Superabsorbent materials from grafting of acrylic acid onto Thai agricultural residues by gamma irradiation

Superabsorbent polymers based on ubiquitous agricultural residues: sugarcane, water hyacinth, rice straw, coconut shell and palm fruit bunch substrates, were successfully synthesized. Gamma radiation from Co-60 was employed to graft acrylic acid (AA) onto the substrates. Rice straw exhibited the highest equilibrium swelling ratio of 78.90 g/g at 6 kGy of absorbed gamma ray dose and 14%v/v AA concentration. The rate of water absorption was rapid at the beginning and became reduced with increasing immersion time. After about 3.5 hours, the absorption reached approximately 90% of the saturation value. Temperature plays a critical role on the rate of water evaporation from the superabsorbent. As for the one experiencing 35degC-40degC temperature, the weight of the saturated superabsorbent reduced to approximately 50% of the original value in 13 hours. However, for the one experiencing room temperature (24.2degC-27.7degC), approximately 58 hours were needed to reduce the weight by half. The superabsorbent polymer was able to absorb about 203% of the polymer's dry weight and did not release urea when eluded by water. Moreover, the polymer was able to hold water very well for at least 3 weeks and did not degrade until at least 6 weeks, ensuring biodegradability. (author)