Effect of weathering on UV-stabilized low density polyethylene films (LDPE) for a multilayer greenhouse cover

Abstract

Multilayer films for greenhouses is a current trend in industry. LDPE films for the top layer, stabilized with different concentrations (0·1, 1·0 and 2·5%) of a nickel quencher, were produced in the laboratory by blow extrusion. The effect of natural weathering on the film properties was investigated over a period of 12 months. Significant changes in the mechanical properties were observed in the later stages of degradation. Films stabilized with 0·1% stabilizer crumbled after 12 months of natural weathering whereas films with higher concentrations retained their mechanical properties. We believe that inclusion of the UV stabilizer interferes with the crystallization process and the stabilizer particles accumulate in the amorphous matrix. Degradation of the imperfect crystalline region with its low oxygen permeability, proceeds via cross linking whereas chain scission predominates in the amorphous region with excess of oxygen. Films stabilized with 2·5% nickel quencher form a barrier against the transmission of UV radiation and the bottom layers are least affected by UV radiation. Recycled material can, therefore, be incorporated at high concentrations into these layers.