ISSN:
0022-3832
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
Oxidation rates of several uninhibited polyolefins were determined in the temperature range 40-140°C. The logerithm of the induction period increased linearly with 1/T, no changes in slope being noted in the melting range with polythylene. At the lower temperatures branched polythylenes were more susceptible to oxidation than the linear types. In the solid statem, oxygen uptake of both modifications were substantially less than that observed for the molten polymer. The amount of oxygen reacting in the solid state was shown to be inversely proportional to the per cent crystallinity, which indicates that reaction with oxygen takes place only in the amorphous region of these semicrystalline polymers. Isotactic polypropylene was only slightly less reactive than the atactic form, and both were more reactive than polyethylene. The effect of temperature on the activity of several moderately effective anotioxidants in branched polythylene was measured. These data also conform to linear Arrhenius-type plots. Activation energies were specific, however, for each antioxidant and varied considerably; thus, an antioxidant rated as relatively ineffective under accelerated testing conditions could be quite effective within the temperature range over which it would normally be used as a polythylene protectant. Carbon black, which is comparable with some to the less effective thermal antioxidants under accelerated test conditions, provided an unexpected high order of protection for polyethylene below the melting point. This increased protection in the solid state was attributed to the impermeability of the crystalline phase to oxygen and increased concentration of the bulky carbon (antioxidant) particles in the amorphous region.
Zusätzliches Material:
9 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1959.1204113801
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