Thermal and rheological properties of cellulose-graft-polyacrylamide synthesized by in situ graft copolymerization

Abstract

In order to prepare a cellulose-based water absorbent material in an environmentally-friendly way, a cellulose-graft-polyacrylamide (cellulose-g-PAM) copolymer is synthesized by in situ graft copolymerization through a co-rotating twin-screw extruder. An ionic liquid, namely 1-N-butyl-3-methylimidazolium chloride, is used as the reaction medium and ceric ammonium nitrate is used as the initiator. The graft copolymerization effect is evaluated by the study of the thermal and rheological properties of the copolymers. FTIR and elemental analysis results show that the amide groups of PAM successfully graft onto the cellulose backbone and the graft ratio of the cellulose-g-PAM is increased with the increase in AM content. Thermal analysis shows that the thermal stability of cellulose-g-PAM and the glass transition temperature of PAM are increased as the graft ratio increases due to the formation of PAM long-chain branches which disturb the segment motion of the cellulose chains. In comparison with cellulose, the dehydration peak of cellulose-g-PAM displays a larger endothermic enthalpy and shifts to higher temperature. Rheological results show that the storage modulus curve of cellulose-g-PAM with a high graft ratio exhibits a plateau at low frequency and the tan δ curve displays a peak value, indicating that the large amount of PAM branches cause the entanglement of copolymer chains and improve the toughness of the copolymers.