This has led to a need for new light stabilizers to protect the plastic such as Tinuvin XT 200, which is registered for REACH and has undergone extensive field trials, including treatment of films with a wide range of current pesticides such as permethrin and methyl bromide.
Test films were set up at sites across the world including Zhejiang, Sicily and Guadalajara, and amounting to over 5000 hectares since 2006. In the BASF portfolio, Tinuvin NOR 371 and Tinuvin ST 200 light stabilisers show the best resistance to agrochemicals.
Kafrit Industries has examined the effect of UV absorbers on film resistance to pesticides. Studies showed that raising sulfur levels from around 1000ppm to 2000ppm reduced the life of greenhouse films by 20-25%. UV absorbers act by absorbing radiation and dissipating it as heat, for example by proton transfer in phenolic based chemicals.
Under artificial weathering testing BZT type absorbers degraded fastest, then TRZ type I and II, whereas TRZ III showed little change. Hindered amine light stabilizers (HALS) were added to different UV absorbers and compounded into PE/EVA films then exposed to sulfur in field trials. HALS I with BZP failed at 16 months and the best performance came from HALS II plus TRZ III, which showed the least reduction in absorbance and lasted around 30 months. Kafrit is seeing new market demand for films resistant to 3,000ppm sulfur.
EVOH (brand name Soarnol) from Nippon Gohsei is used in stretch silage films in agriculture. The material is a copolymer of ethylene for extrudability and vinyl alcohol for barrier properties. The University of Torino has shown that the oxygen barrier properties of standard PE do not preserve the quality of forage in long-term storage, because it allows yeast and fungi to grow, aerobic degradation and a rise in temperature. There are significant improvements with a thinner silage film with an EVOH layer.
Another use of EVOH in agriculture is for fumigation films, to prevent contamination of the surrounding area. EVAL Europe (part of the Kuraray Group) is a supplier of EVOH in the totally impermeable film (TIF) market; this has use in applications such as broadcast fumigation, as a fumigant barrier in mulch, as an oxygen and odour barrier in silage, and to extend the lifespan of fumigant impregnated greenhouse film. A TIF film is multilayer comprising typically, outer layers of PE, adhesive layers and a middle EVOH layer. Nylon can also be used as the barrier layer, but it is not as effective (VIF film).
Polimeri Europa supplies ethylene-vinyl acetate copolymer (EVA) used in coextruded EVA-PE films to the agricultural market and lists the benefits of the material in greenhouse and tunnel use: improved thermicity, toughness, elasticity, transparency, good creep resistance, longer lifespan and photoselectivity beneficial to crops. Use in this market is expected to increase.