Polyolefins environmental oxidation

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. 

Collectively, these technical approaches indicate the potential of polyolefins to environmentally degrade and subsequently biodegrade individually they do not always have enough substantiated evidence and data to be unequivocal. It is the approach using transition metals as oxidation catalysts that has become the predominant technology in the environmental degradation of polyolefins. The... 

Polyethylene (PE) is a member of the polyolefin family, which also includes PP and various plastics with different molecular linearily, densities, polymerization processes, and substitution types. PE densities are relatively low with values ranging from 0.940 to 0.970 g/cm for HOPE and from 0.916 to 0.940 g/cm for LLDPE. Typically, these PEs not only have good processability (e.g., can be converted into bags, films, and bottles) but also exhibit an excellent water vapor barrier property, which is required for many water-sensitive food products such as dried and liquid foods. However, this type of plastic is not appropriate for easily oxidized food products due to its low oxygen barrier property. The properties of polyolefins can be significantly affected by environmental conditions and physical factors, such as the density, crystallinity, presence of free volume, polarity, humidity, and temperature [44]. 

Chromic acid was used for the introduction of carbonyl [15] and carboxylic acid [16] groups on the PE and PP surface. Chromic acid is the most commonly used reagent however, for environmental reasons, its use is avoided. Even very mild treatment conditions result in the substantial oxidation of polyolefins and large increases in adhesion, as confirmed by X-ray photoelectron spectroscopy (XPS) shown in Table 8.1 [17]. 

In spite of some imeertainties in the individual steps of the HAS meehanism in polymer stabilization due to the speerfie effeets of the polymer matrix and the environmental stress, the HAS-based nitroxides are eonsidered the key intermediate in the HAS reaetivity meehanism. Detection and quantification of the formed nitroxides using ESRI spectroscopic technique has been exploited for confirmation of the primary transformation step in HAS mechanism [15, 16, 20], as a consequence of interactions of HAS with oxygenated radical and molecular products of polyolefins (5). Monitoring of the nitroxide development enables tracing of the oxidation process within the polymer matrix. Consequently it is also a tool for marking the heterogeneity of the oxidative transformation of semicrystalline carbon chain polymers [polypropylene (PP), polyethylenes (PE)] or amorphous polymers [copolymers of ethylene with norbomene, polystyrene (PS), high impart polystyrene (HIPS), acrylonitrile-butadiene-styrene polymer (ABS)]. 

Tobias acid t9- bl-9s a-sod n. Intermediate used in the manufacture of dyestuffs. 2-naphthylamine-1 -sulfonic anti-oxidant, generally regarded as safe by the Food and Drug Administration. It has been shown to be a good heat stabilizer in polyolefins, providing protection at levels around 250 ppm. Both ATP and its breakdown products are environmentally safe. 

Decabromodiphenyl ether is a solid, melting at about 304-309°C, substantially insoluble in water, and with negligible vapor pressure. In contrast to the lower brominated diphenyl ethers, it has only rarely been found as an environmental pollutant and is low in toxicity. Risk studies conducted in the United States and the European Union (33,35) indicate a low degree of risk in the use of this flame retardant. It is the major flame retardant used in high impact polyst5Tene (HIPS) with antimony oxide, and has substantial use in polyolefin wire and cable as well as electrical parts made of other plastics such as polyamides and thermoplastic polyesters. 

Uses Intermcxliate for biodeg. surfactants and specialty industrial chems., polyolefin comonomer, 0x0 alcohols, polybutene-1, butylene oxide, butyl mercaptan Fhtrperties Llqu ed gas sp.gr. 0.592 (Iiq.) b.p. -6.1 C 100% cone. Environmental Biodeg. 

The most biodegradable of the commodity polyolefins is polypropylene (PP). Pandey and Singh have recently shown that polypropylene (PP), after removal of antioxidants by solvent extraction, biodegrades much more rapidly than polyethylene by mass loss in compost. PP lost over 60% mass in six months whereas low density polyethylene (LDPE) lost about 10% in the same time. Ethylene-propylene (EP) co-polymers biodegraded at rates intermediate between PP and PE. As expected, prior UV irradiation (photo-oxidation) increased both the rate and extent of the bioassimilation. This is fiilly in accord with the rates of environmental peroxidation of these molecules and it has been shown that PP acts as a sensitiser for the peroxidation of LDPE. ... 

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