Study On The Structural Evolution Of Stretch-induced Polyamide And Its Composite Properties

As a widely used polymer material,polyamide(PA)has a variety of types.Different polyamides also have different mechanical properties and crystal structures.A wide variety of polyamides provides people with lots of choices,but also gives scientists a lot of sample to research the properties,morphology and structure of different polyamides,which also makes the polyamides family has become an enduring research hotspot.In the molding process of semi-crystalline polyamides,the external force will have a great influence on the properties,structure and molecular chain orientation of polyamides,and then affect the mechanical properties of polyamides.These external factors include stress,strain and additives.Therefore,in the process of polyamide molding,the in-depth study of polyamide`s structure evolution can provide knowledge guidance for the processing conditions of polyamide materials.In the post-treatment stage of fiber processing,high-temperature drawing treatment is an important step to prepare high-performance fiber,choosing a right temperature and draft are important.In this study,three kinds of polyamides(polyamide 6,polyamide 612 and polyamide 1212)were used as experimental objects,and the experimental samples were prepared by melt molding.Combining with the spinning forming technology,The relationship between the mechanical properties of different polyamides and their internal crystal structure,temperature and draft is studied.The second phase was added to change the crystal structure of the material,the influence mechanism of adding phase on the internal structure of polyamide is discussed.This paper is divided into the following three parts:1.The 400% strain of polyamide 6,polyamide 612 and polyamide 1212 at 60 ?,80 ?,100 ?,120 ?,140 ?,160 ?,180 ? and 200 ? was studied(Since the melting point of polyamide 1212 is 190?,it would not be drawn at 200?).The effect of processing temperature on the mechanical properties of three kinds of polyamides is analyzed by mechanical test,and the intensity of hydrogen bonded groups is characterized by FTIR.The changes of crystallinity and crystal structure of three polyamides are characterized by DSC and WAXD.The results show that polyamide 6 has the strongest mechanical strength,the strongest hydrogen bond intensity and the highest crystallinity.2.A temperature range(80 ?-160 ?,every 20 ? is an interval)is selected to carry out different degrees of drawing strain on three kinds of polyamides,and the effect of different strain on the crystal structure of polyamide is discussed.According to the results of the previous chapter,120 ?-140 ? is the temperature range that material has the highest mechanical properties after drawing.Therefore,120 ? is selected to test the mechanical strength of the three materials.It is found that the mechanical strength increases with the increase of tensile strain.DSC test shows that the crystallinity of materials with different tensile strain will also increase with the increase of tensile strain.Combined with WAXD test,it was found that the crystalline integrity tended to increase with the increase of tensile strain.3.N-ethyl-p-toluene sulfonamide(N-PTSA)and polyamide1212 are melt blended to prepare the combined material.The effect of this small molecule on the internal structure of polyamide was discussed.It is found that this small molecule can reduce the density of hydrogen bond between polyamide chains and affect the crystallization behavior of the material.A small amount of tensile strength is lost to improve the toughness of polyamide.