Study On The Hygrothermal Process And Mechanism Of Low Modulus Of Hydrophilic Polyester Tows

In order to promote the sustainable development of the polyester industry,the polyesters' shortcomings such as the low moisture absorption,being susceptible to electrostatic,hard feeling,should be overcome.Therefore,the polyester products develop in the direction of high technology,high value addition,multifunction and environmental protection,and this process demands a combination of superfine technique,different density and shrinkage filament composition,hydrophilic modification,and other composite processing.However,the modified tows,especially those subjected to the two-for-one twisting process,still have high modulus,high internal stress and twist instability.If these raw productions are processed directly,it will cause uneven force between the tow and the tangles as well as skew of follow-up processing.As we all know,tow modulus is closely related to the various properties of the textile.And the use of materials with precision function and garment requires lower modulus,which is conducive to deformation.While multi-axial warp knitted fabrics and its composite materials for industrial textiles with promising application need to fabricate complex face and surface.As a result,the fiber with lower modulus is urgently required and it is significant to perform preprocessing of the fiber before the process of warping,like effectively reducing the tow modulus,increasing elongation and lower elongation load,to improve the quality of the final product.Owning to the simple and controllable process,large processing capacity,pollution abatement,easy to high production rate,the hygrothermal treatment is commonly used in industry to change the fiber modulus.In this paper,a self-made atomization heating device was designed to overcome the problems of high energy consumption,large temperature fluctuation,long process time of preheating and cooling,large particle size,excessive liquid destruction of fiber structure and lowering fiber performance.The investigation of polyester multifilament yarn was conducted by utilizing four kinds of hygrothermal treatment(hot air,water bath,water steam,atomized vapor)with four temperature gradients(70,80,90,100 ?),and three different time step(30,45,60 min)for processing,respectively.The comprehensive characterizations of the primary tows and the mechanical properties of the yarns treated with different heat and moisture conditions were tested and analyzed.According to the theoretical analysis and experimental verification,the hygrothermal process and mechanism of low modulus of hydrophilic polyester tows were studied.At the same time,the impact of warp hygrothermal treatment on the corresponding properties of fabric was discussed.First of all,the hygrothermal device designed in this paper changed the traditional humidification principle.The function of ultrasonic cavitation and the role of capillary waves of ultrasonic atomizer were utilized to humidify,which can make the liquid generate steam at low temperatures and ordinary atmospheric.The steaming process change of conventional steam production methods is conducive to infiltrate.The combination of humidifying device,rotary fan device and heating device had realized the requirements of low temperature humidification,uniform heating,recycling steam,inhibiting condensed water droplets and saving energy and other aspects.Those three kinds devices achieved intelligent program requirements by electronic technology,which is beneficial to fine,uniform,stable steam flow running.And they can accurately regulate yarn steaming technology parameters.Secondly,moisture regain,cross-section and surface and mechanical behavior of the original sample were characterized by moisture analyzer,scanning electron microscope(SEM),nuclear magnetic resonance(NMR),and yarn strength meter,respectively.Meanwhile,four kinds of hygrothermal treatment(hot air,water bath,water steam,atomized vapor)of those tows were tested and analyzed.The results showed that the original polyester multifilament yarn had a high moisture regain,because it contained a small amount of diethylene glycol and polybutylene terephthalate,increasing its hydrophilic properties.If the temperature is too high to protect polyester tows,the upper limit of temperature must be strictly controlled.In all conditions,higher temperature conditions caused initial modulus and breaking strength of polyester tows increased while the elongation at break decreased.At low temperature,the change of treatment time caused tows modulus change significantly.Compared with hot air treatment,the elongation rate of yarns with boiled treatment decreased,while the strength,elongation load and initial modulus increased.With different heat and wetting treatment conditions,it indicated that the atomized vapor had optimal heat and moisture flow,and the comprehensive utilization performance of polyester tow is the best.Thirdly,the mechanism of low modulus of hydrophilic polyester multifilament yarns was investigated by analyzing the mechanical model of polyester fiber tensile,the modulus-strain curve model,the relationship between the initial modulus and dynamic elastic modulus,the influence of the parameters on dynamic elastic modulus,changes of unit molecular relaxation in the glass transition temperature region.Original sample and four kinds of polyester tows whose modulus decreased most after four kinds of treatment process were employed to study the mechanical behavior,crystal structure,orientation,and thermal properties by yarn strength meter,X-ray diffractometer(XRD),thermogravimetry analysis(TGA),and differential scanning calorimetry(DSC),respectively,which made the theoretical explanation more reasonable.It was found that the initial modulus was the maximum of tow modulus,and how to reduce the initial modulus was the focus of low modulus research.When the time t approached 0,numerical static elastic modulus was also equal to numerical dynamic modulus of elasticity as the frequency w tended to the infinite.Initial modulus obtained by experiment was the result of a complex viscoelastic nature and fiber cross section turning or curling effect,and the dynamic elastic modulus was related to loss peak width and symmetry.Glass transition temperature region mainly behaved the realization of alpha relaxation phenomena.Thermal effect changed fiber molecular motion.As a result,the crystallinity and orientation were declined while the initial modulus and the stress decreased.Finally,in order to explore the influence of the warp hygrothermal process on fabrics performance,an investigation of fabrics about the basic physical properties and the basic mechanical properties under slight deformation were conducted by using hot air,water bath,and atomized vapor treatment for the warp processing,respectively.The experimental results showed that the permeability of fabric was reduced to a certain extent by the heat and moisture treatment of warp tows.The tensile properties did not changed greatly,the drape performance was improved and the crease recovery was also optimized to a certain extent.The warp stiffness of fabric was decreased,and this change trend was in accordance with that the stiffness variation of tows.When the treating temperature was higher than 90 ?,the average friction coefficient of the fabric increased after the treatment of hot air and boiled,and the temperature had little effect on the friction performance.Compared with the three treatment methods,the effect of the atomized vapor was more detailed,easier and more uniform,which is the best method to improve the quality of the fabric.