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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.

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.

In this work, the intrinsic drawbacks of polyhydroxybutyrate (PHB) such as slow crystallization rate, secondary crystallization and brittle nature were improved by blending with bio-based fillers, i.e. nanofibrillated/microfibrillated cellulose (NFC/MFC). A novel chlorinated-solvent-free based system was developed to blend PHB and NFC/MFC that resulted in homogenous dispersion of fibers in the PHB matrix, without the need for surface modification of fibers. The developed nano/micro-composite materials were fabricated as masterbatch pellets and films. Additionally, the effect of different NFC/MFC fiber morphologies influencing the crystallization behaviour of PHB was investigated in detail by differential scanning calorimetry, polarized optical microscopy and Fourier transform infrared spectroscopy. Both non-isothennal and isothermal crystallization studies (modelled with Avrami's kinetics) were performed on nanocomposites and variations in crystallization kinetics of PHB after addition of NFC/MFC were determined. Addition of NFC/MFC resulted in the drastic increase in the crystallization rate of PHB and hence they acted as nucleating agents. The fine and homogeneous morphology of NFC produced smaller PHB spherulites and restricted the growth of secondary crystals, hence resulted in more flexible films than PHB or PHB-MFC films, as determined by the mechanical testing of films. The more heterogeneous morphology of MFC altered the PHB crystallization mechanism most, as seen from the distorted shape of PHB spherulites along with the higher Avrami exponent, i.e. n >= 3. This work was financially sponsored by the Junioprofessorenprogram Baden-Wurttemberg 'Functional Bio-based Nano-Coating for Paper Applications"('NaCoPa'-project 2012-2015) and the Robert Bosch Foundation in the framework of the Juniorprofessorenprogram 'Sustainable use of Natural Materials' ('Foresnab'-project 2011-2016). Rastogi, VK (reprint author), Aalto Univ, Sch Chem Technol, Dept Bioprod & Biosyst, Vuorimiehentie 1, Espoo 02150, Finland. vibhore.rastogi@aalto.fi

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.

The use of microfibrillated cellulose is mainly constraint by its hydrophilic character, and there is an urgent search for sustainable alternatives towards hydrophobic surface modification. Here, we present a production technique where cellulose fibers are modified by an in-situ reaction with styrene maleic anhydride, ammonium hydroxide and plant wax under aqueous environment. After imidization, the cellulose fibers were fibrillated along with partial coverage of the surface by styrene maleimide nanoparticles and incorporation of wax, resulting in the formation of a stable and hydrophobic micro-porous fiber network.

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.