Fillers, rubber Abrasion resistance

Since EPDM rubber is costly and the price fluctuates widely, high filler and oil loadings are resorted to, to achieve relatively low cost compounds. But these compounds tend to have poor strength and abrasion resistance. High quality stocks, especially those with peroxide cures, are considerably more expensive than NR, BR or SBR stocks. EPDM is used in belts and hoses meant for conveying hot materials because of its excellent heat resistance. Its excellent chemical resistance makes it a preferred rubber for specialty belts, chemical hoses and pump liners. 

The abrasion resistance increases considerably when reinforcing fillers are added to the polymer. This is, in particular, the case with rubbers incorporation of carbon black (e.g. 40 weight parts per 100 rubber parts) increases the life of a tyre bead from 5,000 to 50,000 or even 100,000 km ... 

Several performance characteristics of rubber such as abrasion resistance, pendulum rebound, Mooney viscosity, modulus, Taber die swell, and rheological properties can be modeled by Eq 7.34. " A complex mathematical model, called links-nodes-blobs was also developed and experimentally tested to express the properties of a filled rubber network system. Blobs are the filler aggregates, nodes are crosslinks and links are interconnecting chains. The model not only allows for... 

Rubber, due to its elastomeric properties, usually, has a low abrasion resistance. Fillers such as carbon black and silica can be added to impart abrasion resistance. Figure 8.38 shows the extent to which different grades of carbon black are abraded. As interaggregate distance decreases the abrasion loss decreases as well. 

Fillers are added to the elastomer in order to add bulk, lower cost and/or to improve physical properties such as hardness, strength and abrasion resistance. Typical fillers are materials such as carbon black, talc, china clay and whiting. Carbon black has been shown to contain polynuclear aromatics (PNAs) and there is concern regarding their carcinogenicity (Lee and Hites, 1976). However, despite extra controls there has been a move away from the use of carbon black as a filler in applications involving the primary packaging of parenterals. Its use continues as a pigment or colourant in rubber formulations but at substantially lower levels than that as a filler. 

Another extremely important example is the use of carbon filler for rubber. Rubber would be of little value in modern industry were it not for the fact that the filler carbon greatly enhances its mechanical properties lie tensile strength, stiffness, tear resistance, and abrasion resistance. Enhancement of these properties is called reinforcement, and the fillers which produce the strengthening effect are known as reinforcing fillers. Other fillers may not appreciably increase strength, but they may improve other properties of the polymer, thus, making it easier to mold, which reduces cost. 

Rather peculiar to the rubber industry is the use of the fine particle size reinfordng fillers, particularly carbon black. Fillers may be used from 50 phr to as high as 100-120 phr or even higher proportions. Their use improves such properties as modulus, tear strength, abrasion resistance, and hardness. They are essential with amorphous rubbers such as SBR and polybutadiene that has Kttle strength without them. They are less essential with strain-crystallizing rubbers such as NR for many applications but are important in the manufacture of tires and related products. 

The use of silica in rubber mixes cannot be considered as new at all, because this filler has been used in rubber formulations since the beginning of the 20th century (Voet et al., 1977). Silicas are not reinforcing fillers in the proper sense, because silica-reinforced mixes exhibit much lower mechanical properties, particularly considering modulus at break and abrasion resistance. So silicas weren t used as reinforcing fillers but mainly in association with carbon black. 

The example chosen here to illustrate this type of composite involves a polymeric phase that exhibits rubberlike elasticity. This application is of considerable practical importance since elastomers, particularly those which cannot undergo strain-induced crystallization, are generally compounded with a reinforcing filler. The two most important examples are the addition of carbon black to natural rubber and to some synthetic elastomers and silica to polysiloxane elastomers. The advantages obtained include improved abrasion resistance, tear strength, and tensile strength. Disadvantages include increases in hysteresis (and thus heat buUd-up) and compression set (permanent deformation). 

PROPERTIES OF SPECIAL INTEREST Standard emulsion SBR is a general purpose rubber. Most widely used synthetic rubber in the world. Better tire tread-wear and aging properties than natural rubber. Good abrasion resistance and crack initiation resistance. Poor in tack and heat build-up. Physical properties are poor without reinforcing fillers. Solution SBR is a speciality rubber and more expensive than emulsion SBR. Solution SBR with high vinyl and styrene levels is used in high performance tire treads to improve wet traction. Also used as impact modifier in plastics and as thermoplastic elastomers. 

Chem. Descrip. Cryst. oxidized Ziegler-type polyethylene wax CAS 68441-17-8 EINECS/ELINCS 200-815-3 Uses Lubricant wax PVC lubricant for transparent prods. in anionic emulsions to carry nonemulsifiable microwaxes, paraffins, etc. melting agent, water repellent in paints abrasion-resist, printing inks mixed saponified polishes preservative in textiles for crosslinking with wash-and-wear resins process aid and mold release in rubber compds. improves filler disp. corrosion inhibitor Features Hard, high-melting... 

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