Flame retardancy of PET foams manufactured from bottle waste

Supercritical CO2-assisted extrusion technique was used to produce flame retarded foams from recycled poly(ethylene terephthalate) (rPET). Synergistic combination of aluminium-alkylphosphinate flame retardant (FR) and natural montmorillonite (MMT) was utilised to provide adequate flame retardancy at moderate loadings, i.e. with less than 9% of additives. Addition of FR was found to increase the rate of degradation during production (compounding and foam extrusion), which was effectively compensated by chain extender (CE) addition that ensured the melt strength required to obtain proper foam structure. The effects of the FR content and the CE addition on the viscosity of the rPET compounds and on the morphological, thermal, flammability and mechanical properties of the foam products were comprehensively investigated. When compared to injection moulded bulk materials of identical compositions, the highly porous structure of foams was found to increase flammability according to UL94 tests and LOI measurements but has not been shown to be detrimental to heat release rates as measured by cone calorimetry. It was concluded that with well-balanced composition, i.e. 8% FR + 1% MMT + 1% CE, low-density foams (with porosities higher than 70%) of uniform microcellular structure and prominent flame retardant characteristics (such as V0 rating according to UL94 standard, LOI of 28.5% and by 50% reduced peak of heat release rate and by 30% reduced total heat emission) can be manufactured even from rPET.