Enzymatic hydrolysis of lignocellulosic biomass is highly dependent on the changes in structural features after pretreatment.

A three-stage wood milling process was investigated leading to coarse, fine and amorphization of milled wood (MW) as a pretreatment for enzymatic wood hydrolysis. An eccentric vibratory tube mill (EVTM) and a spring suspended vibratory tube mill (SSVTM) were found to be suitable for wood cellulose amorphization. Both methods gave rise to highly digestible and amorphous wood powders amenable to enzymatic hydrolysis. The SSVTM had superior energy efficiency. The resulting MW afforded a 70% sugar yield via enzymatic hydrolysis and the total energy consumption was around 1.5 kWh kg−1oven-dried wood (odW) for all three milling stages. In contrast, EVTM consumed 17 kWh kg−1odW energy. Accordingly, SSVTM has a high potential for preparing wood for enzymatic hydrolysis.

No abstract

Mechanical pretreatment is an effective process for chemical or biochemical conversion of woody biomass. The deconstruction features of the wood cell wall play an important role in its chemical or biochemical processing. In this work, we evaluated the wood cell wall fracture in the early stage of mechanical pretreatment process conducted with various initial moisture contents. Electronic microscopy (i.e., SEM and TEM) and confocal laser scanning microscopy (CLSM) were used to visualize the cellular structure changes due to cell wall fractures. Results reveal that the enzymatic digestibility of micronized wood produced from different initial moisture contents was improved by 2-6 folder than that of the raw material. The types of cell wall fractures after mechanical pretreatment were distinguished by the initial moisture contents of wood. In wood samples with lower moisture content, interwall fracture occurred predominantly at the middle lamella region, while intrawall fracture occurred primarily at inner cell wall layers, with sever breakage in wood fibers for high moisture content samples.Differences in the distribution of surface chemical composition also resulted from different cell wall fractures. Lignin preferentially covered the fracture surface of low-moisture content samples, while carbohydrates were more predominate in high-moisture content samples. These morphological and structural alternation contributed to improving enzymatic digestibility of micronized wood. Findings from this study demonstrate how mechanical pretreatment modifies the fracture features of wood cell wall for further chemical/biochemical reactions.