Evaluation of the oxidative stability of multiextruded polypropylene as assessed by physicomechanical testing and simultaneous differential scanning calorimetry-chemiluminescence
Pk. Fearon et al., Evaluation of the oxidative stability of multiextruded polypropylene as assessed by physicomechanical testing and simultaneous differential scanning calorimetry-chemiluminescence, J APPL POLY, 79(4), 2001, pp. 733-741
Common physicomechanical tests comprising impact strength, the melt flow in
dex (MFI), and the yellowness index (YI) were used to study the thermooxida
tive stability of polypropylene (PP) following multipass extrusion. Differe
ntial scanning calorimetry (DSC) coupled with chemiluminescence (CL) monito
ring was also used to assess the stability. Three PP formulations were stud
ied: ii) PP-1 containing 0.050% w/w of the phenolic antioxidant Irganox 101
0(TM), (ii) PP-2 containing 0.028% w/w Irganox 1010, 0.056% w/w of the phos
phite costabilizer Irgafos 168(TM) and 0.014% w/w of the lactone processing
stabilizer HP 136(TM), and (iii) PP-3 containing 0.050% w/w Irganox 1010 a
nd 0.100% w/w of the phosphite Ultranox 641(TM). All formulations contained
0.045% w/w of the hydrotalcite acid scavenger DHT-4A(TM). The results sugg
est that physicomechanical tests cannot reliably detect the small differenc
e in the stability between PP-2 and PP-3 but can detect the larger differen
ce between these and the less stable PP-1. The oxidative induction time (OI
T) determined by CL monitoring(i.e., CL-OIT) is consistent with the OIT det
ermined by DSC but has better reliability. The CL-OIT data suggest that PP-
3 has superior oxidative stability to PP-2 in the early stages of multipass
extrusion. However, PP-2 exhibits a better resistance to yellowing. A corr
elation between the CL-OIT data and each of the MFI and YI data was found.
(C) 2000 John Wiley & Sons, Inc.