Compounding high filler levels

Plasticizers. These are used to improve compound processibiHty, modify vulcani2ate properties, and reduce cost. Por many appHcations, where cost and processibiHty are the objective, naphthenic and aromatic oils are preferred. They are inexpensive yet effective in improving processibiHty at high filler levels. The compatibiHty of the naphthenic oils is limited to about 20 parts per hundred mbber. Aromatic oils are more compatible and can be used at higher levels (132). 

The EVAs make it possible to produce compounds with high filler levels and are compatible with many elastomers, plastics and other materials SBR, butyl rubber, EPDM, nitrile rubber, Hypalon, thermoplastic elastomers, epoxies, PVC, PVDC, bitumen. 

The primary use for Vamac in wire and cable is in ATH filled, flame resistant, nonhalogen jackets, usually peroxide cured (Table 6.32). The following typical jacket compounds are based on Vamac D and Vamac G. A color concentrate can be used in place of the carbon black. Armeen 18D and Vanfre VAM can be added to improve release properties but at the high filler levels associated with flame-retardant jacketing compounds, release is usually not a problem. 

Up to this point, the strain amplification factor can be viewed as a mere empirical approach to assign the modulus increase in CB filled compound to filler level. Equation 5.19 above essentially resulted from considerations on the hydrodynamic effects induced by the presence of solid particles ideally dispersed in a matrix with a considerably lower modulus. The empirical factor f in Equation 5.20 adds nothing in this respect and it is well known that both equations do not suit at all either highly loaded compounds, whatever is the grade of CB, or moderately loaded materials with high structure blacks. Over the last decades, several authors have developed theoretical considerations to model the likely effect of a so-called filler network structure and the associated energy dissipation process when filled compounds are submitted to increasing strain. 

Aluminium hydroxide is essentially non-toxic, but does require high addition levels to be effective. As a result, the physical properties of the compound usually suffer. Its fire retardancy action results from the endothermic reaction which releases water under fire conditions and produces a protective char . The endothermic reaction draws heat from the rubber/filler mass and thus reduces the thermal decomposition rate. The water release dilutes the available fuel supply, cooling the rubber surface and mass. 

Very high oil loadings of aromatic oils can be compatible with some grades of CR. However, the level of the oil s aromaticity must be carefully considered, for although compatible with loadings of up to about 100 phr of oil, stickiness of the vulcanised surface can result in highly filler loaded compounds. This has been found to be overcome by the use of oils with lower compatibility, i.e., less aromaticity, and by the incorporation of small amounts of factice or SBR to assist... 

The use of calcined clay as a filler has shown to lead to the release of soluble aluminium from rubber closures into the parenteral solution (Milano et al., 1982). Various techniques for the determination of soluble aluminium in rubber closures have been proposed (Mondimore and Moore, 1983). There has been concern about aluminium since the 1970s, when a link was identified between high aluminium levels in tap water used for renal dialysis equipment and accumulation of the element in the brain. The injection of parenteral solutions into the body effectively bypasses the normal defence mechanisms and under these circumstances may present a challenge to the normal metabolic processes (Massey and Taylor, 1989). In response to these challenges, suppliers have developed rubber formulations that are essentially free from materials containing aluminium compounds. 

The wire and cable industry, for instance, looks for formulations that are easily extrudable and show good physical properties. Low smoke, no halogen compounds are restricted in their extrusion speeds due to the high addition levels of ATH fillers needed to fulfil the FR requirements. 

Nanoeomposites are an environmentally friendly alternative to some types of flame retardants, as they eontain no additional halogens, phosphates or aromaties above those eontained in the ehosen polymer resin. The silicate remains intact at very high temperatures. In addition, whereas many flame retardant compounds, particularly filler types, inerease the earbon monoxide and soot levels produeed during combustion, no similar increases have been observed with nanoeomposites flame retardants. 

Plasticized PVC - Poly(vinyl chloride) polymer is a hard, somewhat brittle plastie. The addition of a plasticizer makes PVC soft, flexible, and extensible. PVC is the thermoplastic most often compounded with fillers, and the polymer used with the highest filler levels due, in part, to compoimding with plasticizer. This lowers polymer viseosity and enables high filler loadings. In addition, the high specific gravity of PVC makes the use of fillers economical, compared with lower specific gravity polymers like polyethylene and polypropylene. 

Since these elastomers are used for applications requiring high abrasion resistance and excellent physical properties they are normally compounded with lower levels of plasticizer. The base polymer is tougher than standard NBR and higher hardness and tensile strength is obtained with the base rubber alone, hence lower levels of filler are usually used. In addition a two pass mix is essential for better processing safety with the zinc peroxide and accelerators added in the second pass. 

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