Properties And Applications Of Polypyrrole Modified Stretchable Textiles

Containing hydroxyl,amide and other functional groups that can combine with conductive substances（such as metals,metal oxides,carbon materials,conductive polymers,etc.）,originally non-conductive textiles（such as cotton fabrics,nylon fabrics,etc.）can be modified into conductive textiles by means of physical or chemical deposition.Conductive textiles have aroused great interest of researchers by virtue of their inherited flexibility,bendability,stretchability,and light-weight from textile substrates,and they are considered the most promising flexible and wearable electronic materials because of the easy integration into clothing.Polypyrrole（PPy）hasπelectron conjugated skeleton,good conductivity,and proton or anion doping characteristics,which enable PPy conductive textiles great application potential in light absorption,solar-thermal conversion,pseudocapacitive energy storage,strain sensors,gas sensors,electrochemical actuators,and so on.PPy conductive textiles can be prepared simply and quickly via in-situ polymerization.However,the mass of PPy deposited on the textile substrates is limited,and most pyrrole（Py）monomers polymerize in the solution and settle to the solution bottom.As PPy content has a great influence on the conductivity and application performance of PPy conductive textiles,how to improve the PPy content further is critical.The type and structure of textiles also affect the properties of PPy conductive textiles,and the commonness and differences of PPy conductive textiles based on different substrates need to be studied.In addition,although PPy has good conductivity,its semiconductor properties still make it unable to replace metal materials.The influence of resistance on the performance of larger PPy conductive textiles cannot be ignored.The purpose of this paper is to develop the preparation process of high-performance PPy conductive textiles and design their inner circuit to further improve their application performance.The preparation conditions,conductivity,sensing mechanism,electrothermal and energy storing performance,and current collecting mode of PPy conductive textiles are studied.The PPy/β-Fe OOH/NS-x(x representing the concentration of Py in reaction system(g L^-1),x=2.5,5.0,10.0,12.5,and 15.0)was fabricated via in-situ polymerizing Py on nylon strip（NS）with surface construction ofβ-Fe OOH scaffold that was deposited through hydrolysis of Fe³⁺.The PPy/β-Fe OOH/NS-x loads more PPy mass than the control sample PPy/NS-x at each x value.The PPy mass loading of PPy/β-Fe OOH/NS-12.5 and PPy/NS-12.5 is 1.45 mg cm^-2and 1.15 mg cm^-2,respectively;and their resistivity is 10.1Ω·cm and 16.5Ω·cm,respectively.The mass loading ofβ-Fe OOH scaffold on NS can be improved by drip-coating method,which further improves the mass loading of PPy.The PPy/β-Fe OOH-coated/NS prepared at Py concentration of 12.5 g L^-1 possesses a PPy mass loading of 3.09 mg cm^-2 and a resistivity of5.2Ω·cm.The better conductivity renders PPy/β-Fe OOH-coated/NS electrothermal temperatures of 30.2,59.4,and 97.2℃at voltages of 4,8,and 12 V,higher than that of PPy/β-Fe OOH/NS-12.5 and PPy/NS-12.5.This paper takes the lead in adoptingβ-Fe OOH scaffold to modify nylon fibers,providing a new way to improve performance of conductive nylon.PPy/β-Fe OOH-coated/NS exhibits a response time of 140 ms at stretching rate of 800 mm min^-1 for 5%strain,and remains relatively good sensitivity after thousands of stretching-recovering process with 50%strain.In the process of constant speed directional stretching,the yarns and fibers of PPy/β-Fe OOH-coated/NS have two processes:slippage and contact,which leads to an increased resistance firstly and a nearly unchanged value then.Because of the existence of internal recovery force,the resistance of PPy/β-Fe OOH-coated/NS has varying cases in the stretching-recovering process according to the stretching-recovering rates and tensile strains.PPy/β-Fe OOH-coated/NS exhibits a firstly increasing then decreasing resistance in pressing situation.When fixed at the knee to monitor its bending process,PPy/β-Fe OOH-coated/NS is in fact subject to both stretching and pressing.The monitored sensing signal is analyzed in combination with the resistance variation mechanisms of stretching and pressing.This method provides a new idea for analyzing sensing signals and can be extended to other strain sensing materials.PPy/CF-x was prepared via in-situ polymerization and deposition of PPy on cotton fabric（CF）substrate,and it was compared with nylon-based PPy conductive textiles（PPy/β-Fe OOH-coated/NS,PPy/β-Fe OOH/NS-12.5,PPy/NS-12.5）to study the effects of substrates on the performance of PPy conductive textiles.The growth mechanism of PPy on NS and CF substrates is similar,and both the PPy mass loading and textiles conductivity increase as Py concentration rises.PPy/CF-15.0 possesses a PPy mass loading of 4.47 mg cm^-2 and a resistivity of 2.5Ω·cm.The electrothermal temperatures of PPy/CF-15.0 are 32.0,68.0,and 116.7℃at4,8,and 12 V,respectively,which are higher than that of nylon based PPy conductive textiles.PPy exists on the fiber surface in granular shapes,which form rough structure and endow PPy conductive textiles with good hydrophobicity.Among PPy/CF-x,PPy/CF-12.5 exhibits the highest area capacitances(823.5-142.0 m F cm^-2 at 5-100 m V s^-1,and 1113.3-800.0 m F cm^-2 at1-10 m A cm^-2);by virtue of higher PPy mass loading and better conductivity,PPy/CF-12.5electrode and its symmetrical supercapacitor also present higher energy storing performance than that of nylon based PPy conductive textiles.Different from the phenomenon that the resistance of nylon based PPy conductive textiles increases during stretching,the resistance of PPy/CF-15.0 increases slightly at initial and then presents a downward trend during stretching.However,the PPy conductive textiles at stretching states show lower electrothermal temperatures than that without stretching.This is because many cavities form at stretching states,which contributes to heat dissipation.PPy/CF-15.0 and PPy/β-Fe OOH-coated/NS due to good conductivity exhibit electrothermal temperature exceeding 136.5℃,which causes the degradation of PPy;thus,the textile resistance increases and the electrothermal temperature gradually reduces.The electrothermal temperature of PPy conductive textiles will also gradually decrease during the continuous electrothermal heating process of 8 days under 8 V voltage,and the sample with smaller resistance presents a lower temperature retention.As water washing will make the doped Cl^-on PPy chains de-doped,the resistance of PPy conductive textiles increases sharply after the washing,and the electrothermal temperature at 16 V is nearly the same as room temperature.Compared with the situation of current collecting using single pair of stainless steel clips,using three pairs of the clips for parallel current collecting not only expands the electrothermal region of PPy/CF-12.5（5 cm×5 cm）,but also reduces the resistance of the whole heater from135.8Ωto 55.9Ω,and the average electrothermal temperature at voltage of 8 V increases from37.0±8.9℃to 51.0±5.5℃.Four stainless steel clips are applied to collect current for PPy/β-Fe OOH-coated/NS in interdigitally parallel mode,the resistance of which is reduced from 175Ωto 19Ω,and the electrothermal temperature reaches 84.1℃at voltage of 4 V.Center current collecting can make more parts of PPy/CF-12.5（2 cm×1 cm、4 cm×1 cm）conduct electrochemical energy storage,performing higher capacitances than the end current collecting.Parallel current collecting for PPy/CF-12.5（4 cm×1 cm）with three current collectors can further improve the capacitances.The area capacitance of the electrode is 542.0-37.2 m F cm^-2at scan rate of 5-100 m V s^-1,and 868.8-853.1 m F cm^-2 at current of 4-20 m A(0.5-2.5 m A cm^-2).This new method of reconstructing internal circuit to improve application performance of PPy conductive textiles can be extended to other materials.