3.2 Impact of the third constituent in ChCl-DHBA DES system on
cellulose degree of polymerization
According to the previous study, the size of cellulose (e.g., degree of
polymerization) is a crucial factor in biomass
conversion.38 The cleavage of cellulose generates more
reducing ends which is beneficial in many biomass conversion processes.
The degree of polymerization (DP) of cellulose isolated from untreated
and pretreated WT and TG sorghum stover is presented in Figure
2 are tabulated in Table S2 in the Supplementary Materials.
The weight-average degree of polymerization (DPw) of
cellulose in untreated WT and TG sorghum stover were 2,042 and 1,805,
respectively. The dispersity (Đ) of cellulose in untreated WT and TG
biomass were 11 and 9, respectively. All three pretreatments
substantially reduced cellulose DPw in this study. The
cellulose of WT biomass was more significantly depolymerized than the
one in TG biomass. The highest reduction of cellulose
DPw of WT biomass was 35% by the binary ChCl-DHBA DES
pretreatment. Binary DES cleaved more cellulose chains in WT biomass
(1,338) than in TG one (1,598), while both ternary DES pretreatments
were more effective in reducing the cellulose DPw in TG
biomass (1,479-1,489) than in WT one (1,499-1,599). Overall, the impacts
of binary and ternary DESs on cellulose DP were not significantly
different, indicating that the third component was not significantly
modified glycosidic bond cleavage. Compared to dilute acid pretreatment,
where up to 90% of reduction in cellulose DP could be
achieved,39 ChCl-DHBA DES pretreatment showed much
less modification on cellulose, which is consistent with the high
cellulose retention.