Phase behavior, interaction and properties of acetic acid lignin-containing polyurethane films coupled with aminopropyltriethoxy silane

A series of novel acetic acid lignin-containing polyurethane (LPU) films coupled with aminopropyltriethoxy silane (APTS) (LPUSi) or the mixture of APTS and trimethylol propane (TMP) (LPUSiT) were prepared. With 2% APTS addition, the crosslinking density increased, and the resultant films were endowed with good mechanical properties and water resistance. It was also found that the hydrogen bonding interaction between –NH and –C=O of urethane was destroyed, and new hydrogen bonds between APTS and LPU were formed. However, when APTS content was greater than 4%, significant phase aggregation were detected, resulting in poor mechanical properties and water resistance. In contrast, the crosslinking density, tensile strength and water resistance can be further improved with TMP addition at 2% APTS. The simultaneous addition of APTS and TMP was beneficial for phase mixing and the formation of uniform network. And the surface morphology of LPUSiT films became smoother and more homogeneous.