Oxo-biodegradable polyolefins

Most scientists, even some polymer chemists, will not be familiar with this type of thermoplastic, so a description is called for. The term oxo-biodegradable plastic is commonly restricted to those plastics that, owing to particular compositional features or by means of additive chemistry, undergo oxidative degradation much more rapidly than would otherwise occur in a variety of environments. Although the plastic initially is bioinert, the oxidation products are biodegradable. 

Polyolefins are generally understood to be relatively bioinert. Indeed, polyethylene is specified as a negative control in the ASTM Standard Test Method (D5338) for Determining Aerobic Biodegradation of Plastic Materials. It is now well established, however, that the oxidation products of polyethylene are readily biodegradable (see section 3.5). In order to achieve rates of oxo-biodegradation for polyolefins that are compatible with established practices of plastics use and disposal, it is necessary to add one or more of an assortment of 

It is worth remembering that oxo-biodegradation is of major significance in nature as a principal pathway by which the chemical elements in organic materials, e.g., wood and other lignin-containing materials, natural rubber, are returned to the biocycle. 

The alkoxy radical (RO ) is exceedingly unstable. It will decompose spontaneously to form ketones or aldehydes (depending on the structure of the parent hydroperoxide group) and these carbonyl compounds will undergo further oxidation to produce acids esters and the like that are similar to naturally occurring materials. Professor Albertsson and her colleagues have 

Unless the parent hydroperoxide group is close to the end of the polymer molecule to which it is attached, the spontaneous reaction (referred to as the /3-scission reaction) of the RO group will lead to significant molar mass reduction two times out of three. The other type of reaction of the alkoxy radical is abstraction of a hydrogen atom from a nearby polymer chain segment (reaction 3.9). 

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Oxo-Biodegradable Polyolefins Carbon-chain polymers Hetero-chain polymers... 

Manufacturers and users of oxo-biodegradable polyolefins view with concern the development of standards for degradable polymers which demand a high level of mineralization as the primary criterion. This protocol was originally developed for hydro-biodegradable polymers, which will primarily end up in sewage. For these polymers and in this application, such test methods are entirely acceptable but they are totally inappropriate for compost, litter and agricultural applications. 

Degradable polymers destined for composting should, therefore, be modelled on the behaviour of lignin as far as possible [12]. Oxo-biodegradable polyolefins, particularly the polyolefins and polystyrene, have been shown to be particularly suitable for this application. They cannot, because of their chemical structures, ultimately produce any products other than carbon dioxide and water. The practical applications of these materials are the main focus of this Chapter and composting standards for degradable polyolefins will be discussed in Section 9. 

Many types of post-consumer plastic packaging that are not recovered by recycling are disposed of in landfills. There are many environmental advantages (see section 3.7) to be achieved by using oxo-biodegradable polyolefins in these applications but safety considerations are equally important. Keller Heckman (the US/Intemational specialist law firm) conducted the certification and validation work for TDPA formulations required by the US Food and Drug Administration. Most TDPA formulations have been cleared for use in any type of food packaging, for any type of food. Likewise, TDPA formulations are considered safe by the SCF (Scientific Committee for Food) of the European Union. 

Discarded plastics are a serious problem in fireshwater as well as marine environments. The difficulties in addressing this situation include the complexity of identifying the origins of this pollution and the variety of plastics involved. Partial alleviation of these problems can be envisaged for those short use-life items that are or could be made fi om polyolefins. If these products are made fi-om oxo-biodegradable polyolefins, then the combination of heat, sunlight and... 

As currently formulated, EN 13432 discriminates against manufacturers of oxo-biodegradable polyolefins since certification of biodegradable plastics as compostable requires compliance with this published Standard. This clearly... 

It is well known that as-produced, commercial polyolefins are bioinert. It was demonstrated unequivocally during the 1990s, however, that the oxidation products of polyolefins are biodegradable (see Ch. 3, section 3.5). The characteristics of specific products made from oxo-biodegradable polyolefins are the focus of the remainder of this chapter. 

The cost of EPFs TDPA-based oxo-biodegradable polyolefins is only incrementally higher than that of the ordinary polyolefins that they replace. 

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