Fillers, rubber Tensile strength

Carbon blacks are the most widely used fillers for elastomers, especially vulcanised natural rubber. They cause an improvement in stiffness, they increase the tensile strength, and they can also enhance the wear resistance. Other particulate fillers of an inorganic nature, such as metal oxides, carbonates, and silicates, generally do not prove to be nearly so effective as carbon black. This filler, which comes in various grades, is prepared by heat treatment of some sort of organic material, and comes in very small particle sizes, i.e. from 15 to 100 nm. These particles retain some chemical reactivity, and function in part by chemical reaction with the rubber molecules. They thus contribute to the crosslinking of the final material. 

The addition of filler to synthetic elastomers may lead to significant increases in tensile strength. For example, butadiene or neoprene rubbers may experience a ten-fold increase in tensile strength in the filled state, typically from about 3.5 to 35 MPa. 

The rubber compound usually requires an inert inoiganic filler and small particle size carbon particle for reinforcement. The rubber polymers vary in inherent tensile strength from very high in the case of natural mbber to almost nonexistent for some synthetic polymers, eg, SBR. The fillers most commonly used for mbber compounds include carbon black, day, calcium carbonate, silica, talc (qv), and several other inorganic fillers. 

The original coupling agents, which were called promotors, were used to ensure a good bond between rubber and the carbon black filler. These promotors increase the tensile strength, modulus, and the bound rubber (the insoluble mixture of filler and rubber) content of rubber. Although natural rubber is soluble in benzene, it becomes less soluble when carbon black or amorphous silica is added. 

Improvement of the mechanical properties of elastomers is usually reached by their reinforcement with fillers. Traditionally, carbon black, silica, metal oxides, some salts and rigid polymers are used. The elastic modulus, tensile strength, and swelling resistence are well increased by such reinforcement. A new approach is based on block copolymerization yielding thermoelastoplastics, i.e. block copolymers with soft (rubbery) and hard (plastic) blocks. The mutual feature of filled rubbers and the thermoelastoplastics is their heterogeneous structure u0). 

Graphitized carbon blacks, thus undoubtly display reinforcing abilities which become obvious when considering the tensile strength of the unfilled vulcanizate. It follows that the formation of a filler-elastomer chemical bond is not a requirement for reinforcement to occur. It strongly participates, however, in its effectiveness, and determines the good mechanical properties connected with rubber reinforce-... 

Tensile strength, modulus at a given elongation and elongation at break depend on the rubber type and the reinforcing filler type and... 

The physical properties of natural rubber and synthetic rubber compounds are affected greatly by the type and amount of fillers used. Carbon black is the most commonly used filler. Increasing amounts of carbon black increases the hardness and modulus of the vulcanizates. Resilience and resistance to impinging type abrasion decrease along with elongation. Tensile strength and tear strength... 

The Teflon-filled vulcanizates have not been included until now since this filler must be considered as a special case, involving poor adhesion at the filler-rubber interface. The marked difference between Teflon and the other fillers is seen in Figure 9, which shows that the Teflon filler exerts only a slight effect on the tensile strength of the polybutadiene vulcanizate. As a matter of fact, although this filler does increase the strength slightly at temperatures above 0°C, it actually appears to de-... 

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