The Microcellular Foam Of EPDM/LDPE Thermoplastic Elastomer Foaming With Supercritical Carbon Dioxide

Thermoplastic elastomer microcellular foam material has high toughness, good mechanical properties, excellent thermal and chemical stability and many other advantages, so the microcellular foam materials are used in many fields with strong competitiveness, and the application prospect is very wide. It is of great importance to study the thermoplastic elastomer foaming.In my thesis, we got the EPDM/LDPE thermoplastic elastomer by melt blending method, compressed standard sample, and then foamed in the high-pressure reaction kettle using supercritical carbon dioxide as physical foaming agent.In the preparation of EPDM/LDPE thermoplastic elastomer, it was discussed the influence on the mechanical properties of thermoplastic elastomer, such as the vulcanization system, rubber and plastic ratio, nano-silicon. By using the differential scanning calorimetry analysis (DSC) and scanning electron microscopy (SEM) to observe the crystale properties of thermpastilc elastomer and the microstructure of tensile section, I found these conclusions.(1) The mechanical properties of thermoplastic elastomers with DCP vulcanizing system is superior to the sulfur vulcanizing system. With the increase in the dosage of curing agent, the tensile strength and tear strength has a maximum value, and the hardness is increased.(2) When the ratio of rubber and plastic is4:6, the mechanical performance is optimal; the maximum tensile strength is7.5MPa, and the biggest tear strength is27.6kN/m.(3) Nano-silica elastomer has a significant enhance in the mechanical properties of elastomer, when the dosage of nano-silica is30, the mechanical properties of the material is best. The maximum tensile strength is10.6MPa, increase by about41%. And the tear strength is35.3kN/m, increase by about26%.(4) Differential scanning calorimetry (DSC) indicated that the crystallinity of DCP crosslinking system is lower than the sulfur vulcanizing system; the crystallinity of elastomer changes with the change of the ratio of rubber and elastic, when the plastic phase of the system increases, its crystallinity increases, the melting point increases.(5) Scanning electron microscopy (SEM) observs the morphology of the tensile fracture surface, suggests that EPDM rubber phase and LDPE plastic phase presents "sea-island" two phase microstructure.EPDM/LDPE thermoplastic elastomer foamed in the high-pressure reaction kettle, we discussed the effects of the dosage of the DCP crosslinking agent, the saturation temperature, the saturation pressure and the initial pressure of carbon dioxide on the foam cell structure and uniformity. The results showed that:(i) When the dosage of DCP is0.9. the foam cell is smaller and distributed uniform and the cell density is biggest; when the average cell diameter is74.48μm. the cell density is5.2×108cell/cm3, the most outstanding foaming properties of the foamed elastome is excellent:(2)When the saturation temperature is170℃.we obtained uniform distribution of the foam., and the cell size is smaller, and the density is larger, and the cell average diameter is55.15μm, the cell density is5.8×109cell/cm3.(3) When the saturation pressure is9MPa. the foam cell distributed uniform, and the cell size is smaller, and the density is larger, the cell average diameter is51.20μm. the cell density is3.5×10qcell/cm3.(4) When the presure of the initial injected carbon dioxide is6MPa. the foam obtained maximum cell density, and the cell size distributed uniform, and the average cell diameter is89.17p.m. the cell density is3.8×108cell/cm3.