Study On Tensile Mechanics Model And Safety Analysis Based On Microstructure Of Spandex

Spandex is a synthetic fiber with excellent properties.It has good corrosion resistance,heat resistance,low temperature flexibility,high elongation at break and elastic recovery rate.It is widely used in textile,medical,firefighting and other fields.Because spandex is subjected to various tensile effects during its use,it is necessary to understand the relationship between stress and strain during its stretching to lay the foundation for its safety use.Therefore,in this paper,tensile mechanical models of spandex were constructed.The relationship between the microstructure,properties of spandex and mechanical model were studied,and the safety analysis of spandex in different usage scenarios was performed.The main contents and conclusions of this paper are as follows:?1?The spandex samples of 5 different chain extender ratios?the molar ratio of the chain extender ethylenediamine to 1,2-propanediamine were 3.4,4.5,6.3,10,21?were ultilized to tensile test and the mechanical model was derived to simulate its tensile curves.The stretching process of spandex can be divided into elastic deformation stage,low viscoelastic deformation stage,and high viscoelastic deformation stage through the tensile curve.The tensile curve in the elastic deformation stage is approximately straight,in which the stress-strain relationship can be expressed by Hooke spring.In the low viscoelastic deformation stage,stress rises gently with strain,in which the stress-strain relationship can be expressed by maxwell model.In the high viscoelastic deformation stage,as the strain increases,the rate of stress increase becomes larger,that is,the slope of the tensile curve increases gradually.The stress-strain relationship can be expressed by the parallel model of Hook spring and non-linear sticky pot.?2?Compared with the existing three-element model,the three-element model proposed in this paper,which consists of a Maxwell element and a non-linear sticky pot in parallel,has a higher fitting degree.The fitting degree of tensile curves of 5 kinds of spandex with different chain extenders ratios are all higher than 0.999.The elastic modulus and initial viscosity coefficient in the mechanical model increase with the increase of the chain extender ratios.Fourier transform infrared spectrum test,small-angle X-ray scattering test,X-ray diffraction test,atomic force microscope test,gel permeation chromatography test were carried out on spandex.The degree of hydrogen bonding,the degree of microphase separation,and the crystallinity of spandex increase with the increase of chain extender ratios,which is consistent with the model parameters.?3?The dynamic mechanical analysis results of spandex show that the glass transition temperature of the soft segment of spandex decreases with the increase of the chain extender ratios,that is,the hard segment mixed in the soft segment decreases,and the degree of microphase separation increases,which corresponds to the elastic modulus and initial viscosity coefficient in the model increase.When the temperature range is-45?to-10?,the storage modulus increases with the increase of the chain extender ratio,which is consistent with the elastic modulus and initial viscosity coefficient in the mechanical model.The larger the elastic modulus and the viscosity coefficient are,the greater the rigidity of the corresponding segments is.In the process of stress relaxation,the spandex with larger chain extender ratio has greater stress at the same time,and the stress relaxation rate is lower.?4?A new model is proposed to describe the sequential deformation of multiple structural units during the tensile process of spandex.When the stress and strain reach the threshold value of the corresponding structural unit,the tensile deformation of the structural unit occurs,and the threshold values of the stress and strain of each structural unit were obtained.One Maxwell model and two Kelvin models can be used as the three structural units.The structural units which correspond to the Maxwell model begin to deform when the strain₁=0.The strain thresholds for the two kelvin models to deform are₂ and₃,respectively.When<₂,the fitting degree of tensile curves are all higher than 0.99.When>₂,the fitting degree are all higher than 0.999.The scale coefficient of sticky pot was defined as the proportion of each model's deformation starting point to the end point of tensile in the entire tensile process.The total viscosity coefficient of 5 kinds of spandex was calculated through the scale coefficient of sticky pot.The result shows that the total viscosity coefficient increases with the increase of the chain extender ratio,which is consistent with the change of the microstructure of spandex.?5?For 5 kinds of spandex with different chain extender ratios,when spandex is used as safety belt or safety rope,the tensile performance is used as the evaluation index,and spandex with the chain extender ratio of 3.4 should be selected.When spandex is used to prepare labor protection gloves,the deformation resistance is used as the evaluation index,and spandex with the chain extender ratio of 21 should be selected.When spandex is used as adaptive fiber in Z-pinch,stress relaxation performance is used as the evaluation index,and spandex with the chain extender ratio of 21 should be selected.