Characterization of graft copolymers of acrylamide on mechanically-activated starch

Graft copolymers of starch are a new kind of functional material.Graft copolymers of acrylamide and starch have been synthesized by inverse emulsion polymerization using mechanically-activated maize starch and acrylamide as raw materials. The crude graft copolymer was treated for 8 hours by Soxhlet extraction with a 60∶40(by vol.) mixture of ethylene glycol and acetic acid,which resulted in complete removal of the homopolymer.Samples produced using starch mechanically activated for 30 min and 60 min are denoted M30-St-g-PAM and M60-St-g-PAM.respectively.The structures of M30-St-g-PAM and M60-St-g-PAM were characterized by Fourier transform infrared spectroscopy(FTIR),differential scanning calorimetry(DSC),X-ray diffraction(XRD) and scanning electronic microscopy (SEM) and compared with a graft copolymer of acrylamide with non-pretreated starch(St-g-PAM).The results showed that polyacrylamide(PAM) was successfully grafted onto the mechanically-activated starch.M30-St-g-PAM and M60-St-g-PAM were found to have a porous mesh-like structure with the graft-copolymerization reaction occurring at both crystalline regions and loose amorphous regions of the starch particles.Mechanical activation was found to enhance the reactivity of the starch.Grafting of acrylamide led to a change in the state of the raw starch from semicrystalline to amorphous.The thermal stabilities of M30-St-g-PAM and M60-St-g-PAM were higher than that of St-g-PAM.The graft-copolymerization reaction for M60-St-g-PAM was uneven and the thermal stability was lower than that of M30-St-g-PAM.