Dynamic FTIR studies of thermo-oxidation of expandable graphite-based halogen-free flame retardant LLDPE blends

The dynamic thermo-oxidative degradation of expandable graphite (EG)-based intumescent halogen-free flame retardant (HFFR) LLDPE blends in the condens ed phase at 300 or 400 degreesC has been studied in situ by real time Fouri er transform infrared spectroscopy. The kinetic characteristics and dynamic changes of various kinds of pyrolysis products during the thermo-oxidative degradation were examined extensively for several LLDPE/EG blends with dif ferent HFFR additives, such as the phosphorus-nitrogen compound NP28, ammon ium polyphosphate (APP), red phosphorus (RP), and zinc berate (ZB). It has been found (i) that the dynamic monitoring of the LLDPE/EG/HFFR blends duri ng the pyrolysis shows that the breakdown of LLDPE main chains and formatio n of various kinds of carbonyl products increase with increasing thermo-oxi dation time and temperature; the latter have been identified as carboxylic acids, ketone, lactone and cyclic anhydrides; (ii) that the fast formation rate and high initial concentrations of P-O-P and P-O-C products in the pho sphorus-containing HFFR systems have a crucial importance for decreasing th e thermo-oxidative degradation rate of LLDPE efficiently (the NP28 system i s the most efficient in the present study); and (iii) that the pyrolysis te mperature has a significant effect on the efficiency of flame retardants, w hich requires the LLDPE/EG/HFFR formulation should be optimized at certain temperature range in order to form compact intumescent charred layers immed iately at the beginning of the thermo-oxidative degradation of the LLDPE bl ends. (C) 2001 Elsevier Science Ltd. All rights reserved.