Characterization of micronized wood and energy-size relationship in wood comminution

• Effectively micronized softwood Douglas-fir feedstock was achieved with ring and puck milling.
• Moisture content was the crucial factor influencing development of particle's properties.
• Linear correlation between cellulose crystallinity index and median aspect ratio of milled particles was obtained.
• Rittinger's model illustrated the strong relationship between particle size changes and specific energy consumption.

Mechanical milling demonstrates potential in the pretreatment arena to valorize lignocellulosic biomass because it eliminates chemicals and simplifies processing. The development of physical properties and energy consumption for generating micronized particles are key factors affecting potential use. This study investigated the effect of input moisture content, and feedstock particle size on developing physical characteristics of micronized particles and the resultant specific energy consumption in the milling process. Wood particles with different sizes were effectively comminuted to < 20-μm within several minutes using a vibratory ring and puck mill. Moisture content was found to be a key factor influencing the development of particle morphology and crystallinity. Lower moisture content resulted in much rounder particles with lower crystallinity, while higher moisture content resulted in the micronized particles with larger aspect ratio and crystallinity. Crystallinity index and median aspect ratio of the micronized particles were linearly correlated. The particle size change during milling was highly correlated to the specific energy consumption of milling through the Rittinger's model (0.91 < R2 < 0.96). Input moisture content and feed size were found to affect the energy intensity of grinding woody biomass. The Rittinger's constant was a good indicator of the material performance in this area. The results will provide a guidance for preferred milling conditions as well as designing scalable micronizing mills.