| dc.description |
<p class="MsoNormal" style="text-indent:35.4pt"><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New Roman","serif";mso-ansi-language:EN-US">In this study, </span><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New Roman","serif";mso-fareast-font-family:Calibri;mso-ansi-language:EN-US">shape memory-polyurethane was reinforced withcellulose nanowhiskers (CNWs) to create heterogeneous-twin-switch shape memoryeffect (thermal and water responsiveness simultaneously) and </span><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New Roman","serif";mso-ansi-language:EN-US">chemical/mechanical characterization of </span><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New Roman","serif";mso-fareast-font-family:Calibri;mso-ansi-language:EN-US">the produced polymericnanocomposite films were conducted. </span><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New Roman","serif";mso-ansi-language:EN-US">Shapememory polymers (SMPs) are among attractive smart materials having thecapability to return their original (permanent) shapes from a temporary shapeunder appropriate external stimulus and the most common type of these materialsare </span><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New Roman","serif";mso-fareast-font-family:Calibri;mso-ansi-language:EN-US">thermal induced SMPs.Among the thermal induced SMPs, segmented shape-memory-polyurethanes (</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New Roman","serif";mso-ansi-language:EN-US">SMPUs</span><span lang="EN-US" style="font-size:11.0pt;font-family:"Times New Roman","serif";mso-fareast-font-family:Calibri;mso-ansi-language:EN-US">) have gained much popularity and they are mainly usedin biomedical and tissue engineering applications. Recently, there are attemptsto modify SMPUs to have a switching temperature within the range of bodytemperature and create dual responsive structure that can be stimulated bydifferent stimuli such as temperature and moisture. This study coversmodification of SMPUs which has a transition temperature suitable for bodyapplications by CNWs to enhance its application areas in case of thermalcomfort. SMPUs having thermal-induced shape memory effect will simultaneouslypossess water-induced shape memory effect by CNWs due to the percolationnetwork of the CNWs whose hydrogen bonding can be regulated by waterreversible. The disadvantages of thermal induced SMPU such as transitiontemperature not suitable for the body and disadvantages of water responsiveSMPs such as low elastic modulus, stiffness strength properties and long shaperecovery time are aimed to be decreased by producing nanocomposites consistingof SMPU and CNWs. This modification process is easier to have the determinedfunction (thermo-water responsive) as synthesis of a dual function polymermatrix needs complex chemical molecular design. The CNW-SMPU nanocompositefilms were produced by introducing CNWs as nanofiller into a SMPU matrix inthis study. A series of nanocomposite films with varying CNW concentrations,ranging from 0-20 wt % was produced by solution blending CNWs and the SMPU. Thenanocomposite films were subsequently prepared by solution casting method. Fouriertransform infrared (FT-IR) analysis was performed to characterize nanocompositefilms. The effects of CNW on the mechanical and shape memory performance offilms were investigated by tensile and thermo-aqueous programming tests. Accordingto FT-IR analysis results, the peaks belonging to cellulose became visible infilms with the increase of the CNW amount. Strength and elongation at breakincreased for until 10% CNW with increasing CNW concentrations however adecrease was observed for 20% concentration. In thermal-aqueous test results,we obtained the least value of 48.5 % shape fixity of neat SMPU where as thenanocomposite containing 20% CNW had the maximum value of 69.3 %. The maximumtotal shape recovery of 91.45 % was also obtained for 20% CNW and 80.41 % ofthis recovery belongs to water-induced shape memory effect. Summing up, it wasobserved that produced nanocomposite maintained its thermal-induced shapeswitchable effect originally existing in SMPU and simultaneously it possessedwater-induced shape memory effect due to the percolation network of thecellulose whiskers whose hydrogen bonding can be regulated by water reversibly.<o:p></o:p></span></p> |
|