Interactions between carbon black and stabilisers in LDPE thermal oxidation

Abstract

The interactions between two commercial hindered piperidine compounds, three 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 related to their chemical structure, with the main contribution being their synergism with HALS and a secondary antioxidant. Differences in the performance of the polymeric type of HALS were evidenced, as well as between the CB grades. Minor synergism and antagonism was found between HALS and CB depending on the chemical structure of the HALS. All the detected antagonisms were widely overcome by the synergistic interaction found in three- and four-additive formulations. Though the presence of CB (at the concentrations studied) was not a decisive factor in the LDPE thermal stability, its presence nevertheless showed a beneficial effect. The nature of the CB plays some role in controlling its performance as a stabilising agent alone, as well as its interactions with HALS and antioxidants, via adsorption-desorption processes as well as other chemical interactions as was evidenced by adsorption studies via flow microcalorimetry (FMC).