Date of Award

8-2014

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forest Resources

Advisor

Stephen M. Shaler

Second Committee Member

Robert W. Rice

Third Committee Member

Barbara J. W. Cole

Abstract

Generating renewable fuels and chemicals independent from fossil sources is a major objective of much research. Pre-extraction of hemicellulose from lignocellulosic feedstock has been a research focus during the last decade within the context of lignocellulosic-biorefineries. While a significant amount of research has been conducted studying and optimizing extraction and conversion rates, little attention has been paid to the effects of hemicellulose extraction on the remaining material, which in the case of wood can be used to produce conventional wood composites (e.g. particle board, OSB).

In this study the effect of hot-water extraction on the topochemistry and ultrastructure of aspen wood (Populus spec.) was investigated by means of scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy paired with selective electron dense staining of lignin using mercurization and potassium-permanganate as well as immunogold labeling of hemicellulose.

The hot-water extracted wood cell wall differs significantly in its ultrastructure from neat wood in form of distorted cells and lignin and extractive agglomerations in the cell lumina. Immunogold labeling results indicate that different types of hemicellulose are extracted at different stages and both concentration and distribution within the wood cell wall layers are effected. Hemicellulose more closely associated with lignin appear to be more easily extractable by hot water extraction. In addition to hemicellulose, lignin in the wood cell wall is partially extracted and altered. The employed lignin selective electron dense stains displayed different reaction mechanisms in hot-water extracted and unextracted wood, indicating a modification of lignin structures. As a result semi-quantification of lignin distribution was only partially successful.

Additionally, the potential use of focused ion beam microscopy to study wood cell wall ultrastructures and chemistries was explored but found to be to complex a technique to aid in the objective of this study.

Results from this study provide a more holistic view on chemical and ultrastuctural changes of wood attributed to hot-water extraction and associated changes in hemicellulose and lignin distribution in hot-water extracted wood. These new insights will help to better understand mechanical properties and adhesion related questions regarding the use of hot water extracted wood for wood-composite production.

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