Acrylonitrile-butadiene-styrene plastics glass transition temperatures

Elastomers or rubbers are flexible materials that are mainly used in tires, hoses, and seals as adhesives or as impact modifiers of thermoplastics. They exhibit high resistance to impact, even at low temperatures at which materials increase their rigidity. Eor some of the applications (e.g., tires or hoses), these materials have to be slightly crosslinked once they are formed into the desired shape in order to impart them dimensional stability, since otherwise they tend to slowly flow. Elastomers are polymers that are used above their glass-transition temperature (Tg). Some examples of common elastomers are polybutadiene, which is used as an impact modifier of rigid plastics SBR (copolymer of styrene and butadiene), mainly used in tires EPDM (copolymer of ethylene, propylene, and a diene monomer, usually norbornene) NBR (copolymer of acrylonitrile and butadiene) and so on. 

Plastics can be divided according to their character into amorphous and crystalline. Crystallization is never complete and the so-called crystalline polymers are virtually semicrystalline ones. Examples of amorphous plastics are polystyrene, acrylonitrile-butadiene—styrene copolymers, styrene—acrylonitrile copolymers, polymethylmethacrylate, poly(vinyl chloride), cellulose acetates, phenylene oxide-based resins, polycarbonates, etc. Amorphous polymers are characterized by their glass transition temperature, semicrystalline polymers by both melting and glass transition temperatures. 

Water-based paints make use of an emulsion of a polymer composed of vinyl acetate, vinyl chloride, acrylics, acrylonitrile, ethylene, styrene, butadiene, and isoprene. The paint consists of an emulsion of polymer known as latex because their appearance is similar to rubber latex or sap from the rubber tree. The oil-in-water emulsion has plasticizers to smooth out the drying surface and to lower the glass transition temperature of the polymer to below room temperature. As drying occurs and water is lost, the polymer particles coalesce, forming a continuous impermeable film. 

Figure 10.21 shows the thermogram obtained from an immiscible mixture of styrene-acrylonitrile (SAN) copolymer and polybutadiene. This blend is a high impact strength material referred to as acrylonitrile-butadiene-styrene (ABS) plastic. Two glass transitions are observed, the low-temperature transition associated with the polybutadiene and the high-temperature transition associated with the SAN copolymer. 

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