Preparation, Morphology And Dynamic Rheological Behavior Of Specific Organosilicone Sealants Composed Of Ultrafine Silica Reinforced Polysiloxanes

Rheological properties of multiphase / multicomponent polymer systems correlate closely with the interactions among components and phase morphologies. While the rheology response can reflect precisely the structural variations, the morphology can in return greatly determine its ultimate application.In this dissertation, SiO2 filled polysiloxanes system, which has been widely used commercially, is selected to be the research focus with the dynamic properties, viscoelastic behavior and corresponding morphology being studied in depth.Meanwhile, the ever-lasting development of modern construction poses much higher requirements on the performance and functionality of the organosilicone sealants. Among these are low modulus, high elongation and surface paintable silicone-based sealants, which will surely make up for domestic tremendous gap and play a considerable role for market competition, protection and promotion of Chinese organisilicon industry.The conventional sol-gel process was applied to initially prepare ultra-fine silica particles from sodium metasilicate and tetraethoxysilane, respectively. Particle size distribution and TEM revealed that synthesized SiO2 has porous (metasilicate) and non-porous structure, with the average size below 100 nm. These primary particles are easy to undergo self-agglomeration and cluster together, which was believed to be the resultrant strong interactions arising from the surface hydroxyl groups on the silica surface. A kind of difunctional silane coupling agent, namely (bis (3-triethoxysilylpropyl) tetrasulfane, was utilized to facilitate the particle distribution which was confirmed by SEM to be very effective. After modification, silica became more hydrophobic, no big agglomerates surfaced and the dispensability was also significantly enhanced.With these two types of ultra-fine SiO2, the influence of microstructure of SiO2 on dynamic rheological properties of silica incorporated polymethylvinylsiloxane was investigated using an advanced rheometric expansion system (ARES). The results revealed that the apparent decrease of G' at critical strain amplitude, i.e., the so called "Payne Effect", was prominently enhanced upon increasing the surface from non-porous SiO2 spheres to porous SiO2 aerogels. Apart from this phenomenon,the SiO2/PMVS system containing inner-porous SiO2 aerogels display an extraordinary frequency-independent rheological behavior in the lower frequencies region. It is predicted that to some extent the promoted filler networks result from the adsorption of PMVS chains onto the surface of silica nanoparticles, since the filler-filler interactions are considerably reduced by treatment of TESPT. Furthermore, the destruction of filler network against deformation may involve in dis-adsorption of polymer chains from the SiO2 particles.Also, the variations of filler network under filler loadings and curing states were studied using dynamic rheological methods. TESPT acted to aid filler dispersion and the structure control agent was diphenyl silandiol, the crosslink agent was dicumyl peroxide. The observations showed that that an incorporation of 5% SiO2 into PMVS at 25℃ could be enough to impact a significant increase on the storage modulus (G') of the uncured system, which is believed to be caused by the strong interactions among silica filler. Meanwhile, strain (y)-dependence of G' related to "Payne Effect" was observed upon increasing y amplitude, presenting a increasingly deviated lgG' ~ lgco and lgG" ~ lg equations. As regarding the cured SiO2/PMVS system, the results revealed that the treated SiO2 particles leads to the frequency-dependent storage modulus (G') approaches linear viscoelastic behavior in the lower frequency region. Based on an examination of the dynamic viscoelastic behavior and TEM observation, we owned these characteristics to improved dispersion of SiO2 particles in the polymer matrix due to their surface-treatment as compared with the untreated case. On the other hand, dynamic viscoelastic behavior sensitively reflected the dispersion of SiO2 par...