Performance of softwood bark comminution technologies for determination of targeted particle size in further upcycling applications

Abstract

Softwood bark is an important souce of biomass, extractive compounds and value-added products. The comminution of larch (Larix decidua Mill.), Scots pine (Pinus sylvestris) and spruce (Picea abies) bark planks is examined in this study, to give an overview of how to apply this knowledge for upcycled products made of bark, especially for bark-based composites. At the moment there is no specific industrial technology for size reduction of tree bark for advanced use in various compounds. Four crushing systems commonly used for other materials (e.g. mineral ores, plastic, wood, biomass) were scrutinized: crusher with sound waves, friction plate mill, 4-shaft shredder and drum chipper. Performance of equipment, sound and dust generation during operation, aspect, grain size and possible applications of the bark particles were analysed. The end product and the processes were assessed on a 1–10 scale. All three bark species fractionated well and with relative similar fraction yield profile. The yield of fine-grained particles was low and the major fractions were larger particles, i.e. from 1% to 20% of grains under 0.5 mm and from 17% to 100% of particles >4 mm. The 4-shaft shredder was the most appropriate tool for crushing the bark planks at industrial capacity. The ground particles cover a broad area of applications, from mulch to insulation or decorative panels.