Grafting of various acrylic monomers on to natural rubber: Effects of glutaraldehyde curing on mechanical and thermo-mechanical properties

Abstract

Natural rubber (NR) grafted with different acrylic-monomers, namely butyl acrylate (BA), methyl methacrylate (MMA), n-butyl methacrylate (BMA) and cyclohexyl methacrylate (CHMA), were prepared via redox polymerization. This aims to enhance the mechanical and thermal properties of pristine NR by using a novel curing system of glutaraldehye (GA). Grafting of acrylic-monomers onto NR molecular chains was clarified using ATR-FTIR and 1H-NMR. It was found that the grafted-NR vulcanizates effectively improved the mechanical properties. Here, NR-g-PBMA showed enhancement in moduli, tensile strength and elongation at break of approximately 100, 280, and 40 %, respectively, when compared to the one without modification. It was also observed that, all the grafted-NR vulcanizates exhibited an improved crosslinking. This was elucidated through the engine oil swelling and the TSSR (i.e. Temperature Scanning Stress Relaxation) measurements. The latter test was also first proposed for characterizing the grafted-NR in terms of mechanical and thermo-mechanical interpretations. The thermogram clearly exhibited that the thermal properties of NR were significantly improved after graft copolymerization owing to the presence of functional groups on the molecular chain which enhanced the intermolecular attraction of the grafted-NR molecules. It can be summarized that two possibilities of interaction were observed: (I) the chemical interaction of GA-Rubber through the CC bonds and through the active ester groups of grafted-NR molecules, and (II) the physical polar-polar interaction through the presence of carbonyl groups of grafted-NR molecules. Thus, the present work is found to be beneficial to the future applications of NR which requires high specific modulus and thermal stability at low strain in case of flexible actuators and sensors. Furthermore, the newly curing technique can be easily used to fabricate article at low temperature with greater ease of processing.