Filler interactions, silicone

A silicone oil plasticiser is desirable to facilitate dispersion and to prevent undesirable polymer-filler interaction prior to vulcanisation. 

A low-resolution proton NMR method is one of the few techniques that have so far proved to be suitable for studying elastomer-filler interactions in carbon-black-filled conventional rubbers and silica-filled silicon rubbers [20, 62, 79]. It was pointed out by McBrierty and Kenny that Many of the basic characteristics of filled elastomers are revealed by low resolution spectra while the more sophisticated techniques and site specific information refine interpretations and clarify motional dynamics [79]. 

Lopour P et al. (1993) Silicone rubber-hydrogel composites as polymeric biomaterials. IV Silicone matrix-hydrogel filler interaction and mechanical properties. Biomaterials 14(14) 1051—1055... 

Considerable effort has been spent to explain the effect of reinforcement of elastomers by active fillers. Apparently, several factors contribute to the property improvements for filled elastomers such as, e.g., elastomer-filler and filler-filler interactions, aggregation of filler particles, network structure composed of different types of junctions, an increase of the intrinsic chain deformation in the elastomer matrix compared with that of macroscopic strain and some others factors [39-44]. The author does not pretend to provide a comprehensive explanation of the effect of reinforcement. One way of looking at the reinforcement phenomenon is given below. An attempt is made to find qualitative relations between some mechanical properties of filled PDMS on the one hand and properties of the host matrix, i.e., chain dynamics in the adsorption layer and network structure in the elastomer phase outside the adsorption layer, on the other hand. The influence of filler-filler interactions is also of importance for the improvement of mechanical properties of silicon rubbers (especially at low deformation), but is not included in the present paper. 

Reduced blood-polymer interaction (Filler-free silicone surface reduces thrombogenic response.)... 

However, when a fumed silica is added to the RTV silicone, it provides excellent tensile strength and elongation compared to the unfilled material with the same formulations. The chain-linked spherical SIO2 particles which interact with themselves (filler-filler interaction) and/or the silicone-resin... 

Another example of the effect of fillers on improving bond strength is reported for a silicone RTV-1 sealant formulated with Cabot Corporation s Cab-O-Sil LM-130 and TS-720 materials. Cab-O-SU fumed silicas are very effective reinforcing agents due to the very-large surface area available for polymer/filler interactions. The very low, 45 psi, tensile strength of the unfilled silicone increased to 210 psi with 14 phr of LM-130 fumed silica and to 150 psi with the same level of TS-720 fumed sUica. ... 

Both the Japanese Synthetic Rubber Company and Nippon Zeon have reported that anionically prepared elastomers that are functionally terminated by active lithium can be chain terminated with Michler ketone, benzophenone, and a variety of enamide groups. Moreover, these chains can be terminated with silicone or tin metals. Chain end functionalization did not change the viscoelasticity of the polymer chains but rather dramatically improved the elastomer-filler interaction and, therefore, reduced its hysteretic properties. 

Heat-cured silicone rubber is commercially available in several forms as gum stock, reinforced gum, or partially filled gum. These compoimds can be im-catalyzed, catalyzed, or can contain catalyst dispersions. Catalyzed compounds are ready for use without additional processing. Silicone rubber is often freshened, ie, the compound is freshly worked on a rubber mill until it is a smooth continuous sheet. The freshening process eliminates the structuring problems associated with pol5uner-filler interactions. Rubber can be extruded on wire and cured in place (479). 

The main applications, by far, are as reinforcing fillers in hydrocarbon elastomers. Organo-silanes, such as the mercapto, polysulfides, amino and vinyl are used to improve filler to polymer interactions and reinforcement. Particnlarly important uses are in tyres and in footwear. There is also significant use as a reinforcing filler in silicone elastomers. 

Silicone Rubber RTV-1 Sealants (Cabot, 1994) - The superior rheology control and reinforcement properties of fumed silica compared to a similar stuface area grade of preeipitated silica has already been shown in Figure 5 and Table 4. The more open ehained structure of the frmred sihea allows the formation of a much more effective silica network with more of the sihea srrrface available for polymer/filler interaction, resulting in superior eured physical properties. 

In recent years it has been demonstrated that NMR methodologies can be effectively utilized in the development and vahdation of predictive models of silicone networks. The information made available on a silicone network though the use of various NMR methodologies such as molecular weight distribution (MWD), effective crosslink density, modahty, polymer-filler interactions and the presence of localized stresses, defects and inhomogeneities, can be used to both test and refine theoretical models, which predict both network dynamics and degradation in sihcone systems. 

Wu, J., et al., Preparation of modified ultra-fine mineral powder and interaction between mineral filler and silicone rubber. Journal of Materials Processing Technology, 2003. 137(1-3 spec) 40 4. 

Stress-strain properties for unfilled and filled silicon rubbers are studied in the temperature range 150-473 K. In this range, the increase of the modulus with temperature is significantly lower than predicted by the simple statistical theory of rubber elasticity. A moderate increase of the modulus with increasing temperature can be explained by the decrease of the number of adsorption junctions in the elastomer matrix as well as by the decrease of the ability of filler particles to share deformation caused by a weakening of PDMS-Aerosil interactions at higher temperatures. 

This paper is devoted to the study of a part of the complex phenomena of reinforcement, namely the behavior of the host elastomer in the presence of filler particles. The results of solid state NMR experiments and some other methods for filled PDMS are reviewed. The short-range dynamic phenomena that occur near the filler surface are discussed for PDMS samples filled with hydrophilic and hydrophobic Aerosils. This information is used for the characterization of adsorption interactions between siloxane chains and the Aerosil surface. Possible relations between mechanical properties of filled silicon rubbers on the one hand and the network structure and molecular motions at flie PDMS-Aerosil interface on the other hand are discussed as well. 

Compression set is an important property of elastomers which is affected by the choice of filler. Studies were conducted on silica in silicon rubber vulcanizates. Figure 8.60 shows the relationship between the surface area of silica and compression set. As the surface area increases compression set increases. The increase surface area contributes to an increase in the number of functional groups on the surface of silica. These groups can potentially react with siloxane. When they do, there is a good interaction of filler with matrix which contributes to reduction of compression set (Figure 8.61). ... 

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