Polyethylene, photodegradation

Three film samples were prepared, each of which contained 20% labelled polyethylene Blend A, Ecolyte low-density polyethylene (photodegraded) Blend B, low-density polyethylene (not photodegraded) and Blend C, low-density polyethylene with 16% starch. 

PL can be used as a sensitive probe of oxidative photodegradation in polymers. After exposure to UV irradiation, materials such as polystyrene, polyethylene, polypropylene, and PTFE exhibit PL emission characteristic of oxidation products in these hosts. The effectiveness of stabilizer additives can be monitored by their effect on PL efficiency. 

At the time of writing photodegradants are in an early stage of development and have not yet been fully evaluated. It is a moot point whether or not manufacturers will put such materials into polymer compounds and thus increase the price about 5% without legal necessity. However, if such legislation, considered socially desirable by many, took place one might expect polyethylene... 

One example of the use of photodegradable polyethylene is for beverage can ring holders in North America. 

Photodegradation of polyethylene waste can be markedly accelerated via its grafting with acrylamide [98], In contrast, photostabilization of polyethylene and polypropylene can be achieved as a result of the grafting of 2-hydroxy-4-(3-methacryloxy-2-hydroxy-propoxy) benzophenone using gamma radiation [ 147], In this case, the grafted compound acting as a U V stabilizer is chemically bound to the backbone chain of the polymer and its evaporation from the surface can be avoided. 

In the present paper, we describe how photodegradation of low density polyethylene films was enhanced by uniaxial elongation. An explanation of the enhancement process is given based on the photooxidation and deformation mechanisms, and the photodegradation products. 

Polyethylene degradation rate enhancement has been claimed for blends with mercaptans,(32) ketones,(32) ethers,(32) and specifically by photodegradation in the presence of benzophenone,(33) and metal promoted oxidations.(34 )... 

There are many reports in the literature describing photodegradation sensitized by aromatic ketones and quinones. Beachell and Chang (24) showed that triplet excited benzophenone accelerates degradation of polyurethanes by hydrogen abstraction. Harper and McKellar (25) showed the same effect with benzophenone on opolypropylene, and Amin and Scott (26) on polyethylene. Rabek and Ranby (27) have demonstrated that triplet excited quinones enhance... 

Although rings made of polyethylene work very well, as we have already found, polyethylene degrades extremely slowly in the environment. A small amount of carbon monoxide (CO) can be polymerized with ethylene to produce a copolymer that degrades in sunlight (undergoes photodegradation) ... 

Figure 14 Photodegradation of chloramphenicol eye drops FNA depending on the container. (A) White glass ampoule, (B) LD-polyethylene container, (C) brown glass container, (D) LD-polyethylene container, white, opaque, (E) LD-polyethylene container in the carton. ( ) 6 weeks diffuse daylight, ( ) 6 weeks sunlight. Source From Ref. 6.

A mixture of 50% v/v propylene glycol or 50% v/v polyethylene glycol (PEG) 400 with phosphate buffer of pH 7 increased the photodegradation rate constant of democlocycline hydrochloride by 1.8 and 2.5 times, respectively, compared to the phosphate buffer alone (76). 

Asker and Colbert (82) found that Tween 80 enhanced the photodegradation of FD C Blue No. 2 dye. In another report, Asker and Canady (83) reported that Tween 80 had little effect on the photostability of sodium nitroprusside solutions, while polyethylene glycol 300 enhanced it, possibly due to its chelating potential. 

The photodegradation of doxorubicin, daunorubicin, and epirubicin solutions is more rapid in clear glass than in polyethylene or amber glass containers (61). Colored glass is not preferred for injections since it is difficult to detect discoloration and particulate matter in the liquid preparation. However, a colorless glass capable of cutting off detrimental radiations is still to be discovered. 

Anotner organic ferric compotuid,namely the ferric acetyl acetonate (PemAcAo) has been found to be an effective initiator for the photodegradation of polyethylene (65) and poly(vinyl chloride)(66). These ferric compounds are easily oxidized and photolyz eT. The following mechanism for radical formation in polyethylene sample was proposed (67,68)1... 

They are well known as compounds which are photoohemically very reactive. The excited singlet and triplet states are the photochemically reactive states,and they also can participate in energy transfer reactions (2,3i10,11). Some of these compoxmds such as anthracene,phenanthrene,pyrene added to polyethylene effect the photodegradation of polymer (118,... 

It is well known that individually, photoinitiators and certain metallic organic compounds cause hydrocarbon polymers, such as polyethylene or polystyrene, to photodegrade faster than the original polymer not containing such an additive. We have discovered that by combining both types of additives in a plastic a striking synergistic effect occurs. 

The dielectric strength of polyethylene has been measured as a function of additive concentration while in stabilised polymers the depth of degradation was found to be uniform . HALS have been found to be effective stabilisers for UV cured coatings and do not influence the cure rate . Bleached wood pulps can be effectively stabilised by ascorbic acid and wool by hydroxy-benzotriazoles and HALS . Hydroxybenzotriazole stabilisers also protect wood pulp and polyurethanes by co-reaction . The spectroscopic properties of monomeric and polymeric benzotriazoles have also been compared . UV absorbers are effective in clear coats and when grafted to wood . Dihydroxybenzophenone stabilisers inhibit the chain scission in the photodegradation of poly(methoxyacrylophenone) while tin stabilisers have also been found to photostabilise PVC . 

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