AGROCHEMICALS CONTAMINATION AND AGEING EFFECTS ON GREENHOUSE PLASTIC FILM FOR RECYCLING

The final results enabled to evaluate how agrochemical contamination and solar radiation influence the technical properties of a PE-LD greenhouse film, as well as its feasibility to be recycled into a new secondary product. It was shown that the contact with agrochemicals plays a decisive role in the degradation process of the plastic film, confirming that agrochemicals generate by-products leading to degradation of greenhouse films together with a decrease in their mechanical and physical properties. The degradation due to agrochemicals was found to be dependent on their active principles, as well as on method and frequency of application. In general, the effect of the UV radiation on the PE-LD film revealed to be dominant, as expected, while the synergistic effects and the relative importance of exposure to the two different agrochemicals in the degradation of the films were significant as well. Hence, the effect of its exposure may result in dramatic deterioration of the film when applied alone, since it may accelerate ageing, with possible unfavourable repercussions on the process of mechanical recycling of the greenhouse plastic film after the end of its useful life.

Agriculture is the most important sector for the application of plastic material as a primary building component. Within civil and industrial constructions, the use of this material is limited to complementary applications, as window or door frames, flooring, insulating or facing covers, etc. In agriculture, when employed as a covering material for protecting cultivation, plastic plays a central role, by performing a passive effectprotecting the crops from negative weather conditionsand, at the same time, an active effect, realizing a more favourable environment for the crops, since it decisively contributes to valorising the solar radiation.
The increasing use of plastic films in protected cultivation calls however for further on-depth studies on their durability and suitability to the Circular Economy concept, to contribute reducing the plastic footprint in agriculture. The use of plastics in agriculture generates, in fact, serious environmental problems, as those connected with the management of large amounts of post-consume material, mainly in areas characterized by a fragile environment and a marked tourist vocation. In order to explore new possibilities in the use of plastic material in the agricultural sector, characterized by a lower environmental impact, a better understanding of the factors hindering its mechanical recycling is needed, so as to transform the post-consume plastic material into a new secondary product. In this sense, the conditions in which plastic materials conclude their useful life after application in agriculture play a decisive role. Among the factors contributing to a faster degradation of agricultural plastics, atmospheric conditions are the main components, mostly if the UV component of the solar radiation is considered. Moreover, other factors are more or less involved, as reported in Table 1.

Table 1: Main ageing factors for a plastic material used for application in protected cultivation
Ageing factor -) solar radiation, mainly the UV component; -) temperature and relative humidity; -) contact with the oxygen contained in the air and in the rain water; -) mechanical effect of wind, rain and snow; -) contact with air dust and atmospheric pollutants; -) contact with agrochemicals; -) contact with the agricultural soil; -) contact with supporting structural frames; -) internal stress connected with the installation phase and the external factors.
Degradation of plastic material plays also a role in the environmental sustainability of their use in agricultural applications. Indeed, the study of the ageing of PE through weathering is of great importance for the development of more resistant materials and of additives that will extend the durability of such polymers, as well as for their mechanical recycling after the end of their useful life. The degradation in the mechanical behaviour of PE-LD film is due to the changes occurring in the molecular structure of the material. The degradation process may be delayed, enabling a longer useful lifetime of the plastic material, by a special balance of inhibitors engineered to the specific application and to the anticipated life expectancy of the plastic. Heat, ultra-violet radiation, stress and other factors (e.g., contamination with agrochemicals) can accelerate the degradation process of the material. Further degradation of the aged agricultural plastics (i.e., agricultural plastic waste) following their useful lifetime is directly related to the various disposal options. Describing plastics degradation, measuring it, and controlling it are all issues that are complicated by many technical, chemical and environmental factors.
The scientific investigations so far performed, have examined the combined effect of ageing and contact with agrochemicals on the greenhouse plastic film, mostly focusing on the time duration of the technical properties of this material employed for covering the greenhouse, rather than the effects on its post-consume recycling. In the present paper, the results of laboratory tests on agricultural plastic film artificially aged for different periods, after being contaminated with two different agrochemicals, are presented, so as to critically assess the effects on mechanical recycling. A PE-LD plastic film was contaminated alternatively with the insecticide EPIK SL VITHAL (Acetamiprid 50 g/l) and the fungicide CUMETA FLOW (Metalaxil-m 1,85% copper), which were sprayed on one side of the plastic film, then aged for 2 and 4 weeks in an ageing chamber (Fig.1), in which also temperature was kept constant at 20°C. After the ageing process, each plastic film was tested through tensile tests to determine its mechanical properties ( fig. 1), as well as in a spectroradiometer, to determine the change in the optical characteristics of the film. In addition, the ageing effects on the polymer´s chemical structuree.g., surface oxidation, chain scissoring and bonds shifts -were evaluated through FTIR and FTNIR spectroscopy. The final results enabled to evaluate how agrochemical contamination and solar radiation influence the technical properties of a PE-LD greenhouse film, as well as its feasibility to be recycled into a new secondary product. It was shown that the contact with agrochemicals plays a decisive role in the degradation process of the plastic film, confirming that agrochemicals generate by-products leading to degradation of greenhouse films together with a decrease in their mechanical and physical properties. The degradation due to agrochemicals was found to be dependent on their active principles, as well as on method and frequency of application. In general, the effect of the UV radiation on the PE-LD film revealed to be dominant, as expected, while the synergistic effects and the relative importance of exposure to the two different agrochemicals in the degradation of the films were significant as well. Hence, the effect of its exposure may result in dramatic deterioration of the film when applied alone, since it may accelerate ageing, with possible unfavourable repercussions on the process of mechanical recycling of the greenhouse plastic film after the end of its useful life.