Resistance to ultraviolet radiation

Acrylic is a generic name for derivatives of acrylic acid, of which methyl methacrylate is the most important. Polymerization is controlled to produce chain length of 800 to 3,000 monomer units. A small amount of plasticizer such as dibutyl phthalate may be added before bulk polymerization to assist in deep molding. The outstanding property of polymethyl metliacrylate is 0 transparency resistance to ultraviolet radiation from fluorescent lamps and ability to be... 

SASPs comprise about 10-20% of the protein in the dormant spore, exist in two forms alfi and y) d are degraded during germination. They are essential for expression of spore resistance to ultraviolet radiation and also appear to be involved in resistance to some biocides, e.g. hydrogen peroxide. Spores (a /3 ) deficient in a//3-type SASPs are much more peroxide-sensitive than are wild-type (normal) spores. It has been proposed that in wild-type spores DNA is saturated with a/j3-type SASPs and is thus protected from free radical damage. 

As noted earlier, poly(methyl methacrylate) plastic has excellent resistance to ultraviolet radiation. Nevertheless, in long-term outdoor applications or in lighting fixtures, small amounts of ultraviolet absorbers are employed to retard the yellowing and degradation in physical properties which would otherwise occur. 

The elastomeric polymer is obtained by extending the prepolymer through its reaction with short-chain diols such as butanediol or diamines such as ethylene diamine, thus completing the formation of hard groups between soft, flexible chains. When amines are used, the final step is typically done in a polar solvent such as dimethyl acetamide. The conversion of these polymers into usable fibers may be accomplished by wet-, dry-, or melt-spinning operations, depending on the polymer. Additives to impart whiteness or improve resistance to ultraviolet radiation and... 

Resistance to Ultraviolet Radiation Volatile Organic compounds... 

Methacrylate-based coating resistance to ultraviolet radiation chemical resistance permeability to water vapour carbon dioxide resistance colour retention anticarbonation coatings for concrete and masonry... 

Acrylic-modified cementitious products excellent bond strength water resistance resistance to ultraviolet radiation low water/cement ratio superior handling and application properties various, depending upon type of product repair mortars floorings tile adhesives renders coatings, etc. 

Beneficial properties Excellent adhesion without the use of primers minimum surface preparation one-component system self-heahng excellent resistance to ultraviolet radiation good chemical resistance non-staining... 

The average shore A hardness of the cured sealant is 20 to 25 but increases with ageing. Resistance to ultraviolet radiation is excellent, but this is not important for indoor applications. The maximum movement accommodation factor (MAF) can be 15% of the total joint width. Joints should be designed so that movement due to shrinkage and thermal changes does not exceed the maximum MAF, related to the joint width. Table 5.4 lists the properties in general for acrylic emulsion sealants. These properties are summarised from the commercial literature of several acrylic emulsion sealant manufacturers and should not be considered as specifications. Table 5.5 lists the standard specifications for these sealants. 

Beneficial properties One-component system good adhesion without the use of primer paintable good resistance to ultraviolet radiation easy application and clean-up good packing stability low cost fast skinning... 

Compared with acrylic glass, polystyrene has a lower light stability and resistance to ultraviolet radiation. The slight degradation when exposed to ultraviolet radiation is a disadvantage that occurs with all optical plastics. The higher refractive index of polystyrene permits its use in conjunction with acrylic lenses for the design of colour-... 

Polycarbonates are strong, heat resistant, and lightweight, making them ideal for applications in construction, electronics, automobiles, and appliances. Many polycarbonates are substituted for glass in safety and athletic goggles, building components, and car instrument panels because they are transparent, yet shatterproof. They are also more resistant to ultraviolet radiation than is glass. Some of the specific products made with polycarbonates include ... 

It is also possible to build into the chemical systems other properties that are desired in the treated wood. Fire retardancy, chemical resistance, or resistance to ultraviolet radiation can be built into the bonding or polymerizing systems. Thus, serious problems can be solved while stability, strength, and integrity are improved. 

Polyurethane ether (PUR-ether) foams are thought to degrade primarily by oxidation, particularly in the presence of light, resulting in discolouration and a loss of mechanical properties. Polyurethanes synthesized from a polyether polyol and an aromatic diisocyanate such as diphenylmethane diisocyanate (MDI) are highly vulnerable to photo-oxidation, whereas polyester-based polyurethanes are more resistant to ultraviolet radiation (Kerr and Batcheller, 1993). Metal ions, particularly copper, aluminium and zinc, form chelates with some polyurethanes imparting increased sensitivity to photo-oxidation (Ranby and Rabek, 1975). 

TPU) and either aromatic or aliphatic. Aliphatics are more expensive, but generally have better resistance to ultraviolet radiation and are clearer. PUs are also either polyether-based or polyester-based, where the former has better low temperature flexibility and the latter tends to be tougher and more chemical resistant. 

High molecular weight, lightstabUizir compounds for imparting improved resistance to ultraviolet radiation to polycarbonate-based polymers are prepared by interfacial condensation of phosgene or its derivatives or carbonate esters with bisphenol derivatives [270]. 

Polypropylene is intrinsically less resistant to ultraviolet radiation. Although polypropylene shows powdering rather than grass surface grazing after sunlight exposure, minute surface cracks are visible under the microscope. Under certain conditions the microcracks can act as points of stress concentration. This can reduce the impact strength of the component. 

Resistance to ultraviolet radiation is limited. This is because of the strong absorption of ultraviolet by the aromatic species. It can be addressed by coating the PAEK components or to some extent by incorporating ultraviolet absorbers of reflectors. Unfortunately many standard ultraviolet stabilisers are too volatile or lack the thermal stability required to work well in PAEK. 

Black iron oxide [ferroso-ferric oxide (FeO-Fe203)]. Black iron oxide gives a coarse particle size pigment. It is a cheap and inert pigment. It is resistant to ultraviolet radiation. 

Acrylic polymers are based on free radical initiated polymers containing monomers based on acrylic acid and methacrylic acid and their esters. Such polymers often also include styrene as a monomer. Acrylic-based coatings are more resistant to ultraviolet radiation and are widely used in applications where outstanding durability and color control are required. In recent years, hybrid coating systems are also being explored to satisfy more demanding performance needs for the coatings [52]. 

The polymers made from 1,1-difluoroethene (or vinylidene fluoride) are known as polyvinylidene fluoride (PVDF). They are resistant to oils and fats, water and steam, and gas and odors, making them of particular value for the food industry. PVDF is known for its exceptional chemical stability and excellent resistance to ultraviolet radiation. It is used chiefly in the production and coating of equipment used in aggressive environments, and where high levels of mechanical and thermal resistance are required. It has also been used in architectural applications as a coating on metal siding where it provides exceptional resistance to environmental exposure. The chemical structure of PVDF is shown in Fig. 11.40. Some products are copolymers. 

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