Eco-friendly water barrier coating for paper packaging: Harnessing bio-calcium carbonate from mussel shell waste

Abstract

In this study, we addressed the issue of non-recyclable and slow-to-biodegrade waste from paper packaging coated with plastic, along with the local problem of accumulating mussel shell waste in Thailand. To improve the water barrier properties of paper, we developed a bio-based coating using ethyl cellulose (EC) and biogenic calcium carbonate (bio-CaCO₃) particles sourced from discarded green mussel shells. Chemical and mechanical treatments were applied to the shells, resulting in plate-like particles with a diameter of 2–5 μm and a thickness of 0.5 μm. Treating the particles with stearic acid (SA) enhanced their surface hydrophobicity, increasing the water contact angle (WCA) from 31 to 110°. Paper samples were coated with a dispersion of bio-CaCO₃ particles in an EC solution, and their molecular characteristics, morphology, thermal stability, and mechanical properties were characterized. Investigation of the effects of SA treatment and coating content revealed significant improvements in water resistance. The water absorptivity (Cobb test) of filter paper decreased from 150 to 9 g/m², and for packaging paper, it decreased from 43 to 7 g/m² after coating. Furthermore, the WCA of filter paper increased from non-measurable to 122°, while the WCA of packaging paper increased from 109 to 132°. These improvements could be attributed to the reduced porosity and increased surface hydrophobicity by coating. Overall, this bio-based coating demonstrated a promising potential as an eco-friendly solution for water barrier coating of packaging paper.