Structure and properties of composites compression-molded from silk fibroin powder and waterborne polyurethane

The degummed silk filament was pulverized with a home-made machine to obtain the silk fibroin (SF) powder with the diameter of around 3 µm. The resulting SF powder was blended with waterborne polyurethane (WPU) aqueous dispersion, and then was dried and compression-molded to prepare novel blended materials with improved miscibility and mechanical properties. WPU acted as a plasticizer and one of the components for the blends during the compression-molded process. The structure, morphology, and properties of the blended films were investigated. The results indicated that β-sheet of SF existed in the blended films. The SEM images showed that the cross-section of the blended films exhibited an overall homogeneous morphology. Furthermore, the transmission electron microscope observation exhibited that some sphere-like SF particles were well dispersed in the WPU matrix. The hydrogen bond interaction between SF and WPU in the blended films led to an increase of the glass transition temperature for the soft segment of WPU in the blended films. The blended films showed an improved Young's modulus and tensile strength from 1.2 to 288.9 MPa and 0.3 to 16.5 MPa, respectively, with the increasing of SF up to a content of 70 wt%. The hydrogen-bonding interactions existing in SF and WPU and compression molding method played the important role in improving the miscibility and mechanical properties of the blended films. Copyright © 2011 John Wiley & Sons, Ltd.