Artificial ageing of tri-layer polyethylene film used as greenhouse cover under the effect of the temperature and the UV-A simultaneously

This study helps to understand the mechanism of artificial ageing of a tri-layer film made of low-density polyethylene (LDPE) Agrofilm with additives (color dye, UV and IR stabilizers) used as greenhouse cover under the variations of the temperature with or without UV-A radiations. Ageing was monitored by observing the change of physical properties (free surface energy, color) mechanical and structural effects (Tensile tests, DSC, FTIR) during 5486 h (almost 8 months). The study shows that increase in the free surface energy is proportional to the temperature and that the increase is more pronounced when the film is subjected to the combined action of the temperature and the UV-A radiations. The mechanical tests reveal that both elongation at break and yield stress decrease with the ageing. The calorific curves exhibit two endothermic peaks of melting close together (100 degrees C and 110 degrees C) which means the presence in the film of at least two types of crystalline structures. From free surface energy results, the life time of these films under artificial conditions is estimated to 12 months when exposed to 40 degrees C but drops to 3 months and 18 days when exposed simultaneously to 50 degrees C and UV-A. (C) 2009 Elsevier Ltd. All rights reserved.