On accumulator-head blow moulding machines with 80–110 mm screw diameters and 25:1–30:1 L/D ratios, PetroChina Daqing HDPE DGDB 6097 is processed into 120 L and 200 L open-head and tight-head drums at melt temperatures of 170–190°C and die head temperatures of 175–195°C. The parison is extruded through a diverging die with land length-to-die gap ratio between 10:1 and 15:1, blow air pressure is maintained at 0.6–0.8 MPa, and cycle times for 200 L drums typically range from 165 s to 240 s depending on wall thickness and cooling water inlet temperature of 10–15°C. The compounding recipe for natural-grade production is 100 phr DGDB 6097, with 1–3 phr carbon black masterbatch when ultraviolet protection is specified and 20–25 phr clean internal flash regrind returned from the same drum line after metal detection and moisture control below 0.05%. Terminal articles are UN 1H1 and UN 1H2 industrial packagings used for solid and liquid chemical transportation. Regulatory compliance for dangerous goods packaging is verified under UN Chapter 6.1 drop, leakproofness, hydraulic pressure, and stacking test sequences, with material qualification performed to ASTM D1693-B and ISO 1133-1:2022. The practical upper regrind limit is set by stress-cracking resistance, because ESCR measured on natural DGDB 6097 declines as regrind content exceeds 25 phr under constant mould fill pressure; at a parison melt temperature above 195°C, observable sag produces thin top chime walls and pinched-off tail sections, while at below 165°C the pinching seam at the drum base develops incomplete fusion. Published comparative data for regrind ratios above 35 phr in this specific grade under ASTM D1693-B is limited; qualification on production tooling is therefore required before use in UN-certified packagings.

For multilayer agricultural chemical containers holding xylene-based formulations

DGDB 6097 is used as the structural high-density polyethylene layer in three-layer and six-layer co-extrusion blow moulded bottles of 0.5 L to 10 L, where the other layers are polyamide or EVOH barrier resin and maleic anhydride-grafted polyethylene tie resin. The parison layer distribution is 70–80 wt% DGDB 6097, 5–10 wt% barrier layer, 3–5 wt% adhesive tie layer, and no more than 15 wt% post-industrial regrind recovered from the barrier bottle line; regrind containing barrier polymer is controlled because dispersed polyamide domains reduce interlayer adhesion. Extrusion temperatures are 190–205°C for the HDPE layer, 220–230°C for the barrier and tie melts, and the co-extrusion head is operated with a die gap of 1.2–2.5 mm and programmed parison wall thickness to maintain sidewall thickness of 0.8–1.5 mm. Terminal products are UN-approved jerrycans, trigger-spray bottles, and agrochemical containers. Compliance for the filled packages is assessed under ADR/RID/IMDG, while material suitability for packaging is evaluated by ASTM D638-14 tensile yield and ASTM D256-23 notched Izod impact. A processing boundary occurs when the barrier layer exceeds 10 wt%, because the melt strength of the parison falls and the bottle pinch-off weld at the bottom becomes brittle; therefore co-extrusion blow moulding of this grade typically limits the barrier fraction to 10 wt% unless a higher-melt-strength barrier grade is used.

Hydrocarbon emission limits for blow moulded automotive fuel reservoirs require a barrier strategy applied to the HDPE shell. In a six-layer co-extrusion line, DGDB 6097 is run as the inner and outer cap layers at a combined 90–94 wt% of the total polymer, EVOH is metered at 3–5 wt%, tie resin at 2–4 wt%, and carbon black concentrate is added at 2 phr to the outer layer only. The process uses six extruders feeding a six-layer spiral mandrel die, with melt temperatures of 210–230°C for HDPE, 200–210°C for tie resin, and 190–205°C for EVOH; parison length is controlled by closed-loop accumulator position to prevent layer redistribution. After demoulding, the tanks are fluorinated with a gas blend of 0.5–1.0% fluorine in nitrogen at 25–40°C to reduce fuel permeation in accordance with hydrocarbon emission limits. Terminal products are 40–70 L automotive fuel tanks and filler pipes. Compliance is documented under ECE R34 and SAE J1737 for permeation, with material density and melt flow verification by ISO 1183-1:2019 and ISO 1133-1:2022. The operational boundary is the HDPE melt temperature: above 230°C the outer layer oxidizes and surface pitting appears; below 205°C the EVOH layer cools too rapidly in the co-extrusion head and forms gel streaks at the die lip.

What limits regrind content in thick sheet extrusion for chemical tank liners?

Extruded high-density polyethylene sheet of 4–12 mm thickness is produced from DGDB 6097 on a single-screw extruder with a 90–120 mm screw diameter, 30:1 L/D ratio, and a static mixer after the screw to homogenize melt temperature. The formulation for weldable chemical containment liner stock is 100 phr DGDB 6097, 0–15 phr clean thermoforming trim, and 2–4 phr antioxidant/UV stabilizer masterbatch; regrind content beyond 25 phr is avoided because melt-flow variation alters sheet gauge uniformity at a die width of 1,500–2,500 mm. The process operates with a flat die temperature profile of 200–215°C and a three-roll stack with roll temperatures of 60–85°C, producing sheet that is cut and butt-fusion welded into liner panels for chemical storage bunds, tank shrouds, and secondary containment. Material quality is verified by ISO 178:2019 flexural modulus and ISO 527-2:2012 tensile yield. When the roll stack temperature is below 55°C, the sheet surface develops flow marks and the fusion weld tensile strength falls below 90% of parent material, which is a critical limit for liner certification.

Because buoyancy foam filling is not used in open-cell fender construction, marine fender shells made from DGDB 6097 are blown at 100 phr base resin with 2–3 phr carbon black UV masterbatch on accumulator-head machines at melt temperatures of 165–185°C to produce air-filled fender bodies and buoy floats, with compliance acceptance based on ISO 1183-1:2019 density and ASTM D1693-B ESCR after salt-spray conditioning.

Large-format double-wall agricultural pallet boxes demand a different parison programming curve

When DGDB 6097 is blow moulded into double-wall agricultural pallet boxes and 30–60 kg industrial containment shells, the accumulator head is configured for slow pre-blow and late inflation to drive material into the pinched corners of the part. The feedstock ratio is 100 phr DGDB 6097 with 15–20 phr internally generated regrind and 1–2 phr lubricant/process additive masterbatch where ejection force and scrap reduction are specified. Process parameters include a 110–130 mm extruder screw with a 25:1 L/D ratio, a shot size 20–30% above finished part mass, a melt temperature of 175–195°C, and an inflation air pressure of 0.5–0.7 MPa. Terminal products are double-wall reusable transport boxes, agricultural crates, and material-handling shells. Dimensional and load-performance compliance is checked under ISO 8611-1:2011, and material toughness is verified by ASTM D256-23 notched Izod impact at −20°C where cold-chain transport is involved. The parison programming must compensate for the difference between the top rim, which solidifies during the initial inflation delay, and the bottom corner, which remains thin if pre-blow pressure exceeds 0.1 MPa during the first 1.0 s.