Using Regrind and Recycled Material in Blow Molding

Blow molding regrind and recycled material stops being a housekeeping exercise the moment a customer writes a post-consumer content figure into a supply contract. In-house regrind from your own scrap is a material you know: same grade, same additives, known heat history. Post-consumer recyclate is a mixture, and a mixture is a different engineering problem.

The failure mode is not dimensional. A container can be moulded to the correct wall distribution, pass the visual check and still split at a seam when it is dropped, or crack three months later while holding a chemical. Odour and migration complaints arrive even later. By the time the pattern is visible, the parts are full and in the field, and the question has changed from how to hit a percentage to why the resin no longer behaves like the resin it replaced.

Sailwin has delivered blow molding machines into 500+ installations across 60+ countries over 15+ years, manufacturing under ISO 9001:2015 with CE marking and supporting installations with a 2-year machine warranty. The extrusion blow molding range covers 0.5 L to 1000 L containers, includes all-electric models SW-60/70/80/90, and runs materials from PE, PP, ABS, EVA, PC and PA to multilayer PE+PA+EVOH structures — which is the hardware answer to most recycled-content targets. This guide covers what regrind changes, how much a line can absorb, the checks that keep parts compliant, and how to configure for it.

1. What Regrind Actually Changes in the Polymer

Every time a polymer is melted it collects a heat history. Regrind has therefore been processed at least twice before it re-enters the machine, and post-consumer recyclate has usually been processed several times by several parties. The consequences are not cosmetic.

Five things change at once, and they interact. Molecular weight falls, which lowers melt strength and toughness. Gel particles and unmelted fractions appear, and they show up as surface defects or as locally thin wall. Contaminants and residues from the previous life of the material volatilise during processing, which is where odour complaints originate. Pellet size and bulk density vary more widely, which disturbs feeding and parison control. Colour and stabiliser content drift, which changes appearance and outdoor durability.

One practical rule follows from the table. Whenever the recyclate share moves by more than a few percentage points, treat it as a material change and re-establish the process window rather than assuming the previous recipe still applies. Machines that log 40+ parameters in real time make that comparison quick: run the new share, compare the melt pressure, cycle and wall control traces against the record for the old share, and you can see in one shift what would otherwise be argued for a week.

2. How Much Regrind Can a Line Actually Absorb?

The limit is set by the part, not by the machine. Three variables dominate: which stream the material came from, how the wall is structured, and what the container has to survive in service. A 20 L jerrycan holding aggressive chemistry and a 200 L drum used indoors do not share a number.

In-house regrind of your own scrap is normally fed back continuously at a modest level, because the material is known and the loop can be bled to stop heat history accumulating indefinitely. Post-consumer recyclate is usually capped much lower in a single-layer wall. Industry practice for demanding containers typically places mono-layer recyclate content in the region of 20–30 percent, with higher figures only for non-critical parts; treat that as an industry typical range for orientation, because the real constraint is the drop and stress-crack result on your own part.

This is why co-extrusion is the practical answer to an aggressive PCR target. Putting recyclate in a core layer keeps it away from the contents and away from the customer’s eye, while the virgin skins carry the surface properties. The machine requirement is a multilayer die head and a control system that holds each layer’s share steadily through the run — a wall thickness controller that watches the parison and corrects layer distribution, not just total weight.

3. Quality Checks That Keep Recycled-Content Parts Compliant

A recycled-content claim is only as good as the evidence behind it. These are the checks that matter, in the order they should be established.

1. Incoming material verification. Check melt index or viscosity on each delivery of recyclate, not once per supplier. A batch that arrives stiffer or softer than the reference changes the whole process window.
2. Drop testing at the declared share and the minimum wall. Test the worst legitimate case rather than the average one. A pass at the nominal condition does not protect the customer who receives the lightest container in the batch.
3. Stress crack resistance for chemical containers. Where the contents are aggressive, environmental stress cracking is the test that reflects real service life, and it is the property most damaged by repeated heat history.
4. Odour and migration for food-contact and personal-care parts. Organoleptic testing on the finished container, with the recyclate in the layer it will occupy in production, is the only reliable check.
5. Wall distribution and weight. Section a part and check distribution, not just total weight, because recyclate changes how the parison stretches as well as how much it weighs.
6. Traceability records. Batch number, recyclate source, declared share, machine settings and test results held together. When a customer audits the claim, the file answers the question instead of the production manager.

4. Case Study: Moving a Chemical Jerrycan to Recycled Content

A producer of chemical jerrycans was asked to meet a defined post-consumer content figure while keeping the same drop height, the same solvent resistance and the same pallet footprint.

Composite scenario based on extrusion blow molding project work, with no customer-identifying detail. Part-specific figures are confirmed during engineering review.

5. Configuring an Extrusion Blow Molding Machine for Recycled Material

Three machine capabilities decide whether a recyclate target is comfortable or a daily argument: multilayer capability, process stability when the input varies, and monitoring detailed enough to prove the run was consistent.

Sailwin builds the extrusion blow molding range from 0.5 L to 1000 L in PE, PP, ABS, EVA, PC and PA, with multilayer PE+PA+EVOH structures available where a barrier is required. All-electric models SW-60/70/80/90 suit plants that measure energy per part, with servo drive systems cutting energy use by up to 30 percent and high-pressure exhaust recovery reducing compressor load by around 20 percent.

• SW-2S1L — containers up to 0.5 L, 950 × 2 per hour
• SW-S30L — up to 30 L at 600 per hour; SW-S60L at 450 per hour and SW-S80L at 360 per hour
• SW-S120L and SW-S160L — the SW-S160L runs 300 per hour
• SW-S260L — containers up to 250 L
• SW-S1000L — containers up to 1000 L, 250 per hour
• All-electric SW-60/70/80/90 — servo-driven profile for plants measuring energy per part

Delivery on a standard configuration is typically 30–45 days, and 45–60 days for a custom or multilayer build. Machines are FAT tested at full load before shipment, installation and commissioning on site takes 3–7 days, common wear parts ship within 48 hours and remote support is available 7×24.

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