Chemical properties of wood pellets and their water extractable organic matter governing pellet disintegration behavior by crushing

Although the physical properties of wood pellets, such as crushability, are crucial for their utilization, the chemical components responsible for disintegration resistance remain poorly understood. This study investigated the mechanical stability and related chemical properties of two commercial acacia pellets of similar dimensions, sourced from the same country (Sample-A and Sample-B). Ball mill tests revealed a significant difference in disintegration behavior between the two samples, with Sample-B exhibiting markedly lower crushability (D50: 12.6 mm) than Sample-A (D50: 7.6 mm). Solvent immersion tests showed that both pellets remained intact in organic solvents but readily disintegrated in water, indicating that the binding components of consistent wood particles are water-soluble. Tetramethylammonium hydroxide pyrolysis GC/MS analysis showed that phenolic components (9.4% of the aromatic fraction) and polymeric saccharides (37.4% of the saccharide fraction) were detected exclusively in Sample-B. Solid-state CP-MAS 13C NMR analysis showed that Sample-B exhibited stronger signals of anomeric carbons (100–108 ppm) and oxygen-substituted aromatic carbons (142–162 ppm) than Sample-A, indicating the coexistence of carbohydrate and aromatic structures in the water-extractable fraction. LC/MS analysis further revealed abundant cello-oligosaccharides in Sample-B, evidenced by ions at m/z 341, 683, and 1025, together with ferulic-acid-derived fragments (m/z 193 and 195), whereas Sample-A showed only a single ion at m/z 341. These analyses provided structural insights into the water-soluble components associated with pellet disintegration behavior. This study highlights the importance of analyzing water-extractable chemical constituents for understanding pellet crushability and for selecting suitable raw materials for pellet utilization.