Effect of mild torrefaction on pulverization of Norway spruce (Picea abies) by oscillatory ball milling: particle morphology and cellulose crystallinity

Abstract

Abstract The effects of mild torrefaction on the pulverization of Norway spruce sawdust have been studied. To this end, sawdust was dried and torrefied below 230°C for different periods of time to obtain samples with mass losses (ML) of 0.2%, 1.4%, and 2.8%, milled in an oscillatory ball mill, and the particle morphology and cellulose crystallinity of the powders were studied. The pretreatment leading to 0.2% ML had no effect on grindability, but that resulting in 1.4% ML improved grindability and a median particle size below 17.4±0.2 μm was attained. Torrefaction involving 2.8% ML reduced the specific energy consumption more than 21% when the targeted median particle size of the torrefied wood was between 18.7±0.5 and 79±3 μm. The mild torrefaction had a negligible influence on the aspect ratio distribution and cellulose crystallinity in the ball-milled wood.