Question

Explain the process that occur in a coagulation bath, use PAN as an example.

Answer 1

The PAN fiber was produced using a simple dry - wet spinning process where the polymer solution was extruded through an air gap following by coagulation process. The formation of PAN fiber was controlled by coagulation temperature inside the bath and the jet stretch. Low coagulation bath temperature was responsible to retard the coagulation rate and controlling the diffision of solvent and non-solvent inside and at the surface of the PAN fiber. Stretching was applied to the as-spun fiber in order to align the molecular chain along the axis thus increases the crystallinity of PAN fiber and to help in raising the Young's modulus. The crystallinity of PAN fiber was determined using X-ray diffraction. The mechanical properties of PAN fiber such as Young's modulus and tensile strength were examined in order to investigate the effect of coagulation bath temperature and jet stretch. The PAN fiber produced at a 15 C coagulation bath and 3 jet stretches exhibited the highest tensile strength and Young's Modulus of 0.96 GPa and 5.21 GPa.

An another study on Physical properties of thermal regulating polyacrylonitrile (PAN) fibers prepared at different concentration of coagulation bath were tested to investigate influences of coagulation bath on properties of the fibers.

Results indicated that linear density of the fibers increased, breaking strength, thermal shrinkage and boil water shrinkage decreased while elongation first increased and then decreased with the increasing of mass fraction of sodium thiocyanate (NaSCN) in coagulation bath.

The optimum NaSCN concentration in coagulation bath should be 10%. Fibers prepared under the above NaSCN concentration showed good mechanical and thermal properties, and the breaking strength was 1.35 cN/dtex, the enthalpy was 26.0 J/g and the thermal efficiency was 78.4%.