Cellulose Fiber Networks Research Articles

Effective embedment of activated carbons into the traditional Korean paper ‘Hanji’ and its application to flexible supercapacitors

Demands for flexible electronic equipment such as wearable devices and wrap-round displays have motivated the development of flexible energy storage devices. Although cellulose paper is one of the most promising substrates for flexible devices, its intrinsic limitations, such as poor mechanical durability, hamper its practical use. In this study, we adopted the traditional Korean paper, Hanji, with superior mechanical robustness as a substrate for supercapacitor electrodes. The effective infiltration of activated carbons (ACs) as an electrode material into the dense network of Hanji cellulose fibers was performed by a simultaneous one-pot process of network formation and AC embedment. The fabricated symmetric supercapacitors based on the AC-embedded Hanji electrode exhibited a specific capacitance (Csp) of 16.0 F/g measured at a scan rate of 10 mV/s with excellent cycle stability, the Csp retention of 94.5%, over 1000 charge-discharge cycles.

Micro-mechanical modeling of irreversible hygroscopic strain in paper sheets exposed to moisture cycles

Paper is a complex material consisting of a network of cellulose fibres at the micro-level. During manufacturing, the network is dried under restraint conditions due to tension in the paper web in machine direction. This gives rise to internal strains that are stored in the produced sheet. Upon exposure to a moisture cycle, these strains may be released. This results in permanent shrinkage that may cause instabilities such as curl or waviness of the sheet. The prime objective of this paper is to model this irreversible shrinkage and to link its magnitude to the properties of the fibres and of the network. For this purpose, randomly generated fibrous networks of different coverages (i.e.ratio of the area occupied by fibres and that of the sheet) are modeled by means of a periodic representative volume element (RVE). Within such RVEs, a finite element method combined with a kinematic hardening plasticity model at the scale of the fibres is used to capture the irreversible response. The computational results obtained demonstrate that the magnitude of the irreversible strains increases with coverage until a certain coverage and beyond that coverage decreases in magnitude. This phenomenon is explained by considering the area fraction of free-standing fibre segments relative to bonded fibre segments in the network. A structure–property dependency of irreversible strains at the sheet-level on the micro-structural parameters of the network is thereby established.

Effect of DMDHEU treatment on properties of bacterial cellulose material

The aim of this study was to estimate the influence of purification and treatment with textile finishing agent procedures on structural, mechanical, and water barrier properties of bacterial cellulose (BC) in order to predict the end-use properties. Kombucha fungus generated by Komagataeibacter xylinus species, formerly known as Gluconacetobacter xylinus, was used to produce the BC material. The BC was purified with 0.5% sodium hydroxide (NaOH) solution and treated with 5%, 10%, and 20% concentration of N, N-dimethylol 4,5-dihydroxy-ethylene urea (DMDHEU). By Fourier transform spectroscopy (FTIR) and X-ray diffractometer (XRD) was estimated, that the purification with a weak alkali solution was effective to remove amorphous matter of the BC material. Scanning electron microscope (SEM) images demonstrated the BC structure, similar to a non-woven textile fabric with clearly visible three-dimensional networks of fine cellulose fibers. After the purification process, the BC material tensile strength increased by 52%; however, the strain decreased by 93%. BC material after treatment with 20% DMDHEU regained deformability and tensile properties analogous to untreated samples. Water vapor permeability (WVP) values increased and water absorption capacity (WAC) decreased in BC material with increasing DMDHEU concentration. According to the FTIR results, the crosslinking reaction of DMDHEU and adjacent BC molecules was proved. The treatment with DMDHEU restores the amorphous properties of BC material, and therefore blocks water absorption, and the decrease in the water absorption parameter might be determined.

One-pot in situ synthesis of eco-friendly cellulose magnetic nanocomposite (Cf-MNCs) for dye adsorption application

Cellulose-based magnetic nanocomposites (Cf-MNCs) have been introduced using a modified one-pot in situ co-precipitation method using iron salts with various concentrations in the alkali solution. Fabricated nanocomposites investigated for structural and functional properties with different spectroscopic characterization techniques prior to use in dye degradation study. The scanning electron microscopy revealed the morphological structure of the synthesized nanofibers and nanocomposites. The elemental analysis and vibrating sample magnetometry emphasized the presence of Fe elements attributed to the iron salts. The HRTEM analysis showed a destructed cellulose fiber network indicating its arrangement into nanocomposites. Moreover, the crystal properties of the Cf-MNCs were accomplished using x-ray powder diffraction (79.3% crystallinity). The Fourier transform infrared analysis and differential scanning calorimetry gives the idea about the structural and functional changes in the cellulose fibers loaded with iron oxide nanoparticles. The functional adsorption properties of the prepared nanocomposites have been evaluated using methylene blue and Alizarin red S carcinogenic dyes. The dye adsorption of the fabricated Cf-MNCs nanocomposites was found to be 93%. We affirmed that this novel eco-friendly degradable polymer-based nanocomposite has great potential in the field of catalyst fabrication for the degradation of organic pollutants in wastewater.

Use of waste mushroom beds for the production of value-added biodegradable fiber sheet

This research focused on the utilization of waste mushroom beds (WMB) after the harvesting of oyster (WMB-O) and lingzhi mushrooms (WMB-L) for the preparation of eco-friendly materials, fiber sheets. The WMB were sterilized and determined for their chemical compositions. The dry fiber of the sterilized WMB were pretreated by a steam explosion, comparing with alkaline pretreatment before the fiber sheet forming process. The results showed that f-cellulose contents of the WMB were in the range of 27-35% by dry weight basis. The fiber from WMB-L treated by alkaline at 13.5% w/w of NaOH for 120 min showed better fiber sheet appearance, compared to the steam explosion. Afterward, tapioca starch was added as a natural binder during the fiber sheet forming and their physical properties were determined. The analytical results indicated that an increase of NaOH concentration in the pretreatment led to an increase in the toughness and water absorption of the fiber sheet. The additional tapioca starch promoted the interaction between cellulose fiber networks, corresponding to the decrease of water absorption and a compressed appearance after water immersion. These finding results disclosed a potential use of the WMB as ecofriendly materials, e.g. biodegradable packaging, packing materials, cultivation vase in the future.

Bacterial nanocellulose membrane as bolus in radiotherapy: "proof of concept"

Boluses characterize materials with an electromagnetic radiation attenuation coefficient similar to biological tissue and used to restrict the penetration of high energy photons and electrons used in radiotherapy for the treatment of superficial tumors. The development of new materials, mainly from sustainable biotechnological routes, will contribute to increase efficiency and expand the use of these technologies. The objective of this research was to develop the “proof of concept” regarding the use of the bacterial nanocellulose membrane (BNCm) as a bolus. For this purpose, BNCm were produced, purified and subjected to the physical–chemical characterization. The radiological density (RD) and radiation attenuation potential (RAP) of the BNCm were established and compared to a commercial bolus (CB). The moldability of BNCm was established and compared to the virtual bolus of dosimetric planning. The physical–chemical analysis demonstrated the constitution of a pure, highly hydrated, homogeneous and nanostructured network of cellulose fibers. BNCm showed superiority in relation to RD and similar RAP values when compared to CB. Moldability analysis showed a profile identical to a virtual bolus. The results validate the concept of using BNCm as a highly efficient biotechnological device, aligned with the idea of sustainability, as a bolus for use in radiotherapy.

Impact of degree of substitution of cationic xylan on strength of cellulose fiber networks along with medium conductivity

Hemicelluloses have been considered as an efficient component to improve the bonding or strength of fiber networks. The degree of substitution (DS) of cationic hemicelluloses and the ionic strength of applied medium are therefore two most important and crucial factors influencing its performance in wet-end of papermaking. Therein, the impact of DS of cationic xylan (CX) derived from corncob on the strength of fiber networks was systematically explored in aqueous media with various ionic strengths. Initially, a series of CXs with DS ranging from 0.051 to 0.113 were synthesized via a microwave-assisted method. The resulting CXs were applied as wet-end additives in the media with conductivity of 500, 2500, and 5000 μs/cm, representing the low, moderate, and high level of electrolytes in closed white water circulation, respectively. Comparing to the control, all CXs improved the tensile and tear strength of paper significantly, while not in burst strength. The medium conductivity had an adverse impact on the performance of CXs, and the optimum DS of CXs was down shifted to about 0.05 ∼ 0.06. To mimic the adsorption of CXs on fiber surface, the adsorption behavior of CXs on negatively charged gold sensor was monitored by SPR in an attempt to reveal the mechanism. It was found that CXs with low DS had a larger adsorption capacity, thicker and softer adlayer, which are beneficial to fiber bonding and paper strength. This study is meaningful to the applications of xylan into value-added products and to the valorization of agricultural and forestry wastes.

Approaching Theoretical Haze of Highly Transparent All-Cellulose Composite Films.

A highly transparent cellulose film with a high built-in haze is emerging as a green photonic material for optoelectronics. Unfortunately, attaining its theoretical haze still remains a challenge. Here, we demonstrate an all-cellulose composite film with a 90.1% transmittance and a maximal transmission haze of 95.2% close to the theoretical limit (∼100%), in which the entangled network of softwood cellulose fibers works as strong light scattering sources and regenerated cellulose (RC) with undissolved fibril bundles functions as a matrix to simultaneously improve the optical transparency and transmission haze. The underlying mechanism for the ultrahigh haze is attributed to microsized irregularities in the refractive index, arising primarily from the crystalline structure of softwood fibers, undissolved nanofibril bundles in RC, and a small number of internal cavities. Moreover, the resulting composite film presents a folding resistance of over 3500 times and good water resistance, and its application in a perovskite solar cell as an advanced light management layer is demonstrated. This work sheds light on the design of a highly transparent cellulose film with a haze approaching the theoretical limit for optoelectronics and brings us a step further toward its industrial production.

Bacterial Nanocellulose Membrane As Bolus in Radiotherapy: “Proof of Concept”

Bolus characterize materials with an electromagnetic radiation attenuation coefficient similar to biological tissue and which are positioned on the skin of patients during radiotherapy treatment. Such devices are responsible for the superficialization of the maximum dose of high energy photons and electrons, restricting its penetration and improving the coverage of the treatment isodose. The development of new materials, mainly from sustainable biotechnological routes, will contribute to increasing efficiency and expanding the use of these technologies. The objective of this research was to develop the “proof of concept” regarding the use of the bacterial nanocellulose membrane (BNCm) as a bolus for radiotherapy procedures. For this purpose, 1.4 cm thick BNCm were produced from static cultivation of the K. rhaeticus, purified and subjected to the physical‐chemical characterization process by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT‐IR). The samples were then subjected to the determination of the radiological density (RD), by computed tomography, and the radiation attenuation potential (%), after being irradiated with 6MV photons in a linear accelerator using ionization and phantom chamber at doses of 100 and 50 UM. The results were compared with data from the analyzes in a commercial bolus (CB) with same thickness. The physical‐chemical analysis demonstrated the constitution of a pure, highly hydrated, homogeneous and nanostructured network of cellulose fibers. The mean RD of BNCm was 1.1 and 5 Hounsfield units respectively, demonstrating high water (0HU) equivalence from BNCm. The values corresponding to the radiation attenuation at the dose of 100 MU were 5.1 ± 0.1% and 4.6 ± 0.2%, for CB and BNCm respectively. The values for the dose of 50 MU were 3.8 ± 0.1% and 3.0 ± 0.2%. In both doses, the attenuation of BNCm was similar to the CB. It stands out the superiority of the BNCm moldability and the possibility to change its composition to improve the radiation attenuation. The results support the concept of use the BNCm as an effective biotechnological device, align to the sustainability idea, as a bolus for radiotherapy treatment.Support or Funding InformationI.P.F.B. Indústria de Produtos Farm. e Biotecnológicos Ltda.

Facile fabrication of functional cellulose paper with high-capacity immobilization of Ag nanoparticles for catalytic applications for tannery wastewater

It has been a research goal to develop macroscopic materials with an optimized surface structure to affix silver nanoparticles which could contaminate water and maximize their practical functions. Cellulose paper is a versatile biomass material valued for its abundance, low cost, biocompatibility, and natural composition. Until now, its potential application in water purification has not been adequately explored. In this study, gallic acid-modified silver nanoparticles (GA@AgNPs) were loaded onto commercial cellulose filter paper using a simple lipoic acid modification process (GA@AgNPs-LA-CP). Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were used to characterize the GA@AgNPs-LA-CP. The catalytic activity of the GA@AgNPs-LA-CP was evaluated by the reduction reaction of methylene blue (MB), Rhodamine B (RhB), and 4-nitrophenol (4-NP) with sodium borohydride (NaBH4). The GA@AgNPs-LA-CP exhibited excellent catalytic activity toward MB, RhB, and 4-NP, taking advantage of its high specific surface area generated by the cellulose fiber network structure. Interestingly, due to the electrostatic interactions between the cationic dyes and the GA@AgNPs, the as-prepared catalytic composite material serves as a better catalyst for MB and RhB, suggesting dual applications of the composite materials for organic wastewater treatment and the removal of harmful dyes. This implies that the immobilization of AgNPs on cellulose papers is an effective method and can be applied to efficient wastewater treatment applications.Graphical abstract

Highly sensitive paper-based electrochemical sensor for reagent free detection of bisphenol A

Bisphenol A is one the most relevant endocrine disruptors for its toxicity and ubiquity in the environment, being largely employed as raw material for manufacturing processes of a wide number of compounds. Furthermore, bisphenol A is released in the drinking water when plastic-based bottles are incorrectly transported under sunlight, delivering contaminated drinking water. For the health of human beings and the environment, rapid and on site detection of bisphenol A in drinking water is an important issue. Herein, we report a novel and cost-effective printed electrochemical sensor for an enzymatic-free bisphenol A detection. This sensor encompasses the entire electrochemical cell printed on filter paper and the reagents for the measurement loaded in the cellulose fiber network, for delivering a reagent-free analytical tool. The working electrode was printed using ink modified with carbon black, a cost effective nanomaterial for sensitive and sustainable bisphenol A determination. Several parameters including pH, frequency, and amplitude were optimized allowing for a detection limit of 0.03 μM with two linear ranges 0.1–0.9 μM and 1 μM–50 μM, using square wave voltammetry as electrochemical technique. The satisfactory recovery values found in river and drinking water samples demonstrated the suitability of this sensor for screening analyses in water samples. These results revealed the attractiveness of this paper-based device thanks to the synergic combination of paper and carbon black as cost-effective materials.

Working with Minions: Assisted Scalable Bio-nanomanufacturing of Functional Materials

The fictional “Minions” from film are single-focused workers, useful for accomplishing a specific task en masse. Here, minion-like bacteria is presented as a useful intermediary craftsman for functionalizing biomaterials, enabling a generic process for integrating desired chemical additives and/or nanoparticles.

Layer-by-layer modified low density cellulose fiber networks: A sustainable and fireproof alternative to petroleum based foams

Wood-based cellulose fibers were used to prepare porous, low density and wet-stable fiber networks (FN). Multilayer coatings consisting of chitosan (CH), sodium hexametaphosphate (SHMP) and inorganic nanoparticles comprising of either sodium montmorillonite (MMT), sepiolite (SEP) or colloidal silica (SNP) were deposited by the layer-by-layer (LbL) technique onto FNs in an effort to impart flame-retardancy. A simulated fire scenario measured by cone calorimetry showed that five quadlayers (QL) of CH/SHMP/CH/MMT, CH/SHMP/CH/SEP and CH/SHMP/CH/SNP can produce significant reduction in peak heat release rate (pkHRR). In detail, the coating containing SEP showed the largest reduction of the pkHRR by 47% relative to the uncoated FN. MMT and SEP coated FNs were also able to self-extinguish fire and to retain their shapes after direct exposure to a methane flame. This study hence shows that the LbL assembly is a highly effective way to impart flame-retardant properties to this new type of porous FN.

Stacked-Cup Carbon Nanotube Flexible Paper Based on Soy Lecithin and Natural Rubber.

Stacked-cup carbon nanotubes (SCCNTs) are generally referred to as carbon nanofibers (CNFs). SCCNTs are much less expensive to fabricate and are regarded as good polymer modifiers suitable for large-scale production. Flexible, SCCNT-based soy lecithin biocomposites were fabricated using liquid natural rubber latex as binder. Natural polymers and the SCCNTs were dispersed in a green solvent using a benchtop high-pressure homogenizer. The inks were simply brush-on painted onto cellulose fiber networks and compacted by a hydraulic press so as to transform into conductive paper-like form. The resulting flexible SCCNT papers demonstrated excellent resistance against severe folding and bending tests, with volume resistivity of about 85 Ω·cm at 20 wt % SCCNT loading. The solvent enabled formation of hydrogen bonding between natural rubber and soy lecithin. Thermomechanical measurements indicated that the biocomposites have good stability below and above glass transition points. Moreover, the SCCNT biocomposites had high through-plane thermal conductivity of 5 W/mK and 2000 kJ/m3K volumetric heat capacity, ideal for thermal interface heat transfer applications.

Switchable Liquid Crystal Composite Windows Using Bacterial Cellulose (BC) Mat Substrates

Performance properties were investigated for transparency switching devices fabricated with nematic LC filled bacterial cellulose (BC) mats as electro-optical components. Biobased BC is a nanoporous bicontinuous network of cellulose fibers produced by bacteria and cultured to form mats of desired thickness. Devices made from BC mats with thicknesses of 6, 20, and 40 μm were compared. Furthermore, the electro-optical response of the devices provides insight into the ordering of the nematic LC within the bicontinuous BC matrix.

Interlocking Enzymes in Graphene-Coated Cellulose Paper for Increased Enzymatic Efficiency.

A simple method for interlocking glucose oxidase and horseradish peroxidase in a network of cellulose fibers coated with bovine serum albumin (BSA)-exfoliated graphene (biographene) is reported here. The resulting paper reactor is inexpensive and stable. Biographene is expected to function as an electron shuttle, making the reaction between the enzyme and the substrate more efficient, and this hypothesis is examined here. The BSA used to separate the sheets of graphene provides extra carboxylic acid groups and primary amines to help interlock the enzymes and the graphene in between the fibers. The decrease in entropy associated with interlocking the enzymes on a solid support is likely responsible for the increase in enzymatic stability/activity observed. Each cellulose disk contained 5.2mg of enzyme per gram of paper and 93% of the enzyme is retained after washing for 0.5-2h. This simple methodology provides a low cost, effective approach for achieving high enzymatic activity and good loadings on a benign, versatile support.

Fabrication of 3D Shapes of Carbon By Origami

We present preliminary experiments leading to a novel approach to manufacture 3D complex shapes of thin carbon using origami. Origami is an ancient art of paper folding, where a 3D complex shape can be fabricated by folding planar paper along the creases. Paper is generally a random network of cellulose fibers. Cellulose decomposes to carbon upon heat treatment around 900 °C in inert atmosphere. The cellulose derived carbon resembles to glass-like carbon and possesses interesting properties such as low density, high electrical conductivity, biocompatibility, and high resistance to high temperature and corrosive environment1,2. Here, we aim to demonstrate the capability to manufacture 3D complex origami structures of carbon by heat treating the precursor paper origami structures. These complex 3D structures of thin cross section carbon have huge potentials as multifunctional material in different applications such as tissue engineering scaffold, catalyst support and biomedical devices. We used Fisherbrand pure cellulose chromatography paper (Sigma Aldrich, Cat. No. 05-714-1) because of its cellulosic nature and minimal impurity. A cutting plotter machine (Graphtec CE6000-40, USA) was used to pre-crease the paper. The pre-creasing method started with generating CAD models to define the location of the creases. CAD models for the creases on both sides of the paper must be created separately. Registration marks were printed on the both sides of the chromatography (CG) paper by a laser-jet printer for accurate alignment during pre-creasing. The CG paper was fed to the cutting plotter machine and pre-creased with a ball-point pen mounted on the cutting plotter machine using specific equipment parameters. Once pre-creasing is done on one side, the CG paper was flipped and creased on the other side. Excess portion of the paper was then trimmed and folded manually along the creases to obtain paper origami structures. The paper origami structures were carbonized in a tube furnace (TF1400, Across International, Japan) at 900 °C for 75 minutes in a nitrogen atmosphere. This process was repeated for three different origami tessellations, which are Miura-ori, Waterbomb-base and Yoshimura in descending order of complexity. SEM and XRD were performed to characterize the effect of carbonization on the microstructure and the material composition of the carbonized sample respectively. The compressive strength of the carbonized Miura-ori was characterized by compression test. Figure 1 shows the origami tessellations before and after carbonization. The carbonized samples retained the original precursor origami structure during the heat treatment, although surface wrinkling could be observed for the carbonized structures. Around 90% weight loss occurred during the carbonization. A significant shrinkage was also observed for the carbonized origami structures. Although the overall shrinkage was dependent on the complexity of the origami structures, around 75-90% shrinkage was observed in the fibril structures when compared the microstructures of CG paper and carbonized samples as shown in Figure 2a and 2b respectively. Our hypothesis is escape of the gaseous substances from the cellulose during the carbonization results in the weight loss and the shrinkage. The XRD pattern of the carbonized sample as shown in Figure 2c confirms the formation of amorphous carbon during the carbonization process. The compressive strength to weight ratio of the carbon Miura-ori was measured to be 96.4 ± 0.48 kPa/g, which is over 5 times that of paper Miura-ori as shown in Figure 2d. Ongoing work is on characterizing the scalability of this manufacturing process; infiltrating the paper origami structure with metal precursor to obtain metal impregnated carbon origami structure through carbothermal reduction reaction for structural electrode or sensor application; and infiltrating the carbon structure with bio-epoxy to increase the strength of the carbon origami structures.

On the transient out-of-plane behaviour of high-density cellulose-based fibre mats

High density cellulose-based materials have been widely used for electrical insulation and (interior) construction or structural material. Similar to typical paper/board materials, the microstructure of high-density fibre mats consists of a porous network of cellulose fibres, which contributes to its highly non-linear mechanical response. Such fibre mats exhibit strong anisotropic material behaviour as well as significant transient (time- or rate-dependent) behaviour. The present investigation is aimed at studying the transient behaviour of high-density cellulose fibre mats, particularly during out-of-plane compression. A viscoelastic–viscoplastic constitutive model dedicated for high-density cellulose-based materials has been used to simulate the responses of the high-density cellulose-based fibre mats upon two types of transient loading, i.e. compressive creep and stress relaxation. The predictions of the model are then compared to the corresponding experimental characterization results, which indicate that material densification mechanism plays a more critical role during out-of-plane compression creep than in stress relaxation.

Synthesis of Tungsten Carbide from Bacterial Cellulose

Here we present preliminary experiments for synthesis of carbide materials from bacterial cellulose that has been infiltrated with tungsten trioxide nanoparticles. Bacterial cellulose decomposes to carbon upon heat treatment around 900 °C. Upon further heat treatment in the presence of the metal oxide, this carbon reacts with the metal oxide to form a metal carbide. Bacterial cellulose is easily obtained using a microbial fermentation process1. The product is a random network of nanometer-scaled cellulose fibers featuring high crystallinity. In contrast to cellulose obtained from plants, bacterial cellulose is pure cellulose. Hence, the carbides that could be obtained from this carbonized material are expected to exhibit superior properties than other bio-synthesized carbides. Furthermore, we aim at fabricating engineered cellulose scaffolds by manipulating bacterial movement in desired trajectories. The functionalization of these scaffolds would then lead to engineered carbides. Bacterial cellulose (BC) is widely used as the base of the desert nata de coco, and is gaining recognition as a performance material in wound dressing. In this work we use commercially available nata de coco (purchased as Jubes Nata de Coco) as the bacterial cellulose and tungsten trioxide (WO3) as the metal oxide nanoparticle, as we aim to synthesis tungsten carbide (WC). Cubes of nata de coco were washed repeatedly in ultra-pure water to eliminate the flavored syrup in which they were originally suspended. Once washed, the BC cubes were immersed in an alcohol-based WO3dispersion and shook gently for 30 minutes. After 30 minutes, the cubes were taken out of the dispersion and directly introduced in a tube furnace. Heat treatment was performed with a heating rate of 5 °C/min and constant nitrogen gas flow. Based on previous heating protocols, a dwell of 30 minutes at 300 °C was first used to eliminate oxygen from the chamber, followed by a dwell of 3 hours at 1300 °C. XRD and SEM/EDS analysis were performed to characterize the carbonaceous materials obtained after the heat treatment. Bacterial cellulose can hold up to 90% water of its total volume 2. Hence significant amount of shrinkage occurs during the heat treatment. XRD characterization was performed after heat treatment and the results shown in Figure 1. Tungsten carbide (WC) has been formed along with its weaker form W2C. A significant amount of metallic tungsten (W) is still present in the material. Heat treatment at higher temperature and longer dwell time may eliminate these W and W2C to obtain only WC. From the SEM image in Figure 2a, it seems like carbide has been formed only on the surface and distribution of the carbide material is non-uniform on the surface. Figure 2b shows the SEM image of the tungsten carbide particles sitting on carbon background. The synthesized WC features particle size ranging from tens of nanometers up to 1.5 μm. The EDS results of the particles (Table 1) also confirm that the particles are of tungsten carbide. Our current hypotheses are that most of the WO3nanoparticles could infiltrate only couple of microns inside from the surface the BC cube. Alternatively, the particles could have been pushed out from the matrix during water evaporation. Ongoing work is on characterizing the extent of nanoparticle infiltration in the BC matrix before and after water evaporation during heating; using critical point drying to obtain an aerogel before heat treatment; and optimizing the heat treatment process to obtain entirely WC.

Optically Transparent Wood from a Nanoporous Cellulosic Template: Combining Functional and Structural Performance.

Optically transparent wood (TW) with transmittance as high as 85% and haze of 71% was obtained using a delignified nanoporous wood template. The template was prepared by removing the light-absorbing lignin component, creating nanoporosity in the wood cell wall. Transparent wood was prepared by successful impregnation of lumen and the nanoscale cellulose fiber network in the cell wall with refractive-index-matched prepolymerized methyl methacrylate (MMA). During the process, the hierarchical wood structure was preserved. Optical properties of TW are tunable by changing the cellulose volume fraction. The synergy between wood and PMMA was observed for mechanical properties. Lightweight and strong transparent wood is a potential candidate for lightweight low-cost, light-transmitting buildings and transparent solar cell windows.