Studies On Preparation Of PAN Pulp By Precipitation Method

Polyacrylonitrile Fibers (PAN) have been widely used as consumable textiles and industrial textiles with high heat-resistance and stability to sunlight, to atmosphere and to chemical reagents. Varieties of PAN are produced, one of which is PAN-Pulps. PAN-Pulps have higher special surface area(SSA) than aramid pulps like PPTA-Pulps, and can be blended with rubbers or resins. Compared to asbestos and costly PPTA-Pulps, PAN-Pulps are more competitive and can be widely used in sealed material, friction material and reinforced material.A new way to prepare PAN-Pulps was introduced in the thesis-precipitation method. That is: PAN/DM Ac solutions with different concentrations and viscosity were injected into a rapidly stirred coagulant. A proposal mechanism of the process is that the dispersed drops were elongated, deformed, coagulated and fibrillated, and PAN-Pulps with certain length and SSA were obtained. This method left out the complicated spinning, cutting and milling procedures.First, the properties of PAN spinning solutions were studied via rotating cylinder viscosity and coagulating characteristics. The concentration and viscosity are important to the dispersion and distortion of the PAN/DMAc drops, and to the formation of PAN-Pulps. The viscosities fell rapidly and the value of coagulation rose slightly with increasing solution temperature. The addition of lithium chloride (LiCl) could reduce the viscosity dramatically without decreasing the concentration of polymer.Second, the influence of related parameters on the formation of PAN-Pulps was studied, systemically, including the concentration and temperature of the PAN solution, the concentration and temperature of coagulant, stirring speed and precipitation time. The typical PAN-Pulps have a diameter distribution of 7~20μm, alength distribution of 0.5~2.4mm, a SSA distribution of 35~80m2/g.Third, poly (m-phenylene isophthalamide) (PMIA) was added into PAN/DMAc solution. It has been found that PMIA is compatible with PAN dynamically, but it is incompatible with PAN thermodynamically. The SSA of PAN-Pulps can be unproved by 30-50% compared to pure PAN/DMAc solution, due to the microcosmic phase separation and the different coagulating properties between PAN and PMIA.New ideas mainly brought forward in this paper are:1) A new approach of precipitation to produce PAN-Pulps;2) Adding LiCl into the PAN/DMAc solution to reduce the viscosity and improve the SSA of PAN-Pulps;3) Blending PMIA into PAN solution to improve the SSA of PAN-Pulps.Liu Yongle (Major: Material Science) Supervised by: Professor Liu Zhaofeng...