In addition to improved hemicellulo

In addition to improved hemicellulose content preservation, PAA delignification also results in less cellulose degradation compared with Kraft pulping.28,29 As shown in Table 2, holocellulose fibers showed higher weight-average molar mass (Mw) of 1.1 × 106 g/mol compared with Kraft fibers (8.1 × 105g/mol). Moreover,there are significant differences in the molar mass distributions (Figure 3). The molar mass distribution for holocellulose shows two distinct peaks with the low molar mass peak dominated by hemicellulose. This observation was also reported for PAA treated cellulose nanofibrils.32 An Mw of ~ 2 × 104 g/mol for hemicellulose is similar to Mw determined for hemicellulose extracted from spruce.In contrast,the molar mass distribution of Kraft fibers is characterized by a broad peak at a lower Mw range for cellulose and with a significantly smaller peak for hemicellulose. The Kraft degradation of cellulose will shift the peak to lower molecular weight,while the hemicellulose peak is weakened due to degradation and removal of hemicellulose. These results imply that degradation is more limited for both cellulose and hemicellulose during PAA delignification process, compared with Kraftpulping.