Plastics oxidative degradation

Oxidatively degradable plastic is a degradable plastic in which the degradation results from oxidation. 

Methylphenol is converted to 6-/ f2 -butyl-2-methylphenol [2219-82-1] by alkylation with isobutylene under aluminum catalysis. A number of phenoHc anti-oxidants used to stabilize mbber and plastics against thermal oxidative degradation are based on this compound. The condensation of 6-/ f2 -butyl-2-methylphenol with formaldehyde yields 4,4 -methylenebis(2-methyl-6-/ f2 butylphenol) [96-65-17, reaction with sulfur dichloride yields 4,4 -thiobis(2-methyl-6-/ f2 butylphenol) [96-66-2] and reaction with methyl acrylate under base catalysis yields the corresponding hydrocinnamate. Transesterification of the hydrocinnamate with triethylene glycol yields triethylene glycol-bis[3-(3-/ f2 -butyl-5-methyl-4-hydroxyphenyl)propionate] [36443-68-2] (39). 2-Methylphenol is also a component of cresyHc acids, blends of phenol, cresols, and xylenols. CresyHc acids are used as solvents in a number of coating appHcations (see Table 3). 

There are some aspects in the raw dry NR grades for adhesive manufacturing to be considered. NR tends to suffer oxidative degradation catalyzed by metals (mainly copper). The susceptibility of NR to oxidation can be measured using the plasticity retention index. The better grades of rubber have the higher plasticity retention index. 

Oxidative degradation can be the most serious problem in the use of plastics at higher temperatures. At ambient temperature oxidation proceeds relatively slowly on its own, but can be stimulated by light (photo-oxidation), ionising radiation (radio-oxidation), certain gaseous and liquid environments and by the presence of transition metals. The rate at which oxidation occurs will therefore depend on the intensity of these agents, on temperature, and on the availability of oxygen, which in turn depends upon its solubility, its rate of diffusion (see Section 4.12.2) and the rate at which it is consumed. 

Similar considerations are relevant to protection of products that are labile to oxidative degradation. The permeability of plastic containers to oxygen ingress has also been evaluated, and is summarised in Table 2.9 [102]. 

Since polyethylene becomes infusible after irradiation, the material should be cross linked before molding. If this is done, easy moldability, one of the prime attractions of the plastic, is lost. However, if polyethylene is irradiated after molding it can be vacuum drawn and formed in very thick sections to extremely deep draws, and with very little temperature control. One must be careful about heating cross-linked polyethylene since (1) above 230° to 240° an article will distort if it is not free from molding strains and (2) above 220° oxidative degradation reactions set in unless, of course, antioxidants have been added. 

Polysulfone Plastics. These plastics which were commercialized by Union Carbide are actually aromatic polyethers containing periodic sulfone groups which provide additional resonance stabilization. They have good mechanical properties, creep resistance, and dimensional stability but their outstanding quality is their high heat distortion temperature (345°F.) and resistance to thermal oxidative degradation. Limitations are difficult thermoplastic processability, amber color, and sensitivity to organic solvents. 

An alternative form of non-carbonated beverage comes in form-fill-seal plastic containers, which are typically square or round section cups with foil or plastic laminate lidding. Such products are difficult to produce to a quality that will satisfactorily compete with the shelf fife of aseptic foil/laminate packs. Fonn-fill-seal containers leave their contents vulnerable to oxidative degradation and are especially at risk of mould spoilage. The packs can be produced in aseptic conditions but the products are typically chemically preserved. 

A. Pifer and A. Sen, Chemical recycling of plastics to useful organic compounds by oxidative degradation, Angew. Chem. Int. Ed., 37, 3306-3308 (1998). 

Ethanox 376 is a stabilizer that provides heat stability by preventing thermo-oxidative degradation during processing and service life. It provides compatibility with resins and extraction resistance. It can be applied in polyolefins, such as polyethylene, polypropylene, polybutene-1 and other polymers such as engineering plastics, styrenes, polyurethanes, saturated and unsaturated elastomers, styrenics, rubber modified styrenics, segmented block copolymers, and PVC. 

Protects against thermo-oxidative degradation in natural and synthetic rubbers as well as plastics. It is commonly used in applications such as tire carcasses, wire breaker retreads, apex, belts, hoses, seals, mechanical goods, footwear and wire. 

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