Swelling of superabsorbents polymers in an aqueous medium

The Effect of SCMs in Blended Cements on Sorption Characteristics of Superabsorbent Polymers

Supplementary cementitious materials (SCMs), such as fly ash (FA) and ground granulated blast-furnace slag (GGBS), are often used as a partial replacement of cements to improve the sustainability of Portland cement-based materials and reduce their environmental impact. Superabsorbent polymers (SAPs) can be successfully used as internal curing agents in ultra-high performance cementitious materials by facilitating the hydration process and controlling the water supply in both fresh and hardened states. This paper intends to characterise the physical and chemical properties of SAPs and their sorption properties in different blended cement environments. The swelling capacity and kinetics of absorption of three superabsorbent polymers with different chemical compositions and grading were tested in different cement environments. Experimental results of their sorption performance in distinct solutions, including deionised water (DI), Portland cement (PC), and blended cements (PC-FA and PC-GGBS) and changes in pH of different solutions over time were investigated. The results showed that PC-FA solution had the lowest pH followed by PC-GGBS solution. Moreover, SAPs samples displayed the highest absorption capacities in PC-FA solutions, and the lowest swelling capacities were found in PC-GGBS solutions. Furthermore, SAP with smaller particle sizes had the greatest absorption capacity values in all solutions.

Pretreatment of used disposable nappies: Super absorbent polymer deswelling

Typical used disposable nappies usually consist of nonwoven fabrics, Super Absorbent Polymer (SAP), and organic material, namely fluffy pulp, urine and/or excreta. Currently, this waste stream is being disposed to landfills causing many environmental issues. An alternative management method could be the valorisation of the biodegradable material through anaerobic digestion, and the recycling of plastics and SAP. Pretreatment of nappies is mandatory to separate SAP and plastics from the organic material. The aim of this work was the development of a process to minimize SAP's volume, as this component can swell up to 1500 times its own mass by water absorbance, thus hindering any further biological process. CaCl₂, MgCl₂, and a range of CaCl₂/MgCl₂ combinations were tested against their deswelling efficiency on SAP, residual reagent concentration and reagent cost. The mixture of 20% CaCl₂ and 50% MgCl₂ (w/w) of SAP was concluded as the suitable combination of salts achieving a final SAP volume reduction of 92.7% with low residual cation concentrations and minimum cost. The physicochemical characterization of nappies' hydrolysate that took place to estimate its adequacy as substrate for anaerobic digestion resulted to a COD:N ratio within the acceptable range for a subsequent anaerobic digestion processing.