Structure and properties of resole resin crosslinked vulcanizates of natural rubber grafted with polymethylmethacrylate

Abstract

The structure and property relationships of graft copolymers from natural rubber (NR) and polymethyl methacrylate (PMMA) crosslinked with a phenolic resin were investigated. The NR grafted with PMMA (NR-g-PMMA) having different grafting levels was initially prepared by emulsion polymerization before compounding and vulcanization. Then, proton nuclear magnetic resonance and transmission electron microscopy were used to verify the resultant NR-g-PMMAs. The graft copolymers crosslinked with phenolic resin exhibited improvements in various properties. Tensile modulus and tensile strength increased at least 18 and 95%, respectively, over the un-grafted counterpart and further improved with grafting percentage, while the elongation at break decreased accordingly. Storage modulus in rubbery plateau increased while tanδ peak height decreased with PMMA content. Moreover, the thermal stability of the graft copolymers was also improved over that of the plain NR at least 23 °C, depending on MMA contents. These improvements are tentatively attributed to the strong adhesion between NR and PMMA phases, based on interactions between the functional groups of PMMA and hydrogen bonding between phenolic resin crosslinker and PMMA. The results clearly suggest that the phenolic resin could be an effective crosslinker for NR-g-PMMA.

Keywords

• crosslinking agent
• natural rubber
• vulcanization
• grafting
• mechanical property