Under UN 3H1 design-type qualification, NUC Corporation HDPE grade DGDN3364 is processed into extrusion blow-moulded jerricans for dangerous goods. A grooved-barrel extruder with a barrier screw of L/D 24:1 to 28:1 and an accumulator head is typically used; barrel zones are held at 170–185 °C, the head at 180–190 °C, and the mould at 8–15 °C. Melt temperature above 200 °C is avoided because oxidative degradation at the pin tip increases gel formation in the pinch-off weld. Die gap is set between 1.8 mm and 2.4 mm, with a blow-up ratio of 2.2:1 to 2.8:1 and blow-air pressure between 0.6 MPa and 0.8 MPa. Wall-thickness mapping for a 20 L jerrican programmes approximately 1.4 mm at the shoulder, 1.0 mm in the sidewall, and 1.8 mm at the base corners. Regrind from trimmed pinch-off flash is limited to 20 wt% for Packing Group II liquids and 30 wt% only where repeat drop testing at -18 °C and stack testing at 40 °C are performed on the specific regrind batch. Incoming melt-flow rate is checked under ISO 1133-1:2022 at 190 °C with a 2.16 kg load, and density is checked under ISO 1183-1:2019; acceptance bands are taken from the current NUC release certificate for DGDN3364 rather than a generic HDPE specification. Pinch-off weld failure is the dominant rejection mode in this application. Weld strength is improved by keeping melt temperature at the pinch-off above 160 °C and by delaying mould closure until the programmed base section is reached. In-line leak testing at 30 kPa detects microleaks but does not replace design-type tests. The terminal articles are 5 L, 10 L, 20 L, and 30 L jerricans for solvents, lubricants, crop inputs, and other regulated liquid chemicals.

What Limits Regrind Addition if Environmental Stress Crack Resistance Must Remain Above 60 Hours?

Household detergent, hypochlorite bleach, and fabric-softener bottles are produced from DGDN3364 only after the pinch-off weld and bottom flash line are evaluated for stress cracking. These regions carry high moulded-in orientation and are exposed to surfactants, oxidisers, and fragrance solvents. The screening method is ASTM D1693-15 Condition A in 10% Igepal CO-630 at 50 °C; a threshold equivalent to 60 h F50 is commonly applied for bleach packaging, though published data for this specific grade and mould configuration is limited and must be confirmed on the production tool. The blow-moulding line uses a shuttle or long-stroke machine with a barrier screw of L/D 24:1 and 100-point parison programming. Melt temperature is held at 175–190 °C, die-head temperature at 180–190 °C, and mould temperature at 10–15 °C. Blow-air pressure is 0.5–0.7 MPa; venting in the neck and base inserts is checked to prevent air entrapment that lowers pinch-off strength. Colour masterbatch is added at 2–4 wt%, antistatic masterbatch at 1–3 wt%, and regrind is limited to 30 wt% unless ESCR retention after five re-extrusion passes remains above 80% of virgin value and tensile elongation at break under ISO 527-2:2012 remains above 300%. Bottle weight reduction below 18 g for a 1 L bottle creates wall-thickness distribution challenges because the label panel and bottom pinch-off zone become controlling regions for drop resistance and ESCR. Parison programming is biased toward the bottom corner, with sidewall target 0.5–0.6 mm and base corner target 0.7–0.8 mm. If the parison hangs too long, sidewall thickness drops toward 0.3 mm and ESCR fails rapidly. Leak testing at 0.2 bar after filling-line simulation is used as a production release test. Compliance documentation includes EU Regulation EC 648/2004 for detergent content and CLP 1272/2008 for labelling; where food-contact detergent transfer is claimed, EU 10/2011 overall migration of 10 mg/dm² applies. The terminal articles are 500 mL, 750 mL, 1 L, and 2 L bottles with screw-neck or push-pull closures.

Because crop-protection solvents such as xylene and cyclohexanone permeate monolayer HDPE rapidly, six-layer coextrusion of DGDN3364 with EVOH is used for 0.5–5 L agrochemical bottles. Layer distribution by mass for a 1 L container is typically outer skin 30–35 wt%, regrind layer 20–25 wt%, adhesive tie 1.5–2 wt%, EVOH 4–7 wt%, second tie 1.5–2 wt%, and inner skin 30–35 wt%. Skin extruders are run at 190–200 °C, while the EVOH extruder is kept below 200 °C because degradation generates acetic-acid-related gels at the layer interface. Die gap is set at 1.5–2.5 mm, and die-head pressure is held below 35 MPa to avoid interfacial flow instability between high-viscosity HDPE and lower-viscosity EVOH. Adhesive tie resins should be maleated polyolefins; amine-based processing aids in the HDPE skin are avoided because they interfere with EVOH interfacial adhesion. Each layer mass is verified by section weighing to a tolerance of ±1.5%, and sidewall EVOH thickness is not permitted to fall below 30 µm. Solvent permeation testing is performed gravimetrically at 50 °C for 28 days using the actual formulation surrogate; a weight-loss threshold of 0.5% is frequently specified by agrochemical brand owners. Regrind from post-consumer sources is excluded from the inner skin because contaminant migration is not controlled by the barrier layer. Compliance for hazardous formulations follows UN 3H1 qualification under ADR/RID/IMDG; European Union product stewardship is addressed under Regulation EC 1107/2009 and CLP 1272/2008. The terminal articles are 0.5 L, 1 L, and 5 L agrochemical containers with barrier neck inserts or induction-sealed closures.

Sheet Gauge Variation, Plug Temperature, and Draw Ratio in Thermoformed Trays

When DGDN3364 is extruded into sheet for plug-assist thermoforming, gauge variation across the web is controlled by a flat die with a flex lip and a three-roll stack operated at 70–85 °C on the middle roll and 40–60 °C on the lower roll. Sheet thickness between 0.3 mm and 1.5 mm is used for trays; draw ratios above 2.5:1 normally require plug temperature above 120 °C and sheet surface temperature of 132–138 °C, measured by infrared pyrometer before the forming station. If the sheet is extruded too cold, frozen-in orientation releases during plug assist and produces uneven wall thickness; if it is too hot, the sheet sticks to the plug and creates gloss variation. Plug material is chosen from syntactic foam or PEEK, with plug temperature of 90–120 °C depending on draw depth. Draw depth above 50 mm requires pre-stretch and sequential vacuum to prevent webbing in corners. Line speed is capped to avoid draw resonance; when sheet neck-in exceeds 10% of die width, melt temperature or die gap is adjusted. Pre-drying is not routinely required at ambient RH below 60%, but regrind stored in open sacks at higher humidity should be dried at 70 °C for 2 h to prevent surface splay. For food-contact trays, the only permissible regrind is clean edge trim from the same FDA-compliant sheet, limited to 50 wt%, and compliance is documented under FDA 21 CFR 177.1520 and EU 10/2011. For non-food industrial trays, REACH and RoHS documentation applies. Thermoformed parts are stacked without post-mould crystallisation because HDPE retains adequate modulus between -20 °C and 60 °C service temperature. The terminal products are refrigerated-food trays, medical device trays, and industrial divider trays.

When Pinch-Off Flash Is Re-Ground for Automotive Reservoir Moulding

In automotive reservoir moulding, DGDN3364 is processed on an accumulator-head blow moulder with clamp force of 150–250 t to compact the pinch-off weld over a length exceeding 300 mm. Barrel zones are set at 175–190 °C, head at 185–195 °C, and mould at 10–15 °C. The mould closing speed is profiled so that trapped air is expelled before the weld freezes; a slow close before final compression reduces fold-back and undercut at the parting line. Flash is granulated in-line, dry-air conveyed, and reintroduced at 15–25 wt%. Higher ratios are allowed only after tensile impact testing under ISO 8256:2004 and heat aging at 100 °C for 168 h show no weld-line splitting. In-line granulate is checked for coolant residue or oil contamination by Fourier-transform infrared spectroscopy before reintroduction; if an oily film persists, regrind fraction is reduced to 10 wt% or the flash is sent to non-automotive sheet. Wall thickness is measured on the production fixture with an ultrasonic gauge; the coolant overflow neck must hold ±0.15 mm. Leak testing is conducted under air at 0.3 bar while the reservoir is clamped in a fixture. Compliance is carried out under ISO 16750-3:2012 for thermal and vibration exposure, and coolant resistance is validated with a 50/50 vol% ethylene glycol/water mixture at 105 °C. The terminal articles are under-hood windshield-washer reservoirs and coolant overflow bottles with integrated mounting tabs, filled weights of 0.8–1.6 kg, and an operating range of -40 °C to 110 °C.

Corrugated Drainage Pipe Ring Stiffness Is Set in the Corrugator, Not the Extruder

Corrugated HDPE drainage pipe made from DGDN3364 is formed by a single-screw extruder with a grooved feed section and a barrier screw of L/D 30:1 to 33:1, followed by a vacuum corrugator. Melt temperature is set at 185–205 °C, die temperature at 200–210 °C, and corrugator vacuum at -0.4 bar to -0.7 bar; the vacuum must be deep enough to fill the rib crest but not so high that the inner wall is drawn thin at the valley. Carbon black masterbatch is added at 2–3 wt%, giving carbon black content of 1.5–2% by mass and a dispersity rating no greater than 1.5 for UV stabilisation. Ring stiffness is tested by EN ISO 9969:2016 and classified as SN4 or SN8, corresponding to 4 kN/m² and 8 kN/m²; creep ratio is assessed under ISO 9967:2016. If valley thickness falls below 0.5 mm, SN8 ring stiffness may pass while long-term creep can fail. Perforation slots are cut after corrugation at 5–8 mm width and spaced to provide 10–20 cm²/m infiltration area, depending on groundwater level and soil type. Perforation direction is offset from the rib crest to avoid stress concentration at the crown. Compliance for European drainage pipe is carried out under EN 13476-2; for North American projects, AASHTO M 294 or ASTM F 2306 may be referenced by the project specification. The terminal articles are agricultural drain lines, roadside edge drains, and cable-ducting conduit in 100 mm to 300 mm internal diameters.