Light stabilization of metallocene polyolefins

Ultraviolet (UV) stabilization of metallocene polyolefins is examined from a practical and theoretical point of view. First of all, the possibility of using existing stabilizers and stabilizer systems is investigated. To this avail, the compatibility of the stabilizers needs to be checked at the concentrations most commonly used. It is found that, in this respect, there is no fundamental difference between conventional high-pressure polyethylene (PE-LD), linear low-density polyethylene (PE-LLD) and metallocene polyethylene (m-PE). With polypropylene (PP), stabilizer compatibility is generally not so much a problem as with polyethylene (PE). The assessment of the performance of light stabilizers is performed with compression molded films. The results so far available show that the UV absorbers and hindered amine light stabilizers (HALS) examined confer comparable UV stability to PE-LD, PE-LLD and m-PE. Similar results are observed with PP. It is found that the lifetimes obtained on artificial weathering of m-PP and third generation PP are comparable. Furthermore, the synergism between two polymeric HALS that has been observed previously with second and third generation PP is also found with metallocene polyolefins. The experimental laws relating the performance of the HALS to their concentration are deduced from the preliminary data available. It is found that they are the same as those found previously for PP and PE. With PP, W stability increases linearly with HALS concentration as long as the last is not too high. With m-PE as with PE-LLD, the performance is directly proportional to the square root of the HALS concentration. From these and additional results it is concluded that the degradation and stabilization mechanisms with m-polyolefins are essentially the same as those developed for the previous types of polyethylene and polypropylene. (C) 2001 Elsevier Science Ltd. All rights reserved.