| Ultra-high molecular weight polyethylene(UHMWPE)fiber has many significant performances such as high strength,high modulus,wear resistance,bending resistance,chemical resistance,impact resistance and good machinability,but the poor interface performance,poor high-temperature resistance and poor creep resistance that greatly limit its applications in the ropes and composite materials.Electron beam irradiation can be carried out at room temperature with the advantages of energy saving and environmental protection,simple operation,strong radiation penetration,etc.Supercritical CO2 fluid technology is a kind of environmentally friendly processing technology which has no pollution to the environment and low energy consumption.Therefore,in this paper,UHMWPE fibers were modified by electron beam irradiation and supercritical CO2 fluid technology together.The effects of electron beam irradiation were studied.The optimum process conditions of supercritical CO2 pretreatment and electron beam irradiation were determined.The creep and recovery behavior of UHMWPE fibers were studied and the electron beam irradiation crosslinking mechanisms were discussed furtherly.The main contents and results are as follows:1.The effects of basic electron beam irradiation on the structure and properties of UHMWPE fibers were studied.The surface properties and microstructure of the fibers before and after irradiation were characterized,and the effects of irradiation dose and dose rate on the gel content and mechanical properties of UHMWPE fibers were analyzed.The basic electron beam irradiation crosslinking mechanisms were discussed.The results show that:(1)The higher the dose,the lower the dose rate,the more obvious the degree of fiber damage.The new characteristic absorption peaks of C-O-C,C=O and-OH appeared on the infrared spectra of irradiated fibers.With the increase of irradiation dose,the crystallinity of the fibers decreased,the melting point decreased and the melting enthalpy first increased and then decreased.The crystallinity and he melting point slightly increased as the dose rate increased.(2)With the increase of irradiation dose and dose rate,the gel content increased first and then decreased,and the elongation at break increased first and then decreased;as the irradiation dose increased,the breaking strength has been declining,the creep rate originally rose and then declining slowly,but as the irradiation dose rate increased,the breaking strength decreased first and then increased,and the creep rate decreased first and then increased.(3)The irradiation crosslinking of UHMWPE fibers without sensitizers is a typical free radical reaction,and the equation data are fitted well with and the experimental data.The relationship between the gel content and the dose is consistent with the Chen-Liu-Tang relationship(?=0.5),and does not accord with Charlesby-Pinner(?=1).2.The blending processes of UHMWPE and sensitizers were studied.The UHMWPE pellets with different molecular weights,different types and the amount of sensitizers were blended and then injected into the mechanical spline.The effect of UHMWPE molecular weight,the type and amount of sensitizers on the gel content,tensile strength and flexural strength of the blends after irradiation were studied,and the optimum type and mount of sensitizers were determined.The results show that: The amount of sensitizers is the most important influencing factor,the type of sensitizers is the second influencing factor and the molecular weight of UHMWPE is the most minor influencing factor.The optimum combination is the molecular weight of 4 million,the TMPTMA amount of 6%.3.The supercritical CO2 pretreatment process of UHMWPE fibers was studied.The effects of supercritical CO2 pretreatment pressure,temperature and time on the infiltration rate of TMPTMA,the gel content and the creep rate of UHMWPE fibers after irradiation were analyzed and the relationships between them were studied.Then the optimum supercritical CO2 pretreatment process conditions were determined.The results show that:(1)The most obvious influencing factor was the temperature,followed by the stress,the time was minimal,the interactions between the two factors were more significant and the interaction of the three factors were not significant.The infiltration rate of TMPTMA could be improved by higher pressure,temperature and time,and the optimum conditions were determined preliminarily as the treatment pressure of 35 MPa,the temperature of 90?,the time of 60 min.(2)As the treatment pressure,the temperature and the time increased,the infiltration rate of TMPTMA gradually increased then became gently,and the gel content showed the similar trend,but the creep rate showed declining trend.The most reasonable process conditions were the pressure of 25 MPa,temperature of 80?,time of 30 min.4.The effects of enhanced electron beam irradiation on the structure and properties of UHMWPE fibers were studied.The surface properties and microstructure of the fibers were characterized by different irradiation conditions and the effects of irradiation dose,dose rate and atmosphere on the gel content and mechanical properties of UHMWPE fibers were analyzed.The enhanced electron beam irradiation crosslinking mechanisms were discussed.The results show that:(1)Compared with the fibers after irradiation in the nitrogen and vacuum,the degree of damage to the fibers after irradiation in the air is more serious.The crystallinity is obviously improved,the melting point and the melting enthalpy slightly increased.(2)Under different irradiation conditions,the changes of gel content and mechanical properties of UHMWPE fibers with TMPTMA were similar to the changes of which during the basic electron beam irradiation.The nitrogen and vacuum irradiation effect is significantly better than the radiation effect in the air at the same irradiation dose and dose rate.(3)The enhanced irradiation crosslinking with sensitizers was mainly due to the macromolecular chain transfer and the formation of macromolecule free radicals,which results in the formation of crosslinking networks between monomer polymers and macromolecules.This process describes the sensitized irradiation crosslinking mechanism of UHMWPE fibers in the presence of TMPTMA.5.The effects of different treatment processes on the structure and properties of UHMWPE fibers were studied,and the creep and recovery behavior of the fibers were analyzed by DMA.The Burgers model and the Weibull distribution model were used to fit the creep and recovery process.The results show that:(1)The structure and properties of UHMWPE fibers after different treatments have varying degrees of change.The fibers treated both supercritical CO2 pretreatment and electron beam irradiation changed significantly,and the fibers treated through electron beam irradiation also undergone significant changes,but the fibers only treated by supercritical CO2 pretreatment had no significant changes.(2)In the process of creep and recovery of UHMWPE fibers,the creep rate of fibers irradiated by electron beam reduced obviously,and the creep rate of fibers irradiated by enhanced electron beam irradiation was the smallest,which indicated that the enhanced electron beam irradiation is more favorable to the creep resistance.(3)The creep and recovery curves of UHMWPE fibers were well fitted with the measured data.The proportion of the instantaneous elastic deformation increased and the proportion of irreversible deformation decreased,which indicated that the flexibility,rigidity and resistance to permanent deformation of the fibers improved greatly by electron beam irradiation. |
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