Ozone Protection

Blends of diene and backbone-saturated mbbers are frequently used in appHcations where discoloration by chemical antiozonants caimot be tolerated, yet where cost is stiH a primary consideration (eg, white sidewalls of tires). Disadvantages are that physical properties have to be compromised and the two mbbers usually differ greatly in their rates of vulcanization. Usually, at least a 25% replacement by the ozone-resistant mbber is needed for an appreciable enhancement in ozone protection (6). 

I iL-un 12 (CCljFj) which is now banned by the ozone protection treaty. Also used is Dichloro-difluoromethane, Freon 22 (CHClFj), and chloro-difluoromethane. Several analogous compounds containing carbon, fluorine, chlorine, and sometimes hydrogen are available. 

Warrach and Tsou [115] reported that bis-(l,2,3,6-tetrahydrobenzaldehyde)-pentaerythrityl acetal provides superior ozone protection for polychloroprene, butyl rubber, chlorobutyl, and... 

The most prevalent approach to achieve long-lasting and nonstaining ozone protection of rubber compounds is to use an inherently ozone-resistant, saturated backbone polymer in blends with a diene rubber. The ozone-resistant polymer must be used in sufficient concentration (minimum 25 phr) and must also be sufficiently dispersed to form domains that effectively block the continuous propagation of an ozone-initiated crack through the diene rubber phase within the compound. Elastomers such as ethylene-propylene-diene terpolymers, halogenated butyl mbbers, or brominated isobutylene-co-para-methylstyrene elastomers have been proposed in combination with NR and/or butadiene rubber. 

Benzofuran derivatives and enolethers are offered as chemical antiozonants for light coloured rubber compounds. Benzofuran derivatives are used in CR and its blends with other rubbers and give ageing protection in addition to ozone protection. 

The enolethers give ozone protection but not ageing protection with natural rubber (NR) and polyisoprene (IR), styrene-butadiene rubber (SBR) and butadiene rubbers (BR), but are less... 

Today we know that CFCs break up when they reach the ozone layer, releasing chlorine atoms. The chlorine atoms destroy ozone molecules faster than the ozone can regenerate from oxygen gas. Studies in the past ten years have shown dramatic drops in ozone concentration at specific locations. Since ozone protects... 

Lower in the atmosphere, ozone is a component of photochemical smog and a cause of oxidative damage to lungs. So ozone protects us in the upper atmosphere, where we are not in direct contact with it, but threatens us at ground level, where we are. We need to keep it but keep it where it belongs. 

Antiozonants (qv) also protect mbber surfaces by the formation of a protection layer on the surface of mbber by reaction of the antiozonant with ozone, the ozonides (4) formed in reaction with the mbber. Certain polymers also provide good ozone protection. The use of 20—30 parts of EPDM, alow diene mbber, in natural mbber or SBR compounds significantly increases ozone resistance. 

Stratospheric Ozone Protects Earth from Ultraviolet Radiation... 

STRATOSPHERIC OZONE PROTECTS EARTH FROM ULTRAVIOLET RADIATION... 

Hoses -ofLLDPE [OLEFIN POLYMERS - POLYETHYLENE - LINEAR LOW DENSITY POLYETHYLENE] (Vol 17) -ozone protection [ANTIOZONANTS] (Vol 3) -cis-l,4-polyisoprene m [ELASTOMERS SYNTHETIC - POLYISOPRENE] (Vol 9) -precipitated silica m [SILICA - AMORPHOUS SILICA] (Vol 21)... 

Montreal protocol Treaty signed in 1987 that governs stratospheric ozone protection and research, and the production and use of ozone-depleting substances. It provides for the end of production of ozone-depleting substances such as CFCS. Under the protocol, various research groups continue to assess the ozone layer. The multilateral fund provides resources to developing nations to promote the transition to ozone-safe technologies. 

Title VI Stratospheric Ozone Protection Title VI of the 1990 Clean Air Act Amendments established a program to implement the provisions of the Montreal Protocol, a worldwide agreement to reduce the use and emission of ozone-depleting substances. EPA s regulations adopted in response to Title VI outline a series of requirements for facilities that use equipment containing ODS compounds. Facilities must be certain that they handle and manage ODS compounds as prescribed in the rules. Only certified technicians and staff may maintain... 

Stratospheric ozone protects life on the surface of the Earth by screening the harmful UV light coming from the Sun through a photodissociation mechanism ... 

In the winter of 1984, massive losses of stratospheric ozone were detected in Antarctica over the South Pole (Halley Bay). This ozone depletion is known as the ozone hole. We know now that it also forms over the Arctic, although not as dramatically as in the Antarctic. Stratospheric ozone protects life on the surface of the Earth by screening harmful UV radiation coming from the sun through a photodissociation mechanism (see Chapter 4). 

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