Thermoplastic polyurethanes with varying hard segment content. Morphology evolution mechanism under strain

Poster presented at the 16th International Conference on Small-Angle Scattering, held on 13-18th September, 2015, Berlin (Germany).Preparation and composition of thermoplastic polyurethanes (TPU) are varied systematically. The samples are strained and monitored by SAXS. The analysis comprises longitudinal projections [1], and in real space the chord distribution function (CDF) [2]. We aim to identify straining mechanisms and to retrieve characteristic parameters for the modeling to design customized TPU materials. Part of the work is presently being published [3-5]. 3 groups of TPU materials with different hard-segments content are compared. Figure1 demonstrates a fundamental morphological difference between hard-segment (MDI+BD) for HSC=30%, HSC=43% and HSC=56%. An interesting result concerns the occurrence of relaxing HHS sequences when stretching. The systematic variation of sample parameters has led to clear indications herein. Correspondingly, more domains are sacrificed and less experience relief when the HSC is rising from 30% to 43%. Finally relaxation is absent in the material with HSC = 56wt.-%. Material in HSC=56%, the long period increases linearly with strain. Materials with lower HSC% have CDF long periods that reside in stationary bands. Their positions form a Fibonacci series. This sequence of hard and soft domains relates to the synthesis route (polyaddition). The differences are explained by different homogeneity of the reacting mixture of raw materials. Straining mechanisms are discussed