NEW TRENDS IN THE STABILIZATION OF POLYOLEFIN FIBERS

Stabilization of polyolefin fibers is discussed with special emphasis on UV stability and long-term heat aging (LTHA). Hindered amine light stabilizers (HALS) show significantly better performance in polyolefin fibers than other classes of light stabilizers. Furthermore, combination of HALS with a light stabilizer of a different type does not usually lead to synergistic effects in polyolefin fibers. The best effects in this respect are obtained with combinations of two light stabilizers of the HALS type. Combinations of low molecular mass HALS with high molecular mass or polymeric HALS as well as combinations of two high molecular mass HALS can be envisaged. It is shown that, depending on the substrate form and the application, one or other combination type gives the best results in PP fibers. LTHA of polyolefin fibers was achieved classically by using high molecular mass phenolic antioxidants. In this respect, the major development consists of an increasing use of high molecular mass or polymeric HALS. The choice of a HALS or a phenolic antioxidant for improved LTHA is dictated by the projected application because the performance advantage can be either in favor of the HALS or the phenolic antioxidant. This depends mainly on the testing temperature and the chosen test criterion. The quantitative laws relating the performance of the HALS on UV exposure or thermooxidative aging to their concentration are formulated and discussed in detail.