additives feature | Oxo-degradable debate involves: a) an induction period during which oxidation
catalysis by the pro-oxidant(s) is prevented by the antioxidant stabilisers. The antioxidants prevent the creation of free radicals – but are sacrificial in this process. During this period there is no change in the polymer properties but the antioxidants are consumed. b) a rapid oxidation of the polymer, during which free
The OPA says that oxo-degra- dable master- batch is easy to produce and use
process takes several months or even years, depending on the environment. Degradation will not take place in oxygen-depleted environments such as landfill. It should be pointed out that the Wikipedia entry, which appears to be more the work of the proponents of the technology rather those that are against it, talks about ‘oxo-biodegradation’. The opponents of the additives prefer to use the expression ‘oxo-fragmenta- tion’. At the risk of pleasing neither side, this article will use the term ‘oxo-degradation’, or simply ‘oxo’, unless it is quoting an individual or concern.
The OPA claims that a bag made from
oxo-biodegrad- able plastic will turn into a
material that will biodegrade in the same way as a leaf
The case for oxo-degradables The Oxo-biodegradable Plastics Association (OPA), which is based in the UK, claims to represent additive producers and sellers, as well as manufacturers of oxo-degradable products. Symphony Environmental is a founder and active member of the association. This is how the organisation replied:
‘‘ 28
It is an unpleasant fact of life that unauthorised disposal of plastic packaging will occur. In many
nations this is an uncontrollable hazard to health and safety. Plastic packaging is an essential aid to the hygienic distribution and collation of foodstuff. But, when it has successfully performed its function it is no longer required. If it cannot be collected and recycled it is bound to become a hazard. Furthermore, waste plastic can end up floating in rivers and oceans. It has been proven that oxo-biodegradable materials will continue to degrade in aquatic environments. According to CEN (European Standards Organisation)
oxo-biodegradation is “degradation identified as resulting from oxidative and cell-mediated phenomena, either simultaneously or successively” (CEN TR 15351). ASTM 6954, BSI 8472 and UAE Standard 5009 are standards by which oxo-biodegradability can be measured. The basic technology of an oxo technology material
COMPOUNDING WORLD | August 2013
www.compoundingworld.com
radical generated chain scission produces low molecu- lar weight fragments, which are oxidised, hydrophilic, denser and polar. At that stage it is no longer a plastic and has become a material which is inherently biode- gradable in the open environment in the same way as a leaf. It therefore simulates the way nature disposes of wastes such as twigs and straw, but much more quickly than many, notably wood (lignocellulose) residues. c) a period of bio-assimilation of the oxidised .
fragments leading to mineralisation to CO2 As the period of functionality (a) is controllable, it is
perfectly possible to collect and recycle the material where collection systems exist. The following countries have already recognised the benefits of oxo-biodegradability and have introduced legislation and/or standards requiring the use of oxo-biodegradable technology: United Arab Emirates, Pakistan, Morocco, Singapore, Mauritania, DR Congo, Mali, Togo, Cameroun, Yemen, Iran, Slovenia, Serbia, Montenegro, Albania, Ecuador, Brazil, and Argentina. From a compounding perspective, the masterbatch
is relatively straightforward to produce. Twin-screw compounders operating at normal polyolefin processing temperatures are used. The active ingredients are carried in an appropriate polyolefin carrier – typically
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