Improving the thermal stability of wood-based cellulose by esterification

Improvement in the thermal stability of wood-based cellulose; the needle-leaf, bleached, krafp pulp (NBKP) and the wood cellulose nanofibers (WCNF) obtained from the NBKP, was achieved by esterification. Initially, four different types of NBKP esters (acetyl, C2; myristoyl, C14; benzoyl, BNZ; and pivaloyl, PIV) with different degree of substitution (DS) values were prepared to evaluate the effect of esterifying the hemicellulose. The findings revealed that an optimum DS, which possibly completely esterifies the hemicellulose and amorphous cellulose, is needed to achieve significant improvement in thermal stability. Moreover, BNZ and PIV gave higher thermal stability than that of the C2 and C14. BNZ was selected over PIV to modify the WCNF. Benzoylation increased the 1% weight loss temperature (WLT) of WCNF by 25 °C and improved its resistance against thermal weight loss at the early stage of degradation and discoloration. Unlike the results of NBKP, changing the DS from 0.4-1.1 did not show variation in the thermal behavior of WCNF esters. The effect of esterifying the hemicellulose in WCNF was not clearly observed possibly due to the formation of reducing ends brought by mechanical fibrillation during WCNF preparation. Finally, the thermal stability of wood-based celluloses can be comparable to that of highly crystalline and pure bacterial cellulose after benzoylation at an optimum DS.