Biosystems Engineering (2004) 88 (2), 131–143 doi:10.1016/j.biosystemseng.2004.02.010 Available online at www.sciencedirect.com SE}Structures and Environment REVIEW PAPER Degradation Characterisation of Agricultural Low-density Polyethylene Films D. Briassoulis 1 ; A. Aristopoulou 1 ; M. Bonora 2 ; I. Verlodt 3 1 Department of Agricultural Engineering, Agricultural University of Athens, Iera Odos 75, 11855, Athens; Greece; e-mail of corresponding author: briassou@aua.gr 2 CIBA, Pontecchio Marconi, Italy 3 Hyplast, Belgium (Received 16 November 2002; accepted in revised form 23 February 2004; published online 27 April 2004) Low-density polyethylene (LDPE) film is currently the most widespread greenhouse covering material in the countries of the Mediterranean region. The exposure of LDPE film to weathering conditions, especially to solar irradiation in the range of 290–400nm, affects its chemical structure and consequently its mechanical and physical properties. At present (current practice), the final characterisation of degradation of LDPE films is mainly based on the changes in percentage elongation at break. However, it is considered more realistic to base the characterisation of degradation of LDPE films on a combination of quantitative criteria. These criteria, analysed in the present review paper, represent critical properties, which should be measured in a very specific and well-harmonised way under pre-defined conditions. # 2004 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd 1. Introduction The degradation of low-density polyethylene (LDPE) film is a complicated process. The main degradation mechanisms are known but in most cases more than one mechanism takes place simultaneously and in an interactive way during the weathering of the film. Many studies have been focused on the degradation of LDPE films (Rabek, 1996; Amin et al., 1995; Schnabel, 1981; Wypych, 1995). Tests of accelerated and natural ageing are commonly used by many companies to predict film life. Accelerated ageing exposure follows the ISO 4892-2 (1994) and ASTM G155 (2000) standards. Natural ageing exposure follows the ISO 877 (1994) standard. The exposure of films to accelerated ageing in specially designed apparatus (e.g. Weather-O-Meter testers) aims at an accelerated simula- tion of the natural weathering. Several research efforts have been directed towards the establishment of a relation between the natural and artificial ageing exposures (Rabek, 1996; Wypych, 1995; Nijskens et al., 1990/3). However, no generally accepted scheme has been established so far. Moreover, the degradation under real protected cultivation conditions (e.g. films covering tunnel greenhouses) depends on the weathering conditions, the crop inside the greenhouse, the agro- chemicals used and many other factors (Dilara & Briassoulis, 2000), e.g. loads, temperature and humidity inside the greenhouse, film installation, etc.). The recently completed European Standard for ‘Covering plastic films for use in agriculture and horticulture’ (CEN/TC 249, 2002) concerns, as stated therein: ‘transparent and diffusing plastic films based on polyethylene and its copolymers which are designed to be used as covers for permanent and temporary greenhouses for forcing and semi-forcing vegetable, fruit and flower crops’ and is intended to ‘establish the basic requirements for the physical and mechanical characteristics of various types of film’. An annex has been included in this European Standard for informative purposes, which describes an ‘empirical correlation between the duration of films under artificial weathering and on the greenhouses’ (CEN/TC 249, 2002; Dilara & Briassoulis, 1998). Of course, this information should be used carefully and only as a rough indication of the real correspondence between measured artificial and predicted natural weathering. A systematic research work is needed to establish a well-justified and harmonised artificial ageing procedure which may lead to a more reliable correlation with real protected cultivation weathering conditions. ARTICLE IN PRESS 1537-5110/$30.00 131 # 2004 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd