Termoplastik poliüretan ürelerin mekano-optik ve enerji davranışları üzerine deneysel ve teorik çalışmalar

ABSTRACT In the experimental part of this thesis, effect of composition on the mechano-optical prop erties of thermoplastic polyurethaneureas was investigated by selectively varying the type and content of soft and hard segments. Real time stress-strain-birefringence experiments were coupled with the off-line Wide Angle X-Ray Scattering measurements. These experi ments together with Differential Scanning Calorimetry measurements revealed that soft seg ments and chain extenders play dominant roles on the chemical structures of the polyuretha neureas. In general, samples with lower fraction of hard segment exhibited higher crystal- lizability than their high hard segment counterparts. Long term holding of poly(ethylene oxide) samples in stretched state was found to increase crystallinity. The strain rate is found to have a considerable effect on the crystallization behavior of poly(ethylene oxide) based samples. Prom birefringence-true stress data, linear and non-linear stress optical behavior were investigated. It was observed that the span of the initial linear stress optical region varied primarily with composition (slope ranging from 0.1 to 2.2 GPa-1) and secondarily with the deformation rate. Hysteresis experiments showed that there is a considerable loss of energy in cyclic loading of these materials and hysteresis increases as the chain extender is changed from 1,6-diaminohexane to ethylene diamine. In the theoretical part of the thesis, hysteretic energy behavior of the same materials was investigated. The amount of energy that is permanently lost and the amount of energy that may be recoverable in hysteresis is distinguished and a model to calculate these energies has been proposed. IV