Fabrication, Characterization Of Non-Equal Convergence Point Elastic-Conductive Composite Yarns Based On Triaxial Ring Spinning System And Its Application

The elastomeric,conductive wrapped yarns prepared on a hollow spindle spinning system and its applications have been systematically studied;however,almost no work has been reported on the fabrication of non-equal convergence point elastic-conductive composite yarns based on a modified multi-axial ring spinning frame both at domestic and abroad.The main purposes of this research are to innovatively prepare tri-component elastic-conductive composite yarns?t-ECCYs?on a modified ring spinning frame based on previous work done by TMT-FSM?Textile Materials and Technology&Fibrous Soft Matter?team of Donghua University first,and then focus on formation mechanism of t-ECCYs,its structure and performance as well as Joule heating behavior in wearable field.Such fundamental work is of crucial academic significance and practical value.Composite ring-spun technique with non-equal convergence point owing original intellectual property right is first proposed by TMT-FSM team.The output position and tension of each substrand are precisely controlled,and the core innovation of this novel technique is the multistage variation of convergence points in the twisting triangle zone.The t-ECCYs were prepared on a modified ring frame,which was elaborately retrofitted with a grooved roller,positive feed rollers and a tension disc.Specifically,a stainless steel filament?SSF?was positioned at the center of rayon fibers?RFs?whilst elastane filament?EF?was fed in at a certain distance by means of grooved roller.The draw ratio of EF was controlled through speed differences between positive feed rollers and front rollers,and the pretension of SSF was conducted by a tension disc.Finally,t-ECCYs with special structure were created.Furthermore,from the views of spinning geometry and mechanics,the movement of secondary convergence point was analyzed at individual technological parameters of strand spacing,twist level,spindle speed and elastane draft via theoretical derivation and experimental verification.It is well established that the above process variables play a significant role in deciding the physical yarn characteristics,and the optimized process variables were selected at strand spacing of 10.5 mm,twist of 700 tpm,spindle speed of 7000 rpm,and elastane draft of 3.0.If not otherwise specified,the aftermentioned t-ECCY refers to a yarn spun with the above optimized process parameters.A special self-designed instrument was prepared to capture the external morphologies?e.g.,the overall appearance,screw pitch and apparent diameter?of yarns during stretch.The t-ECCY sample has a three-dimensional helical-coiled structure in its free-load state,thus it can be approximately regarded as a cylindrical spiral spring.The screw pitch becomes larger,whereas apparent diameter becomes smaller with an increase of the applied strain.Furthermore,some structure-characteristic indicators are proposed,that is,yarn elongation e_y,pitch ratio?,elastic recovery ratio R and plastic deformation ratio P of t-ECCY,elastic recovery ratio R?and plastic deformation ratio P?of helical angle,radial shrinkage r and passion?s ratio?,all of which can be used to accurately characterize the structural deformation of a t-ECCY during stretch.Experimental results reveal that the indicators of e_y,?and r are proportional to the stretching level.Both R and R?are higher than 95%,and the corresponding P and P?are less than 5%.In addition,the elastic recoveries of t-ECCY following single/cyclic stretch at larger constant elongation slightly decrease,indicating its acceptable elastic behavior.With respect to electrical property,The t-ECCY shows an approximately constant linear resistance changes as a function of the consecutive length,regardless of the applied weights and smaller applied strains following cyclic stretch,demonstrating its stable electrical conductivity and structural regularity.In short,the superior elastic stretchable and electrical characteristics verify the reliable practicability of our as-prepared t-ECCY.The mechanical prediction of yarns continues to be an extensively researched topic.On the basis of sophisticated yarn structure?the t-ECCY is assumed to be comprised of two components;the SSF core wrapped in a rayon sheath and the EF in core?and clarifying the effect of constituent proportion on the final characteristics,a tensile predictive model of t-ECCYs with varying EF draft was proposed and the tenacities of yarns were predicted using a modification to Hamburger?s model.In the modification,the tenacities of the constituent fibers inside a yarn considered in Hamburger?s original model are replaced with the corresponding breaking tenacities of its single component yarns?i.e.,sheath and core?.Further,a four-component constitutive model based on Vangheluwe?s tensile model was proposed to fit experimental stress-strain curves of t-ECCY under different strain rates.The constitutive tensile model consists of three components placed in parallel,the first of which is a Maxwell model characterizing the viscoelastic behavior of s-RY?nominal staple rayon yarn?,the second of which is a nonlinear spring representing the nonlinear mechanical behavior of SSF,and the third of which is a linear spring characterizing the linear tensile behavior of EF within the range of t-ECCYs?extension at break.It was indicated that the proposed analytical model can fairly well replicate the tensile behavior of t-ECCY as a function of strain rates qualitatively and quantitatively.The change of characteristic parameters with respect to varying strain rates was reasonably analyzed.Such model can enrich the theoretical research of viscoelastic mechanics of composite yarns.Furthermore,a modified two-parameter Weibull strength predictive model,taking into account the effects of extension rate and gauge length,can be reasonably employed to quantify the degree of variability in tensile strength of t-ECCY and to obtain individual Weibull parameters for practical uses.The yarn exhibits an extension-rate strengthening effect,a higher extension rate results in a higher breaking strength and fracture strain,irrespective of the gauge length considered.Expressed in terms of gauge length,yarn tenacity shows a drop for a longer testing length at all extension rates,based on the well-known weakest-link theory.In addition,different fracture mechanisms of t-ECCY are demonstrated at lower and higher extension rates.An even and orderly break happens at lower extension rates mainly due to the stronger interactive force and sufficient time available for the fiber realignment.Nevertheless,an irregular break dominates at higher extension rates by virtue of the reduced reorientation of some disordered fibers and intensive instant impact force of SSF element inside the yarn along the load direction.Finally,a highly stretchable and flexible t-ECCY-incorporated heater was prepared.The results showed that a single t-ECCY responded rapidly in terms of thermal response and showed a uniform surface temperature distribution under various applied voltages and strain deformation conditions.The stability of the yarn was also confirmed by alternating voltage on-off cycles.Furthermore,the t-ECCY-decorated knit fabrics were not only suitable for local heating functon,but also possessed good cyclic stability with little degradation in their functional properties after expand-release cycles.The electrical conductivity of t-ECCY mainly origins from SSF inside,and the electric conversion efficiency h_r+c is 7.90-8.96 mW/?within the voltage range of 3-12 V.The steady-state temperature of t-ECCY at a given voltage depends on the amounts of generated and lost heat under static state according to heat conduction theory,and the temperature is directly proportional to the square of the voltage.The equilibrium temperature of t-ECCY can be precisely controlled by the voltage applied.In addition,the diameter-decreasing effect and decreased thermal coupling effect are two key factors influencing the gradual decrease of surface temperature of t-ECCY under larger stretch-deformation conditions.The maximum temperature of yarn shows a slightly drop within the stretch limit of 50%.All these excellent characters revealed their practicability in wearable Joule heating field.The multi-axial composite spinning technique with non-equal convergence points based on the ring spinning system not only innovately enriches the yarn-forming mechanism,but also provides technical basis for the high-quality and multifunctional processing.The straightforward fabrication approach and excellent performances of our as-fabricated t-ECCYs in Joule heating field provide new strategies and reference on broad applications.