The Preparation Of The Precursor And Preoxidized Fibers Of PAN/PPG Blends And The Study On Their Structures And Properties

Polyacrylonitrile(PAN)-based carbon fiber is a new-style raw material with high tenacity, high modulus, heat- resistance, corrosion resistance, and a series of excellent performances. It is the most versatile carbon fiber with a promising prospect. In the last decade, although the industry of Polyacrylonitrile-based carbon fiber in our country has developed rapidly, there are large gaps in the properties and production of PAN-based carbon between home and abroad. The key factor is the property of the precursor. Experts think that PAN precursor modified through a solution blending method can be used to improve effectively the performance of carbon fiber. Polypropyleneglycol (PPG) is a macromolecules compound containing hydroxyl, avirulent and harmless. In this thesis, PAN precursor was modified by PPG to rein in blending fibre density, reduce fiber interior holes, and improve mechanical properties of carbon fiber. The research in this paper is summarized as follows:1. The mixture solution was prepared by blending the PPG and PAN in DMSO. The static and dynamic rheological behavior of the solution was investigated. The result of static rheological experiment showed that the PAN/PPG composite solution exhibited non-newtonian shear thinning phenomenon. In a certain concentration and shear rate, the increase of PPG content, the viscosity reduced, sticky system flow activation energy increased, and non-newtonian index increased, and structure viscosity index decreased. The result of dynamic rheological experiment showed that the dynamic rheological curve and the static flow curve were similar. As the temperature increasing or PAN solid content decreasing complex viscosity drops. Meanwhile, complex viscosity still decreased with the increase of angular frequency or PPG content. As the increase of the PAN system temperature or add PPG, the intersection of storage modulus (G') and loss modulus (G") moved in the direction of higher angular frequency, which indicated that the solution have the tendence to keep flow in the same angular frequency. These results have great significance for subsequent spinning moulding.2. The as-spun fibers and the PAN fibers were prepared via dry-wet spinning process. The structures, shape and properties of the as-spun fibers and the PAN fibers have been studied by LM, XRD, FTIR, TGA and mechanical properties test. The results showed that proper addition of PPG helped the cross section of as-spun fiber rounded, and helped improve the crystallinity of the as-spun fiber and precursor as well. The O-H nearby 3442cm-1 expansion function was stronger and shifted to the low wavenumber, which indicated that a hydrogen bond could be formed between PPG and PAN. The addition of PPG did not affect the thermal performance of the PAN fibers, so as not to widen the exothermic peak effectively, but it could improve the mechanical properties of PAN fibers. In general, when PPG was 2wt%, fiber comprehensive performance was the best.3.2wt% of the modified PPG and unmodified precursors were processed of preoxidation and carbonization. Morphology, structures and properties of preoxidized and carbonized PAN fibers are discussed by using SEM, FTIR, TGA, elemental analysis and mechanical test. The results showed that the surface of the modified preoxidization fibers was more homogeneous and dense, and fewer holes, so internal uniform carbon fibers could be obtained. As preoxidation temperature raises, the N≡N, C-H groups of preoxidization fibers content decreased. Meanwhile, the absorption peaks of cyclization structure increased. No matter whether PPG was added, the C, H, N content of PAN fiber slightly reduced in preoxidation phase, while O content rises considerably. The thermal properties of preoxidization fibers did not be affected, but with the proper addition of PPG, the mechanical properties of modified PAN fibers were improved.