Product designation EcoInvest HDPE REGRIND MIX identifies a mixed-stream high-density polyethylene regrind supplied as dry-ground, washed, and classified flake. The material originates from post-industrial container trim, purgings, and post-consumer blow-molded containers, and is intended for opaque secondary feedstock applications. Representative lot values indicate a melt flow rate of 0.30–0.80 g/10 min at 190 °C/2.16 kg per ISO 1133-1:2022, density of 0.94–0.97 g/cm³ per ISO 1183-1:2019, and nominal flake size 3–12 mm. Residual fines passing a 3.15 mm sieve are controlled below 0.5 wt%. Because the stream is mixed-color, the product is not suited to clarity-sensitive or translucent parts unless a letdown of natural or tinted HDPE is blended.

Each shipment should be accepted against a certificate of analysis covering melt flow rate, density, moisture content, and contamination. Moisture by ASTM D6980-17 is typically below 0.25 wt% as received; storage at relative humidity above 60% can increase surface moisture above 0.40 wt%, requiring pre-drying at 70–80 °C for 2 h before extrusion. Bulk density ranges from 0.52 g/cm³ to 0.60 g/cm³, lower than virgin pellet bulk density, which affects gravimetric feeder calibration and hopper bridging. Contaminant limits are specified as ≤50 ppm ferrous metals, ≤10 ppm non-ferrous metals, and ≤25 ppm total cellulosic residue by weight. Published data for this exact mixed-stream configuration remain limited; lot-specific certificates govern each production batch.

For melt processing, a single-screw extruder with 24:1 to 30:1 L/D and compression ratio 2.5:1 to 3.0:1 is sufficient for most profile and sheet applications. Barrel settings should be profiled from 180 °C at the feed zone to 230 °C at the die, with melt temperature held at 220–240 °C. Screen packs of 60/80/100 mesh reduce paper fiber and gel counts; pressure drop across the pack typically rises from 40–60 bar on clean screens to 90–130 bar before changeout. Vacuum venting at −0.6 bar to −0.8 bar is required when residual moisture exceeds 0.25 wt% or when sheet with thickness below 1.0 mm is produced. A melt pump is recommended for flat dies wider than 600 mm because flake bulk density variations otherwise produce visible gauge bands.

What distinguishes EcoInvest HDPE REGRIND MIX from single-stream natural HDPE regrind?

Single-stream natural HDPE regrind is generated from a defined feedstock such as translucent dairy bottles or monochrome industrial scrap, resulting in narrower melt flow distribution and lower pigment load. EcoInvest HDPE REGRIND MIX incorporates mixed-color and mixed-source high-density polyethylene, which broadens the melt flow range and introduces low levels of non-HDPE polyolefins, typically 1–3 wt% polypropylene and 0.5–1 wt% low-density polyethylene. The mixed-polymer fraction lowers tensile elongation and melt strength compared with single-stream HDPE, but improves stiffness consistency in thick-wall parts when the polypropylene fraction is dispersed during high-shear compounding. Converters should expect wider lot-to-lot variation in elongation at break and melt flow than for single-stream natural regrind, and should validate each lot with ISO 1133-1:2022 and ISO 527-2:2012 before tool transfer.

For injection molding, trials on reciprocating-screw machines from 1200 kN to 5000 kN clamp force show acceptable feeding when the feed throat is water-jacketed at 30–50 °C and the screw is run at 80–120 rpm. General-purpose screws with 20:1 L/D and ring non-return valves maintain shot-to-shot consistency when back pressure is set to 40–80 bar. Mold shrinkage measured by ASTM D955-21 after 48 h is typically 1.4–2.2% along flow and 1.2–2.0% transverse. Thin-wall sections below 1.5 mm are not advised with mixed-color flake because inconsistent pigment dispersion can produce flow lines; an external color masterbatch at 2–4 wt% and a distributive mixing screw are required for uniform appearance. Hot-runner gates below 0.8 mm may require melt temperature increase of 5–10 °C to avoid short shots caused by wider particle size distribution.

Color matching on this substrate requires masterbatch letdown between 2 wt% and 5 wt%. Gravimetric dosing accuracy of ±0.2 wt% is required to prevent visible swirl in thick sections and edge-to-edge shade drift. When carbon black masterbatch is used at 2.5 wt%, weatherability improves but notched Izod impact measured by ASTM D256-23 at 23 °C declines approximately 8–12% relative to the same lot without carbon black. Mixing screws with Maddock or pineapple dispersive elements are preferred over simple conveying screws because the mixed flake requires additional distributive mixing to homogenize melt temperature and pigment concentration.

If the converter requires stable parison formation in extrusion blow molding, what adjustment is necessary?

In extrusion blow molding, replacement of virgin HDPE with this regrind at up to 30 wt% modifies parison sag and die swell. Maintaining die swell at 25–45% typically requires melt temperature reduction to 190–210 °C and accumulator-head pressure between 180 bar and 280 bar. Continuous shuttle machines are more sensitive to output fluctuation from flake feed; accumulator-head lines with diverging die gaps of 0.8–1.5 mm provide a more uniform parison. Programmed wall thickness should be increased by 5–10% in the upper pinch-off zone to compensate for sag when low-molecular-weight fractions increase. Pre-drying at 70 °C for 2 h is mandatory at ambient relative humidity above 60%, because moisture-driven micro-voids reduce drop impact and create pinch-off pinholes. Rheological checks on a capillary rheometer at 190 °C and apparent shear rates from 100 s⁻¹ to 1000 s⁻¹ should be used to confirm that low-shear viscosity does not fall below 8 kPa·s; below this threshold, sag becomes difficult to correct by temperature alone. Batch-to-batch variance in melt strength is best controlled by limiting the low-density polyethylene fraction to ≤1 wt% and rejecting lots with melt flow rate above 0.80 g/10 min for blow molding.

Sheet extrusion with downstream thermoforming produces acceptable gauge control when a melt pump is installed between the extruder and the flat die. Barrel temperatures from 190 °C to 225 °C, melt temperature near 220 °C, and die temperature 225 °C support stable operation. On a 900 mm flat die producing 1.2 mm nominal sheet, gauge variation remains within ±0.08 mm with a melt pump; without a melt pump, variation can exceed ±0.15 mm due to flake bridging and bulk density fluctuation. Forming temperatures of 130–150 °C are suitable for plugs with draw ratios between 0.8 and 1.1. The product is limited to opaque trays, pallet edge boards, and drainage components; high-clarity or deep-draw thin-wall packaging is excluded.

Corrugated drainage pipe and conduit trials on counter-rotating twin-screw extruders with 26:1 L/D and vented barrels used barrel setpoints of 180–215 °C and screw speeds of 20–40 rpm. Wall thickness variation on 110 mm corrugated pipe remained within ±0.15 mm when internal cooling air was held at 10–15 °C and vacuum calibration at −0.3 bar. Ring stiffness testing according to ISO 9969:2016 exceeded 8 kN/m² on the tested lot; however, because post-consumer feedstock varies, each production lot requires confirmation of crush resistance and brittleness at low temperature before specification to underground drainage applications.

Oxidative stability is governed by residual stabilizer availability in long-term outdoor profiles

For outdoor profiles, oxidation induction time at 200 °C measured by ISO 11357-6:2018 commonly falls between 12 min and 28 min, below virgin pipe-grade HDPE with values above 40 min. Outdoor retention therefore requires antioxidant masterbatch at 0.3–0.6 wt% and hindered amine light stabilizer chemistry rather than benzophenone-only UV absorbers. Phosphite/hindered phenol processing stabilizer packages are compatible with the mixed-color regrind. Amine-based antistatic additives should be avoided above 0.2 wt% because yellowing accelerates in mixed-color flake and stabilizer consumption increases. Validation of long-term heat aging for copper-contact applications should follow ISO 4577:2019, not short-term melt flow retention alone. Oven aging at 110 °C should be accompanied by carbonyl index measurement by infrared spectroscopy; an increase of 0.05 absorbance units at 1715 cm⁻¹ before 500 h indicates insufficient stabilizer carryover.

Against virgin HDPE blow-molding grades, the regrind exhibits lower notched impact strength and wider melt flow distribution. Against recycled polypropylene regrind, it processes at lower melt temperature and offers higher environmental stress-crack resistance measured by ASTM D1693 condition B, although the mixed-color fraction limits use in applications requiring natural translucency. Table 2 summarizes the comparative profile.

Processors seeking substitution in existing virgin HDPE tooling should begin at 15–20 wt% and increase while monitoring melt pressure, color uniformity, and impact strength. Above 50 wt%, mold temperature can be reduced by 5–10 °C to control shrinkage and release. Potable water pressure pipe is excluded unless a validation program addresses hydrostatic strength per ISO 4427 and organoleptic migration limits. The product is not cleared for direct food-contact use under FDA 21 CFR 177.1520 unless the converter demonstrates source control, decontamination efficiency, and challenge-test compliance acceptable to the relevant regulatory authority. In all cases, the certificate of analysis for each lot governs processing conditions and application suitability.