Electron‐beam modification of nitrile rubber in the presence of polyfunctional monomers

Abstract

AbstractThe structural changes of nitrile rubber in both the presence and the absence of polyfunctional monomers, such as trimethylolpropane triacrylate (TMPTA), tripropyleneglycol diacrylate (TPGDA), and trimethylolmethane tetraacrylate (TMMT), at different doses of electron beam irradiations, were investigated with the help of FTIR spectroscopy (in the ATR mode), solid‐state NMR, dynamic mechanical thermal analysis, and sol–gel analysis. There was a significant decrease in the concentration of olefinic groups for modified system with 3% TMPTA compared to that of the unmodified nitrile rubber on irradiation. This was also confirmed by the increase in the carbon resonances attributed to CC linkages from solid‐state NMR for the modified system, indicating more crosslinkages. The increase in crosslinking was also revealed by the increase in % gel content and dynamic storage moduli with radiation dose. The lifetime of spurs formed and the critical dose, an important criterion for overlapping of spurs, were determined for both grafted and ungrafted nitrile rubber using a mathematical model. The ratio of scissioning to crosslinking for nitrile rubber was determined using the Charlesby–Pinner equation. Mechanical properties were studied for the modified and the unmodified systems and the tensile strength was found to increase with grafting of polyfunctional monomers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 435–447, 2005