Chemical and Enzymatic Fiber Modification to Enhance the Mechanical Properties of CMC Composite Films.

Carboxymethyl cellulose (CMC) is a cellulose derivative that can be obtained from wood, bamboo, rattan, straw, and other cellulosic materials. CMC can be used to produce biofilms for many purposes, but the properties of these resulting films make them unsuitable for some applications. The effects of three kinds of plant fiber addition on CMC film properties was investigated using CMC derived from eucalyptus bark cellulose. Tensile strength (TS) and elongation at break (EB) of CMC/sodium alginate/glycerol composite films were 26.2 MPa and 7.35%, respectively. Tensile strength of CMC composite films substantially increased, reaching an optimum at 0.50 g of fiber. The enhancement due to industrial hemp hurd fiber on CMC composite films was more obvious. Pretreatment with hydrogen peroxide (H2O2) and glacial acetic acid (CH3COOH) produced films with a TS of 35.9 MPa and an EB of 1.61%. TS values with pectinase pretreated fiber films was 41.3 MPa and EB was 1.76%. TS of films pretreated with pectinase and hemicellulase was 45.2 MPa and EB was 4.18%. Chemical and enzymatic treatment both improved fiber crystallinity, but film tensile strength was improved to a greater extent by enzymatic treatment. Surface roughness and pyrolysis residue of the film increased after fiber addition, but Fourier transform infrared spectroscopy (FTIR), opacity, and water vapor transmission coefficients were largely unchanged. Adding fiber improved tensile strength of CMC/sodium alginate/glycerol composite films and broadened the application range of CMC composite films without adversely affecting film performance.

Two-dimensional graphene oxide-reinforced porous biodegradable polymeric nanocomposites for bone tissue engineering.

This study investigates the mechanical properties and in vitro cytotoxicity of two-dimensional (2D) graphene oxide nanoribbons and nanoplatelets (GONRs and GONPs) reinforced porous polymeric nanocomposites. Highly porous poly(propylene fumarate) (PPF) nanocomposites were prepared by dispersing 0.2 wt % single- and multiwalled SONRs (SWGONRs and MWGONRs) and GONPs. The mechanical properties of scaffolds were characterized using compression testing and in vitro cytocompatibility was assessed using QuantiFlour assay for cellularity and PrestoBlue assay for cell viability. Immunofluorescence was used to assess collagen-I expression and deposition in the extracellular matrix. Porous PPF scaffolds were used as a baseline control and porous single and multiwalled carbon nanotubes (SWCNTs and MWCNTs) reinforced nanocomposites were used as positive controls. Results show that incorporation of 2D graphene nanomaterials leads to an increase in the mechanical properties of porous PPF nanocomposites with following the trend: MWGONRs > GONPs > SWGONRs > MWCNTs > SWCNTs > PPF control. MWGONRs showed the best enhancement of compressive mechanical properties with increases of up to 26% in compressive modulus (i.e., Young's modulus), ~60% in yield strength, and ~24% in the ultimate compressive strength. Addition of 2D nanomaterials did not alter the cytocompatibility of porous PPF nanocomposites. Furthermore, PPF nanocomposites reinforced with SWGONRs, MWGONRs, and GONPs show an improvement in the adsorption of collagen-I compared to PPF baseline control. The results of this study show that 2D graphene nanomaterial reinforced porous PPF nanocomposites possess superior mechanical properties, cytocompatibility, and increased protein adsorption. The favorable cytocompatibility results opens avenues for in vivo safety and efficacy studies for bone tissue engineering applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1143-1153, 2019.

Atomic Layer Deposition of Metal Oxide on Nanocellulose for Enabling Microscopic Characterization of Polymer Nanocomposites.

Analysis of cellulose nanocrystals (CNCs) at low volume fractions in polymer nanocomposites through conventional electron microscopy still remains a challenge due to insufficient contrast between CNCs and organic polymer matrices. Herein, a methodology for enhancing the contrast of CNC, through atomic layer deposition (ALD) of alumina (Al2 O3 ) on CNCs is demonstrated. The metal oxide coated CNC allows clear visualization by transmission electron microscopy, when they are dispersed in water and polyol. A coating of about 6 ± 1 nm thick alumina layer on the CNC is achieved after 50 ALD cycles. This also enables the characterization of CNC dispersion/orientation (at 0.2 wt% loading) in an amorphous cellular system rigid polyurethane foam (RPUF), using backscattered electron microscopy with energy-dispersive X-ray spectroscopy. Microscopic analysis of the RPUF with alumina-coated CNC confirms that the predominant alignment of CNC occurs in a direction parallel to the foam rise.

Description of a Naphthoquinonic Crystal Produced by the Fungus Scytalidium cuboideum.

Intarsia was an art form popular between the 15th⁻18th centuries that used wood pigmented by spalting fungi to create detailed landscapes, portraits, and other imagery. These fungi are still used today in art but are also finding relevance in material science as elements of solar cells, textile dyes, and paint colorants. Here we show that the spalting fungus Scytalidium cuboideum (Sacc. and Ellis) Sigler and Kang produces a red/pink pigment that forms two distinct colors of crystals (red and orange)-a very rare occurrence. In addition, a second structure of the crystal is proved through nuclear magnetic resonance (NMR). This is only the second instance of a stable, naphthoquinone crystal produced by a fungus. Its discovery is particularly valuable for solar cell development, as crystalline materials have a higher electrical conductivity. Other fungi in this order have shown strong potential as thin films for solar cells.

Current characterization methods for cellulose nanomaterials.

A new family of materials comprised of cellulose, cellulose nanomaterials (CNMs), having properties and functionalities distinct from molecular cellulose and wood pulp, is being developed for applications that were once thought impossible for cellulosic materials. Commercialization, paralleled by research in this field, is fueled by the unique combination of characteristics, such as high on-axis stiffness, sustainability, scalability, and mechanical reinforcement of a wide variety of materials, leading to their utility across a broad spectrum of high-performance material applications. However, with this exponential growth in interest/activity, the development of measurement protocols necessary for consistent, reliable and accurate materials characterization has been outpaced. These protocols, developed in the broader research community, are critical for the advancement in understanding, process optimization, and utilization of CNMs in materials development. This review establishes detailed best practices, methods and techniques for characterizing CNM particle morphology, surface chemistry, surface charge, purity, crystallinity, rheological properties, mechanical properties, and toxicity for two distinct forms of CNMs: cellulose nanocrystals and cellulose nanofibrils.

Cellulose nanomaterials emulsion coatings for controlling physiological activity, modifying surface morphology, and enhancing storability of postharvest bananas (Musa acuminate).

Cellulose nanomaterials (CNs)-incorporated emulsion coatings with improved moisture barrier, wettability and surface adhesion onto fruit surfaces were developed for controlling postharvest physiological activity and enhancing storability of bananas during ambient storage. Cellulose nanofiber (CNF)-based emulsion coating (CNFC: 0.3% CNF/1% oleic acid/1% sucrose ester fatty acid (w/w wet base)) had low contact angle, high spread coefficient onto banana surfaces, and lower surface tension (ST, 25.4mN/m) than the critical ST (35.2mN/m) of banana peels, and exhibited good wettability onto banana surfaces. CNFC coating delayed the ethylene biosynthesis pathway and reduced ethylene and CO2 production, thus delaying fruit ripening. As the result, CNFC coating minimized chlorophyll degradation, weight loss, and firmness of bananas while ensuring the properly fruit ripening during 10d of ambient storage. This study demonstrated the effectiveness of CNF based emulsion coatings for improving the storability of postharvest bananas.

Cellulose Nanocrystal Reinforced Chitosan Coatings for Improving the Storability of Postharvest Pears Under Both Ambient and Cold Storages.

Cellulose nanocrystal (CNC, 0%, 5%, and 10% w/w, in chitosan, dry basis) reinforced 2% chitosan aqueous coatings were evaluated for delaying the ripening and quality deterioration of postharvest green D'Anjou (Pyrus communis L.) and Bartlett (Pyrus communis L.) pears during 3 wk of ambient storage (20 ± 2 °C and 30 ± 2% RH) or 5 mo of cold storage (-1.1 °C and 90% RH), respectively. Ethylene and CO2 production, color, firmness, and internal fruit quality were monitored during both storage conditions. Moisture and gas barrier, antibacterial activity, and surface morphology of the derived films were also evaluated to investigate the mechanisms of delayed fruit ripening and quality deterioration. In the ambient storage study, the 5% CNC reinforced chitosan coating significantly (P < 0.05) delayed green chlorophyll degradation of pear peels, prevented internal browning, reduced senescence scalding, and improved retained fruit firmness. During cold storage, the 5% CNC reinforced chitosan coating showed a competitive effect on delaying fruit postharvest quality deterioration compared to a commercial product (Semperfresh™, Pace International, Wapato, Wash., U.S.A.). The 5% CNC coating strongly adhered to the pear surface, provided a superior gas barrier and a more homogenous matrix in comparison with the other coatings tested. Hence, it was effective in delaying ripening and improving the storability of postharvest pears during both ambient and cold storage.

Boron nitride nanotubes and nanoplatelets as reinforcing agents of polymeric matrices for bone tissue engineering.

This study investigates the mechanical properties and in vitro cytotoxicity of one- and two-dimensional boron nitride nanomaterials-reinforced biodegradable polymeric nanocomposites. Poly(propylene fumarate) (PPF) nanocomposites were fabricated using crosslinking agent N-vinyl pyrrolidone and inorganic nanomaterials: boron nitride nanotubes (BNNTs) and boron nitride nanoplatelets (BNNPs) dispersed at 0.2 wt % in the polymeric matrix. The incorporation of BNNPs and BNNTs resulted in a ∼38 and ∼15% increase in compressive (Young's) modulus, and ∼31 and ∼6% increase in compressive yield strength compared to PPF control, respectively. The nanocomposites showed a time-dependent increased protein adsorption for collagen I protein. The cytotoxicity evaluation of aqueous BNNT and BNNP dispersions (at 1-100 µg/mL concentrations) using murine MC3T3 preosteoblast cells showed ∼73-99% viability. The cytotoxicity evaluation of media extracts of nanocomposites before crosslinking, after crosslinking, and upon degradation (using 1×-100× dilutions) showed dose-dependent cytotoxicity responses. Crosslinked nanocomposites showed excellent (∼79-100%) cell viability, cellular attachment (∼57-67%), and spreading similar to cells grown on the surface of tissue culture polystyrene control. The media extracts of degradation products showed a dose-dependent cytotoxicity. The favorable cytocompatibility results in combination with improved mechanical properties of BNNT and BNNP nanocomposites opens new avenues for further in vitro and in vivo safety and efficacy studies towards bone tissue engineering applications. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 406-419, 2017.

The Microstructure of Cellulose Nanocrystal Aerogels as Revealed by Transmission Electron Microscope Tomography.

The microstructure of highly porous cellulose nanocrystal (CNC) aerogels is investigated via transmission electron microscope (TEM) tomography. The aerogels were fabricated by first supercritically drying a carboxylated CNC organogel and then coating via atomic layer deposition with a thin conformal layer of Al2O3 to protect the CNCs against prolonged electron beam exposure. A series of images was then acquired, reconstructed, and segmented in order to generate a three-dimensional (3D) model of the aerogel. The model agrees well with theory and macroscopic measurements, indicating that a thin conformal inorganic coating enables TEM tomography as an analysis tool for microstructure characterization of CNC aerogels. The 3D model also reveals that the aerogels consist of randomly orientated CNCs that attach to one another primarily in three ways: end to end contact, "T″ contact, and "X″ contact.

Impacts of chemical modification on the toxicity of diverse nanocellulose materials to developing zebrafish.

Cellulose is an abundant and renewable resource currently being investigated for utility in nanomaterial form for various promising applications ranging from medical and pharmaceutical uses to mechanical reinforcement and biofuels. The utility of nanocellulose and wide implementation ensures increasing exposure to humans and the environment as nanocellulose-based technologies advance. Here, we investigate how differences in aspect ratio and changes to surface chemistry, as well as synthesis methods, influence the biocompatibility of nanocellulose materials using the embryonic zebrafish. Investigations into the toxicity of neutral, cationic and anionic surface functionalities revealed that surface chemistry had a minimal influence on the overall toxicity of nanocellulose materials. Higher aspect ratio cellulose nanofibers produced by mechanical homogenization were, in some cases, more toxic than other cellulose-based nanofibers or nanocrystals produced by chemical synthesis methods. Using fluorescently labeled nanocellulose we were able to show that nanocellulose uptake did occur in embryonic zebrafish during development. We conclude that the benign nature of nanocellulose materials makes them an ideal platform to systematically investigate the inherent surface features driving nanomaterial toxicity in order to create safer design principles for engineered nanoparticles.

Investigation of the mechanisms of using metal complexation and cellulose nanofiber/sodium alginate layer-by-layer coating for retaining anthocyanin pigments in thermally processed blueberries in aqueous media.

This study investigated the mechanisms of anthocyanin pigment retention using Fe(3+)-anthocyanin complexation and cellulose nanofiber (CNF)/sodium alginate (SA) layer-by-layer (LBL) coatings on thermally processed blueberries in aqueous media. Anthocyanin pigments were polymerized through complexation with Fe(3+) but readily degraded by heat (93 °C for 7 min) in the aqueous media because of poor stability. CNF/SA LBL coating was successful to retain anthocyanin pigments in thermally processed blueberries. Fruits coated with CNF containing CaCl2 followed by treatment in a SA bath formed a second hydrogel layer onto the CNF layer (LBL coating system) through cross-linking between Ca(2+) and alginic acid. Methyl-cellulose-modified CNF improved the interactions between CNF, the fruit surface, and the SA layer. This study demonstrated that the CNF/SA LBL coating system was effective to retain anthocyanin pigments on thermally processed whole blueberries, whereas no combined benefit of complexation with coating was observed. Results explained the mechanisms of the new approaches for developing colorful and nutritionally enhanced anthocyanin-rich fruit products.

Thermomechanical and morphological properties of nanocomposite films from wheat gluten matrix and cellulose nanofibrils.

The aim of this investigation was the optimization of preparing gluten film containing cellulose nanofibrils (CNF). An optimization procedure using central composite design (CCD) with three factors (CNF, glycerol, and sodium dodecyl sulfate (SDS) concentrations) was used in order to investigate the effect of these parameters on the mechanical (tensile strength--TS, elongation at break--ε(b)) and thermal properties of gluten films and to establish a formulation to depict the relationship between the mentioned factors and mechanical properties. Through regression analysis, it was found that TS and ε(b) well fitted by quadratic polynomial equations (R² = 0.99 and 0.98, respectively) and the glycerol concentration was the most significant factor influencing them. The optimization was based on maximizing TS and ε(b). The optimum conditions determined using response surface methodology (RSM) were defined as: CNF concentration, 11.129 g/100 g, glycerol concentration, 35.440 g/100 g and SDS concentration, 6.259 g/100 g. The predicted responses for these film preparation conditions were a TS of 3.630 MPa and ε(b) of 86.033%. The verification experiments were conducted under optimal conditions to compare predicted and actual values of dependent variables. This experiment indicated that both predicted and actual values (TS of 3.721 MPa and ε(b) of 88.935%) almost coincide each other and therefore the estimated models were reasonable and of high accuracy to predict dependent variables values. The scanning electron microscopy (SEM) images showed non-agglomerated and well dispersed CNF in the gluten matrix. Differential scanning calorimetry (DSC) results indicated that there is not any significant difference (P > 0.05) between the glass transition temperature (T(g)) of optimum nanocomposite (-29.12 °C) and control film (-29.64 °C) and their thermogravimetric analysis (TGA) thermograms showed similar degradation behavior.

Cellulose nanomaterials review: structure, properties and nanocomposites.

This critical review provides a processing-structure-property perspective on recent advances in cellulose nanoparticles and composites produced from them. It summarizes cellulose nanoparticles in terms of particle morphology, crystal structure, and properties. Also described are the self-assembly and rheological properties of cellulose nanoparticle suspensions. The methodology of composite processing and resulting properties are fully covered, with an emphasis on neat and high fraction cellulose composites. Additionally, advances in predictive modeling from molecular dynamic simulations of crystalline cellulose to the continuum modeling of composites made with such particles are reviewed (392 references).

Cellulose/DNA hybrid nanomaterials.

Cellulose nanocrystals (CNXLs) have drawn attention from researchers for their remarkable reinforcing abilities and excellent mechanical properties. CNXLs typically have high aspect ratios of around 20-50 (length/width), low density of around 1.6 g/cc, high stiffness (135 to 155 GPa), and strength (estimated at 7500 MPa). Here we utilize CNXLs in a bottom-up hierarchical assembly to produce a macroscale material. Single-stranded oligonucleotides with an amino modifier were successfully grafted on CNXLs. The molecular recognition ability of the oligomeric base pairs was then utilized by duplexing complementary oligonucleotides grafted onto separate CNXL populations. The resulting hybrid nanomaterials were analyzed using dynamic light scattering, atomic force microscopy, and UV spectroscopy.

Cellulose nanocrystal-filled carboxymethyl cellulose nanocomposites.

Polymer nanocomposites are one of the important application areas for nanotechnology. Naturally derived organic nanophase materials are of special interest in the case of polymer nanocomposites. Carboxymethyl cellulose is a polyelectrolyte derived from natural materials. It has been extensively studied as a hydrogel polymer. Methods to modify the mechanical properties of gels and films made from CMC are of interest in our lab and in the commercial marketplace. The effect of nano-sized fillers on the properties of CMC-based composites is of interest in the development of novel or improved applications for hydrogel polymers in general and CMC in particular. This project investigated cellulose nanocrystals (CNXLs) as a filler in CMC and compared the effects to microcrystalline cellulose (MCC). The composite material was composed of CMC, MCC or CNXL, with glycerin as a plasticizer. CNXL and MCC concentrations ranged from 5% to 30%. Glycerin concentrations were kept constant at 10%. CNXLs improved the strength and stiffness of the resulting composite compared to MCC. In addition, a simple heat treatment was found to render the nanocomposite water resistant.