Fillers in Elastomers

The remainder of this section provides some additional details on the use of this technique.16,18 In particular, the methods can be quite general, in that a variety of other 

A variety of catalysts work well in the typical hydrolyses reactions used, including acids, bases, and salts.29 Basic catalysts give precipitated phases that are generally well-defined particles, whereas the acidic catalysts give more poorly defined, diffuse particles.4,30 In some cases, particles are not formed at all, and bicontinuous (interpenetrating) phases result.17,31 

Interesting aging effects are frequently observed in these systems. If the precipitated particles are left in contact with the hydrolysis catalyst and water they appear to reorganize, so that their surfaces become better defined and their sizes become more uniform.15 The process seems quite analogous to the Ostwald ripening 33 much studied by colloid chemists. 

The samples in which the Si02 was introduced in situ have higher decomposition temperatures. A possible mechanism for this improvement would be increased capability of the in situ produced silica to tie up hydroxyl chain ends that participate in the degradation reaction. 

A variety of techniques have been used to further characterize these in situ filled elastomers.1618 Density measurements, for example, yield information on the nature of the particles. Specifically, the densities of the ceramic-type particles are significantly less than that of silica itself, and this suggests that the particles presumably contain some unhydrolyzed alkoxy groups or some voids, or both. 

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Clay minerals are widely used in the filler industry and the production of the various types has been described by Hancock and Rothon [85]. The products available range from unaltered kaolin to products produced by calcination. Kaolin deposits are widespread throughout the world. While simple clay minerals are extensively used as fillers in elastomers, their use in thermoplastics is more restricted and the principal products used are those obtained by calcination of ka-olinite. Thus metakaolinite finds application in PVC and silane treated calcined clay in polyamides. The production of these forms only is discussed below. 

A typical application Is the use of small colloidal particles as fillers In elastomers, where cross linking Is achieved because many macromolecules can bind to one particle. Another potential application would be for water-ln-oll mlcroemulslons where the oil would be polymerized arovmd and between the water droplets. In all those cases, we will have gel formation through percolation rather than phase separation. The spheres do not attract each other, but they remain crossllnked at their original spacing d. 

Hi) Shear Dependence of Viscosity, Non-Newtonian Behavior The presence of reinforcing fillers also increases the non-Newtonian behavior of elastomers. This effect is mainly due to the fact that the incorporation of fillers in elastomers decreases the volume of the deformable phase. As discussed in the following text, this decrease is not limited to the actual volume of the filler, but must also include the existence of occluded mbber. So, when filled mixes are submitted to shear forces, because of the lower deformable volume, the... 

These materials have been chosen due to their economic expediency and the valuable combination of physical and chemical, physical and mechanical and other properties of individual polymers - PHB is a brittle thermoplastic PIB - an elastomer. Preparation of composite materials based on combinations of plastics and elastomers is well known plastics are used as polymeric fillers in elastomers, improving their technological and working characteristics elastomers effectively improve strike viscosity and reduce brittleness in compositions based on plastics. 

Reinforcement. There is little agreement on the mechanism for reinforcement of elastomers by fillers in elastomer vulcanizates. Some investigators believe that chemical... 

Boonstra, B.B. (1979) Role of particulate fillers in elastomer reinforcement a review. Polymer, 20, 691. 

Carbonaceous Nanofillers Recently research efforts have focused on nano-scale variants of carbon black (carbon nanotubes, carbon nanofibers and exfoliated nanographite) as possible reinforcing fillers in elastomers. Among these, nanotubes are attracting the most attention. 

G.Ivan, E.Danila, V.Ionescu, and A.Toader, Fine ground vulcanzed rubber as an elastic filler in elastomer matrix, Symp. of ICPCMP Polymers Composite Materials , Tg.Mures, Romania, 1988. 

ATH is widely used as a flame-retardant filler in elastomers, thermosets and some thermoplastics. It is also used in significant quantities as a filler in other applications. 

The traditional areas of use have been as fillers in elastomers and PVC. In elastomer applications they give a unique combination of low modulus, high strength and low set. Today they are widely used as rheological control agents in sealants, especially PVC plastisols. 

Typical effects obtained by use of these treatments on fillers in elastomer systems can be found in the work of Dannenberg and Gotten [63]. They examined trimethylsilane treatment of a fumed silica and found effects consistent with reduced filler rubber interaction. Thus rebound resilience, modulus, tear strength and bound rubber were all reduced. Surprisingly, the treatment gave a considerable improvement in abrasion resistance, which it was believed resulted from the increased hysteresis. 

Silane coupling agents are widely used to improve the performance of mineral fillers in elastomer systems. The silanes most commonly used are the various sulfur-based ones and the vinyl and amino functional. The sulfides are generally used both pre-coated and in situ . The fillers most often used in conjunction with silane coupling agents are precipitated silicas and clays. The primary objective of the treatment is to improve polymer to filler bonding, although other benefits such as lower viscosity, better dispersion and reduced water adsorption are also observed. 

This chapter is devoted to the use of particulate fillers in elastomers, which make greater use of fillers than do most other polymers, largely because fillers are able to improve greatly many of their properties to an extent not found in other composites. This is particularly true of their use in automobile tyres where the high performance levels taken for granted today would not be possible without very sophisticated carbon blacks and silicas. Because of the value of fillers to the elastomer industry, it is not surprising that the most advanced work on filler characterisation and links with composite properties have been carried out in this area. Many of the filler characterisation aspects have been covered elsewhere. This chapter concentrates on the basic principles of elastomer formulation and the role of fillers in this. 

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