Uniformly crosslinked algal bioplastic with triggerable decomposition in salt water

Abstract

Addressing marine pollution caused by single-use plastic waste has become an important sustainability goal for preventing ecological hazards caused by microplastics. This work focuses on the reversible crosslinking of dehydrated, sodium alginate plastic films and their selective degradation in seawater into benign byproducts. Films are crosslinked by divalent ions, Ca²⁺ and Sr²⁺, via the hydrolysis of CaCO₃ and SrCO₃ by glucono-δ-lactone. The rate of Ca²⁺ release in simulated seawater (3.5 wt% NaCl) is quantified as a function of initial Ca²⁺ concentration. At the highest crosslinking densities, there is a seven-fold increase in the amount of Ca²⁺ released in the presence of salt water compared to DI water. Moreover, the calcium release rate increases more strongly with crosslinking density in salt water than DI water, showing that saltwater promotes the reversible crosslinking of the film into alginate salts that are fully soluble in water. Mechanical properties including elastic modulus and ultimate strength, show improvement with crosslinking density until the ion saturation concentration at which point both properties decrease abruptly. Reversible and selective crosslinking is not limited to Ca²⁺, but extends to other divalent ions including Sr²⁺, which is also demonstrated. Broadly, these results illustrate how noncovalent interactions in naturally occurring biomaterials can be used to create more sustainable plastics with tunable mechanical properties.