Effect of adding micronized eggshell waste particles on the properties of biodegradable pectin/starch films

Abstract

Upcycling agroindustry residues into new valuable products is a strategy for mitigating environmental impacts while increasing material circularity. In this study, two sizes of eggshell particles (D90 = 7.1 μm (ESAJ) and D90 = 16.3 μm (ESBU)) were obtained and their incorporation as fillers into biodegradable pectin/starch film was evaluated. The effect of the presence of eggshell particles (2–8 w/w%) on the structural and morphological aspects, water barrier, and mechanical, optical, and thermal properties of the biocomposites was evaluated and then the reinforced film was applied on the surface of kraft paper. The release of calcium in an acidic solution was inverse to the size and concentration of particles and the released íon may contribute to the crosslinking of pectin. The incorporation of only 2 % eggshell resulted in 42% lower solubility of the film. The eggshell-reinforced films proved to be more opaque and rigid. The addition of 6% ESAJ significantly improved the tensile strength (an increase of 32%), modulus of elasticity (an increase of 29.7%), and water vapor barrier (59% of improvement). DSC analysis suggests that the calcium from the eggshell interacts with the pectin polymeric structure, reducing the sites available for water molecules, which may have caused more mobility of the chains through the matrix. The reinforced pectin/starch film was very well adhered to the kraft paper in the application test by continuous casting, but the coated paper showed no improvement in oil and water resistance, which means that other coating processes need to be explored.