Study On The Preparation And Properties Of The Micro-porous Liquid Silicone Rubber

The microporous liquid silicone rubber material is a new type of multi-functional material,which combines the virtues of silicone rubber and microporous materials.Microporous silicone rubber material gives advantages of low density,high low temperature resistance,good absorption of mechanical vibration or shock,insulation and sealing etc.The outstanding properties have led to its wide use in the applications of industrial and living fields.Nowadays,chemical and physical foaming methods are two of the most widely-used methods in preparing microporous silicone rubber.However,the size,morphology and uniformity of the microporous silicone rubber prepared by these two methods are difficult to control.Besides,the decomposition products and residues of some foaming agents are toxic,which are detrimental to human body and environment.To solve the above mentioned problems,in this paper,microporous liquid silicone rubber were prepared based on liquid silicone rubber matrix,hollow microspheres and stearic acid modified sodium bicarbonate as the pore-forming agent respectively.The characteristics of the two pore-forming agents have been studied,some efforts have also been made to investigate the effect of technology parameters and formula on the structure and performance of the microporous silicone rubber.The main achievements are as follows:(1)Thermally expandable microspheres have been used as the filler,liquid silicone rubber as the matrix.The syntactic foam was obtained by mixing the microspheres with liquid silicone rubber,followed by curing and post-processing.On the basis of this above,the effect of processing temperature,the dosage of hydrogen silicone oil and thermally expandable microsphere on the properties of microporous silicone rubber were explored,respectively.The result shows that the mechanical properties,density and hardness of the syntactic foam decrease with the increase of the addition of thermally expandable microspheres.The optimal overall performance of the syntactic foam can be obtained when the processing temperature is 115 ? the dosage of hydrogen silicone oil is 10 parts and thermally expandable microsphere is 2 parts.In this condition,the thermally expandable microspheres are uniformly dispersed in liquid silicone rubber with a regular shape,the diameter distribution of the expanded is between 20 and 50 ?m.The density and Shore A hardness of the syntactic foam reduced to 0.65 g/cm3and 30,respectively.In addition,by changing the processing technology,the expansion rate of the thermally expandable microspheres was significantly reduced.The statistic result shows that the diameter distribution of the microspheres in the liquid silicone rubber has reduced to 15-30 ?m,which decreases the cell diameter and increase cell density of the syntactic foam.(2)Using the rigid hollow glass microspheres and elastic 920DET40D25 hollow plastic microspheres as fillers and liquid silicone rubber as matrix material,by blinding a mixture of these two hollow microspheres with different proportion into liquid silicone rubber,a new type of syntactic foam was established.The mechanical and physical properties,microstructure of the syntactic foam were investigated.We found some synergistic effects achieved by the combination of these two hollow microspheres filled in the liquid silicone rubber,the existence of 920DET40D25 hollow plastic microspheres can reduce the hollow glass microspheres' broken rate effectively.In addition,the results show that by changing the ratio of the addition of these two kinds of hollow microspheres,the mechanics,heat resistance and electrical properties can be adjusted to meet the different application requirements.(3)Sodium bicarbonate was milled using a planetary ball mill,after the ball-milling treatment,the sodium bicarbonate possesses a narrower particle size distribution and smaller particle size than original sodium bicarbonate.Besides,stearic acid was used to modify sodium bicarbonate by melting method and solution coating method.The results show that sodium bicarbonate was modified by solution coating method with a mass ratio of 1:0.1 obtained in the optimized condition,in which its decomposition temperature range is decreased to 30 ?.Furthermore,the decomposition rate and disperse uniformly have been dramatically improved.The microporous liquid silicone rubber foamed by modified sodium bicarbonate has uniform cell structure and size where the foam cell size is 10?m or less.