Elastomers, additives Fillers

The term s plastic, polymer, resin, elastomer, and reinforced plastic (RP) are some-what synonymous. However, polymer and resin usually denote the basic material. Whereas plastic pertains to polymers or resins containing additives, fillers, and/or reinforcements. Recognize that practically all materials worldwide contain some type of additive or ingredient. An elastomer is a rubberlike material (natural or synthetic). Reinforced plastics (also called composites although to be more accurate called plastic composites) are plastics with reinforcing additives, such as fibers and whiskers, added principally to increase the product s mechanical properties. 

In addition to the broad categories of TPs and TSs, TPs can be further classified in terms of their structure, as either crystalline, amorphous, or liquid crystalline. Other classes (terms) include elastomers, copolymers, compounds, commodity resins, engineering plastics, or neat plastics. Additives, fillers, and reinforcements are other classifications that relate directly to plastics properties and performance. 

Silicone elastomer-based rubber compounds are prepared in conventional apparatuses (closed agitators, roll mills, etc.) and consist of the following ingredients elastomer, active fillers, vulcanising agent, stabiliser, pigment additives. 

The materials being reviewed in this book, as in the industry, are identified by different terms such as polymer, plastic, resin, elastomer, reinforced plastic (RP), and composite unreinforced or reinforced plastic. They are somewhat synonymous. Polymers, the basic ingredients in plastics, can be defined as high molecular weight organic chemical compounds, synthetic or natural substances consisting of molecules. Practically all of these polymers are compounded with other products (additives, fillers, reinforcements, etc.) to provide many different properties and/or processing capabilities. Thus plastics is the correct technical term to use except in very few applications where only the polymer is used to fabricate products. 

In this work, we have investigated one aspect of this problem i.e. the effects of adding two types of particulate elastomeric additives and of filler content on two recognized stress factors (coefficient of thermal expansion and modulus) of a model molding compound. From this work, we have concluded that particulate elastomer additives can not only lower stress by modulus reduction but also by CTE reduction and possibly by reduced dimensional changes when the part cools from the molding temperature. 

Thermal mechanical analysis (Dupont 990/942 IMA), and dynamic mechanical analysis (Dupont 1090/982 DMA) curves for a designed set of model formulations were evaluated for CTE and tensile storage modulus as a function of filler level and elastomer additive type and level. Fifteen formulations were prepared with 68-75% filler, 0-4% silicone elastomer A, 0-4% non-silicone elastomer B and the balance 17-32%. Both elastomers have Tg s below room temperature. An extreme vertices formulation design was generated by computer (Table I). 

It is not easy to define the term plastic , which is usually considered as equivalent to the term polymer. Plastics are polymeric materials, but not all polymers are plastics. In general, the term plastic is used to refer to any commercial polymeric material other than fibres and elastomers. Moreover, commercial plastics include other components such as additives, fillers, and a variety of compounds incorporated into the polymers to improve their properties. The term resin is usually used to describe the virgin polymeric material without any of these components. 

This is one of the most important synthetic thermoplastic elastomers. Nitrile rubber is a copolymer of butadiene and acrylonitrile. The copolymer usually contains enough acrylonitrile (>25%) so that good resistance to oil and grease can be obtained. Adhesive properties also increase with increasing nitrile content. These adhesives are used to bond vinyls, other elastomers, and fabrics where good wear, oil, and water resistance are important. Compatibility with additives, fillers, and other resins is another advantage of this material.Table 5.1 summarizes the properties of nitrile rubber. 

Up until World War II, almost all elastomers were based on natural rubber. During the war, synthetic rubbers began to replace the scarce natural rubber. Since that time production of synthetics has increased until it now far surpasses that of natural rubber. There are thousands of different elastomer compounds. Not only are there many different classes of elastomers, but also individual types can be modified with a variety of additives, fillers, and reinforcements. In addition, curing temperatures, pressures, and processing methods can be varied to produce elastomers tailored to the needs of specific applications. 

MRE composites were prepared according to the commonly used methods. It was found that micro- and nano- sized iron oxides and carbonyl iron powder were active fillers improving mechanical properties of elastomers. Additionally, they... 

Some topics involving additives, curing, and reinforcement of elastomers by fillers that were covered at the symposium are additives (Perry), curing (Tsiang, Singh, Chu, Priou, Wu, Taylor), reinforcement (Osaheni, Okel, Cosgrove, Cohen-Addad, Matejka), and water-based elastomers (Liles, Bowens) (26). 

Provorov et al. [520] have studied a rather extensive group of elastomer additives (accelerators, stabilisers, softeners, fillers, and other ingredients) for possible analysis by fluorescence techniques. No fluorescence lifetime measurements have been applied for discriminating stabilisers in polymers. UV microscopy is another means of measuring the concentration (and distribution) of UV absorbing or fluorescent additives in plastics (cfr. Chp. 5.3.2). 

Due to the virtually limitless combination of elastomer types, fillers and additives that can be compounded, a huge variety of elastomeric materials are available for almost any application requiring elastomeric properties. For this reason, it is very nnlikely that there will be bond strength data for every adhesive/elastomer combination. 

Grade Selection Criteria Melt flow characteristics for injection moulding, extrusion and blow moulding. Filler/reinforcement additions, elastomer additions, food contact approvals, electrical properties. ... 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

Silicone Heat-Cured Rubber. Sihcone elastomers are made by vulcanising high molecular weight (>5 x 10 mol wt) linear polydimethylsiloxane polymer, often called gum. Fillers are used in these formulations to increase strength through reinforcement. Extending fillers and various additives, eg, antioxidants, adhesion promoters, and pigments, can be used to obtain certain properties (59,357,364). 

Plasticizers. Addition of plasticizers (qv) to polyether elastomers alters physical properties, improves processing, and can improve low temperature flexibiUty. Plasticizers also reduce vulcanizate costs by allowing the use of higher levels of less expensive fillers. 

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