Mechanical Film Recycling using Twin Screw Extruders

From LDPE, agricultural, and multi-layer films to post-consumer packaging waste, Marina Matta explains how advanced washing, devolatilization, degassing, and melt filtration technologies help transform challenging film waste streams into high-quality recycled pellets. Marina also shares insights on recyclate quality, recycled content levels, NIAS reduction, odor removal, and the role of mechanical recycling in comparison to chemical recycling.

Which recycling process is best suited for my plastic film waste stream?

The most suitable recycling process depends on the type, composition, and contamination level of the film waste stream. The most suitable recycling process depends on the type, composition, and contamination level of the film waste stream, as well as the intended end use of the recyclate. Different applications place different demands on material quality, making the final application a key consideration when selecting the recycling process.

For LDPE film waste, one of the most efficient approaches is a mechanical recycling process in which washed film flakes are fed directly into a ZSK twin screw extruder. During extrusion, the material is homogenized, volatile substances are removed through efficient devolatilization and degassing, and remaining contaminants are eliminated by melt filtration before pelletizing. The intensive mixing and melt homogenization capabilities of twin screw extruders significantly reduce the level of gels in the final product, resulting in a higher gel reduction rate and improved pellet and film quality compared to conventional recycling technologies.

For post-consumer film waste, the best results can typically be achieved by separating transparent and colored films before washing and extrusion. Combined with efficient degassing and melt filtration, twin screw extrusion enables the production of high-quality recycled pellets even from challenging waste streams.

When recycling mixed polyolefin films, it is important to recognize that film waste often contains varying amounts of LLDPE, PP, and HDPE. While complete separation is sometimes possible, it is often not economically justified. Instead, mixed polyolefin film can also be recycled using twin screw extruders. However, the recycled material is then usually used for applications such as garbage bags, shipping films, construction films, geomembranes, pallets, and crates.

By combining washing, twin screw extrusion, degassing, and filtration technologies, a wide variety of film waste streams can be converted into valuable secondary raw materials while minimizing energy consumption and environmental impact.

What types of plastic films can be mechanically recycled, and which cannot?

A wide range of plastic films can be mechanically recycled, including mono-layer films, multi-layer films, agricultural films, and printed PE films. The achievable recycled resin quality depends on the film structure and contamination level.

Multi-layer films can often be mechanically recycled in house without the need of costly compatibilizers and reused in new multi-layer film structures. This keeps valuable materials in circulation while maintaining the performance of the final product.

Agricultural films, including silage, mulch, and greenhouse films, can also be mechanically recycled. Since these materials are often heavily contaminated with soil, sand, and organic residues, efficient washing is a critical process step. With the right combination of washing, drying, and extrusion technologies, even film-to-film recycling can be achieved.

Printed PE films are likewise suitable for mechanical recycling. Recyclability depends on the type and amount of printing inks used. Efficient devolatilization and degassing during extrusion help remove volatile substances that could otherwise cause defects such as bubbles or holes in new films. Even heavily printed production scrap can often be effectively recycled.

Advanced washing, twin screw extrusion, degassing, homogenization, and filtration technologies help maximize recycled resin quality and expand the range of film waste streams that can be economically recycled.

Can odors and volatile substances be removed during film recycling?

Yes. Efficient devolatilization and vacuum degassing in twin screw extrusion can remove moisture, residual solvents, printing ink components, odors, and other volatile substances from the polymer melt. This helps improve recycled resin quality, reduce defects in downstream processing, and broaden the range of potential end-use applications.

Can NIAS (Non-Intentionally Added Substances) be reduced during mechanical film recycling?

Yes. Advanced devolatilization and degassing technology can remove a wide range of unwanted substances from the polymer melt, including both low- and high-molecular-weight compounds. This helps reduce NIAS levels and contributes to improved recycled resin quality.

What recycled resin quality can be achieved from film recycling?

The quality of recycled film resin depends primarily on the incoming waste stream, contamination levels, and the processing technology used.

Depending on these factors, recycled PE resin can be used in applications ranging from construction and industrial films to demanding packaging film applications, including thin film structures. Achieving high-quality recycled resin requires effective gel reduction, contaminant removal, and devolatilization.

In particular, efficient degassing is essential for removing residual solvents, odors, and other volatile substances that could negatively affect pellet quality and final film performance.

What percentage of recycled film pellets can be used in the production of new films?

The amount of recycled content that can be incorporated into a final film product depends on the application and performance requirements.

For products such as garbage bags, recycled content levels of up to 100% are possible. Post-industrial recyclate (PIR) can often be used at very high inclusion rates due to its consistent composition and low contamination levels. 

For post-consumer recyclate (PCR), recycled content levels of approximately 50% are commonly achievable, although the actual percentage depends on recyclate quality and the requirements of the final application.

How does mechanical film recycling compare with chemical recycling?

Mechanical and chemical recycling are complementary technologies designed for different waste streams.
Mechanical recycling is generally the preferred option for most post-industrial and post-consumer film waste because it preserves the polymer structure and enables the efficient production of high-quality recycled resin.

Chemical recycling may become a valuable option for waste streams that are too complex, contaminated, or heterogeneous for economically viable mechanical recycling. In these processes, polymers are broken down into chemical feedstocks that can be used to produce new materials.

From a sustainability perspective, mechanical recycling typically offers a substantially lower carbon footprint and lower energy consumption because the polymer chains remain intact throughout the process.
As a result, mechanical recycling is generally the most energy-efficient and environmentally favorable solution whenever the waste stream is suitable for direct recycling, while chemical recycling can complement it for material streams that are difficult to recover mechanically.