Polystyrene thermal

Table 10.1 Physical properties of commercial extruded polystyrene foams ASTM C578 - Standard for Rigid, Cellular Polystyrene Thermal Insulation... 

ASTM C S78-87a Standard Specification for Preformed, Cellular Polystyrene Thermal Insulation, 7 pp (DOD Adopted) (FSC 5640) (YD) (Comm C-16)... 

The list of compounds generated in polystyrene thermal decomposition shown in Table 6.2.2 do not include char and hydrogen. However, both char (mostly carbon) as well as hydrogen result in polystyrene pyrolysis, mainly at higher temperatures and at high heating rates [6]. 

Polystyrene - Thermal degradation is the simplest of the current techniques used to recover feedstock chemicals from styrene-based polymers and has therefore been studied extensively. Investigations of the product distributions from thermal degradation of polystyrene have mainly focused on liquid products. It has been observed that the yield and the composition of liquid products vary strongly with temperature and the reactor configuration,... 

Any polystyrene thermal insulation found should not be in contact with the cables as PVC is adversely affected by it. 

Vittoria, V., Ruvolo Filho, A., de Candia, F. Structure of syndiotactic polystyrene thermally crystallized from the glassy state. J. Macromol. Sci Phys., B29(4), 411 28 (1990). 

Styrene—acrylonitrile (SAN) copolymers [9003-54-7] have superior properties to polystyrene in the areas of toughness, rigidity, and chemical and thermal resistance (2), and, consequendy, many commercial appHcations for them have developed. These optically clear materials containing between 15 and 35% AN can be readily processed by extmsion and injection mol ding, but they lack real impact resistance. 

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). 

Coefficient of Linear Thermal Expansion. The coefficients of linear thermal expansion of polymers are higher than those for most rigid materials at ambient temperatures because of the supercooled-liquid nature of the polymeric state, and this applies to the cellular state as well. Variation of this property with density and temperature has been reported for polystyrene foams (202) and for foams in general (22). When cellular polymers are used as components of large stmctures, the coefficient of thermal expansion must be considered carefully because of its magnitude compared with those of most nonpolymeric stmctural materials (203). 

In a study (206) of the moisture gain of foamed plastic roof insulations under controlled thermal gradients the apparent permeabiUty values were greater than those predicted by regular wet-cup permeabiUty measurements. The moisture gains found in polyurethane are greater than those of bead polystyrene and much greater than those of extmded polystyrene. 

Steam-Chest Expansion. In steam-chest expansion the resin beads in which gas is already present are poured into molds into which steam is injected. The steam increases the temperature close to the melting point and expands within the stmcture to create beads with food cushioning and insulating properties. Expanded polystyrene is widely used in this process for thermal insulation of frozen food packaging. 

Cross-linked macromolecular gels have been prepared by Eriedel-Crafts cross-linking of polystyrene with a dihaloaromatic compound, or Eriedel-Crafts cross-linking of styrene—chloroalkyl styrene copolymers. These polymers in their sulfonated form have found use as thermal stabilizers, especially for use in drilling fluids (193). Cross-linking polymers with good heat resistance were also prepared by Eriedel-Crafts reaction of diacid haUdes with haloaryl ethers (194). 

A variety of cellular plastics exists for use as thermal iasulation as basic materials and products, or as thermal iasulation systems ia combination with other materials (see Foamed plastics). Polystyrenes, polyisocyanurates (which include polyurethanes), and phenoHcs are most commonly available for general use, however, there is increasing use of other types including polyethylenes, polyimides, melamines, and poly(vinyl chlorides) for specific appHcations. 

Fig. 3. Aging effect on thermal conductivity of cellular plastics A, extmded polystyrene B, unfaced polyurethane C, unfaced phenolic and D, polyurethane...

Polyurethane, PVC, and extruded polystyrene provide the bulk of the cellular plastics used for low and cryogenic temperature appHcations. In some cases, eg, the insulation of Hquid hydrogen tanks on space systems, foams have been reinforced with continuous glass fibers throughout the matrix. This improves strength without affecting thermal performance significantly. 

Alkanolamines can also be used to improve thermal stabiUty in PVC copolymers and polystyrene. 

In modem PMR constmction, thermal iasulation that is unaffected by water or that can be kept dry ia some manner is required. Extmded polystyrene (XEPS) foam iasulation boards ate commonly employed (see Insulation, thermal). They ate placed on top of the waterproofing roof membrane, which is next to the deck. The iasulation should not be adhered to the membrane. Ballast at the rate of >48.8 kg/m (1000 lb/100 ft ) holds the iasulation ia place and offers protection from the sun. The iasulation joiats ate open and drainage must be provided. Various other materials, eg, patio blocks and concrete slabs, ate also used as sutfaciags and ballast. The extra weight imposes mote exacting requirements on constmction. 

Styrene is a colorless Hquid with an aromatic odor. Important physical properties of styrene are shown in Table 1 (1). Styrene is infinitely soluble in acetone, carbon tetrachloride, benzene, ether, / -heptane, and ethanol. Nearly all of the commercial styrene is consumed in polymerization and copolymerization processes. Common methods in plastics technology such as mass, suspension, solution, and emulsion polymerization can be used to manufacture polystyrene and styrene copolymers with different physical characteristics, but processes relating to the first two methods account for most of the styrene polymers currendy (ca 1996) being manufactured (2—8). Polymerization generally takes place by free-radical reactions initiated thermally or catalyticaHy. Polymerization occurs slowly even at ambient temperatures. It can be retarded by inhibitors. 

Polystyrene (PS). Common appHcations include packaging, food containers, and disposable tableware toys furniture, appHances, television cabinets, and sports goods and audio and video cassettes. For some of these appHcations, PS is modified by blending or graft polymerization with SBR to form impact polystyrene, which is less sensitive to breakage. Expandable polystyrene is widely used in constmction for thermal insulation. 

General-Purpose Polystyrene. Polystyrene is a high molecular weight M = 2 — 3 x 10 ), crystal-clear thermoplastic that is hard, rigid, and free of odor and taste. Its ease of heat fabrication, thermal stabiUty, low specific gravity, and low cost result in mol dings, extmsions, and films of very low unit cost. In addition, PS materials have excellent thermal and electrical properties that make them useful as low cost insulating materials (see Insulation, ELECTRIC Insulation, thermal). 

Polyurethane. Polyurethanes (pu) are predominantly thermosets. The preparation processes for polyurethane foams have several steps (see Urethane polymers) and many variations that lead to products of widely differing properties. Polyurethane foams can have quite low thermal conductivity values, among the lowest of all types of thermal insulation, and have replaced polystyrene and glass fiber as insulation in refrigeration. The sprayed-on foam can be appHed to walls, roofs, tanks, and pipes, and between walls or surfacing materials directly. The slabs can be used as insulation in the usual ways. 

Thermal Insulation. Foamed plastics (qv) are used as thermal insulation for aU types of constmction because of their low heat- and moisture-transmission values. Polystyrene is used either as foamed board or expandable beads. The foam may be faced with a stmctural surfacing material, eg, a kraft liner-board, to form a panel for insulating mobile homes. These foams can dupHcate the appearance of wood and be used as trim. Foams can also be used as backing, for example, on aluminum siding, to provide heat and sound insulation. Foamed beads can be incorporated in concrete to reduce its density and provide some thermal insulation. 

Foams have limited use for these purposes. Rigid cellular PVC is good as a thermal barrier but aot for stmctural parts. Doors and frames of stmctural molded foam, eg, foamed high impact polystyrene, can be made by iajection mol ding, with recesses for hinges, striker plates, and miter corners. Sohd polystyrene and stmctural foam-molded polyurethane have been molded for door frames. 

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