Studies of synergism between carbon black and stabilisers in LDPE photodegradation

The interaction between two commercial hindered piperidine compounds, three commercial anti-oxidants, a secondary antioxidant and two types of furnace carbon black (CB) (with a different surface area and surface chemistry) in the photo-oxidation of LDPE film have been studied using FTIR infrared spe ctroscopy. The nature of stabiliser-CB interactions has also been analysed through the use of flow microcalorimetry. The stabilisers used are, a comme rcial polymeric HALS, namely Chimassorb 944(R), and Tinuvin 622(R) LD(R), p rimary and secondary antioxidants, namely Irganox 1010(R) and Irganox 1076( R), Cyanox 1790(R) and Irgafos 168(R). For the fillers, two carbon blacks w ere chosen with different features as the specific surface particle size an d chemistry. During photo-oxidation the interactions are variable, being bo th antagonistic and synergistic. Generally for the primary antioxidants alo ne their photostabilising effects on the polymer film are low or negligible and can be related to the stability of the additives. However, in the pres ence of a hindered piperidine light stabiliser no such correlations between polymer and antioxidant stability exist. In most of the eases, antagonisti c interactions were found between HALS and the antioxidants. Differences in the performance of the polymeric type of HALS were evidenced, as well as b etween the CB grades. Less antagonism was found between primary and seconda ry antioxidants with CB for two-additive formulations. This effect is overc ome by a powerful synergistic interaction in three additive formulations. A ntagonism was found between one HALS and CB. It is concluded that the natur e of the CB plays an important role in controlling their performances as a stabilising agent alone, as well as their interactions with light stabilise rs and antioxidants. (C) 2001 Elsevier Science Ltd. All rights reserved.