Structure-property Study Of Poly(Ethylene-Terephthalate) Industrial Yarns During Drawing Process

Poly(ethylene terephthalate)(PET)industrial yarns has excellent mechanical properties(such as high mechanical strength and modulus),heat resistance and dimensional stability(small elongation),and is widely used as a car seat belt,airbag,tire meridian,and paddle,Boats,marine cables and geotextiles.With the continuous development of human society,the production of polyester is increasing.At the same time,China’s polyester industrial yarn industry is also developing at a high speed,and the main problem currently exists is how to product differentiated fibers that meet the individual needs of different fields,and the difference in performance of differentiated polyester industrial yarns is inseparable from its microstructure.Therefore,the microstructure analysis has a good guiding significance for studying the performance difference of polyester industrial yarn and the future design of individualized industrial yarns varieties.In this paper,two-dimensional wide-angle X-ray diffraction(WAXD)and X-ray small angle scattering(SAXS)are used for study the four types of polyester industrial yarns:super high strength(GHT),high strength(HT),super low shrinkage(SLS)and high modulus low shrinkage(HMLS).The microstructure of the HMLS fiber has the highest amorphous orientation,while the SLS fiber has the lowest amorphous orientation(fa)and mechanical strength.The amorphous orientation is an important factor affecting the mechanical strength.The degree of crystal orientation is improved.In the stress stretching,the amorphous and crystalline regions of the polyester industrial yarn will be deformed,and the final elongation is opposite to the change of the sound velocity orientation degree,that is,the maximum elongation at break with the increase of the sound velocity orientation(fs).The elongation at break decreases with the degree of amorphous orientation increases,the degree of sound velocity orientation increases accordingly.The degree of sound velocity orientation is mainly controlled by the degree of amorphous orientation,that is,the degree of orientation of the amorphous phase affects the degree of sound velocity orientation,and the degree of amorphous orientation is the main factor affecting the elongation at break.In addition to WAXD and SAXS,combined with differential scanning calorimetry(DSC),dynamic mechanical analysis(DMA)and sonic velocity method,the microstructure of polyester industrial yarns was analyzed to obtain the crystallinity of four different types of polyester industrial yarns.The orientation degree and its microscopic platelet structure were finally obtained.The three-dimensional model of the polyester industrial filament microstructure was obtained by the measured platelet microstructure parameters.The microstructure evolution process of low shrinkage(LS)polyester industrial yarns in various processing processes was studied by online sampling method.It was found that the DSC curve of polyester industrial yarn without drawing heat setting process has glass transition point and crystallization.The peak,after stretching and heat setting fiber,hinders the movement of the molecular chain of the amorphous region due to the increase of the content of the crystalline region without the glass transition point;the trans and guache conformation content of the ethylene glycol segment in the PET molecular chain are analyzed by infrared spectroscopy.The change found that with the continuous heat-setting stage,the content of trans conformation in the fiber molecular chain increased continuously,while the guache was reversed,indicating that the crystallization degree of the low-shrinkage polyester industrial yarns is constantly improving;After the stretching stage,the orientation of the crystalline region of the low-shrinkage polyester industrial yarn is already very high.With the subsequent stretching and heat setting stages,the orientation of the crystal region shows an upward trend,indicating that after the processing,the crystal of PET structure is constantly improving.In this paper,the microstructure of polyester industrial yarns are analyzed by various methods,and the microstructure of the fiber is finally obtained.At the same time,the microstructure change of polyester industrial yarns during processing is discussed by online sampling method,which is the structure of polyester industrial yarn.The difference corresponds to the performance,and can be related to the change history of the microstructure during the actual processing,which has certain guiding significance for the production and processing of polyester industrial yarns.