Recycled LDPE Granules for Blown Film: Quality, Gels and Blending

Blown film is one of the most common uses for recycled LDPE in India. Garbage bags, carry bags where permitted, construction film, agricultural film and shrink or stretch applications with lower appearance demands all use recycled material. But film is also unforgiving. A bubble that is only tens of microns thick shows every gel, speck and contaminant, and weak spots tear or puncture easily.

This guide explains what to look for in film grade recycled LDPE granules and how to reduce problems on your line.

What makes recycled LDPE "film grade"

Film grade recycled LDPE should melt evenly, have a low enough MFI to give a stable bubble, and be clean enough to pass through the die without leaving holes or specks. In practice that means:

• feedstock that was mostly film to begin with, such as LDPE film scrap from packaging or industrial use;
• good washing and drying, especially for post-consumer film;
• melt filtration during pelletising;
• consistent MFI from lot to lot.

Ask for MFI tested per ASTM D1238 or ISO 1133 at 190 C with 2.16 kg, and compare it with the grade you run today. Agree a target and tolerance with your supplier. See recycled LDPE granules for typical forms and sources.

Gels and black specks

Gels are small, unmelted or cross-linked particles that show up as lumps or "fish-eyes" in the film. Black specks are usually degraded or burnt material, dirt or contaminants. Both weaken the film and spoil its appearance.

Common causes include:

• overheated or repeatedly reprocessed material;
• other polymers mixed in, such as PP, PET or nylon from multilayer packaging;
• paper, dirt and labels not removed during washing;
• poor filtration at the recycler.

A simple way to check a lot is to run a short trial and hold the film up to the light, or press a thin sheet in a lab press. Count the gels and specks in a set area and compare against a retained sample of a lot you were happy with.

Filtration mesh

Recyclers remove contaminants by forcing the melt through a screen pack or continuous screen changer. A finer mesh catches smaller particles and generally gives cleaner granules, but it clogs faster and reduces output. Ask your supplier what filtration they use and whether it is the same for every lot.

Many film makers also run their own screen pack on the extruder. If you see pressure rising quickly or screens clogging, that is a sign the granules carry more contamination than expected. For more on contamination sources, see contamination and the post on reducing contamination.

Blending with LLDPE

LDPE gives bubble stability and easy processing; LLDPE gives toughness, puncture and tear resistance. Many film makers blend recycled LDPE with virgin or recycled LLDPE granules to get the balance their product needs. Note that much post-consumer "LDPE" film scrap is already a mix of LDPE and LLDPE, so the recycled granule is often a blend before you add anything.

Start trials with your current recipe, replace part of the LDPE with recycled granules, and adjust. Our article on LDPE vs LLDPE film recycling covers the differences in more detail.

Film thickness and end use

Thicker films are more forgiving of gels and minor contamination because a single particle is less likely to cause a hole. Thin films need cleaner material. Match the grade to the product:

• Thicker construction and garbage films: can usually take a higher share of recycled material and darker colours.
• Thinner films: need cleaner, more consistent granules, often blended with virgin.
• Coloured or printed film: needs natural or light-coloured recycled feed if the colour matters.

Odour and moisture

Recycled film granules can carry odour from inks, residues and the previous contents of the packaging. This matters for consumer-facing products and anything stored indoors. Ask about the source of the feedstock and smell the sample bag when it is opened.

LDPE is not hygroscopic, but poorly dried washed material can carry surface moisture, which causes bubbles, streaks and holes in film. Store bags indoors and check moisture on arrival.

Getting quotes for film grade granules

When you post a requirement, include the film product, thickness range, MFI range, colour, whether LLDPE content is acceptable, any gel or odour expectations, and monthly quantity. PlasticSetu's sourcing desk collects quotations from verified suppliers, arranges samples for line trials and tracks dispatch. Get quotes to begin.