Monitoring the degradation of partly decomposable plastic foils

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.

Behavior of Polyethylene Films in Soil

“…This type of monitoring degradation was done first time by us. These results are reported in a previous publication [42]. Temperature of the soil was 20±2°C.…”

“…Compared to the polyethylene films the BASF film degraded the most in the soil. Results of conductivity and capacity measurenents are reported in [42].…”

“…The bags made from the films were buried in soil and monitored monthly for one year. The soil served as a condenser, and capacity and conductivity of the soil were tested weekly and proved to be adequate tools for monitoring degradability [42]. Macroscopic changes of the films were tested monthly, namely visual appearance, mechanical, structural, morphological changes and the molecular mass.…”

“…Total C % was determined by Walkley-Black methods [42] Total nitrogen % was measured by using micro-Kjehldal analysis NO 3 -N+NH 4 -N: Mineral form of Nitrogen in soil. Determined by Parnas-Wagner distillation from soil extraction (1% KCl solution ).…”