Master of Engineering Science
Chemical and Biochemical Engineering
Charpentier, Paul A.
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.
Summary for Lay Audience
Expanded polystyrene (EPS, or “Styrofoam™”) is a widely used plastic foam that significantly contributes to our current plastic waste challenge. We investigated recycling EPS waste from the construction industry via melt blending (melting and mixing it with other melted plastics) to improve its mechanical performance (the recycled EPS material is brittle otherwise) and produce useful recycled materials for the construction industry.
Results suggest that flame retardants (FRs, chemical agents required to prolong the time-of-escape during fires) present in the EPS react during melt blending, leading to significant degradation of the blended materials. This severely hinders efforts to improve mechanical properties. Two approaches found to significantly improve mechanical performance include: 1) using an EPS waste that contains a recently developed FR possessing greater thermal stability (less reactive during processing) and 2) adding modified polyphenylene oxide (mPPO, a material believed to help recover lost mechanical properties after reaction of the FR).
We investigated if a recycled EPS material could be utilized for a structural component that required thermal (must resist deforming under its own weight at 120°C) and mechanical (strength and toughness) properties while being cheaper than the currently used material. The best performing recycled material contained waste EPS, rubber-based materials and mPPO. This blend is believed to meet thermal requirements and exhibited greater strength and low temperature (-25°C) toughness than the currently used material. However, it is not expected to be economically viable. With reduced thermal requirements, modifications are possible to reduce cost while further enhancing toughness, potentially facilitating use in other applications.
This work concludes that potentially useful and economically attractive materials can be created from mechanically recycling FR-containing EPS waste via melt blending. Such materials could be created in-house by EPS producers for their own use or for re-sale as value-added recycled materials.
Ng, Harrison E., "Mechanical Recycling of Flame Retardant-Contaminated Expanded Polystyrene Waste into Structural Materials" (2022). Electronic Thesis and Dissertation Repository. 9065.
Available for download on Saturday, December 21, 2024