Preparation And Performance Of Conductive Aramid Fibers

Ordinary fibers, especially chemical fibers, are easy to accumulate staticelectricity, which may result in fire and blasting accidents under flammable andexplosive conditions. However, most of chemical fibers are flammable, and they canmelt into liquid and drip when exposed to heat or fire, which may damage users andburns them. The aramid fiber is a synthetic material made from high performancemacromolecules and it has been widely used in military industry, protection fields andreinforcing fibers in composites due to its outstanding properties, such as thermalstability, chemical durability and mechanical performance. The metal clading aramidfiber is conductive, which can eliminate static electricity, and can be used in theElectro-Magnetic Interference （EMI） shielding and conductive fiber field. The conductivearamid fiber is lighter and softer compared to metal fibers. Surface modification ofaramid fiber is performed by the metalation swelling method before metal depositionby the electroless process. Various metal coated aramid fibers, e.g. Ni-Cu compositecoating and Ag coating of fibers are prepared, respectively in the present work.Furthermore, the performance of metal coated aramid fibers are studied.The conclusions in these investigations are as follows:（1） Metalation swelling method as surface modification of fiber is used beforeelectroless deposition in this work. The aramid fibers were immersed in5gNaH-150gDMSO solution with stirring at30℃for10min. After metalationswelling treatment, numerous nano-scale pits with diameter from50nm to300nmdistribute uniformly on the surface. Furthermore, those nano-scale pits weregenerally considered as “anchoring sites” for metal particles deposition, meanwhileimproved the adhesion between the coating and the fiber substrate.（2） The pretreatment of aramid fibers before electroless plating was as follows:metalation swelling treatment （5g NaH-150g DMSO for10min at30℃）,sensitization （20g/L SnCl₂and20ml/L HCl for10¹5min at30℃）, activation （0.3g/L PdCl2and3ml/L HCl for10min at30℃）, neutralizing （NaOH10g/L，HCHO20ml/L; room temperature for2min）.（3） Thermodynamic feasibility of electroless plating Ni and Cu was studied throughpotential-pH diagram. The electroless Ni plating process was investigated byorthogonal experiments. The electroless plating process of Ni is carried out with asolution consisting of NiSO4of25g/L, C6H5Na3O7·2H2O of16g/L, NH4Cl of28g/L, NaH2PO2·H2O of28g/L, SC（NH2）2of2mg/L at a pH of8.5and atemperature of50℃. The kinetic equation of electroless copper plating is obtainedby a regression analysis:r=16.68[Cu²⁺]^0.73[HCHO]^0.64[OH^-]^0.14exp[6.515*（（T-308）/T）The electroless plating process of Cu was investigated by orthogonal test. The bestprocess of electroless Cu plating is CuSO4·5H2O18g/L, HCHO10ml/L,C4H4O6KNa·4H2O45g/L, CH3OH5ml/L, PEG60004mg/L, K4Fe（CN）6·3H2O10mg/L, pH12.5and35℃.The Ni-Cu deposited aramid fiber exhibits goodconductivitywith a surface resistance of0.4/cm. The breaking strength of theNi-Cu deposited aramid fibers was45N, and the strength retention reached up to97%of that of original aramid fibers without Ni-Cu coatings. Thermal-cold cyclingexperiments demonstrate a good adhesion of Ni-Cu coating on the fiber.（4） Thermodynamic feasibility of electroless plating Ag was studied throughpotential-pH diagram. The potential-pH diagram of Ag-H2O system， with doublecomplexes of ethylene diamine and ammonia and composite reductants ofglucose and seignette salt， was drawn. The electroless silver plating process wasinvestigated by orthogonal test. The best combination of processing parameters ofelectroless silver plating includes AgNO3of10g/L, NH3·H2O of60ml/L, C2H8N2of20ml/L, KOH of6g/L, C6H12O6of8g/L, C4H4O6KNa·4H2O of2.5g/L, C2H5OHof40ml/L, PEG（1000） of75mg/L at a temperature of25～30°C. The depositionrate of electroless plating of silver is obtained by regression analysis: r=2.4591[Ag⁺]^0.27[L₁]^-0.25[L₂]^-0.57[C₄O₆H₄²]^0.21[C₆H₁₂O₆]^0.24[OH^-]^0.05exp[4.95*（（T-298）/T） The silver deposited aramid fiber exhibits good conductivity with a surfaceresistance of0.25/cm. The breaking strength of the silver deposited aramidfibers was44N, and the strength retention reached up to95.7%of that of originalaramid fibers without silver coatings. Thermal-cold cycling experimentsdemonstrate a good adhesion of silver coating on the fiber.（5） The anti-tarnish capability of silver coatings was improved significantly aftertreated with Benzotriazole and Acrylic resin.