Recycled PP moulding on a household machine: what changes and what to check
| What changes | Effect at the machine | What to check or set |
|---|---|---|
| Melt flow varies from lot to lot | Fill, packing and part weight drift between lots | Test MFR on each lot; keep the recycled share fixed |
| Metal or other contamination | Blocked hot-runner tips, specks, weak spots | Cold runners, magnets at the hopper, larger gates |
| Extra heat history | Degradation at high melt or long residence | Lowest practical melt; residence of about 5 minutes or less |
| Volatiles from mixed feedstock | Out-gassing, mould deposits, burns | Well-vented cavities and cold runners |
| Lower or variable impact strength | Cracks in parts that get dropped | Drop and stacking tests at each recycled share |
Recycled PP moulding works on a 220 t household machine when you control lot-to-lot melt flow, contamination and heat history. Keep the recycled share fixed, run cold runners with a magnet at the hopper, hold melt temperature low and residence short, vent well, and repeat drop tests whenever the share or the supplier changes.
Food-contact parts are the exception, and the rules below limit where recycled PP can go in a household range. The bigger changes for recycled PP sit in the mould, the barrel size and the incoming checks, and each matters more than it does with prime resin.
Key Takeaways
- Entec Polymers suggests a melt of about 199 to 227 °C for its post-industrial recycled PP compounds, with a maximum of about 238 °C.
- The same guide limits residence time to about 5 minutes and advises against hot runners for recycled compounds.
- Rigid plastic packaging must carry at least 30% recycled material in 2025-26, rising to 60% by 2028-29.
- FSSAI allows recycled plastics in food contact only as and when it frames standards and guidelines for them.
Where Can Household Products Use Recycled PP?
Non-food parts are the natural fit: utility buckets, dustbins, crates, flower pots, hangers and storage boxes for non-food goods. Rigid plastic packaging must now carry recycled content by rule. Food-contact houseware is restricted, because FSSAI allows recycled plastics for food only as it frames standards.
Minimum recycled content in plastic packaging under the PWM (Amendment) Rules notified 31 March 2026, as reported by Polymerupdate
| Packaging category | 2025-26 | 2028-29 |
|---|---|---|
| Category I: rigid plastic packaging | 30% | 60% |
| Category II: flexible plastic packaging | 10% | 20% |
| Category III: multilayer plastic packaging | 5% | 10% |
Polymerupdate's report also notes reuse targets for rigid packaging, carry-forward of 2025-26 shortfalls for up to three years, exemptions where FSSAI and similar rules restrict recycled content, and penalties of ₹10,000 to ₹15,00,000. Check the notified text for your own obligations. A bucket sold empty for home use and a tub that ships paint or ghee can fall under different rules.
For food, the FSSAI Packaging Regulations, 2018, provide that recycled plastics may be used as and when FSSAI frames standards and guidelines, a provision operationalised on 18 January 2022. Unless your recycled grade and its supplier can show compliance with what FSSAI has framed, keep it out of lunch boxes, food containers and kitchen tubs.
How Should You Set the Machine for Recycled PP Moulding?
Run the lowest melt temperature that fills the part, keep residence time short and hold the recycled share fixed. Entec Polymers suggests about 199 to 227 °C for its recycled PP compounds, a maximum of about 238 °C, and residence of 5 minutes or less.
Entec's guide gives the reason. Recycled compounds carry extra heat history, so they tolerate high melt temperatures and long barrel times less well than prime resin, which it says can handle about 260 °C. If residence must run longer, lower the melt further; if degradation appears, extra antioxidant can be added through a masterbatch.
Measure residence rather than estimating it. John Bozzelli, in Plastics Technology, describes dropping a few granules of a different colour into the feed throat while the machine cycles, counting shots until the colour is gone and multiplying by the cycle time. Swirls in the mixed colour also reveal poor melt uniformity.
This matters on a 220 t machine because household parts vary widely in weight. A small basin or hanger shot on a barrel sized for buckets stays in the heat for many cycles, and recycled PP can show the damage as odour, colour shift and brittleness.
Our view: blend recycled and virgin PP at one fixed ratio, test MFR on each incoming lot, and reject lots outside your window rather than re-tuning the machine for every bag. A process that is reset for each lot never settles.
How Do You Deal With Contamination and Out-Gassing?
Keep contamination out of small passages and give gas a way out. Entec advises cold runners rather than hot runners for recycled compounds, larger gates and runners where possible, and well-vented cavities and runners, because mixed feedstocks can out-gas and leave mould deposits.
The hot-runner advice follows from how recycled PP is made. Feedstock is ground before compounding, and although magnets and melt screens remove most metal, Entec notes that a small piece can still end up in a pellet and plug a hot tip. It describes such particles as generally not an issue in cold-runner tools.
Entec's guide is written for post-industrial compounds. Post-consumer material, recovered from household and packaging waste, can carry a wider mix of polymers, label residue and dirt, so expect a wider spread between lots. Agree incoming checks with the recycler, such as MFR, ash or filler content and a moulded colour plaque, before the first lot arrives.
Clean vents on a schedule, because deposits from out-gassing close them gradually and bring back burns and short shots. Add a magnet at your own hopper too, and keep regrind from recycled parts clean and sorted by colour.
What Should You Do Before Moving a Mould to Recycled PP?
Agree the recycled share and test plan with your customer, check the mould for hot-runner tips and vents, measure residence time at the planned cycle, and run drop tests at that share. Then confirm the machine and barrel suit the part. See the 220 ton horizontal injection moulding machine page.
Frequently Asked Questions About Recycled PP Moulding
Does recycled PP smell, and can that be fixed?
Odour can come from contaminants in the feedstock, from degradation in the barrel, or both. Lower melt temperature and shorter residence reduce the second. The first depends on how the recycler washes and processes the material, so ask for odour-checked lots and compare suppliers before using it in parts kept indoors.
What share of recycled PP can a bucket take?
There is no single figure; it depends on the grade, the bucket design and the drop and stacking loads it must survive. Trial the share you need on the actual part. For rigid packaging, test at the 60% level due by 2028-29 so the process does not need rework later.
Does recycled PP need drying?
PP itself absorbs little moisture, but washed recycled flakes or pellets stored open can carry surface moisture, which shows as splay or bubbles on the part. If those appear, dry the material as the supplier advises, and store bags closed and off the floor to keep moisture out.
Why do recycled PP parts vary in colour?
Recycled feedstock can arrive in mixed colours, so the material may be grey, black or a variable natural shade. Dark colours hide lot-to-lot variation best. A fixed recycled share, lots blended before use and a consistent masterbatch keep colour steadier, while bright or pastel shades are hard to hold.
Can recycled PP from two suppliers be mixed?
It can, but their melt flow, colour and additive packages may differ, which widens the variation you must absorb. If you mix, test MFR on each supplier's lots, blend at a fixed ratio and trial the blend on the part. One approved supplier per product keeps the process easier to hold.
Related Articles
- What Can You Make on a 220 Ton Household Moulding Machine?
- Larger Buckets and Tubs on a 220 Ton Machine
- Deep Houseware Moulds: Daylight and Ejector Stroke on a 220 Ton Machine
Sources & References
- Entec Polymers: Processing ECHO Post-Industrial Recycled Polypropylene Compounds
- Plastics Technology, J. Bozzelli: Injection Molding: A Practical Approach to Calculating Residence Time
- Polymerupdate, D. K. Jha: India eases plastic recycling regulations
- FSSAI: Food Safety and Standards (Packaging) Regulations, 2018, compendium
Technical Disclaimer
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