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 the first approach, PHB particles in the 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°–122° and 129°–144° after additional wax coating. In the second approach, PHB particles with submicron sizes (PHB-SP) were synthesized by an oil-in-water emulsion (o/w) solvent evaporation method and mixed in aqueous suspensions with 0–7 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°–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 the binding agent in the retention of more crystalline PHB-SP at the paper surface, hence contributing to higher hydrophobicity.
Highlights
Inspired by nature, surface science is continuously advancing towards deeper analysis and understanding of natural materials in order to further exploit them in modern technology.The exceptional properties and functionality of materials in nature often rely on their hierarchical structure combining features at the micro- to nano-length scales
The chemical interactions between the more amorphous polyhydroxybutyrate structured microparticles (PHB-MP) particles and paper fibers were identified as an esterification reaction, while the morphology of the nanofibrillated cellulose (NFC) fibrillar network was playing a key role as the binding agent in the retention of more crystalline PHB-SP at the paper surface, contributing to higher hydrophobicity
The morphology of dried PHB-MP and PHB-SP powders was studied by scanning electron microscopy (SEM)
Summary
Surface science is continuously advancing towards deeper analysis and understanding of natural materials in order to further exploit them in modern technology. The surface hydrophobicity of papers can be enhanced by controlling the surface morphology through deposition of micro- to nano-scale structured particles, providing hierarchical structures in combination with the macroscale fibers Several inorganic nanoparticles, such as TiO2 , SiO2 and Al2 O3 , coupled with low surface energy chemicals, like 3-(trimethoxysilyl) propyl methacrylate (MPS) or silanes, acted as highly hydrophobic materials when coated over papers [15,16].
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