Plasticizers high-temperature performance

Ester plasticizers are used mainly in very polar elastomers, such as neoprene and nitrile mbber, to improve low or high temperature performance or impart particular oil or solvent resistance to a compound 5—40 parts are commonly used (see Plasticizers). Resins and tars are added to impart tack, soften the compound, improve flow, and in some cases improve filler wetting out, as is the case with organic resins in mineral-filled SBR. Resinous substances are also used as processing agents for homogenizing elastomer blends. 

Differences among the processes have a major impact on the use of the products. Products from a particular process or manufacturer may dominate one market, while products from a different process may be preferred in a different appHcation. Major uses include hot-melt adhesives for appHcations requiring high temperature performance, additives to improve the processing of plastics, sHp and mb additives for inks and paints, and cosmetic appHcations. 

In recent years a whole new generation of high performance engineering plastics have become commercially available. These offer properties far superior to anything available so far, particularly in regard to high temperature performance, and they open the door to completely new types of application for plastics. 

In many fields of use polysulfones have replaced or are replacing metals, ceramics, and thermosetting plastics, rather than other thermoplastics. Since commercial polysulfones can be injection molded into complex shapes, they avoid costly machining and finishing operations. Polysulfones can also be extruded into film and foil. The latter is of interest for flexible printed circuitry because of its high-temperature performance. 

Table 6.10 RPs and other high temperature performance materials (courtesy of Plastics FALLO)...

There are of course many plastics materials which have better high temperature performances than the polysulphones, for example the polyimides and fluorocarbon polymers, but most of these materials are thermosetting resins and all require somewhat specialised techniques for handling eg sintering or thin layer coating techniques (12). 

An accepted criterion for describing high-temperature performance of a plastic is the deflection temperature under load (DTUL). This is based on a short-term test that identifies the temperature at which a polymer distorts beyond acceptable limits. It has the limitation of not being able to predict long-term behavior but is a convenient method by which to compare materials. 

Different plastics are used to meet different gasket and seal requirements. An example is PTFE (polytetrafluoroethylene) that provides a virtually inert exposure to all kinds of elements and has outstanding high-temperature performance. Unreinforced PTFE can be vulnerable to creep and stress relaxation. However, reinforced PTFE modifies these limitations. 

Kemlra 470 is a rutile titanium dioxide pigment designed to meet the needs of the most demanding plastics applications. It has the same brightness and tone properties as standard Kemira 460 but is end-treated to impart hydrophobic properties. This results in outstanding dispersibility and significantly improved high temperature performance. Kemira 470 rutile titanium dioxide meets the requirements of specification ASTM D 476-84 (1989), Type II III. 

They exhibit excellent dielectric properties over a wide range of frequencies and temperatures. PPE/ PS alloys are supplied in flame-retardant, filled and reinforced, and structural foam molding grades. PPE can also be alloyed with polyamide (nylon) plastics to provide increased resistance to organic chemicals and better high-temperature performance. 

Polyethersulfone (PES) is an amorphous polymer and a high-temperature engineering thermoplastic. Even though PES has high-temperature performance, it can be processed on conventional plastic processing equipment. Its chemical structure is shown in Fig. 12.15. PES has an outstanding ability to withstand exposure to elevated temperatures in air and water for prolonged periods. 

Ethylene-Propylene-Diene Terpolymer (EPDM) is used for weather protection, tire sidewalls and coverstrips, wire, cable, mechanical goods, sheeting, hoses, tubing, and plastics modification and TPO. EPDM can be modified with silicone to reinforce high temperature performance of silicone and mechanical and physical strength of EPDM. Maleated EPDM (0.5 to 1.0%) is used to toughen nylon (impact modifier of nylon) and polyester thermoplastics (impact modifier for polycarbonate and polyester/carbonate alloys, PVC). Typical EPDM recipes are... 

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