Non-black fillers

The main non-black fillers are, for example calcium carbonates, broadly used in PVC talcs, broadly used in polypropylene titanium dioxide used as a white pigment clays or kaolins ... 

If non-black fillers are used they produce excessive swelling and softening of the rubber sealing rings in the aqueous medium, where oxides become hydroxides and silicates are converted to water soluble bicarbonates by carbon dioxide and water. 

Excessive swelling and softening in the aqueous environment if non-black fillers are used (oxides become hydroxides or sols, silicates can convert to water-soluble bicarbonates by carbon dioxide/water mixtures etc.). 

For many decades carbon black has enjoyed a practical monopoly as a filler in the tire industry. It retains this position today, the tire industiy consumes 70% of carbon black production. A major breakthrough for non-black fillers came in the early 1970s when a winter tire containing silica in its treading compound was introduced. This resulted in numerous problems with rubber compound processing. The tire compound had different flow and molding characteristics. The development initiated friendly competition (friendly because the major producers of carbon black are also major manufacturers of precipitated silica) which continues to bring improvements to tire performance. 

Figure 19.30 shows end use opportunities for non-black fillers. The tire elements show highlights of various opportunities for white fillers. Figure 19.30 omits to show that silica can be used to advantage in treading compound. This is discussed below. 

Sakurai and his associates91 were able to demonstrate that the tensile stress in a strip of reinforced rubber held at constant extension for 900 sec was related to its initial tensile stress by a linear relation covering all extensions and loadings of each of the blacks studied. Similar relations for non-black fillers could not be drawn, as each filler loading resulted in a different line these, however, were parallel. Starting with a given stress, ISAF showed the most drastic fall in stress ( relaxation ), followed by GPF, activated silica, FT and silicate . The fact that more rapid relaxation appears to be related to increased reinforcement supports the main features of the model. 

Reinforcing fillers used are carbon black and non-black fillers such as silica, clay, and calcium carbonate although the latter two are used more in lower cost industrial applications and not in tires. Protectant systems consist of antioxidants, antiozo-nants, and waxes. The vulcanization system essentially ensures that the optimum mechanical properties of the polymer system are achieved. Finally, the tire compound can contain various miscellaneous materials such as processing aids and resins. The materials scientist when designing a tire compound formulation has a range of objectives and restrictions within which to operate. Product performance objectives define the initial selection of materials. These materials must not raise environmental concerns, be processable in tire production plants, and be cost effective for the end user [4]. 

Due to its advanced technology and low cost the rubber industry often prefers the use of sulphur-vulcanized polyurethane elastomers even though some of their technical properties, e.g. resistance to thermal degradation, are inferior to the peroxide- and diisocyanate-cured grades which often have short processing times (i.e. they are scorchy) and whose cure may be adversely affected by the presence of moisture in the unvulcanized rubber mix water is present in rubber fillers, e.g. carbon blacks usually contain about 0-5-1% and some non-black fillers such as silicas and clays 2-10%. Also to maximize scorch time it is common practice to quench-cool the rubber after internal mixing by immersion in cold-water tanks or by cold-water spray application to the surface of the hot-milled sheet. 

Millable urethane responds to various types of carbon-black loading in the same manner as does SBR (Styrene-Butadiene Rubber). The qualitative effects of various carbon blacks and non-black fillers on several properties of vulcanizates of millable urethanes are shown in Table 7.9 and Figs 7.3 and 7.4. 

Fig. 7.4. Effect of non-black fillers on properties of a millable polyurethane...

EFFECT OF NON-BLACK FILLERS ON URETHANE ELASTOMER PROPERTIES... 

Neff, J.M. (2005). Composition, environmental fates, and biological effect of water-based drilling muds and cuttings discharged to the marine environment A synthesis and annotated bibliography. Submitted to Petroleum Environmental Research Forum (PERF). ht //perf.org/pdf/APIPERFreport.pdf, last visited 29 June 2012. Non-Black Fillers for Rubber, http //www.rtvanderbilt.com/NonBlackFillers.pdf, last visited 26 June 2012. 

Semi-conductive materials may be produced by addition of conventional carbon blacks. Resistivity is lowest for those grades with the highest structure and highest surface areas. Non-black products generally rely on the use of antistatic additives, which reduce the surface resistivity of the product, since most non-black fillers are insulating in nature. 

Most rubber products are black because of the supremacy of carbon black as a reinforcing agent, so colour does not play an important role in most industrial applications. For those applications where colour is important, the selection of filler is restricted to those non-black fillers, which are able to provide the properties required. The effect of these materials on colour is readily predictable from the whiteness of the filler. It is important, however, not to rely too heavily on the optical qualities of fillers as they are not produced for primary pigmentation purposes. 

While most fillers are not produced for their primary pigmenting properties, consistency of colour may be of concern for non-black applications. Most non-black fillers are produced to a basic colour or whiteness specification. Carbon blacks, too, may be categorised by their colour or tinting strength. While this is useful to know, it is often of little value to the end-user who rarely possesses the equipment necessary for colour determination. There are also a large number of measurement methods in use, which leads to some confusion in this area. Most processors must content themselves with making visual comparison with an established reference sample. 

Non-black Fillers for Rubber from ECC International, Fillers in Compound Design, Reference R87, ECC International (now Imerys), St. Austell, UK, 1981, p.5. 

Excess stearic acid is released to combine with more zinc oxide. If allowed to proceed to completion, this mechanism would eventually rob all the zinc, leaving none to activate the vulcanization reaction. Lower surface area non-black fillers also react with the zinc ion, but show less effect because they have fewer silanol groups available. 

In general terms, the effect of a filler on rubber physical properties can be related mainly to how many polymer chains are attached to the filler surface and how strongly they are attached. Filler surface area and activity are the main determinants, supplemented by structure. Since the filler particles can be considered crosslinks for the elastomer chains, the presence or absence of a coupling agent on the surface of non-black fillers is also important. 

Miscellaneous Fillers - Although kaolin clay, calcium carbonate, and precipitated silica accoimt for most of the non-black fillers used in rubber today, there are a munber of other fillers routinely used for their low cost or imique fimtionality. 

Light-colored fillers do play an important role in NBR compounding, especially in the roller business. The main types of non-black fillers used with nitrile rubber are silica, silicate, clay, talc, and calcium carbonate. In addition there are many specialty light-colored fillers such as diatomaceous earth, barium sulfate, titanium dioxide, aluminum trioxide, antimony trioxide, magnesium hydroxide, and zinc oxide to name a few. 

Since NBR/PVC has basic good flame resistance it may be used in hose and belt applications where this is a requirement. A 70/30 or 50/50 NBR/PVC base elastomer should be selected and use non-black fillers, including alumina trihydrate (e.g.. Hydrated Alumina 983), magnesium hydroxide, and zinc borate (e.g., Firebrake ZB) as flame retardant fillers. Calcium carbonate will assist in reducing smoke emission. In addition a phosphate plasticizer such as Kronitex 100 or chlorinated paraffin like Chlorowax 40 should be used as the only plasticizer types. 

The wide variety of non-black fillers make for a wide variety of finished compound properties. Studies done by Zeon [11,12] show very different reinforcing effects, which do not correlate with particle size of the fillers suggesting some very strong interactions with particular non-black fillers. Information from that study is shown in... 

Source From Zeon Chemicals L.P., Evaluation of Larger Particle Non-Black Fillers in Peroxide Cured Zetpol 2010 (Z5.3.3.) [Brochure], Louisville, KY. 

Non-Black Filler Loading to Increase Shore A by One Point Unfilled Base Elastomer Hardness Shore A24... 

Non-black fillers may also be employed, but it is important to use neutral or medium high pH grades such as silane-treated calcined clay, synthetic sodium aluminum silicate, platy talc, neutral pH silicas, diatomaceous earth, hydrated aluminum silicate, calcium meta silicate, precipitated calcium carbonate, and so on. An indication of non-black filler requirements for one point of hardness increase is shown in Table 5.10. 

The Diuron cure system provides excellent scorch safety, good shelf life, but moderate cure rates. The use of up to 6 pphr will improve cure rates at some sacrifice in scorch safety. This product is not recommended with non-black fillers. The physical properties obtained with Diuron are excellent, except the elongation is lowered with higher loadings. The compression set is good and heat aging is excellent with Diuron compounds. Rhenocure Diuron is an 80% dispersion that is recommended in place of the pure Diuron. 

It is advisable to include a silane appropriate for the curing system employed in order to achieve lower compression set and water resistance plus higher modulus. Some fillers, including clays, talc, and sihca, have a silane already incorporated in them and are suggested for electrical and low water swell applications. If the product is meant for acid resistant uses carbon black and acid resistant non-black fillers such as barium sulfate should be selected. 

Although CSM has good basic weather resistance, carbon black imparts improved UV resistance. Light-colored articles need to have up to 35 phr of a rutile titanium dioxide, depending upon other non-black fillers used, for good weather resistance and color stability. Non-black fillers recommended are clays up to 50 phr, whitings up to 200 phr, all in combination with titanium dioxide. Low levels of talc may be employed and silica fillers are NOT good for UV resistance. 

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