Sunlight weatherability

Applications. Products of Bulk Polymerization. The principal example of bulk polymerization is the production of cast sheets of methyl methacrylate (see Fig. 15-40), which are well known for their outstanding optical clarity, resistance to sunlight, weather, and most chemicals, and for... 

Weathering Procedures. Samples (7 x 12 cm) of untreated and formladehyde-treated wools were exposed to simulated sunlight weathering in an Atlas Weather-ometer, Model C135W equipped with a filtered xenon arc. The samples were irradiated continuously for 168 hours total with 18 minute water spray following every 102 minutes of Irradiation throughout the cycle. The fabric surface received 0.67 w/m irradiation at a black panel temperature of 63°C and 45% RH during the irradiation. 

Hypalon s advantages include some oil resistance, excellent resistance to ozone, sunlight, weathering, chemicals, as well as resistance to permeation and abrasion. It is unaffected by cold weather or rapid temperature changes. Hypalon is difficult to apply, is more costly than natural rubber, is not resistant to oxygenated solvents, and requires a pressure cure. 

The polyamides have a very low absorption of moisture, which means that parts produced from these materials will have a good dimensional stability regardless of the humidity of the environment. They are resistant to sunlight, weather, and ozone. Polyamide is used to coat many metals to protect them from harsh weather. 

The perfluoroelastomers (FPMs) are true rubbers, as compared to other elastomeric compounds. They are more resistant to swelling and embrittlement and retain their elastomeric properties over the long term. These elastomers display excellent resistance to sunlight, weather, and ozone. 

Warmth without weight, durable, soft hand, shape retention, resistant to sunlight, weather, oil and chemicals... 

The polymer can be vulcanized to give a rubber with very good chemical (solvent) resistance, excellent resistance to aging and weathering, and good color retention in sunlight. 

A.STM D4364, PracticeforPeformingMccelerated Outdoor Weathering of Plastics Using Concentrated Natural Sunlight, Vol. 8.03, ASTM, Philadelphia, Pa., 1984. 

Wea.ther lbillty. One of the more destmctive elements is exposure to sunlight specifically, ultraviolet (uv) light. AH sealants are affected by weathering, but there is much difference in the effect of weathering on different sealants. Most sHicones are stable with respect to uv exposure. Urethanes and polysulfides show effects of uv exposure, but can be formulated with uv absorbers to provide reasonable lifetimes in most appHcations. However, there are exceptions in aH classes of sealants and specifiers must be carehil to look for test data that has proven a specific sealant s durabHity. The source of the test data is also important data from an independent testing laboratory is generaHy apt to be more reHable. 

People who experience the exclusion of sunlight (living in northern climates cultures where apparel limits sunlight), as weU as infants and children that are confined to bed or limited outdoor activity because of weather or illness, also can show a tendency towards vitamin deficiency. 

Polyethylene is the lowest-cost plastic commercially available. Mechanical properties are generally poor, particularly above 50°C (120°F), ana pipe must be hilly supported. Carbon-filled grades are resistant to sunlight and weathering. 

Because the polybutadiene component is liable to oxidation, ABS materials are embrittled on prolonged exposure to sunlight. By replacing polybutadiene rubber with other elastomers that contain no main chain double bonds it has been possible to produce blends generally similar to ABS but with improved weathering resistance. Three particular types that have achieved commercial status are ... 

Other factors which can affect impact behaviour are fabrication defects such as internal voids, inclusions and additives such as pigments, all of which can cause stress concentrations within the material. In addition, internal welds caused by the fusion of partially cooled melt fronts usually turn out to be areas of weakness. The environment may also affect impact behaviour. Plastics exposed to sunlight and weathering for prolonged periods tend to become embrittled due to degradation. Alternatively if the plastic is in the vicinity of a fluid which attacks it, then the crack initiation energy may be reduced. Some plastics are affected by very simple fluids e.g. domestic heating oils act as plasticisers for polyethylene. The effect which water can have on the impact behaviour of nylon is also spectacular as illustrated in Fig. 2.80. 

Important properties of polyesters are the relatively high melting temperatures (= 265°C ), high resistance to weather conditions and sunlight, and moderate tensile strength (Table 12-6). ... 

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