An Investigation Of The Preparation And Properties Of High Performance Carbon Nanotube Fiber

Carbon nanotubes（CNTs）were found occasionally with the gas phase growth of carbon fiber,but was treated as additional product and did not cause enough attention initially.Until 1991,Iijima（NEC Corporation）found its microstructure formed in the process of arc evaporation of graphite anode and reported for the first time.Since then,CNTs have gradually become a hot spot material in the world.Because of the particularity in its structure and size,CNTs show the excellent properties,its elastic modulus is more than 1 TPa,able to withstand more than 40%of the strains without brittle fracture or covalent bond rupture;Specific tensile strength can be up to 50-200 GPa,more than 50times of steels;It can be resistant to high torque by distortion.To obtain high purity of nanotubes there are many different methods at present,such as laser evaporation,modified arc discharge,chemical vapor deposition（CVD）,and so on.Scientists tried to prepare CNTs macroscopic materials,such as fiber,film and block materials,according variety methods.Among these,fiber,is owned the great application potential,has received the widespread attention in particular.The synthesis methods of CNTs fiber which frequently used are:CVD in situ spinning;Liquid spinning;Array spinning,etc.Individual CNTs had a high tensile strength（13-150 GPa）,but macroscopic fibers exhibit only 0.5-2 GPa and are not suitable for conventional mechanical processing.In this thesis,synthesis of CNTs and their formation into yarns,sheets,and sponges are summarized.The formation of CNTs is very important for developing their applications in different engineering fields.To sum up,the investigation made the following aspects:We report a new substrate line method involving layer-by-layer wrapping of a continuously produced CNTs cylinder for making fibers.These fibers are strong,so they can subject to conventional rolling or twisting for densification.The new fibers have a tensile strength up to 5.5 GPa,in combination with a ductility to 20%,specific modulus to100 N/tex,and electrical conductivity to 6.7×10⁵S/m.This strength is well above those for any other fibers synthesized so far.Our study demonstrates new strategies for performance maximization and large-scale production.And then,an alternative form of energy storage is proposed based on the elastic deformation of CNTs.We report continuous preparation of long CNTs fibers and twisting of the fibers to springs.The prepared long springs have a tensile strength of 325 MPa and/or an energy density of 42.1 J g^-1,both of which are higher than the counterparts previously reported in the literature.Considering their low density and high performance,these new CNTs springs have a great potential for applications in many areas such as automobile,aerospace,and mechanical devices.Based on the substrate line method,the CNTs hollow cylinder is continuously combined with the poly-p-phenylenebenzobisoxazole（PBO）fibers.The wrapping of CNTs can protect PBO fibers from light radiation,especially ultraviolet（UV）light radiation.The more the number of wrapping layers is,the better the protection performance is.After the aging test of being exposed to 500 h of light radiation,the tensile load of PBO fibers is just about 40%of the initial.However,the load of PBO fibers with the multi-layers CNTs wrapping shows no losses.And the anti-aging mechanism analysis,show that CNTs parcel layer can be effective as ultraviolet-visible shielding layer to the application.