Abstract: The relationship of the crystallinity, glass transition temperature (T_g) and thermal stability of carboxymethylcellulose (CMC) with substitution degree (DS) from 0. 4 to 1. 55 were studied, by using WAXS, DSC and TGA methods. The crystallinities.rapidly decrease with the increase of DS. In the meanwhile, T_g of CMC also decreases with increasing DS, except the sample with DS=1. 55. The activation energies of the thermal degradation for the main chain of CMC lie between 251 and 293 kJ/ mol, similar to precursor cellulose. However, the initial temperature of the thermal degradation (T_d) of CMC is influenced by the -CH₂COONa contents on the chains, which increase somewhat with the increase of DS. This may be attributed to the interaction of metal ions and-carboxylate groups, on the polymer chains.The effects of counterions: H⁺, Na²⁺, Mg²⁺, Ca²⁺ and Al³⁺ on the crystallinity of CMC are quite different. The crystallinity decreases in either case when the radiis of counterions with the same valence increase or when the valences of counterions with the similar radius increase. The effects of the counterions on the thermal behavior of CMC are quite complicate, therefore only a preliminary discussion is presented.

Key words: CMC, Thermal behavior, DSC, TGA