Structure and thermal-mechanical properties of shape memory polyurethanes and textiles

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Structure and thermal-mechanical properties of shape memory polyurethanes and textiles


Author: Yeung, Lap-yan
Title: Structure and thermal-mechanical properties of shape memory polyurethanes and textiles
Degree: Ph.D.
Year: 2011
Subject: Shape memory polymers.
Textile fabrics -- Technological innovations.
Shape memory effect.
Hong Kong Polytechnic University -- Dissertations
Department: Institute of Textiles and Clothing
Pages: xxvii, 255 p. : ill. ; 30 cm.
Language: English
InnoPac Record:
Abstract: This thesis presents a systematic study of structure and thermal-mechanical behavior of the shape memory polyurethane (SMPU) upon temperature stimulation. This research provides a foundation study of SMPU based textile materials, including the structure and shape retention performance of SMPU treated cotton fabric, the structure and thermal-mechanical properties of SMPU fibers produced by wet-spinning and melt-spinning process. It is also aimed to provide better understanding of the shape memory mechanism and interaction between the PU coating and textile substrate. The study covers five related topics, namely (1) SMPU used as finishing agent, (2) effects of SMPU finishing combined with existing treatments, (3) structure, thermal-mechanical properties and effects of thermal-humidity conditioning for melt-spun SMPU fibers, (4) structure, thermal-mechanical properties and effects of thermal-humidity conditioning of wet-spun SMPU fibers and (5) influence of solvent concentration in coagulation bath of wet-spinning process to SMPU fibers. SMPU solution is used as an easy-care finishing agent on cotton fabric. Traditional pad-dry-cure procedures were applied and the mechanical properties, flat appearance, crease retention and surface morphology of the SMPU treated cotton fabrics were studied. The SMPU layer on cotton fabric provides a recovery force during heating, resulted in a better flat appearance and crease retention upon thermal stimulation. Comparing with the traditional easy-care finishing method, SMPU finishing has the advantages of high strength retention, and zero formaldehyde content.Liquid ammonia (LA) is used in mercerization of cellulose materials, and dimethyloldihydroxylethyleneurea (DMDHEU) is widely used in for easy-care finishing. SMPU was applied on fabrics after LA and/or DMDHEU treatment, the mechanical properties and surface appearances support that SMPU can be used with the existing treatments. The micro-Raman spectra support that the internal stress of DMDHEU or PU treated cotton yarn was reduced after combining the two treatments. This result suggests a reaction mechanism of the SMPU and/or DMDHEU treated cotton.
Crystallized SMPU fiber prepared by the melt-spinning process exhibits an excellent shape recovery ratio of 92% and shape fixity ratio of 89% at 100% strain. The melt-spun SMPU fiber were conditioned at two temperatures, either lower or higher than its crystal melting temperature and at two humidity levels (30% and 80%). The shape memory effects, thermal-mechanical properties and crystallinity of the SMPU fibers were strongly affected by the temperature-humidity conditions. It is found that the crystallinity reduced from 40% to 15%, and both the shape recovery and fixity ratios increased to 98% after 190 hours conditioning at 80 °C and 80RH%. This result indicates that even crystallization is a necessary condition for the shape memory effect, but the shape memory effect is not directly related to the crystallinity. The chemical structure, the crystal perfection and the chain alignments are also important to the shape memory effects of SMPU. Amorphous SMPU fiber prepared by the wet-spinning process exhibits the shape recovery ratio of 79% and shape fixity ratio of 92% at 100% strain. Unlike the crystallized SMPU fiber, the thermal-humidity conditioning did not increase the shape fixity ratios. The shape recovery and fixity ratios are 88% and 82% respectively after 190 hours conditioning at 80 °C and 80Rh%. SEM observation shows some holes appeared on the multi-filament structure of the 80 °C conditioned fibers, which is one of the results of the reduction of shape fixity ratio. Furthermore, the intensities of N-H stretch (hydrogen bonded to carbonyl) band decreased and Hydrogen bonded C=O stretch band increased in the FTIR spectrum after the 190 hours conditioning at 80 °C and 80Rh%, this change of FTIR spectrum is probably a result of breakdown of urethane bonds in the high-temperature and moisture condition. Four crystallized SMPU fibers were prepared with different solvent concentrations (1%, 2%, 4% and 8%) in the coagulation bath of wet-spinning process. The influences of solvent concentrations to the fibers' surface morphology, mechanical properties, chemical structure and shape memory effects were studied. A higher solvent concentration in coagulation bath provides a higher efficiency in solvent recycling process, and the better shape recovery and fixity ratio. As a trade off, the crystallinity and the breaking tenacities of the SMPU fibers decreased with the solvent concentration. The structures, thermal-mechanical properties of the newly developed SMPU as a textile material were studied in this project. The research results build up knowledge basis for the development of SMPU based smart textile materials.

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