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Ceramic foam materials have received great attention in recent years for their light weight, thermal/electrical insulation, high crack tolerance and good machinability properties. However, some applications demand higher mechanical strength, better resistivity of the surface against mechanical impact or improved abrasion resistance. In this paper, the feasibility of dip coating 89 vol% porous, green alumino-silicate foam bars with dimensions in the centimeter range was studied and a dip coating route was proposed. The surface morphology of uncoated and coated foam bars was first analyzed by scanning electron microscopy (SEM) and later detailed using the GelsightTM method. Mechanical properties were determined by 4-point bending. A dense coating layer with a uniform thickness and good interfacial adhesion was obtained over the foam. Consequently, a three-fold increase in the flexural strength was measured for coated parts. In addition, the versatility of the developed dip coating route was demonstrated coating samples of bigger size like panels as well as complex geometries like cylindrical crucibles.

In this study, a biodegradable film from bacterial biopolymer, i.e., poly (3-hydroxybutyrate-co-4-hydroxybutyrate) or P(3HB-co-4HB) incorporating Thyme essential oil as an antimicrobial agent was developed as an active packaging for shelf-life extension of bread. Thin solvent-cast films containing 10, 20, and 30% v/w of Thyme oil were prepared and studied for the morphological, thermal, chemical, mechanical, barrier, and antimicrobial behaviors. The presence of oil in P(3HB-co-4HB) films and their purity without detectable remains of solvent, i.e., chloroform, was confirmed by infrared spectroscopy. In parallel, the time-bound release of volatile Thyme oil from the films was demonstrated when stored in a controlled environment. The plasticizing effect of Thyme oil in films was evidenced by decreased tensile strength and crystallinity. In contrast, an increase in elongation at break and water vapor permeability of oil films were measured. Finally, the antimicrobial activity of oil films was checked against total bread molds and observed that when bread was sealed in P(3HB-co-4HB) films containing 30% v/w Thyme oil, its shelf-life extended to at least 5 days compared to 1–4 days for the neat film.

After successful preparation of master batch formulations including polyhydroxybutyrate (PHB) and fibrillated cellulose additives, the compositions with different types and concentrations of fillers were used for the deposition of a coating on packaging paper grades, by using compression moulding in a hydraulic press. The resulting paper coatings are considered to provide a green solution for the production of protective barrier layer films with tunable hydrophobicity and oxygen barrier resistance. The processing of the nanocomposites into flat and homogeneous coatings was optimized for different conditions of moulding temperature and times, in particular, the flow conditions of the coating under pressing in contact with the substrate strongly depends on the presence of fillers. The effects of filler types on adhesion of the coating at the paper/polymer interface were investigated and the poor adhesion of native PHB coatings was tremendously improved after hydrophobic surface modification of the nanocellulose fillers. The inclusion of a wax and nanoparticles attached to the nanocellulose fiber surface enhanced the flowing properties of the coating by eliminating fiber agglomeration in contact with the paper substrate and reducing the effects of fiber pull outs. Therefore, hydrophobic fiber modification is necessary to obtain a homogenous dispersion during compressing moulding of coating materials for paper applications. Furthermore, the effect of processing on the final crystallinity of the master batches, films and paper coatings is presented by considering the reduction in degree of crystallinity for coatings in contact with a paper substrate owing to the surface confinement of crystallization processes. On the other hand, also the time-effects of secondary crystallization of the coatings as a function of aging time were lower for the coatings as compared to the free-standing films, in relation with the reduction of molecular mobility of the polymer chains under confined conditions.

Although films of microfibrillated cellulose (MFC) have good oxygen barrier properties due to its fine network structure, properties strongly deteriorate after absorption of water. In this work, a new approach has been followed for actively tuning the water resistance of a MFC fiber network by the inclusion of dispersed organic nanoparticles with encapsulated plant wax. The modified pulp suspensions have been casted into films and were subsequently cured at 40 to 220 °C. As such, static water contact angles can be specifically tuned from 120 to 150° by selection of the curing temperature in relation with the intrinsic transition temperatures of the modified pulp, as determined by thermal analysis. The appearance of encapsulated wax after curing was followed by a combination of morphological analysis, infrared spectroscopy and Raman mapping, showing balanced mechanisms of progressive release and migration of wax into the fiber network controlling the surface properties and water contact angles. Finally, the appearance of nanoparticles covered with a thin wax layer after complete thermal release provides highest hydrophobicity.

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.