Research On Preparation And Performance Of Conductive Aromatic Polysulfonamide Fibers

Common textile fibers are prone to generate and accumulate static electricity,which may act as cognition spark that leads to fire and blasting accidents in flammable and explosive environments.Moreover,most synthetic fibers are flammable and may hurt and burn users.At the same time,electromagnetic radiation has become the fourth major pollution in people's life after the water pollution,air pollution,and noise pollution.Electromagnetic interference and electromagnetic compatibility problems caused by electromagnetic radiation will not only interfere with the normal operation of the electronic equipments,but also pose serious threats to human health.Information security issues caused by electromagnetic leakage will also threaten the national security.Aromatic polysulfonamide?PSA?fiber is the first originally developed high performance aramid fiber with sole intellectual property in China.Functional metal coatings on PSA fiber are of great importance considering the combined properties of the engineering fiber and the metal,thus further enhance the applicability of the fiber as a microwave absorption and reflection,electromagnetic interference shielding,and static charge dissipation material in aerospace,aviation,microelectronics,military industry,and telecommunications.In the present work,the preparation of modified PSA fibers,the pretreatment method of the PSA fibers,electroless silver plating,electroless Ni and Ni alloy plating,and silver electroplating were developed and studied,and then the microstructures,morphologies,and properties of the obtained fibers were thoroughly investigated and discussed.The contents in the present study are as follows:?1?P-phenylenediamine was used to replace 3,3'-diaminodiphenylsulfone,and after appropriate polymerization and wet spinning process,the modified PSA fiber with PPTA chain segment was obtained with higher crystallinity,tensile strength,glass transition temperature,and initial decomposition temperature.The hot drawing process played the most important role in enhancing the fiber crystallinity,crystallization orientation,tensile strength,and glass transition temperature.?2?The pretreatment of PSA fibers before electroless plating is as follows: the chlorine treatment in NaClO solution?pH=3,room temperature,15 min?,the activation in AgNO₃ solution?0.1mol?L?1,75°C,15 min?,and the reduction in NaBH₄ solution?0.25 wt%,room temperature,15 min?.The mechanism of the pretreatment was studied.The chlorine physically absorbed together with the surface chlorination enhanced the affinity of the fiber surface to silver ions.After activation in AgNO₃ solution,AgCl particles were generated in the fiber surface area,and Ag/AgCl interfacial layer was then formed after reduction by NaBH₄.The Ag/AgCl interfacial layer owned excellent activating and anchoring abilities that could enhance the binding between the fiber substrate and the coating.?3?The composition of the electroless silver plating included several complexing agents and two reducers.The mechanism of the silver deposition was studied.Silver adatoms tended to deposit and nucleate in grooves and micropits where silver seeds were located.The deposited silver atoms stacked around the seeds,coagulated together,grew into isolated flat islands.These islands continued to form and grow,not only stacked in the radial direction,but also expanded laterally in a two-dimensional manner over the substrate.They interconnected and gradually covered the whole substrate surface,which then served as autocatalysts for the ensuing deposition.The thickness of the silver plated layer formed by compact crystalline grains was around 300⁴00 nm.The silver plated PSA fibers had an average electrical resistance of 200 m??cm^?1 with an average weight gain of 65.05 wt%.The silver plated PSA fibers exibited good tensile strength,weak paramagnetism,excellent corrosion resistance,and durablility.The electromagnetic shielding performance was excellent especially against the microwave region.?4?Electroless Ni and Ni-P-B plating was carried out by adjusting the concentration of the bath composition and the pH value,and the plating mechanism was also studied.Nickel element in the outermost surface of the coatings existed in its metal state and the Ni?OH?₂ state,while P and B elements mainly existed in their elementary states.The Ni and Ni-P-B plated PSA fibers both had a weight gain of 35.00 wt%,but presented different morphologies and structures due to the codeposition of P,B and Ni.The obtained Ni and Ni-P-B plated PSA fibers also exhibited different performances in electroconductivity,magnetism,eletromagnetic shielding effectiveness,and corrosion resistance,which thus could be used as different electromagnetic shielding and static charge dissipation materials under different application situations.?5?The Ni and Ni-P-B plated PSA fibers remained quite stable in the silver electroplating bath and the silver pre-leaching was then not carried out before the electroplating.Silver electroplating was carried out on Ni and Ni-P-B plated PSA fibers in an electrochemical workstation,where the working electrode was the plated fibers,a platinum wire was used as a counter electrode,and a Hg/HgO electrode acted as a reference.Constant potential deposition was carried out under ?0.45V at which the silver complexing ion began to be reduced.The obtained Ni/Ag and Ni-P-B/Ag plated PSA fibers had the same weight gain?45.05 wt%?after deposition for 60 min at 30°C,which exhibited different surface and cross-sectional morphologies and structures.Ni/Ag plated PSA fibers was ferromagnetic because of the presence of the Ni metal,and Ni/Ag and Ni-P-B/Ag plated PSA fibers showed similar performances in electrical resistance,electromagnetic shielding,thermal,interfacial bonding,corrosion resistance,and durability.The electromagnetic shielding effectiveness of both Ni/Ag and Ni-P-B/Ag plated PSA fibers with lower weight gain was 1²dB higher than that of the silver plated PSA fibers via electroless plating,and was much higher than that of the Ni and Ni-P-B plated PSA fibers.The silver electroplated PSA fibers demonstrated better electromagnetic shielding performance in microwave region.