Development of bioplastic multilayer films fabricated with PHA and HPMC using a water-based spray coating process

Abstract

This study presents a scalable, aqueous-based method for fabricating multilayer biopolymer films using polyhydroxyalkanoate (PHA) in aqueous suspension, eliminating the need for organic solvents. Conventional solvent-based casting is often used due to the poor interfacial adhesion and incompatible thermal properties of bioplastics, which hinder co-extrusion. However, this process suffers from low processing efficiency, solvent dependency, and weak interlayer adhesion, limiting its large-scale applicability. To address these limitations, aqueous PHA suspension was spray-coated onto hydroxypropyl methylcellulose (HPMC) films, followed by hot pressing to form a cohesive multilayer structure. Spray-coating alone caused cavities and uneven PHA distribution. In contrast, hot pressing fused the particles, improving not only the surface smoothness from 5.66 to 0.08 μm (at 5 MPa) but also interfacial bonding among layers. This significantly enhanced barrier properties, lowering the oxygen transmission rate from 120.49 ± 4.63–52.24 ± 1.19 cm3/(m2·day) and the water vapor transmission rate from 1170.31 ± 12.85–423.14 ± 7.75 g/(m2·day). Tensile strength also increased from 42.29 ± 2.47–70.17 ± 3.11 MPa. These results demonstrate the potential of this solvent-free method for scalable production of sustainable, high-performance multilayer packaging films.