Styrenic polymers applications

The heat distortion temperature of styrene polymers is insufficient for some applications, but can be improved by copolymerization with monomers such as -methylstyrene or maleic anhydride. Maleic anhydride copolymers are excellently suited to the manufacture of foamed articles. The advantages of glass-fiber reinforcement are greater in such copolymers than in polystyrene itself. 

Styrene acrylonitrile copolymer (SAN) copolymers have been commercially available since the 1940s. Due to their comparatively high price, initially they have been used in rather special applications. The history of styrenic polymers has been reviewed by various authors (1,2). 

Vanadyl phthalocyanine (7) is effective as a smoke reducer for various styrene polymers.31 Vanadyl sulfate, V0(S04)2, finds application in the production of water resistant polymer foams.32... 

Cobalt complexes find various applications as additives for polymers. Thus cobalt phthalocyanine acts as a smoke retardant for styrene polymers,31 and the same effect in poly(vinyl chloride) is achieved with Co(acac)2, Co(acac)3, Co203 and CoC03.5 Co(acac)2 in presence of triphenyl phosphite or tri(4-methyl-6- f-butylphenyl) phosphite has been found to act as an antioxidant for polyenes.29 Both cobalt acetate and cobalt naphthenate stabilize polyesters against degradation,73 and the cobalt complex of the benzoic acid derivative (12) (see Section 66.4) acts as an antioxidant for butadiene polymers.46 Stabilization of poly(vinyl chloride)-polybutadiene rubber blends against UV light is provided by cobalt dicyclohexyldithiophosphinate (19).74 Here again, the precise structure does not appear to be known. 

Styrenic polymer foams have been commercially accepted in a wide variety of applications since the 1940s [1,4]. The total usage of polystyrene foams in the United States rose from about 4.10 x 105 metric tons in 1982 to an estimated 5.35 x 105 metric tons in 1987. It is expected to grow at a rate of 3-4% for the next several years [5]. For example, a recent Fredonia report on foamed plastics estimates that the 2008 volume will be 10.77 x 105 metric tons [6]. 

Flame-retardant polystyrene is used primarily in expanded foam for building insulation. Rubber-modified styrenic polymers are flame retarded for use in a number of applications, such as enclosures for electronics and business equipment. By far the largest volume flame-retardant HIPS application is television enclosures (Figure 29.1) these are made primarily from flame-retardant HIPS [3]. Flame-retardant HIPS has an attractive balance of mechanical properties, processability and cost. Flame-retardant styrenic blends such as HIPS-PPO and PC-ABS also find utility in a number of electrical applications such as printers, computers and monitors. These blends have received increasing attention recently because of their ability to be flame retarded with nonhalogen flame retardants (see Section 7). 

Many tests and methods have been developed to study flammability, but only those which are important for flame-retardant styrenic polymers will be considered here. Some of these tests are regulatory requirements for specific applications, while others are more for research purposes. The flame retarding of styrenic polymers is often done to pass a specific test, and the formulation needed to pass one test may be completely different to that required for another test. 

Flame-retardant styrenic polymers find utility in applications such as building insulation (expanded polystyrene foam) and electronic enclosures (flame-retardant HIPS, ABS and styrenic blends). The most effective flame retardants are halogen-(particularly bromine)-containing compounds these flame retardants act by inhibiting the radical combustion reactions occurring in the vapor phase. Flame-retardant plastics are in a state of flux, due to influences of... 

Data have been published dealing with successful applications of HAS in stabilization of other polymers than PO elastomers, styrenic polymers, polyamides, polycarbonates, polyacetals, polyurethanes, linear polyesters, thermoplastic polyester elastomers, polyacrylates, epoxy resins, poly(phenylene oxide) or polysulfide [12]. In spite of their basicity, HAS may also be used for stabilization of PVC. This application includes less basic derivatives of piperidine and 1,4-dihydropyridine [12,13,145,146]. 

Antioxidants. Certain components of heat stabilizers (polyols, phosphites) also serve as antioxidants. The protection against oxidative attack is not as great in PVC as it is in certain ethylenically unsaturated materials. However, PVC compounds may require protection in the high-temperature service as in electrical wire insulation bisphenol A is often incorporated into the plasticizer for this purpose. Impact modifiers containing unsaturation such as acrylonitrile-butadiene-styrene polymers often require antioxidant protection. Hindered phenols such as butylated hydroxytoluene are often used for this purpose, especially when outdoor applications are involved. 

The area of application of Py—GC for identification is extensive. Its use is especially recommended for substances that are either difficult to identify by other techniques (e.g., insoluble polymers) or necessitate sophisticated and expensive instrumentation. The applications of Py-GC are steadily increasing we shall consider only those areas in which Py—GC has become a traditional technique, which include the analysis of polymers, drugs, biochemical substances and microorganisms. In addition to the work discussed above in connection with applying Py—GC for the identification of polymers, we may mention other studies. The identification of acrylate, methacrylate and styrene polymers and copolymers was described by McCormick [104]. Fischer and Meuser... 

Flammability ratings are required for certain electrical applications, such as the internal components of electronic devices. Flame retardancy can be imparted by blending an inherently flame retardant polymer such as PVC with one providing improved processability, such as a styrenic. Primary application areas are in business machine and appliance housings. 

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