A superabsorbent polymer (SAP) is a special polymer material that can absorb up to 500 times its own weight of pure water, but has a problem that it does not biodegrade itself and cause environmental pollution. Therefore, we aim to prepare a biodegradable SAP by using biomass-based IA. The SAP must be able to retain absorbed water and absorb water under a given pressure. We have carried out studies to improve the surface hardness of the SAP to enhance absorption of water under a given pressure by surface-crosslinking. Four types of surface-crosslinkers, ethylene glycol diglycidyl ether (EGDGE), ethylene carbonate (EC), 1,4-butanediol (BD), or glycerol, were used. We confirmed the water absorption capacity of the SAP by measuring its centrifuge retention capacity (CRC) and absorbency under load (AUL). The structural characteristics of the SAP were confirmed by attenuated total reflection (ATR) and X-ray photoelectron spectroscopy (XPS), and the surface characteristics were confirmed by scanning electron microscopy (SEM).

An elaborate surface-crosslinking method was introduced to enhance the low absorbency under load (AUL) and liquid permeability of itaconic-acid-based superabsorbent polymer (SAP). The effects of the surface-crosslinking reaction parameters of the absorption properties of the SAP were investigated. An increase in the content of distilled water and 1,4-butanediol used as the surface-crosslinking solution improved the AUL and liquid permeability of the SAP, whereas an increase in the distilled water content resulted in a sharp decrease in the centrifuge retention capacity (CRC) of the SAP. Therefore, controlling the content of 1,4-butanediol is an effective strategy to improve the AUL while maintaining the CRC of the SAP to some extent. Increasing the surface-crosslinking temperature tends to decrease the CRC of the SAP. The AUL of the SAP is the highest at a reaction temperature of 160 °C. As a result, the SAP prepared under optimal surface-crosslinking conditions showed a CRC, AUL and liquid permeability of 36.0, 27.2 g g -1 and 80 s, respectively. The cell viability and cytotoxicity of the SAP on human dermal fibroblasts were confirmed using a live/dead assay and the adapted method from the ISO 10993-5 protocol. These investigations suggested that itaconic-acid-based SAPs could be potential materials for diaper products.

Itaconic acid‐vinyl sulfonic acid based super absorbent polymer (SAP) was synthesized by aqueous solution polymerization using ammonium persulfate as the initiator, tetra (ethylene glycol) diacrylate as the internal crosslinking agent, and sodium hydroxide as the neutralizing agent. Surface‐crosslinking was introduced to improve the low absorbency under load of the itaconic acid‐based SAP. Hollow glass microspheres were added during surface‐crosslinking to improve the absorption properties and permeability of the SAP. Hollow glass microspheres increased the specific surface area of SAP and acted as an incompressible filler resulting in the improvement of gel strength and the relief of gel blocking by preventing adhesion between SAP particles. The surface‐crosslinked SAP with 2 wt% hollow glass microspheres showed the highest permeability and absorbency under load. The absorption rate of the synthesized material was also increased.