Thermo-oxidative degradation behaviors of expandable graphite-based intumescent halogen-free flame retardant LLDPE blends

The thermo-oxidative degradation behaviors of expandable graphite (EG)-based intumescent halogen-free flame retardant LLDPE blends under different thermo-oxidation conditions have been studied by real time Fourier transform infrared (FTIR) spectroscopy or FTIR photoacoustic spectroscopy (FTIR–PAS), X-ray photoelectron spectroscopy (XPS), and wide-angle X-ray diffraction (WAXD). The real time FTIR results show that the pyrolysis of LLDPE at high temperature leads to the breakdown of PE chains and the formation of various kinds of thermal oxidation products. The addition of EG can improve the stability of thermo-oxidative degradation effectively. The FTIR–PAS and XPS data show that the thermo-oxidative degradation of LLDPE decreases remarkably with the increase of EG concentration and/or its synergists and increases dramatically with the increases of pyrolytic temperature and thermal degradation time. The thermo-oxidative degradation products have been identified as various kinds of carbonyl compounds, such as ethers, esters, ketone or carboxyl products. The WAXD measurements demonstrate that the crystalline structures of LLDPE/EG or LLDPE/EG/HFFR blends after the thermo-oxidation degradation have been destroyed partly or totally dependent on the pyrolytic temperature and thermal degradation time. The changes of crystalline structure in the LLDPE/EG/HFFR blends are due to the breakdown of LLDPE chains and a series of reaction products with FR additives.