A recyclable strategy for the preparation of monolithic porous carrageenan

Polysaccharides can be regarded as sustainable materials during utilization and disposal. However, this is not the case in their extraction processes. For instance, substantial amounts of alkali (e.g., NaOH and KOH) and heating energy are consumed in the extraction of κ-carrageenan, and polluted water is generated concomitantly. In this study, a light-weight thermal insulation material was prepared from κ-carrageenan, and a recycling strategy was developed as an alternative to degradation to improve the utilization efficiency of κ-carrageenan. In the preparation of monolithic porous κ-carrageenan (MPC), glyceryl monostearate (GMS) was used as a micro-bubble stabilizer for the stirred κ-carrageenan solution, followed by gelation and ambient pressure drying (APD). When the weight ratio of GMS to κ-carrageenan reached 0.5, the MPC exhibited the lowest density of 0.038 g·cm⁻³ and a thermal conductivity of 0.0400 W·m⁻¹·K⁻¹. Subsequently, this sample was subjected to 3 regeneration cycles; Fourier‑transform infrared spectroscopy (FTIR) and thermal conductivity analyses revealed no significant changes in the characteristic chemical bands and thermal insulation properties of recycled samples. Another advantage of MPC is that water was used as the sole solvent during both its preparation and recycling, with no organic solvent waste generated. Consequently, the recycling strategy not only provides novel insights into advancing the sustainable application of bio-based materials, but also improves the economic potential of such materials.