Synthesis of Polyhydroxybutyrate Particles with Micro-to-Nanosized Structures and Application as Protective Coating for Packaging Papers

Abstract

This study reports on the development of bio-based hydrophobic coatings for packaging papers through deposition of polyhydroxybutyrate (PHB) particles in combination with nanofibrillated cellulose (NFC) and plant wax. In a first approach, PHB particles in micrometer range (PHB-MP) were prepared through a phase-separation technique providing internally nanosized structures. The particles were transferred as a coating by dip-coating filter papers in the particle suspension, followed by sizing with a carnauba wax solution. This approach allowed partial to almost full surface coverage of PHB-MP over the paper surface resulting in static water contact angles of 105° to 122° and 129° to 144° after additional wax coating. In a second approach, PHB particles with submicron sizes (PHB-SP) were synthesized by an oil-in-emulsion (o/w) solvent evaporation method, and mixed in aqueous suspensions with 0 to 7 wt% NFC. After dip-coating filter papers in PHB-SP/NFC suspensions and sizing with a carnauba wax solution, static water contact angles of 112 to 152° were obtained. The intrinsic properties of the particles were analyzed by scanning electron microscopy, thermal analysis and infrared spectroscopy, indicating higher crystallinity for PHB-SP than PHB-MP. The chemical interactions between the more amorphous PHB-MP particles and paper fibers were identified as an esterification reaction, while the morphology of the NFC fibrillar network was playing a key role as binding agent in the retention of more crystalline PHB-SP at the paper surface, hence contributing to higher hydrophobicity.

Nanocellulose for Paper and Textile Coating: The Importance of Surface Chemistry

“…Low cost, availability, and renewability expand the likelihood of using nanocellulose as a coating. It is a bio‐based agent that can be chosen as a coating component among other green alternatives that are less economically feasible than their petrol‐based counterparts [16] . Because of its large specific surface area, good chemical reactivity, and good rheological properties, nanocellulose can display unique efficiency in paper coatings [116‐119] .…”

“…Most of these agents result in non‐biodegradable contaminants. In general, paper coating materials, applied particularly to binding covers and corrugated boxes, include components of fossil origin: certain polymers, such as waxes, polyethylene or polypropylene, polyethylene terephthalate (PET), or other polyesters are commonly adopted as coating materials, also in combination to kaolin clay or talc, widely used as coating fillers [15,16] . Furthermore, deposition processes of these polymers often require the use of organic solvents, which may imply the manipulation of hazardous chemicals.…”