Study On The Preparation Of Microcellular Silica/silicone Rubber Foam With Supercritical Carbon Dioxide

Microcellular silicone rubber is a kind of porous elastic material combining the advantages of silicone rubber and microcellular foam materials.It not only can be used for the protection and filling materials of spacecraft and rocket under the condition of radiation or extreme conditions,but also can be used as medical drugs release carrier,chemical reaction catalyst carrier,etc.Now the preparation methods of this kind of foam materials mainly include chemical foaming method and solvent foaming method.But these two methods both have drawbacks on handling and environmental friendliness during the foaming processes which are difficult for green and simple preparation of microcellular silicone rubber with low-cost.In this paper,the supercritical carbon dioxide was used as foaming agent for the preparation of microcellular silicone rubber through the technical process of pre-vulcanization,foaming and complete vulcanization.The effects of silica types,degree of pre-vulcanization,silica content and foaming process parameters on the preparation of microcellular silicone rubber were investigated,and the mechanical properties and structure of silicone rubber were also stuied.Based on this study,several conclusions can be given.(1)Pre-vulcanization is the key factor for the preparation of microcellular silicone rubber with supercritical carbon dioxide.The cell growth and cross-linking are in balance during the foaming process,namely there is an optimum foaming balance point of each kind of silica/silicone rubber compound.During the foaming process of fumed silica/silicone rubber compounds,the nucleation method is dominated by homogeneous nucleation.The silicone rubber compound with 30 parts by mass of fumed silica is the most suitable for the preparation of microcellular foam,and the optimum pre-vulcanization time is 12 minutes.During the foaming process of precipitated silica/silicone rubber compounds,homogeneous nucleation and heterogeneous nucleation occursimultaneously.The silicone rubber compound with 20 parts by mass of precipitated silica is the most suitable for the preparation of microcellular foam,and the optimum pre-vulcanization time is 11 minutes.(2)Microcellular fumed silica/silicone rubber with a foam density of0.80g/cm~3,a cell density of 3.58×109cells/cm~3 and an average cell size of5.6?m was successfully obtained under the condition of foaming temperature of 45?,pressure of 14 MPa and swelling equilibrium time of30 minutes.And microcellular precipitated silica/silicone rubber with a foam density of 0.80g/cm~3,a cell density of 1.21×109cells/cm~3 and an average cell size of 6.7?m was successfully obtained under the condition of foaming temperature of 40?,pressure of 14 MPa and swelling equilibrium time of 30 minutes.(3)The influence of foaming process parameters on the preparation of microcellular foam of these two kinds of silica/ silicone rubber from largest to smallest are foaming pressure,foaming temperature and swelling equilibrium time.(4)The compression set of obtained microcellular fumed/silicone rubber is 3.3%,and its tensile strength is 3.18 MPa,raising 34% and 43%respectively compared with related articles.The compression set of obtained microcellular precipitated /silicone rubber is 2.2%,and its tensile strength is 2.46 MPa,raising 56% and 11% respectively compared with related articles.