Phase transition of cellulose solutions in N-methyl morpholine N-oxide hydrates

Abstract

Melting dissolution conditions of cellulose in N-methyl morpholine N-oxide(NMMO) hydrate had a profound effect on the phase behavior of cellulose/NMMO/H2O systems. Introducing an antioxidant, n-propyl gallate (PG; 0.5 wt% for cellulose), during melting dissolution proved effective in obtaining reproducibility of results. Cellulose with higher molecular weight gave anisotropic to isotropic transition at lower temperature. Rheological analysis of cellulose solution systems in NMMO hydrate with hydration number (n)=0.65 revealed that cellulose with weight-average degree of polymerization (DPw) of 600, 694, and 940 exhibited the transition over the temperature range of 112-127.5, 105 -125, and 105-120 in the concentration range of 15-20, 15-21, and 15-21 wt%, respectively. This result was ascertained by optical microscopy as well. The transition temperature previously observed in the temperature range 85-92 degreesC seemed to originate from experimental errors associated with existence of unmelted NMMO hydrate crystals. The unmelted NMMO hydrate crystals were confirmed by thermal characterization.