The In-situ Modification Of PDMS With Nano Silica And Its Application Research On Liquid Silicone Rubber

Thanks to its excellent properties,the liquid silicone rubber products have been widely used in our daily life,and the preparation of liquid silicone rubber is based on polydimethyls iloxane?PDMS?.In this paper,we use in-situ polymerization method and choose DMC as monomers,surface modified nano-SiO₂ as the reinforcing agent to synthesize SiO₂/PDMS nanocomposite and prepare liquid silicone rubber,and both workability and mechanical properties are studied.We systematically discuss the effect of different types of SiO₂,addition content of SiO₂,and in-situ polymerization and mechanical blending methods on liquid silicone rubber.Moreover,in-situ polymerization and mechanical blending methods are used together to synergistically improve the additive amount of nano SiO₂ and mechanical properties of silicone rubber.The main research contents and results are as follows:1.In-situ polymerization method is applied to synthesize SiO₂/PDMS nano composite:DMC experiences ring opening polymerization with the catalysis of tetramethyl ammonium hydroxide?TMAH?;nano SiO₂ is added during the chain growth process.Results show that SiO₂ and PDMS are covalently bonded,resulting in the enhancement of the combination of the filler with matrix and improvement of the filler dispersity.Then RTV liquid silicone rubber is prepared based on the SiO₂/PDMS composite,and different dosages of crosslinking agent are discussed.The optimal formula is:100 phr SiO₂/PDMS,6 phr CG-310,1.5 phr CG-1310 and 0.05 phr D80.2.Different types of dispersible nanos ilica?DNS?are used to prepare a series of SiO₂/PDMS nano composites and liquid silicon rubbers.The results indicate that squeeze time,tack-free time and adhesion of the LSRs are all satisfactory,according with national standards;LSRs based on DNS-3 exhibit better mechanical properties and transparency except for less superior elongation at break.Moreover,the addition amount and approach of DNS-3 are investigated,and results show that the viscosity of SiO₂/PDMS,rubber hardness and mechanical properties are increasing with the increase of SiO₂ content;with the same amount of SiO₂,in-situ method has lower viscosity,higher rubber hardness,better mechanical properties,adhesion strength and transparency than physical mixing method.More importantly,in-situ addition of DNS-3,compared with mechanical mixing of fumed silica R106,can dramatically improve the tensile strength,modulus at 100%and tear strength.In conclusion,in-situ polymerization method endows the nano composites more superior properties in low viscosity and high mechanical performance.3.Investigation of combined methods of in-situ addition and physical mixing:a low content of silica including DNS-3 and R106 is in-situ added,respectively,to prepare two types of low viscosity SiO₂/PDMS composites?marked as Y6 and YR2?,followed by physically mixing additional SiO₂?DNS-3?to prepare LSRs?Series A and Series B?.Results show except the elongation at break,the tensile strength,tear strength and modulus at 100%of series A have been improved compared with single method.YR2-based Series B has the highest tear strength of 14.22kN/m with the total silica amount for 14phr;the maximum elongation at break approximately 343%with silica usage for 10phr.Both A and B increase silica usage by 2 phr,and the adhesion performance is still satisfactory when the silica amount reaches 12 phr.