Degradation ultraviolet

Chalking also occurs to some extent with several other types of polymers. It does not directly affect corrosion protection but is a concern because it eventually results in a thinner coating. The problem is easily overcome with epoxies, however, by covering the epoxy layer with a coating that contains a UV-resistant binder. Polyurethanes are frequently used for this purpose because they are similar in chemical stfucture to epoxies but are not susceptible to UV breakdown. 

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The ECPI approach has been adopted by the European Commission in their "Technical Guidance Document on the Risk Assessment of Notified New Substances" as the model for assessment of environmental exposure from additives in plastics. It is important to note, however, that due to the effect of ultraviolet degradation and microbial attack, a significant proportion of the emissions from flexible PVC consists of plasticizer degradation products. In these instances, therefore, the level of plasticizers appearing in the environment will be significantly less than indicated by the plasticizer loss data. 

Finishes Thermal insulations require an external covering (finish) to provide protection against entry of water or process fluids, mechanical damage, and ultraviolet degradation of foamed materials. In some cases the finish can reduce the flame-spread rating and/or provide fire protection. 

Because polycarbonates are good light absorbers, ultraviolet degradation does not occur beyond a depth of 0.030-0.050 in (0.075-0.125 cm). Whilst this is often not serious with moulded and extruded parts, film may become extremely brittle. Improvements in the resistance of cast film may be made by addition of an ultraviolet absorber but common absorbers cannot be used in moulding compositions because they do not withstand the high processing temperatures. 

Light-stable and weather-resistant Resistant to weather and ultraviolet degradation. Structural panels, skylighting, glazing. 

Feist, W.C. and Rowell, R.M. (1982). Ultraviolet degradation and accelerated weathering of chemically modified wood. In Graft Copolymerization of Lignocellulosic Fibers, Hon, D.N.S. (Ed.). ACS Symposium Series, 187, pp. 349-370. 

USP acid test analy chem A United States Pharmacopoeia test to determine the carbonizable substances present In petroleum white oils. yti es pe as ad. test) UV stabilizer chem Any chemical compound that, admixed with a thermoplastic resin, selectively absorbs ultraviolet rays used to prevent ultraviolet degradation of polymers. Also known as ultraviolet stabilizer. yu ve sta ba.iTz ar)... 

Most research on chemical modification of lignocellulosic materials has focused on improving either the dimensional stability or the biological resistance of wood. This paper reviews the research on these properties for wood and other lignocellulosic composites and describes opportunities to improve fire retardancy and resistance to ultraviolet degradation. 

A series of four samples of different initial but prepared by analogous procedures, were subjected to near-ultraviolet degradation (Figure 7). The expected family of straight, parallel lines is obtained. Therefore, we could predict an ultimate tensile failure for PMMA when the molecular weight Mw had degraded beyond a certain threshold—ca. 70,000. This behavior was indeed observed (Figure 8). 

When the chemist first receives a toxicant for formulation, a determination of the following physical properties will be of material aid to his studies (a) melting point or boiling point, (b) rate of hydrolysis, (c) vapor pressure, (d) specific gravity, (e) solubility, (f) ultraviolet degradation, and (g) inherent biological activity. 

Dacron fiber is used to make fabric and tire cord, and Mylar film is used to make magnetic recording tape. Mylar film is strong, flexible, and resistant to ultraviolet degradation. Aluminized Mylar was used to make the Echo satellites, huge balloons that were put into orbit around the Earth as giant reflectors in the early 1960s. Polyethylene terephthalate) is also blow-molded to make plastic soft-drink bottles that are sold by the billions each year. 

Fabrication conditions have a significant effect on optics. Also the environmental properties of LDPE are subject to thermal and ultraviolet degradation. However, additives are available that can extend outdoor service up to several years. 

An ideal MIO pigment should not contain very fine particles in order to keep the wettable pigment surface small. High PVC in the coating can only be achieved when the oil absorption value of the MIO pigment is low [5.103]. In addition to the barrier mechanism, MIOs are recommended for use in topcoats as a protection against ultraviolet degradation [5.55]. 

Different component materials have different rates of expansion and contraction. If they are connected, temperature changes can cause leaks if the expansion and contraction rates are too different. Some materials such as PVC are prone to ultraviolet degradation. Phenomenon like fog, dew, rain, and snow can cause electrical shorts in process control units if their housing does not protect against moisture. Most commercial units are placed outdoors with some sort of shelter to temper their exposure to ambient weather conditions. 

TABLE 6 Guidance for Ultraviolet Degradation Experimental SetUp ... 

Adams, M. R. Carton, A. Far-Ultraviolet Degradation of Selected Polymers. In Polymer Durability Degradation, Stabilization, and Lifetime Prediction Clough, R. L., Billingham, N. C., Gillen, K. T., Eds. Advances in Chemistry Series 249 American Chemical Society Washington, DC, 1996 pp 139-158. 

Hard hats should be stored out of direct sunlight and periodic inspections should be made of all hard hats. Those exposed to sunlight for prolonged periods are susceptible to ultraviolet degradation. At the first sign of a loss of surface gloss or flaking, the hard hat should be replaced. Replace the liner about once a year. 

N. Z. Searleand R. C. Hirt, Bibliography on ultraviolet degradation and stabilization of plastics,... 

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