UBC Theses and Dissertations

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UBC Theses and Dissertations

Measurement of the changes to the liquid transport properties of wood due to compression McIntosh, Nicholas Joseph


Compression of wood chips coupled with chemical treatment in a liquid bath has been shown to be an effective method to reduce the energy required to mechanically produce wood pulp. Though the utility of such compression/chip impregnation processes has become well known through implementation at pilot and mill scales, a fundamental understanding of the operational mechanism of these processes remains to be obtained. Towards this end, an experimental and statistical study has been conducted. In this work, better understanding the mechanism of action and measuring the effectiveness of a given compression/impregnation process has come about via developing two complementary methods to characterize arbitrarily compressed wood chips. The first method, applied to chips compressed at mill and pilot-scale, involves extracting a pore size distribution from a wood sample by use of a combination of microscope imaging, digital image analysis, and model fitting to the data obtained from image analysis. The second method, applied to wooden blocks compressed at lab-scale, involves directly measuring liquid uptake of a wooden block from a reservoir. Results from image analysis suggest that compression changes the structure of wood in a way which hinders liquid uptake. This observation, taken with existing heuristic relationships between compression and liquid uptake ability of wood chips, implies that the effectiveness of a wood chip compression/impregnation process relies on the alteration of chip properties on a length scale larger than that captured by the image analysis (i.e., that of individual fibres). Direct measurement of liquid uptake of compressed wood blocks at lab-scale resulted in the emergence of a stochastic relationship between compression conditions (compression rate and total strain applied to a block) and the changes imparted to wood’s micro-structure. Taken in combination, the results of the experimental program conducted suggest that the effectiveness of wood chip compression/impregnation processes lies within the ability of compression to modify the structure of an aggregate of wood chips rather than individual wood chips on a fibre scale.

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