A STUDY ON RADIATION CROSSLINKING OFPOLYDIMETHYLSILOXANE （PDMS） RUBBER LATEX

Polydimethylsiloxane (PDMS) rubber latex with two sorts of sensitizers, trimethylol propane tri-methacrylate (TMPTMA) and diethylene glycol di-acrylate (DEGDA), was irradiated with y-rays and electron beams in various conditions. The radiation crosslinking reaction of PDMS occurs in the inner phase of the latex and is relatively isolated from the water phase. Therefore the oxygen and the radicals produced by the radiolysis reaction of water almost have no effect on the crosslinking reaction of polymer. The experimental data correspond with the Charlesby-Pinner relationship in the main. The gelation doses, degree of crosslinking and degradation as well as G values of crosslinking were calculated. From them, the sensitization coefficients were derived to offer a quantitative measurement of the enhancing effect of sensitizer on the radiation crosslinking.     

REINFORCEMENT OF POLYDIMETHYLSILOXANE NETWORKS BY NANOCALCIUM CARBONATE

Although a number of investigations have been devoted to the analysis of silica or carbon black filled elastomer networks, little work has been done on the reinforcement of CaCO3 filled elastomer network. In this work, the reinforcement of polydimethylsiloxane (PDMS) network by using CaCO3 nano-particles was investigated. We have found a simultaneous increase of tensile strength, modulus and elongation with the increase in nano-CaCO3 content, which suggests that nano-CaCO3 particles can indeed be used as a reinforcing agent, just like silica or carbon black. Interestingly, the tensile strength,modulus and elongation were seen to leave off for the first time when the content of nano-CaCO3 particles reaches to 80%.PDMS also showed an enhanced elastic modulus and storage modulus with the increase in nano-CaCO3 content, particularly for samples with high nano-CaCO3 content. SEM was used to investigate the dispersion of the filler in PDMS matrix. A better dispersion was found for samples with high nano-CaCO3 content. A great increase of viscosity was found for samples with higher filler content, which is considered to be the reason for the good dispersion thus the reinforcement, because high viscosity will be helpful for breaking the agglomerates of fillers into small size particles under effect of shear. Our work provides a new way for the reinforcement of elastomer by using an adequate amount of nano-CaCO3 particles instead of as mall quantity of silica, which is not only economically cheap but also very effective.     

Quantum-chemical study on the mechanical behaviour of polydimethylsiloxane under deformation: interaction with fumed silica surfaces

Silicone elastomers filled by fumed silica reveal peculiar technical behaviour. Chemical modification of the silica surface is commonly used to control the rheological and mechanical properties of uncured and cross-linked silicone elastomers. To study the microscopic aspect of the problem, quantum-chemical (QCh) modelling in the framework of originally elaborated semiempirical techniques has been performed. The response of a silicone polymer fragment, interacting with a silica model cluster, to external stress is considered in terms of a mechanochemical reaction. The impact of silicone-water and silicone-modified filler interactions on stress-strain characteristics, i.e. Young's modulus, energy and force of deformation and tensile strength have been studied on a molecular level.     

Water at the interface modified silica filler-polydimethylsiloxane: quantum-chemical modelling

Intermolecular interactions determine the reinforcement of polydimethylsiloxane (PDMS) elastomers by fumed silica, and a water interlayer on the fumed silica/PDMS interface may act as a lubricant, decreasing the interaction energy and promoting the PDMS molecule motion over the filler surface. A quantum-chemical (QCh) modelling has been performed to study a microscopic aspect of water impact on the intermolecular interactions in the system. The results obtained for a series of superclusters simulating fragments of the real silica filler surface, both hydroxylated and silylated, interacting with five-member PDMS oligomer in presence of individual water molecules and of a 'water drop', of several H-bonded water molecules, are in good agreement with results from IGC adsorption experiments.