Studies On Chemical Silver Plating Process On Fiber Surface Using An Environment Friendly Reducing Agent And The Optimization Of Process Condition

Silver-plated fibers is a kind of fibrous material which is coated with a layer of silver on the fibers surface. Silver-plated fiber has been applied to electrical and clothing field because of its good antibacterial, conductive and electromagnetic performance. Among various kinds of silver plating method, chemical plating is widely used in mass production because of its simple operation and low cost. In chemical silver plating process, the silver ions were reduced, using a reducing reagent such as formaldehyde, to produce the silver atoms and deposited on the fiber surface. However, formaldehyde caused serious pollution to the environment, and also threaten the health of operation personnel.This study is aiming to develop a novel chemical silver plating technology which replaces formaldehyde with environment friendly agent as reducing agent in chemical plating. We firstly studied the chemical silver plating process with several kinds of reduction agent, and identify a potential candidate reduction agent with good efficiencies to replace formaldehyde. And then we optimize the reaction system by changing the complexing agent and adjust process conditions(such as temperature and pH value) to further promote the efficiencies in silver plating.We have studied the silver plating behavior on nylon surface using sodium borohydride,glucose, sodium potassium tartrate tetrahydrate as reducing agent, based on the original technological formula. The results showed that there is few silver on the fibers surface, when the sodium borohydride was used as the reducing agent. The silver content on the fiber surface is2.5 %,the plating efficiency of silver is 15.4 %. The obtained silver fiber is in an ashen color. If sodium potassium tartrate tetrahydrate was used as reducing agent, the silver content of silver-plated fibers is 4 %; the efficiency of the silver plating process is 25 %. The prepared fiber is in a yellow color without metallic lustre. The silver content of silver-plated fibers which is produced by using glucose as reduction agent is up to 7 %, the efficiency of silver plating reaction reaches 43.8 %. The silver-plated fibers show bright metallic lustre. The resistance of the fiber is about 1200 ?/10 cm. It is possiblely that the reducing ability of sodium borohydride is too strong and leads to the reduction rate much higher than deposition rate and silver cannot grow on the fiber. The reducing ability of sodium potassium tartrate tetrahydrate is too poor and the reaction rate is slow. Comparing these three silver-plating process, it was shown that thecontent of silver on the fiber surface and silver-plating efficiency is much larger when glucose is used as reducing agent than that in the cases using sodium borohydride and sodium potassium tartrate as reducing agent. Therefore, glucose is a better candidate for the silver plating reaction.We speculate that glucose would be a new reducing agent which is more environment friendly, to replace formaldehyde used in the chemical silver plating reaction.We then optimize the reaction system and technological process of silver plating reaction using glucose as reducing agent. The results showed that best silver plating efficiency can be achieved when using ammonia and chelating reagent B as a mixed complexing agents. The optimal reaction condition is: molar ratio of ammonia and silver ions is 2, concentration of B is6.1 × 10-4 mol/L, temperature is 30 ?, pH is 10, reaction time is 90 min. On this condition,The resistance of the obtained silver fiber is about 140 ? / 10 cm; the silver content is 15.5 %;the efficiency of silver plated reach up to 96.5 %. The color of fiber is silver white. In addition,we use a thermal treatment to further improve the conductivity of the silver plated fibers. In this post treatment process, the obtained silver fiber was annealed under Na2CO3 solution at various temperatures. Results showed that the resistance of silver fiber can be further reduced to 100 ? /10 cm, after annealing the fiber at 80 ? for 20 min The color of fiber is slight-yellow.Comparing with the fibers produced by formaldehyde, the conductivity of the new fibers produced using the current method is a bit higher, and there are not obvious changes in color of the fiber after thermal treatment. The currently developed method has been used to pilot scale test.The properties of silver plated fiber are depend on the reduction rate of silver ions and the deposition rate of silver growth on the surface of fiber. The deposition rate is related to the surface structure of the fiber, reduction rate is influenced by multiple factors. In the reaction system which adding adding ammonia and chelating reagent B as a compound complaxing agents, chelating agents moleculars and silver ions form and reducing the concentration of free silver ions. The reduction rate is adjusted effectively and match to the deposition rate of silver on the fiber. It makes silver deposite on fiber surface stably and the fibers has good electrical conductivity eventually.