Investigation on the effects of polyaniline/lignin composites on the performance of waterborne polyurethane coating for protecting cement-based materials

Waterborne polyurethane (WPU) coatings are widely used for the protection of cement-based materials by reducing surface permeability. However, poor mechanical property and moisture permeability caused by good hydrophilicity of WPU coatings limit the protecting application for building engineering. This work has investigated the effect of reinforcing WPU coating with polyaniline/lignin (PL) in protecting cement-based materials. Through the XRD, FT-IR and SEM characterizations, the successful preparation of PL complex has been proved. After the reinforcing of WPU coating by PL, the mechanical property and water contact angle has increased from 1.63 MPa to 2.07 MPa (by 26.99%), and from 72.1° to 116.5° (by 61.58%), respectively. Besides, as shown by capillary water absorption test, the impermeability of mortar with PL-modified WPU (LWPU) coatings has improved, and the capillary water absorption of mortar samples with LWPU coatings at 8 days decreased from 0.3074 mm3/mm2 to 0.1763 mm3/mm2 (by 42.65%). As a result of barrier effect and increased hydrophobicity, the rapid chloride migration (RCM) coefficient of mortar samples with LWPU coatings decreased from 8.52*10−12 m2/s to 6.34*10−12 m2/s by 25.59%. This study demonstrates that PL composites could be used as an effective additive to enhance WPU coating performance in protecting cement-based materials. Such green and effective waterborne coating shows great promises in civil engineering applications.