Rotational moulding of vertical storage tanks and transportable containment vessels using LyondellBasell MDPE CP812 is specified where low-temperature dart impact and Environmental Stress Crack Resistance (ESCR) must satisfy ASTM D1998-21 and AS/NZS 4766:2020. The resin is processed as a 35-mesh powder with bulk density in the 0.38–0.50 g/cm³ range under ISO 60. The formulation addition ratio for a natural stabilisation package is 0.15–0.30 phr hindered phenolic antioxidant and 0.20–0.40 phr HALS UV stabiliser, dry-blended before oven charging; zinc stearate is held below 0.15 phr to avoid surface pitting. In a closed-loop carousel rotational moulding machine with 4:1 primary-axis and 1:4 secondary-axis rotation, the oven set point is 280–300 °C and the peak internal air temperature (PIAT) is controlled to 195–210 °C; a PIAT below 185 °C leaves incomplete densification at weld lines, while a PIAT above 215 °C accelerates oxidative degradation at the inner air-polymer interface. Forced-air cooling to 70 °C before water-mist cooling reduces warpage and residual stress. Terminal products include 1,000–10,000 L upright chemical storage tanks, sodium hypochlorite dosing vessels, UN 31H1 intermediate bulk containers, and agricultural sprayer tanks.

What Limits Carbon Black Dispersion in Gas Distribution Pipe Extrusion with Medium-Density Polyethylene?

In ISO 4437-1:2024 gas distribution pipe, CP812 is compounded to a final carbon black content of 2.0–2.5 wt%, determined by ISO 6964. The extruder feed blend is 97.5 parts by weight CP812 and 2.5 parts by weight of a 40 wt% carbon black polyethylene masterbatch; antioxidant level is 0.10–0.25 phr, and residual moisture is kept below 0.02 wt% by drying at 80 °C for 2 h whenever silo storage RH exceeds 60%. Extrusion is run on a single-screw grooved-barrel extruder with L/D 30:1 and a barrier screw, with barrel temperatures 180–220 °C, adapter 210 °C, and die 220 °C. Immersion thermocouple melt temperature must remain below 230 °C to prevent thermal degradation; melt pressure at the screen pack must not exceed 30 MPa to avoid excessive shear heating and carbon black aggregate breakdown. Vacuum sizing is maintained at 0.02–0.06 MPa with cooling water at 15–20 °C. The resultant pipe is qualified under ISO 9080:2012 long-term hydrostatic testing at 20 °C and 60 °C, typically as a PE80 grade with an MRS of 8.0 MPa. Terminal products include buried gas distribution mains, service lines, and electrofusion sockets for gaseous fuel transport up to 0.4 MPa operating pressure.

Extrusion blow moulding of industrial containers from CP812 is selected for ESCR-intensive packaging that must pass UN 1H1 drum drop tests at -18 °C and, where food contact is involved, 21 CFR 177.1520. The resin is used at 100 parts by weight with external colour masterbatch at 2.0–4.0 phr; if static dissipation is required, conductive carbon black masterbatch is added at 2.0–4.0 phr, and total conductive filler must not exceed 5.0 phr to avoid parison melt fracture and weld-line weakness. Processing on an accumulator-head extrusion blow moulding machine with a 70–100 mm screw and L/D 25:1 uses melt temperatures 185–210 °C, die gap 2.0–4.0 mm, blow pressure 0.6–1.0 MPa, and mould temperature 10–20 °C. Die swell is controlled by parison length programming to maintain a minimum sidewall thickness at the pinch-off and chime regions, where ASTM D256 notched Izod impact and ASTM D1693-15 condition B ESCR tests are used for batch release. Terminal products include 20–60 L jerry cans, 120–220 L open-top drums, IBC inner bottles, and automotive washer fluid tanks.

Table 1 lists the formulation ratios and processing limits for the CP812 downstream methods described above.

Heavy-Duty Blown Film Processing Limits and Puncture Resistance Thresholds

Heavy-duty sack production with CP812 uses a blend of 80 parts by weight CP812 and 20 parts by weight linear low-density polyethylene (LLDPE) to raise dart impact and machine-direction tear resistance. Increasing LLDPE beyond 30 wt% causes the secant modulus at 1% elongation to fall below 180 MPa and raises blocking tendency on wound rolls; therefore the LLDPE fraction is held at 20–30 wt%. Slip and antiblock masterbatch is added at 0.5–1.0 wt%. Compliance testing uses ISO 527-3:2018 tensile properties, ASTM D882-18 film tensile, ASTM D1709-16 dart impact, ISO 6383-2 tear resistance, and 21 CFR 177.1520 for direct food contact if required. The film is run on a single-screw blown film extruder with L/D 30:1, a die gap of 1.8–2.4 mm, blow-up ratio 2.0–3.0, melt temperature 195–225 °C, frost line height 8–12 times die diameter, and cooling air at 10–20 °C. Terminal products include heavy-duty shipping sacks, construction aggregate bags, chemical packaging liners, and FIBC liners.

When 30 wt% Post-Consumer Recyclate Is Added to CP812 in Rotational Moulding of Non-Potable Water Tanks

When 30 wt% post-consumer MDPE recyclate is incorporated into CP812 for non-potable water tanks, the blend is subject to REACH 1907/2006 and RoHS 2011/65/EU limits for lead, cadmium, mercury, and chromium(VI), with plastics recyclate traceability under EN 15343:2007. The formulation is 70 parts by weight CP812 and 30 parts by weight recycled MDPE whose melt flow rate is within ±1.0 g/10 min of the virgin resin at 190 °C and 2.16 kg; antioxidant is added at 0.20 phr and HALS at 0.30 phr. The combined stream is pre-compounded in a co-rotating twin-screw extruder with L/D 40:1 and vacuum devolatilization at -0.08 MPa, then pulverised to 35-mesh. Rotational moulding of the recyclate-containing blend reduces the PIAT to 190–200 °C and limits oven dwell time to 25–30 min to avoid brittle short-chain oxidation products. Published data for this specific CP812/recyclate configuration under UN 31H1 drop testing is limited; batch requalification is required. Terminal products include non-potable water collection tanks, septic tanks, and agricultural retention basins.