Grafting the carboxyl groups onto DPNR by seeded emulsion polymerization to enhance the compatibility with silica filler

Abstract

The modification of deproteinized natural rubber (DPNR) with maleic anhydride (MAH) was synthesized to enhance the better compatibility between silica filler and natural rubber (NR). The presence of carboxylic acid groups (-COOH) of MAH after hydrolysis in the grafted DPNR with MAH (DP-g-MAH) would directly interact with the hydroxyl groups (-OH) of silica filler, resulting from the formation of the ester bonds due to the esterification reaction. It is leading to form the chemical bonding, which is the significantly strong interaction between DPNR and silica filler. The structural characterization of DP-g-MAH was analyzed by Fourier transform infrared spectrometer (FTIR) and proton nuclear magnetic resonance (1H-NMR), respectively. The % grafting level of MAH approximately highs to 99.37 % with the low gel content approximate 14.45 (wt%). In addition, the DP-g-MAH latex was compounded with silica nanofiller 10 phr by latex compounding method. The morphology of silica filled DP-g-MAH (DP-g-MAH/Si 10) was characterized by field-emission scanning electron microscope (FE-SEM) in order to observe the silica dispersion into the DP-g-MAH rubber. The FE-SEM shows that silica filler could disperse in grafted rubber more than the DPNR. In addition, the crosslink density was investigated to confirm the chemical networks, which could occur from esterification between DP-g-MAH and silica filler.