Fabrication And Strain Sensing/electrothermal Properties Of CNT Film Twisted Yarns With High Tenacity And Wearability

With the rapid development of society,smart textiles have caught everyone's interest.Smart textiles should monitor human health and exercise while maintaining the basic functions of the fabric,which are employed in medical,entertainment and various other fields.However,the main concern remains the method of utilizing carbon nanotube(CNT)yarn with excellent mechanical and electrical performance in smart textiles.The CNT yarn made by wet spinning,aerogel spinning and array spinning exhibit small diameter,low strength and elongation,making it difficult to be woven or knitted into the fabrics,which limits its application in the field of smart clothing.In order to solve this problem,a self-designed controllable preparation device for film twisted yarns was used to twist the CNT film and convert it into the yarn with adjustable diameter,high tenacity and strong reliability,with its potential for smart textile applications.The research in this thesis gives a detailed information about solving above discussed problems in steps.First of all,the controllable preparation device for film twisted yarn was designed and set up.The twisting process parameters were determined according to the basic mechanical properties of CNT film to realize the spinning of the 12 kinds of film twisted yarns with different width and twist per meter(TPM)of CNT films.Whereas,the structure of the low-twist yarns was loose and uneven.As the width and TPM of CNT film increased,the structure of the yarn became uniform and compact,showing a good helix-twisting structure.Secondly,the surface morphology,mechanical properties and tensile fracture mechanism of the film twisted yarn were systematically characterized by polarized light microscopy,single fiber tensile strength tester and scanning electron microscope(SEM).The results showed that the elongation at break and the tensile strength of CNT film twisted yarns were improved with the increase in TPM and width of the CNT film.The tensile strength and elongation at break of 7-900 film twisted yarn were 265.9 MPa and 34.1% respectively,which were 194.8% and 74.9% higher than that of CNT film having 90.2 MPa and 19.5%.The tensile breaking force and strength of single aerogel-spun CNT yarn were 135.9 cN and 102.3 MPa,whereas,for the CNT film twisted yarn with similar diameter were 260.8 cN and 177.1 MPa,respectively,which was increased by 91.9% and 73.1%.The tensile breaking force and strength were 1305 cN and 165 MPa for CNT multi-yarns(7 strands)and 1904.7cN and 265.9MPa for CNT film twisted yarns with similar diameter,with 45.9% and 61.2% increase.The CNT film twisted yarns had high abrasion frequency,which was 175.2% higher than that of the CNT multi-yarns.The diameter of the CNT film twisted yarns(130-450?m)and elongation(about 35%)is almost an order of magnitude greater than the CNT yarns reported in the previous literature,promoting its promising use in textiles.Thirdly,the electrical and strain sensing properties and electrical stability under the cyclic tensile loading of the CNT film twisted yarns were systematically studied by single fiber tensile strength tester and two-probe digital multimeter.The results showed that the low-twist yarns with loose structure showed the lowest electrical conductivity,whereas,for film twisted yarn of 7-900 it can be up to 886 S/cm with the increase of TPM.The strain range for sensing(35%)of CNT film twisted yarns was around two times higher than that of CNT film(18%).The compact structure of CNT film twisted yarn brought its excellent electrical stability under 10% cyclic tensile strain.At last,in order to employ CNT film twisted yarn in the field of wearable textiles,the infrared thermal imager was used to study its electric heating properties systematically under different applied voltages.Furthermore,the CNT film twisted yarns were hand woven and knitted fabric samples,verifying its good weaving ability.Moreover,the results showed that the temperature of CNT film twisted yarn can be precisely controlled by the applied voltage,with instantaneous respond and a stable equilibrium state can be achieved after about 5s.The heating temperature of the CNT yarn was higher than that of the CNT film under the same voltage or power.For instance,when P = 1 W,the temperature of 7-900 film twisted yarn and 7-yarn multi-yarn were 206 ? and 239 ?,whereas,CNT film had only 116 ?.The above phenomenon indicated the heating efficiency of the CNT yarn(h= ~5)was much higher than that of CNT film(h= ~11).The electro-thermal effect of CNT material was repeatable and stable.The CNT film twisted yarn are promising applicant as high-strength and wear-resistant intelligent electrothermal yarn in the field of single devices or textiles based on their improved mechanical,electrical,strain sensing and electro-thermal properties discussed in this research.