Study On Oxidation Characteristics Of Various Mesophase Pitch Based Fibers

Compared to other kinds of carbon fibers,carbon fibers based mesophase pitch has the property with high modulus,good thermal conductivity and thermal conductivity and so on,because the microstructure of mesophase pitch fibers are longitudinally oriented well along the fiber axis.P reoxidation as a key process among the preparation of carbon fiber,both controlling the appropriate degree of oxidation and optimization of oxidation process are very critical for the properties of carbon fiber and the production efficiency.In adiition,pitch is a complex mixture of polycyclic aromatic hydrocarbons.However,the Influence of diversity of pitch on the oxidation of mesophase pitch fibers is not reported detailed currently.The main content of this paper is to study the oxidation characterist ics of mesophase pitch fibers from different raw materials,so as to provide a reference for the formulation of oxidation process in production practice.In this paper,pitch fibers that prepared by melt spinning precursor through different raw pitch were studied by thermogravimetric analysis(TGA),scanning electron microscopy(SEM),electron probe micro-analysis(EPMA),thermo-mechanical analysis(TMA),nanoindentation and so on.,systematically studied the oxidation properties of mesophase pitch fibers from d ifferent angles,and focus on how raw material,oxidation process parameters affect the stabilization.The oxidation characteristics of five different mesophase pitch fibers were investigated systematically under isotherm(230℃,250℃,270℃)and gradual heating(3℃/min and 0.5℃/min)conditions by TGA.The experiment results indicated that oxidation characteristics of mesophase pitch fibers is mainly decided by the asphalt material,and mesophase pitch fibers with lower softening point exhibited an initial weight gain at a lower temperature,and kept gaining weight more rapidly,showing higher oxidation reactivity,in both isotherm and increasing temperature modes.Reduced heating rate and richer oxygen concentration(pure oxygen)both promoted the oxidation of the pitch fibers,especially for those with high oxidation reactivity.The examination of carbon fibers which produced from different raw materials and oxidatived in various conditions by scanning electron microscopy(SEM)shows that the morphologyof carbon fiber have a great relationship with raw pitch.In general,pitch fibers with high oxidation reactivity could accomplish oxidative stabilization more easily,with no adhesion or melting observed in the resultant fibers after carbonization,but more easily have defect because of excessive oxidation.The oxygen distributions in the mesophase pitch fibers after oxidation were investigated by EPMA,the results shows that oxygen distributions were decided by raw pitch and were affected by oxidation process parameters.In general,pitch fibers with high oxidation reactivity increased the gradient of oxygen led to skin-core structure.Both reducing the heating rate,and oxidating in 100% oxygen can increase the oxygen content of fibers,depress the radial gradient of oxygen,and weaken the skin core structure of oxygen element distribution.And oxygen distribution was more uniform when fibers were oxidation under oxygen.Micro hardness and modulus of fibers obtained from nanoindentation test indicated that the test on radial mechanical properties and distribution of crystallite structure of carbon fibers become possible.The study found that the indentation of oxidized fiber is obvious,shows plasticity,but indentation of carbon fiber almost completely disappeared finally,shows elasticity.