MRI investigation of swelling of super absorbent polymer: effects of particle size

Journal article, 2026

Superabsorbent polymers (SAP) are crucial components of hygiene products. Their method of manufacture, particle size, and the presence of ions enable the performance of SAP to be tailored towards different applications. The efficacy of their function could be attributed to the distribution of H2O molecules within the sample, e.g. transporting the liquid away from the skin. We therefore aim to further elucidate this process using magnetic resonance imaging (MRI). Here we utiliszed MRI techniques, relaxation times, diffusion coefficient measurements and 1D profiling, to investigate the distribution of H2O molecules in SAPs while varying particle size and the presence of NaCl in the solution to be absorbed. Through detailed analysis of the MRI results, factors such as the pushed height of the plunger, spatial swelling heterogeneity, and the swelling of the SAP particles could be monitored. As expected, SAP particles swelled less in saline solution. The H2O absorption appeared the most homogenous for the smallest particle size. It shows, in a comparable manner, the position of water and its state in terms of being free or strongly associated. The analytical measures and representative maps of fluid distribution were proved to shed light on fluids absorption in a bed of gelling particles. The results suggest that a homogeneous swelling and a faster H2O absorption might occur with smaller SAP particles. These findings provide valuable insights into fluid transport and mechanical response in SAPs, which are critical for optimising their application in hygiene products.