Monitoring the degradation of partly decomposable plastic foils

Gabriella RÉTHÁTI, 1* Krisztina POGÁCSÁS,1 Tamás HEFFNER,2 Barbara SIMON,1 Imre CZINKOTA,1 László TOLNER,1 Ottó KELEMEN,3 Viktória VARGHA2

1Szent István University, Institute of Environmental Sciences, Department of Water and Waste Management, H-2103 Gödöllő, Páter K. St. 1. (*corresponding author)

2Budapest University of Technology and Economics, Department of Physical Chemistry and Materials Science, H-1111 Budapest, Műegyetem rkp. 3-9.

3Qualchem Zrt., H-2072 Zsámbék Új Gyártelep

Manuscript received 07. 21. 2014; revised 07. 20. 2014; accepted 05. 09. 2014

Abstract: We have monitored the behaviour of different polyethylene foils including virgin medium density polyethylene (MDPE), MDPE containing pro-oxydative additives (238, 242) and MDPE with pro-oxydative additives and thermoplastic starch (297) in the soil for a period of one year. A foil based on a blend of polyester and polylactic acid (BASF Ecovio) served as degradable control. The experiment was carried out by weekly measurements of conductivity and capacity of the soil, since the setup was analogous to a condenser, of which the insulating layer was the foil itself. The twelve replications allowed monthly sampling; the specimen taken out from the soil each month were tested visually for thickness, mechanical properties, morphological and structural changes, and molecular mass. Based on the obtained capacity values, we found that among the polyethylene foils, the one that contained thermoplastic starch extenuated the most. This foil had the greatest decrease in tensile strength and elongation at break due to the presence of thermoplastic starch. The starch can completely degrade in the soil; thus, the foil had cracks and pores. The polyethylene foils that contained pro-oxydant additives showed smaller external change compared to the virgin foil, since there was no available UV radiation and oxygen for their degradation. The smallest change occurred in the virgin polyethylene foil. Among the five examined samples, the commercially available BASF foil showed the largest extenuation and external change, and it deteriorated the most in the soil.

Keywords: polyethylene foil in soil, capacity, conductivity, tensile strength, elongation at break