Valorization of Bio-Derived Calcium Carbonate from Asian Green Mussel Shell Waste in Hydrophobic Coatings for Reducing Pesticide Deposition on Mandarin Orange Surfaces

This study developed an oleic acid (OA)-functionalized, bio-derived calcium carbonate (Bio-CaCO3) filler recovered from Asian green mussel (Perna viridis) shell waste for incorporation into a hydroxypropyl methylcellulose (HPMC)-glycerol (Gro) matrix as a hydrophobic composite coating for reducing pesticide deposition on mandarin surfaces. Aragonite-rich Bio-CaCO3 was extracted through a combined chemical treatment and mechanical pulverization process. The extracted Bio-CaCO3 was characterized by scanning electron microscopy, X-ray diffraction, laser diffraction, and ATR FT-IR spectroscopy. At the optimal OA concentration, surface functionalization yielded OA-functionalized Bio-CaCO3 (OA-Bio-CaCO3) powder beds that exhibited apparent superhydrophobicity; successful functionalization was confirmed by X-ray photoelectron spectroscopy. The resulting HPMC-Gro-OA-Bio-CaCO3 coating dispersion (CD-OA) formed hydrophobic composite films (f-CD-OA), as demonstrated by water contact-angle measurements and surface-morphology analysis. The CD-OA coating formulation was successfully applied to mandarin surfaces by a dip-coating process. Colorimetric screening indicated that organophosphate pesticide residues on coated mandarins did not exceed hazardous levels, even at 20 times the manufacturer-recommended application rate. Quantitative LC-MS/MS and GC-MS/MS analyses demonstrated that the optimized CD-OA coating formulation provided substantial short-term protection against acetamiprid and chlorothalonil with pesticide-deposition reductions of 89% and ≥96%, respectively, after 1 d relative to pristine mandarins. These findings advance the functional reuse of biogenic CaCO3 and offer a simple, water-based dip-coating approach that provides temporary surface protection for citrus production and food-safety management.