Plastic foams, insulation material

A low (<0.4 W / (m-K)) thermal conductivity polymer, fabricated iato alow density foam consisting of a multitude of tiny closed ceUs, provides good thermal performance. CeUular plastic thermal insulation can be used in the 4—350 K temperature range. CeUular plastic materials have been developed in... 

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

Plastic Foam Materials and Koofinginsulation, 1983—1989, Peter Sherwood Associates, Inc., White Plaias, N.Y., Apr. 1984 KoofingJ Siding Insul 61, 82 (Oct. 1984). 

Extruded Rigid Foa.m. In addition to low temperature thermal insulation, foamed PSs are used for insulation against ambient temperatures in the form of perimeter insulation and insulation under floors and in walls and roofs. The upside-down roof system has been patented (256), in which foamed plastic such as Styrofoam (Dow) plastic foam is appHed above the tar-paper vapor seal, thereby protecting the tar paper from extreme thermal stresses that cause cracking. The foam is covered with gravel or some other wear-resistant topping (see Roofing materials). 

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

Container Insulation Tanks containing materials above atmospheric temperature may require insulation to reduce loss of heat. Almost any of the commonly used insulating materials can be employed. Calcium silicate, glass fiber, mineral wool, cellular glass, and plastic foams are among those used. Tanks exposed to weather must have jackets or protective coatings, usually asphalt, to keep water out of the insulation. 

At very low temperatures with hquid air and similar substances, the tank may have double walls with the interspace evacuated. The weh-known Dewar flask is an example. Large tanks and even pipe hues are now built this way. An alternative is to use double walls without vacuum but with an insulating material in the interspace. Perlite and plastic foams are two insulating materials employed in this way. Sometimes both insulation and vacuum are used. 

Cables with multiple-layer sheathing have plastic-insulated cores. Solid PE or sintered PE is used as the plastic. Sintered PE is a foamed polyethylene material that has different electrical properties than solid PE. Under certain circumstances the core region is filled with a petrolatum material to give protection against... 

Plastic also refers to a material that has a physical characteristic such as plasticity and toughness. The general term commodity plastic, engineering plastic, advanced plastic, advanced reinforced plastic, or advanced plastic composite is used to indicate different performance materials. These terms and others will be reviewed latter in this chapter. Plastics are made into specialty products that have developed into major markets. An example is plastic foams that can provide flexibility to rigidity as well as other desired properties (heat and electrical insulation, toughness, filtration, etc.). 

Epoxy resins find a large number of uses because of their remarkable chemical resistance and good adhesion. Epoxy resins are excellent structural adhesives. When properly cured, epoxy resins can yield very tough materials. They are used in industrial floorings, foams, potting materials for electrical insulations, etc. One of the principal constituents in many of the Fibre-reinforced plastics (FRP) is an epoxy polymer. 

On the contrary, a beneficial aspect of the low heat conductivity is the possibility to apply plastics as thermally insulating materials, in particular as foams. The heat conduction of a polymer foam is composed of four components ... 

In terms of fire safety, there are no fire resistance requirements and all interior surfaces must comply with the FSI of 200 in the Steiner tunnel test, ASTM E 84,114 or a radiant panel index of 200 in the radiant panel test, ASTM E 162.55 Thermal insulation materials, other than foam plastics, must meet an ASTM E 84 Class A requirement (i.e., FSI < 25 and SDI < 450) and loose-fill insulation must meet the same requirements as the building codes, which are mostly based on smoldering tests (as the materials tend to be cellulosic). Foam plastic insulation must be treated as in the building codes as well (see Table 21.13) it cannot be used exposed (expensive foam that meets the NFPA 286 test is not used in manufactured housing) and must meet an ASTM E 84 Class B requirement behind the thermal barrier. 

The thermal conductivities of various commercial insulating materials are given in Table 10.7. Plastic foams containing a captive blowing agent have much lower thermal conductivities than other insulating materials. 

The most suitable containers for cooling baths are plastic bowls (ice baths), Pyrex dishes (solid CO2 baths) and Dewar flasks (solid CO2 and liquid nitrogen baths). If Pyrex dishes are to be used below —20 °C, an insulated container can be prepared by placing a smaller Pyrex dish inside a larger one and filling the space between with an insulating material such as cotton wool, cork chips or polyurethane foam chips. Remember that foam chips will dissolve if they come into contact with many organic solvents. 

For practical calculations of durability and for the determination of application conditions it should be taken into account that these materials are composed of a three-phase structure (gas - solid - liquid). A certain amount of a liquid phase, due to the condensation of water vapor in the air, is practically always present inside plastic foams. The presence of the liquid phase plays a decisive role in mass, gas and heat transfer and sharply reduces the heat and electrical insulation properties of polymeric foams (see Chap. 6). 

Moisture absorptfon of plastic foams is closely connected with cell properties, including thermal insulation properties. Investigation of heat insulation of plastic foams containing a liquid phase helps to elucidate the mechanisms of moisture and mass transfer as weU as of heat transfer in gas-filled materials. 

---