KPC (Kuwait) HDPE 6888 is a high-molecular-weight high-density polyethylene produced by Kuwait Polymers Company for extrusion blow moulding, thick sheet extrusion, and large industrial container applications where low standard-load melt index and high parison strength are required. The product designation 6888 distinguishes the grade within the producer’s HDPE portfolio. Producer-published typical values place density at 0.947 to 0.950 g/cm³ under ISO 1183-1:2019 and high-load melt index at 7.0 to 9.0 g/10 min at 190°C/21.6 kg under ISO 1133-1:2022. The standard-load melt index at 190°C/2.16 kg remains below 0.40 g/10 min, distinguishing the grade from conventional injection-moulding HDPE and thin-wall packaging grades. The resulting melt flow ratio between 21.6 kg and 2.16 kg loads is approximately 20 to 30, indicating a broad molecular weight distribution that contributes to parison strength and low sag during large-part extrusion blow moulding.

Short-term mechanical data associated with the grade include tensile stress at yield between 22 and 26 MPa under ISO 527-2:2012, tensile strain at break above 600%, flexural modulus between 850 and 1000 MPa under ISO 178:2019, and notched Charpy impact at 23°C between 18 and 25 kJ/m² under ISO 179-1:2023. Vicat softening temperature A50 is reported in the 122°C to 126°C range under ISO 306:2022. Environmental stress crack resistance is the more service-relevant descriptor; values above 300 h are associated with the grade under ASTM D1693-15 in 10% Igepal at 50°C, although published data for specific container geometries is limited.

These values are producer-typical characterisation data and should not be read as guaranteed specifications. The governing lot certificate of analysis and the current product datasheet remain the controlling documents for release testing. Where the prospective converter requires a narrower property band, incoming resin should be tested for high-load melt index, density, and ESCR before production lock.

What Limits Melt Temperature and Die Pressure During Extrusion Blow Moulding?

On a single-screw extruder with a 60 mm screw diameter and 24:1 to 30:1 L/D ratio, the melt temperature measured at the die exit is maintained between 190°C and 210°C. Exceeding 220°C for more than 10 min can initiate oxidative chain scission, producing a permanent increase in high-load melt index and a loss of parison integrity. Barrel temperature settings are typically 180°C to 205°C from the feed zone to the metering zone, with the head and die zones set to 195°C to 210°C. Head pressure at the breaker plate normally falls between 15 and 25 MPa, depending on screw speed, melt temperature, screen pack condition, and accumulator head geometry. Screw speeds are commonly 40 to 80 rpm, and screw compression ratio should be 2.5:1 to 3.5:1 to avoid excessive shear heating.

Die swell for this grade is observed in the 25% to 35% range; mandrel and die gaps must be sized accordingly. Accumulator-head machines with shot capacities of 1 to 2 L and clamp forces between 600 and 1000 kN are suitable for containers above 30 L. Parison programming with 10 to 20 point wall-thickness control is required for drums and intermediate bulk containers because high-molecular-weight HDPE exhibits measurable sag if the parison cycle exceeds 4 s. Blow pressure is typically 0.6 to 0.9 MPa; preblow delay is set between 0.1 and 0.4 s. Mould cooling water is controlled at 15°C to 25°C. The grade is not intended for rotomoulding or cast film; its standard-load melt index is too low for thin-wall injection filling.

At extrusion outputs above 45 kg/h on a 60 mm extruder, sharkskin or melt fracture can occur if the die land length is below 15 mm. A spiral mandrel die with land lengths of 15 to 25 mm is preferred for large containers. The onset of melt fracture for high-molecular-weight HDPE at 190°C is often observed near a wall shear stress of 0.14 MPa; production rates should be set to remain below this threshold unless a fluoropolymer processing aid is added at 200 to 500 ppm. Surface haze and die deposit are reduced when the die exit is free of condensation and the melt stream is not contaminated with lower-viscosity resin residues.

Comparative Melt Rheology and Density-Stiffness Trade-Offs

Compared with a conventional injection-moulding HDPE having a standard-load melt index of 8 g/10 min, KPC HDPE 6888 requires higher extruder torque and produces greater parison stability. The high-load melt index of 7.0 to 9.0 g/10 min places it among blow moulding grades with moderate flow, whereas thin-wall high-flow blow moulding grades typically exceed 18 g/10 min at 21.6 kg. The density of 0.947 to 0.950 g/cm³ is lower than that of stiff injection grades in the 0.958 to 0.965 g/cm³ range. This reduces flexural modulus but improves stress crack resistance and impact behaviour. The trade-off is normal for large-part blow moulding and must be evaluated through filled-container testing rather than resin property comparisons alone.

The comparison indicates that HDPE 6888 is selected when environmental stress crack resistance and impact behaviour in service outweigh maximum top-load stiffness. Substituting a higher-density grade may increase flexural modulus by 200 to 400 MPa, but ESCR can decline below 50 h in aggressive environments. Conversely, lower-density polyethylene grades may increase impact resistance but fail stack-load requirements for drums. Published data for this specific configuration is limited for exact lot-to-lot comparisons; incoming batches should be tested for high-load melt index, density, and ESCR before running on production equipment. The grade should not be interchanged with injection-moulding or pipe formulations without revalidation. Use of an injection grade in large blow moulding leads to parison sag, thin corners, and unacceptable drop impact; use of HDPE 6888 in injection moulding would require melt temperatures above 220°C and would risk gate freeze-off.

When Environmental Stress Crack Resistance and Chemical Contact Define Container Service Life

Chemical contact and stacking loads create the primary failure mode for blow-moulded containers. The ESCR value measured under ASTM D1693-15 in 10% nonylphenoxy poly(ethyleneoxy) ethanol at 50°C ranks the grade against lower-molecular-weight alternatives. A reported ESCR above 300 h does not guarantee service life in a specific formulation; finished containers must be tested with the actual liquid, closure load, and temperature. ESCR failure initiates at surface defects and weld lines, and the broad molecular weight distribution of high-molecular-weight HDPE increases craze propagation resistance. The F50 value is statistical and non-linear with time, so it cannot be linearly extrapolated to service life.

The grade is generally supplied with food-contact conformity statements under 21 CFR 177.1520(c) for olefin polymers, but the converter remains responsible for end-use migration testing under 21 CFR 177.1520(d) or EU Regulation 10/2011. Under EU Regulation 10/2011, the overall migration limit is 10 mg/dm² of food-contact surface area. REACH candidate list and RoHS 2011/65/EU compliance are typically addressed in the producer’s regulatory documentation; no SVHC above 0.1% w/w is expected in the unfilled polymer. The raw resin does not contain intentionally added perfluoroalkyl substances; however, the converter must verify the full formulation after the addition of masterbatch, process aids, or lubricants.

Immersion testing under ISO 175:2021 or ASTM D543-21 should be used for chemical compatibility screening. Published data for this specific grade with proprietary formulations is limited; laboratory immersion at 50°C for one month is a typical screening procedure before commercial container qualification. Operational boundaries include pre-drying at 70°C to 80°C for 2 h when ambient relative humidity exceeds 60% or condensation is observed on pellet surfaces. HDPE is not hygroscopic; the drying step removes surface moisture to prevent splay and melt pressure fluctuation. The material should not be blended with acetal, polyamide, or PVC traces because phase incompatibility can create delamination and weak knit lines. Prolonged contact with strong oxidizing acids, such as 50% nitric acid above 50°C, or with low-boiling aromatic hydrocarbons, can swell or degrade the polymer. For outdoor service, carbon black or UV stabilizer masterbatch should be added at 2.0 to 2.5 wt%; unpigmented parts are not suitable for prolonged outdoor exposure.

Batch-to-Batch HLMI Variation and Production Line Adjustment Protocols

Production-scale behaviour is most sensitive to high-load melt index and molecular weight distribution shifts. On an accumulator-head blow moulder, a 1.0 g/10 min HLMI increase can reduce head pressure by 0.8 to 1.5 MPa and alter parison sag by approximately 3%. If incoming HLMI is at the upper end of the specification, melt temperature should be reduced by 5°C to 10°C and die gap adjustments made before parison programming is changed. If HLMI is at the lower end, screw speed may be reduced or head zone temperature increased by 3°C to 5°C. A standardised incoming material check includes high-load melt index under ISO 1133-1:2022 condition G, density under ISO 1183-1:2019, and surface moisture content by weight loss at 105°C.

During shutdowns and start-ups, the extruder should be purged with a high-load melt index HDPE similar to 7 to 9 g/10 min. LLDPE-rich purge can create unstable pressure and melt fracture; PVC residues are not acceptable because corrosion of tooling can occur. The use of a fluoropolymer processing aid at 200 to 500 ppm may reduce die deposit and sharkskin in high-output operations. Processors should not exceed 220°C melt temperature and should limit residence time above 180°C to less than 10 min. If a colour masterbatch is added above 2 wt%, melt temperature should be reduced by 5°C to 10°C because the masterbatch carrier resin can lower melt viscosity and increase sag.

For tight-head drums and large industrial containers, HDPE 6888 is processed with wall thickness from 1.5 to 5.0 mm. The material’s balance of density and ESCR supports containers for detergents, agrochemicals, and lubricants where stack loads and drop impact at -18°C are specified. Top-load strength under ISO 12048 and drop-impact testing under ASTM D5276-19 are performed on finished articles rather than predicted from resin datasheet values; the converter must validate the specific container design. In sheet extrusion, thicknesses between 2 and 12 mm are typical, with melt temperature kept below 210°C to avoid surface oxidation. The product is not recommended for rotomoulding, monofilament, or thin-wall injection moulding due to the low standard-load melt index. Storage should be in a dry, UV-shaded area below 50°C and away from strong oxidizing agents.