High-impact polystyrene manufacture

The oxidative coupling of 2,6-dimethylphenol to yield poly(phenylene oxide) represents 90—95% of the consumption of 2,6-dimethylphenol (68). The oxidation with air is catalyzed by a copper—amine complex. The poly(phenylene oxide) derived from 2,6-dimethylphenol is blended with other polymers, primarily high impact polystyrene, and the resulting alloy is widely used in housings for business machines, electronic equipment and in the manufacture of automobiles (see Polyethers, aromatic). A minor use of 2,6-dimethylphenol involves its oxidative coupling to... 

This lower has a number of ramifications on the properties of polybutadiene. For example, at room temperature polybutadiene compounds generally have a higher resilience than similar natural rubber compounds. In turn this means that the polybutadiene rubbers have a lower heat build-up and this is important in tyre applications. On the other hand, these rubbers have poor tear resistance, poor tack and poor tensile strength. For this reason, the polybutadiene rubbers are seldom used on their own but more commonly in conjunction with other materials. For example, they are blended with natural rubber in the manufacture of truck tyres and, widely, with SBR in the manufacture of passenger car tyres. The rubbers are also widely used in the manufacture of high-impact polystyrene. 

In the late 1940s, the demand for styrene homopolymers (PS) and styrene-acrylonitrile copolymers (SAN) was drastically reduced due to their inherent brittleness. Thus, the interest was shifted to multiphase high-impact polystyrene (HIPS) and rubber-modified SAN (ABS). In principle, both HIPS and ABS can be manufactured by either bulk or emulsion techniques. However, in actual practice, HIPS is made only by the bulk process, whereas ABS is produced by both methods [132,133]. 

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. 

The phase relationships of two-phase polymer systems also have been of considerable interest in recent years. In an important series of papers, Molau and co-workers (19-24) studied systems, which were denoted POO emulsions (polymeric oil-in-oil), prepared by dissolving a given polymer in monomer and then polymerizing the monomer. During polymerizations of this type the composition of the respective phases reverses, and a phase inversion process was proposed to explain this. A similar process has been suggested as the mechanism by which poly-butadiene forms the dispersed phase in the manufacture of high-impact polystyrenes (22,25). Recently, Kruse has pointed out that this phase-inversion point may correspond to that point on a ternary phase diagram at which the reaction line bisects a tie line (26), and we have advanced a similar point of view in our earlier reports (17,18, 27). 

Expanded polystyrene (EPS) articles are made using high impact polystyrene formulations with incorporation of a blowing agent (this is usually a volatile solvent such as pentane). Often, EPS containers will have a crystal polystyrene skin applied to the food contact surface to act as a barrier between food and container. Applications of EPS include thermoformed packaging for eggs, meat, fish and fast food trays. Substances typically used in the manufacture of polystyrene are given in Table 10.3. 

Table 9-2 summarizes differences between polybutadiencs produced by different processes. The low c/i-content polybutadienes are branched. Tliey have lower solution viscosities than their linear counterparts and are preferred for manufacture of high impact polystyrene (HIPS) in which polymerization takes place in a solution of the elastomer in styrene. As the reaction proceeds under agitation, polystyrene becomes the continuous phase, with dispersed droplets of rubber (see Chapter 11). The high m-content, linear polybutadienes are more elastomeric... 

In the industrial field, this separation technique has been used for purposes as diverse as the analysis of odour and taste problems in high-density polyethylene [93], contaminants in recycled high-impact polystyrene [94], benzene residues in recycled polyethylene terephthalate [95] and denture adhesives [96], residual toluene in medical plasters [97], and lipstick (for assignation of products to manufacturers) [98,99]. 

Styrene and butadiene also form copolymers known as high impact polystyrene, or rubber-modified polystyrene, when the content of butadiene is 10%. This type of material has excellent mechanical properties, and it is widely used in practice for the manufacturing of numerous objects, including parts for household appliances, furniture, etc. Rubber-modified polystyrene is commonly used as wood replacement and also for packaging. The synthesis of this material typically is done by dissolving polybutadiene in styrene monomer, followed by free radical polymerization achieved using a peroxide catalyst. This procedure leads to block or graft type copolymers. 

Styrene is produced by the alkylation of benzene with ethylene followed by catalytic dehydrogenation. It is used in the manufacture of general-purpose and high-impact polystyrene plastics ( 50%), expanded polystyrene ( 7%), copolymer resins with acrylonitrile and butadiene ( 7%) or acrylonitrile only ( 1%), styrene-butadiene latex ( 6%) and synthetic rubber ( 5%), unsaturated polyester resins ( 6%), and as a chemical intermediate. 

High impact polystyrene (HIPS) is synthesized by emulsion polymerization of styrene in styrene-butadiene latex. The higher impact characteristics of HIPS make it suitable for use in the manufacture of sheets, food containers, window frames, household goods, etc. 

In general, high impact polystyrenes are multiphase systems consisting of a continuous rigid polystyrene phase and discrete rubber particles 0.5-lOjU in diameter. The incorporated rubber particles are crosslinked and contain grafted polystyrene, and their inner structure is determined by the manufacturing process and can vary considerably. The principle polystyrene structures have been described in detail (I, 2). 

A number of important commercial resins are manufactured by suspension polymerization, including poly(vinyl chloride) and copolymers, styrene resins [general purpose polystyrene, EPS, high impact polystyrene (HIPS), poly(styrene-acrylonitrile) (SAN), poly(acrylonitrile-butadiene-styrene) (ABS), styrenic ion-exchange resins], poly(methyl methacrylate) and copolymers, and poly(vinyl acetate). However, some of these polymers rather use a mass-suspension process, in which the polymerization starts as a bulk one and, at certain conversion, water and suspending agents are added to the reactor to form a suspension and continue the polymerization in this way up to high conversions. No continuous suspension polymerization process is known to be employed on a... 

As we said earlier, the introduction of aromatic units into the main chain results in polymers with better thermal stability than their aliphatic analogs. One such polymer is poly(phenylene oxide), PPO, which has many attractive properties, including high-impact strength, resistance to attack by mineral and organic acids, and low water absorption. It is used, usually blended with high-impact polystyrene (HIPS), to ease processability in the manufacture of machined parts and business machine enclosures. 

Polybutadiene Higher resilience than similar natural rubber compounds, good low-temperature behavior and adhesion to metals, but poor tear resistance, poor tack, and poor tensile strength Blends with natural rubber and SBR manufacture of high-impact polystyrene... 

MAJOR APPLICATIONS Automotive, business machine, and electrical/electronics industries. PPO is mainly used to manufacture blends with high-impact polystyrene (HIPS). PPO/nylon, PPO/PBT, and PPO/polyolefin blends are also available on the mcuket. PPO based materials rank first in terms of total consumption among blends based on engineering resins such as nylon, polycarbonate (PC), polyacetal, and reinforced terephthalate polyesters (PET and PBT).( ... 

The Canadian Polystyrene Recycling Association (CPRA), with a plant in Mississauga, ON, accepts polystyrene from all over Canada. Over 95 percent of its revenue comes from the sale of recycled resins, mostly black high-impact polystyrene (HIPS). The remainder comes from member companies, representing manufacturers, distributors, and end users of polystyrene products. The plant, which has a capacity of 5000 tonnes of PS per year, accepts both food-service PS and cushioning materials. While it uses mostly postconsumer materials as feedstock, it also accepts obsolete PS materials from manufacturers, such as scrap from sign manufacturing. ... 

Most of the current clarifiers are sorbitol derivatives. They include Great Lakes Clearlite NU 005, and Ciba s Irgaclear additives, some of which are now manufactured by Roquette in France, as well as NC-4 sorbitol acetal clarifiers supplied by Mitsui Toatsu Chemicals in Japan. One exception is Dover Chemical s Doverlube FL-599, a polyethylene glycol ester offered for clarifying polypropylene and also as a process aid for high impact polystyrene. 

This chapter describes the development and manufacture of the Thorn 1 IC 40 Model television-screen frame, sandwich moulded in high-impact polystyrene (HIPS) by Elco Plastics Ltd, Hemel Hempstead. The sandwich moulding (SM) process is described in some detail in PST 2 and comparisons are drawn with structural foams (SF) which share many common features with SM. 

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