Water sorption-desorption behaviour of methyl methacrylate-starch copolymers: effect of hydrophobic graft and drying method

Moisture sorption and desorption isotherms were measured at 25 °C and analysed according to GAB and Young-Nelson equations, which distinguish between different physical forms of moisture distribution. The Young-Nelson model gave the best fit to the experimental data. The results obtained showed that the presence of the acrylic component modified not only the total hygroscopicity of the copolymers, as compared with the original starch derivatives, but also the water distribution in the solid, which might have an important role in the effect of moisture content on copolymer characteristics. The main water-sorption mechanism seemed to be absorption into the copolymer particles structure, in agreement with their starching nature. In terms of water sorption-desorption characteristics, no marked differences were found between the two drying methods used.