Polyamides and Intermediates

Mechanical recycling of polyamides in multilayer film structures

Polyamides in multilayer film structures are currently classified as non-recyclable materials.

We cannot confirm this as it has been known for a long time that:

  1. Limited concentrations ( < 10%) of polyamides are miscible with polyolefines.
  2. Higher concentrations ( > 10%) of polyamides can be compatibilized with polyolefines by using sufficient modifiers and processing conditions.

Why is this topic important?

The singular focus on state-of-the-art mechanical recycling technologies does not consider the benefits provided by polyamides for high-performance and flexible food packaging. Criteria, such as reducing the amount of plastics used, the demand for downgauging and extended shelf life of the packaged foods as significant contributor to securing the food supply for a growing global population and reducing waste of both packaging and food are not recognized appropriately.

The benefits of packaging containing polyamides will be sacrificed for the sake of recycling purposes only.

Our test steps in detail

1. Definition and manufacturing of sufficient polyethylene (PE)/polyamide (PA) structures (multilayer) films containing up to 30% nucleated PA 6  (Ultramid® B40LN) as “worst case”. Some of the original structures already contain pre-processed compatibilizers.

2. Regranulation of films using standard NGR single screw device(s).

3. Analysis of regranulate pellet morphologies.

4. Manufacture of monolayer films (40μm) in semi-tech scale using 100% regranulated materials including additional blending with PE regranulates and/or compatibilization during film making process. This step covers also a “dilution” approach to quantify certain blending limits.

5. Analysis of monolayer films concerning mechanical  properties as well as optical evaluation.

6. Implementation of regranulates into manufacturing of multilayer film structures including variations of component ratios using different machinery.

“Film-to-film” approach for PE/PA waste blends is a real recycling option including manufacturing of  “new” monolayer films:

Our series of tests show:

  • PE/PA blend systems without any compatibilizers are recyclable (miscible) with PA contents < 10%, excellent distribution has been analyzed in an area of 5 – 7.5%
  • Implementation of suitable compatibilizers is an efficient way to generate homogeneous PE/PA mixtures containing PA concentrations of > 10%. During our investigations PE/PA blends with up to 30% PA6 have been compatibilized efficiently by using 3-5% of modifiers
  • Copolyamides with lower melt points (</= 200°C) and lower crystallinity levels are recyclable with higher PA con-centrations in final blends compared to standard PA 6.
  • Amount of compatibilizers might be incorporated 
    • already in original multilayer film structures,
    • during reganulation by using standard single screw machinery,
    • by adding as individual component during final processing step (here film manufacturing). 
  • PE/PA mixtures containing PA 6 only need a regranulation temperature of 240°C for proper downstream processing. Nevertheless, real packaging waste streams also contain significant amounts of copolyamides with lower melting temperatures, processing of such PA mixtures is already possible at 210 °C.
  • It is possible to manufacture monolayer films made from 100% PE/PA regranulate blends as well as using highly concentrated PE/PA regranulate core layers in multilayer structures with sufficient mechanical and optical properties without using a dedicated twin screw extrusion processing step.

Please contact us if you are interested in further information or in case of questions: