Polypropylene oxygen induction time

Figure 20 An increase of induction time of oxidation of polypropylene stabilized by Irganox 1010 (points 1) due to prior sample annealing at 130°C (points 2) in oxygen. The induction time corresponds to the time of cross-section of the straight line passing the CL inflexion point and time axis. It was determined for an oxygen atmosphere and temperature 150°C.

Fig. 2. The plot of induction time of oxidation of polypropylene (oxygen, 150 °C) on time tA of the polymer annealing in nitrogen at 150 °C...

Fig. 7. Plots of oxygen uptake against time [333] (a) linear, polymers that show no induction period but absorb oxygen at a relatively constant rate (polymethylmethacrylate, polystyrene, polycarbonate) (b) autoretardant, polymers that exhibit no induction period but initially absorb oxygen at a relatively rapid rate, followed by a slower steady rate (polyethylene, polypropylene, nylons) (c) polymers that display autocatalytic behaviour (the modified acrylics, acrylonitrile—butadiene—styrene copolymer) (d) polymers that can be considered a combination of autocatalytic and autoretardant, (c) and (d) can be considered as autocatalytic, since the processes usually become autoretardant in the later stages of oxidation.

We cannot doubt that the large number of cases of mutual intensification of the effectiveness, observed when mixtures of antioxidants with sulfides are introduced into polymers [73, 74], is explained by the theory formulated above. Of all the mixtures investigated up to this time, a mixture of pyrocatechol phosphite ionol with di-tert-butyl-p-cresol sulfide (SAO-6) has proved the most effective. At a summary concentration of 0.015 mole/kg, this mixture lengthened the induction period of the oxidation of polypropylene to 400 min at 200°C and an oxygen pressure of 200 mm Hg (Fig. 26). 

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