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.
Blends of poly‐ϵ‐caprolactone (PCL) with two different molar masses are deliberately varied to change viscosity independent of polymer concentration enabling to separate viscosity and a direct concentration dependence of the fiber diameter in the electrospinning process. Multiple distributions as a result of jet splitting are determined and analyzed. The existence of essentially two modes in fiber diameter frequency distribution, the base mode and the split mode, is revealed, whereas the scaling laws for each mode can be validated according to the latest theory. Finally, the theoretical predicted upper limit 22 of the ratio of standard deviation of fiber diameter and average fiber diameter is validated.
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