Preparation of poly (vinyl alcohol)/gelatin composites via in-situ thermal/mechanochemical degradation of collagen fibers during melt extrusion: effect of extrusion temperature

By in-situ degradation of collagen fibers into gelatin under the thermal/mechanochemical effects of the extruder, PVA/gelatin composites were successfully prepared using PVA and collagen fibers derived from cattle hide limed split wastes as raw materials. The effect of extrusion temperature on the degradation of collagen fibers and the thermal processability and mechanical properties of the composites were studied. The results showed that the controllable degradation of collagen fibers in extruder could be realized by adjusting the extrusion temperature. Particularly, high extrusion temperature promoted the generation of low-molecular-weight gelatin and the esterification between the hydroxyl of PVA and the carboxyl of gelatin, as well as the hydrogen bonding between O-H, C = O, N-H in gelatin and water or O-H in PVA, thus endowing gelatin with the good compatibility with PVA, and significantly increasing the content of non-freezable bound water in system. Ascribing to the plasticization of the gelatin with lower molecular weight and more non-freezable bound water, PVA/gelatin composites exhibited the improved thermal processability and the decreased mechanical properties with the increase of extrusion temperature. Even so, the tensile strength and Young’s modulus of the composite obtained at 175 °C still above 40 MPa and 1.0 GPa respectively, satisfying some practical applications.