LLDPE is almost never bought as “a resin” — it is bought as a layer inside a film structure. This page does not repeat the density comparison or the melt index grade tables (see below); it works by layer function: what the sealant, core, skin and stretch layers are each asked to survive, and where metallocene grades change the processing window.
Density and melt index are what a data sheet leads with, yet a converter is really buying one position in a coextruded structure. Ask what the resin is for and the answer is a layer name — sealant, core, skin or stretch — not a density. Start from the layer and the grade argument mostly settles itself.
Must seal fast, seal through dust or oil, and hold while the pack is still hot. Seal initiation and hot tack matter more than tensile numbers.
Where puncture and tear resistance live. Dart impact and tear are the acceptance tests, and why LLDPE displaced much LDPE in heavy-duty sacks.
Bought for friction, haze, gloss and print treatment. Slip and antiblock are dosed here — migration can weaken a seal.
Pallet wrap follows another logic: prestretch, cling and holding force, not sealability.
| Layer | Must survive | Ask the supplier for | Accepted by |
|---|---|---|---|
| Sealant | Hot load, dust | Seal initiation, hot tack | Seal strength curve |
| Core | Puncture, tear | Dart impact, tear | Film, not plaque |
| Skin | Friction, print | Slip, antiblock, haze | COF and haze data |
| Stretch | Prestretch, holding | Cling, puncture, yield | Wrap trial on line |
| Sack, liner | Drop, rough handling | Dart, tear, seal | Drop and seal tests |
mLLDPE is not simply better LLDPE. It is a narrower molecular weight distribution, and that shifts film properties and processing behaviour together.
More uniform comonomer placement gives better puncture and tear at a given density, lower seal initiation and stronger hot tack — hence its use where packs seal through contamination or lines run fast. Downgauging is usually the commercial argument.
Narrow distribution means less shear thinning: higher extrusion pressure, higher torque, and more tendency to melt fracture or bubble instability. Most lines need a screw change, wider die gap, processing aid or slower rate. Never assume a drop-in replacement.
Cast wrap is clear, quiet and consistent and dominates machine wrap; blown wrap resists puncture better and suits hand wrap and awkward loads. Buy by pallets wrapped, not by roll count — ask for prestretch, holding force and puncture together.
No. Short-chain branching from the comonomer drives film toughness far more than density; the density side is set out in HDPE vs LDPE.
Only if you are chasing downgauge, seal-through-contamination or hot tack. Otherwise a conventional hexene or octene LLDPE usually costs less and runs more easily.
Octene generally gives the best toughness and puncture, at a price. Buy on measured dart and puncture rather than the comonomer name.
Yes, in the core layer of non-food film, where gel count and odour set the limit. Require the percentage and the measured film properties in writing.
Rarely. Sealants are built for hot tack and low initiation; wrap resins are built for cling and holding force. Treat them as separate purchases.
Sourcing LLDPE? Send the film structure, the layer it is for, annual tonnage and discharge port to the plastic materials desk. For finished bags, go to plastic packaging; for the family, start from PE resin or compare with HDPE.
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