Degradation enhanced photo- degradable

FIGURE 6.8 Weathering of unstabilized LDPE films open symbols) and enhanced photo-degradable ECO copolymer (filled symbols) exposed ontdoors in Miami, FL. 

Andrady AL, Pegram JE, Tropsha Y. Changes in carbonyl index and average molecular weight on embrittlement of enhanced photo-degradable polyethylene. J Environ Degrad Polym 1993b l 171-179. 

B. Enhanced Photo-Oxidability Additives to Increase the Environmental Degradation... 

Beecroft, R. A., Davidson, R. S., Goodwin, D. C., and Pratt, J. E., Quenching of singlet and triplet excited aromatic hydrocarbons by sulphides the amine and sulphide enhanced photo-induced degradation of chloro- and cyanoaromatic hydrocarbons. Tetrahedron, 40, 4487,1984. 

It is no surprise that a combination of different agents that cause polymer instability increases the degradation rate. For example, the presence of heavy metals (left behind catalyst or brought in with, for example, clay nano-particles) enhances photo- or thermo-oxidative degradation. Dynamic flow behavior of the polymeric nanocomposites (PNC) with either PS or PP matrix... 

Increase the oxidation rate of polymers, e.g. metal ions which increase the hydroperoxide decomposition rate. Photodegradation and thermal degradation are enhanced by transition metal ion containing pro-oxidants, such as iron dithiocarbamate (as opposed to nickel dithiocarba-mate, which acts as a photo-antioxidant). 

Water, methanol, and n-hexane do not influence the photooxidation of PVC (43), but the photodegradation is accelerated by ferric chloride (70,71) and certain other compounds containing iron (70,71,72). Purification of the polymer might be expected to enhance its photostability by removing deleterious impurities such as iron compounds that are derived from metal equipment. This type of result was obtained in one recent study (58) but not in others (30,59). In contrast, the photo-oxidative degradation of PVC should be enhanced by admixture of the polymer with materials that are unusually susceptible to photooxidation themselves. Such behavior has been observed for impact-modified PVC containing polybutadiene-based polyblends (69,73). 

The addition of Fe ions to the solution also increased the rate of photo-catalytic degradation. The TOC reduction was 80% in the presence of Fe ions and 10% in the absence of Fe ions. pH is the key parameter in determining the photocatalytic degradation of anilines as well as other compounds previously studied. The high photocatalytic degradation near the pHpzc has also been observed for other compounds studied with Ti and Zn. The major mechanism is the attack of photogenerated OH radicals on the aniline molecule under alkaline conditions. The addition of Fe ions to the solution can enhance the formation of OH radicals and lead to higher photocatalytic rates. 

It may be anticipated that the antioxidant consumption during use leads to a shorter remaining life-time and that it is necessary to add more. Recycled plastics suffer from the consequences of degradation during processing and first-life application. This leads to the introduction of new functional groups, which in particular for oxidisable polymers such as PE, enhance the sensitivity of the recyclate to thermal- and photo-degradation. With the formation of new pro-oxidative moieties, a substantial part of the stabilisers are simultaneously consumed [14]. 

Pervaporation - photocatalysis In the described systems the membrane usually permeates water and rejects the reactants, enhancing their residence time in the photoreactor. However, it is known that some intermediate products of the photo-catalytic degradation of organic compounds can negatively affect the reaction rate, therefore, in some cases it is useful to eliminate these by-products in order to improve the thermodynamic and/or the kinetics of the reaction. 

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