Drive-throughs to driveways: high-strength composites from multi-material post-consumer waste collected from fast food restaurants

Abstract

Mixed post-consumer fast food waste poses a formidable challenge for chemical recycling due to its diverse composition of plastics, paper, and remnant foodstuffs. Herein is presented a strategy for kilogram-scale upcycling of such waste into high strength composites. This is accomplished by thiocracking fast food restaurant waste pulp (10 wt%) with sulfur (90 wt%) at 180 °C and 230 °C, giving composites RWS₉₀@180 and RWS₉₀@230, respectively. These composites display compressive strengths of 12.2–16.3 MPa and flexural strengths of 2.80–5.39 MPa, competitive with common construction materials such as standard building brick (C62 classification) and approaching values for Ordinary Portland Cement (OPC). Both materials exhibit favorable properties under acid challenge (retaining up to 91% of their compressive strength after immersion in 0.5 M H₂SO₄) and show exceptionally low water uptake (<0.5%). Composites RWS₉₀@180 and RWS₉₀@230 also showed low E factors, (0.1 and 0, respectively) and low global warming potentials (−0.0450 kg CO₂e per kg and 0.0450 kg CO₂e per kg, respectively). This work highlights an approach to upcycling otherwise problematic mixed-material restaurant waste into durable, corrosion-resistant composites with a low environmental impact.