). Many types of fillers have potential to stabilize a Pickering emulsion. These fillers can be organic or inorganic, such as block polymers, clay, silica, and calcium carbonate, with particle size of micrometer to nanometer (Chevalier & Bolzinger 2013). When the water contact angle of the filler is close to 90º, the stability of the resulting Pickering emulsion is the best. Polymer grafting is an option to change the contact angle of inorganic fillers, switching its hydrophilicity to slight hydrophobicity. Laponite RD, which is synthetic clay, is used to prepare Pickering emulsion. And in a next step, polymerization of styrene can be proceeded in the dispersed oil phase (Cauvin et al. 2005). These disc-like clay particles with negative surface charge can stabilize an oil-in-water emulsion (Guillot et al. 2009). And the three-phase contact angle is slightly lower than 90°, which serves as a requisite of Pickering emulsion stability. The addition of salt favors the flocculation of clay and contributes to the stability of Pickering emulsion (Ashby & Binks 2000). The diameter of oil droplet is submicron. In addition to inorganic fillers, some carbohydrate-based particles, such as cellulose nanocrystals and hydrophobically modified starch microparticles can stabilize Pickering emulsions (Dickinson 2012). Several researchers investigated improved stabilization of Pickering emulsions by using hydrophobic microfibrillated cellulose (MFC) (Lif et al. 2010; Andresen & Stenius 2007; Rein et al. 2012), nanofibrils (Klodian Xhanari et al. 2011), starch-based nanosphere (Tan et al. 2012), and polymer grafted cellulose nanocrystals (Zoppe et al. 2012). Their studies also covered the influence of particle concentration, oil/water ratio, and degree of hydrophobization of cellulose/starch on the stability of the Pickering emulsion (K. Xhanari et al. 2011). In recent years, cellulose 	 11	nanocrystals derived from plant, and bacterial sources are found to stabilize Pickering emulsions without hydrophobization, since the crystalline region of cellulose is amphiphilic in comparison with the amophorous one (Kalashnikova et al. 2011; Wen et al. 2014). In further study, it is shown that surface charge density (SCD) of cellulose nanocrystals plays a significant role in the stabilization. Cellulose nanocrystals with SCD below 0.03 e/nm2 are able to act as stabilizers (Kalashnikova 2012). In a Pickering emulsion, many literatures assume that the solid particles uniformly distribute at the interface of oil/water and form monolayer coverage. However, based on a study on the morphology of microparticles at Pickering emulsion interface, it is shown that aggregated structure exist as well (Dai et al. 2008). The extent of agglomeration depends on the concentration and chemistry of particles. The properties of Pickering emulsion are function of factors, such as surface energy of components, oil-to-water volume ratio, physical properties, and the concentration of particles, surfactant, and electrolyte (Aveyard et al. 2003). As mentioned at the beginning of this section, in a Pickering emulsion, the oil droplets are encapsulated by solid particles. However, this may not be sufficient to form a long-term stable emulsion system. If the particles self-assemble a framework (like a gel) in the continuous phase (water), driven by the surface charge, the viscosity of emulsion will be enhanced and the network can protect the dispersed phase (oil) from coalescence (Thieme et al. 1999). This phenomenon is observed in Pickering emulsion stabilized by clay (Chen et al. 2011). The disc-like clay forms a card-house-like structure in water phase and favors the stability of emulsion. At the beginning of the preparation of a Pickering emulsion, mixing is essential to disperse oil in water well. However, after the emulsion is stable, simple shear flow may destabilize the system, due to the disruption of the droplet-particle network (Whitby et al. 2011). Thus, it is better not to apply mixing after the emulsifying stage. Different oil-to-water ratio results in different state, such as O/W emulsion, W/O emulsion and powdery state (Nonomura & Kobayashi 2009). Phase inversion occurs when the oil-to-water ratio changes (e.g. the addition of extra water). Among these states, O/W emulsion without separation of excess oil and water is regarded as the optimum 	 12	state in this study. Caifu Li et. al (2009) used Laponite clay to stabilize a paraffin wax/water Pickering emulsion. It is reported that, the proper oil/water ratio ranges from 3:7 to 7:3, which is a relatively wide range (Li et al. 2009). The optimum oil-to-water ratio to prepare stable Pickering emulsion depends on the nature of particle solids. Hydrophilic particles favor the formation of an oil/water (O/W)  emulsion, while hydrophobic particles favor the formation of a water/oil (W/O) emulsion (Aveyard et al. 2003). Partially hydrophobic particles are able to stabilize both O/W and W/O emulsions. The selection of oil affects the type of emulsion as well. It is common that the size of oil droplet reduces when increasing the concentration of solid particles. However, there is no obvious relation between the extent of particle adsorption at the interface and the stability of the emulsion. Even at very low surface coverage of droplet, stable emulsion can be formed (Vignati & Piazza 2003). Surfactant, like Tween 60 and Sodium Caseinate, can be added into a Pickering emulsion, serving as co-emulsifer. The surfactant decreases the surface tension of water, and promotes the break and dispersion of oil droplets. Thus, the O/W emulsion has higher long-term stability and smaller size of droplets. More hydrophilic silica particles are adsorbed at the interface between oil and water, due to higher surface area of oil droplets. However, much too high concentration of surfactant may lead to the displacement of particles at the interface (Pichot et al. 2010). The interaction between particles and surfactant also influences the structure and the stability of Pickering emulsion (Whitby et al. 2008; Whitby et al. 2009; Wang et al. 2010). The addition of salt, such as sodium chloride, also affects the stability of Pickering emulsion. When increasing the salt concentration, the zeta potential of particles decreases, and the flocculation of particles both at the interface and in the suspension are favored (Yang et al. 2006). But the three phase contact angle of particles barely changes.	1.6 Silanization The silane agent involved in this research refers to the compounds containing silicone, fatty groups and chloride/ethoxyl. It has a relatively low surface energy and can be used to functionalize cellulose and fillers, in order reduce their hydrophilic character. The process of performing chemical modification with a silane agent on hydrophilic 	 13	substrates is defined as silanization. After silanization, the treated samples obtain higher water contact angle and lower moisture adsorption. The grafted quantity of a silane agent on a cellulosic fiber surfaces depends on the chemical structure and the initial concentration of silane (Rachini et al. 2012). It is shown that higher concentration results to higher grafted quantity. A silane agent with amino group may cause higher grafted quantity, due to the hydrogen bonding between the –NH2 and the hydroxyl groups on the fiber (Rachini et al. 2012; Ifuku & Yano 2015). In a recent study, three different types of silanes (PFDTES, MODDCS, and DCDMS) were used to treat filter paper through a solution-immersion process and chemical vapor deposition (Oh et al. 2011). Reaction time and silane concentration are considered as the two experimental factors. After sufficient reaction with dichloro-dimethylsilane (DCDMS), the filter paper has a water contact angle ranging from 120º to 130º. Compared with doing silanization in liquid-solid system, a solvent-free process is remarkably simple and efficient. Chlorosilanes with low boiling point provide the possibility of vapor-phase silanization. Especially, trichloromethylsilane (TCMS) and dichloro-dimethylsilane (DCDMS) are volatile and capable in modifying the fiber/filler surface at modest conditions, such as room temperature and atmospheric pressure (Cunha et al. 2010; Jiang et al. 2008). In this study, DCDMS is adopted as the silane agent.  Figure 1.6: Schematic of silanization on hydrophilic surface by DCDMS 1.7 Criteria for Superhydrophobic Surface The idea of a superhydrophobic surface comes from the Lotus leaf surface, which exhibits extreme water-repellency and self-cleaning properties (Barthlott & Neinhuis 1997; Neinhuis 1997). Superhydrophobicity refers to a water contact angle larger than 150°, with a contact angle hysteresis less than 10º (Yan et al. 2011; Latthe et al. 2014). HO HO HO HO HO O O HO Hydrophilic surface Hydrophobic surface (CH3)2SiCl2 Si CH3 CH3 O O Si CH3 CH3 	 14	The wettability of a surface depends on the chemical nature of material and the surface roughness. To establish a superhydrophobic surface, low surface energy and dual sale roughness are both required. Generally, the approach to fabricate a superhydrophobic surface is either enhancing the surface roughness of a hydrophobic surface, or coating low-surface-energy chemicals on a rough surface (Li et al. 2007). The water barrier property of the surface is assessed through the measurement of the water contact angle, water vapor transmission rate, and oxygen transmission rate. In the paper manufacturing industry, surface treatment is mainly referred to as sizing, generally including internal and external sizing. In an external sizing process, polymer-based hydrophobic particles are dispersed in starch solution. Then the hydrophobic particles deposit onto untreated papers through a dip-coating process. The loading of particles on paper is highly dependent on the type of surface charge, which is responsible for the interactions between hydrophobic particles and negatively charged starch (Iselau et al. 2015). Stanssens et al. (2011) utilized a coating material to fabricate hydrophobic papers. They synthesized an organic nanoparticle, partially imidized poly(styrene-co-maleimide), under pure conditions and in palm oil solvent. Then the nanoparticle is deposited onto paper, followed by further thermal curing, to achieve outstanding hydrophobic performance (Stanssens et al. 2011). The nanoparticles formed in oil provide better water repellency. The water static contact angle reaches 148°. The water droplets can roll off the surface giving rise to the self-cleaning property. Gao et al. (2015) developed a superhydrophobic film on the surface of filter paper. In their work, TiO2 is adhered onto paper, and provides both micro and nano structures. Then the paper is coated by octadecyltrichlorosilane, which serves as a low surface energy agent (Gao et al. 2015). The resulting paper has a water contact angle of 153° and the oil contact angle of 135°.  Mirvakili et al. (2013) applied plasma enhanced chemical vapor deposition (PECVD) to make superhydrophobic handsheet consisting of cellulose and filler (Mirvakili et al. 2013). The results show that the wettability of a handsheet is highly affected by oxygen plasma etching, which increases the roughness before fluorocarbon deposition. Moreover, 	 15	the contact angle is also a function of the fiber length and the filler properties. Although oxygen etching resulted in high water repellency of handsheets, it adversely affects its strength properties. Glavan et al. (2014) reported an omniphobic paper prepared by fluoroalkyltrichlorosilanes. The water contact angle of this paper is higher than 140°. In addition, it resists to a variety of liquids, such as organic liquids, aqueous solutions, and even blood (Glavan et al. 2014). Based on their work, the molecular length and fluorination degree of organosilane have a large effect on the liquid-resistant property of the paper. After silanization, the mechanical flexibility of the paper is retained and thus the papers can be folded into any desired shapes for certain application, such as gas sensor. Interestingly, this technology is much less expensive than the advanced hydrophobic treatment of Gore-Tex and Nafion. 1.8 Wettability Wettability of smooth surface Consider a liquid droplet is placed on a smooth solid surface statically. The contact angle θ is defined as the angle between the solid-liquid interface and the tangent line of the droplet contour curve at the three-phase interface, as shown in Figure 1.7. This angle depends on the adhesion between the liquid and solid. The higher the adheison, the lower the contact angle. If the contact angle is lager than 90°, the surface is non-wetting. And if the liquid is water, the surface of solid is known as hydrophobic. In extreme case, when the water contact angle approaches 180°, superhydrophobic or perfectly dewetting performance exists.  The contact angle θY can be expressed by Young-Laplace equation as shown below. The interficial surface tension between solid-vapor, liquid-vapor and solid-liquid are represented as γsv, γvl, and γsl respectively (Groenendijk, 2008). cos θ! = !!"!!!"!!"                                                       (1-4) 	 16	 Figure 1.7: Wetting models (Left) at a smooth surface; (Middle) in Wenzel state; (Right) in Cassie-Baxter state (Adapted from https://en.wikipedia.org/wiki/Hydrophobe) Wettability of rough surface If the solid surface is rough, the Young-Laplace equation is not applicable any more. Here the surface roughness factor ωr is introduced to correct the above equation. It is defined as the ratio of effective, non-linear length of the surface profile and the linear length between two points. For a flat surface, the roughness term equals to 1. ω! = !!""!                                                                                                 (1-5) Wenzel model (Wenzel, 1936): there is no air trapped between the liquid and the rough solid face, which means that the liquid droplet fills up all the grooves on solid surface. Then the corrected contact angle θ* is shown as: cos θ∗ = ω!× cos θ!                                                   (1-6) Cassie-Baxter model (Cassie, 1944): some air is trapped in the grooves between the liquid and solid surface, due to very high roughness. Then the contact angle θ*CB is as follows: cos θ!"∗ = −1+ f!× cos θ! + 1                                                      (1-7) where fs is the fraction of the solid surface in contact with liquid. To decide whether the Wenzel or the Cassie-Baxter model is applicable, the critical roughness ωr,cr is needed. If ωr > ωr,cr , Cassie-Baxter model applies. In the following equation, the contact angle is given by eq. (1-4). ω!,!" = 1+ !"#! !!!                                                                                  (1-8) 			 17	1.9 Applications in Packaging and Fundamental Device Cellulose based materials are widely used in packaging, as they are both environmentally friendly and cost-efficient. In some specific cases, such as packaging, the barrier properties of the cellulosic materials are always under concern. The packaging materials are required with low water vapor and air permeability as well as water repellency. These properties highly depend on the chemistry and microstructure of the papers. Besides traditional use in packaging, hydrophobic paper can be designed as microfluidic device (Renault et al. 2013) and for oil/water separations (Gao et al. 2015). By selectively modifying the surface properties of paper (hydrophilic or hydrophobic), the patterned paper can be used to trap chemical and biological liquid for analysis (Chitnis et al. 2011).   	 18	CHAPTER 2: THESIS OBJECTIVES Packaging is an important application that paper is used. In some specific applications, water repellent packaging materials are needed and the traditional way is to use wax to create a hydrophobic surface. Despite its low cost, wax hampers the recyclability of paper used in these applications. As a result, there is a need for fabrication methods of hydrophobic/superhydrophobic papers driven by sustainability considerations. Rendering paper hydrophobic is expected to broaden its applications. In this research, the main goal is to prepare hydrophobic paper through three different routes engaging fillers, MFC and silanization. One of the challenges here is how to obtain Janus hydrophobic/hydrophilic particles.  So the key point of this research is to apply hydrophilic fillers, hydrophobic MFC and Janus particles into pulp/paper. During the process, silane, which serves as low surface energy agent, is used to modify the fillers, MFC and paper. After that, the study will explore the barrier properties of the resulting papers. The water contact angle, water vapor, and air permeability, will be measured to assess the barrier properties of the paper.  The objectives of the present study are: 1. Prepare handsheets loaded with mineral fillers and then apply a silanization treatment of the handsheets. Determine the effect of fiber size, filler properties (filler type, size, content) and silanization on the barrier performance of the handsheets (wettability, water vapor resistance and air permeability). 2. Prepare hydrophobic MFC and deposit it onto the surface of paper and then apply  silanization. Determine how the loading of hydrophobic MFC affects the wettability of paper. 3. Prepare Janus filler particles through a wax-in-water Pickering emulsion and silanization. Prepare handsheets loaded with Janus filler and determine the surface wettability of the handsheets.	  	 19	CHAPTER 3: MATERIALS AND METHODS This following section presents the experimental setups, chemicals used for handsheet preparation and the related measuring equipment. Along with that, the methodology and the characterization technologies will be described as well. 3.1 Materials and Experimental Apparatus Materials: Softwood Kraft pulp with different fiber sizes was used to prepare handsheets. The pulp is supplied by a leading pulp mill in British Columbia, Canada. The average fiber size in the pulp suspension is measured using Scircco 2000 Malvern Mastersizer (Malvern Instrument, Malvern, UK). The results of fiber size are reported as a mean diameter of a volume equivalent sphere, and the associated errors are within ±4µm to ±10µm. The specifications of pulp are given in Table 3.1. Table 3.1: Pulp and fiber specifications Pulp type Fiber size/µm Wet pulp consistency Kraft Unrefined (KU) 927 2.9% Kraft Refined-1 (KR1) 807 2.3% Kraft Refined-2 (KR2) 724 1.9% The fillers used in preparation of handsheets include kaolin clay and precipitated calcium carbonate particles in micrometer and nanometer. Table 3.2: The specifications of fillers Filler type Particle size Zeta potential/mV Supplier Kaolin clay 13.5µm -15.1±0.7 Pulp&Paper center, UBC, CA Calcined clay 6.92µm -17.9±0.8 Dry Branch, GA, USA Nanoclay 12-20nm* -12.1±0.4 Sigma-Aldrich, ON, CA PCC 10.22 µm -17.8±0.3 Specialty Minerals, PA, USA NPCC 15-40nm* -14.4±1.1 Nanotech, Xiamen, CN 	 20	Note: * The information is provided by the company. The particle size is measured by Scircco 2000 Mastersizer, and the zeta potential is determined by Zetasizer 2000 at a concentration of 0.002 wt% in distilled deionized water (DDW). Clay consists of Al2O3, SiO2, and crystal (bound) water with different ratio. Except for pulp and fillers, the following chemicals were used in the preparation of handsheets, among which cPAM and silica served as the filler retention system. • Cationic polyacrylamide (cPAM) supplied by Eka Chemicals (Magog, QC, Canada) with the average molecular mass of 10 million Da.   • 8.1 wt% Silica suspension supplied by Eka Chemicals (Magog, QC, Canada) with the mean size of 5 nm.   • Distilled deionized water (DDW) with a typical resistivity of less than 18.2 ΜΩ.cm at 25 °C, a total organic carbon content of less than 10 ppb, and a neutral pH value of 7. • Dichlorodimethylsilane (DCDMS) with a boiling point of 70º, supplied by Sigma-Aldrich Canada Co. (Oakville, ON, Canada). • Compressed nitrogen gas. • Anhydrous calcium chloride powder (desiccant, 20mesh and finer, >96%) supplied by Fisher Scientific. • Microfibrillated cellulose with average particle size of 8µm, supplied by J. Rettenmaier USA LP. The chemicals used to fabricate Pickering emulsions and Janus particles are as follows: • Paraffin wax chunks with melting point of 53-57ºC, supplied Sigma-Aldrich Canada Co. (Oakville, ON, Canada). • Didodecyldimethylammonium bromide (DDAB), serving as a cationic surfactant, supplied Sigma-Aldrich Canada Co. (Oakville, ON, Canada). • Chloroform (>99.5%) supplied Sigma-Aldrich Canada Co. (Oakville, ON, Canada). • Kaolin clay, calcined clay, nanoclay, precipitated calcium carbonate (PCC) and NPCC, as shown in Table 3.2. 	 21	Experimental apparatus: The equipment employed for making handsheets includes a customized handsheet former, and a vapor-phase silanization setup. The equipment engaged in the preparation of Pickering emulsion and Janus particles includes conical flask, magnetic stirrer, plate heater, funnel, screenings, and centrifugal machine. Characterization: A high-resolution camera and a micropipette for contact angle measurement, Gurley machine for determining air permeability, an analytical balance and a Hitachi S-3000N-VP Scanning electron microscope. 3.2 Preparation of Handsheets Loaded with Fillers All handsheets are prepared by the apparatus originally fabricated by Montgomery (2010). It consists of two blocks, the filtration part and vacuum system. A 76-mm diameter forming fabric is immobilized between two acrylic cylinders with flanges. In the middle of the flange plate, a circular gum gasket is placed to provide an airtight seal. A flush-mounted gauge pressure transducer (GP:50 Model 218-C-SZ-10-GS) is attached to the inner wall of cylinder below the forming fabric. The prepared pulp/filler suspension is added above the forming fabric. To simulate the papermaking process, a vacuum pump is employed. The vacuum chamber, with a 20mm PVC pipe on top, is constructed by 13mm thick PVC plated. During operation, the pressure is controlled between -5 to -10 in Hg. And the electrically actuated solenoid valve is controlled by software. Before starting the drainage of a pulp suspension, the cylinder between the valve (closed) and the forming fabric is filled with deionized water. The dewatering step can be finished in several filtration cycles. 	 22	 Figure 3.1: Schematic of customized handsheet former (Montgomery 2010) The types of pulp used to prepare handsheets are KU, KR1 and 50%-50% mixed pulp (KU+KR1, KU+KR2). The fillers applied in preparation of the handsheets include micro or nano clay and precipitated calcium carbonate, with the filler loading concentrations of 0%, 20% and 40% in the handsheet. Before the addition of filler into pulp, the fillers are dispersed in deionized water at a concentration of 1.02%. To help retain the fillers, chemical retention aids are used. The loading of cationic polyacrylamide (cPAM) is 0.3kg per ton of pulp, which suggests 0.72ml cPAM solution (0.011wt%) per sheet. And the loading of silica is 0.4kg per ton of pulp, which suggests 1.82ml silica solution (0.006wt%) per sheet. Table 3.3: Pulp Suspension Concentrations 1.02% Dry mass 0.011% 0.006% Filler/% V/ml Pulp/% W/g cPAM(kg/t) V/ml Silica(kg/t) V/ml 0 0 100 0.27 0.3 0.72 0.4 1.82 20 5.34 80 0.22 0.3 0.72 0.4 1.82 40 10.68 60 0.16 0.3 0.72 0.4 1.82 	 23	The pulp suspension concentrations are given in Table 3.3. A certain weight of wet pulp was diluted into total weight of 300 g with deionized water, followed by the additions of filler solution, cPAM solution, and silica solution. The suspension was mixed and poured into the handsheet former. After filteration, the wet handsheet was removed from the forming fabric and placed onto a blotter and pressed by a roller the handsheet samples were dried in the condition room (50% relative humidity, 25 °C) for 24 hours prior to further property tests. The total grammage/basis weight (fibers and fillers) of paper is 60g/m2. The diameter of handsheet is 76 mm, and the area is 45.4 cm2. Thus, the target weight per dried handsheet is 0.2724 g. And the tolerant range of weight is within 30%. 3.3 Silanization on Handsheets The prepared handsheets are hydrophilic due to the existence of hydroxyl groups. A vapor phase silanization process is done over these handsheets to make the surface hydrophobic. The schematic of the apparatus is shown below.  Figure 3.2: Schematic of silanization equipment (Adapted from Jiang et al. 2008) The boiling point of silane agent (DCDMS) is 70ºC, thus, it is easy to be vaporized at room temperature (Oh et al. 2011). The compressed nitrogen gas is plugged into the 	 24	bubbler to vaporize the silane. The sand-core frit, which serves as the chamber for vapor phase silanization, is filled with silane and nitrogen gas in few minutes. Then the handsheets cut in “2x2 cm” is put into the frit for 1 min to be silanized. 3.4 Preparation of Handsheets with Hydrophobic MFC Preparation of hydrophobic microfibrillated cellulose 1. Stoichiometry of silanization The chemical formula of MFC powder can be described as (C6H10O5)n, same as cellulose fibers. In each hexose structural unit, there are three hydroxyl groups, which are responsible for the hydrophilic nature of MFC. In order to render MFC hydrophobic, these hydroxyl groups are functionalized by a low surface-energy chemical (DMDCS). Assume that the hydroxyl groups existing at the surface and inside the bulk of MFC powder are thoroughly reacted with the silane agent. The calculation of stoichiometry is performed below. (C6H10O5)  ~ 3/2Si(CH3)2Cl2                                          (3-1) The purity of MFC is 99.5%. The molecular weights of cellulosic unit and silane are 162 and 129.06, respectively. The density of silane is 1.07g/cm3 at 25ºC. For 1g of sample, the volume of required silane equals to 1g×99.5%÷ 162g/mole× !!×129.06g/mol÷ 1.07g/cm!                (3-2) which is 1.11ml. Alternatively, this can be written as 0.9g-MFC/ml-silane. 2. Solvent-free silanization of MFC Different volumes of DMDCS are used to modify a certain mass of MFC powder, which is 0.9g. The volume of DMDCS varies from 0.4ml, 0.7ml to 1.0ml. This is designed to show how the hydrophobic performance of MFC depends on the quantity of silane changes. The silanization setup is the same as shown in Figure 3.2. The MFC is placed in the frit, while the silane agent is in the bubbler. Dry nitrogen released from a gas container flows through the setup at a rate of 2-3 bubbles per second.  Silane agent with low boiling point then vaporizes and mixes with nitrogen. Finally, silane agent reaches the frit and reacts with MFC. During this procedure, shake the frit every five minutes to ensure the adequate contact between silane and MFC.  	 25	Deposition of hydrophobic microfibrillated cellulose on handsheets Prepare KU handsheets without any filler using filtration equipment, which consists of Buchner funnel and suction flask. Hydrophobic MFC is dispersed in deionized water with the aid of sonication lasting 30min. Then the suspension is added onto KU handsheet surface. After the water drains away and drying at room temperature, a thin film of hydrophobic MFC is established at the handsheet surface. The loadings of hydrophobic MFC on handsheets are 10%, 30% and 50%, based on the dry mass of pulp. After the deposition of hydrophobic MFC, another silanization treatment is performed on the resulted handsheets to render the surface totally hydrophobic. 3.5 Pickering Emulsion Stabilized by Fillers In this process, solid particles are added into an oil/water mixture to stabilize the emulsion. The solid particles employed here include kaolin clay, calcined clay, nano-clay, and micro/nano precipitated calcium carbonate. Paraffin wax with melting point of 53-57ºC is preheated to 85ºC to be in its liquid oil phase. And solid particles are dispersed into DI water under magnetic stirring, followed by heating up to the same temperature as wax. Then the melt wax is added into water. Keep stirring for 5-10 min, and the oil breaks into small droplets. Driven by the thermodynamic force, solid particles are immobilized at the surface of oil droplets. Ideally, the emulsified oil phase ends up at the top without coalescence, while the water phase remains at the bottom. After cooling down to the room temperature, the wax solidifies and the solid particles are locked into the position.  The wax pellets are filtered from the prepared Pickering emulsion and undergo a washing step. Wax pellets in large size are screened away. The excessive fillers remaining in water are discarded. The rest are collected and dried at room condition for further treatment. 3.6 Fabrication of Janus Kaolin Clay Particles Many approaches have been proposed to fabricate Janus particles in liquid or gas phase. Generally, precipitated calcium carbonate is rendered hydrophobic by reaction with stearic acid in a solvent. Clay has hydroxyl groups, which provides the possibility of reacting with a silane agent. Silane with low boiling point, such as DCDMS, is easily 	 26	vaporizing at room temperature. Then a vapor phase silanization process can be conducted. Compared with reaction in solvent, vapor phase silanization is free of post-treatment, such as liquid separation. The method adopted here is vapor phase silanization, using the same setup as doing silanization on handsheets. The wax pellets with kaolin clay are transferred into the frit. At room temperature, silane (DCDMS) is vaporized with nitrogen blowing by and reaches the frit to modify the solid particles. To sufficiently modify clay, the reaction time is kept at 1 hr, with three bubbles per second. During the process, the outer face of clay particles is functionalized with hydrophobic methylsilane groups. Transfer the obtained wax pellets into centrifugal tubes, and add chloroform to 20ml scale line. Shake the tube up and down several times. Then the paraffin wax is dissolved and Janus clay particles are released. After centrifuging, the insoluble Janus clay particles precipitate and the rest solution is decanted away. Repeat the centrifuging step with chloroform and ethanol three times each. Keep the Janus clay particles in ethanol for further use. Finally, the geometry of the Janus particles is confirmed by the distributive behavior at toluene/water interface. The obtained wax/filler colloidosome was transferred into centrifugal tubes, and 20 ml chloroform was added to the tube. Shake the tube up and down several times. Then the paraffin wax was dissolved and Janus clay particles were released. After centrifuging, the insoluble Janus clay particles precipitated at the bottom, and the rest of the solution was decanted away. The centrifuging step was repeated with chloroform and ethanol three times each. The Janus clay particles were kept in ethanol for further use. Finally, the geometry of the Janus particles is confirmed by the distributive behavior at toluene/water interface. 3.7 Incorporation of Janus Clay Particle Coating on Handsheet A KU pulp suspension was used to prepared handsheets with basis weight of 60g/m2. The pulp suspension was transferred into a funnel, followed by the addition of aqueous Janus clay particles solution on top. Due to the hydrophobic/hydrophilic geometry, Janus particles evenly distributed on the surface of water automatically with their hydrophobic sides facing the air. The amount of Janus clay particles applied on each trial should guarantee a full coverage over the handsheet surface. After the water is totally drained, 	 27	Janus clay particles deposit at the surface of handsheets and a hydrophobic film is established. More than one deposition cycles are essential to achieve a dense hydrophobic coating. 3.8 Handsheet Properties Characterization 3.8.1 Weight of Handsheets After the paper specimen is kept in condition room for more than 24hrs. The weight of paper is determined by analytical balance. Generally, the moisture content takes 10% over the total mass. 3.8.2 Thickness (L&W Micrometer) The thickness of dried paper is determined by L&W Micrometer. For each specimen, the reported thickness is the average at five spots on handsheets surface. 3.8.3 Air Resistance (Gurley Method) According to TAPPI standard of T460 om-02, the air resistance of paper is measured by Gurley machine. The time required for 100ml air to pass through a certain circular area (6.45 sq.cm.) of paper at a pressure differential of 1.22kPa, is considered as indicator of the air resistance. Both the internal structure and the surface finish of paper have a main effect on the air permeability. The type, length, and also the alignment of fibers influence the structure of paper, as well as the fillers. 3.8.4 Water Vapor Transmission Rate (WVTR) WVTR test can be performed by cup method similar as the TAPPI standard method of T-448. All the handsheets are preconditioned at 23℃ and 50% relative humidity for 24hrs prior to measurements. Then the handsheets are cut into discs with a diameter of 1.6cm. These paper specimens are sandwiched between two rubber gaskets, and tightly mounted on a glass analyzer with a hollow cap to secure well sealing. The actual diameter of paper exposed to the environment is 0.9cm. Inside the analyzer, there is anhydrous calcium chlorides powder serving as desiccant. During the measurement, water vapor transports through the paper and adsorbed by the desiccant. The change of the total weight of the analyzer is recorded for a week and an average value is reported. 	 28	The water vapor transmission rate (WVTR) result is calculated as the equation below, in the unit of g/(m2·day). 𝑊𝑉𝑇𝑅(𝑔 ∙𝑚!! ∙ 𝑑𝑎𝑦!!) = ∆! !∙!"#!!!"#$(!!)                                    (3-3) 3.8.5 Water Contact Angle Measurement The static contact angle of a water droplet can be measured with capturing images by a high-resolution camera, Nikon D90 digital camera. The prepared paper sample is horizontally placed before a light source, and then a 3µL deionized water droplet is loaded on the surface by pipette.  For each sample, the images are taken on five spots. Then the software FTA32 Version 2.0 is used to analyze the contact angle.   	 29	CHAPTER 4: RESULTS AND DISCUSSION 4.1 Thickness and Density of Handsheets The results of thickness (mm) and density (kg/m3) of handsheets are shown in Table 4.1 to 4.4. The density of handsheet is calculated as eq. (4-1). 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 = !"#$!!!!!"#$%&&×!"#$                                            (4-1) Table 4.1: The thickness and density of handsheets with KU Loading Test Calcined clay Nanoclay PCC NanoPCC No Load Thickness 0.3657 Density 225 20% Thickness 0.2853 0.2823 0.2947 0.3075 Density 203 200 209 191 40% Thickness 0.2025 0.2298 0.2239 0.2876 Density 194 190 213 228  Table 4.2: The thickness and density of handsheets with KR1 Loading Test Calcined clay Nanoclay PCC NanoPCC No Load Thickness 0.2836 Density 595 20% Thickness 0.2585 0.2164 0.2592 0.2523 Density 601 566 450 559 40% Thickness 0.2304 0.2254 0.2933 0.2385 Density 511 608 433 571    	 30	Table 4.3: The thickness and density of handsheets with KU+KR1 Loading Test Calcined clay Nanoclay PCC NanoPCC No Load Thickness 0.3315 Density 372 20% Thickness 0.2705 0.2645 0.2966 0.2821 Density 425 401 383 466 40% Thickness 0.2499 0.1933 0.2731 0.2427 Density 381 419 316 480  Table 4.4: The thickness and density of handsheets with KU+KR2 Loading Test Calcined clay Nanoclay PCC NanoPCC No Load Thickness 0.3284 Density 497 20% Thickness 0.2937 0.2796 0.3007 0.2834 Density 486 559 431 547 40% Thickness 0.2683 0.2163 0.2620 0.2839 Density 462 490 371 543 From the tables above, it is concluded that the density of handsheet mainly depends on the fiber size. As the fiber size decreases, the handsheets become denser.       	 31	4.2 Water Vapor Transmission Rate (WVTR) of Handsheet The results for the WVTR in g(water vapor)/(m2·day) at 23℃ and 50% RH are shown in Tables 4.5 to 4.9. Table 4.5: The WVTR values of handsheets with KU (g/(m2·day))  Calcined clay Nanoclay PCC NanoPCC No load 807 20% 801 789 840 819 40% 831 824 844 840  Table 4.6: The WVTR values of handsheets with KR1 (g/(m2·day))  Calcined clay Nanoclay PCC NanoPCC No load 123 20% 303 272 478 380 40% 474 307 665 633  Table 4.7: The WVTR values of handsheets with 50%-50% KU + KR1 (g/(m2·day))  Calcined clay Nanoclay PCC NanoPCC No load 430 20% 508 487 714 639 40% 654 517 759 732  Table 4.8: The WVTR values of handsheets with 50%-50% KU + KR2 (g/(m2·day))  Calcined clay Nanoclay PCC NanoPCC No load 273 20% 438 327 670 496 40% 608 412 706 659     	 32	Table 4.9: The WVTR values of handsheets before and after silanization  #1 #2 #3 #4 #1 CC #1-2 PCC Untreated 807 123 430 273 801 840 Treated 813 95 334 148 825 850 Index statement: #1 stands for KU. #2 stands for KR1. #3 stands for 50%-50% KU + KR1. #4 stands for 50%-50% KU + KR2. #1 CC stands for KU with 20% loading of calcined clay. #1 PCC stands for KU with 20% loading of precipitated calcium carbonate.  The errors of WVTR tests are shown in the following Table 4.10. Table 4.10: The errors of WVTR values of handsheets Handsheets WVTR ST. DEV. Error% KR1 123 32 26 KU+KR1 431 71 16 KU+KR1+20%MC 508 60 12 KU+KR1+40%MC 654 55 8 KU+KR1+20%NC 487 85 17 KU+KR1+20%MP 714 47 7 KU+KR1+20%NP 638 48 8             	 33	4.2.1 Effect of Fiber Size on WVTR of Paper  Figure 4.1: The WVTR values of handsheets with different fiber sizes KU, KR1 and KR2 have the longest, medium and shortest fiber size, respectively. It is observed that as fiber size decreases, the WVTR value decreases significantly. Especially, the KU handsheet has a WVTR value of 807 g/(m2·day), while KR1 handsheet has a WVTR value of 123 g/(m2·day). And when half of KU pulp is replaced by KR1 or KR2, the WVTR values drop to 1/2 and 1/3 levels. The reason is that, refined pulp fiber has lager surface area and more exposed hydroxyl groups, compared with that of unrefined pulp (Mirvakili et al. 2016). Therefore, more hydrogen bonding between fibers can be formed. This results to the formation of denser handsheets and the decrease of porosity. Finally, the water vapor resistance increases.      0 100 200 300 400 500 600 700 800 900 KU KR1 KU+KR1 KU+KR2 WVTR (g∙	m-2∙	day-1 at 23ºC and 50% RH) 	 34	4.2.2 Effect of Filler Type on WVTR of Paper  Figure 4.2: The WVTR values of handsheets loaded with different fillers As shown in the figure above, filler type has an obvious effect on WVTR values. Except for the case of KU, the handsheets loaded with PCC has a highest WVTR value.  The hypothesis to explain the above observations is that clay has a disc-like shape (Murray & Kogel 2005) and blocks the diffusion path for water vapor molecules to pass through the handsheets (Mirvakili, 2012). In another word, the tortuosity in handsheet with clay fillers is higher than the one with rosette PCC. In the figure, it is also clear that WVTR values of KU are barely affected by filler type. It is due to the high porosity in handsheets. There is low resistance for water vapor to pass through the Z-direction. Thus the effect of filler type on WVTR is concealed. The hypothesis can also be confirmed by the high air permeability of less than 5 seconds for KU handsheets.      0 100 200 300 400 500 600 700 800 900 KU KR1 KU+KR1 KU+KR2 WVTR (g· m-2· day-1 at 23ºC and 50% RH) No filler 20% calcined clay 20% PCC 	 35	4.2.3 Effect of Filler Content on WVTR of Paper   Figure 4.3: The WVTR values of handsheets loaded with Calcined clay (upper) and PCC (below) at different filler content 0 100 200 300 400 500 600 700 800 900 KU KR1 KU+KR1 KU+KR2 WVTR (g· m-2· day-1 at 23ºC and 50% RH) No filler 20% filler 40% filler 0 100 200 300 400 500 600 700 800 900 KU KR1 KU+KR1 KU+KR2 WVTR (g· m-2· day-1 at 23ºC and 50% RH) No filler 20% filler 40% filler 	 36	As is explained above, the filler effect on WVTR of KU handsheets can be ignored. For the rest of the handsheets, it is concluded that, higher filler content results in larger WVTR values. It happens in both the cases of calcined clay and precipitated calcium carbonate on handsheets made of refined fibers. As we know, cellulosic fibers form strong networks due to hydrogen bonding. The occurrence of filler between fibers may disrupt the inter-fiber attraction force, which results in the loss of handsheet’s density and increase of the porosity. This would lead to the decreases of water vapor resistance in bulk. The same trend is observed on the handsheets with nanosized fillers as well. 4.2.4 Effect of Filler Size on WVTR of Paper  Figure 4.4: The WVTR values of KR1 handsheets with different filler size By comparing the WVTR values of handsheets loaded with microsized and nanosized fillers, it is obvious that nanosized fillers have less negative effect on the water vapor barrier properties of handsheets. The hypothesis is that, the paper with nanosized fillers is denser in bulk and less porous, compared with the paper with microsized fillers. Also, the reason might be that the retention of nanosized fillers in the handsheets is less than that of microsized fillers. Thus, the hydrogen bonding between fibers is less disrupted in hansheets with nanosized fillers. 0 100 200 300 400 500 600 700 Blank 20% Clay 40% Clay 20% PCC 40% PCC WVTR (g· m-2· day-1 at 23ºC and 50% RH) No filler Micro filler Nano filler 	 37	4.2.5 Effect of Silanization on WVTR of Paper  Figure 4.5: The WVTR values of handsheets without filler before and after silanization Except for the KU handsheet, the WVTR values reduced by 23%, 22% and 46% for “KR1”, “KU+KR1”, and “KU+KR2” handsheets, respectively. After silanization, the hydrophobic methylsilane group chemically bonded on the surface of fibers, stenches towards the interspace between fibers. This may reduce the transmission rate of water vapor molecules through the bulk. 4.3 Air Permeability of Handsheets The air permeability values are less than 5 seconds for KU handsheets, which is beyond the applicable condition of Gurley machine.  Table 4.11: Air Permeability of KU+KR2 handsheets (s/100cc)  Calcined clay PCC NPCC 20% 2171 454 2875 40% 1370 94 1118 From the data above, it can be concluded that the air permeability value is a function of porosity and tortuosity in the handsheets: 0 100 200 300 400 500 600 700 800 900 KU KR1 KU+KR1 KU+KR2 WVTR (g· m-2· day-1 at 23ºC and 50% RH) Untreatd Silanized  	 38	1. As the fiber size decreases, more hydroxyl groups exist at the surface of a fiber. Thus, more intermolecular hydrogen bonding occurs and the fiber-fiber network becomes stronger and denser. The porosity of handsheet decreases and its air permeability increases. 2. The more fillers loaded into the handsheets, the more intermolecular hydrogen bonding is disrupted. As a result, the tensile strength of handsheet suffers a loss, and the handsheet becomes less dense. Thus, the air permeability values increase. 3. Compared with handsheet with microsized fillers, the handsheet loaded with nanosized fillers are less porous, due to the small size of filler. So their air permeability is lower. 4. The handsheets with clay have larger air permeability values, compared with handsheets with PCC. The clay has a disc-like shape, while PCC is rosette, so the tortuosity is higher and the path for air to pass through the bulk of handsheet is more complicated in the case of handsheets with clay. 4.4 Wettability of Handsheets after Silanization Tables 4.12 to 4.15 show WCA results of the handsheets with different fiber sizes, filler types, and concentrations. Wire side refers to the side of handsheet facing the forming fabric, while felt side is the top side.  Table 4.12: Water contact angle (WCA) of KU handsheets Wire side Calcined clay Nanoclay PCC NanoPCC No load 134.7±4.9 20% 130.3±7.1 128.1±5.0 123.5±4.1 Hydrophilic 40% 132.0±1.8 125.5±6.5 125.4±6.7 Hydrophilic Felt side Calcined clay Nanoclay PCC NanoPCC No load 130.8±3.1 20% 130.3±4.5 132.9±5.0 122.3±3.3 Hydrophilic 40% 130.4±3.1 130.9±4.0 118.3±5.4 Hydrophilic    	 39	Table 4.13: Water contact angle (WCA) of KR1 handsheets Wire side Calcined clay Nanoclay PCC NanoPCC No load 128.0±4.0 20% 124.1±6.0 129.0±4.1 116.7±7.4 Hydrophilic 40% 121.2±7.9 121.3±5.7 124.4±3.1 Hydrophilic Felt side Calcined clay Nanoclay PCC NanoPCC No load 126.6±6.8 20% 129.8±9.3 131.1±5.2 135.0±1.4 Hydrophilic 40% 118.3±10.4 127.9±3.9 129.4±3.7 Hydrophilic  Table 4.14: Water contact angle (WCA) of KU+KR1 handsheets Wire side Calcined clay Nanoclay PCC NanoPCC No load 128.6±5.4 20% 123.9±3.3 123.7±9.4 Hydrophilic Hydrophilic 40% 129.1±2.8 127.4±2.5 Hydrophilic Hydrophilic Felt side Calcined clay Nanoclay PCC NanoPCC No load 127.8±5.3 20% 134.7±2.5 131.4±1.5 Hydrophilic Hydrophilic 40% 126.4±3.7 131.6±6.8 Hydrophilic Hydrophilic  Table 4.15: Water contact angle (WCA) of KU+KR2 handsheets Wire side Calcined clay Nanoclay PCC NanoPCC No load 128.5±3.6 20% 131.4±4.1 134.7±5.7 Hydrophilic Hydrophilic 40% 127.2±3.7 123.5±3.1 Hydrophilic Hydrophilic Felt side Calcined clay Nanoclay PCC NanoPCC No load 128.5±3.3 20% 128.5±4.9 125.3±4.5 Hydrophilic Hydrophilic 40% 134.0±8.4 132.1±4.6 Hydrophilic Hydrophilic 	 40	The water contact angle on filter paper after silanization of DCDMS is between 120º and 130º, based on literature reports (Oh et al. 2011). Most of the data fall into this range, except for the handsheets with PCC and NPCC cases. 4.4.1 Effect of Fiber Size on Water Contact Angle  Figure 4.6: The water contact angle of handsheets without filler  It is observed that KU hansheets have the highest water contact angle on both sides. And KR1 handsheets have the lowest water contact angle. This is attributed to the highest surface roughness of unrefined handsheets (Mirvakili et al. 2016). In addition, it is found that wire side has higher water contact angle than felt side. As wire side faces the forming fabric, thus, it copied the morphology of the fabric and became rougher than the felt side (Mirvakili, 2012). 4.4.2 Effect of Filler Type on Water Contact Angle From the data in the tables above, handsheets with clay are more hydrophobic than the ones with PCC (except the felt side of KR1 handsheets with PCC). The reason is that, clay can be rendered hydrophobic by silanization due to the existence of hydroxyl groups on its surface. By contrast, CaCO3 is inert during silanization, and keeps it hydrophilic 110 115 120 125 130 135 140 145 KU KR1 KU+KR1 KU+KR2 Water Contact Angle in degree Wire side Felt side 	 41	property after treatment. As a result, the hydrophobicity of handsheets with CaCO3 exposed towards the environment is lowered. 4.4.3 The Influence of Other Factors on Water Contact Angle The effects of filler size, and filler content on surface wettability of handsheets are not obvious. Low surface energy, along with high roughness, is required to fabricate superhydrophobic handsheets. And the smoothness of surface may be the limit to further improve the water contact angle value. 4.5 Wettability of Handsheets Loaded with Hydrophobic MFC The effect of silane concentration on wettability of MFC In the experimental part 3.4, different volume of silane agent (DCDMS) (i.e. 0.4ml, 0.7ml, 1.0ml) is used to modify 0.9g MFC. After silanization, all the treated MFCs perform hydrophobic. The hypothesis is that, the wettability of MFC is only related to its surface hydrophilic/hydrophobic character. More silane agent used in the treatment may result to a thorough modification of both the bulk and the surface of MFC fiber bundles. But a small amount of silane agent (0.4ml) is able to sufficiently replace the –OH groups on fiber surface by –O-Si(CH3)2. And the internal –OH groups of fibers remain hydrophilic. Water contact angle of handsheets with hydrophobic MFC After hydrophobic MFC is prepared, it is deposited onto the surface of KU handsheets. The designed loading of hydrophobic MFC ranges from 10%, 30% to 50%. The actual loading is shown in Table 4.16, along with the corresponding water contact angle value.         	 42	Table 4.16: Water contact angle of silanized KU handsheets with hydrophobic MFC Exp. No. Loading 10% 30% 50% 1 Retained 2.46% 15.3% 28.0%  WCA/º 136.2±4.6 133.8±6.5 135.7±6.0 2 Retained 5.77% 19.4% 30.1%  WCA/º 135.2±4.2 141.4±5.5 138.7±5.0 3 Retained 6.06% 22.1% 36.0%  WCA/º 144.1±4.2 133.9±6.2 135.5±5.5 Blank experiment result: The water contact angle of KU handsheet after silanization is 133.9±1.6º. From the table above, it is observed that the water contact angle (WCA) is between 134º and 144º, which is higher than that of silanized KU handsheet without hydrophobic MFC. The chemical nature of MFC and fiber in KU pulp is similar. However, the deposition of hydrophobic MFC onto KU handsheet may introduce micro and nano scale roughness somehow, since MFC has a fiber length in micrometer and a fiber diameter in nanometer. Thus, the roughness of KU handsheet increases after the loading of hydrophobic MFC, and finally the surface hydrophobic performance is enhanced. 4.6 The Stability of Pickering Emulsions Pickering emulsion is defined as an oil/water emulsion stabilized by solid particles. And it has been reported that many types of solid particles (e.g. colloidal silica) are able to adsorb at the oil/water interface, thus a stable Pickering emulsion can be established. The stability of Pickering emulsion highly depends on the surface energy of oil, water and solid particles, the oil/water ratio, the concentration and size of solid particles, the surfactant concentration, pH and salt, and the force applied on the system (e.g. agitation, sonication). In this study, melted paraffin wax is used as oil phase, several types of filler are considered to stabilize the Pickering emulsion, including Kaolin clay, calcined clay, nano-clay, PCC and nano-PCC. Didodecyldimethylammonium bromide (DDAB) serves 	 43	as a co-emulsifier. The stability results of these Pickering emulsions are given in the following table.  Table 4.17: The stability of Pickering emulsion stabilized by Kaolin clay No. Wax/g Water/g DDAB(mg/ml) Filler/g Observation 1 6 14 0 0.28 Coalescence 2 6 14 0.0001 0.28 Coalescence 3 6 14 0.0011 0.28 Large droplet 4 6 14 0.014 0.28 Small droplet 5 6 14 0.1 0.28 Stable From this table, the effect of DDAB (cationic surfactant) concentration on the stability of Pickering emulsion is obvious. When the concentration of DDAB is at a relatively low level (Case 1&2), the oil droplets coalesce right after stopping the agitation. It means that the adsorption of Kaolin clay at the interface is very weak and Kaolin clay cannot solely stabilize Pickering emulsion. As the concentration of DDAB increases, the size of oil droplet decreases. At DDAB concentration of 0.1mg/ml, a stable Pickering emulsion is formed, and there is no excess oil existing in the mixture. There are two mechanisms of how surfactant favors the stability of Pickering emulsion. First, DDAB can help stabilize emulsions by lowing interfacial tension between oil and water. Besides, DDAB adsorbs on the surface of Kaolin clay and modifies hydrophilic Kaolin clay into intermediate hydrophobic. Thus, the capability of Kaolin clay as emulsifier is improved. Table 4.18: The formula of Pickering emulsion stabilized by other fillers Filler type Wax/g Water/g DDAB(mg/ml) Filler/g Calcined Clay 6 14 0.05 0.28 Nano-clay 6 14 0.1 0.28 PCC 6 14 0.1 0.28 Nano-PCC 7 35 0.005 0.5 	 44	In summary, based on the observations in preparing stable Pickering emulsion, the following phenomena are observed. • The oil-to-water ratio is important, and the ideal range is from 0.2:1 to 0.45:1 in this study. • The proper concentration of DDAB ranges from 0.005mg/ml to 0.1mg/ml. If its concentration is too high (e.g. 0.2mg/ml), the oil phase is stabilized by DDAB without filler, and does not from in Pickering emulsion. • There should be sufficient amount of fillers to cover the whole surface of the oil droplet, otherwise, the stability of Pickering emulsion is poor. And it is inefficient to add excessive fillers into the mixture. • The agitation should last for about 5-10min. The stability of Pickering emulsion decreases after 10min, as the formed structure of emulsion is destroyed again. 	 45	 Figure 4.7: SEM images of colloidosome (a, b) Kaolin clay, (c) calcined clay,  (d) Nano-clay, (e) PCC, (f) Nano-PCC After the preparation of a Pickering emulsion, the colloidosomes are filtered from the suspension. The SEM images in Figure 4.7 confirm the successful fabrication of a stable Pickering emulsion. The surface of wax colloidosomes is covered by fillers. The aggregation of fillers is observed as well. Meanwhile, at some spots, the wax is exposed to the environment without fillers. This uneven coverage of filler does not hamper the (c) (d) (f) (e) (a) (b) 	 46	stability of Pickering emulsion. However, it is not favorable for the surface modification of filler, such as preparation of Janus particles. Only the very outmost layer of fillers can be modified. 4.7 Wettability of Handsheets Coated with Janus Clay Particle Janus Kaolin clay is prepared through Pickering emulsion route. Hydrophilic kaolin clay adsorbs at the interface of wax/water. In vapor-phase silanization treatment, one side of kaolin clay particle is modified as hydrophobic. After releasing the clay fillers from the wax, Janus kaolin clay is obtained and then deposited onto KU handsheets. Several cycles of deposition of Janus particles on handsheets are performed to ensure a sufficient coating. After that, the resulting hansheets undergo silanization for 1 min as post-treatment, in order to ensure that there is no hydrophilic spot exposed at the paper surface. 	Figure 4.8: Static water contact angle on handsheets coated with Janus clay particle The resulting handsheet exhibits an excellent hydrophobic performance, with static water contact angle of 141º, which is much higher than the hydrophobic handsheets with fillers (120º~130º). This is mainly attributed to its higher surface roughness with Janus Kaolin clay in micrometer. 	  	 47	CHAPTER 5: CONCLUSION AND RECOMMENDATION In this study, hydrophobic handsheets with different types of fillers or MFC were prepared. The effects of fiber size, filler characters (filler type, size, loading) and silanization on the barrier performance of the handsheets (wettability, water vapor transmission rare (WVTR) and air permeability) were determined. As fiber size decreases, the surface area increases and more hydroxyl groups are exposed at the fiber surface. More hydrogen bonding between fibers may form. As a result, the WVTR values of handsheets with short fibers are significantly lower than those with long fibers. Compared with PCC, clay has less negative effect on the water vapor resistance of handsheets. This is attributed to the disc-like shape of clay, which blocks the path of water vapor/air molecules to pass through the bulk of paper. Also, it is shown that handsheets with higher filler loading suffer a loss of water vapor resistance. The reason is that fillers hamper the intermolecular hydrogen bonding and the density of paper decreases. In addition,  the WVTR values of handsheets with micrometer size fillers are higher than that with nanometer fillers. Silanization treatment can render the surface of handsheets from hydrophilic to hydrophobic, and enhance the water vapor resistance. Correspondingly, high WVTR values always come with high air permeability, since these barrier properties are highly depends on the porosity and density of the paper.   The water contact angle of handsheets loaded with fillers, Janus clay particles and hydrophobic MFC, was found to be 120~130º, 141º and 134~144º respectively. Wire side of paper exhibits better hydrophobic performance, compared with felt side. Handsheets with clay have higher water contact angle than that with PCC, since PCC is inert (not responsive) to silanization and remains hydrophilic. The effects of filler size, and filler content on surface wettability of handsheets are not obvious. As the silanization treatment is performed in all cases, the surface energy of these hydrophobic handsheets is the same. Thus, the difference of the water contact angle on hydrophobic handsheets prepared in three approaches is attributed to the surface roughness of paper. 	 		 48	BIBLIOGRAPHY 1. Andresen, M. & Stenius, P., 2007. Water‐in‐oil Emulsions Stabilized by Hydrophobized Microfibrillated Cellulose. Journal of Dispersion Science and Technology, 28(6), pp.837–844. 2. Ashby, N.P. & Binks, B.P., 2000. Pickering emulsions stabilised by Laponite clay particles. Physical Chemistry Chemical Physics, 2(24), pp.5640–5646. 3. Aveyard, R., Binks, B.P. & Clint, J.H., 2003. Emulsions Stabilized Solely by Colloidal Particles. Advances in Colloid and Interface Science, 100-102, pp.503–546. 4. Barthlott, W. & Neinhuis, C., 1997. Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta, 202(1), pp.1–8. 5. Binks, B.P. & Clint, J.H., 2002. Solid Wettability from Surface Energy Components: Relevance to Pickering Emulsions. , 18(1), pp.1270–1273. 6. Cassie, B.D., 1944. Of porous surfaces,. , (5), pp.546–551. 7. Cauvin, S., Colver, P.J. & Bon, S.A.F., 2005. Pickering stabilized miniemulsion polymerization: Preparation of clay armored latexes. Macromolecules, 38(19), pp.7887–7889. 8. Cerruti, P. et al., 2008. Morphological and Thermal Properties of Cellulose - Montmorillonite Nanocomposites. , pp.3004–3013. 9. Chauhan, V.S. & Bhardwaj, N.K., 2014. Cationic Starch Preflocculated Filler for Improvement in Filler Bondability and Composite Tensile Index of Paper. Ind. Eng. Chem. Res., 53, pp.11622–11628. 10. Chen, J. et al., 2011. Influence of the particle type on the rheological behavior of Pickering emulsions. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 382(1-3), pp.238–245. 11. Chen, Y. et al., 2010. Facile preparation of cubic calcium carbonate nanoparticles with hydrophobic properties via a carbonation route. Powder Technology, 200(3), pp.144–148. 12. Chevalier, Y. & Bolzinger, M.A., 2013. Emulsions stabilized with solid nanoparticles: Pickering emulsions. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 439, pp.23–34. 13. Chitnis, G. et al., 2011. Laser-treated hydrophobic paper: an inexpensive microfluidic platform. Lab on a chip, 11(6), pp.1161–1165. 14. Cunha, A.G. et al., 2010. Preparation of highly hydrophobic and lipophobic cellulose fibers by a straightforward gas-solid reaction. Journal of Colloid and Interface Science, 344(2), pp.588–595. 15. Dai, L.L. et al., 2008. The structure and dynamics of microparticles at pickering emulsion interfaces. Scanning, 30(2), pp.87–95. 16. Dickinson, E., 2012. Use of nanoparticles and microparticles in the formation and stabilization of food emulsions. Trends in Food Science and Technology, 24(1), pp.4–12. 17. Dufresne, A. et al., 2014. Effect of Cationic and Anionic Surfactants on Application of Calcium Carbonate Nanoparticles in Paper Coating. ACS Appl. Mater. Interfaces, 6, pp.2734−2744 18. Figueiredo, J.A., Ismael, M.I. & Anjo, C.M.S., 2010. Cellulose and Derivatives 	 49	from Wood and Fibers as Renewable Sources of Raw-Materials. Top Curr Chem, 294(1), pp.117–128. 19. Gao, Z. et al., 2015. Fabrication of TiO2/EP super-hydrophobic thin film on filter paper surface. Carbohydrate Polymers, 128, pp.24–31. 20. Glavan, A.C. et al., 2014. Omniphobic “rF paper” produced by silanization of paper with fluoroalkyltrichlorosilanes. Advanced Functional Materials, 24(1), pp.60–70. 21. Groenendijk, M., 2008. Fabrication of Super Hydrophobic Surfaces by fs Laser Pulses. Laser Technik Journal, 5(3), pp.44–47. 22. Guillot, S. et al., 2009. Internally structured pickering emulsions stabilized by clay mineral particles. Journal of Colloid and Interface Science, 333(2), pp.563–569. 23. Hong, L., 2006. Simple Method to Produce Janus Colloidal Particles in Large Quantity. Langmuir, 22(12), pp.9495–9499. 24. Hu, J. et al., 2012. Fabrication, properties and applications of Janus particles. Chemical Society Reviews, 41(11), p.4356. 25. Ifuku, S. & Yano, H., 2015. Effect of a silane coupling agent on the mechanical properties of a microfibrillated cellulose composite. International Journal of Biological Macromolecules, 74, pp.428–432. 26. Iselau, F. et al., 2015. Role of the aggregation behavior of hydrophobic particles in paper surface hydrophobation. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 483, pp.264–270. 27. Jiang, S. et al., 2008. Solvent-free synthesis of janus colloidal particles. Langmuir, 24(18), pp.10073–10077. 28. Jiang, S. & Granick, S., 2008. Controlling the geometry (Janus balance) of amphiphilic colloidal particles. Langmuir, 24(6), pp.2438–2445. 29. Kalashnikova, I. et al., 2011. New Pickering Emulsions Stabilized by Bacterial Cellulose Nanocrystals, pp.7471–7479. 30. Kalashnikova, I. et al, 2012. Modulation of cellulose nanocrystals amphilic properties to stabilize oil/water interface. Biomacromolecules, 13(1), pp.267–275. 31. Kalia, S. et al., 2014. Nanofibrillated cellulose: Surface modification and potential applications. Colloid and Polymer Science, 292(1), pp.5–31. 32. Kumar, A. et al., 2013. Amphiphilic Janus particles at fluid interfaces. Soft Matter, 9(29), pp.6604–7202. 33. Latthe, S.S. et al., 2014. Superhydrophobic surfaces developed by mimicking hierarchical surface morphology of lotus leaf. Molecules, 19(4), pp.4256–4283. 34. Lavoine, N. et al., 2012. Microfibrillated cellulose - Its barrier properties and applications in cellulosic materials: A review. Carbohydrate Polymers, 90(2), pp.735–764. 35. Li, C. et al., 2009. Pickering emulsions stabilized by paraffin wax and Laponite clay particles. Journal of Colloid and Interface Science, 336(1), pp.314–321.  36. Li, X.-M., Reinhoudt, D. & Crego-Calama, M., 2007. What do we need for a superhydrophobic surface? A review on the recent progress in the preparation of superhydrophobic surfaces. Chemical Society reviews, 36(8), pp.1350–1368. 37. Liang, F., Zhang, C. & Yang, Z., 2014. Rational design and synthesis of Janus composites. Advanced Materials, 26(40), pp.6944–6949. 	 50	38. Lif, A. et al., 2010. Fischer-Tropsch diesel emulsions stabilised by microfibrillated cellulose and nonionic surfactants. Journal of Colloid and Interface Science, 352(2), pp.585–592. 39. Liu, Z., Hunt, J.F. & Cai, Z., 2013. Fire Performance of Fiber Board Coated with Nano Kaolin-Clay Film. BioResources, 8(2), pp.2583–2593. 40. Ljungberg, L.Y., 2007. Materials selection and design for development of sustainable products. Materials and Design, 28(2), pp.466–479. 41. McCarthy, P. & Urmanbetova, A., 2011. Production and cost in the US paper and paperboard industry. Applied Economics, 43(22), pp.2883–2893. 42. Mirvakili, M.N. et al., 2016. Enhanced Barrier Performance of Engineered Paper by Atomic Layer Deposited Al2O3 Thin Films. ACS Applied Materials & Interfaces. 43. Mirvakili, M.N., 2012. Superhydrophobic Fibre Networks Loaded With Functionalized Fillers. 44. Mirvakili, M.N., Hatzikiriakos, S.G. & Englezos, P., 2013. Superhydrophobic lignocellulosic wood fiber/mineral networks. ACS Applied Materials and Interfaces, 5(18), pp.9057–9066. 45. Montgomery, J., 2010. The Role of Suction Boxes on Forming Section Retention and Filler Migration. 46. Murray, H.H. & Kogel, J.E., 2005. Engineered clay products for the paper industry. Applied Clay Science, 29(3-4), pp.199–206. 47. Neinhuis, C., 1997. Characterization and Distribution of Water-repellent, Self-cleaning Plant Surfaces. Annals of Botany, 79(6), pp.667–677. 48. Nonomura, Y. & Kobayashi, N., 2009. Phase inversion of the Pickering emulsions stabilized by plate-shaped clay particles. Journal of Colloid and Interface Science, 330(2), pp.463–466. 49. Oh, M.J., Lee, S.Y. & Paik, K.H., 2011. Preparation of hydrophobic self-assembled monolayers on paper surface with silanes. Journal of Industrial and Engineering Chemistry, 17(1), pp.149–153. 50. Pichot, R., Spyropoulos, F. & Norton, I.T., 2010. O/W emulsions stabilised by both low molecular weight surfactants and colloidal particles: The effect of surfactant type and concentration. Journal of Colloid and Interface Science, 352(1), pp.128–135. 51. Pickering, S.U., 1907. CXCVI.-Emulsions. Journal of the Chemical Society, Transactions, 91(0), pp.2001–2021. 52. Prasad, M.S., Reid, K.J. & Murray, H.H., 1991. Kaolin: processing, properties and applications. Applied Clay Science, 6(2), pp.87–119. 53. Rachini, A. et al., 2012. Chemical Modification of Hemp Fibers by Silane Coupling Agents. Applied Polymer Science, 123, pp.601–610. 54. Rein, D.M., Khalfin, R. & Cohen, Y., 2012. Cellulose as a novel amphiphilic coating for oil-in-water and water-in-oil dispersions. Journal of Colloid and Interface Science, 386(1), pp.456–463. 55. Renault, C. et al., 2013. Hollow-Channel Paper Analytical Devices.	Anal. Chem., 85, pp.7976−7979 56. Shen, J. et al., 2009a. A preliminary investigation into the use of acid-tolerant precipitated calcium carbonate fillers in papermaking of deinked pulp derived 	 51	from recycled newspaper. BioResources, 4(3), pp.1178–1189. 57. Shen, J. et al., 2011. A review on use of fillers in cellulosic paper for functional applications. Industrial and Engineering Chemistry Research, 50(2), pp.661–666. 58. Shen, J. et al., 2009b. Modification of papermaking grade fillers: A brief review. BioResources, 4(3), pp.1190–1209. 59. Shen, J. & Qian, X., 2012. Application of fillers in cellulosic paper by surface filling: An interesting alternative or supplement to wet-end addition. BioResources, 7(2), pp.1385–1388. 60. Siro, I. & Plackett, D., 2010. Microfibrillated cellulose and new nanocomposite materials: A review. Cellulose, 17(3), pp.459–494. 61. Stanssens, D. et al., 2011. Creating water-repellent and super-hydrophobic cellulose substrates by deposition of organic nanoparticles. Materials Letters, 65(12), pp.1781–1784. 62. Subramaniana, R., Fordsmandb, H. & Paulapuroa, H., 2007. PCC-cellulose composite fillers. BioResources, 2(1), pp.91–105. 63. Synytska, A. et al., 2011. Water-repellent textile via decorating fibers with amphiphilic janus Particles. ACS Applied Materials and Interfaces, 3(4), pp.1216–1220. 64. Tan, Y. et al., 2012. Fabrication of starch-based nanospheres to stabilize pickering emulsion. Carbohydrate Polymers, 88(4), pp.1358–1363. 65. Thieme, J., Abend, S. & Lagaly, G., 1999. Aggregation in Pickering emulsions. Colloid and Polymer Science, 277(2-3), pp.257–260. 66. Tingaut, P., Zimmermann, T. & Sèbe, G., 2012. Cellulose nanocrystals and microfibrillated cellulose as building blocks for the design of hierarchical functional materials. Journal of Materials Chemistry, 22(38), p.20105. 67. Vignati, E. & Piazza, R., 2003. Pickering Emulsions: Interfacial Tension, Colloidal Layer Morphology, and Trapped-Particle Motion. Langmuir, 19(6), pp.6650–6656. 68. Wang, J. et al., 2010. Pickering emulsions stabilized by a lipophilic surfactant and hydrophilic platelike particles. Langmuir, 26(8), pp.5397–5404. 69. Wen, C. et al., 2014. Preparation and stabilization of d-limonene Pickering emulsions by cellulose nanocrystals. Carbohydrate Polymers, 112, pp.695–700.  70. Wenzel, R.N., 1936. Resistance of solid surfaces to wetting by water. Journal of Industrial and Engineering Chemistry (Washington, D. C.), 28, pp.988–994. 71. Whitby, C.P. et al., 2011. Shear-induced coalescence of oil-in-water Pickering emulsions. Journal of Colloid and Interface Science, 361(1), pp.170–177.  72. Whitby, C.P., Fornasiero, D. & Ralston, J., 2009. Effect of adding anionic surfactant on the stability of Pickering emulsions. Journal of Colloid and Interface Science, 329(1), pp.173–181. 73. Whitby, C.P., Fornasiero, D. & Ralston, J., 2008. Effect of oil soluble surfactant in emulsions stabilised by clay particles. Journal of Colloid and Interface Science, 323(2), pp.410–419. 74. Wu, W. & Lu, S.C., 2003. Mechano-chemical surface modification of calcium carbonate particles by polymer grafting. Powder Technology, 137(1-2), pp.41–48. 75. Xhanari, K. et al., 2011. Structure of nanofibrillated cellulose layers at the o/w interface. Journal of Colloid and Interface Science, 356(1), pp.58–62. 	 52	76. Xhanari, K., Syverud, K. & Stenius, P., 2011. Emulsions Stabilized by Microfibrillated Cellulose: The Effect of Hydrophobization, Concentration and O/W Ratio. Journal of Dispersion Science and Technology, 32(3), pp.447–452. 77. Yan, Y.Y., Gao, N. & Barthlott, W., 2011. Mimicking natural superhydrophobic surfaces and grasping the wetting process: A review on recent progress in preparing superhydrophobic surfaces. Advances in Colloid and Interface Science, 169(2), pp.80–105. 78. Yang, F. et al., 2006. Pickering emulsions stabilized solely by layered double hydroxides particles: The effect of salt on emulsion formation and stability. Journal of Colloid and Interface Science, 302(1), pp.159–169. 79. Zoppe, J.O., Venditti, R.A. & Rojas, O.J., 2012. Pickering emulsions stabilized by cellulose nanocrystals grafted with thermo-responsive polymer brushes. Journal of Colloid and Interface Science, 369(1), pp.202–209.  

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