Search

Artificial photosynthesis has rapidly developed as an actual field of research, mimicking natural photosynthesis processes in plants or bacteria to produce energy or high-value chemicals. The nanocelluloses are a family of biorenewable materials that can be engineered into nanostructures with favorable properties to serve as a host matrix for encapsulation of photoreactive moieties or cells. In this review, the production of different nanocellulose structures such as films, hydrogels, membranes, and foams together with their specific properties to function as photosynthetic devices are described. In particular, the nanocellulose's water affinity, high surface area and porosity, mechanical stability in aqueous environment, and barrier properties can be tuned by appropriate processing. From a more fundamental viewpoint, the optical properties (transparency and haze) and interaction of light with nanofibrous structures can be further optimized to enhance light harvesting, e.g., by functionalization or appropriate surface texturing. After reviewing the basic principles of natural photosynthesis and photon interactions, it is described how they can be transferred into nanocellulose structures serving as a platform for immobilization of photoreactive moieties. Using photoreactive centers, the isolated reactive protein complexes can be applied in artificial bio-hybrid nanocellulose systems through self-assembly, or metal nanoparticles, metal-organic frameworks, and quantum dots can be integrated in nanocellulose composites. Alternatively, the immobilization of algae or cyanobacteria in nanopaper coatings or a porous nanocellulose matrix allows to design photosynthetic cell factories and advanced artificial leaves. The remaining challenges in upscaling and improving photosynthesis efficiency are finally addressed in order to establish a breakthrough in utilization of nanocellulose for artificial photosynthesis. [ABSTRACT FROM AUTHOR]

Recently, terms such as sustainable, bio-based, biodegradable, non-toxic, or environment-benign are being found in the literature, suggesting an increase in green materials for various applications in the future, particularly in the packaging application. The unavoidable shift from conventional polymers to green materials is difficult, as most bio-sourced materials are not water-resistant. Nonetheless, Shellac, a water-resistant resin secreted by a lac insect, used as a varnish coat, has been underutilized for packaging applications. Here, we review Shellac's potential in the packaging application to replace conventional polymers and biopolymers. We also discuss Shellac's isolation, starting from the lac insect and its conversion to Sticklac, Seedlac, and Shellac. Further, the chemistry of shellac resin, the chemical structure, and its properties are examined in detail. One disadvantage of Shellac is that it becomes stiff over time. To enable the usage of Shellac for an extended time in the packaging application, a modification of Shellac via physical and chemical means is conferred. Furthermore, the usage of Shellac in other polymer matrices and its effect are reviewed. Lastly, the non-toxic and biodegradable nature of Shellac and its potential in packaging are explored by comparing it with traditional crude-based polymers and conventional bio-based materials. [ABSTRACT FROM AUTHOR]

In this work, two types of pre-consumer textile waste, namely, viscose-rayon and nylon yarn, were utilized for nanocomposite filmmaking using the green solvent casting method. The nanocellulose was extracted from the viscose-rayon and incorporated as a filler in nylon films. The effects of nanocellulose on thermal, chemical, mechanical, structural, and barrier properties of films containing 0.1, 0.5, and 1 wt% nanocellulose were investigated in detail. The thermal study of films using differential scanning calorimetry (DSC) confirmed that adding nanocellulose into the nylon matrix does not act as a nucleating agent as nylon yarn waste already had ~5 wt% nucleating agents (thermogravimetric analysis, TGA). Rather, a decrease in the crystallinity of films was determined with the addition of nanocellulose. No significant changes in the mechanical properties were observed for nylon nanocomposite films. However, an increased hydrogen bonding was observed between the nanocellulose and nylon, along with the reorientation of hydrogen bonds (Fourier-transform infrared spectroscopy, FTIR). A dense cross-section and structured surface were observed in the scanning electronmicroscopic (SEM) images for nanocomposite films. The water vapor barrier of films increased as the concentration of nanocellulose increased in the nylon films and resulted in a 55% decrease in water vapor transmission rate (WVTR) compared to neat nylon film. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Surface modification of micro- and nanofibrillated cellulose (MFC and NFC) under aqueous environment was performed by deposition of poly(styrene- co -maleimide) nanoparticles synthesized by imidization of poly(styrene- co -maleic anhydride) in presence of wax and ammonium hydroxide in variable amounts. Specifically, the influences of fiber fibrillation on nanoparticle formation (i.e., reaction efficiency) and permanent nanoparticle deposition on the fiber surface (i.e., retention) were investigated. The surface modification was mainly governed by the fiber diameter, surface charges and amount of wax. As such, the MFC affected the imidization reaction to a smaller extent (i.e., high reaction efficiency) and was more densely deposited by nanoparticles than NFC (i.e., high retention). Moreover, wax protected the fibers against fibrillation and peeling-off at high temperature and favored nanoparticle deposition. As a result, water contact angles of 142° were obtained for modified MFC in parallel with a surface coverage of 92%. [ABSTRACT FROM AUTHOR]

The barrier resistance and wettability of papers are commonly controlled by the application of petroleum-based derivatives such as polyethylene, waxes and/or fluor-derivatives as coating. While surface hydrophobicity is improved by employing these polymers, they have become disfavored due to limitations in fossil-oil resources, poor recyclability, and environmental concerns on generated waste with lack of biodegradation. Alternatively, biopolymers including polysaccharides, proteins, lipids and polyesters can be used to formulate new pathways for fully bio-based paper coatings. However, difficulties in processing of most biopolymers may arise due to hydrophilicity, crystallization behavior, brittleness or melt instabilities that hinder a full exploitation at industrial scale. Therefore, blending with other biopolymers, plasticizers and compatibilizers is advantageous to improve the coating performance. In this paper, an overview of barrier properties and processing of bio-based polymers and their composites as paper coating will be discussed. In particular, recent technical advances in nanotechnological routes for bio-based nano- composite coatings will be summarized, including the use of biopolymer nanoparticles, or nanofillers such as nanoclay and nanocellulose. The combination of biopolymers along with surface modification of nanofillers can be used to create hierarchical structures that enhance hydrophobicity, complete barrier protection and functionalities of coated papers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. • Thyme oil completely inhibited the growth of bread molds than other essential oils. • P(3HB-co-4HB) films containing Thyme oil were successfully developed. • Thyme oil influenced the physicochemical and thermal properties of composite films. • Films showed antimicrobial activity against the total bread molds. • The film containing the 30% v/w Thyme oil extended the shelf-life of packed bread. [ABSTRACT FROM AUTHOR]

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.