A Comparative Evaluation of Alginate and Maltodextrin as Binder Systems for Cast Sodium Chloride (NaCl)-Based Composites

In arid, desalination-dependent regions, byproduct sodium chloride (NaCl) presents both an environmental burden and an unexplored feedstock opportunity. The intensive sourcing and disposal of conventional materials is increasing the need for sustainable alternatives. This study investigates the transformation of sodium chloride (NaCl) into a cast composite made with biodegradable, carbohydrate-based binders, using lab-grade NaCl as a standardized proxy for brine-derived salt; no brine-derived salt was tested, and biodegradation was not evaluated. Eight formulations using sodium alginate and maltodextrin binders at 0%, 5%, 10%, and 15% w/w dry solid concentration were evaluated for moldability, flexural and compressive strength, hygroscopic mass gain, and dimensional shrinkage. Specimens were hand-cast in silicone molds and cured for 14 days (25 °C, 50% RH), with flexural strength tested on prisms, compressive strength on cubes, and hygroscopic mass gain measured after 14 days at 70% RH. Maltodextrin at 5% achieved optimal performance (4.09 MPa flexural, 5.88 MPa compressive), while all alginate formulations underperformed, with the best (5%) reaching only 1.10 MPa flexural and 2.88 MPa compressive. This could be attributed to incomplete Ca2+ diffusion under surface-spray cross-linking used in this study. Differences between binder systems were statistically significant (pooled flexural p < 0.001; compressive p = 0.003), and all formulations remained stable below the 75.3% NaCl deliquescence threshold (70–75% RH). These findings establish a flexural dataset for hand-cast NaCl composites, comparative evaluation between 2 different binder formulation-and-process systems, and show optimal binder concentrations diverge from digitally fabricated literature (11–20%). Maltodextrin outperformed alginate under the water contents and cross-linking protocol tested; these results do not isolate binder chemistry. The results indicate material-level feasibility only; validation with salt recovered from actual desalination brine is left for future work.