A Study On The Application Of Nanoparticles In Nature Rubber Foaming Compounds

Zinc oxide (ZnO) and Calcium carbonate (CaCO3) are the common additives for natural rubber (NR) foams. Nano-ZnO or nano-CaCO3 has smaller particle size and larger specific surface area, more and more attention has been paid to their application in rubber materials in recent years. In this paper, these nanoparticles are applied in NR foam compounds comparing with micron-scaled particles. The effect of nano-particles on the foaming performance, the curing characteristics and properties of NR foams were discussed.The differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM) and moving-die rheometer (MDR) were used as analytical methods in this paper. At first, the particle size and morphology of ZnO and CaCO3 were characterized. Then, the effect of the nano-sized particles on the thermal decomposition behavior of the blowing agent azodicarbonamide (AC) was studied. The vulcanization and foaming characteristics of NR were also studied filling with these nano-sized particles. The results show that, ZnO can activate the decomposition of AC by decreasing the decomposition temperature and nano-sized ZnO show more efficient activation function than micron-sized chemical-pure ZnO in NR compounds. The degree of vulcanization of NR and the activation effect on AC will be achieved at the same level with 2 phr nano-sized ZnO instead of 5 phr micron-sized ZnO. Nano-ZnO shows more practical value in NR foam compounds.The characterization of CaCO3 shows that the median particle size of the heavy, light and nano-CaCO3 were 14.9,5.9,2.1μm respectively. There are 4% surfactant on the surface of the nano-CaCO3. NR vulcanizates have the best mechanical properties when filled with nano-CaCO3 other than heavy or light CaCO3. NR compounds were foamed in the mold under high temperature and pressure. When NR compound was fully filled in the mold, the foam would be jump out with the release of the mold pressure (jump-mode method), the expansion ratio and foam shrinkage of nano-CaCO3 filled NR was the smallest among three types of CaCO3. When NR compound was partially filled in the mold (40%-75%), the foam would expand in the mold freely (free-foaming method), the expansion ratio of nano-CaCO3 filled NR was the largest among three types of CaCO3. These results show that nano-CaCO3 can increase the modulus of NR vulcanizates efficiently, and the wall strength of the cells is stronger. Particle size of CaCO3 has obvious influence on the cell structure of NR foams, nano-CaCO3 filled NR has the most uniform and fine cell structure, light-CaCO3 filled NR shows the worst cell structure.The compression curve of NR foam has two stages:linear elastic stage and compact stage. The nano-CaCO3 filled NR foam shows narrow linear elastic stage and earlier compact stage.In this paper, all the micron-sized inorganic particles were subsitituted by the corresponding nano-sized particles in NR foaming compounds, the optimum cell structure and excellent foam properties were successfully prepared. These results provide practical data for the application of inorganic nano-particles in the rubber foams.