Failure Mechanism And Service Life Of Different Modified PBT/PET Composite Elastic Fibers

The long-term service of the composite elastic fiber will lead to the change of mechanical strength,crimp elasticity,and affect its performance,especially in different application scenarios,the performance failure is different.In order to study the practical application performance of composite elastic fibers,this topic designed and prepared two different modified two-component parallel composite elastic fibers(block modified PTMG-PBT/PET,graft modified POE-gPBT/PET),and simulated the application environment of sweat impregnation,soap washing,low temperature,summer drying,high temperature ironing,etc.Study the changes of aggregate structure and properties of composite fibers,explore the effects of different main and side chains of composite fibers on the failure of elastic and mechanical properties,and predict the service life of composite fibers.The main research contents are as follows:(1)After the perspiration and soap treatment of the block modified PTMG-PBT/PET composite elastic fibers,the ester bond hydrolysis is more likely to break,the surface roughness of the fibers increases,the sweat and soap penetrate into the fibers,resulting in the decrease of the molecular chain regularity,energy storage modulus and loss factor,and the mechanical and curling properties are also reduced.At the same time,the destruction of chain regularity leads to the decrease of orientation factor,the degree of solution orientation also decreases,and the thermal shrinkage of the composite fiber decreases.It was found that the mechanical and crimp properties of the composite fibers were less affected by heat treatment at a temperature lower than the glass transition temperature.When the fibers are treated at 140℃,the mechanical properties and curl properties of the composite fibers are reduced.This is because the fibers are easy to be oxidized at high temperature,the molecular structure is damaged,the orientation is reduced,the internal stress is reduced,and the energy storage and loss performance of viscoelastic energy and dynamic frequency become worse.(2)After the perspiration and soap treatment of the chemically grafted POE-g-PBT/PET composite elastic fibers,its performance change trend is similar to that of block modified bicomponent fibers,the ester bond is easy to hydrolysis,roughness increases,thermal shrinkage decreases,breaking strength and crimp ratio decreases.After high temperature treatment,the orientation of the composite elastic fiber decreases,the energy storage and loss properties of viscoelastic energy and dynamic frequency decrease,and the mechanical properties and crimp properties also decrease.(3)Two kinds of modified PBT/PET composite elastic fibers were treated with PH and temperature cycles.The results showed that with the increase of treatment times,the molecular structure changes were irreversible,and the mechanical properties and crimp properties continued to decline.The service life of the composite fibers is predicted by Weibull distribution model.The results show that the PTMG-PBT/PET composite fibers will fail after at least 159 times of sweat and soap treatments,while the POE-g-PBT/PET composite fibers will fail after about 50 times of soap washing.At low temperature,the fibers can be reused for many times.But at 140℃,PTMGPBT/PET composite fibers will fail after only 41 treatments.POE-g-PBT/PET composite fibers have better heat resistance than PTMG-PBT/PET composite fibers.In conclusion,after being sweat impregnation and soap washing,the modified PBT/PET composite elastic fibers will undergo hydrolysis reaction,which leads to the decrease of mechanical and curling properties.PTMG-PBT/PET composite fibers have better sweat stain resistance and soap washing properties.POE-g-PBT/PET composite fibers have good sweat stain resistance.But the graft structure of the fibers makes the molecular chain spacing larger and there is a large amount of free volume.Under the infiltration of surfactants,a large amount of soap enters the fiber and causes hydrolysis,which greatly reduces the strength.The properties of the modified PBT/PET fibers hardly change when it is used below the glass transition temperature,but the properties of the modified PBT/PET fiber decrease greatly when it is processed at high temperature such as ironing.Compared with PTMG modification,POE macromolecular chain is saturated aliphatic hydrocarbon and has good thermal stability.The modified fibers molecular chain has a micro cross-linking reaction to improve its heat resistance.Therefore,it has a longer service life at high temperature and can still maintain excellent function after multiple ironing.