Scientists decode the glossy surface layer that makes premium wood pellets work
Researchers have identified how wood's natural polymers migrate to pellet surfaces, creating a thin protective layer that signals quality to buyers. Understanding this formation process could help manufacturers improve pellet performance and consistency—key factors for the growing biomass energy market.
Originaltitel: Probing the physicochemical properties of wood pellet surfaces in an axial direction with confocal Raman microscopy
<p>The pelletization of lignocellulosic biomass is essential for producing energy-efficient and easily transportable products due to high density and low moisture content. A hard, glossy surface is often associated with high-quality pellets; however, the composition and formation of this surface layer remain insufficiently understood. This study examines the surface and what components it contains using confocal Raman imaging. Four pellet types were analyzed: pure cellulose and three spruce-based variants. Scanning electron microscopy (SEM) revealed a glossy layer in all the samples, with thicknesses of 2.1 +/- 0.3 & micro;m for cellulose, 2.9 +/- 1.3 & micro;m for spruce, 4.8 +/- 1.5 & micro;m for spruce from cross-laminated timber (CLT), and 5.7 +/- 1.1 & micro;m for the spruce-starch pellet. The glossy upper layer was further characterized using confocal Raman imaging with a 532 nm laser. The results of Raman imaging indicate that biopolymer migration reduced crystallinity of the cellulose structure near the pellet surface, reflected by a decreased I380/I1096 ratio. A method to evaluate the migration of lignin - and potentially hemicellulose or lipophilic extractives - to the surface of spruce-based pellets is also proposed. These findings provide new insights into the factors contributing to pellet surface gloss and may support improved pellet production.</p>