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