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Thermal insulation materials represent one the most straightforward, yet effective, technologies for improving the energy efficiency of buildings (and not only) – one of the key strategies for reducing carbon emissions. Natural-based materials and downcycled industrial and agricultural waste, thanks to their potentially reduced environmental footprint, have already made their way up to the market with the aim of limiting the ever-growing waste stream generated by the industrial sector. Research efforts on the topic are currently mainly focused on developing new insulation solutions, in which waste is reconverted as a new valuableresource. Carbohydrates, such as alginate, cellulose or chitosanare currently extensively studied base materials for thermal insulation systems, in the form of aerogels or as low-impact binding agents in waste-filled panels. Unfortunately, little or no attention has been paid to the end-of-life fate of these recycled materials; disposal (or incineration) still represents the only available option. This unprofitable scenario is even more critical in the case of polysaccharide-based composites specifically developed to reuse industrial waste.
The authors developed a recycling process for an alginate-based thermal insulation foam, in which the original material is fully recovered and the thermal and acoustic insulation performances are maintaine. The original foam is produced with a patented process in which alginate is used as the host poly-anionic matrix for industrial fiberglass waste. Upon addition of a cation (calcium), the alginate is capable of forming a gel via ionotropic gelation due to electrostatic interaction with its negatively charged backbone. The dried foam is finally obtained by freeze-drying. The recycling process starts with the addition of a water solution of a chelator (Ethylenediaminetetraacetic acid disodium salt, EDTA-2Na) which possess a higher affinity toward the cation. This results in the cation chelation in the disassembling of the material alginate matrix; a homogeneous solution is thus obtained. Upon deactivation of the chelator via acidification, the cations become available to crosslink the polymer. With a subsequent freeze-drying step, the recycled foam is re-obtained. As a proof of concept, an alginate was used as the polyanion; however, in principle, any composite material based on a matrix made via ionotropic gelation can be recycled with this process.
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Retrieve article
Recycling alginate composites for thermal insulation, M. Cibinel, G. Pugliese, D. Porrelli, L. Marsich, V. Lughi, Carbohydrate Polymers 251, 116995 (2021); doi: 10.1016/j.carbpol.2020.116995
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