Fillers polymers processing characteristic

Although our concern has been with polymer molecular characteristics and the influence that these have on properties, commercial polymeric materials are rarely pure polymers. Numerous compounds are added to the polymers to enhance their performance in use. Typical additives include antioxidants, light stabilizers, pigments, particular fillers, antistatic agents, processing aids, flame retardants and many others [54]. It is not uncommon for there to be a cocktail... 

The role of mineral fillers in plastic compounds is changing. In the past they were used to reduce costs by replacing polymer content by a less expensive material. Now they have a more important role to play since their use can modify processing characteristics or the properties of the finished part. Other uses include their ability to reduce the content of more expensive additives, notably pigments, flame retardants and impact modifiers. Nanomaterials are coming to the fore as potential fillers along with the more traditional options of alumina trihydrate, barium sulfate, calcium carbonate, kaolin and talc. 

Fillers are different from additives that are commonly used in polymer processing, such as paints, heat stabilizers, flame retardants, and lubricants, and also are different from other liquid fertilizers. Fillers used in polymer modification have the following characteristics. 

A comparison of carbon blacks, the preferred fillers for XNBR, is given in Table 2.29. An unfilled compound is shown to illustrate the properties of the base elastomer. The unhlled polymer has a Shore A hardness of 62 compared with a standard NBR with a hardness of 45, hence this factor needs consideration when designing an XNBR formulation. Other carbon blacks may be considered, but the enhancement of properties by reinforcing hllers is less than in standard NBR, hence the selection should be made based upon abrasion resistance, tear, and process characteristics. 

For composites with polymerization-modified filler it is typical that the physico-mechanical characteristics should increase symbatically with the quantity of polymer which becomes attached to the filler in the polymerization process. This effect has been observed for polyethylene [293, 321], poly(vinyl chloride) coats [316], and in [336, 337] for kaolin coated with poly(vinyl acetate) and introduced into the copolymer of ethylene and vinyl acetate. 

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