Physical properties of methylcelluloses in relation with the conditions for cellulose modification

Water-soluble methylcellulose (MC) samples were synthesized by a new homogeneous reaction using DMAc/LiCl as solvent, a dimsyl sodium solution as activator and CH3 . as alkylating reagent. Different degrees of substitution were obtained (0.9 < <(DS)over bar> < 2.2). A commercial MC (<(DS)over bar> = 1.7) was also studied. The structural characterization of the samples was carried out using C-13-NMR and h.p.l.c. measurements. Rheological and steric exclusion chromatography studies in the dilute regime were performed as a function of the temperature and the properties of the samples were compared. According to the <(DS)over bar> value, two different behaviours were observed. For <(DS)over bar>>1.5, interactions occur for T > 45 degrees C. If <(DS)over bar> < 1.5 there is no clear evidence for aggregation. (C) 1997 Elsevier Science Ltd.