Refining energy is a critical production variable for the thermomechanical processing of wood into composites such as medium density fiberboard. This work represents an industry/university cooperation to understand how refining energy (i.e. the gap between refiner plates) impacts the chemical and physical properties of Douglas fir (<i>Pseudotsuga menziesii</i>) fiber. Besides effects on specific surface area, and porosity, refining energy was correlated to an increase in the free phenol and biogenic formaldehyde content of the fiber. This is consistent with classic lignin acidolysis reactions, and oftentimes such reactions result in lignin repolymerization and additional crosslinking. However in this case, refining resulted in a reduced lignin glass transition temperature, suggesting that lignin benzyl cations were diverted from repolymerization and crosslinking reactions. The diversion of benzyl cations from repolymerization and crosslinking has implications for biorefinery technologies. However we discuss how lignin repolymerization might be promoted in the manufacture of wood-based composites, in direct opposition to biorefinery strategies for lignin removal.

Lignin acidolysis during thermomechanical wood refining

255th National Meeting (2018)

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