Is Your SABIC HDPE Genuine? Five Checks Before You Pay

Verification of high-density polyethylene supplied under a SABIC designation should be conducted before the invoice is cleared and before resin is pneumatically conveyed into a plant silo. Pellet geometry, translucency, and surface gloss are not reliable indicators of molecular architecture, additive package, or lot origin. Incoming-material control on a production-scale 75 mm twin-screw compounding line operating at screw speed 520 min⁻¹ may reveal a substituted resin only as a drift in die pressure, melt temperature, or strand stability after 20 min of running. The five pre-payment checks below use test methods referenced to ISO, ASTM, and supplier release limits; each provides a separate layer of evidence.

For each silo intake, a retained sample of at least 1 kg should be taken from the top, middle, and bottom of the vessel before blending. The sample is then split with a rotary divider. This retains the possibility of physical retest if the lot is later suspected of substitution after payment.

The table is a triage guide, not a release specification; only the supplier’s grade datasheet and certificate of analysis define the acceptance interval.

The first check is melt flow rate under ISO 1133-1:2022 Procedure A or ASTM D1238-20. The measurement uses a die of diameter 2.095 mm ± 0.005 mm, a die length of 8.000 mm, a piston load of 2.16 kg, and a test temperature of 190 °C. Before a result is accepted, the melt indexer should have barrel temperature stability no worse than ± 0.1 °C and the die orifice should be cleaned with a brass tool to remove oxidised polyolefin. A single MFR value between 0.2 g/10 min and 35 g/10 min does not prove authenticity; it must be compared with the declared grade’s release band. For SABIC HDPE grades, the certificate of analysis is the controlling reference, and a deviation greater than ± 10% from the nominal value after clean-die repetition should stop payment. Low MFR in a high-flow order is frequently due to blow-moulding or pipe-grade substitution, while unusually high MFR may indicate LLDPE dilution, recycled resin addition, or thermal degradation. Confirm with capillary rheology if the melt flow result is in dispute, measuring apparent viscosity at shear rates of 100 s⁻¹ and 1000 s⁻¹ on a dual-bore instrument before release.

Moisture on pellet surfaces from cold-to-hot transfer can induce feed slip and false low throughput readings on hopper loss-in-weight systems, but it rarely shifts true MFR by more than the uncertainty of the method itself. Therefore, if a hopper load reported at 200 kg/h drops to 175 kg/h without a change in screw speed, the material should be sampled for MFR and pellet moisture rather than automatically attributed to counterfeit resin.

Why Does a Density Offset Below 0.940 g/cm³ Indicate Comonomer or Recycled Dilution?

Density measurement by ISO 1183-1:2019 or ASTM D792-20 at 23 °C is the second check because it detects comonomer-rich polyethylene and filler dilution that may pass a visual pellet inspection. The gradient-column method is preferred to immersion methods for incoming QC when acceptance windows are narrow. A column containing certified glass floats calibrated from 0.930 g/cm³ to 0.980 g/cm³ in steps no greater than 0.001 g/cm³ provides sufficient resolution. Vacuum-degas the pellets before testing to avoid entrapped air lowering the apparent result. Genuine unfilled HDPE grades typically occupy 0.940 g/cm³ to 0.968 g/cm³, and the supplier’s release interval for a single grade is usually not wider than ± 0.002 g/cm³. A sample measured below 0.940 g/cm³ should be treated as evidence of LDPE, LLDPE, or a comonomer-rich HDPE outside the declared grade unless the COA explicitly supports that value. A reading above 0.968 g/cm³ can indicate an inorganic filler, black masterbatch contamination, or a bimodal pipe grade outside the order. Confirmatory differential scanning calorimetry per ISO 11357-3:2018 at 10 K/min may help distinguish HDPE from LLDPE: the first-heating melt enthalpy of virgin HDPE is generally 140 J/g to 190 J/g, while LLDPE may sit below 130 J/g depending on comonomer content.

Mechanical Yield, Flexural Modulus, and Notched Charpy as an Identity Block

If melt flow rate and density are within specification, many counterfeit or off-spec lots are still identified only when mechanical properties are compared with the datasheet block. Specimens should be prepared by compression moulding according to ISO 293 or injection moulding according to ISO 294-1, then conditioned at 23 °C and 50% relative humidity per ISO 291:2008. Tensile testing per ISO 527-2:2012 with a 10 kN load cell and testing speed 50 mm/min provides the yield stress reference. Where North American specifications apply, ASTM D638-14 may be used. Unfilled HDPE at 23 °C generally yields between 20 MPa and 30 MPa; some high-molecular-weight pipe grades lie near the upper end, while high-flow injection grades may lie near the lower end. Flexural modulus per ISO 178 or ASTM D790-17 for unfilled HDPE commonly ranges from 800 MPa to 1400 MPa. Notched Charpy impact per ISO 179-1 at 23 °C is grade-dependent; pipe-grade HDPE can exceed 20 kJ/m², whereas high-flow injection grades may fall below 10 kJ/m². If the modulus or yield stress deviates from the supplier’s release limits by more than 15% despite a correct MFR and density, suspect recycled addition, incorrect molecular weight distribution, or an undeclared comonomer package.

A process conflict arises when a candidate lot passes MFR and density but fails the mechanical block. MFR is disproportionately controlled by the low-molecular-weight fraction, while Charpy impact and flexural modulus are sensitive to the high-molecular-weight fraction and to chain branching. A recycle-rich blend can therefore be engineered to a target MFR while reducing notched Charpy below the specified floor. Incoming inspection should trigger a molecular weight distribution evaluation by high-temperature gel permeation chromatography using a column set at 145 °C with trichlorobenzene when this conflict occurs. A bimodal HDPE pipe grade shows a characteristic two-peak refractive index trace; a broadened or shoulder peak in a film-grade resin suggests the presence of a foreign molecular weight distribution. Published data for this specific configuration is limited, so GPC should be treated as a confirmatory test only when the primary five checks are inconclusive.

Documentation verification should occur before physical testing is programmed. A genuine SABIC HDPE shipment is released with a certificate of analysis that carries the grade designation, production lot number, date of manufacture, and numeric test results for that lot. If a declared grade is encoded by the ISO 1872-1:2007 designation system, the designatory block should match the polymer type, density, and melt flow class printed on the package. The same lot code must appear on the package label, on the COA, and on the delivery note. If the grade code has been over-labelled, the distribution site is not an authorised manufacturer’s agent, or the COA lists a different production site from the packaging imprint, payment should be withheld. Physical package checks include intact shipper seals, legible laser lot coding, no resewn bag seams, no mismatched label stock, and no signs of pallet re-wrapping that obscure original stretch film. A COA with an unusually narrow set of results or a single line entry for “specification met” without numeric values is insufficient for a genuine resin shipment. For food-contact grades, the technical documentation should reference FDA 21 CFR 177.1520 for olefin polymers or EU 10/2011 migration compliance where applicable; absence of such citations in a food-contact transaction is a further hold signal.

If Ash, Carbon Black, or Oxidative Stability Data Exceed the Supplier’s Release Limits, Reject the Lot

The fifth check involves contamination and stabiliser-package analysis. Ash content per ISO 3451-1:2019 after combustion at 850 °C for unfilled virgin HDPE should normally be below 0.05%. Values above 0.5% indicate mineral filler, pigment carry-over, or reclaim contamination. Black HDPE used for pipe, sheet, or geomembrane applications is not exempt: carbon black content should be measured by ISO 6964 and compared with the order-specified level, commonly 2.0% to 2.5% for outdoor pressure pipe. Carbon black dispersion assessed by ISO 18553 uses microtome sections and a six-class rating scale; a rating outside the designated class for the application is a failure even if carbon black content is within the specified range. Oxidative induction time by ISO 11357-6:2018 or ASTM D3895-19 at 200 °C in oxygen is a check of antioxidant retention. Prepare specimens of 5 mg to 10 mg in open aluminium pans, purge with oxygen at 50 mL/min, and record the oxidation exotherm. Many HDPE formulations show OIT above 20 min, but the binding value is the supplier’s listed minimum for the grade and application. A low OIT result in a lot that otherwise passes MFR, density, and mechanical tests suggests thermal history abuse or an under-stabilised substitute resin, and the lot should be isolated pending root-cause analysis.