Effects of coagulation conditions on properties of multifilament fibers based on dissolution of cellulose in NaOH/urea aqueous solution

Effects of coagulation temperature, coagulants, and wet-spinning methods on structure and properties of novel regenerated cellulose (RC) fibers prepared from cellulose in 7.5 wt % NaOH/11 wt % urea aqueous solution on pilot scale spinning machine by one- and two-stage coagulation were investigated by tensile testing, optical microscopy, scanning electron micrograph, and wide-angle X-ray diffraction. The results indicated that H₂SO₄/Na ₂SO₄ and H₂SO₄ aqueous solutions are potential coagulants for NaOH/urea system and fibers wet-spun from the two-stage coagulation obviously exhibited the better mechanical properties than those from the one-stage coagulation. The optimal coagulation conditions for two-stage coagulation are 10 wt % H₂SO₄/15 wt % Na ₂SO₄ for the first coagulation bath and 5 wt % H ₂SO₄ for the second bath or 5 wt % H₂SO ₄/15 wt % Na₂SO₄ for the first coagulation bath and 10 wt % H₂SO₄ for the second bath. Moreover, the tensile strength of novel fibers increased with a drop in coagulation temperature. The diffusion rate between the coagulant and solvent plays a major role in determining the mechanical properties of the cellulose fibers. Our spinning process was quite different from that of the viscose process, in which orientation and coagulation proceed more or less simultaneously. The production method of this fiber wet-spun could be suitable in the wide range of coagulation conditions, compared to the viscose one.