What Limits Bubble Stability When 5000S Runs on High-Stalk Film Lines?

Producer technical literature for PetroChina Lanzhou HDPE 5000S lists a nominal density of 0.954 g/cm³ when tested per ISO 1183-1:2019. The nominal melt flow rate is 0.90 g/10 min at 190°C/5.0 kg per ISO 1133-1:2022. These values place the grade in the high-molecular-weight HDPE envelope. On a production-scale blown film line, the material is run through a grooved-feed extruder with a barrier screw and an L/D ratio of 30:1. The spiral mandrel die is set to a die gap of 1.2–1.8 mm. Melt temperature measured at the die entry is held between 190°C and 210°C. The blow-up ratio is set from 3.0:1 to 4.5:1. Frost line height is adjusted between 800 mm and 1200 mm. Internal bubble cooling is used when high-output operation is required on 90 mm screw diameters. Bubble instability occurs when frost line height is pushed beyond 1200 mm without increasing melt temperature. The instability appears as a low-frequency oscillation of the bubble neck. Output is reduced before the failure becomes a bubble collapse.

Formulation ratios follow the end-use stiffness requirement. A 100% 5000S monolayer is used where high modulus and low creep are dominant. Where side-seal strength or low-temperature dart impact is specified, 10–20 wt% metallocene LLDPE is introduced at the gravimetric dosing station. The LLDPE modifier reduces film modulus relative to the 100% 5000S film. This trade-off is accepted only when the application standard requires lower-temperature impact performance. The blend is dry-mixed before the hopper. The extruder zone profile is 180°C, 190°C, 200°C, 205°C, 210°C from feed to die. Die pressure is maintained between 300 bar and 420 bar. Specific energy consumption rises when the LLDPE fraction exceeds 20 wt% because screw slip decreases. Surface melt fracture is more likely below 190°C at high screw speed. The die entry temperature is therefore not trimmed below the lower limit without reducing line speed.

Mechanical acceptance is tested on film samples conditioned at 23°C and 50% relative humidity for at least 40 h per ASTM D618-21. Dart impact is measured under ASTM D1709-16a, method A, with a 1.5 lb dart. Elmendorf tear is measured in machine direction and transverse direction per ASTM D1922-15. Tensile yield strength and elongation at break are measured per ASTM D882-18. For heavy-duty industrial liners intended for non-food contact, the formulation is reviewed against REACH (EC) No 1907/2006, Annex XVII restrictions. Where the liner is used to store dry food ingredients, FDA 21 CFR 177.1520 conditions of use apply. The producer certificate of analysis should be checked for lot-specific extractables data. Published data for this specific film configuration is limited. Converters typically qualify the film on their own line before commercial release.

Terminal products in this segment include layflat tubing for large-format industrial sacks, temporary containment liners for construction debris, and FIBC inner liners. The film thickness ranges from 60 µm to 200 µm. Below 60 µm, melt fracture risk increases on polished spiral mandrel dies. Above 200 µm, bubble cooling becomes the line-rate limiting factor. The grade should not be combined with high levels of random copolymer PP in the same monolayer because the viscosity mismatch creates visible interfacial distortion. Pre-drying is not normally required when resin is stored in sealed packaging. If the resin is exposed to relative humidity above 60% for more than 24 h, surface moisture can generate bubble pinholes.

For extrusion blow moulding of 20 L to 60 L jerry cans, 5000S is charged as the primary material at 100 wt%. The same material is also used as regrind at up to 20 wt% in the same part after lot-specific verification of melt-flow stability. The melt temperature at the accumulator head is held between 190°C and 205°C. The die gap is set to 1.5–2.5 mm. Parison programming uses 30–50 points to adjust wall thickness along the length of the parison. A divergent die is preferred over a straight die because it reduces parison curl. The parison length for a 20 L container is typically 700–900 mm. The sag ratio is kept below 1.5:1 by increasing extrusion speed and reducing melt temperature. At head temperatures above 215°C, the low-molecular-weight tail in the MWD reduces melt strength. The parison thins in the upper pinch-off area and causes thick-top failure.

Blow air pressure is set between 0.6 MPa and 0.8 MPa. Mould clamp force for 20 L to 60 L moulds is in the range of 300–600 kN. The blow time is 60–120 s. The mould temperature is held at 15–25°C. The pinch-off weld is the critical quality point. In 5000S, the weld strength depends on melt temperature and mould close speed. A high close speed combined with a low melt temperature produces a weak weld because the polymer chains at the pinch interface do not interdiffuse sufficiently. The weld is tested by a 1.5 m drop impact after filling with water and sealing. The pass criterion is no leakage and no crack longer than 3 mm. Wall thickness distribution is measured by ultrasonic gauge at least every 2 h during continuous production.

The acceptance criteria below are commonly applied by non-food chemical container converters. They are not producer-promised specifications for every lot.

Where jerry cans are intended for transport of dangerous goods, qualification follows the test series in ADR 6.1.5 or UN Model Regulations Chapter 6.1. The finished container is subjected to a leakproofness test, a hydraulic pressure test, and stack loading. 5000S is suitable only for non-food chemical packaging unless a food-contact migration assessment is completed under FDA 21 CFR 177.1520 and EU 10/2011. Lot certificates should be reviewed for density, melt-flow rate, and ESCR before the material is placed in a dangerous goods container line. Published data for this specific container configuration is limited.

Terminal articles include 20 L UN-rated narrow-mouth jerry cans, 25 L wide-mouth agricultural chemical cans, and 60 L open-head drums. These articles are blow-moulded in single-station or double-station shuttle machines. Cycle time is governed by wall thickness and cooling time. Typical cycle time for a 20 L container is 60–120 s. The finished products are used for automotive coolants, screenwash, agricultural chemicals, and diesel exhaust fluid packaging.

When Thermoforming Reaches the Sag Threshold of 5000S Sheet

Sheet extrusion from 5000S is carried out on a single-screw extruder with an L/D ratio of 32:1 and a coat-hanger die. The die gap is set to 2.0–3.0 mm. Melt temperature is controlled at 200–215°C. The polished three-roll stack is set to 70–90°C for the middle and lower rolls. Sheet thickness for industrial dunnage ranges from 2.0 mm to 5.0 mm. The sheet is cut into blanks after cooling. Thermoforming is conducted on a single-sheet or twin-sheet machine with quartz or ceramic IR heaters. The sheet surface temperature is brought to 150–170°C. At this temperature, sheet sag becomes the main process limit. 5000S retains enough melt strength to hold a 2.5 mm sheet over a 600 mm draw distance when the lower oven temperature is reduced by 10–15°C relative to the upper oven. If the sheet sags more than 25% of the clamp frame depth before forming, wall thinning in the corner becomes unacceptable.

The material is processed at 100 wt%. Regrind from the sheet skeleton is added at 10–30 wt% in non-visual industrial dunnage. The regrind content is limited by the loss of melt strength after repeated heat history. Above 30 wt% regrind, the sag rate increases and the formed part shows a measurable reduction in bottom corner thickness. Twin-sheet thermoforming is used for pallet top decks and separator trays. The two sheets are pressed at a clamp force of 0.4–0.8 MPa on the part area. Plug assist is used for deep draw ratios above 1.5:1. The plug material is syntactic foam or POM-C. The plug temperature is held below 120°C to avoid surface marking.

Finished dunnage trays are tested for static load and impact. Flexural modulus of the formed sheet is measured per ISO 178:2019. Tensile properties are measured on specimens cut from the flat bottom per ASTM D638-14. Heavy metals are controlled under RoHS Directive 2011/65/EU. REACH SVHC screening is performed at the colour masterbatch level. The material is not rated for direct food contact unless the specific structure is tested under EU 10/2011 and FDA 21 CFR 177.1520.

Terminal products include returnable dunnage trays, automotive component separator sheets, and logistics pallet top decks. The articles are used in closed-loop transport between manufacturing plants. The useful service range is -40°C to 70°C. Below -40°C, impact brittleness increases. Above 70°C, creep under continuous load becomes the design limit.

Corrugated Conduit Wall Distribution and Vacuum Calibration Windows

For corrugated conduit extrusion, 5000S is processed on a single-screw extruder with an L/D ratio of 30:1 and a grooved feed section. The melt temperature is set from 200°C to 220°C. The die gap is maintained at 0.8–1.2 mm. The parison is pulled into a corrugator with vacuum-assisted mould blocks. Vacuum pressure is set between 0.6 bar and 0.8 bar. The mould block temperature is controlled at 15–35°C. The line speed for conduit diameters from 25 mm to 110 mm is 1.5–4.0 m/min. The critical wall-thickness location is the root of the corrugation. Insufficient vacuum or a high melt temperature moves material away from the root. The result is an oval cross-section and reduced crush strength.

The formulation is 100 wt% 5000S. A carbon black masterbatch is added at 2–3 wt% for UV protection in outdoor cable duct installations. The masterbatch is selected for a carrier resin compatible with HDPE. A higher masterbatch loading reduces melt strength and increases the risk of corrugation collapse. The corrugator clamping force is set to 5–10 kN per metre width depending on conduit diameter. The blow-up ratio inside the corrugator is fixed by the block geometry and cannot be adjusted without changing tooling. The die-to-corrugator distance is kept below 200 mm. A longer distance cools the parison skin and causes surface tearing at the corrugation tip.

Conduits for electrical cable protection are tested per EN 61386-24 for compression resistance and impact resistance at -5°C and +60°C. The outer diameter and wall thickness are measured per ISO 3126:2005. For drainage pipe applications, the ring stiffness is tested per EN ISO 9969:2016. Resin compliance is checked against REACH (EC) No 1907/2006 and RoHS Directive 2011/65/EU Annex II.

Terminal products include corrugated cable protection ducts for solar farms, underground optical fibre conduits, and land drainage laterals. The service temperature range is -30°C to 60°C in outdoor exposure. Continuous immersion in hot drainage water above 60°C is not recommended because long-term creep rupture data for this specific grade in that medium is limited.

Mono-oriented filament extrusion of 5000S produces 0.20 mm to 0.40 mm filaments at 100 wt% or with a UV stabilizer masterbatch at 2–4 wt%. The extruder is a single-screw machine with an L/D ratio of 24:1–30:1. Melt temperature is held at 190–215°C. The extrudate is quenched in a water bath at 25–40°C. The quenched filaments are drawn in two stages. The first-stage draw ratio is 4:1–6:1. The second-stage draw ratio is 1.5:1–2.0:1. Total draw ratio ranges from 6:1 to 9:1. Drawing is carried out in a hot air oven at 90–120°C. The tensile strength of the drawn filament is measured per ASTM D2256-10.

The linear density is controlled between 200 denier and 800 denier. Line speed is set from 150 m/min to 250 m/min. Above 250 m/min, filament break frequency increases unless the quench bath length is extended. The resin should not be blended with PP in this process. The viscosity mismatch causes delamination in the drawn filament. Terminal products include safety netting, anti-bird netting, monofilament rope yarns, and agricultural twine. Compliance is limited to general chemical safety under REACH. No food-contact status is claimed for this segment.

Restoring ESCR in Recyclate Compounds Involves More Than Melt Index

In recycling lines that upgrade post-consumer HDPE for non-food injection or extrusion applications, 5000S is added at 20–40 wt% to restore viscosity and environmental stress crack resistance. The recyclate stream is pre-sorted, washed, and dried to a moisture content below 0.1 wt%. Compounding is performed on a co-rotating twin-screw extruder with an L/D ratio of 40:1 and vacuum devolatilisation at -0.8 bar. Barrel temperatures from feed to die are 180°C, 190°C, 200°C, 205°C, 210°C. The melt is filtered through a 150–250 µm screen pack. The pelletized compound is intended for thick-wall articles where ESCR is more important than high-flow injection moulding. The addition of 5000S raises the melt viscosity. Injection moulders report that clamp force requirements increase by 10–20% compared to a standard recyclate compound.

The ESCR of the compounded recyclate is measured per ASTM D1693-15, Condition B. The compound is screened against EN 15344:2021 for recycled plastics. REACH SVHC screening is performed on the input recyclate. Terminal products are non-food transport packaging, drainage fittings, and material handling bins. Published data for this specific recyclate blend is limited. The actual ESCR improvement depends on the contamination level and the melt-flow drift of the incoming recyclate.