Fabrication And Properties Of Surface-Silvered Polyimide Fibers

Polyimide fibers are one series of high performance organic fibers that have excellent thermal stability, electromagnetic radiation resistance, chemical corrosion resistance and high mechanical properties, whereas silver particles are famous for superior electrically conductivity and antibacterial property. The combination of polyimide and silver provides a sort of novel electrically conductive organic fibers by using new spinning method or technical treatment. These fibers can be weaved to clothes, twisted to ropes or incorporated to composite materials, thus used in producing heat resistant and fire proof clothing, antistatic and dustproof coats, antibacterial garments, radiation shielding enclosers, electrothermal bandages and smart textiles which are widely used in electrical industry, bioengineering, semiconductive industry, medical textile industry, military industry, and aerospace field. In this dissertation we employed two feasible methods, which are called direct ion-exchange self-metallization technique and surface-modification ion-exchange self-metallization technique, to fabricate surface electrically conductive silvered polyimide fibers. Surface micromorphology, thermal stability, mechanical property, electrically conductivity and antibacterial property were characterized, whereafter the influence factors and related mechanism were investigated.PMDA/ODA-based polyimide fibers were prepared after wet spinning procedure and thermal treatment. Investigation was made on how the spinning conditions influenced the microstructures and mechanical properties of the polyimide fibers. The results showed that the microstructure was related to the length and composition of the coagulation bath. Moderate draw ratio helped to form regular molecular chain structure which was in favor of high mechanical properties. Step-wise heating procedure was beneficial to cycloimidization of PAA to PI and sequentially promoted the mechanical and thermal properties of the fibers. The polyimide fibers could reach a maximum tensile strength, modulus and elongation at break of 820.8MPa,13.4GPa and 17.1% respectively.Direct ion-exchange self-metallization approach was applied in preparation of polyimide/silver fibers. We employed wet spinning process, ion-exchange reaction and thermal treatment to obtain the composite fibers. The polyimide/silver fibers were of superior thermal stability in N2 with T10 over 570℃and inferior thermal stability in air with T10 over 417℃due to the silver particles. The mechanical properties were lower in contrast to pure polyimide fibers, for the existence of silver particles was obstructive to orderly molecular chains structure. The fibers would be electrically conductive (10-1～100Ω/cm) after adequate curing procedure and addition of enough silver amount. Furthermore the polyimide/silver fibers had excellent antibacterial property that more than 99.99% of E.coli bacterial strains were denatured in contact with polyimide/silver fibers after 24h.Surface silvered polyimide fibers were fabricated according to surface modification ion-exchange self-metallization method. After a series of treatments including surface modification in hot alkali solution, ion-exchange reaction in silver ammonia solution and chemical reduction in hydrazine hydrate solution, polyimide/silver fibers with numerous uniformly distributed silver particles on the outer surface were obtained by using polyimide fibers prepared beforehand as substrates,. The fibers were electrically conductive with a surface resistance of 10-1～100Ω/cm owing to a continuous silver layer with a thickness of more than 300nm. The tensile strength and modulus of the polyimide/silver fibers could get a maximum of 1835.0MPa and 33.2GPa respectively, meanwhile the elongation at break was less than 2%,...