Properties Enhancement of Waterborne Polyurethane Bio-composite Films with 3-aminopropyltriethoxy Silane Functionalized Lignin

With the aim to enhance the tensile properties and thermal stability of waterborne polyurethane (WPU) film, a comparative study was conducted to investigate the use of unfunctionalized lignin and 3-aminopropyltriethoxy silane functionalized lignin as natural reinforcing filler. The ultimate tensile strength of the WPU film that filled with 0.5 wt% functionalized lignin was found elevated by 9% compared to the unfunctionalized lignin, which was only increased by 0.3%. The functionalized lignin-filled WPU films also becomes more flexible and possess higher deformation resistance (lower Young’s modulus and higher elongation at break) compared to the one filled with unfunctionalized lignin. In addition, the functionalized lignin is proven to reinforce the fabricated bio-composite films without significantly compromising their thermal stability, since the initial degradation temperature (296.79 °C) is comparable to the pristine WPU film (297.40 °C). The Fourier-transform infrared and morphological analyses confirm the formation of extra carbamate, urea and hydrogen bonds between the functionalized lignin and WPU is the main reason for the functionalized lignin to reinforce the fabricated films without significantly compromising their thermal stability. Ultimately, the current findings and proposed chemical reaction between the functionalized lignin and WPU, also serve as a guideline to facilitate the future design and development of other functionalized lignin-based products.