Development of blend films from soy meal protein and crude glycerol-based waterborne polyurethane

• Blended crude glycerol-based waterborne PU (CGWPU) with soymeal-derived protein (SMP).
• Good compatibility between SMP and CGWPU was found.
• Water resistance and thermal stability were improved with increased CGWPU content.
• Increased CGWPU content caused higher tensile strength and lower elongation of film.
• Blending SMP with CGWPU or Minwax urethane obtained films with similar performance.

In the present work, crude glycerol-based waterborne polyurethane (CGWPU) was used to modify soymeal-derived protein (SMP) with improved tensile strength and water resistance. SMP–CGWPU blend films were successfully prepared by casting the aqueous dispersions of SMP and CGWPU. The effects of CGWPU content on the structure and properties of the resulting films were investigated by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile tests, and water uptake measurements. Good compatibility was observed in the blend films, which resulted from strong intermolecular interactions, such as hydrogen bonding, that existed between SMP and CGWPU. With increasing CGWPU content, SMP–CGWPU blend films had improved water resistance, thermal stability, and tensile strength, but had decreased elongation at break. The performance of SMP–CGWPU blend films was comparable to the SMP films blended with commercial oil-based Minwax urethane (MU).