Polypropylene, metal impurities

On the other hand, with polypropylene, metal impurities play by far a more significant role [15] which is probably due to a considerably higher concentration of metal ions in this polymer (particularly in samples prepared from the gas phase), lower content of unsaturation, and also to the fact that polypropylene does not crosslink when oxidized. 

Polyester polyurethanes display greater oxidative stability than do polyether polyurethanes. Among polyether polyurethanes, polyethylene oxide and PTMO are more resistant than polypropylene oxide. Metal impurities, such as iron and copper, will catalyze the oxidation of polyurethanes. Copper is found to be particularly detrimental. ... 

In separate work aimed at elucidating filler effects on surface, oxidation Vesely and coworkers [39] have examined the oxidation of polyethylene and polypropylene containing high levels of calcium carbonate. The grade of filler used was found to decrease polymer thermal stability, an effect they associated with transition metal impurities. They also believe that, in the presence of fillers, heteregeneous oxidation reactions become more important. They observed black polyenes to be formed above about 320 °C and postulated that these could be acting as photo-sensitisers. 

In severe conditions of exposure, polypropylene (PP) products and films have a lifetime of only 700-1000 h, still decreasing 2 3 times in the presence of metallic impurities [29]. PP fibers are more stable, due to their morphological characteristics. 

Transition metal impurities, both from catalyst residues and from contamination picked up during processing, are present in polyolefin samples [447, 468,642,1843]. The accelerating effect of the presence of such species on the auto-oxidation of liquid hydrocarbons and polymers has been demonstrated [62, 1247]. Metal impurities play a more significant role in polypropylene than in polyethylene, probably due to the higher concentration of these moieties in polypropylene [63]. 

Hydrogen fluoride can be handled in apparatus of suitable metals (copper, nickel, magnesium, or aluminum, which all form a protective fluoride coating, or platinum), or plastic materials [especially polypropylene. Teflon, and polyvinylidene fluoride (Viton)] polychlorotrifluoroethylene (Kel-F) can be made into transparent windows. A capillary for a dropping mercury electrode may be made from Teflon [307]. Hydrogen fluoride is obtained commercially in steel cylinders in a purity of 99.5%. The impurities may be removed by distillation [308] or electrolysis [309]. During the electrolytic removal of water the explosive FoO is formed, which must be taken into consideration [305]. 

Reaction of the parent amine with transition-metal ions is also a possibility. The hindered piperidines have also been found to inhibit the photolysis of luminescent a,/3-unsaturated carbonyl groups (impurities) in polypropylene. 

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