LDPE and LLDPE are both low-density polyethylenes, but they are made differently and behave differently on a film line. Most blown-film producers use both, in a blend that suits the film.
How they differ
- LDPE is made at high pressure and has long branches. It gives clarity, gloss and a stable bubble, and it is easy to process.
- LLDPE is made with a comonomer (butene, hexene or octene) and has short branches. It gives toughness, puncture and tear resistance, and lets you make thinner film.
Why lines blend them
A blend combines LLDPE strength with LDPE processability. Typical examples: shrink and heavy-duty sacks use more LDPE for bubble stability and shrink; stretch film and liners use mostly LLDPE for toughness and cling. The right ratio depends on your film, extruder and thickness.
Comonomer matters
Butene LLDPE is the general-purpose choice. Hexene and octene grades give higher toughness and puncture resistance and are chosen for thinner or more demanding film.
Melt index and density
- Melt flow index (MFI): film grades are usually low, around 0.3 to 2 g/10 min. Lower MFI means more melt strength and toughness; higher MFI means easier flow.
- Density: lower density gives softer, clearer, tougher film; higher density gives stiffer film.
What to send for a quote
- Film type and thickness (shrink, stretch, liner, agricultural, packaging)
- LDPE, LLDPE or both, and the comonomer if you specify one
- MFI and density range, and any slip or antiblock additives
- Food-contact needs for your market
- Quantity, packing, destination port and Incoterm