Polyolefins biodegradation

The CNEP [LEM 12] recommended this method to demonstrate the biodegradability of pre-treated additive polyolefins. Biodegradability is said to have occurred if after 180 days, the ATP assay gives a value of at least 100 times greater than the content of ATP determined during the initial incubation with the selected micro-organisms Rhodococcus, Nocardia, Aspergillus, Mortierella and Cladosporium. 

The mechanism of polyolefin biodegradation is not entirely clear but a likely hypothesis is that it follows paraflin biodegradation by microorganisms (Albertsson, 1978). In this case, abiotic degradation converts the polyethylene into low molecular weight fatty acids that are sorbed by the cells and undergo p oxidation. 

AC Albertson, B Ranby. Polyolefines biodegradation. Proceedings of the Third International Symposium on Biodegradation, Kingston, 1975, pp 743-745. 

Nocardia and P. aeruginosa were shown to break the cw-PI chain by an oxidative mechanism since aldehyde groups were found to accumulate during microbial degradation. This is always the first product formed during the abiotic peroxidation of cw-PI and the evidence suggests that the bacteria initiate a radical-chain peroxidation. This will be discussed further in the context of polyolefin biodegradation. 

Rayon is unique among the mass produced man-made fibers because it is the only one to use a natural polymer (cellulose) directly. Polyesters, nylons, polyolefins, and acryflcs all come indirectly from vegetation they come from the polymerization of monomers obtained from reserves of fossil fuels, which in turn were formed by the incomplete biodegradation of vegetation that grew millions of years ago. The extraction of these nonrenewable reserves and the resulting return to the atmosphere of the carbon dioxide from which they were made is one of the most important environmental issues of current times. CeUulosic fibers therefore have much to recommend them provided that the processes used to make them have minimal environmental impact. 

Compared with more common plastics used as packaging materials, the compound does have some disadvantages, such as a high water vapour permeability and limited heat resistance, losing dimensional stability at about 70°C. It is also substantially more expensive than the high-tonnage polyolefins. Last but not least its biodegradability means that it must be used in applications that will have completed their function within a few months of the manufacture of the polymer compound. 

Other uses of blends include controlled rate of fertilizer release(77) based on ethylene/vinyl acetate/carbon monoxide polymers which is U.V. sensitive, polyolefin blends with any biodegradable polymers,(78) and polyolefins blended with metals and autoxidizable substrates. (79) Doane and co-workers(80) at the U.S.D.A. have used grafted starches in many applications, including soil stabilization. 

Paraffins may not only be additive in PE but can also be regarded as the low molecular coimter part of S3mthetic polyolefins. Several groups have performed studies on the biodegradation of alkanes. Jen-Hao and Schwartz (12) were probably the first to claim that the number of bacteria that PE was able to support was dependent on the molecular weight of the pol3nner. 

There have been more efforts to use blends such as Nova Chemicals Arcel (an ethylene styrene interpolymer in bead form) to create a more durable foam than EPS. EPP can be moulded into complex shapes, with the steam bonding of the beads (291). These packaging foams compete with polyolefin film products such as Jiffy foam (bubblewrap) and macrobubbles made by heat sealing 150 mm lengths of tubular LDPE film. As it is difficult or costly to recycle such foam products, in some countries there is a move towards biodegradable starch foams and moulded paperboard. 

Biodegradable polymer prices are generally much higher than commodity polymers for a number of reasons. Most biopolymers have only been commercially available for a couple of years and production volumes are very low compared with the mass produced polyolefins. Initial development costs are also very high. 

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... 

Films containing filler may have a substantially improved UV stability due to the addition of carbon black. It is also possible to produce films which will be biodegradable by the combined action of UV degradation and biodegradation. It was confirmed that china clay increases the degradation rate of polyolefins by consuming stabilizers and thus reducing polymer stability... 

The development of commercially useful polymers in the early 20th century ushered in an era where mass-produced, organo-polymeric materials have become a ubiquitous part of daily life. " Sixty years after the Nobel prize-winning discovery by Ziegler and Natta, " the scale of worldwide polyolefin production is massive. The current estimated aimual global production of polyolefins is over 150 million metric tons. However, the inherent chemical inertness of these substances causes them to persist in the environment centuries after they have been discarded. The detrimental environmental impact of a man-made waste problem of this scale has generated an interest in commercially viable, biodegradable alternatives. ... 

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