Recycling and Reprocessing of Thermoplastic Polyurethane Materials towards Nonwoven Processing.

Bastian Wölfel,Christopher Holmes,Dirk Schubert,Vincent Allen,Andreas Seefried,Joachim Kaschta

doi:10.3390/polym12091917

Bastian Wölfel, Christopher Holmes + Show 4 more

Open Access

https://doi.org/10.3390/polym12091917

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Journal: Polymers	Publication Date: Aug 25, 2020
Citations: 26	License type: CC BY 4.0

Affiliation: Adidas (Germany), University of Erlangen-Nuremberg

Abstract

Thermoplastic Polyurethane (TPU) is a unique tailorable material due to the interactions of hard and soft segments within the block-copolymer chain. Therefore, various products can be created out of this material. A general trend towards a circular economy with regards to sustainability in combination with TPU being comparably expensive is of high interest to recycle production as well as post-consumer wastes. A systematic study investigating the property changes of TPU is provided, focusing on two major aspects. The first aspect focuses on characterizing the change of basic raw material properties through recycling. Gel permeation chromatography (GPC) and processing load during extrusion indicate a decrease in molar mass and consequently viscosity with an increasing number of recycling cycles. This leads to a change in morphology at lower molar mass, characterized by differential scanning calorimetry (DSC) and visualized by atomic force microscope (AFM). The change in molar mass and morphology with increasing number of recycling cycles has an impact on the material performance under tensile stress. The second aspect describes processing of the recycled TPU to nonwoven fabrics utilizing melt blowing, which are evaluated with respect to relevant mechanical properties and related to molecular characteristics. The molar mass turns out to be the governing factor regarding mechanical performance and processing conditions for melt blown products.

Highlights

Thermoplastic Polyurethane (TPU) belongs to the class of thermoplastic elastomers, combining desirable elastomeric properties at application temperatures and thermoplastic processability.Their characteristics are based on the intra- and intermolecular interactions in the block-copolymer chain consisting of hard and soft segments
The molar mass is not dropping under roughly 40 kg/mol when reaching an equilibrium state, which may be due to concurrent degradation and build up processes in the TPU which have been described in literature [18]
As the degradation mechanisms are of mechanical and thermal nature resulting in a decay of molar mass (Mw ) over recycling steps (n), this context can be described by an exponential decay function: Mw σBreak (Mw) (n) = (Mw,0 − Mw,∞ ) ∗ exp(−n/ñ) + Mw,∞

Summary

Introduction

Thermoplastic Polyurethane (TPU) belongs to the class of thermoplastic elastomers, combining desirable elastomeric properties at application temperatures and thermoplastic processability. Their characteristics are based on the intra- and intermolecular interactions in the block-copolymer chain consisting of hard and soft segments. The possibility of creating different soft-to-hard-block-ratios makes it a unique tailorable material and implies the main advantage over classic homo-polymers. The application range comprises e.g., biomedical products, filtration, furniture, construction materials, insulation, and footwear amongst others, making polyurethane products the fifth-biggest polymer market globally [1,2,3,4,5,6,7]. With TPUs being comparably expensive, it is of high interest to recycle production wastes like trim-cuts or gating systems as well as post-consumer waste.

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