Aqueous dispersion of birch bark suberin stabilized by carboxymethylated galactoglucomannan for barrier coating applications

Abstract Addressing global plastic pollution requires new packaging innovations, while valorizing underused forest industry side streams benefits both economy and environment. Birch bark, largely burned for energy today, was historically used as packaging due to its barrier properties derived from the biopolymer suberin. In this work, suberin hydrolysate from outer birch bark was formulated into aqueous barrier dispersions using carboxymethylated galactoglucomannan (CM-GGM) as dispersant. Modification of GGM improved its dispersing efficiency, enabling higher solids content than previously reported. Stability and rheological analyses confirmed that CM-GGM-stabilized dispersions were suitable for coating at 30 wt.%. Prolonged oven curing rendered the coatings water resistant, with curing efficiency depending on pH—excessive neutralization hindered repolymerization. Polymerization began with epoxy ring opening, followed by ester formation. The composition of suberin hydrolysate influenced dispersion viscosity and curing rate: epoxy-rich C18 fatty acids accelerated curing, while unsaturated hydroxy fatty acids reduced viscosity. This study demonstrates a route to bio-based barrier coatings by combining birch bark and spruce galactoglucomannan, two major forest industry side streams.