Mechanical Recycling of Flame Retardant-Contaminated Expanded Polystyrene Waste into Structural Materials
Abstract
Expanded polystyrene (EPS) is a widely used thermoplastic foam that contributes a significant portion of plastic waste. We investigated the mechanical recycling of flame retardant (FR, includes FR-130 and PolyFR)-containing EPS waste via melt blending to produce useful recycled materials for industrial adoption.
Tertiary bromides on the FRs are believed to cause β-scission of polymer chains during melt compounding. This results in significant (~39%) molecular weight loss for wastes with FR-130 and brittleness in blends with 10 wt% polystyrene-block-polybutadiene-block-polystyrene (SBS). Comparatively, EPS waste with PolyFR (believed to contain less tertiary bromides) exhibited substantially higher ductility (>100%) in the 10 wt% SBS blend. Modified polyphenylene oxide (mPPO, believed to increase entanglements between fragmented chains) was added in 10 wt% to EPS (with PolyFR)/SBS (90/10 wt%), yielding similar mechanical performance to a virgin polystyrene/SBS (90/10 wt%) reference blend while having a lower estimated material cost by ~40%.
A recycled EPS material was formulated for use as a structural component with thermal (120°C dimensional stability), mechanical and cost requirements. A blend containing waste EPS, SBS, waste rubber and mPPO is believed to meet thermal requirements and exhibits greater yield strength (by ~25%) and -25°C impact resistance (by ~100%) than the currently used recycled polypropylene. However, it is expected to be too expensive (by ~20%). With reduced thermal requirements, modifications are possible to reduce cost while further enhancing toughness, potentially facilitating use in other applications.
This work indicates that potentially useful and economically attractive materials can be created from mechanically recycled FR-containing EPS waste.