High-impact plastics polystyrene

Once the use was postulated of solid domains (second-phase particles) in polystyrene to produce a high impact plastic, it was reahzed that this concept could work for epoxy resins if discrete, so-called second-phase particles could be produced throughout the continuous phase of the cured adhesive matrix. 

Laboratory tests indicated that gamma radiation treatment and cross-linking using triaHylcyanurate or acetylene produced a flexible recycled plastic from mixtures of polyethylene, polypropylene, general-purpose polystyrene, and high impact grade PS (62). 

Structural Components. In most appHcations stmctural foam parts are used as direct replacements for wood, metals, or soHd plastics and find wide acceptance in appHances, automobUes, furniture, materials-handling equipment, and in constmction. Use in the huil ding and constmction industry account for more than one-half of the total volume of stmctural foam appHcations. High impact polystyrene is the most widely used stmctural foam, foUowed by polypropylene, high density polyethylene, and poly(vinyl chloride). The constmction industry offers the greatest growth potential for ceUular plastics. 

To complete the assembly of a cell, the interleaved electrode groups are bolted to a cov er and the cover is sealed to a container. Originally, nickel-plated steel was the predominant material for cell containers but, more recently plastic containers have been used for a considerable proportion of pocket nickel-cadmium cells. Polyethylene, high impact polystyrene, and a copolymer of propylene and ethylene have been the most widely used plastics. 

Polystyrene. Polystyrene [9003-53-6] is a thermoplastic prepared by the polymerization of styrene, primarily the suspension or bulk processes. Polystyrene is a linear polymer that is atactic, amorphous, inert to acids and alkahes, but attacked by aromatic solvents and chlorinated hydrocarbons such as dry cleaning fluids. It is clear but yellows and crazes on outdoor exposure when attacked by uv light. It is britde and does not accept plasticizers, though mbber can be compounded with it to raise the impact strength, ie, high impact polystyrene (HIPS). Its principal use in building products is as a foamed plastic (see Eoamed plastics). The foams are used for interior trim, door and window frames, cabinetry, and, in the low density expanded form, for insulation (see Styrene plastics). 

In the period 1945-1955, while there was a noticeable improvement in the quality of existing plastics materials and an increase in the range of grades of such materials, few new plastics were introduced commercially. The only important newcomer was high-impact polystyrene and, at the time of its introduction, this was a much inferior material to the variants available today. 

In addition to polystyrene and high-impact polystyrene there are other important styrene-based plastics. Most important of these is ABS, with a global capacity of about 5 X 10 t.p.a. and production of about 3 X 10 t.p.a. The styrenic PPO materials reviewed in Chapter 21 have capaeity and production figures about one-tenth those for ABS. Data for the more specialised styrene-acrylonitrile copolymers are difficult to obtain but consumption estimates for Western Europe in the early 1990s were a little over 60000 t.p.a. 

Polystyrene (PS) The volume of expanded polystyrene produced probably exceeds the volume production of all other plastics (excluding the polyurethanes) put together. At least half the weight of polystyrene produced is in the form of high impact polystyrene (HIPS)—a complex blend containing styrene-butadiene rubber or polybutadiene. 

Polystyrene One of the high volume plastics, is relatively low in cost, easy to process, has sparkling clarity, and low water absorption. But basic form (crystal PS) is brittle, with low heat and chemical resistance, poor weather resistance. High impact polystyrene is made with butadiene modifiers provides significant improvements in impact strength and elongation over crystal polystyrene, accompanied by a loss of transparency and little other property improvement. PS is used in many different formulations. 

In a block copolymer, a long segment made from one monomer is followed by a segment formed from the other monomer. One example is the block copolymer formed from styrene and butadiene. Pure polystyrene is a transparent, brittle material that is easily broken polybutadiene is a synthetic rubber that is very resilient, but soft and opaque. A block copolymer of the two monomers produces high-impact polystyrene, a material that is a durable, strong, yet transparent plastic. A different formulation of the two polymers produces styrene-butadiene rubber (SBR), which is used mainly for automobile tires and running shoes, but also in chewing gum. 

Transition from liquid behavior to solid behavior has been reported with fine particle suspensions with increased filler content in both Newtonian and non-Newtonian liquids. Industrially important classes are rubber-modified polymer melts (small rubber particles embedded in a polymer melt), e.g. ABS (acrylo-nitrile-butadiene-styrene) or HIPS (high-impact polystyrene) and fiber-reinforced polymers. Another interesting suspension is present in plasticized polyvinylchloride (PVC) at low temperatures, when suspended PVC particles are formed in the melt [96], The transition becomes evident in the following... 

Union Carbide (34) and in particular Dow adopted the continuous mass polymerization process. Credit goes to Dow (35) for improving the old BASF process in such a way that good quality impact-resistant polystyrenes became accessible. The result was that impact-resistant polystyrene outstripped unmodified crystal polystyrene. Today, some 60% of polystyrene is of the impact-resistant type. The technical improvement involved numerous details it was necessary to learn how to handle highly viscous polymer melts, how to construct reactors for optimum removal of the reaction heat, how to remove residual monomer and solvents, and how to convey and meter melts and mix them with auxiliaries (antioxidants, antistatics, mold-release agents and colorants). All this was necessary to obtain not only an efficiently operating process but also uniform quality products differentiated to meet the requirements of various fields of application. In the meantime this process has attained technical maturity over the years it has been modified a number of times (Shell in 1966 (36), BASF in 1968 (37), Granada Plastics in 1970 (38) and Monsanto in 1975 (39)) but the basic concept has been retained. 

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. 

The concept is similar to the grafting of plants in botany. To form a styrene-butadiene graft polymer, already polymerized butadiene is dissolved in monomeric styrene and an initiator is added. Because polybutadiene readily undergoes chain transfer at the allylic sites, polystyrene chains grow on the polybutadiene backbone. This forms high impact polystyrene, a low cost plastic that is otherwise too brittle without the grafting. 

High impact polystyrene is widely used as amorphous engineering plastic and in (food) packaging. 

As of this date, there is no lithium or alkyl-lithium catalyzed polyisoprene manufactured by the leading synthetic rubber producers- in the industrial nations. However, there are several rubber producers who manufacture alkyl-lithium catalyzed synthetic polybutadiene and commercialize it under trade names like "Diene Rubber"(Firestone) "Soleprene"(Phillips Petroleum), "Tufdene"(Ashai KASA Japan). In the early stage of development of alkyl-lithium catalyzed poly-butadiene it was felt that a narrow molecular distribution was needed to give it the excellent wear properties of polybutadiene. However, it was found later that its narrow molecular distribution, coupled with the purity of the rubber, made it the choice rubber to be used in the reinforcement of plastics, such as high impact polystyrene. Till the present time, polybutadiene made by alkyl-lithium catalyst is, for many chemical and technological reasons, still the undisputed rubber in the reinforced plastics applications industries. 

PBDEs are used in different resins, polymers, and substrates at levels ranging from 5 to 30% by weight (EU 2001). Plastic materials that utilize PBDEs as flame retardants include ABS polyacrylonitrile (PAN) polyamide(PA) polybutylene terephthalate (PBT) polyethylene (PE) cross-linked polyethylene (XPE) polyethylene terephthalate (PET) polypropylene (PP) polystyrene (PS) high-impact polystyrene (HIPS) polyvinyl chloride (PVC) polyurethane (PUR) and unsaturated polyester (UPE). These polymers and examples of their final products are summarized inTable 5-2 (Hardy 2002 WHO 1994a). 

B.J. Jody, B. Arman, D.E. Karvelas, J.A. Pomykala, Jr., and E.J. Daniels, Method for the separation of high impact polystyrene (HIPS) and acrylonitrile butadiene styrene (ABS) plastics, US Patent 5 653867, assigned to The University of Chicago (Chicago, IL), August 5,1997. 

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