Plastic foams moisture resistance

Electrical Properties. CeUular polymers have two important electrical appHcations (22). 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 ceUular polymers as electrical-wire insulation (97). The other combines the low dissipation factor and the rigidity of plastic foams in the constmction of radar domes. Polyurethane foams have been used as high voltage electrical insulation (213). 

Phenylene oxide Based (PPO) plastic that is a choice for electrical applications, housings for computers and appliances, both neat and in structural foam form. It has superior dimensional stability, moisture resistance due to styrene components, which, however, cause some sacrifice of weather and chemical resistance. Use includes automobile wheel covers, pool plumbing, consumer electronic external and internal components. 

Rodents chew through cellular polymers but do not ingest the foam as a foodstuff. The resistance to rot, mildew, and fungi is related to moisture absorption [64]. Therefore, open-cell foams support such growth better than closed-cell foams. High humidity and temperature are necessary for the growth of microbes on any plastic foam. 

Clay n. Any naturally occurring sediment rich in hydrated silicates of aluminum, predominating in particles of colloidal or near-colloidal size. There are many types of clays and clay-like minerals. Those of particular interest to the plastics industry are varieties refined by nature and man to a state of good color and particle-size distribution, such as kaolin (China clay). They are used as fillers in epoxy and polyester resins, PVC compounds, and urethane foams. Calcined clays are those that have been heated to a high temperature to drive off the chemically bound water, sometimes also surface-treated to improve their chemical inertness and moisture resistance. They are used primarily in vinyl insulation. 

Moisture Resistance. Plastic foams are advantageous compared with other thermal insulations in several applications where they are exposed to moisture pickup, particularly when snbjected to a combination of thermal and moisture gradients. In some cases the foams are exposed to freeze-thaw cycles as well. The behavior of plastic foams has been studied imder laboratory conditions simulating these use conditions as well as imder the actual use conditions. 

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. 

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