The interactions between two commercial hindered piperidine compounds, thre
e commercial antioxidants, a secondary antioxidant and two types of furnace
carbon blacks (with a different surface area and surface chemistry) in the
thermal oxidation of LDPE have been studied using the oxidation induction
time test. During thermal degradation the interactions were variable, being
both antagonistic and synergistic. Generally, for the primary antioxidants
alone their thermal stabilising effects on the polymer were decisive and r
elated to their chemical structure, with the main contribution being their
synergism with HALS and a secondary antioxidant. Differences in the perform
ance of the polymeric type of HALS were evidenced, as well as between the C
B grades. Minor synergism and antagonism was found between HALS and CB depe
nding on the chemical structure of the HALS. All the detected antagonisms w
ere widely overcome by the synergistic interaction found in three- and four
-additive formulations. Though the presence of CB (at the concentrations st
udied) was not a decisive factor in the LDPE thermal stability, its presenc
e nevertheless showed a beneficial effect. The nature of the CB plays some
role in controlling its performance as a stabilising agent alone, as well a
s its interactions with HALS and antioxidants, via adsorption-desorption pr
ocesses as well as other chemical interactions as was evidenced by adsorpti
on studies via flow microcalorimetry (FMC). (C) 2001 Elsevier Science Ltd.
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