Construction plastic foam

Uses. Plastics and synthetic rubber are the major uses for styrene. They account for the exponential growth from a few million pounds per year in 1938 to more than 8 billion pounds today. The numerous plastics include polystyrene, styrenated polyesters, acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile (SAN), and styrene-butadiene (SB). Styrene-butadiene rubber (SBR) was a landmark chemical achievement when it was comrner-cialized during World War II. The styrene derivatives are found everywhere—in food-grade film, coys, construction pipe, foam, boats, latex paints, tires, luggage, and furniture. 

Moisture. Absorbed and retained moisture, especially as ice, has a significant effect on the structural and thermal properties of insulation materials. Most closed-cell plastic foams have low permeance properties most notably where natural or bonded low permeance surface skins exist (29,30). Design, building, and construction practices require adequate vapor retarders, skins, coatings, sealants, etc, in order to prevent the presence of moisture. However, moisture vapor cannot be completely excluded, thus the possibility of moisture absorption and retention is always present. The freezing of moisture and rupturing of cells result in permanent reduction of thermal and structural performance. 

The insulating value and mechanical properties of rigid plastic foams have led to the development of several novel methods of building construction, including polyurethane foam panels as unit structural components [95] and expanded polystyrene as a concrete base in thin-shell construction [96]. 

In the last decade several novel types of gas-filled polymers appeared which belong to the second generation integral (structural) plastic foams syntactic foams reinforced polymer foams multilayer foams (foamed laminates), metallized plastic foams mineral and metallic foamed materials obtained on the basis of foamed polymers laminated constructions on the basis of foamed polymers and monolithic (unfoamed) plastics, metals, paper, leather, etc. 

Aleksandrov, A. Ya., Borodin, M. Ya., Pavlov, V. V. Constructions with plastic foam fillers. Moscow, Mashinostroenie 1972 (in Russian)... 

A 2.54-cm Styrofoam plastic foam with thermal conductivity of ca 0.03 W/(mK) (0.21 (Btuin.)/(fth°F)) is equivalent to 61 cm of gravel. Any synthetic foam having compressive strength sufficiently high and thermal conductivity sufficiently low is effective. However, the resistance of PS-type foams to water, frost damage, and microorganisms in the soil makes them especially desirable. An interesting and important application of this concept was the use of Styrofoam in the construction of the Alaska pipeline. In this case, the foam was used to protect the permafrost. 

The majority of plastics foams are not applied on their own, but rather as parts of more complex constructions. For this reason, testing the individual expanded plastics elements is not satisfactory without corresponding examinations involving the foam-containing complete constructions in full-scale fire tests. 

The demand for foamed plastics is driven by the desire for (a) weight reduction, (b) improved thermal insulation and (c) lower part costs. The size of the global plastic foam market was estimated in 2002 as 6.8 M tonnes/year (of which the US share was approximately half), growing at 3% a year, with more rapid growth in insulating foam for the construction industry. Because of the obviously low density of foams, consumption expressed in terms of tonnage fails to convey the high volmne of product sold. 

To separate the fibers from the debris, a device utilizing air currents was constructed from foam core and fiberglass screen. Fiberglass insect screening was stapled to the bottom of 0.48 cm-thick foam core frames that were 30.5 x 30.5 cm in size. Two such frames with screens were constructed and stacked, with one frame and screen on top of the other. A cylindrical piece of plastic, 40.6 cm in length and 20.3 cm in diameter and open on both ends, was fashioned from a plastic bag. This piece was secured to the top screen with duct tape so that the cylinder projected above the frame. The fiber and debris mix was placed in the plastic cylinder. Another piece of plastic, similar to that used to create the inner cylinder, was used to cover the cylinder and extend above it by 61 cm. This enclosure was... 

Electrical Properties. Cellular polymers have two important electrical applications (16). One takes advantage of the combination of inherent toughness and moisture resistance of polymers along with the decreased dielectric constant and dissipation factor of the foamed state to use cellular polymers as electrical-wire insulation (94). The other combines the low dissipation factor and the rigidity of plastic foams in the construction of radar domes. Polyurethane foams have been used as high voltage electrical insulation (221). 

For obtaining a low -weight, high-bending-stiffness structure, sandwich constructions are a conunon choice for composite components. To make a sandwich, low-density materials are inserted as sandwich cores between two faces of the structural material itself (so in this case between two stacks of prepreg plies). Commonly used core materials are plastic foams (for example, made from PVC, PS, or PET) and balsa wood. Examples of core materials for more sophisticated, structured sandwich cores are honeycombs (made from aluminium, or resin-impregnated paper sheets), or fibre-reinforced foams. 

Highly combustible materials, such as flammable liquids, paints or plastic foams, ignite very easily and quickly produce large quantities of heat and/or dense toxic smoke. Such materials should be stored outside buildings under construction in secure storage areas. 

Figure 1-22. The RP sandwich wing of the BT-15. Sandwich construction of glass-fiber-TS polyester skins with cellular cellulose plastic foam core was used in different processes including that of the lost-wax technique.

However, the majority of sandwich panels now utilise a honeycomb core rather than either balsa wood or plastic foam the adhesive can be based on either thermosetting or thermoplastic chemistries. The three basic components used in honeycomb sandwich construction are discussed below. 

Commercial Construction. The same attributes desirable on residential constmction appHcations hold for commercial constmction as weU but insulation quaHty, permanence, moisture insensitivity, and resistance to free2e—thaw cycling in the presence of water are of greater significance. For this reason ceUular plastics have greater appHcation here. Both polystyrene and polyurethane foams are highly desirable roof insulations in commercial as in residential constmction. 

They range from structural foam molded products (which come from the mold as completed molded products) incorporating low density cores and high density skins of the same materials to products vacuum formed of a plastics material, the core of which becomes cellular during the heating process (Chapter 8). RP translucent structural panels for curtain wall building construction using... 

The other approach to the reduction of the power loss to the dielectric material is by reducing the amount used. This is done by replacing part of the dielectric by air, an inert gas, or by vacuum. As examples there are three cable constructions in common use which employ these approaches to minimize dielectric loss. The first is the use of a foamed dielectric PS plastic that is commonly used in either twin lead transmission lines or in coaxial cables used for antenna lead-in wires in the UHF-TV antenna applications. The second system, which is illustrative of several sectional spacers, is used widely in communications cables of the coaxial type to minimize losses to the dielectric by reducing the amount of dielectric material in the cable. 

Finally, for practical reasons it is useful to classify polymeric materials according to where and how they are employed. A common subdivision is that into structural polymers and functional polymers. Structural polymers are characterized by - and are used because of - their good mechanical, thermal, and chemical properties. Hence, they are primarily used as construction materials in addition to or in place of metals, ceramics, or wood in applications like plastics, fibers, films, elastomers, foams, paints, and adhesives. Functional polymers, in contrast, have completely different property profiles, for example, special electrical, optical, or biological properties. They can assume specific chemical or physical functions in devices for microelectronic, biomedical applications, analytics, synthesis, cosmetics, or hygiene. 

Foams. Sulfur can be foamed into a lightweight insulation that compares favorably with many oiganic foams and other insulating materials used in construction. It has been evaluated as thermal insulation for highways and other applications to prevent frost damage (63) (see Foamed PLASTICS Insulation, thermal). 

Thermal Insulation. Foamed plastics (qv) are used as thermal insulation for all types of construction 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 structural surfacing material, eg, a kraft liner-board, to form a panel for insulating mobile homes. These foams can duplicate 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. 

Because of low injection pressure, some cost savings are possible in mold and press construction. Molding cycles are somewhat longer than for injection molding. The part must be cooled in the mold long enough to be able to resist swelling from internal gas pressure. In structural foam parts there is almost a total absence of sink marks, even in the case of unequal section thickness. Structural foam has replaced wood, concrete, solid plastics, and metals in a variety of applications. 

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