Design and fabrication of shape memory filaments into knee high compression stockings

xvi, 201 leaves : ill. ; 30 cm.PolyU Library Call No.: [THS] LG51 .H577M ITC 2011 OnkaraiahCompression stockings are used for centuries as a prophylaxis method to treat thromboembolism, varicose veins and its complications for long term. Previous studies have shown that compression stockings should produce appropriate graduated pressure profile in order to relieve the symptoms of venous disorder. However, pressure profile and performance of the stockings are variable; compliance on their usage is poor and patients often find it ineffective in relieving the pain. Moreover, compression stockings are not free from risk and complications namely tourniquet effect, reversed pressure profile, wrinkling of stockings fabric with their usage. Lately, there have been very few attempts to effectively control these complications and application of shape memory fibers in the stockings is so never contemplated. Henceforth, this study was carried out with the main objective to design and fabricate shape memory filaments in compression stockings and evaluate their performance by objective and subjective method. To successfully achieve this objective, a consolidative study was carried out involving 3 main segments, 1) objective evaluation of commercial compression stockings for pressure magnitude at ankle and pressure profile along the leg on human subjects, 2) Evaluation of shape memory effect of shape memory filaments and 3) Study on the implication of shape memory filaments in compression stockings by comparing the performance of commercial stockings and stockings with shape memory fibers. Pressure delivered by graduated compression stockings from class I to class IV was evaluated at ankle on both legs of 20 human subjects. Each of the stockings delivered varied pressure on leg. The physical determinants of compliance issue were also estimated. It was noted that difficulty in the application of stockings, high pressure sensation at bony prominences, welt and skin redness were the major compliance issues; the obtained results formed the basis to design the later study. Furthermore, a comprehensive experiment was carried out to evaluate the pressure profile of commercial compression stockings from ankle to welt on a sample of 10 human subjects. It was noted that the pressure profile was divergent in vertical and horizontal direction for different stockings with higher pressure at anterior direction. The evaluated pressure at the welt was significantly higher than the standard designated pressure.The shape memory properties of the shape memory filaments were evaluated by cyclic thermomechanical testing on Instron which was fitted with a heating chamber. Furthermore, the influence of parameters namely deformation temperature, speed during the thermomechanical testing, pre-setting and stress relaxation were evaluated. The recovery percentage of filaments was least at lower temperature (less than 45 degree Celsius). The shape memory properties were stable after 5 cycles of elongation and recovery steps. The stress relaxation of fibers remained stable after 15 minutes. Finally, the mechanical properties of different counts of the shape memory core yarn spun with cotton fibers as sheath was tested. Although, the elasticity of yarn was improved with shape memory fiber as core, the total elasticity of yarn was limited to 11%. Henceforth, shape memory fabric knitted with bare shape memory filament and nylon fibers, tension set to 60 degree Celsius was applied in compression stockings. Shape memory filaments were applied at ankle bow and welt as these sections form the substantive regions of stockings. In the final segment, the implication of shape memory filaments in stockings was verified and its performance was compared with commercial stockings. The results showed that circumferential pressure variation of stockings and the wrinkling at the ankle bow in stockings with shape memory filaments was lesser compared to commercial stockings. Moreover, in in-vivo mechanical testing of compression stockings with shape memory filaments at the ankle bow it was found that the slippage of the stockings was relatively easy and easy to apply on to the leg and the participants rated the stockings to be comfortable at welt region. This study on the vital application of shape memory filaments into knee high compression stockings demonstrates the advantages of fabricating shape memory filaments with shape memory properties in compression stockings and add to our knowledge on performance of fibers in stockings. The stockings with shape memory fibers delivered uniform pressure across the girth. Nevertheless, the limitation of this study is that shape memory filaments were applied in elusive regions such as ankle and welt by sewing the fabric on to ready stockings rather than knitting the stockings.Institute of Textiles and ClothingM.Phil., Institute of Textiles and Clothing, The Hong Kong Polytechnic University, 201