Thermoplastic polyurethanes with varying hard segment components. Mechanical performance and a filler crosslink conversion of hard domains as monitored by SAXS

When monitoring tensile tests of thermoplastic polyurethanes TPU by small angle X ray scattering SAXS we find a filler to crosslink conversion of hard domain function. Its strength is related to the chemical composition and governs the mechanical performance of the TPUs. Acting as fillers, the domains provide a high modulus of elasticity. Once the domains take load, they lose their filler function and the material gains in extensibility. All the five machine cast TPUs have soft segments from PTHF 1000 and a hard segment content amp; 8776; 45 . The hard segments are built from different diisocyanates DI and diols chain extenders, CE . The base material has hard segments made from 1,4 butanediol BD and methylene diphenyl diisocyanate MDI . Two other TPUs contain as DIs either the hydrogenated, isomeric MDI H12MDI or hexamethylene diisocyanate HDI , respectively. In two other materials the CE is varied. Here the BD is replaced by either the shorter 1,3 propanediol PD or by the longer 1,6 hexanediol HD . A morphological model is fitted to the SAXS data. It returns nanoscopic parameters, e.g. discriminating between the total Vt and the crosslinked Vx volume of hard domains. Fillers are Vf Vt amp; 8722;Vx. Results show that Vf domains can be converted into Vx domains. Hydrogenation of the aromatic base DI does not change Vt, but Vx lags behind. Young s modulus is higher filler function, high Vf , but the material breaks earlier low Vx . Generally, Vt increases for small strains strain induced domains, SIDs and decreases for strain gt;1. SIDs start as fillers. When MDI is replaced by HDI the formation of SIDs is boosted leading to strain induced hardening only at low strain. At higher strain the modulus lowers conversion Vf amp; 8594; Vx . Only in this material are so many domains converted that Vx increases during stretching. The material breaks late. The long CE increases the average distance between crosslink domains and narrows the distribution of the distances. With the medium CE domains appear less stable at low strai