Biodegradation of PE Films using Polybatch DEG® Technology .

Is Polyethylene Degradable? It is a commonly held fallacy that Polyethylene is not degradable. In fact, auto-oxidation reactions, accelerated by heat and light will rapidly reduce the physical strength of unstabilised polyethylene articles. The reaction mechanism is given by Zweifel(1998) in “Stabilisation of Polymeric Materials” pp.2-5, Springer-Verlag. Considerable resources are dedicated to extending the life of polyethylene articles by including light and thermal stabilisers.

Acceleration of the auto-oxidation reaction It is well known that the addition to Polyethylene of certain Organo-transition metal complexes will catalyse the auto-oxidation of Polyethylene. The reaction mechanism is discussed by Zweifel. This is the principal utilised by our Polybatch® DEG technology.

Accelerated Degradation of PE films using Polybatch® DEG 68 A. Photodegradability KLy to total embrittlement of films containing 4% DEG 68: Film thickness (microns): 12 50 150 KLy to embrittlement: 18 24 34 (The UK typically receives 80KLy of solar radiation per annum).

Accelerated degradation of PE films using Polybatch® DEG 68 B.Thermodegradability Days at 70ºC to total embrittlement of films containing 4% DEG 68: Film Thickness (microns) 12 50 150 Days to embrittlement 30 58 96 (70C is typical of the temperatures reached in composting situations).

Is PE Biodegradable? In its unoxidised state, Polyethylene is not capable of being assimilated by soil microorganisms. However, the oxidation process discussed earlier results in the following changes: A. Drastic reduction in molecular weight. B. Introduction into the polymer chain of carboxylic acid functional groups. (See Scott(1997) “Abiotic Control of Polymer Degradation”, Trends in Polymer Science, Vol.5, No. 11, Elsevier Science Ltd).

Biodegradation of PE (1) As long ago as 1974, Nykvist, at the Royal College of Forestry in Stockholm used Polyethylene labeled with Carbon 14 to show that after exposure to UV radiation and mixing with compost, evolution of Carbon 14 Dioxide took place. The rate of evolution was greatly accelerated when a photodegradation catalyst (Polybatch® DEG technology) was used.

Biodegradation of PE (2) Arnoud et.al. (1994) in “Polymer Degradation and Stability” Vol. 46. Using a mixture of techniques, including Gel Permeation Chromatography, microbial growth techniques, Scanning Electron Microscopy and FTIR, were able to show that oxidised polyethylene would support the growth of microorganisms at molecular weights as high as 40,000. The significant factor was the presence of carboxylic acid and ester groups in the polymer chain.

Conclusions. The use of Polybatch DEG 68 will accelerate the auto-oxidation of Polyethylene under the influence of heat and light.The effectiveness of this system has been proven over many years in applications such as agricultural mulch films. Scientific research has shown that oxidised polyethylene will biodegrade, the ultimate degradation products being Carbon Dioxide, Water, and a small amount of inert mineral matter.