การประยุกต์ใช้ยางธรรมชาติกราฟต์พอลิ 2-ไฮดรอกซีเอทิลอะคริเลทต่อการกระจายตัวของซิลิกาในยางธรรมชาติคอมพอสิท

Abstract

The grafting of poly (2-hydroxyethyl acrylate) on to natural rubber (NR-g- PHEA) was done by emulsion copolymerization method. The influences of reaction temperature, reaction time, initiator concentration and monomer concentration on percent grafting, monomer conversion and grafting efficiency were investigated. The structures of copolymers were characterized by nuclear magnetic resonance ('H-NMR and C-NMR) Fourier transforms infrared spectrometry (FTIR) and Transmission electron microscope (TEM). Thermal properties were examined by thermalgravimetric analysis (TGA). The NR/silica compounds were prepared with various grafting percentages of NR-g-PHEA (0, 6.5, 10.5 and 14.5%) and fixed amounts of 3 phr NR-g- PHEA and 20 phr silica. The cure characteristics were examined using a moving die rheometer (MDR). The physico-mechanical properties of NR/silica composites were determined in terms of tensile strength, bound rubber content, and dynamic mechanical analysis (DMA). The results showed that scorch time and cure time tend to decrease with the level of grafting in NR-g-PHEA. The NR-g-PHEA decreased tan, whereas bound rubber content in NR/silica compounds increased, which indicates improved silica dispersion in the NR matrix. The mechanical properties improved with level of grafting in NR-g-PHEA. In addition, the effect of NR-g-PHEA content on properties to NR composites was investigated with various NR-g-PHEA contents from 0 to 12 phr, while the 14.5% grafting level in NR-g-PHEA and 20 phr silica content were held fixed. The results showed that scorch time and cure time decreased, while cure rate index (CRI) increased with NR-g-PHEA content. The highest 100% modulus, 300% modulus, reinforcing index and tensile strength were obtained with 3 phr NR-g- PHEA. When NR-g-PHEA was compared with epoxidized natural rubber with 50 mol% expoxidation (ENR50) was used as compatibilizer at 0 to 12 phr. The ENR50 compatibilizer increased bound rubber content and decreased the Payne effect in the NR/silica composites, due to interactions of silanol groups on silica surfaces with epoxide groups in ENR50. This increased hardness, tensile strength, and 100% and 300% modulus, but slightly decreased elongation at break. NR-g-PHEA enhanced the cure characteristics and mechanical properties than ENR50 was used as compatibilizer and sialne coupling agent.