Biorenewable, transparent, and oxygen/moisture barrier nanocellulose/nanochitin-based coating on polypropylene for food packaging applications.

Aluminum-coated polypropylene films are commonly used in food packaging because aluminum is a great gas barrier. However, recycling these films is not economically feasible. In addition, their end-of-life incineration generates harmful alumina-based particulate matter. In this study, coating layers with excellent gas-barrier properties are assembled on polypropylene films through layer-by-layer (LbL) deposition of biorenewable nanocellulose and nanochitin. The coating layers significantly reduce the transmission of oxygen and water vapors, two unfavorable gases for food packaging, through polypropylene films. The oxygen transmission rate of a 60 µm-thick, 20 LbL-coated polypropylene film decreases by approximately a hundredfold, from 1118 to 13.10 cc m-2 day-1 owing to the high crystallinity of nanocellulose and nanochitin. Its water vapor transmission rate slightly reduces from 2.43 to 2.13 g m-2 day-1. Furthermore, the coated film is highly transparent, unfavorable to bacterial adhesion and thermally recyclable, thus promising for advanced food packaging applications.

Rediscovery of nylon upgraded by interactive biorenewable nano-fillers.

Inorganic nanomaterials can only stiffen nylon with a significant loss of its toughness and ductility. Furthermore, they are not eco-friendly. In this study, the facile tuning of nylon's mechanical properties from stiff to tough was achieved, using cellulose nanocrystals (CNC) and chitosan nanowhiskers (CSW) as biorenewable fillers. The interaction between the matrix and filler was controlled by varying the types of fillers and the employed processing methods, including in situ interfacial polymerization and post-solution blending. Particularly with CSW, the in situ-incorporated filler with a 0.4 wt% loading strengthened nylon and led to a 1.9-fold increase in its Young's modulus (2.6 GPa) and a 1.7-fold increase in its ultimate tensile strength (106 MPa), whereas the solution-blended filler with a 0.3 wt% loading toughened the polymer with a 2.1-fold increase (104 MJ m-3). Compared with inorganic nanocomposites, these interactive biofiller-nanocomposites are unrivaled in their reinforcing performance when normalized by filler content. This stiff-to-tough tuning trend is more pronounced in the CSW system than in the CNC system. Covalent polymer grafts on the amine surface of CSW enhanced interfacial interactions in the in situ method, whereas its cationic surface charges plasticized the polymer matrix in the blending method. This proteinaceous composite-mimicking all-organic nylon nanocomposite opens new possibilities in the field of reinforced engineering plastics.

Crab-on-a-Tree: All Biorenewable, Optical and Radio Frequency Transparent Barrier Nanocoating for Food Packaging.

Plastic packaging effectively protects foods from mechanical, microbial, and chemical damage, but oxygen can still permeate these plastics, degrading foods. Improving the gas barrier usually requires metallic or halogenated polymeric coatings; however, both cause environmental concerns and metallic coatings block visible light and electromagnetic signals. This paper reports a design of a highly flexible, visible light and radio frequency transparent coating on commercial poly(ethylene terephthalate) (PET) film. Nanoscale blending was achieved between negatively charged cellulose nanofibers and positively charged chitin nanowhiskers by employing spray-assisted layer-by-layer assembly. Synergetic interplay between these highly crystalline nanomaterials results in a flexible film with superior barrier characteristics. The oxygen transmission rate was below 0.5 mL m-2 day-1. Moreover, this coating maintains its performance even when exposed to common hazards such as bending stress and hydration. The coating also notably reduces the haziness of PET with a negligible loss of transparency and provides effective inhibition of antibacterial growth. This "crab-on-a-tree" nanocoating holds high potential for biorenewable and optical and radio frequency transparent packaging applications.

Five different chitin nanomaterials from identical source with different advantageous functions and performances.

Chitin is a renewable and sustainable biomass material that can be converted into various one-dimensional crystalline nanomaterials different in 1) length, 2) diameter, 3) charge density, 4) type of charge, and 5) crystallinity via diverse top-down synthetic methods. These nanomaterials have great potential as sustainable reinforcing and biologically functional materials. The proper design of chitin nanomaterials maximizes their performances in specific applications. Extensive efforts are devoted to understanding each type of chitin nanomaterial produced from different chitin sources; however, few studies have compared different chitin nanomaterials. Herein, we synthesize five different types of chitin nanomaterials from identical sources and compare their physical and chemical properties, including suitability for assorted purposes. Factors 1)-5) are discussed regarding their dominance in determining functionality depending on the specific goals of a) gas barriers, b) mechanical reinforcements, c) dispersibility in various pH aqueous buffers, d) thermal dimensional stability, and e) antibacterial activity. This study gives insights to design new chitin nanomaterial-based materials.

The Renewable and Sustainable Conversion of Chitin into a Chiral Nitrogen-Doped Carbon-Sheath Nanofiber for Enantioselective Adsorption.

Well-known hard-template methods for nitrogen (N)-doped chiral carbon nanomaterials require complicated construction and removal of the template, high-temperature pyrolysis, harsh chemical treatments, and additional N-doping processes. If naturally occurring chiral nematic chitin nanostructures [(C8 H13 NO5 )n ] in exoskeletons were wholly transformed into an N-doped carbon, this would be an efficient and sustainable method to obtain a useful chiral nanomaterial. Here, a simple, sacrificial-template-free, and environmentally mild method was developed to produce an N-doped chiral nematic carbon-sheath nanofibril hydrogel with a surface area >300 m2 g-1 and enantioselective properties from renewable chitin biomass. Calcium-saturated methanol physically exfoliated bulk chitin and produced a chiral nematic nanofibril hydrogel. Hydrothermal treatment of the chiral chitin hydrogel at 190 °C produced an N-doped chiral carbon-sheath nanofibril hydrogel without N-doping. This material preferentially adsorbed d-lactic acid over l-lactic acid and produced 16.3 % enantiomeric excess of l-lactic acid from a racemic mixture.

Poisonous Caterpillar-Inspired Chitosan Nanofiber Enabling Dual Photothermal and Photodynamic Tumor Ablation.

As caterpillars detect the presence of predators and secrete poison, herein, we show an innovative and highly effective cancer therapeutic system using biocompatible chitosan nanofiber (CNf) installed with a pH-responsive motif that senses tumor extracellular pH, pHe, prior to delivering dual-modal light-activatable materials for tumor reduction. The filamentous nanostructure of CNf is dynamic during cell interaction and durable in blood circulation. Due to its amine group, CNf uptakes a large amount of photothermal gold nanoparticles (AuNPs, >25 wt %) and photodynamic chlorin e6 (Ce6, >5 wt %). As the innovative CNf approaches tumors, cationic CNf effectively discharges AuNPs connected to the pH-responsive motif via electrostatic repulsion and selectively binds to tumor cells that are generally anionic, via the electrostatic attraction accompanied by CNf. We demonstrated via these actions that the endocytosed Ce6 (on CNf) and AuNPs (free from CNf) significantly elicited tumor cell death under light irradiation. As a result, the synergistic interplay of thermogenesis and photodynamic action was observed to switch on at the pHe, resulting in a striking reduction in tumor formation and growth rate upon light exposure.

A ball milling-based one-step transformation of chitin biomass to organo-dispersible strong nanofibers passing highly time and energy consuming processes.

Chitin, a sustainable and functional biological macromolecule, can be converted into chitin nanofibers (ChNFs), and are applicable as a mechanically reinforcing and bioactive filler for polymer matrices. Improving the performance of ChNFs typically relies on their nanofibrilization and miscibility with matrices. To transform chitin biomass into organo-dispersible ChNFs, a series of time-/energy-consuming chemical and mechanical treatments are required: 1) deacetylation, 2) disintegration, 3) surface modification to minimize their aggregation through hydrogen bonds, 4) drying, and 5) re-dispersion. This paper presents a one-step method to transform chitin biomass to organo-dispersible acetylated ChNFs via a ball-milling method in the presence of relatively low toxic acetic anhydride without water. This method minimizes water contaminations and energy for dehydrating. The resulting chitin nanofiber material is mixed with poly(l­lactic acid) (PLLA) to produce all-bio-based nanocomposites. The composite indicated a 66% increase in Young's modulus and a 100% increase in tensile strength compared to the pristine PLLA. Furthermore, it did not exhibit any observable cytotoxic effect, thus potentially applicable as a biomedical material.

Sustainable Boron Nitride Nanosheet-Reinforced Cellulose Nanofiber Composite Film with Oxygen Barrier without the Cost of Color and Cytotoxicity.

This paper introduces a boron nitride nanosheet (BNNS)-reinforced cellulose nanofiber (CNF) film as a sustainable oxygen barrier film that can potentially be applied in food packaging. Most commodity plastics are oxygen-permeable. CNF exhibits an ideal oxygen transmission rate (OTR) of <1 cc/m²/day in highly controlled conditions. A CNF film typically fabricated by the air drying of a CNF aqueous solution reveals an OTR of 19.08 cc/m²/day. The addition of 0⁻5 wt % BNNS to the CNF dispersion before drying results in a composite film with highly improved OTR of 4.7 cc/m²/day, which is sufficient for meat and cheese packaging. BNNS as a 2D nanomaterial increases the pathway of oxygen gas and reduces the chances of pinhole formation during film fabrication involving water drying. In addition, BNNS improves the mechanical properties of the CNF films (Young's modulus and tensile strength) without significant elongation reductions, probably due to the good miscibility of CNF and BNNS in the aqueous solution. Addition of BNNS also produces negligible color change, which is important for film aesthetics. An in vitro cell experiment was performed to reveal the low cytotoxicity of the CNF/BNNS composite. This composite film has great potential as a sustainable high-performance food-packaging material.