additives feature | Oxo-degradable debate
simply fragment, Wells has proven that this is not the case. The fragmentation is simply the fi rst step in the oxo-biodegradation process. Properly formulated Reverte fi lms can be made to degrade at ambient temperature in short periods to materials whose molecular weights are such as to make them biodegradable. Properly formulated Reverte fi lms, once degraded, can be shown to mineralise to O; greater than 90% mineralisation has been
CO2 and H2
demonstrated in independent laboratory testing. It is not possible to prescribe a timescale in a general stand- ard for oxo-biodegradable plastics because the conditions found in the open environment are variable. Moreover, the time taken for oxo-biodegradable plastics to commence and complete the processes of degrada- tion and biodegradation is also variable.
Oxo-biodegradable technology is effective particu-
larly for short-life fi lm product applications made with polyethylene and polypropylene. End products with short shelf and service lives and physical properties essentially identical to the conventional polyolefi n have been shown to degrade (as controlled by the additive formulation) in a predictable timeframe at the end of service life, and then biodegrade into the environment. The incremental cost of using the additive to the
processor is small and processing continues in the same way with the same processing equipment as for conventional polyolefi ns. Oxo-biodegradable plastics have been shown to be
compatible with post production and existing post-con- sumer recycle streams, and they are compatible with all methods of plastic disposal including landfi ll, recycling and incineration. Oxo-biodegradable end products are fully compliant with the current European food contact and US Food & Drug Administration requirements. The technology can be applied to most PE and PP applica- tions from food packaging to shopping bags, agricul- tural fi lms to construction covers, and medical to personal care product containers. Wells Plastics laboratories measure the fi rst stage of degradation (oxidation) using carbonyl indexing and embrittlement point determination, processes which were developed at Wells and are now adopted by the
General scheme of oxo-biodegration of aliphatic polyolefi ns
Source: Emo Chiellini
industry. What makes Reverte stand out is the profi le of degradation. The curve of carbonyl index versus time starts off very fl at. After this “dwell time” has been passed, the degradation then proceeds rapidly until the embrittlement point is reached and beyond that the plastic falls apart. The molecular weight is lowered and the material available for bio-digestion.
Professor Emo Chiellini, at the INSTM Research Unit within the University of Pisa’s Laboratory of Bioactive Polymeric Materials for Biomedical & Environmental Applications in Italy, has done a considerable amount of research in the fi eld of oxo-degradation. This is his contribution:
’’ ‘‘
The specifi c tandem role of oxo-biodegradable additives Source: Emo Chiellini
32 COMPOUNDING WORLD | August 2013
Oxo-biodegradable additives exhibit a tandem feature – a pro-oxidation step followed by a pro-degradation reaction cascade – in aliphatic poly-alpha-olefi ns that, upon conversion to functional fragments, become attractive to micro-organisms (see illustration). As such, they can play a key role in the mitigation of the burden tied up with the uncontrolled littering of fl exible and semi-fl exible packaging items based on different PE and PP grades.
Questions that are often posed by the antagonists of oxo-biodegradable plastics (OBPs) are:
1) “OBPs are not recyclable.” This is false, as it is amply demonstrated by scientifi c literature and reports that OBPs are mechanically recyclable in streams with additive-free counterparts, and can be also used as solid combustibles in incineration plants with energy recovery (1,2).
2) “The oxidized fragments abandoned in the
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