Research On Wet Gel Spinning Technology And Crystallization Behavior Of Uhmwpe Fibers

As one of the three high performance fibers,ultra-high molecular weight polyethylene(UHMWPE)fibers has high strength,high modulus,low density(0.97 g/cm3),excellent chemical stability and good wear resistance.It is widely used on the military,aerospace,marine engineering,medical,sports equipment and other fields.As a country which masters UHMWPE fibers preparation technology in a few countries,our country has ability to produce UHMWPE fibers that have meet most of the market demand and have been exported to some countries and regions in Europe and the United States and Asian,but superior performance UHMWPE fibers still need to rely on import.There is still a big gap between the performance of domestic UHMWPE fibers and the world advanced level.Therefore,the processing technology of UHMWPE fibers needs to be studied further.At the present stage,UHMWPE fibers are mainly produced by gel spinning-super times hot stretching method at home and abroad.According to the different solvents,the technology is divided into wet gel spinning line and the dry gel spinning route.And most of the UHMWPE companies in the country use the wet gel spinning route.Therefore,the main research of this topic is the wet gel spinning process of UHMWPE fibers,and the change of crystallization during the UHMWPE fibers forming process.Firstly,the pre-stretching process of gel fibers was studied.The results showed that the oilbearing rate of gel fibers after pre-stretching had decreased,but the effect was not very significant,when pre-stretching for four times,the gel fibers oil rate was only reduced about 2%.The prestretching made the gel fibers internal network structure deformed and oriented.When the prestretching ratio was small,pre-stretching has played a role in the stretching,and made the breaking strength of the first-stage stretch fibers increased.When the pre-stretching ratio is large,The relative slippage between the molecular chains in the network of the gel fibers results in structural defects,resulting in a decrease in the tensile stability of the extracted fibers The process of spinning jet stretch was studied at the same time,the results showed that appropriate jet stretch will raise the breaking strength of UHMWPE fibers,when jet stretch was too large,it will cause the network structure of gel fibers break,structure defects and the breaking strength of UHMWPE fibers reduced.In addition,the pre-swelling process of the spinning solution has been explored.The results showed that the molecular weight degradation of UHMWPE increases with spinning temperature increasing.The swelling treatment slowed down the degradation of UHMWPE at high spinning temperature.Secondly,the effect of the stretching temperature and the stretching ratio on the breaking strength of the three-stage stretched fibers during the super-hot stretching process of UHMWPE fibers was studied by means of orthogonal experiment design.The experimental results showed that the first stage tensile temperature had the most significant effect on the breaking strength of the three-stage stretched fibers.At a first stage stretching temperature of 70 ?,a first stretching ratio of 15 times,a secondary stretching temperature of 100 ?,a secondary stretching ratio of 2 times,a tertiary stretching temperature of 120 ? and a tertiary stretching ratio of 1.4 times,the tensile strength of UHMWPE three-stage stretched fibers was the largest.The relationship between the tensile strain rate and the fibers properties during the stretching process was also studied.The increase of tensile strain rate was found that led to the defect of UHMWPE fiber structure,which made the mechanical properties of fibers decrease.Finally,the molecular crystal morphology of UHMWPE fibers were studied by scanning electron microscopy(SEM),differential scanning calorimetry(DSC),wide angle X-ray diffractometer(WAXD)and two-dimensional X-ray diffraction.The results showed that the UHMWPE powder particles were composed of many spherical structure with a diameter of about 60 ?m,and the spherical structure were formed by spherical particles with a diameter of about 10 ?m,and the spherical particles were connected with fibrous structure.In the process of wet gel spinning,the molecular chain of UHMWPE was entangled and the untouched state was held in the gel fibers.A large amount of loose crystalline structure was formed after extraction and drying.With the increase of the stretching ratio,the loose crystalline structure was densified,the melting point and crystallinity of the fibers were gradually increased,and the solid phase transition of the orthorhombic system to the hexagonal system occurred.With the increase of the stretching ratio,the defects of the crystal area gradually decreased,the grain self was perfect and the degree of orientation of the crystal area gradually increases.