Why does film plastic sometimes deteriorate where it contacts the high tunnel structure?
Film plastic is often weakened when in contact with greenhouse structural components, especially PVC framing materials. The background on this starts with the green tint greenhouse films produced from 1960 through the early 1980s, which used a nickel-based ultra-violet (UV) stabilizer that was not affected by free chlorine, fluorinated hydrocarbons, and the volatile plastizers found in PVC. By 1983, long-life films were UV-protected not by the nickel-based UV-stabilizer, but by clear UV-inhibitors called ‘hindered amine light stabilizers’ (HALS). These films had high clarity and did not darken with age. One of the drawbacks with the HALS UV-stabilizers is that as the film is exposed to free chlorine, fluorinated hydrocarbons, selected pesticides, sulfur, and volatile plastizers found in PVC pipe, the stabilizer complex becomes inactivated. When this happens, the life of the greenhouse film is shortened, especially where it contacts the PVC. For this reason, all polyethylene manufacture
