# Agrochemical Contamination and Ageing Effects on Greenhouse Plastic Film for Recycling
## 2 The Effect of Agrochemicals on Greenhouse Plastic Film for Recycling  
The progressive degradation of plastic materials causes a change in their visible appearance, as well as in their chemical structure, and consequently on their physical and mechanical properties. Factors contributing to the more rapid degradation of plastics used in agriculture are related to atmospheric conditions, in particular the UV component of solar radiation [8; 9]. Other factors that also intervene, albeit to a lesser extent, are [10] air temperature and humidity, possible mechanical stress (especially caused by wind), contact with agrochemicals and possible internal stress related to the installation phase. The degradation of plastic materials can be reduced, through the use of special additives [11; 12; 13; 14; 15]. The further degradation of agricultural plastics at the end of their utilization period is directly related to the various disposal options. Describing, measuring and controlling the level of degradation of plastics is complicated by numerous technical, chemical and environmental factors [16; 17]. Assessing the effects of polyethylene (PE) ageing through weathering is a crucial task to developing more durable materials, along with a better understanding of which additives can contribute to extending the life of these polymers [18]. The global energy irradiated by the sun and arriving at a geographical area is usually accepted by the technical and scientific literature as being a relevant parameter and it is expressed in Langleys (Ly), the unit of energy distribution over an area (1 Ly = 1 cal/cm\({}^{2}\) = 41,840 l/m\({}^{2}\)). In order to understand the mechanisms of natural and artificial ageing processes of a triple-layer film made of low-density polyethylene (PE-LD) used as greenhouse cover, [PERSON] et al. [19] performed some experimental tests through natural ageing in Northern Algeria and artificial ageing at four different agricultural greenhouse simulating conditions of temperature and UV-A radiation. The results showed a significant decrease in the mechanical properties with ageing, which could be correlated with the structural changes in the film material. The natural ageing of the film in North Africa induced cleavage of the polymer chains, leading to more rapid degradation in the plastic film and, consequently, a reduction in its durability and service life, as well as mechanical recycling potential. The existing standard test methods for measuring the mechanical properties of plastic films, however, do not provide the conditions for measuring the degradation of these properties when the plastic film is used as a covering material. Various accelerated ageing tests for plastic films have been proposed in recent years, but their relationship to actual ageing has not yet been sufficiently proven [20]. In some cases, increased generation of degradation products, such as ketones, esters and alcohols (which is normal under natural conditions) was not observed under accelerated ageing conditions. A simple explanation may be that, under accelerated ageing conditions, cross-linking reactions occur due to the high number of radicals present in the polymer, thereby reducing the concentration of radicals taking part in the oxidation process. Under natural conditions, this \"surplus\" of radicals is not present and the radicals created combine with oxygen, resulting in peroxide radicals, which propagate oxidation. This observation is supported by the changes observed in the elongation at break. Under accelerated conditions, the direct consequence of cross-linking reactions is that the high elongation at break is maintained, until a relatively high level of oxidation occurs. The scientific investigations performed so far have examined the combined effect of ageing and contact with agrochemicals on plastic greenhouse film. These mostly address the variations occurring in the technical properties of this material, rather than the consequences for its end-of-life phase.