Study On The Preparation And Properties Of EPDM Microcellular Foam By Supercritical CO₂

EPDM foams not only has the excellent properties of insulation and ageing resistance,but also has the characteristics of foam materials,such as heat insulation,sound insulation and lightness,etc.EPDM foams have been widely used in precise instruments,electrical equipment and medical devices.At present,the preparation method of EPDM foams is mainly limited to chemical foaming method.The chemical foaming method is not only environmentally harmful,but also tend to produce large cellular structure that is difficult to control and lead to poor performance,so its application is limited.However,as an advanced foaming method for the preparation of polymer foams,the supercritical fluid method is not only environmentally friendly,but also can achieve a microcellular or even nanoporous structure of polymer foams with more excellent performance by changing the foaming conditions.At present,there are few reports on the preparation of EPDM microcellular foams by supercritical fluid method,and a complete system has not been formed yet.In this paper,supercritical CO₂is used as the physical foaming agent,and the cellular structure and performance of EPDM foams are systematically studied from the selection of reinforcing filler,the adjustment of process parameter and the improvement of mechanical performance.A variety of silica with different properties were selected as reinforcing filler,and the effects of silica on the vulcanization performance,rheological properties and cellular structure of EPDM were investigated.The silica/EPDM composite has better rheological properties when small-size silica is used as reinforcing filler,which is beneficial to the formation of cellular structure during the foaming process.At the same time,the strength and modulus of silica/EPDM composites are significantly different due to different reinforcing fillers,which determines the differences in their cellular structure and mechanical properties.The matrix with lower strength and modulus facilitates the preparation of foams with lower apparent density,while the matrix with higher strength and modulus facilitates the preparation of foams with smaller cell and higher mechanical properties.The effects of foaming process parameters on the cell structure of EPDM foams were studied,and the relationship between the cellular structure and the properties was further investigated,including its thermal insulation and mechanical properties.It shows that increasing the saturation pressure or decreasing the saturation temperature can significantly refine the cellular structure,which is beneficial to obtain silica/EPDM microcellular foam with more excellent mechanical properties.Increasing the saturation temperature can make silica/EPDM foams obtain lower apparent density,which is beneficial to reduce the thermal conductivity.The lowest thermal conductivity of silica/EPDM foam can reach 0.05 W/m K,which exhibits its excellent thermal insulation performance.Silica/SR/EPDM blends were prepared by taking advantage of the difference between crosslinking temperatures of silicone rubber(SR)and EPDM as well as the reinforcing and compatibilizing effects of silica.During the pre-crosslinking process of EPDM,SR forms a complete crosslinking network,which can make up for the strength of EPDM matrix without the post-crosslinking.Meanwhile,the presence of silica can significantly reduce the domain size of SR phase and enhance the compatibility between EPDM and SR.The addition of SR greatly improves EPDM's storage modulus,viscosity and matrix strength,which shows dramatically enhanced mechanical properties of microcellular SR/EPDM foams.When the cell size and foam density are basically the same,the tensile strength and compressive strength of silica/SR/EPDM foam are increased by 461%and 283%respectively compared with that of silica/EPDM foam.