Recycled & Bio-Based Plastics for Injection Moulding
Recycled and bio-based plastics for injection moulding are no longer niche or experimental — they are commercially mature. PCR grades of PP, HDPE, ABS, and PET are available as consistent injection-moulding compounds from major compounders. Bio-based polyolefins (bio-PE, bio-PP) drop in directly for fossil grades with certified renewable carbon content. PLA and PHA offer fully bio-derived, compostable options for ambient-temperature applications. Each family has a distinct sustainability profile and real engineering trade-offs; the right choice depends on application requirements, regulatory context, and which end-of-life route the product will actually reach.
What categories of sustainable plastic are available for injection moulding?
The market for sustainable injection-moulding resins divides into distinct propositions with different sustainability profiles. Getting the distinction right matters for accurate product environmental claims.
| Category | Feedstock | End-of-life | Fossil carbon reduction | Examples |
|---|---|---|---|---|
| Post-consumer recycled (PCR) | Waste plastic | Recyclable (same stream) | High (avoids virgin production) | rPP, rHDPE, rABS, rPET |
| Post-industrial recycled (PIR) | Manufacturing scrap | Recyclable (same stream) | Moderate | PIR-PA6, PIR-ABS |
| Bio-based drop-in (identical chemistry) | Sugar cane / tall oil | Recyclable (same stream) | Moderate–high (feedstock) | Bio-PP, bio-PE, bio-PET |
| Bio-based novel chemistry (non-drop-in) | Plant starch / sugar | Industrially compostable | High (feedstock + end-of-life) | PLA, PHA |
| Bio-based engineering grades | Castor oil / bio-intermediates | Recyclable or compostable | Moderate–high | Bio-PA11, PA610, PEF |
PCR directly diverts plastic waste from landfill or incineration and avoids the fossil energy of virgin resin production. Bio-based drop-ins reduce the fossil carbon embedded in the product without changing downstream recycling behaviour at all — the product still enters the same polyolefin recycling stream. Novel bio-based materials (PLA, PHA) offer compostability but only if the product reaches an industrial composting facility; in mixed recycling they cause contamination.
What are the properties of PCR grades for injection moulding?
PCR resins are mechanically adequate for many applications, but there are systematic differences that must be accounted for in material selection and process design.
| Property | Virgin PP | PCR-PP (30% PCR) | PCR-PP (100% PCR) | Test Standard |
|---|---|---|---|---|
| Tensile Strength | 30–40 MPa | 25–38 MPa | 20–35 MPa | ISO 527 |
| Flexural Modulus | 1,400–1,800 MPa | 1,200–1,700 MPa | 1,000–1,600 MPa | ISO 178 |
| Izod Impact (notched) | 30–80 J/m | 25–70 J/m | 15–60 J/m | ISO 180 |
| MFI variability | Low | Low–moderate | Moderate–high | ISO 1133 |
| Colour options | Full palette | Limited | Grey / black | — |
| Odour | Neutral | Slight | Noticeable (grade-dep.) | — |
| Batch consistency | High | High (certified compounder) | Moderate | — |
For well-sorted, well-compounded PCR grades, the practical property reduction is modest — typically 5–20% below virgin equivalents — and acceptable for a wide range of product categories. The main engineering challenges are colour restriction (grey and black dominate PCR; bright colours require more masterbatch loading), MFI batch-to-batch variability, and occasional odour from contaminated source streams.
Certified PCR compounders — ISCC Recycled, GRS, or Recyclass certification — deliver consistent, traceable material that behaves predictably in production. For production programmes, only certified PCR grades, not uncertified regrind, should be specified.
What are the properties of PLA for injection moulding?
PLA is the highest-volume bio-based, non-drop-in polymer and the most widely available commercial bioplastic for injection moulding.
| Property | Standard PLA | PLA + impact modifier | Test Standard |
|---|---|---|---|
| Tensile Strength | 50–70 MPa | 35–55 MPa | ISO 527 |
| Elongation at Break | 3–6% | 10–50% | ISO 527 |
| Flexural Modulus | 3,000–4,000 MPa | 2,000–3,500 MPa | ISO 178 |
| Heat Deflection Temp (0.45 MPa) | 50–55°C | 45–52°C | ISO 75 |
| Heat Deflection Temp (annealed) | 95–110°C | — | ISO 75 |
| Density | 1.20–1.25 g/cm³ | 1.15–1.22 g/cm³ | ISO 1183 |
| Mould Shrinkage | 0.3–0.6% | 0.3–0.8% | ISO 294-4 |
| Water Absorption (24 h) | 0.4–0.6% | 0.3–0.5% | ISO 62 |
PLA's 50–55°C HDT is its most significant limitation — a PLA part left in a car parked in summer or placed in a dishwasher will deform. Annealing after moulding, holding parts at 70–80°C for several hours to crystallise the amorphous matrix, raises HDT to 95–110°C and substantially extends the application window. Standard PLA is also brittle; impact-modified grades sacrifice some stiffness to add practical toughness at the cost of a modest HDT reduction.
What are the properties of bio-based drop-in grades (bio-PP, bio-PE)?
Bio-PP and bio-HDPE are chemically identical to their fossil counterparts. Every mechanical property, processing parameter, mould temperature, and shrinkage value from the conventional PP or HDPE data sheet applies unchanged — the only difference is feedstock provenance, confirmed by mass-balance or physical-segregation chain-of-custody certification.
This means zero product redesign, zero tooling modification, and zero process adjustment. Bio-based drop-ins are a direct substitution for product lines where bio-based carbon content is a commercial or regulatory requirement.
Bio-based content for bio-PP typically falls in the 30–100% range by carbon mass depending on the supply chain pathway (bio-naphtha steam cracking vs direct bio-propylene). Recognised certification bodies include ISCC+, RSB, and REDcert2.
Processing guidance for sustainable grades
PCR grades (PP, HDPE, ABS, PET):
- Drying requirements mirror the base resin: rPP and rHDPE do not require drying; rABS requires 2–4 h at 80°C; rPET requires 4–6 h at 130°C.
- Process windows are typically slightly narrower than virgin grades; start conservatively and adjust to MFI of the specific lot.
- Filtration: a fine screen pack (100–200 mesh) in the barrel helps capture residual contamination from PCR streams.
- Colour: pigment systems for dark or neutral colours mask PCR's natural grey cast; bright colour coverage requires higher masterbatch loading.
PLA:
- Dry at 80°C for 4 hours before moulding; PLA is hygroscopic and moisture causes severe hydrolytic degradation (molecular weight reduction) during processing, resulting in brittle parts and splay defects.
- Melt temperature: 175–220°C. Do not exceed 240°C — rapid degradation and foaming occur above this threshold.
- Mould temperature: 20–30°C for amorphous parts; 80–100°C for annealed/crystallised parts.
- Clean the barrel fully when transitioning from or to PLA — PLA and most other thermoplastics are incompatible in the melt at processing temperatures.
- Injection pressure: 70–120 MPa. PLA has low melt viscosity; it fills thin sections readily.
Bio-PP / Bio-PE:
- Identical processing parameters to virgin PP/HDPE. No adjustments required.
Design rules for recycled and bio-based parts
Wall thickness: No changes from standard guidelines for the base resin. PCR grades benefit from uniform walls to minimise the impact of MFI variability on fill consistency.
Colour strategy: Plan for dark, natural, or pigmented designs early if using PCR. Attempting pastel or bright colours with high PCR content requires more masterbatch and may reduce PCR percentage.
Labelling and marking: Parts moulded from certified recycled or bio-based content should carry appropriate resin identification codes and, where commercial claims are made, reference the specific certification standard (e.g. "Made with GRS-certified recycled PP").
Annealing for PLA: If parts will be used above 60°C, specify post-mould annealing. Nordmould can incorporate annealing as a secondary operation for PLA programmes.
Weld lines in PCR parts: Impact strength at weld lines is lower for PCR grades than virgin equivalents. Position weld lines away from impact or stress concentration zones.
Sustainability trade-offs: what to verify before making claims
Recycled and bio-based plastics each have genuine environmental benefits and real limitations that must not be overstated.
PCR plastics: The primary benefit is keeping plastic in productive use and avoiding the energy of virgin resin production. Mechanical recycling has a finite number of effective cycles before polymer chains degrade, and collection infrastructure for many plastic types remains incomplete — so the theoretical recycled-content claim and the actual recovered fraction can differ.
Bio-based drop-ins (bio-PP, bio-PE): Reduce the fossil carbon embedded in the product but do not reduce end-of-life plastic burden. The product remains a conventional polyolefin and must be recycled or landfilled in the same way as its fossil equivalent.
PLA: Genuinely bio-derived and industrially compostable — but the composting benefit only materialises if the product reaches an industrial composting facility. Mixed into conventional plastics recycling, PLA contaminates the stream. Clear end-of-life routing must be designed in, not assumed.
Sustainability claims should be verified against the certified content of the actual material lot, not the theoretical maximum of the grade, and end-of-life routing must match the material's actual capability.
Frequently asked questions
What is post-consumer recycled (PCR) plastic in injection moulding?
PCR plastic is resin produced by mechanically recycling consumer waste — sorted, cleaned, shredded, and re-pelletised into injection-moulding grades. Common PCR grades include rPP, rHDPE, rABS, and rPET. Properties are slightly lower than virgin equivalents; colour is restricted. Nordmould can specify PCR grades where product specifications and regulatory requirements permit.
Is PLA suitable for injection moulding?
Yes. PLA (polylactic acid) is commercially processed by standard injection moulding. It is derived from fermented plant starch (corn, sugar beet) and is industrially compostable. PLA's limitations — HDT of only 50–55°C and brittleness below 0°C — restrict it to ambient-temperature, short-service-life applications such as packaging inserts, promotional items, and disposable medical devices.
What is bio-PP and how does it compare to conventional PP?
Bio-PP is polypropylene produced from bio-naphtha or bio-propylene derived from sugar cane or tall oil. The molecular structure and processing conditions are identical to fossil PP; mechanical and chemical properties match conventional PP grade for grade. The difference is in feedstock origin — bio-PP can carry certified bio-content (e.g. ISCC+, RSB) reducing fossil carbon intensity without any product redesign.
Can recycled plastic hold the same tolerances as virgin material in injection moulding?
Recycled grades typically show slightly higher variability in melt flow index (MFI) than virgin equivalents, which can affect dimensional consistency between production batches. For non-critical dimensions, PCR grades perform reliably. For tight-tolerance precision parts, Nordmould recommends a qualification trial with the specific recycled compound to confirm process stability before committing to volume tooling.
What sustainability claims can I make for a product moulded from bio-based plastic?
Bio-based content claims must be supported by certified material traceability (ISCC+, RSB, or mass-balance chain of custody) and should accurately state bio-based carbon content as a percentage of total carbon. Bio-based does not mean biodegradable — bio-PP and bio-PE are identical in end-of-life recyclability to fossil equivalents. Nordmould can provide material documentation to support product environmental declarations.
Is PLA recyclable or compostable?
PLA is industrially compostable under EN 13432 conditions (58°C, 60 days). It does not compost in home composting bins or in standard municipal organic waste streams in most EU countries. PLA is NOT mechanically recyclable in standard polyolefin or PET streams — it contaminates those streams. Dedicated PLA collection and industrial composting infrastructure is required to realise the end-of-life benefit.
What proportion of recycled content is feasible in injection moulding?
Most injection-moulded parts can accommodate 30–100% PCR content for non-structural, non-regulated applications using well-sorted, consistent-grade PCR resin. Structural or regulated parts typically use 10–30% PCR blended with virgin resin to maintain property and process consistency. Nordmould assesses the appropriate PCR ratio during the DFM review.
Are there bio-based or recycled alternatives to engineering plastics like nylon or PC?
Yes. Bio-based PA (nylon from castor oil, e.g. PA11, PA610) and bio-based PEF (a PET substitute) are commercially available engineering-grade bio-plastics. Recycled PA6 and PA66 from industrial waste streams are available from specialist compounders. Nordmould sources bio-based and recycled engineering polymer grades through its partner network for projects with sustainability mandates.
Send your part drawings and sustainability requirements for a free DFM review — the right recycled or bio-based grade will be recommended and a written quote returned within one business day.