Thermoplastic also polystyrene

Commodity and engineering polymers. On the basis of end use and economic considerations, polymers can be divided into two major classes commodity plastics and engineering polymers. Commodity plastics are characterized by high volume and low cost. They are used frequently in the form of disposable items such as packaging film, but also find application in durable goods. Commodity plastics comprise principally of four major thermoplastic polymers polystyrene, polyethylene, polypropylene, and poly(vinyl chloride). 

One method of classifying plastics is by their response to heat. Thermoplasts, also known as thermoplastic polymers, soften and liquefy on heating and harden again when cooled. The process is reversible and can be repeated. On heating, the weak secondary bonds between polymer chains are broken, which facilitates relative movement between the chains. If the molten polymer is further heated until the primary covalent bonds also break, degradation of the thermoplast follows. Thermoplastic polymers are linear or exhibit branching with flexible chains and include polyethylene, polystyrene and polypropylene (Figure 4.10). 

Polypropylene is generally used as oriented polypropylene. Polyvinyl chloride film is commonly used in plasticized form. Polyvinylidene chloride is often known as Saran and is generally used in copolymer form with acrylonitrile. Polyethylene terephthalate is a thermoplastic polyester. Polystyrene is sometimes used in biaxially oriented form. Polycarbonates, polysulfones, polyether sulfones, poly-imides, polyetherimides, and several fluoropolymers are also used for specialty applications. 

Triphenyl phosphate [115-86-6] C gH O P, is a colorless soHd, mp 48—49°C, usually produced in the form of flakes or shipped in heated vessels as a hquid. An early appHcation was as a flame retardant for cellulose acetate safety film. It is also used in cellulose nitrate, various coatings, triacetate film and sheet, and rigid urethane foam. It has been used as a flame-retardant additive for engineering thermoplastics such as polyphenylene oxide—high impact polystyrene and ABS—polycarbonate blends. 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

Considerable amounts of EPM and EPDM are also used in blends with thermoplastics, eg, as impact modifier in quantities up to ca 25% wt/wt for polyamides, polystyrenes, and particularly polypropylene. The latter products are used in many exterior automotive appHcations such as bumpers and body panels. In blends with polypropylene, wherein the EPDM component may be increased to become the larger portion, a thermoplastic elastomer is obtained, provided the EPDM phase is vulcanked during the mixing with polypropylene (dynamic vulcani2ation) to suppress the flow of the EPDM phase and give the end product sufficient set. 

The regular syndiotactic and isotactic structures are capable of crystallisation whereas the atactic polymer carmot normally do so. In the case of polypropylene the isotactic material is a crystalline fibre-forming material. It is also an important thermoplastic which can withstand boiling water for prolonged periods. Atactic polypropylene is a dead amorphous material. Polystyrene as commonly encountered is atactic and glass-like but the syndiotactic material... 

As with other rigid amorphous thermoplastic polymers such as PVC and polystyrene (see the next chapter) poly(methyl methacrylate) is somewhat brittle and, as with PVC and polystrene, efforts have been made to improve the toughness by molecular modification. Two main approaches have been used, both of which have achieved a measure of success. They are copolymerisation of methyl methacrylate with a second monomer and the blending of poly(methyl methacrylate) with a rubber. The latter approach may also involve some graft copolymerisation. 

Tbe term structural foam was originally coined by Union Carbide to describe an injection moulded thermoplastic cellular material with a core of relatively low density and a high-density skin. The term has also been used to describe rigid foams that are load bearing. Today it is commonly taken to imply both of the above requirements, i.e. it should be load bearing and with a core of lower density than the skin. In this section the broader load-bearing definition will be used. Whilst structural foams are frequently made from polymers other than polystyrene, this polymer is strongly associated with such products and it is convenient to deal with the topic here. 

Polycarbonate is perhaps the most notoriously notch-sensitive of all thermoplastics, although nylons arc also susceptible to ductileAjrittle transitions in failure behaviour caused by notch sharpening. Other plastics such as acrylic, polystyrene and thermosets are always brittle - whatever the crack condition. 

Polystyrene. A thermoplastic used as a binder and fuel in expls and rocket propints. See Plastic fuels (Vol 3, C465-L) under Composite Propellants also Dinitropolystyrene in this Vol, N143-L to N144-R under Nitro Polymers and Propellants, Solid , also in this Vol... 

Alkanesulfonates act as an external lubricant in PVC, polystyrene, and engineering thermoplastics. They have a good release effect and assist flow. Addition is in the concentration range between 0.1 and 2.0 parts per 100 parts resin (phr). Because of their low volatility, alkanesulfonates are also used as a processing aid for high-melting engineering thermoplastics. 

Styrene-butadiene-styrene (SBS) block copolymers are adequate raw materials to produce thermoplastic mbbers (TRs). SBS contains butadiene—soft and elastic—and styrene— hard and tough—domains. Because the styrene domains act as cross-links, vulcanization is not necessary to provide dimensional stability. TRs generally contain polystyrene (to impart hardness), plasticizers, fillers, and antioxidants processing oils can also be added. Due to their nature, TR soles show low surface energy, and to reach proper adhesion a surface modification is always needed. 

The use of lightly crosslinked polymers did result in hydrophilic surfaces (contact angle 50°, c-PI, 0.2 M PhTD). However, the surfaces displayed severe cracking after 5 days. Although qualitatively they appeared to remain hydrophilic, reliable contact angle measurements on these surfaces were impossible. Also, the use of a styrene-butadiene-styrene triblock copolymer thermoplastic elastomer did not show improved permanence of the hydrophilicity over other polydienes treated with PhTD. The block copolymer film was cast from toluene, and transmission electron microscopy showed that the continuous phase was the polybutadiene portion of the copolymer. Both polystyrene and polybutadiene domains are present at the surface. This would probably limit the maximum hydrophilicity obtainable since the RTD reagents are not expected to modify the polystyrene domains. 

The styrenic thermoplastic elastomers are the only type which are fully compounded in the manner of conventional elastomers. In this case, however, the addition of carbon black, or other fillers, does not give reinforcement. Additions of polystyrene, or high impact polystyrene, and oil are used to vary hardness and tear strength, and fillers can be used to cheapen the material. Other added polymers, e g., EVA, can be used to increase ozone resistance. These materials also require antioxidants for protection during processing and service life, and the poor UV stability restricts their use in outdoor applications. 

The commodity thermoplastics are the most-used plastics in this sector, accounting for 95% of all thermoplastic packaging. Polyolefins are the most important, accounting for more than 65% of the total plastic weight. Polyethylene terephthalate, polystyrene and PVC are also commonly used. 

Thermoplastics are predominant among the plastics used for the household, entertainment office appliance industry with styrenics pre-eminent, including polystyrene, high-impact polystyrene, EPS, ABS, SAN, ASA. .. followed by PP. Several engineering thermoplastics such as PA, PC, PBT, PPO and POM are also used. 

Such thermoplastics have also been used as DNA microarray substrates (Matson et al., 1995 Shchepinov, 1997 Beier and Hoheisel, 1999) and in the construction of protein microarrays in microwells (Matson et al., 2001 Moody, 2001). Pierce (see searchlight perbio.com) introduced the Search-Light series of microarray-based ELISA assays immobilizing capture antibodies in a low density array format into polystyrene microwells. 

The annual worlwide production of triblock thermoplastic elastomers, clear impact-resistant polystyrene, and other styrene-diene products produced by anionic polymerization exceeds a couple of billion pounds. (Commercial utilization of anionic polymerization also includes the polymerization of 1,3-butadiene alone.)... 

Unlike simple mixtures of polystyrene and polybutadiene such blends can be thermoplastically processed without phase separation ( splicing ) Furthermore, they can to a certain extent withstand mechanical impact without disintegration. This is because the above-mentioned graft polymers function also as compatibilizer at the borderline of the hard phase and the rubber-elastic dispersed phase (already at concentrations below 3%). 

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