Structure, optical and thermal decomposition characters of LDPE graft copolymers synthesized by gamma irradiation

Methyl methacrylate (MMA) monomer was grafted onto Low density Polyethylene by the direct method of radiation grafting. The effect of cohesive energy density of different organic solvents on the degree of grafting was investigated. It was found that the extent of grafting depends largely on the kind of solvent, in which the highest degree of grafting was achieved in the presence of dioxane, whereas the lowest degree of grafting occurred in the presence of methanol. This behaviour was attributed to the solubility parameters of the solvent, monomer and polymer. The change in structure of the LDPE graft copolymer films was characterized by scanning electron microscopy, X-ray diffraction, UV/vis absorption and thermogravimetric analysis. The X-ray diffraction results showed a decrease in the crystallinity of LDPE graft copolymer matrix at high degree of grafting. Studies were made on the UV-absorption edge, indirect allowed transitions with their optical energy gaps are determined. At the same time the Urbach energy was evaluated. The activation energy of the thermal decomposition was calculated according to Horowitz and Metzger method.