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process at high temperature (e.g. 180 C for PVC, 220 C for the PP);
high shear stress during the process (e.g. injection of the PP with 240 C);
light
ionizing radiations
metals, residues of polymerization catalysts
critical conditions
critical conditions
radicalar mechanism
radicalar mechanism
(thermal oxidation for polyolefines and PVC)
PH
P
initiation = alkyl P
P + O
2
POO
conversion in peroxi POO
POO + PH
POOH + P
propagation, hydroperoxide POOH
POOH
PO + HO
PO = alcoxy
2 POOH
PO + POO + H
2
O
2 PO
POOP
peroxide
POOP
2 PO
PO, PS ARE ALWAYS FORMULATED
TO PREVENT THE THERMO-OXIDATION
+heat
Initiation
PH (polymer)
+ O
2
+PH
carbonyled products
chain breaking
PO + HO
POOH
POO
P
if present
reactions with secondary
antioxidants
(phosphite, thioether)
if present
reactions with
primary
antioxidants
(phenolic)