Clarity of films from wool keratin

The keratin in wool is a highly crosslinked protein. The high molecular weight, crosslinked structure prevents its shaping into films without extensive decomposition. Since the crosslinks are -S-S- bridges, reducing agents can break them up, resulting temporarily in lower molecular weight polymers. In this work, wool fibers are pretreated with an aqueous solution of various reducing agents to open the disulfide bonds, and then pressed into films at 130-150 degrees C and pressures of 41.7-66.7 MPa in a hydraulic press. The optimum conditions to obtain clear, transparent films include using Na2SO3 in aqueous alcohol solutions before pressing 135 degrees C and 55.6 MPa.