Application of tapping-mode AFM-IR to a post-consumer waste Polyolefin recyclate

Abstract

The recycling of polyolefins remains a challenge. The need to sort polyolefin waste into its individual polymer types such as Polyethylene (PE) and Polypropylene (PP) to avoid undesired mechanical properties of the blends leads to increased recycling costs and decreased recycling rates. Therefore, recycled blends that retain the desired mechanical properties, but avoid the separation step of the recycling process be cost-advantageous. To understand the origin of a material´s mechanical properties a look at its nanoscale constitution is indispensable. Currently, the standard techniques used to analyze the nanoscale (TEM, SEM, and AFM), provide no direct chemical information, and are thus dependent on a previous good knowledge of the polymer´s composition which may not be available for complex heterogeneous samples such as recyclates. AFM-IR is a scanning probe technique that combines the resolution of AFM with the possibility to obtain IR spectra at the nanoscale with resolutions down to 10 nm. In this work, we apply tapping-mode AFM-IR to a commercially available polyolefin recyclate derived from post-consumer municipal waste. We were able to detect the presence of sub-micrometer sized polyamide and polyurethane impurities, as well as PP inclusions within the PE phase. Furthermore, the interface between the PP and PE phase was found to be composed of rubber present in the waste. The rubber distribution could be imaged with the help of a gaussian mixture model, and its location is in agreement with reference TEM measurements. The obtained results thus showcase the potential of AFM-IR in a recycled polymer characterization context.