LLDPE Arrives Wet or Contaminated: Claim Procedure and Evidence Pack

Linear low-density polyethylene (LLDPE) is a semi-crystalline ethylene copolymer produced with C4, C6, or C8 alpha-olefin comonomers in low-pressure polymerisation units. The short-chain branching distribution is controlled by catalyst selection; Ziegler-Natta grades tend to have a broader short-chain branching distribution, while metallocene grades provide a narrower comonomer distribution and different sealing characteristics. Commercial LLDPE film and injection moulding grades are commonly specified with a density of 0.915–0.940 g/cm³ using ISO 1183-1:2019 or ASTM D792-20 and a melt mass-flow rate from 0.5 g/10 min to 100 g/10 min at 190 °C with a 2.16 kg load per ISO 1133-1:2022 or ASTM D1238-20. Packaging formats include 25 kg bags, octabins, and bulk hopper trucks; the selected format influences the types of wetting and contamination that are likely to occur at receiving.

Neat LLDPE absorbs very little water, typically below 0.01% by mass after 24 h immersion at 23 °C under ISO 62:2008. External free water on packaging is therefore the dominant moisture issue, not polymer hydrolysis. Water can enter through torn stretch wrap, open container roof seals, leaky railcar hatches, or condensation formed during temperature cycling in humid coastal terminals. Contamination can be present as wood splinters from pallets, sand, metal shavings, paper fibre, insect matter, or pellets of another resin. When the delivery condition deviates from the purchase specification, a formal claim procedure and evidence pack become necessary to establish technical risk and commercial responsibility.

When LLDPE Bags Show Free Water or Surface Condensation

When free water is present on LLDPE packaging, the immediate processing consequence is often feed-throat slip rather than hydrolytic degradation. Because LLDPE is a non-hygroscopic polyolefin with a water absorption below 0.01% by mass per ISO 62:2008, free water is generally external to the pellet. Water entering the extruder feed throat can reduce pellet-to-screw friction, producing irregular solids conveying and unstable melt pressure. In vacuum conveying systems, wet pellets can form clumps around rotary airlocks and cause bridging in silo cones. A desiccant wheel dryer delivering air at a dew point of ≤ -40 °C and a temperature of 60–70 °C for 2 h is usually sufficient to remove surface water from LLDPE pellets, but drying must be confirmed by moisture analysis because overdrying can consume energy without improving conversion and may increase additive bloom.

If the measured moisture value by ISO 15512:2019 exceeds 0.05% by mass, water is almost certainly present as free surface water or as a contaminated aqueous layer, and the lot should not be blended with dry resin until the source is identified. Wet resin should not be blended with dry production stock until the free water is quantified. A composite sample can be tested by Karl Fischer oven method using ISO 15512:2019; the result should be compared with the supplier certificate of analysis, which usually reports moisture below 0.05% for neat LLDPE. For heavily wetted loads, the preferred disposition may be rejection rather than drying because paper labels and stretch wrap may have disintegrated into the pellet mass.

Does Visual Contamination Alter Blown Film Bubble Stability?

In blown film conversion, visual contamination changes melt filtration load, die lip deposit formation, and bubble geometry. On a monolayer line with a 45 mm barrier screw and L/D ratio 30:1, a screen pack of 60/100/60 mesh can retain coarse particles above roughly 100 µm, but finer particles and gels pass through the filter and become visible optical defects in thin film. A single foreign polymer granule with a higher melting point than LLDPE can survive as an unmelted particle, anchor at the die lip, and create a continuous die line. Optical properties are then measured as increased haze per ASTM D1003-21 and reduced gloss at 45° per ASTM D2457-21.

Differential scanning calorimetry per ISO 11357-3:2018 is an effective contamination identification tool because a butene-based LLDPE with a main melt peak near 120 °C will show separate endotherms if high-density polyethylene, polypropylene, or cyclic polyolefin particles are present. Published thresholds for visible defects vary with film thickness, die gap, melt strength, and gel size; no single universal ppm value applies across all film products. For sub-50 µm gel populations, published threshold data for LLDPE film are limited because optical gel counts depend on scanning sensitivity and pigment/dust interference. Screen pressure rise should be tracked; an increase of 20–30% over the baseline at constant screw speed and melt temperature often indicates filter loading by contaminants.

Mechanically, abrasive contamination in twin-screw compounding of LLDPE-based masterbatches produces a slower but more damaging failure signature. Hard mineral particles of sand or metal oxides can increase specific mechanical energy and barrel wear, while iron fragments may lodge in screw channels and score hardened barrel liners. The ash content rise can be quantified by ASTM D5630-22, and an elevated ash value above 0.1% for neat LLDPE suggests non-polymeric contamination. Contamination by an incompatible polymer may not alter ash value but will produce delamination or poor dispersion. Processing with a 75/100/75 µm melt screen is not always sufficient to remove all suspended foreign particles because melt viscosity may force deformable polymer contaminants through.

Claim File Structure for Wet or Contaminated LLDPE Shipments

A claim file for wet or contaminated LLDPE should function as a chain-of-custody record from dockside inspection to analytical conclusion. The claim must be supported by numerical data and standard test results rather than visual opinion alone. A supplier certificate of analysis establishes the expected baseline; the receiving plant’s inspection data establish the deviation. The following elements are required.

1. Update the affected lot to quarantine status in the warehouse management system and prevent automatic release to production. Record the bill of lading number, container or trailer number, bag lot code, and supplier order confirmation.
2. Photograph the delivery using a camera with at least 12 MP resolution and a calibrated timestamp. Include images of complete pallets, partial bags, visible water, foreign material, damaged stretch wrap, and lot labels. Place a scale bar or reference object in each frame.
3. Draw a composite sample from at least three pallet positions per affected lot and from top, middle, and bottom bag layers per pallet. A minimum of 1 kg retained sample per lot should be stored in a sealed polyethylene bag.
4. Split the composite into three portions: one retained sample, one for third-party analysis, and one for supplier submission. Use tamper-evident seals and record seal numbers.
5. Subject the laboratory portion to moisture, melt flow, density, ash, and contamination identification testing. Use the standards listed in the analytical evidence pack.
6. If practical, run a short pilot comparison against a retained approved reference lot on a laboratory blown film or cast film line. Record melt pressure, output, filtration pressure rise, and optical defect count. This comparative run links contamination to conversion risk.

The claim notification should be sent to the supplier within the period defined in the purchase contract, commonly 24–72 h from time of discovery for transport-damage claims, and the full evidence pack should follow once analytical data are available. Without retained samples and photographic lot evidence, a claim can be rejected because laboratory results alone may not prove that the wetting or contamination occurred prior to receipt.

Analytical Evidence Pack and Instrumentation

An analytical evidence pack for wet or contaminated LLDPE should pair each observed deviation with a method, instrument type, and quantitative result. The following test package is suitable for typical pellet and film-grade LLDPE claims.

If the claim involves visual gels or film defects rather than free water, the evidence pack may also include a pilot-line comparison with a film scanner generating defect counts per square metre. Published data for gel-count repeatability in LLDPE film are limited because scanner sensitivity and gain settings differ among installations; therefore, any defect-count deviation should be reported alongside scanner model, threshold settings, and film thickness. Comparison against the retained reference lot is more informative than an absolute gel count, because it removes line-specific background noise from evaluation of the shipment deviation.