Synthesis of a spherical starch-based superabsorbent polymer and its influence on the microstructure of hardened cement paste

The traditional superabsorbent polymers (SAPs) are usually irregular particles prepared from petroleum derivatives. Additionally, they often encounter issues such as premature water desorption and inadequate water absorption when applied in cement-based materials. This research synthesized a spherical starch-based super- absorbent polymer (SSSP) with stable water absorption using inverse suspension polymerization, analyzed the influencing factors, adsorption-desorption performance and microstructure of SSSP, and investigated its influence on the cement paste. The results indicate that, the factors affecting the sphericity of SSSP are stirring speed, N2 flow rate, dosage of suspending agent, and the mass ratio of organic phase to aqueous phase in sequence. The water absorption and water storage of starch-based SAP are 2.8 times and 1.4 times higher than those of traditional petroleum-based SAPs. The salt (alkaline) resistance of SSSP is enhanced by grafting stronger hydrophilic -SO3H and non-ionic -CONH2 groups, with the former being more readily grafted onto starch. The dried SSSP particles exhibit a smooth surface with a sphericity of 0.98, forming spherical hydrogels upon water absorption. SSSP mitigates 75 % of the autogenous shrinkage of cement paste, with a compressive strength 8.6 % lower than the control group, but still higher than that of other SAP pastes. The voids formed by SSSP desorption are mainly spherical, containing hydration products inside, and the pore distribution in its paste tends towards a smaller scale, with a higher proportion of high-density and ultra-high-density C-S-H.