Abstract
•Synthesising of chitosan–poly(N-isopropylacrylamide) methylbisacrylamide [Cs–PNIPAM–MBA].•Investigating an influence of NIPAM composition on thermal, kinetic, solid state and life time.•Using Flynn–Wall–Ozawa, Kissinger and Coats–Redfern methods to determine activation energy.•Higher Ea has been attributed to the greater cross-linking density of Cs hydrogel.•F2 type degradation mechanism proposed and lifetime decreases when service temperature increase.
This study attempted to clarify the influence of a cross-linker, N,N-methylenebisacrylamide (MBA), and N-isopropylacrylamide (NIPAM) on the non-isothermal kinetic degradation, solid state and lifetime of hydrogels using the Flynn–Wall–Ozawa (F–W–O), Kissinger, and Coats–Redfern (C–Red) methods. The series of dual-responsive Cs–PNIPAM–MBA microgels were synthesized by soapless-emulsion free radical copolymerization in an aqueous medium at 70°C. The thermal properties were investigated using thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) under nitrogen atmosphere. The apparent activation energy using the chosen Flynn–Wall–Ozawa and Kissinger methods showed that they fitted each other. Meanwhile, the type of solid state mechanism was determined using the Coats–Redfern method proposed for F1 (pure Cs) and F2 (Cs–PNIPAM–MBA hydrogel series) types, which comprise random nucleation with one nucleus reacting on individual particles, and random nucleation with two nuclei reacting on individual particles, respectively. On average, a higher Ea was attributed to the greater cross-linking density of the Cs hydrogel.