# Agrochemical Contamination and Ageing Effects on Greenhouse Plastic Film for Recycling
## 5 Discussion

Table 3: Variations in the Carbonyl Index during the ageing period. ageing in combination with agrochemicals, was examined by [PERSON] et al. [35]. The authors showed that the presence of a barrier layer (ethylene vinyl alcohol--EVOH or polyamide--PA) adversely affects the mechanical behavior of multilayer films. The reduction in mechanical performance is due to the low ductility of these barrier layers, the failure of which propagates to the other layers, leading to premature failure of film structures. From a morphological point of view, polyethylene is a semi-crystalline polymer with alternating crystalline and amorphous layers (two-phase system). Oxidation damage confined to the amorphous phase causes a break of the tie molecules that link the various crystalline lamellae and leads to a sudden loss in properties at the break. The previous observation is relevant to the assessment of the effect of ageing on the degree of crystallinity within the PE-LD film and correlating these with the changes in the overall mechanical properties. The degradation of the mechanical behavior of a PE-LD film is due to the changes that occur due to ageing of the molecular structure of the material. Any loss in chain length lowers the tensile strength and is a primary cause of premature failure and cracking. The gradual changes in the molecular structure due to ageing do not allow the polymer chains to reorient as before and provide additional resistance following the initial yield of the material. The energy carried by the UV portion of the sunlight is absorbed by a variety of structural defects. In this instance, additional groups (carbonyl, hydroxyl and/or hydroperoxide) will be built into the structure of the macromolecules as a result of photo-oxidation, leading to chain scissoring, a reduction in the average molecular weight and then deterioration of the physical-mechanical properties, to the extent that it makes the polymer no longer usable [36]. The degradation process may be delayed by a special balance of inhibitors, engineered to the specific application and anticipated life expectancy of the plastic, thereby enabling a longer lifetime of the plastic material. In the case of plastic materials employed for crop protection, it is important to determine whether the design (i.e., the physical/chemical properties) of agricultural plastics allows them to be recycled. [PERSON] et al. [37] tested the intrinsic characteristics (e.g., tensile strength, moisture, contaminants) of various categories of agricultural plastics during use, storage and transport, to determine the extent to which these characteristics may change over time and hinder the recyclability of the plastic material. The applications studied included plastics used in greenhouses, high tunnels, low tunnels, much and silage films. The study found that the intrinsic characteristics of most of the tested agricultural plastics did not present elements hindering their recyclability, with the exception of the PE films with pro-oxidants, which were considered as not being recyclable. The experimental data also showed that the Melt Flow Index (MFI) measurement may be considered to be a useful indication for the analysis of the degradation of some polymers after their useful lifetime, as well as after reprocessing. Finally, the exposure of most agricultural plastic waste categories to UV radiation from the sun during their useful lifetime does not lead to severe degradation that would make them \"not recyclable\" (because of their stabilization/additive systems). The results of the present study appear in agreement also with other experimental research as well, as the one performed by [PERSON] and [PERSON] [38], who tested multilayer PE-LD/EVAC greenhouse films manufactured on purpose by adding different anti-UV stabilizer systems, that were exposed to natural, outdoor weathering at an experimental farm.