Electron beam radiation curing of natural rubber filled with silica-graphene mixture prepared by latex mixing

Abstract

The mechanical properties of irradiated natural rubber (NR) composites filled with silica (SiO2) and graphene nanoplatelets (GE) mixture have not been studied sufficiently for more understanding since they are interesting composites. SiO2/GE mixture produced by mixing method were added to NR by latex mixing. The products were subsequently cured by EB irradiation to form NR composites. Filler content (1, 2.5 and 5 phr), the proportion of GE in the fillers (0.008%, 0.056%, 3.23% and 14.29%), and EB irradiation dose (100, 150, 200 and 250 kGy) were varied in these NR composites. The results of EDXS elemental mapping confirmed the presence of GE in the SiO2/GE filler, while the FTIR results confirmed that no new functional groups occurred between SiO2 and GE. Mechanical and thermal properties of NR composites were investigated. Scanning electron microscope (SEM) indicated good dispersion of GE and SiO2/GE in the NR matrix. The results showed that EB irradiation could be used as a mean of crosslinking NR composites to improve their tensile properties. NR filled with 2.5 phr of the SiO2/0.056%GE mixture cured by an EB irradiation dose of 150 kGy (NR/SiO2/0.056%GE-EB) showed the highest tensile strength, as well as acceptable moduli at 100, 300, and 500% strain. The tear strength of the composites was higher than that of NR filled with only SiO2 (NR/SiO2-EB), while NR filled only with GE (NR/GE-EB) added in an equivalent amount and using the same irradiation dose could greatly improve moduli and tear strength. It was found that high GE content (3.23% or higher) in SiO2/GE mixture lowered the tensile strength of the composites. The effect of the curing step in EB irradiation on tensile properties was also studied by comparison between one-time irradiated composites and two-times irradiated composites. It was found that crosslink density increased when repeating the EB irradiation step on the NR composites and increasing EB irradiation dose to more than 150 kGy, which impacted negatively on movement of the molecular chain, resulting in a negative effect for tensile strength. Thermogravimetric analysis results indicated that there was a small improvement of thermal stability of NR/SiO2/0.056%GE-EB compared with NR-EB. Moreover, the degradation temperature (Td) of the composites decreased with applying high EB doses to the composite. Therefore, GE could be used as an individual filler or hybrid filler with SiO2 to improve mechanical properties of irradiated NR composites.