Plastic deterioration

Plastics—Deterioration—Congresses. 2. Photochemistry—Congresses. 3. Stabilizing agents—Con-... 

Potymers—Deterioration—Congresses. 2. Potymets— Biod radation—Congresses. 3. Plastics—Deterioration— Congresses. 4.Plastics—Biodegradation—Congresses. I. Glass,... 

Support spacing must be much closer than for carbon steel. As temperature increases, the allowable stress for many plastic pipes decreases very rapidly, and heat from sunlight or adjacent hot uninsiuated equipment has a marked effect. Many plastics deteriorate with exposure to ultraviolet light if not provided with a UV-resistant coating or other surface barrier. Successful economical underground use of plastic pipe does not necessarily indicate similar economies outdoors aboveground. 

Disposal of waste plastics is expensive. Plastics deteriorate but never decompose completely and they involve a high percentage ( 42% by weight) of waste. Fortunately, in recent years recycling of plastics has become an important technology. Some plastics can be blended with unused virgin plastics to reduce the cost of waste disposal. 

Most plastics transmit at UV wavelengths, and these plastics are often affected by UV-caused degradation. This degradation almost always manifests itself in color deterioration. However, in many plastics deterioration can extend to a significant loss in mechanical and other properties. 

In June 1996, the U. S. Consumer Product Safety Commission reported that nonglossy vinyl miniblinds from China, Taiwan, Indonesia, and Mexico contain lead. The lead, which is added to stabilize the plastic, deteriorates from exposure to sunlight, leaving lead dust on the surface of the blinds, which can be ingested by young children who touch the blinds. Ingesting the dust from just one square inch of the blinds each day, a child could become lead poisoned in just a couple of weeks to a month. 

Equipment for storing and handling methanol may be made of carbon or stainless steel. Methanol is aggressive toward copper, zinc, magnesium, tin, lead, and alurninum, which should therefore be avoided. Gasket materials must also be chosen carefiiUy, because some elastomers swell and deteriorate when exposed to methanol. Similarly, the use of plastics for storage is not recommended. 

Plasticizer esters are relatively iaert, thermally stable Hquids with high flash points and low volatihty. Consequently they can be stored safely ia mild steel storage tanks or dmms for extended periods of time. Exposure to high temperatures for extended periods, as encountered ia dmms ia hot climates, is not recommended since it may lead to a deterioration in product quaUty with respect to color, odor, and electrical resistance. 

Corrosion of the fasteners occurred due to their galvanic interaction with passive stainless steel. Deterioration was rapid because of the unfavorable area ratio formed by the large areas of stainless steel and the small area of the fasteners, which was further reduced by the incomplete plastic covering overexposed fastener surfaces. 

Finally mention may be made about the influence of humidity on the electrical insulating properties of plastics. Once again the polymers may be classified into two groups, those which do not absorb water and those which do. The nonabsorbent materials are little affected by humidity whereas the insulation characteristics of the absorbent materials deteriorate seriously. These latter materials are generally certain polar materials which all appear capable of forming some sort of bond, probably a hydrogen bond, with water. Three reasons may be given for the deleterious effects of the water. 

Free-radical chain inhibitors are of considerable economic importance. The term antioxidant is commonly appUed to inhibitors that retard the free-radical chain oxidations, termed autoxidations, that can cause relatively rapid deterioration of many commercial materials derived from organic molecules, including foodstuffs, petroleum products, and plastics. The chain mechanism for autoxidation of hydrocarbons is ... 

Whereas coiTosion of metals is due to chemical or substantial electrochemical attack, the deterioration of plastics and other non-metals which are susceptible to swelling, cracking, crazing, softening etc. is essentially physicochemical rather than electrochemical. 

---