Effect of sub-atmospheric pressure on combustion and pyrolysis behavior of flame-retardant polyethylene

Abstract

With the rapid increase in the number of cruise aircraft and high-altitude greenhouses, internal electrical cables and polyethylene films are often exposed to low-pressure environments. However, current flame-retardant designs for polyethylene do not sufficiently account for the effects of low-pressure conditions, under which the combustion behavior and flame-retardant effectiveness may change significantly, leading to a considerable risk of functional failure. This study systematically investigates the combustion and pyrolysis mechanisms of low-density polyethylene (LDPE) with varying intumescent flame retardant (FR) contents in a pressure range of 55 kPa–101 kPa. The findings reveal that FR significantly enhances char formation under sub-atmospheric pressures, reducing ignition time compared to pure LDPE. Decreased pressure leads to a marked increase in heat release rate (HRR) and a reduction in CO emissions, as measured by a cone calorimeter in a low-pressure chamber. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) further reveals that low-pressure promotes the generation of more alkene and a higher proportion of long-chain pyrolysis products. Intumescent FR effectively reduce HRR, decrease CO production, and minimize the formation of saturated hydrocarbons under low-pressure conditions, while enhancing the char formation. Among these, a 35 wt% FR shows the best performance. However, ammonium polyphosphate, a common flame retardant, tends to make the material more susceptible to ignition. This work enhances the understanding of fire dynamics in low-pressure environments and provides a scientific foundation for designing safer, flame-retardant polyethylene materials tailored for sub-atmospheric applications.