Ammonium persulphate induced synthesis of polymethyl methacrylate grafted sodium alginate composite films with high strength for food packaging

The graft copolymerization of methyl methacrylate (MMA) onto alginate was carried out in aqueous media by initiators of ammonium persulphate under a nitrogen gas atmosphere. Then, the grafting of PMMA chains onto the alginate backbone was confirmed through the study of Fourier transform infrared, X-ray diffraction, scanning electron microscopy and 1H nuclear magnetic resonance spectroscopy. At last, a thin and transparent polymethyl methacrylate grafted alginate film with high strength was obtained by the casting method. The effect of MMA/SA ratio or percentage of graft (G%) on mechanical properties, thermal stability (thermogravimetric analysis/differential thermogravimetry analyses), color, opacity and water resistance of composite films were characterized. Results showed the homogeneous transparent films could be obtained while G% was lower than 8.64%. After being grafted by PMMA, the tensile strength of the films was distinctly improved by 205.3%, as well the elongation at break (E%) by 41.7% while the MMA/SA (g/g) is 0.3. On the other hand, water resistance, thermal stability and crystallinity of the films were improved, however, the transparency was slightly decreased.