| Silica and Montmorillonite?MMT?are the common additives for silicone rubber?MVQ?foams.Silica or MMT 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 particles of nano-mineral filler are applied in MVQ foam composites.To study the effect of changing the content and type of nano-mineral fillers on the vulcanization characteristics,foaming characteristics,and compression properties of foamed rubber.At first,the morphology of Silica?H2000?particles and their dispersion in silicone rubber had been characterizated.Then,the effect of nano-mineral filler on the vulcanization properties of silicone rubber,and the mechanism of nucleation as a nucleating agent in foaming had been investigated.The results show that,the silica not only acts as reinforcing agent,but also plays an important role in the cellular nucleation.When the content of silica increases from 40 phr to 70 phr,the range of the calculated surface tension of silicon rubber composites/scCO2(?mix)and radius of the critical nucleus?r*?are 158.951092.74 nN/m and 14.4599.34 nm,respectively.Meanwhile,aggregated silica has good heterogeneous nucleation as the diameter of aggregated silica particles is approximate to twice r*.The smallest cell diameter and the highest cell density of the silicone rubber foam can reach to 708 nm and 1.02×1011cells/cm3,which indicate that the silicone rubber nanofoams can be obtained by means of the supercritical foaming technology.Secondly,this paper took the lead in the use of silica as a nucleating agent,prepared foamed silicone rubber foam with open-celled nanostructures,and studied the cell morphology and mechanical properties of micro-nanostructured silicone rubber foams.The cell size and cell density of microcellular silicone rubber foams can reach to 14?m and 1011 cells/cm3,respectively.The nanocellular silicone rubber foams have upper limit diameter of 59 nm,and the density of nanocellular silicone rubber foams is the order of 1014 cells/cm3,which is several orders of magnitude larger than that of the typical microcellular silicone rubber foams.The stretching-induced cavitation can play an important role in the formation of the nanocellular structure on the cell walls.The effect of the cellular structure on the mechanical properties is investigated.As a result,the nanocellular structure causes an early breakdown,resulting in decreasing of tensile stress.Meanwhile,with the open-cell content?OCC?increasing,the compressive curves changes from three regions to two regions,indicating that the compression plateau disappears when the OCC is beyond of 0.45.Finally,the MMT was added to the silica/MVQ composite.The rheological properties of the MMT in the composite and the influence of the nucleation mechanism were studied.The effect of the MMT on the compression performance of the foaming system was also investigated.The results show that the dispersion of silica in silicone rubber is better than MMT,and the reinforcement of silicone rubber is also better than that of MMT.Due to the interface between the lamellar structure of MMT and silicone rubber matrix,that is a low potential energy point and is conducive to nucleation of the cells.In the MMT-SiO2/MVQ multiphase composites,the energy barriers to be overcome for the nucleation of the two nano-mineral fillers are different,the nucleation of the two nano-mineral fillers is not synchronized,and the growth time of the cell nuclei is different,so a bimodal foam is obtained.The cell walls of the foamed system filled with MMT are obviously thickened,and the formed double peak structure is favorable for improving the compression performance of the foaming system.In this paper,nano-mineral fillers in MVQ foaming composites,the optimum cell morphology and excellent foam properties were successfully prepared.These results provide practicaldata for the application of nano-mineral fillers in the rubber foams. |
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