Discoloration Resistant Polyolefins: Part IV; Gamma Irradiated LLDPE Film, 2005 PLACE Conference

The preservation of physical properties and aesthetics are two important aspects of the film industry. As such, forethought and care need to be taken in terms of the type of polymer and stabilization systems that are used to derive robust and attractive film products. For most applications, a combination of a phenolic antioxidant and a phosphite melt processing stabilizer can provide the base stabilization that is necessary to provide the retention of physical properties, good processability, and long term thermal stability without compromising the overall aesthetic appearance of the film product. However, in selected end-use applications, it is particularly desirable to have film products that do not discolor during initial processing or while the product is kept in storage. Under a selected set of circumstances, certain types of phenolics have been shown to be susceptible to discoloration, due to inadequate stabilization, harsh processing, film storage with oxides of nitrogen (pollution), and various types of ionizing radiation. In particular, gamma irradiated polyolefins films are finding a variety of end use applications in areas such as medical packaging as well as hygiene related articles where sterilization plays a key role in the life cycle of the plastic product. There is also significant potential with food packaging. While this sterilization technique is valued by end users, the stress on the plastic article is quite significant in terms of not only maintaining the original physical properties of the product, but also it’s aesthetic appearance. The study described below was carried out in a film grade linear low density polyethylene where “phenol” and “phenol free” stabilization systems were compared in regard to their ability to maintain physical and aesthetic (discoloration) properties of the polymer. The results of this study demonstrate that “phenol free” systems were better than the phenol based systems.