Crosslinkable poly(lactic acid)-based materials: Biomass-derived solution for barrier coatings

The demand for biobased barrier packaging alternatives is constantly growing. Poly(lactic acid) (PLA)-based polymers are one of the most extensively studied biomass-derived synthetic polymers; however, they typically lack water-barrier properties. We synthesized a copolymer of d,l-lactic acid, 1,4-butanediol, and itaconic acid [poly(d,l-lactic acid-1,4-butanediol-itaconic acid) (PLABDIA)] via bulk polycondensation. The radical crosslinking reactions of the synthesized polymer were investigated with bulk crosslinking trials to find a formulation that was suitable for a rapidly crosslinkable barrier coating. The crosslinking efficiency was tested with methacrylate and acrylate crosslinkers together with peroxide radical initiators. Poly(ethylene glycol) diacrylate (number-average molecular weight = 250 g/mol) together with dilauroyl peroxide proved to be the best crosslinker-initiator combination. An aqueous dispersion of PLABDIA was prepared with a thermomechanical method and applied to commercial boxboard on a pilot-scale line coater. With a coating weight of 10 g/m², a water vapor transmission rate of 22.8 g/m²d was achieved, and this coating outperformed commercial extruded PLA coatings. The samples also showed very good grease resistance and would, therefore, be a good solution for the packaging of dry and fatty goods.