Microstructure And Properties Controlling Of Natural Rubber/Nanosilica Composites Using Latex Compounding Techniques

Natural rubber (NR), as a superior comprehensive performances renewable resource, possesses high elasticity, high strength, high elongation and abrasion resistance, etc. It has been comprehensive applied to aviation, military, vehicle, tire and medical elastomer, and plays a pivotal role in national economic construction. Recently, the international price of NR is so high that most enterprise cannot afford. It is necessary to research a novel technique and high properties of NR composites. The traditional method is mixing dry rubber with much strengthening agent, but this process is either consuming energy and polluting the environment or harming the heath of manipulator. Therefore, in this paper we set a new technique differentiated with "dry mixing", and do huge studies on "latex compounding".Natural rubber/Nanosilica (NR/SiO2) composite was developed with latex compounding techniques. SiO2 was first modified by 3-(trimethoxysilyl)propyl methacrylate (MPS), and then grafted with polymethyl methacrylate (PMMA) through polymerization in order to obtain core-shell SiO2-MPS-PMMA nanoparticles. On the other hand, NR-PMMA was obtained by emulsion polymerization (NR-PMMA). Finally, NR/SiO2 nanocomposites were formed by blending SiO2-MPS-PMMA with NR-PMMA. The effect of nanocomposites caused by different loadings of SiO2 was discussed. The properties of modified SiO2, modified NR and nanocomposites were characterized by the fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic-mechanical thermal analysis (DMA), thermal gravimetric analysis (TGA) and mechanical testing.FTIR results showed that unsaturated double bond(C=C) was introduced on the surface of SiO2 because of the addition of MPS and MMA monomers had successfully grafted onto the surface of SiO2. On the other hand, NR-PMMA was obtained by emulsion polymerization.TEM results indicated that it was better to use 95wt% ethanol solution than by water and absolute ethanol. The core-shell SiO2-MPS-PMMA nanoparticles were formed by copolymerization. The dispersibility of SiO2-MPS-PMMA nanoparticles in solution was excellent while the MMA/SiO2 ratio was 0.3.With the increasing of MMA, the molecule of weight of PMMA grafted on the surface of SiO2 also increased, resulting in interwining molecular chains and aggregation. SiO2-MPS-PMMA particles were bigger than 100nm with 3 of MMA/SiO2 ratio and it was no longer in a nanometer dimensional range. SEM analysis illustrated that NR-PMMA/SiO2-MPS-PMMA nanocomposites possessed dim interface, and almost all SiO2-MPS-PMMA nanoparticles were homogenously distributed throughout the NR matrix as individual core-shell structure with an average size in the range of 60-100nm when the SiO2 content was less than 3wt%.DMA analysis manifested that the glass transition temperature of NR-PMMA/SiO2-MPS-PMMA nanocomposites was higher than pure NR. Nanocomposites possessed lower temperature tolerance, higher storage modulus and better elastic resilience.TG and DTG curves demonstrated that MMA monomers were almost copolymerization and less grafted at 0.3 of MMA/SiO2 ratio; while the more MMA were added, most of the monomers were grafted onto the surface of SiO2. The thermal stability of nanocomposites was enhanced by the adding SiO2 contents compared with pure NR.The tensile strength of nanocomposites was superior to pure NR, and reached a peek when 0.5wt% SiO2 was loaded. However the SiO2 loadings increased, the tensile strength gradually decreases because the site of SiO2 aggregation is easy to concentrate stress and brings about breaking of the sample.