Structure, morphological and thermal properties of thermoplastic polyurethane/organically modified montmorillonite nanocomposites

The aim of this work was to synthesize a new series of thermoplastic polyurethane (TPU) nanocomposites in order to improve thermal, mechanical, barrier and biocompatible properties of TPUs for potential biomedical applications. Nanocomposites with 20 wt. % of hard segments were prepared with addition of organically modified montmorillonite clay (Cloisite 30B) by in situ two-step polyaddition reaction in solution. Hard segment of TPU prepared in the form of film, consist of 4,4'-methylenediphenyl diisocyanate and 1,4- butanediol, while α,ω-dihydroxyethoxy propyl poly(dimethylsiloxane) was used as the soft segment. Different content of organoclay (1, 3, 5, 8 and 10 wt. %) was incorporated into TPU matrix in order to examine the influence of the nanoclay content on the structure, morphology and thermal properties. The structure of obtained nanocomposites was confirmed by FTIR spectroscopy. Morphological characterization of nanocomposites was carried out using wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) techniques. SEM and WAXD results confirmed a well dispersion of intercalateed/exfoliated structure of organoclay nanofillers in the TPU matrix, when the content was up to 5 wt. %. Thermogravimetric analysis (TGA) revealed that incorporation of organoclay particles significantly enhances the thermal stability of nanocomposites in comparison with pure TPU. Differential scanning calorimetry (DSC) was used to determine the melting, crystallization and glass transition temperatures of hard segments, which was found to shift toward higher temperatures upon increasing the organoclay content to 5 wt. %, but then there were no changes when the organoclay content increased to 10 wt. %. The presence of layered silicates from organically modified montmorillonite clay in TPUs can result in more ordered hard segments having higher melting temperature, that in other hand show loss in crystallinity of the hard segments. It is estimated that the total degree of crystallinity of nanocomposites was in the range from 3.1 to 3.9 %, while for pure TPU it was 4.3 %. It can be concluded that the organoclay particles are homogeneously dispersed in TPU matrix with lower content of organoclay and preferentially embedded in the hard segment phase of TPUs