Study On The Preparation Technology, Structure And Properties Of Carbon Fiber From Cnts Reinforced Lyocell Fiber

With the characteristics of smooth surface.circular cross section,uniform skin-core structure, controllable linear density and high intensity.orientation degree and crystallinity,Lyocell fiber can be used as the precursor for making cellulose-based carbon fiber.It is well known that the mechanical properties,especially intensity, of the precursor or the final carbon fiber can be reinforced by introducing sonme appropriate additives into it.As a potential additive,carbon nanotube is favorited owing to its high young's modulus,hardness,flexibility,electrical conductivity and large draw ratio,which has been used to improve the mechanical properties of Lyocell fiber so as to receive high intensity cellulose-based carbon fiber.In order to inhibit the production of levoglucose and increase the final char yields,the cellulose fiber must be pretreated with catalyst.The main purpose of this study is to discuss and determine the most appropriate catalyst for Lyocell/CNT composite fiber.to analyze the structure and performance changes in the process of low temperature heat treatment and carbonization and compare that with Lyocell-based carbon fiber prepared in the same conditions,so as to prove the feasibility to prepare high intensity cellulose-based carbon fiber using Lyocell/CNT composite fiber as the precursor.In this paper.the research situation of viscose fiber.Lyocell fiber and their carbon fiber was introduced.the changes of structure.performance and products in the process of heat treatment and carbonization of cellulose fiber were interpreted,and the influence factors on the yields and properties of cellulose-based carbon fiber were also summarized.Firstly.recognizing the important role that catalysts play in manufacturing cellulose-based carbon fiber,we successfully perepared new cellulosed-based carbon fiber enhanced by carbon nanotubes from Lyocell/CNT composite fiber using N,P containing catalysts.The technologies of TG, elementary analysis and mechanical properties testing were used to evaluate the catalytic conditions such as catalyst kinds, concentration and ultrasonic treatment. The most suitable catalyst for Lyocell/CNT composite fiber was found to be phosphoric acid/urea (P:N= 2:1) with a concentration of 7%, the tensile strength of the carbon fiber prepared from which was 985 MPa. And the order of thermal degradation of this fiber increased from 1.07 to 3.93 and the activation energy reduced from 107 to 99kJ/mol.Secondly, the structure and performance changes of Lyocell/CNT composite fiber in the process of heat treatment and carbonization were studied by means of TG, GC-MS, elemental analysis. XRD. FT-1R and mechanical properties testing, and the catalytic mechanism of phosphoric acid/urea was also analyzed. The results showed that the thermal decomposing temperature was decreased and the char yields were increased, the generation of CO2 in the pyrolysis was promoted and the levoglucose was restrained significantly after the impregnation with catalysts. Along with the low temperature heat treatment and carbonization, the H content in the fiber was gradually decreased, the C content was increased, the stretching vibrations of OH, C-H and H-O-H were degraded, and the stretching vibrations of C=O, C=C were observed. In this process, the crystallinity and tensile strength of the fiber were firstly decreased and then increased, and they were 18.74% and 985 MPa when the temperature rose up to 1300℃.At last, the properties of Lyocell/CNT composite fiber, Lyocell fiber and their carbon fibers were comparatively studied through the above characterization methods and SEM. The results showed that the thermostability of Lyocell/CNT composite fiber was poorer, but its carbon content, crystallinity and tensile strength were all superior to those of Lyocell fiber. And the carbon content, crystallinity and tensile strength of Lyocell/CNT carbon fiber were increased respectively by 2.62%,10.24% and 171 MPa compared to Lyocell-based carbon fiber. In addition, the two precursors and their carbon fibers were all with bright and clean surfaces as well as similar circular cross sections, without obvious holes and defects.