(547b) Effects of Mechanical Refining On the Enzymatic Digestibility of Acid Pretreated Corn Stover

Mechanical refining has been applied in the pulp and paper industry for decades. It has been shown that mechanical refining provides better pulp quality through three different mechanisms: 1) shortening the fiber; 2) crushing and fibrillating the fibers internally; and 3) abrasion and fibrillation of the fibers on the exterior surfaces. However, mechanical refining has not been widely studied for the purpose of application to the concept of the bio-refinery. Recent studies by Koo et al. showed that mechanical refining using a laboratory PFI mill could potentially increase glucose yields in enzymatic saccharifications up to 20% using green liquor pretreated hardwood.  The refining reduced the enzyme usage by ~50%. However, studies on disk refining and blending reported by Zhu et al and Dibble et al, respectively, showed minor effects on digestibility in terms of increased glucose yields.  In this research, we explored the effects of five different refining methods including PFI milling, disk refining, extrusion, Szego milling and blending. The effects of the various refining methods on enzymatic hydrolysis using low severity pretreated corn stover substrates were investigated. The effects of different methods of refining on pretreated biomass are characterized by measurements of particle size distributions, degree of polymerization (DP), and crystallinity of cellulose, ultrastructural changes using SEM imaging, and enzymatic digestibility are reported.