Recycling alginate composites for thermal insulation

[Display omitted] •Recyclability is enabled by pH control of chelator and alginate multiple ligands pK.•Cation chelation dismantles the alginate matrix.•Cation release, by chelation inhibition, allows full recovery of the alginate matrix.•Alginate-based thermal insulation material was fully recycled with full functionality.•Multiple recycling cycles are possible (proof of principle). We present a new method for the total functional recycling of alginate-based composite materials made via ionotropic gelation. The original material, an alginate/fiberglass foam with thermal insulation characteristics, was produced following a patented process in which fiberglass waste is embedded into the polyanionic gel matrix, and the resulting compound is then freeze-dried. The functional recycling is carried out by disassembling the ionic matrix – which is initially formed by the interaction between a cation (e.g. calcium) and the negatively charged alginate backbone – with the use of a chelator (Ethylenediaminetetraacetic acid disodium salt) with a high affinity for the cations, thus obtaining a homogeneous solution. An ionotropic gel can then be re-formed upon deactivation of the chelating activity under mild acid conditions. We managed to maintain or improve the thermal, mechanical and acoustic performances of the original material and we successfully tested the possibility of multiple recycling cycles.