Polystyrene expandable

The process involves two major steps. The first consists of a preexpansion of the virgin beads by heat (steam, hot air, radiant heat, or hot water). Steam is the most used medium as it is the most practical and most economical. 

An outstanding property of EPS is its extremely low density (when compared to other processes), that by alteration of the preforming treatment can be varied according to the end use. Other types of plastics are employed to produce expandable plastic foam (EPF), including PE, PP, PMMA, and ethylene-styrene copolymers. They can use the same equipment, with only slight modifications. These plastics have different properties from those of EPS and open up different markets. They provide improved sound insulation, resistances to additional heat deformation, better recovery of shapes in moldings, and so on. 

This time disadvantage is avoided in the discontinuous unit, where within certain limits the change is made directly. Equipment manufacturers provide units with different capabilities based on production needs. 

Sophisticated control systems are available to manage existing variables. They are needed to handle rapid tooling changes, withdrawal and stacking devices, interactive control systems, and vacuum cooling incorporating steam condensers and/or a central vacuum system. 

The most reliable method for filling cavities has been to use a filling gun operating on an injector principle. A method gaining popularity uses compressed air in the hopper. Of the two approaches, the injector method provides a lower capital cost, smaller air requirement, and lower material unit cost, whereas compressed air provides a significant shorter fill time. 

Cooling by means of a controlled quantity of water and consolidation under vacuum using condensers now represents the state of the art. With rapid tool-changing systems, the changeover time can be reduced from the usual 1 to 2 h to 15 to 20 min. Another important means of reducing the processing cost is the use of devices that remove parts from the mold and stack them. 

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Other Plastics Uses. The plasticizer range alcohols have a number of other uses in plastics hexanol and 2-ethylhexanol are used as part of the catalyst system in the polymerization of acrylates, ethylene, and propylene (55) the peroxydicarbonate of 2-ethylhexanol is utilized as a polymerization initiator for vinyl chloride various trialkyl phosphites find usage as heat and light stabHizers for plastics organotin derivatives are used as heat stabHizers for PVC octanol improves the compatibHity of calcium carbonate filler in various plastics 2-ethylhexanol is used to make expanded polystyrene beads (56) and acrylate esters serve as pressure sensitive adhesives. 

Polystyrene. There are two types of expandable polystyrene processes expandable polystyrene for molded articles and expandable polystyrene for loose-fill packing materials. 

Fig. 3. Effect of density on compressive modulus of rigid cellular polymers. A, extmded polystyrene (131) B, expanded polystyrene (150) C-1, C-2, polyether polyurethane (151) D, phenol—formaldehyde (150) E, ebonite (150) E, urea—formaldehyde (150) G, poly(vinylchloride) (152). To convert...

The insulating value and mechanical properties of rigid plastic foams have led to the development of several novel methods of buUding constmction. Polyurethane foam panels may be used as unit stmctural components (220) and expanded polystyrene is employed as a concrete base in thin-sheU constmction (221). 

CeUular urea—formaldehyde and phenoHc resin foams have been used to some extent in interior sound-absorbing panels and, in Europe, expanded polystyrene has been used in the design of sound-absorbing doors (233). In general, cost, dammabUity, and cleaning difficulties have prevented significant penetration of the acoustical tile market. The low percent of redection of sound waves from plastic foam surfaces has led to their use in anechoic chambers (216). 

Economics. Rigid foam systems are typically in the range of 32 kg/m (2 Ibs/fT) and, in 1992, had a foam price of about 3.63/kg ( 1.65 per lb) with hquid foam systems at about 2.75/kg. Unit prices for pour-ia-place polyurethane packaging systems fall between the competitive expandable polystyrene bead foam at 3.30/kg and low density polyethylene foams at 5.80/kg. 

There are five basic types of polystyrene foams produced in a wide range of densities and employed in a wide variety of apphcations (/) extmded polystyrene board (2) extmded polystyrene sheet (2) expanded bead mol ding (4) injection molded stmctural foam and (5) expanded polystyrene loose-fiU packaging. 

Expanded polystyrene bead mol ding products account for the largest portion of the drinking cup market and are used in fabricating a variety of other products including packaging materials, iasulation board, and ice chests. The iasulation value, the moisture resistance, and physical properties are inferior to extmded boardstock, but the material cost is much less. 

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. 

Initiators (1) and (2) have 10-h half-life tempeiatuies of 237°C and 201°C, respectively. It has been reported that, unlike organic peroxides and ahphatic azo compounds, carbon—carbon initiators (1) and (2) undergo endothermic decompositions (62). These carbon—carbon initiators are useful commercially as fire-retardant synergists in fire-resistant expandable polystyrenes (63). 

Styrene [100-42-5] (phenylethene, viaylben2ene, phenylethylene, styrol, cinnamene), CgH5CH=CH2, is the simplest and by far the most important member of a series of aromatic monomers. Also known commercially as styrene monomer (SM), styrene is produced in large quantities for polymerization. It is a versatile monomer extensively used for the manufacture of plastics, including crystalline polystyrene, mbber-modifted impact polystyrene, expandable polystyrene, acrylonitrile—butadiene—styrene copolymer (ABS), styrene—acrylonitrile resins (SAN), styrene—butadiene latex, styrene—butadiene mbber (qv) (SBR), and unsaturated polyester resins (see Acrylonithile polya rs Styrene plastics). 

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. 

Roofiag panels have been made from polyisocyanurate foams, both foam- and felt-reiaforced with glass fiber. PhenoHc resias are used especially for decorative laminates for paneling. The substrate may be fiberboard or a core of expanded polystyrene beads. In one case the beads are coated with phenoHc resia, then expanded ia a mold to form a stmctural foam panel. 

In another appHcation expanded polystyrene foam panels, 1.2 x 2.4 m, are faced with a wire mesh and mounted ia a metal channel bolted to a coacrete slab. These panels are then sprayed on both sides with plaster, which is anchored to the wire mesh and forms the iaterior and exterior surfaces. Roof and iaterior partitioas provide low cost housiag for mild climates. 

The foams, marketed by Rohm as Rohacell, are stable at room temperature to hydrocarbons, ketones, chlorinated solvents and 10% sulphuric acid. They may be used under load at temperature up to 160°C. Uses quoted for these materials include bus engine covers, aircraft landing gear doors, radar domes, domes, ski cores and tennis racket cores. Their potential is in applications demanding a level of heat deformation resistance, solvent resistance and stiffness not exhibited by more well-known cellular polymers such as expanded polystyrene and the polyurethane foams. 

Polystyrene is now available in certain forms in which the properties of the product are distinctly different from those of the parent polymer. Of these by far the most important is expanded polystyrene, an extremely valuable insulating material now available in densities as low as 1 Ib/ft (16kg/m ). A number of processes have been described in the literature for the manufacture of the cellular product of which four are of particular interest in the manufacture of large slabs. 

One alternative approach to the two-stage steam moulding process is that in which impregnated beads are fed directly to an injection moulding machine or extruder so that expansion and consolidation occur simultaneously. This approach has been used to produce expanded polystyrene sheet and paper by a tubular process reminiscent of that used with polyethylene. Bubble nucleating... 

Nearly all the expanded polystyrene that is not used for thermal insulation is used for packaging. Uses range from individually designed box interiors for packing delicate equipment such as cameras and electronic equipment, thermoformed egg-boxes to individual beads (which may be up to 5 cm long and about 1 cm in diameter) for use as a loose fill material. There is also some use of thin-wall containers for short-term packaging and conveying of hot food from... 

Expanded polystyrene accounts for over 20% of the weight consumption of polystyrene and high-impact polystyrene. The volume of expanded material produced annually exceeds even the volume production of the aliphatic polyolefins. 

Except where the foam is surrounded by a skin of relatively impermeable material, it would be expected that the blowing gas would diffuse out and be replaced by air and that the thermal conductivities of the foams would increase until they approached that of expanded polystyrene of similar density. Whilst this... 

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