PROPERTIES OF FIBERS PRODUCED FROM SOY PROTEIN ISOLATE BY EXTRUSION AND WET-SPINNING

Fibers were produced from soy protein isolate by both wet-spinning and extrusion. In the wet-spinning process, aged, alkaline protein soluti on was forced through a spinnerette into an acid coagulating bath. In the extrusion process, a twin-screw extruder forced a protein isolate- water mixture through a die. The physical properties of the fibers wer e measured at various water activities. The fibers produced by both me thods were brittle and lacked tensile strength (tenacity). The additio n of glycerol reduced brittleness in extruded fibers. Zinc and calcium ions decreased the brittleness of wet-spun fibers. The tenacity of so y fibers was significantly improved by post-spinning treatments, inclu ding acetic anhydride, acetaldehyde, glyoxal, glutaraldehyde, a combin ation of glutaraldehyde and acetic anhydride, and stretching. The best extruded fibers were produced with a mixture of 45% soy protein, 15% glycerol, and 40% water, finished with a combination of glutaraldehyde and acetic anhydride and then stretched to 150% their original length s. The best wet-spun fibers were produced with a 19.61% soy protein su spension at pH 12.1; coagulated in a 4% hydrochloric acid solution tha t contained 3.3% sodium chloride, 3.3% zinc chloride, and 3.3% calcium chloride; and followed by treatment with 25% glutaraldehyde and stret ching to 170% their original lengths.