EcoInvest HDPE REGRIND is supplied under article designation EIR-HDPE-5502 as a washed, densified high-density polyethylene recyclate composed of segregated post-consumer and post-industrial HDPE containers, crates, and extrusion trim. The production sequence includes magnetic separation, near-infrared polymer sorting, hot alkaline washing at 85–90 °C, sink-float separation with a cut-point of approximately 1.0 g/cm³, and melt filtration through 150-µm breaker plates. The material is pelletized on a twin-screw compounding line and released as cylindrical pellets with a bulk density of 0.52–0.58 g/cm³ and a pellet count of 55–65 pellets/g. Two standard designations are available: EIR-HDPE-5502 IM, intended for injection moulding and melt compounding, and EIR-HDPE-5502 EX, intended for sheet extrusion, blow moulding, and profile extrusion. Both designations are tested against release criteria that include melt flow rate, density, ash, moisture, and tensile yield strength; certificates of analysis accompany each production lot.

The primary difference between the two designations is melt flow rate. The EX designation retains a fractional-melt viscosity to preserve die swell and parison stability in extrusion processes, while the IM designation is adjusted to a mid-range melt flow to reduce injection pressure and improve knit-line strength in complex moulds. Both designations are supplied without intentional addition of filler, and both are limited in ash and moisture to reduce screw wear, melt-filtration pressure spikes, and surface defects in thin-wall parts.

What Distinguishes Regrind Lot Homogeneity from Single-Source Recyclate?

Single-source post-industrial regrind can be highly uniform when the upstream scrap stream is one polymer and one colour, but mixed post-consumer HDPE regrind typically exhibits wider variation in molecular weight, ash, and contamination. The EcoInvest material is normalized through near-infrared sorting to maintain HDPE purity at ≥98.5%, with polypropylene limited to ≤1.0% and other polymer fractions limited to ≤0.5%. Residual aluminium from induction seals is reduced by eddy-current separation to a nominal concentration below 5 mg/kg; this is lower than the level frequently observed in unprocessed baled HDPE, where aluminium flakes can exceed 30 mg/kg and create melt-filtration pressure spikes.

The melt flow rate release band is held to ±0.05 g/10 min against the lot mean for the EX designation, which is tighter than the ±0.15 g/10 min band commonly accepted for generic post-consumer HDPE regrind. On a 75-mm co-rotating twin-screw extruder with 40 L/D and a vacuum vent, pressure variation at the screen changer remained within 1.2 MPa over an 8 h production run when processing EIR-HDPE-5502 IM at 220 °C barrel temperature. This level of stability supports dosing at low throughput fluctuations in gravimetric systems. When compared with mixed-colour regrind derived from commingled collection, the EIR-HDPE-5502 grades contain fewer polypropylene caps and PET bottle fragments, which reduces the incidence of delamination and weld-line weakness in moulded parts.

Moisture uptake in regrind lots stored at ambient humidity is a processing variable that separates this product from dried virgin HDPE. Although the release moisture is ≤0.10%, storage in unprotected silos at relative humidity above 60% can increase surface moisture within 24 h. Pre-drying at 80 °C for 2–4 h in a desiccant dryer is required before processing in sheet extrusion or profile lines where splay, melt strength loss, or surface defects are unacceptable. The recommended melt temperature range is 180–230 °C; processing above 260 °C is not recommended because prolonged residence can generate hydroperoxide-derived gel particles and increase yellowness index.

The material is not recommended for unvented single-screw extrusion without melt filtration, because surviving contaminants can accumulate on breaker plates. When a converter substitutes this regrind for virgin HDPE at 20 wt% in a thin-wall injection moulding application, a 5–8% reduction in melt flow is typical due to the broader molecular weight distribution, and clamp force requirements may rise by 3–6% on a 1100-kN hydraulic injection moulding machine. These shifts are smaller than the shifts usually observed with unsorted regrind, where polypropylene contamination can cause inconsistent shrinkage and visible flow lines.

Virgin-Resin Replacement Ratios and Mechanical Property Retention

Property retention after blending with virgin HDPE depends on the regrind addition level and the test method. The data below were generated on ISO 527-2:2012 Type 1A specimens and ISO 179-1:2010 notched Charpy specimens. The observed reduction in tensile yield strength is modest at addition levels up to 20 wt%, while impact and environmental stress-crack resistance show earlier decline because the recycled fraction contains short-chain branches, oxidised species, and minor particulate contamination. At 50 wt% addition, the fracture mode in thin sections can become mixed ductile-brittle, and at 100% regrind the material is not recommended for gas-pipe pressure applications without additional stabilizer and melt filtration.

Published data for this specific formulation configuration is limited; therefore these retention values should be treated as comparative screening data rather than design allowables. The difference from virgin HDPE is not limited to mechanical properties. The regrind has a higher peroxide concentration and a wider molecular weight distribution, which lowers low-shear viscosity but increases die swell. This combination can alter filling patterns in large injection moulds and requires verification through short-shot studies on the production tool.

When Regrind Is Introduced into Blow Moulding or Pipe Extrusion Lines

If the EX designation is used in a continuous blow moulding line with a 60-mm grooved-feed extruder and 30 L/D, the addition of 30 wt% regrind to virgin HDPE typically increases head pressure by 8–12% at constant screw speed and raises die swell by 3–5%. The parison drawdown ratio is usually reduced from 3.8:1 to 3.5:1 to maintain wall thickness. The difference from virgin HDPE arises from a broader bimodal molecular weight distribution and the presence of long-chain branching from prior processing. For corrugated pipe extrusion, the EX grade can be used at 10–20 wt% without changing the dry-blend feeder calibration; above 30 wt%, processors observe lower melt strength and an increased tendency for melt fracture at die gaps below 1.5 mm.

These boundaries are narrower than for single-source post-industrial regrind because the post-consumer fraction contributes slightly higher ash and oxidised polyolefin species. A stabilizer addition of 0.05–0.10 wt% hindered phenolic antioxidant is sometimes used in pipe extrusion to compensate for oxidative history, but this should be validated with OIT testing under ISO 11357-6:2018. In blow moulding, colour variation is more visible in thin parison walls; lots should be visually inspected or measured with a spectrophotometer against a reference standard before full production.

Because the regrind contains post-consumer feedstock, regulatory status depends on the finished article and the intended market. The product is not automatically food-contact compliant; direct food-contact use requires either a valid FDA letter of no objection for the recycling process under 21 CFR 177.1520 or an authorization under Commission Regulation (EU) 2022/1616 based on article-specific challenge testing. For industrial and construction applications, the material can be assessed against REACH Article 33 SVHC communication duties and EU RoHS Directive 2011/65/EU; typical heavy-metal residues for the cleaned bottle fraction fall below 100 mg/kg for lead, 100 mg/kg for cadmium, 1000 mg/kg for chromium, and 1000 mg/kg for mercury. Lot-specific verification is required because feedstock composition varies with collection geography.

The material is not recommended for use in medical devices, toys intended for oral contact, or pharmaceutical packaging unless a dedicated regulatory assessment is performed. Compared with generic mixed regrind, EcoInvest HDPE REGRIND provides more restrictive limits on polypropylene, aluminium flake, and ash; compared with virgin HDPE, it carries broader lot-to-lot colour variation and a lower resistance to slow crack growth measured by ASTM D1693-15. These limitations define the operational boundary for substitution in industrial, packaging, and construction applications.