Reinforcing fillers vulcanized rubber

The subject of filler reinforcement on vulcanized rubber is very wide and complex. Fillers can be classified as reinforcing, semi-reinforcing and non-reinforcing. All fillers increase the hardness, modulus and stiffness of vulcanized rubber whether or not they are reinforcing or non-reinforcing. It has been established for a very long time that the term reinforcement has been widely used by the rubber technologist to denote the enhancement in the tensile... 

The subject of filler reinforcement of rubbers has been an area of interest to the rubber industry for more than a century. Various models had been proposed in the past to explain the filler reinforcement in vulcanized rubber. The use of modern finite element analysis (FEA) and various mathematical models have made further progress to understand the mechanisms of reinforcement in filled vulcanized rubber. But this does not imply that a complete understanding of the subject has been achieved. The detailed effects of filler properties such as surface area and shape on the filler reinforcement are still not completely understood. A detailed understanding of the filler reinforcement should provide an insight into the increase in modulus and strength. 

A typical tire rubber formulation for tire tread will contain various rubbers, mainly styrene-butadiene (50%) and cA-polybutadiene (12%), various processing aids (2%), softeners (3%), vulcanizing agent (mainly sulfur 1%), accelerators, and reinforcing filler (namely carbon black 30%) so that by bulk, carbon black is the second most used material. 

Abstract Plasma polymerization is a technique for modifying the surface characteristics of fillers and curatives for rubber from essentially polar to nonpolar. Acetylene, thiophene, and pyrrole are employed to modify silica and carbon black reinforcing fillers. Silica is easy to modify because its surface contains siloxane and silanol species. On carbon black, only a limited amount of plasma deposition takes place, due to its nonreactive nature. Oxidized gas blacks, with larger oxygen functionality, and particularly carbon black left over from fullerene production, show substantial plasma deposition. Also, carbon/silica dual-phase fillers react well because the silica content is reactive. Elemental sulfur, the well-known vulcanization agent for rubbers, can also be modified reasonably well. 

Keywords Blends Plasma polymerization Reinforcing fillers Rubber Surface polarity Vulcanization... 

The basic compounding formulation specifies the minimum requirement of fillers, vulcanizing agents, and other substances that must be added to the rubber compound to achieve the desired properties. After the rubber, cure system and reinforcing filers have been selected it will be necessary to make several adjustments before all requirements are satisfied. It is generally sensible to start with the simplest mix formula for meeting the requirements. The recipe or the formula is usually written on the basis of hundred parts of rubber. For example if 5 parts of zinc oxide is to be added it is denoted as 5 phr (five parts per hundred rubber). Elementary compounding... 

The desirability of segregation in block copolymers can be demonstrated by considering the behaviour of SBS, which is one of the oldest types. It has about the same chain composition as SBR, but, rather than SBR, it shows two glass-rubber transitions, namely that of polybutadiene and that of polystyrene. Between these two temperatures it behaves as a rubber, in which the PS domains act as cross-links it is, therefore, a self-vulcanizing rubber (see also Figure 3.8 see Qu. 9.14). Moreover, the hard domains play the role of a reinforcing filler. 

Radiation vulcanization of carbon fiber reinforced styrene-butadiene rubber causes a substantial increase in crosslink density (Figure 11.4) and tensile strength (Figure 11.5). This magnitude of change is possible only when the interaction between the filler and the matrix is improved. When irradiated in the presence of air, carbon fibers gain functionality which substantially increases their adhesion resulting in a spectacular improvement in properties. SEM studies show that as the dose of radiation increases, the adhesion of the... 

Room-temperature vulcanizing silicone rubbers (RTV rubbers) are low-molecular-weight liquid silicones with reactive end groups and loaded with reinforcing fillers. Several types are available on the market. 

The phenomenon of bound rubber has played a crucial role in the chemistry of elastomer reinforcement. Very simply, if vulcanized rubber is masterbatched with a reinforcing filler, a certain fraction of the rubber is found to become insoluble, and to remain as a gel. This gel, a swollen mass of rubber and dispersed carbon particles, is called bound rubber. The percentage of bound rubber depends, of course, on the quantity of filler employed, and also on mixing conditions and choice of solvent (typically benzene). Working under standardized conditions, the percentage of bound rubber was found to correlate with the specific surface area of the filler as shown in Figure 10.12. 

The particles of carbon black are not discrete but are fused clusters of individual particles. The reinforcement conferred by the black is not influenced to any extent by the size of the unit but predominantly by the size of the particles within the unit. The primary particle typically has cross-sectional dimensions" of 5-100 nm. It is well established that the most appropriate way of describing the size of the primary particles is to express it as speciflc surface area/weight Particle size of itself has relatively little effect on the modulus. But tensile and tear strengths are affected by the particle size and both properties are normally enhanced as the surface area increases (i.e. surface area increases with decreasing particle size). The high surface area enhances the ability of the filler to wet the rubber and thus enhances the interaction at the rubber filler interface. It is the enhancement of the filler-rubber interface that provides the desired reinforcement in filled vulcanized rubber. 

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