Abstract
The difference in compatibility at the molecular level can lead to a change of microphase separation structure of thermoplastic polyurethanes blend systems, which will improve their thermal and mechanical properties. In this study, TDI-polyester based TPU was blended with MDI-polyether-based TPU and MDI-polyester based TPU, with different ratios. In the blend system, the obvious reduction of the melting temperature of the high-temperature TDI-polyester based TPU component indicates its hard segments can be mutually integrated with the other component. For TDI-polyester based TPU/MDI-polyether based TPU blends, their similar hard segment ratio and similar chemical structure of the soft segment give the molecular chains of the two components better compatibility. The aggregation structure of the two kinds of chains can rearrange at the molecular level which makes the hard domains mutually integrate to form a new phase separation structure with larger phase region distance. As a result, the yield strength of this blend increased by almost 143% when the elongation at break was only reduced by 12%. In contrast, the other group of blends still partly maintain their respective micro domains, forming a weak interface and leading to a decreased of elongation at break.
Highlights
thermoplastic polyurethane elastomers (TPUs) is a linear segmented-block copolymer composed of alternating hard and soft segments connected by urethane groups (–NH–COO–)
The microphase separation structures of TPU have been controlled by adding different methylene chain units on the same soft segments of TPU [5] to compare the effects of different soft segments with the same molecular weight [6], and by regulating the hydrogen bonds between the soft and hard segments [7]
TPUs’ crystallization kinetics and melting behaviours were studied with Differential Scanning Calorimetry (DSC), and the microphase separation structure was studied with SAXS and Atomic Force Microscope (AFM)
Summary
TPU is a linear segmented-block copolymer composed of alternating hard (adduct of di-isocyanate and small glycols) and soft (e.g., polyester, polyether) segments connected by urethane groups (–NH–COO–). The microphase separation structures of TPU have been controlled by adding different methylene chain units on the same soft segments of TPU [5] to compare the effects of different soft segments with the same molecular weight [6], and by regulating the hydrogen bonds between the soft and hard segments [7] These manipulations are intended to improve the mechanical properties of TPU. The microphase separation structure was observed after blending different soft and hard components of TPU, and the influence of microstructural changes on the thermal and mechanical properties of TPU were analysed. When the melting point of the blend is not significantly different from those of its constituents and the elongation at break decreases slightly, the tensile strength is significantly improved
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