| A series of nanosilica(RNS) surface-capped with organic modifiers hexamethyldisilazane(HMDS) and KH570 containing C=C double bond were prepared by in situ surface-modification method. They were used to reinforce silicone rubber(SR) in order to improve the mechanical properties. And mechanical properties of RNS/SR nanocomposites were compared with those of SR nanocomposites filled with fumed silica(R-106). The addition cure liquid silicone rubber(LSR) nanocomposites were prepared with nanoSi O2 by the optimization of formulation. And the mechanical properties and viscosity characteristics of LSR nanocomposites added different type nano-Si O2 were analyzed. Besides, the effects on the properties of silicone sealants were analyzed with the amount of nano-Si O2 and the physical properties of nano-Si O2(moisture content, surface hydroxyl content, et al). The methods to improve the amount of nano-Si O2 in silicone sealants were studied. The main research contents and conclusions of this paper are as follows:1. A series of reactive nanosilica(RNS) surface-capped with different dosages of silane coupling agents hexamethyldisilazane(HMDS) and KH570 were prepared by in situ surface-modification route. Asobtained nano-Si O2 particles were used to reinforce silicone(SR) rubber in order to improve the mechanical properties. Results showed that RNS nano-Si O2 particles were homogenously distributed in SR matrix, and the reactive of nano-Si O2 was improved because of the existence of C=C. It was found that the tensile strength, elongation at break and tear strength of nano-Si O2/SR nanocomposites were comparable to or even better than those of R-106/SR nanocomposite(R-106: commercially obtained fumed nano-Si O2 that was modified with silane coupling agent). The reason might lie in that the introduction of KH570 leaded to increase in the amount of reactive sites inside the bound rubber thereby facilitating the interactions between SR molecular chain and nano-Si O2 by way of the C=C bond and enhancing the mechanical strengths. It was found that the mechanical properties of nanocomposites were changed with the different content of C=C. The incorporation of reactive nano-Si O2 resulted in a slight increase in the Shore-A hardness of SR, and the hardness of SR nanocomposites increased with increasing the content of C=C. The hardness of the RNS-2/SR nanocomposites was 76, which still maintained high mechanical strength. The mechanical properties of RNS nano-Si O2/SR nanocomposites vary with varying content of C=C in the surface-modifying layer on nano-Si O2 surface, which implied that it could be well manipulate IV the nano-Si O2/SR nanocomposites by properly adjusting the mole fractions of HMDS and KH-570 for industry demands.2. RNS-D/SR nanocomposite possessed highly hardness and poor tensile strength(4MPa), while the mechanical strengths of DNS-3/SR nanocomposites were better and the hardness of DNS-3/SR nanocomposites was poor. Therefore, the properties of SR nanocomposites could be improved with using these two fillers. And the tensile strength and tear strength of SR nanocomposites increased with increasing RNS-D content, the hardness of SR nanocomposites decreased with increasing RNS-D content.3. The optimal formula of the addition cure liquid silicone rubber(LSR) nanocomposites was obtained by the adjustment of components. The optimal formula was 100 phr Vi-PDMS, 2phr H-PDMS, 6ppm Pt, 0.005 phr inhibitor. And the LSR nanocomposite was vulcanized at 100 ℃, 10 min. The LSR nanocomposites filled with different types of nano-Si O2 were prepared and the properties of those nanocomposites were analyzed. The results showed that the tensile strength and tear strength of DNS-2/LSR and DNS-3/LSR were comparable to or even better than those of R-106/LSR nanocomposite. After placement for a certain time of RNS-D/LSR, the phenomenon of layered was found in the composites, which was due to big apparent density of RNS-D nano-Si O2. The RNS-A/LSR nanocomposite was prepared while the curing of this nanocomposite couldn’t be completed, which attributed to the dehydrogenation reaction between H-PDMS and amino group in the surface-modifying layer on RNS-A surface.4. The silicone sealants were prepared by adding nano-Si O2. The silicone sealants filled with HL-200 showed high extrusion rate(76.7g·min-1) and low surface curing time(15min), while the silicone sealant filled with DNS-3 possessed good extrusion rate(60.5g·min-1) and surface curing time(40min). The reason was that the content of surface hydroxyl group of HL-200 was four orders of magnitude higher than that of DNS-3, which led to reduction of surface curing time of HL-200. The moisture content of nano-Si O2 played a greater influence in vulcanization of silicone sealants, and the silicone sealant filled with DNS-2 cured in rubber sleeve after 24 h when the moisture content of DNS-2 was 4.4%. The extrusion rate of silicone rubber filled with 14 phr DNS-3 that the moisture content was 1% was 15 times higher than that of silicone rubber filled with 14 phr DNS-3 that the moisture content was 2.03%.5. The filling contents of DNS-3 could be improved with the introduction of additive, such as dimethylsilicone, HMDS, KH-570, WD-20 and so on. Among those additives, the properties of silicone sealant filled with WD-20 were highly improved. And the extrusion rate and surface curing time were 81g·min-1, 35 min respectively. |
PDF Full Text Request