Additivation of the ethylene–vinyl acetate copolymer (EVA) with maleic anhydride (MA) and dicumyl peroxide (DCP): the impact of styrene monomer on cross-linking and functionalization

The functionalization of the ethylene–vinyl acetate copolymer (EVA) was carried out in an internal mixer, using maleic anhydride (MA), dicumyl peroxide (DCP) and styrene monomer (St) as additives. Torque rheometry, Fourier transform infrared spectroscopy (FTIR), titration, gel content, thermogravimetry (TG) and differential scanning calorimetry (DSC) were evaluated. The EVA/MA/DCP and EVA/MA/DCP/St torque curves showed a significant increase, indicating the cross-linking process. FTIR confirmed the appearance of a new band in the EVA chain, at 1780 cm −1 , attributed to the carbonyl group of maleic anhydride. However, maleic anhydride grafting to the EVA/MA/DCP system only occurred for the 5% MA/0.3% DCP ratio. When the EVA/MA/DCP system is additivation with the styrene monomer (St), all compositions grafted maleic anhydride into the EVA chain, suggesting that styrene increases the effectiveness of the degree of grafting. In addition, FTIR indicated the emergence of a band at 702 cm −1 , due to the vibration of the aromatic core of styrene and, therefore, forming a multiphase copolymer (EVA-g-(St-co-MA)). The thermal stability was practically not altered when functionalizing the EVA with maleic anhydride, as verified by TG. The crystalline melting temperature, the crystallization temperature, the enthalpy of crystalline melting and the degree of crystallinity decreased with the EVA functionalization process. In general, a high degree of grafting of maleic anhydride in the EVA chain is difficult, due to the competitive effect with the cross-linking process.