Experimental investigation on effects of polyaniline-modified-lignin on cement-based materials: Strength, hydration and dispersion

Abstract

The application of lignin dispersants in cementitious materials has been limited due to its strong retarding effect on cement hydration. In this study, polyaniline modified lignin (PL) was prepared to be as a new lignin additive to increase the dispersion of cement system and maintain good mechanical properties of cementitious materials. This investigation systematically revealed that different contents of PL (0%, 0.5%, 1.0%, 2.0%) had various effects on the early hydration, the work performance and the microstructure of cement paste and mortar. Appropriate dosage of PL was beneficial to achieve better dispersion and improve the fluidity of cement system. The retarding effect on cement hydration was significantly reduced by PL, compared to unmodified lignin. When the content of PL was 0.5% and 1.0%, the mechanical properties of the mortar was maintained as well as mortar without PL. However, excessive content of PL (2.0%) decreased the flexural strength and compressive strength significantly. XRD and TG tests exhibited that no new hydration products were generated and the formation of calcium hydroxide was inhibited after the addition of PL. Besides, SEM and MIP results showed that low dosage of PL could decrease the porosity due to the filling effect. When the dosage of PL in cement exceeds 2.0%, the structure was more loose and porous, attributed to the delayed hydration and air entertainment. The dispersion mechanism was also discussed and ascribed to electrostatic repulsion caused by PL adsorbed on the surface of cement particles and the steric effect due to the branched chains of PL. This study provides a new idea for high-value application of lignin and the promotion of low-carbon building materials by using renewable resources.