Effects of Agrochemicals on the Mechanical Properties of Plastic Films for Greenhouse Covering

Greenhouse plastic films are subjected to degradation due to their exposure to solar radiation and to agrochemicals used during cultivation. This results in a reduction of life, which ranges from some months to 3–4 years relative to the thickness of the plastic film and to the degree of stabilisation. A research was carried out in order to evaluate the variation of the mechanical properties of 4 different polyethylene-co-vinyl acetate (EVA) films exposed to the climatic agents and to agrochemicals used during cultivation. The test was carried out at the University of Bari (Italy) in 2006. Four EVA films, one without anti-UV additive and three experimental films with different anti-UV additives, were installed on steel arches of four low tunnels. The films were sprayed with agrochemicals containing iron, chlorine and sulphur. The same films, mounted over other four low tunnels, were not sprayed in order to be used as control. Mechanical laboratory tests were carried out on the film samples, taken at fixed time intervals in the field, in order to assess the variations of the stress and strain at break. The different anti-UV stabilizers influenced the behaviour of the films in presence of the sprayed agrochemicals. The tests showed that the highest resistance to the agrochemicals was recorded for the EVA film stabilized with NOR-HALS plus UV filter.