Linear Low-Density Polyethylene (LLDPE) import procurement requires the specification sheet to be fixed before requests for quotation are issued. The working specification title used by procurement teams is “LLDPE Import Procurement: The Specification Sheet to Fix Before You Ask for Quotes.” Without a locked specification, suppliers may offer butene-comonomer film resin against an extrusion line designed for hexene or octene grades, or a rotational-moulding powder against a blown-film die gap. The quote comparison collapses because the base resin architecture, melt flow rate, density, additive loading, and catalyst residue are not equivalent.

What Must Be Locked in the Specification Sheet Before Quotation

The first block of the specification sheet fixes melt flow rate (MFR) at 190 °C under 2.16 kg load using ISO 1133-1:2022 or ASTM D1238-13. Blown film grades commonly require 0.5–2.0 g/10 min, cast stretch film grades 1.5–3.5 g/10 min, injection moulding grades 10–50 g/10 min, and rotomoulding powders 2–6 g/10 min. The nominal value should carry an explicit tolerance of ±0.2 g/10 min for fractional-melt film grades and ±0.5 g/10 min for high-flow grades; a wider tolerance permits the supplier to ship material at the edge of the process window. Density is fixed by ASTM D1505-18 or ISO 1183-1:2019. Film resins are typically specified at 0.918–0.925 g/cm³; injection and rotomoulding resins at 0.924–0.940 g/cm³. The density tolerance should not exceed ±0.002 g/cm³ because density shifts alter tensile yield stress, tear behaviour, and barrier properties through crystallinity changes.

LLDPE is a copolymer of ethylene with an alpha-olefin, usually 1-butene, 1-hexene, or 1-octene. The short-chain branching frequency and distribution determine the balance among dart impact, tear, and stiffness. Butene-based grades generally show lower dart impact and tear resistance than hexene- or octene-based grades at equal density and MFR because the shorter branch lowers tie-chain entanglement. Hexene and octene comonomers also reduce heat-seal initiation temperature more effectively than butene. The specification sheet should therefore state the alpha-olefin and, where possible, the heat-seal initiation temperature per ASTM F2029-16. If the buyer does not fix comonomer type, a supplier may offer butene-based resin with identical density and MFR that passes the certificate of analysis but fails on machine direction tear or seal performance. A supplier COA reporting only melt flow rate and density cannot distinguish a broad-MWD blown-film resin from a narrow-MWD cast-film resin; the melt flow ratio under 21.6 kg and 2.16 kg loads should be requested when molecular weight distribution is a process variable.

When Blown Film Lines Expose Bubble Instability and Die Lip Deposit

On blown film lines, the specification must move beyond melt flow rate and density. A 90 mm grooved-feed extruder running a 300 mm spiral mandrel die responds to shear viscosity at the die lip and extensional viscosity in the bubble rather than to MFR alone. Capillary rheometry at apparent shear rates of 100 s^-1 and 1000 s^-1 should be obtained from the supplier. LLDPE grades with shear-thinning behaviour outside the supplier’s published range can develop melt fracture at high output, while low extensional viscosity contributes to bubble sag and gauge variability. Typical LLDPE blown film operation uses a die gap of 1.5–2.5 mm, a blow-up ratio of 2.0–3.5, and a frost line height of 6–12 die diameters. The specification sheet should state these machine boundaries so the supplier cannot ship a resin with a melt index of 0.5 g/10 min when the line was qualified with 1.0 g/10 min; the lower-melt-index resin raises motor load and may destabilize the bubble at the available frost line height.

Die lip deposit is observed as oily or oxidized residue on the die face and produces gauge bands in the finished film. LLDPE is more prone than LDPE to deposit formation from oxidized low-molecular-weight fractions and additive breakdown when melt temperature exceeds 240 °C. Processing aid concentrates, typically fluoropolymer-based at 200–500 ppm, are specified when the die must run for extended cycles without cleaning. Melt temperature is maintained at 190–230 °C, while die setpoints are held at 200–230 °C. Bubble stability failures on LLDPE often lead operators to blend 10–20 wt% LDPE, but the import specification should not rely on downstream blending to compensate for resin with inadequate melt strength. The specification sheet should fix the maximum permissible gel count according to the buyer’s optical inspection protocol; published data for this specific configuration is limited, so the threshold is negotiated per supplier rather than taken from a universal standard.

Cast stretch film specifications shift from bubble geometry to melt curtain uniformity and edge trim yield. LLDPE cast grades typically carry an MFR of 1.5–3.5 g/10 min and a density of 0.917–0.920 g/cm³. Chill roll temperature is fixed at 15–25 °C to control crystal nucleation; deviations above 35 °C can produce blocking and loss of tack in stretch grades. The specification should request a narrow molecular weight distribution and a gel count acceptable to the buyer’s downstream optical inspection; published data for this specific configuration is limited, and the gel threshold is negotiated per supplier.

Injection Moulding Rheology, Shrinkage and Dimensional Clearance

Injection moulding grades of LLDPE are specified by flow length, shrinkage, and impact rather than by bubble stability. A typical injection grade carries an MFR of 10–50 g/10 min at 190 °C/2.16 kg to fill thin-wall closures or housewares. The density range is usually 0.924–0.935 g/cm³; higher density within this range raises flexural modulus but reduces environmental stress crack resistance. The specification sheet fixes mold shrinkage using ASTM D955-08, with LLDPE commonly exhibiting 1.5–2.5% parallel shrinkage and 1.0–2.0% perpendicular shrinkage. A shrinkage deviation of ±0.2 percentage points is large enough to shift gate-to-cavity dimensions in a multi-cavity tool. The melt temperature is maintained at 200–240 °C, and capillary shear viscosity at 1000 s^-1 and 230 °C should be obtained from the supplier to confirm that the resin will fill the projected thin-wall section without excessive injection pressure. For freezer-grade containers, notched Izod impact per ASTM D256-10 and low-temperature brittleness per ASTM D746-20 are fixed rather than assumed from density.

Because rotomoulding cycles subject the material to long oven residence at high temperature, the specification emphasizes oxidative stability and particle packing rather than shear viscosity. The powder must pass a 35 mesh 500 µm screen per ASTM D1895-17 and exhibit dry-flow behaviour suitable for uniform wall thickness. Typical rotomoulding LLDPE carries an MFR of 2–6 g/10 min and a density of 0.934–0.940 g/cm³. The critical specification lines are environmental stress crack resistance (ESCR) per ASTM D1693-15, condition B, and low-temperature impact per ASTM D1790-21 or the ARM dart impact method. A specification sheet should fix minimum ESCR hours, not just resin density, because two suppliers can supply 0.938 g/cm³ resin with markedly different ESCR depending on comonomer distribution and catalyst residue. Oven cycle temperature is typically 260–290 °C for LLDPE; high catalyst residue degrades the inside surface and creates pinholes, so the specification should include maximum ash content of 0.02 wt% per ASTM D5630-22.

What the Bill of Lading Must Carry for Customs and End-Use Clearance

Each import lot should be accompanied by a certificate of analysis containing the lot number, reactor date, MFR, density, additive loadings, and the test method used. The COA must reference the buyer’s specification revision number, not a generic grade data sheet. A safety data sheet in GHS format is required for customs release; if the grade contains no hazardous components, the SDS still identifies the product as non-hazardous under the importing jurisdiction. For food-contact applications, the supplier must provide a food contact statement citing FDA 21 CFR 177.1520 for olefin polymers used in contact with food, or Commission Regulation (EU) No 10/2011 and its amendments. For electrical or automotive applications, the supplier may be required to provide RoHS compliance under Directive 2011/65/EU and REACH candidate list confirmation under Regulation (EC) No 1907/2006. The specification should state the sampling standard for pre-shipment inspection; ISO 2859-1:1999 provides acceptance sampling by attributes, but the buyer must fix the inspection level and acceptable quality limit. A retained sample of 1 kg per lot is often archived for six months to resolve destination-country disputes.

At destination ports in tropical climates, the specification sheet should include a moisture limit of ≤0.05 wt% because surface condensation on pellets can destabilize the feed section and create melt temperature variation. Testing by ISO 15512-2019 or Karl Fischer titration should be performed on arrival if the shipping container shows evidence of condensation or if the resin is stored in unheated warehouses at relative humidity above 60%. LLDPE is not hygroscopic; absorbed water is low, but surface water must be removed by a drying hopper at 60–70 °C for 1–2 h before extrusion if the limit is exceeded. The procurement sheet should also fix packaging as 25 kg valve bags or 1000 kg FIBC with inner liners, and it should prohibit reworked pellets beyond a declared percentage because regrind shifts the melt flow rate and gel count.