Open Collections

Fracture and blending of wood composites with discontinuous adhesive bonds

University of British Columbia

To minimize resin consumption in the manufacture of oriented strand board, while maintaining the mechanical properties of the finished product, several factors must be optimized. The focus of this work is to answer the following questions: what is the optimum droplet diameter and dot-pitch (distance between droplet centres), and how should the rotary drum blender be operated to achieve this? This work examines the effect of droplet diameter and dotpitch on the Mode I fracture toughness of a discontinuous adhesive bond and presents preliminary results on the blending dynamics of oriented strand board. The major conclusions from the work are that the fracture toughness appears to increase linearly with resin droplet diameter and with the square root of bonded area, a finding that is supported by an analytical model. Furthermore, the study shows that the fracture toughness is not strongly dependent on the amount of resin applied. Therefore, by modifying the droplet diameter and dot-pitch it should be possible to maintain the current mechanical properties of the board with reduced resin consumption. Since the bond fails in the substrate, a similar square root relationship between the retention of solid wood fracture toughness by the discontinuous bond and the area of solid wood failure is postulated and confirmed. A minimum ratio of bonded area to total area of 0.3 is suggested, below which the bond does not form. To determine the above results a modified flexographic printing technique was used to deposit resin droplets of known size and spacing. The mass of resin applied was relatively constant, however, the mass applied is affected by resin viscosity, relative humidity and substrate moisture content. The preliminary work on blending examines the effect of blender rotation speed and drum-wall friction on the tumbling behaviour of strands. Increasing the rotation speed causes the strands to pass through various tumbling regimes, from sliding to centrifuging. Experiments on drum-wall friction show the necessity of flights. Initial models in the area ignore the effect of friction, which limits their usefulness.

Thesis/Dissertation

application/pdf

2009-08-20

For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.

http://hdl.handle.net/2429/12435

Materials Engineering

University of British Columbia

UBCV

DSpace