UV BLOCKING ADDITIVE COMBINATIONS FOR EXTENDED SERVICE TIME

摘要

The use of UV Absorbers (UVA) as light stabilizers for polyolefin is well documented. Less known, but not less important is their use as a barrier to UV light. These organic molecules "dissolve" in the plastic medium, thus maintaining high absorption of UV radiation, and, when properly chosen, do not interfere with the visible radiation. Their solubility, though, when combined with their polar character, renders them incompatible with the non-polar polyolefin matrix. The end result being a limited life span of the blocking effect in greenhouse films. Certain inorganic compounds absorb and reflect much of the UV radiation and they disperse (and not dissolve!) as particles, within the polymeric matrix. Being large and heavy (relative to molecules) these particles are practically non-migrating. However that particulate property may cause the film to lose part of its clarity. One way of resolving the problem is by combining these two types of UV blocking additives in order to get an optimal effect. Previously we have reported data collected under accelerated, artificial exposure, and now we can already report preliminary results of our natural exposure results. Presentation of the results of these two different exposure methods will demonstrate lack of correlation between them. We shall try to elaborate this discrepancy.