Recycled materials

Definition

Recycled materials are metals, polymers, glass, paper, textiles, elastomers, and composites that have been recovered from post‑consumer or post‑industrial waste streams and reprocessed into feedstock or products for new applications. Recovery may be mechanical, metallurgical, or chemical. Recycled materials are distinct from reused or remanufactured items and exclude energy recovery.

Material categories (non‑exhaustive)

  • Metals: recycled (secondary) steel, aluminum, copper and alloys.
  • Polymers: recycled thermoplastics such as rPET, rPP, rPE, rPS, rPA, rABS; chemically recycled monomers/feeds used to make “as‑new” polymers.
  • Glass: container and flat glass cullet for remelt or insulation/fiberglass.
  • Paper and board: recycled pulp for packaging, tissue, printing grades.
  • Textiles: recycled polyester (rPET), nylon (e.g., from fishing nets), cotton and cellulosics.
  • Elastomers: ground tire rubber (GTR), devulcanized rubber.
  • Composites: reclaimed carbon or glass fibers; thermoset/thermoplastic recyclates used as fillers or reinforcements.

Key properties and design considerations

  • General: lower embodied energy and greenhouse‑gas footprint than virgin equivalents; composition and properties depend on source, sorting quality, and reprocessing route; batch‑to‑batch variability and potential legacy additives/substances require quality control and traceability.
  • Polymers: often show reduced molecular weight/viscosity, potential loss of impact strength/ductility, and variability in color and odor. Properties can be restored or tailored via stabilizers, compatibilizers, chain extenders, impact modifiers, fillers, and reactive extrusion. PET may use solid‑state polymerization to restore intrinsic viscosity.
  • Metals: can achieve near‑virgin mechanical properties when chemistry and impurities are controlled. Accumulation of tramp elements (e.g., Cu, Sn in steel) and inclusions require sorting, dilution, and melt treatment; aluminum benefits from alloy‑specific scrap streams.
  • Glass: indefinitely recyclable with careful color separation and removal of ceramics/metals; contamination affects clarity and processing.
  • Paper/textiles: fiber shortening reduces strength; blending with virgin fiber or chemical recycling (for polyesters/cellulose) mitigates property loss.
  • Elastomers: crosslinking limits full recycling; devulcanization and fine grinding enable use as modifiers/fillers.
  • Composites: mechanical reclaim shortens/misaligns fibers; thermal/chemical processes (pyrolysis, solvolysis) recover fibers with properties dependent on process and fiber length/orientation.

Benefits

  • Environmental: conserves resources (ore, bauxite, petroleum, forests), reduces waste to landfill/incineration, and lowers energy use and GHG emissions. Typical energy savings versus primary production include aluminum (~95%), steel (~60–74%), and PET/plastics (often 40–60%, process‑dependent).
  • Economic: potential cost reductions, reduced price volatility via local scrap/feedstock loops, and avoided disposal costs.
  • Regulatory and market: supports recycled‑content targets, extended producer responsibility (EPR) schemes, and corporate sustainability goals; can improve product environmental declarations and life‑cycle assessments.

Typical applications across sectors

  • Packaging: rPET bottles and films, rPE/rPP containers, recycled paperboard and corrugated.
  • Construction and infrastructure: reinforcing steel rebar, aluminum extrusions, fiberglass and glass cullet insulation, plastic lumber and drainage pipes from rPE/rPP, asphalt modified with ground tire rubber.
  • Consumer goods and electronics: housings and enclosures from rABS/rHIPS/rPP, rPET textiles and yarns, footwear foams incorporating recycled content.
  • Transportation: recycled steel and aluminum in structures; rPP/rABS exterior and interior trim; rPET nonwovens for liners and insulation; ground tire rubber for NVH components; reclaimed carbon fiber in thermoplastic compounds.

Processing and quality assurance

  • Plastics (mechanical): collection, sorting (NIR, color, density, sensor‑based), washing, flake production, melt filtration, extrusion/regranulation; property tuning with additives; devolatilization and odor control.
  • Plastics (chemical): depolymerization (e.g., glycolysis/methanolysis/hydrolysis for PET), pyrolysis/gasification to monomers or feedstocks for polyolefins and polystyrene, and solvolysis for thermosets; often allocated to products via mass‑balance chain‑of‑custody.
  • Metals: shredding, magnetic/eddy‑current/sink‑float/sensor sorting, de‑coating; remelting, alloying, fluxing, degassing, filtration; casting and downstream forming.
  • Glass: cullet cleaning and color separation; remelting into container glass or fiberglass.
  • Paper/textiles: pulping, screening, de‑inking; mechanical/chemical recycling of polyester and cellulose; re‑spinning fibers.
  • Elastomers/composites: ambient/cryo grinding, devulcanization, pyrolysis/solvolysis; recompounding into thermoplastics or use as fillers in SMC/BMC and asphalt.
  • QA and testing: contaminant control (moisture, halogens, silicone, metals), spectroscopic identification (FTIR/NIR/XRF), rheology (MFR/MVR), intrinsic viscosity (PET), ash/filler content, odor/VOCs, mechanical/thermal testing, and traceability/lot control.

Standards, claims, and terminology

  • Recycled content types: post‑consumer recycled (PCR) versus post‑industrial recycled (PIR).
  • Chain‑of‑custody and verification (examples): ISO 14021 (environmental claims), ISO 22095 (chain of custody), certification schemes such as ISCC PLUS, Recycled Claim Standard (RCS)/Global Recycled Standard (GRS), SCS Recycled Content, UL 2809. Mass‑balance accounting is common for chemically recycled feedstocks.
  • System boundaries: closed‑loop recycling returns material to the same or equivalent application; open‑loop may result in downcycling or upcycling.
  • Not to be confused with: recyclable (a design attribute), reused/refurbished/remanufactured (product‑level strategies), or bio‑based (origin attribute).

Design and procurement tips

  • Specify minimum PCR content, acceptable property ranges, and test methods; allow controlled blending with virgin to meet performance.
  • Favor mono‑materials or compatible blends; design for disassembly and clear labeling to improve end‑of‑life recovery.
  • Avoid incompatible additives and restricted substances that hinder recycling; select colors and surface finishes tolerant of recyclate variability.
  • Use grade separation and identification (e.g., alloy families, polymer resin codes) to preserve material value.
  • Validate with representative lots; manage variability via statistical qualification, modeling, and safety factors.
  • Quantify environmental benefits with transparent LCA/EPD assumptions and confirm claims via third‑party certification where appropriate.

Limitations and risks

  • Property variability, color/odor differences, and aesthetic challenges versus virgin materials.
  • Contamination and legacy substances (e.g., brominated flame retardants, restricted plasticizers) require screening and may limit applications.
  • Supply consistency depends on collection and sorting infrastructure; economics vary with commodity prices.
  • Some streams (thermosets, mixed or multilayer plastics) remain difficult to recycle at scale; washing and processing can entail energy/water use that should be managed responsibly.

Sector note: automotive and EVs

  • High recycled content in steel and aluminum supports low life‑cycle carbon footprints; alloy‑specific scrap management preserves properties.
  • Recycled polymers (rPP, rABS, rPET) are widely used in interior/exterior trim, underbody shields, nonwovens, and NVH components; property restoration relies on compatibilizers/stabilizers.
  • Reclaimed carbon fibers can reinforce thermoplastics for semi‑structural parts; feasibility depends on fiber length/orientation and processing route.
  • Recycled copper, glass, and textiles are usable with rigorous purity control and specification.
  • Recycled content helps meet OEM targets and regulatory requirements (e.g., ELV, ecodesign, EPR) while contributing to mass and CO₂ reduction goals.

Synonyms and related terms

Secondary materials; recyclate; recycled content; PCR and PIR materials; scrap‑based metals; reclaimed fiber; closed‑loop recycling; open‑loop recycling; downcycling; upcycling.

Examples

rPET bottle‑to‑bottle flakes and fibers; rPP/rPE for injection‑molded housings and pipes; secondary aluminum sheet and castings; recycled steel rebar and sheet; ground tire rubber in asphalt and mats; reclaimed carbon fiber mats in non‑structural panels; recycled paperboard for packaging.