Molecular Weight Distribution of Cellulose from Thermally Modified Spruce Wood

The molecular weight distribution (MWD) of cellulose and its degree of polymerization (DP) have a significant influence on the strength properties of wood. The most widely used method for analyzing MWD and DP is size exclusion chromatography (SEC). In this study, we monitored changes in the MWD and DP of cellulose in spruce wood after thermal treatment at temperatures of up to 280 °C. We employed the two most prevalent SEC methods: after direct dissolution of cellulose in a solution of dimethylacetamide and lithium chloride, and after its derivatization to tricarbanilates (CTCs). Both methods yield comparable results that correlate well with each other, although CTCs yield approximately 15% higher absolute values of DP. Our results show that a drop in DP begins at 100 °C, particularly above 220 °C, where significant cellulose degradation occurs. Both methods are appropriate for analyzing cellulose in thermally degraded wood. CTCs have the advantage of greater sensitivity and are suitable for small sample quantities. Direct dissolution can also provide information on the aromatic compounds formed during the thermal treatment of wood when used in conjunction with a refractive index (RI) detector and an ultraviolet (UV) detector. There is a strong linear relationship between DP and the modulus of rupture (MOR), as well as between the modulus of elasticity (MOE) and DP.