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Designing Index of Void Structure and Tensile Modulus in Wet-spun Poly(acrylonitrile) Proto-fibres. Part II: Synergistic Effect of Dope Non-solvent Concentration and Jet Draw Ratio

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Synergistic effects of dope non-solvent concentration and jet draw ratio of poly(acrylonitrile) on as-spun fibre void structure and tensile properties were investigated and rationalized based on a modified designing index, namely CXrrJ. The notations C, X, and T] are the non-solvent diffusion coefficient normalized by the solvent diffusion coefficient through the proto-fibre, a parameter defined by solubility differences among the system components and jet elongation viscosity, respectively. An increase of dope non-solvent concentration enhanced CXrr1 leading to minute porosity decrease. On the other hand, the simultaneous dope non-solvent concentration and draw ratio increases up to 5 vol% and 4, led to reduction of CXrr l and therefore to severe fibre porosity . The modulus-porosity relationship of the free drawn fibres were best fitted with the Wangיs second order equation E =Eoe-(ap+bp2) (R2 = 0.96) and hence assigned to liquid -liquid de-mixing as the governing phase separation mechanism. On the other hand, the mechan ical behaviour/porosity of proto-fibre containing non-solvent in their dope and drawn with the draw ratio value of 4 was best fitted with the Eshpriegיs first order equation, E =Eoe-ap (R2 = 0.97) and accordingly assigned to the solid-liquid based phase separation . Where Eo and p are modulus of the virgin sample and its porosity , respect ively, while a, and b are the Eshprieg יs and Wangי s equation constants.

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