Polystyrene, production

Eoamed polystyrene sheet has exceUent strength, thermal resistance, formabUity, and shock resistance, as weU as low density. It is widely known for its use in beverage cups, food containers, building insulation panels, and shock absorbent packaging. Polystyrene products can be recycled if suitable coUection methods are estabUshed. Eoamed polystyrene sheet can also be easily therm oformed (see Styrene plastics). 

World polystyrene production in 1997 was approximately 10 million tons. The demand is forecasted to reach 13 million tons by 2002. The 1997 U.S. production of polystyrene polymers and copolymers was approximately 6.6 billion pounds. ABS, SAN, and other styrene copolymers were approximately 3 billion pounds for the same year. 

Alkanesulfonates are an important internal antistatic agent for polystyrene (PS) as well. If it is not possible to apply the pure active surfactant with the intended processing machine, the use of a master batch of alkanesulfonates and an appropriate polystyrene product is recommended. The addition of alkanesulfonates in amounts greater than 0.3 phr can cause hazing also in transparent PS articles. The antistatic effect of alkanesulfonates in PS is demonstrated in Fig. 41. 

Vinyl polystyrene, production from (toluenesulfoxyethyl) polystyrene, 30 Vinyl units, protective effect in 1,4- and 1,2-polybutadienes, 351... 

The majority of commercial polystyrene molecules consist of a backbone of carbon atoms with phenyl groups attached to half of the carbon atoms, as shown in Fig. 21.1. Free radical initiator residues terminate each end of the chain. Minor variants include chains terminated by anionic or cationic initiator residues. All commercial polystyrene products are atactic that is, the placement of the phenyl groups on either side of the chain is essentially random, as illustrated in Fig. 21.2. 

Another successful development was based on morphological studies of traditional impact-resistant polystyrenes. Products with unusually big particles and a certain combination of composition and properties are particularly resistant to stress cracking (84). They have achieved considerable success on the... 

Copolymerization allows the synthesis of an almost unlimited number of different products by variations in the nature and relative amounts of the two monomer units in the copolymer product. A prime example of the versatility of the copolymerization process is the case of polystyrene. More than 11 billion pounds per year of polystyrene products are produced annually in the United States. Only about one-third of the total is styrene homopolymer. Polystyrene is a brittle plastic with low impact strength and low solvent resistance (Sec. 3-14b). Copolymerization as well as blending greatly increase the usefulness of polystyrene. Styrene copolymers and blends of copolymers are useful not only as plastics but also as elastomers. Thus copolymerization of styrene with acrylonitrile leads to increased impact and solvent resistance, while copolymerization with 1,3-butadiene leads to elastomeric properties. Combinations of styrene, acrylonitrile, and 1,3-butadiene improve all three properties simultaneously. This and other technological applications of copolymerization are discussed further in Sec. 6-8. 

Most polystyrene products are not homopolystyrene since the latter is relatively brittle with low impact and solvent resistance (Secs. 3-14b, 6-la). Various combinations of copolymerization and blending are used to improve the properties of polystyrene [Moore, 1989]. Copolymerization of styrene with 1,3-butadiene imparts sufficient flexibility to yield elastomeric products [styrene-1,3-butadiene rubbers (SBR)]. Most SBR rubbers (trade names Buna, GR-S, Philprene) are about 25% styrene-75% 1,3-butadiene copolymer produced by emulsion polymerization some are produced by anionic polymerization. About 2 billion pounds per year are produced in the United States. SBR is similar to natural rubber in tensile strength, has somewhat better ozone resistance and weatherability but has poorer resilience and greater heat buildup. SBR can be blended with oil (referred to as oil-extended SBR) to lower raw material costs without excessive loss of physical properties. SBR is also blended with other polymers to combine properties. The major use for SBR is in tires. Other uses include belting, hose, molded and extruded goods, flooring, shoe soles, coated fabrics, and electrical insulation. 

In 2005, Japanese company Kaneka developed the first beads-process, foamed resin moulded product, which is based on polylactic acid. The new KanePearl product has the strength and shock-absorbing properties of existing beads-process, foamed polystyrene products. 

Encouraging results on the bonding of plastics to wood using tailor-made cellulose-polystyrene graft polymers as compatibilizers or interfacial agents may offer a new approach to the engineering of wood-plastic products with improved mechanical and physical properties for a variety of applications. It also holds the potential of opening up new markets for renewable resources in the form of woody materials. For example, polystyrene production is currently 3.9 billion... 

The GPPS and HIPS reactor sections each contain several polymerization reactors in series, two-stage devolatilization and a pelletizing line. The devolatilization equipment is designed to deliver polystyrene product with a concentration of residual total volatile material (TVM) of less than 100 wt-ppm. Common equipment includes sections for feed preparation, SM recovery, water removal and bulk-resin handling. 

Blowing agents-such as hydrazine, which forms nitrogen gas on decomposition-are used to produce porous plastics like these polystyrene products. 

Although there are clearly some specific advantages with the wiped film evaporators, they have not been widely applied for commercial polystyrene production. Reasons for this are most likely the high equipment and maintenance costs associated with these types of units. 

Probably no part of the polystyrene production plant has changed as much over the last 30 years as the methods of process control. The early polystyrene processes required little process control because they were operated at reaction rates that were inherently stable. For polystyrene, a rule of thumb is that the reaction rate doubles with every increase in temperature of 10 °C. If the reaction is conducted at rates that evolve heat at a rate that requires a temperature... 

The success of obtaining polystyrene products by free radical processes is affected to a significant extent by the quality and performance of initiators. Monofunctional initiators such as benzoyl peroxide or azobisisobutyronitrile have been utilized in bulk and solution polymerizations for theoretical studies... 

SPEEDING UP THE RATE OF POLYSTYRENE PRODUCTION USING CHEMICAL INITIATORS... 

The inverse relationship between rate and MW traditionally presents a problem for the economic production of high MW polystyrene products owing to their slow production rates. The production rate of high MW products is generally increased by the use of peroxides. The addition of a simple monofunctional peroxide such as tert-butyl perbenzoate results in about a 15 % production rate increase over the use of auto-initiation. The use of difunctional peresters [2] and perketals [3] results in >30% rate increases over auto-initiation. However, these... 

Another type of initiator that has been evaluated for increasing polystyrene production rates are the multifunctional peroxides. Examples include 2,2-bis [4,4-bis(tert-butylperoxy)cyclohexyl]propane (I) [9], peroxyfumaric acid, 0,0-te/Y-butyl O-butyl ester (II) [10], ter t-butyl peritaconate (III) [11], and poly (monopercarbonates) (IV) (Figure 7.4) [12]. Although all of these initiators indeed show extremely fast production rates of high MW polystyrene, they all suffer from a flaw, i.e. the polystyrene produced is branched and special precautions must be taken to keep the continuous bulk polymerization reactors from fouling [13]. This is likely why none are currently used commercially for polystyrene manufacture. 

The commercial manufacture of polystyrene was batch mode through the 1930s and 1940s, with a gradual transition to continuous bulk polymerization beginning in the 1950s. Suspension polymerization was a common early polystyrene production process, where a single reactor produced a polymer slurry that had to be separated from the water and dried. This process was ideal for free radical... 

Table 31.3 Contents of styrene dimers and trimers in polystyrene products [4]". Reproduced by permission of the Food Hygiene Society of Japan... 

Table 31.5 Migration of styrene dimers and trimers from polystyrene products [A a h... 

Ongoing advances in new catalyst technology and controlled radical polymerisation will undoubtedly yield new styrenic polymers with well-defined architecture (as we have recently seen with the introduction of syndiotactic PS and ethylene-styrene interpolymers). Advances in the synthesis of dendritic and hyperbranched styrenic polymers will also contribute to the state of new polystyrenic products. 

Decomposition according to both previous schemes combined (PS, PIB). In a polystyrene production plant, PS could conveniently be converted into monomer, since facilities for separating the various pyrolysis products (styrene and its oligomers, ethylbenzene, toluene, benzene, etc.) are available already on site. However, huge PS production plants generally generate insufficient off-spec, scrap to feed a pyrolysis unit of even a small industrial size ... 

Styrene copolymer with divinylbenzene is used frequently in many polystyrene products, and the similarity between the two comonomers makes this copolymer almost identifiable with the homopolymer itself. In terms of production volume, styrene copolymer with butadiene is probably the most important copolymer (SBR). Depending on the butadiene/styrene ratio, the copolymer is used as an elastomer with large applications in the tire industry, in the manufacturing of conveyor belts, etc. when butadiene/styrene ratio is 75/25 parts wt., or when butadiene/styrene ratio is 40/60 parts... 

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