Fabrication Method Of Ultra-Fine Metal Fibers And Particles By Plastic Processing Process And Their Application

In this thesis, a novel method based on plastic processing process and equipment for preparing ultra-fine metal fibers and particles was researched. By using this new method, both ultra-fine metal fibers and particles can be produced by using the same plastics processing equipment. Based on this method, polymer composites with improved conductivity were also prepared.Firstly, the dispersion of low melting point alloy (LMPA) in polymer was studied by blending at a temperature higher than the melting points of them. Unfortunately, The LMPA was difficult to be uniformly dispersed in polymer matrix because of its poor compatability with polymer. Then, different polymer matrices were blended with micron scale LMPA powders by twin-screw extruder, followed by die drawing process. Surprisingly, the dispersion of LMPA was improved; and the LMPA particles tend to break into ultra-fine particles in polyethylene (PE) matrix, while they tend to form ultra-fine fibers in nylon6and polyvinyl alcohol (PVA) matrixces by die drawing process.A special PVA with cold-water solubility was used as the polymer matrix for making ultra-fine fibers; and PE was used as the polymer matrix tor making ultra-fine particles. LMPA powders with higher melting point are filled into polymer by twin-screw extruder at a temperature below the melting point of LMPA, followed by die drawing process at a temperature around the melting point of the LMPA. Metal fibers or particles can be obtained after washing away the polymer matrix. Based on the principle, finer or even nano-size metal fibers and particles are possible to produce. During the preparation process, the fibers and particles can be protected from oxidation by the polymers or solvents.A new method for preparing conductive PE composites was developed since LMPA particles can break into smaller particles in PE melt during die drawing process. Firstly, LMPA powders with higher melting point were filled into PE by using twin-screw extruder at a temperature below the melting point of LMPA, and followed by die drawing process at a temperature around the melting point of the LMPA. Then PE/LMPA composites were prepared by using the PE/LMPA filaments obtained by die drawing process. It is interesting to find that the conductivity of the composites could be improved by repeating the die drawing process and adding nano-fillers, even a non-conductive montmorillonite (MMT). The conductivity improving has been attribute to the reducing of metal particle size. It has been found that die drawing process, repeating the die drawing process and adding nano-fillers, such as MMT and Multi-Wall Carbon Nanotubes (MWCNTs), all could reduce the metal particle size in PE matrix. The filaments mentioned above were also used to prepare thermoplastic vulcanizates (TPVs) by blending with elastomeric nano-particles (ENPs). It has also been found that repeating die drawing process, adding small amount of MWCNTs or MMT could reduce the LMPA particle size further during the die drawing process and the conductivity of TPVs was enhanced further as well. Therefore, conductive composites of PE/LMPA/nano-filler with high conductivity and conductive TPVs with low content of conductive fillers are possible to be prepared by using this new method.