Study On Preparation And Properties Of Electrically Conductive Poly (Metaphenylene Isophthlamide) Fibers

First commercial poly（metaphenylene isophthalamide）（PMIA）fiber is developed by Du Pont in the 1960s（trade name:Nomex）,the successful development of PMIA fiber is an important milestone in the history of the development of chemical fibers in the world.PMIA fiber has good mechanical properties,excellent self-extinguishing flame retardant properties and excellent heat resistance,chemical corrosion resistance.As protective material,it is widely used in the fields of fire protection clothing and high temperature flue gas filtration material.Although,the flame retardant and high temperature resistance of PMIA fiber is excellent,but the inherent excellent insulation properties of PMIA fiber makes its products easy to generate electrostatic sparks in the use process.In high temperature filtration,fire protection,oil and gas fields and gas stations and other industries,the generation of electrostatic spark is easy to cause fire and explosion and other safety accidents.Hence,the corresponding filtration and protection fabrics need to have antistatic or conductive properties.However,there are few reports on commercial PMIA conductive fiber products.The base materials of industrialized conductive fibers are mostly general-purpose fibers such as nylon,which have the low melting point and are far from meeting the requirements of high-temperature applications above 200°C.Electrically conductive PMIA fibers,with excellent properties such as electrically conductivity,flame retardant,light weight and high temperature resistance,could be widely used in high temperature filtration,antistatic protective clothing and intelligent textiles and other fields.Common conductive modification methods of fibers include conductive filler blending,electroless plating,vapor deposition and surface coating,etc.Among them,the dispersibility of the conductive blends in the matrix is often poor,which results in a significant decrease in the tensile strength of the fibers;the coating films deposited on the fibers’surface by the vapor deposition method is often imperfect and has general conductivity,and the cost is relatively high,so it is difficult to realize industrialization;the conductive fibers prepared by surface-coating method often has weak bonding force between the metal coating and the fiber matrix,the coating is easy to fall off and the distribution is uneven.Therefore,how to improve the electrical conductivity of PMIA fiber while maintaining its inherent mechanical properties and lower production costs is a key issue.Among various electrically conductive fibers preparation methods,the electroless plating method has many advantages for preparing conductive fibers,such as,relatively simple process,moderate production cost,almost no damage to the inherent mechanical properties of the fibers and a wide variety of metals that can be applied to electroless plating.Hence,it’s suitable for the industrial production of electrically conductive PMIA fibers particularly.However,the surface of PMIA fibers are inert and have no reactive reactive groups.At the same time,in the traditional electroless plating process,the palladium activation process is expensive,cumbersome,and environmentally expensive,which is another problem in the preparation of electrically conductive PMIA fibers by electroless plating.Based on the above questions,this paper focused on the study of palladium-free activation pretreatment process,using silver nanomaterials to activate PMIA fibers,to ensure the preparation of electrically conductive PMIA fibers on the basis of not damaging its inherent mechanical properties.Meanwhile,the potential applications of electrically conductive PMIA fibers were investigated.In addition,the possibility of preparing surface metallized PMIA conductive fibers directly by blending-spinning and without the need of precious metal activation pretreatment was explored,using the strong chelating adsorption effect of the nitrile group（-CN）in the PAN molecular chain on the metal copper ions in the copper sulfide.Specific research contents and results are as follows:（1）Electrically conductive PMIA fibers were prepared by silver nanoparticles（AgNPs）catalytic electroless plating method（two-step activation method）Based on the swelling effect of DMSO on PMIA fibers surface,AgNPs/DMSO activation suspension was prepared to activate and modify PMIA fibers.AgNPs were obtained by"hydrothermal method".Subsequently,the AgNPs/DMSO dispersion,used for surface activation treatment of PMIA fibers,was prepared and good activation effect was obtained.The optimal reaction condition for the formation of AgNPs catalytic coating on PMIA fiber’s surface was80°C for 8 h.And the morphology,structure,thermal stability,electrical conductivity and other properties of the Ni-Ag-PMIA fibers were characterized by SEM,XRD,XPS,TG,multimeter and other test methods.The Ni-Ag-PMIA composite fibers prepared under the optimized conditions exhibited good morphology,showing obvious silver-gray metallic luster,and its resistivity was 2.8*10^-3Ω·cm.（2）Eelectrically conductive PMIA fibers were prepared by DOPA-silver nanoparticle assemblies（DOPA@AgNAs）catalytic electroless plating（one-step activation method）Based on the chelating adsorption and reduction properties of dopamine on silver ions,the PMIA fibers were modified by the improved one-step activation method using the prepared DOPA@AgNAs.First,an“one-pot”method at room temperature was adopted to make use of DOPA/[Ag（NH₃）₂OH]mixed aqueous solution for surface activation treatment of PMIA fibers.The DOPA@AgNAs mixed coating with catalytic activity was bonded on the surface of PMIA fibers,and then electrically conductive PMIA fibers were prepared by electroless nickel plating method（Ni-DOPA@AgNAs-PMIA）.The reaction mechanism of DOPA@AgNAs formation was introduced,confirmed by TEM,XPS,XRD and reference experiments.In this study,the construction conditions of DOPA@AgNAs catalytic coating on the surface of PMIA fibers were optimized,and 5 h was selected as the optimal reaction time for the preparation of DOPA@AgNAs-PMIA fibers.At this time,not only could promote the activation pretreatment process quickly and efficiently completed,but also could make DOPA@AgNAs in the subsequent electroless nickel plating process to show good catalytic activity,and finally got the Ni-DOPA@AgNAs-PMIA fibers with best coating morphology and electrical conductivity.The morphology,structure,thermal stability,electrical conductivity and other properties of Ni-DOPA@AgNAs-PMIA fibers prepared under optimized conditions were characterized.The Ni-DOPA@AgNAs-PMIA fibers prepared under the optimized conditions had uniform and dense coating morphology,and its volume resistivity was 5.58*10^-3Ω·cm.In addition,twisting test confirmed that the good interfacial adhesion between the nickel coating and the internal PMIA fibers.After 1000 twisting cycles,the bulk resistivity of the Ni-DOPA@AgNAs-PMIA fibers increased from 5.58*10^-3Ω·cm to 4.46*10^-2Ω·cm,and the nickel-coated fibers still have good electrical conductivity.（3）Electrically conductive PMIA fibers were prepared by blending-spinning methodElectrically conductive PMIA/PAN-CuS fibers were prepared by blending PMIA solution with PAN solution,based on the strong chelating effect of the nitrile group（-CN）in polyacrylonitrile on the metal copper ions in the copper sulfide.The possibility of preparing metallized PMIA conductive fibers without precious metal activation pretreatment was explored.The PMIA/PAN blend films and blend fibers were prepared by blending PMIA and PAN solution,and the nitrile group（-CN）in the PAN molecular chain was used to strongly chelate copper cations in metal sulfides,and the uniform conductive CuS coating was formed on the surface of the PMIA/PAN blend films and blend fibers through reduction reaction.First,PMIA/PAN blend solutions with a series of blending ratios were prepared,and a proper amount of Li Cl was added as compatibilizer to ensure that the PMIA/PAN blend solution had a long-term storage stability.The influence of the blend ratio of PMIA/PAN solution on the morphology,mechanical properties,thermal stability and the CuS conductive coating of PMIA/PAN-CuS blend films were discussed,and the optimal blend ratio of PMIA/PAN was determined.When the blend ratio of PMIA/PAN was 10/1,the mechanical properties of the prepared PMIA/PAN films were moderate,and the maximum tensile strength was about 9.73MPa.The CuS conductive coating plated on the PMIA/PAN-CuS film had the good morphology and its volume resistivity was 5.48*10^-2Ω·cm.The XPS and XRD tests confirmed that the Cu_xS_ycoating on the surface of PMIA/PAN-CuS composite film was indeed CuS coating.The tape stripping experiment and ultrasonic test proved that the good interface bonding performance between the PMIA/PAN film and the surface CuS conductive coating.In the process of wet spinning of PMIA/PAN fibers,a new wet spinning process was determined by studying the effects of coagulation bath concentration,spinneret negative tensile ratio and hot water tensile ratio on the morphology,structure,mechanical properties,thermal stability and other properties of PMIA/PAN fibers.When the coagulation bath concentration,jet stretch ratio of spinning and hot water drawing ratio of PMIA/PAN were 50 wt%,-50%and 5times,respectively,the PMIA/PAN fibers obtained had the good morphology and mechanical properties,its tensile strength and elongation at break were about 4.7 c N/dtex and 16.9%,respectively.The CuS coating on the outer surface of the electrically conductive PMIA/PAN fibers prepared under optimized conditions was uniform and complete.The tensile strength and elongation at break of the PMIA/PAN-CuS fibers were about 4.1 c N/dtex,and 15.7%,respectively,and its volume resistivity was 1.13*10^-2Ω·cm,showing good mechanical properties and electrical conductivity.In addition,the EDS of PMIA/PAN-CuS fibers confirmed the presence of Cu and S elements on the surface of the PMIA/PAN-CuS fibers,and the atomic ratio of Cu/S was 1/1.02,which was basically consistent with the theoretical expectation of 1/1stoichiometric ratio.（4）Exploring the potential application of PMIA conductive fabricBased on the flame retardant and high temperature resistance properties of PMIA fibers and the Joule thermal effect of electrically conductive materials,the potential applications of PMIA conductive fabric in electrical heating and pressure sensing were explored.The Ni-DOPA@AgNAs-PMIA conductive fabrics were prepared using the same method in Chapter3,and its potential applications were explored.The Ni-DOPA@AgNAs-PMIA conductive fabric had good surface morphology,its volume resistivity was 1.23*10^-2Ω·cm by using four-probe method,and its conductivity was also proved by LED series lighting experiment.The flexibility and durability of Ni-DOPA/Ag-PMIA fabrics were characterized through repeated half-folding experiments.The Ni-DOPA@AgNAs-PMIA fabrics exhibited good flexibility,and there was no significant change in the real time relative resistance（R/R₀）during 150 times repeated bending.The Joule thermal properties of the flexible Ni-DOPA@AgNAs-PMIA fabrics under constant voltage were studied.When the DC power was connected 100 times repeatedly,the maximum equilibrium temperature of the flexible conductive fabric could be kept stable.The flexible conductive Ni-DOPA@AgNAs-PMIA fabric presented corresponding uniform temperature distribution at different bending degrees.In addition,Ni-DOPA@AgNAs-PMIA fabric,with specific shape,could still work normally under constant supply voltage.The potential application of Ni-DOPA@AgNAs-PMIA fabrics in electric heating（hypertherapy）was explored,the flexible conductive Ni-DOPA@AgNAs-PMIA fabric could be used as the heating device for water heating and human joint hyperthermia.In addition,Ni-DOPA@AgNAs-PMIA conductive fabric could also be used in the field of wearable pressure sensors to detect the movement of human joints,the pressure sensor exhibited stable and repeatable response during cyclic bending tests of the joint under different bending conditions.