UV radiation degradation

A treatability study was conducted at the Milan AAP. Bench-scale tests indicated that UV radiation degraded explosive contaminants and that longer UV exposure times yielded better contaminant removals. HjOj levels were found not to affect contaminant degradation, and UV oxidation was found to be most effective at pHs of 7 or greater. The level of 1,3,5-TNB, which is a product of the UV oxidation of TNT, was the rate-limiting factor in each test 1,3,5-TNB concentrations actually increased after 40 minutes of UV exposure. 

Keywords Interlayer adhesion loss Epoxy coatings Weathering Erosion mechanism UV absorber Humidity Water Crosslinking Network degradation Oxygen diffusion and solubility Photoproducts Oxidation zone Rain Lag time UV radiation degradation... 

A review of the Hterature on degradation mechanisms of rubbers is presented, covering thermooxidative degradation, thermal decomposition, radiation degradation, UV radiation degradation (weather resistance) and ozone degradation. 66 refs. (Full translation of Nippon Gomu Kyokaishi, No.5,1995, p.284)... 

Unstabilised PE very rapidly becomes brittle when exposed (prolonged exposure) to sunlight, caused mainly by UV radiation. Degradation is accompanied by marked deterioration in mechanical properties, gloss loss, and cracking. 

Pigments are added to the ABS to make pipe and fittings resistant to ultraviolet (UV) radiation degradation. Pipe and fittings specified for buried instaUations may be exposed to sunlight during construction, however, and prolonged exposure is not advised. 

The primer must have good chip resistance and exterior durability. Weakness in the layer will lead to UV radiation degradation causing loss of adhesion of primer to basecoat/clearcoat and ultimately delamination. 

Like almost all synthetic polymers, styrene plastics ate susceptible to degradation by heat, oxidation, uv radiation, high energy radiation, and shear, although... 

Additionally, organotin mercaptides can act as antioxidants, as they can sequester free-radical degradation mechanisms (48). The one drawback of mercaptide-based tin stabilizers is the discoloration of the sulfur after exposure to uv-radiation. Special precautions or formulations need to be developed for outdoor apphcations. 

Ozonation can be enhanced by the addition of ultraviolet (uv) radiation. This combination can be effective in degrading chlorinated organic compounds and pesticides. In addition, metal ions such as iron, nickel, chromium, and titanium [7440-32-6] can act as catalysts, as can ultrasonic mixing. 

The effects of UV radiation on degradable plastics are usually confined to the exposed surface layers. Tlie general effect is one of embrittlement. Tensile strength may either increase or decrease, but the elongation upon breaking is always reduced. A loss of impact... 

Other elements of weather and outdoor exposure can interact with UV radiation to accelerate degradation in degradable types of plastics. They include humidity, salt spray, wind, industrial pollutants, and atmospheric impurities such as ozone, biological agents, and temperature. The wavelengths that have the most effect on plastics range from 290 to 400 nm (2,900 to 4,000 A). 

Effect of UV Radiation on Sodium Pentachlorophenate. Sodium pentachlorophenate is quickly degraded in the presence of ultraviolet light as well as daylight, as shown in Table III. The degradation is almost complete after 16 hours exposure to the General Electric R.S. sunlamp. Three and one-half days of rainy and overcast skies account for the somewhat lower degradation observed in the sample exposed to daylight. 

Since our main objective was to remove all the chlorine and hydrogen atoms from the polymer chain, C-PVC films were further exposed to the UV radiation of the medium pressure mercury-lamp. This led to a dark brown material w.hich was found to be unable to carry an electrical current, even after extended irradiation time. Therefore we turned to a powerful laser source, a 15 W argon ion laser tuned to its continuous emission at 488.1 nm. At that wavelength, the degraded polymer film absorbs about 30 % of the incident laser photons. The sample was placed on a X-Y stage and exposed to the laser beam at scanning rates in the range of 1 to 50 cm s, in the presence of air. 

UV stabilisers protect polymers by restricting UV penetration to the surface and therefore confine the damage to surface layers. Protection is important because the energy possessed by UV radiation is sufficient to break chemical bonds. The initial breakage can either be by a radical (Norrish type I) or non-radical (Norrish type II) pathway. The effects are similar to degradation of the polymer by oxidation routes the radical intermediates can be neutralised by anti-oxidants. 

Because of UV filters are substances designed to absorb solar energy, photolysis and photocatalysis have been tested as a feasible treatment to degrade the recalcitrant compounds. To date, very few studies have examined UV filters response under UV radiation when exposed in aqueous samples [41-44], Results indicate that the extent of degradation is quite variable, from no photodegradation of BP3 to complete mineralization of BP1 after 24 h of UV light irradiation. 

---