Financial support from an Industrial Research Chair funded by FPInnovations and NSERC for a NSERC Discovery grant and from the NSERC Innovative Green Wood Fiber Products Network are acknowledged.

CAUTION: Read the material safety data sheets (MSDS) of all the chemicals before touching them. Many of the chemicals used in this work may cause severe health damages. Using personal protection such as lab coat, gloves, and goggles is a must. Do not forget that safety comes first. The water used throughout the synthesis is distilled water.
1. Preparation of Partially Oxidized Fibers as an Intermediate
<ol>
	<li>Tear 4 g Q-90 softwood pulp sheets into small pieces of approximately 2 x 2 cm2.</li>
	<li>Soak the torn pulp sheets in water for at least one day.</li>
	<li>Disintegrate the wet pulp using a mechanical disintegrator to achieve an almost-uniform dispersion.</li>
	<li>To assemble the vacuum filter, secure a nylon filter in a Buchner funnel and place the funnel in a filter flask. Then, connect the filter flask to a vacuum pump using proper tubing. Turn on the pump and pour the disintegrated pulp solution in the funnel to separate the pulp from the liquid.</li>
	<li>Measure the weight of wet pulp (m1), and calculate the amount of absorbed water by pulp: mw,1 = m1 - 4.</li>
	<li>Preparation of periodate oxidizing solution
	<ol>
		<li>For SNCC/DAMC synthesis: separately, dissolve 2.64 g sodium periodate (NaIO4) and 15.48 g sodium chloride (NaCl) in 200-mw,1 ml water.</li>
		<li>For ENCC/DCC synthesis: separately, dissolve 5.33 g sodium periodate (NaIO4) and 15.6 g sodium chloride (NaCl) in 266-mw,1 ml water.</li>
	</ol>
	</li>
	<li>Add the wet pulp separately to the solutions prepared in 1.6. Make sure that the total amount of water (absorbed by pulp plus added water) is equal to 200 ml for SNCC and 266 ml for ENCC syntheses.</li>
	<li>Cover the beaker thoroughly with aluminum foil to prevent periodate deactivation while stirring at speed ~ 105 rpm in RT for a desired amount of time according to Table 1 to achieve a favored aldehyde content. As an example, to obtain ~ 6.5 mmol/g aldehyde, react for 96 hr.</li>
	<li>When the reaction time is elapsed, open the aluminum foil and add 1 ml (in case of SNCC/DAMC synthesis) or 3 ml (in case of ENCC/DCC synthesis) ethylene glycol to the mixture and stir for 10 min to stop the oxidation reaction by quenching periodate.</li>
	<li>Collect the oxidized pulp by vacuum filtration (according to 1.4), redisperse it in 500 ml water, and stir it for 30 min. Repeat this step at least 5 times to clean the pulp from periodate thoroughly.</li>
	<li>After the 5th water wash on the oxidized pulp, separate the pulp from solution by vacuum filtration and store it in a cold (4 &#176;C) place.</li>
</ol>
2. Synthesis of SNCC and DAMC
<ol>
	<li>Divide the partially oxidized wet pulp (m1), obtained in 1.11, by four: m2 = m1/4, and measure the weight of absorbed water: mw,2 = m2 - 1.</li>
	<li>Disperse the pulp in (100 - mw,2) g water in a round bottom flask (total water content = 100 g).</li>
	<li>Place the round bottom flask in an oil bath and heat the partially oxidized pulp at 80 &#176;C for 6 hr while gently stirring. 
	Note: If pulp is completely oxidized with periodate (DS = 2), e.g., by reacting 1 g pulp with 1.85 g NaIO4 (8.65 mmol) in a solution comprising 3.87 g NaCl (8.64 mmol) and 65 ml water while stirring for 6 days, depending on the heating condition and residence time in water, the property of the dialdehyde cellulose (DAC) is changed (Table 2).</li>
	<li>Cool down the solution to RT.</li>
	<li>Centrifuge the solution at 18,500 x g for 10 min. The precipitate is unfibrillated cellulose (fraction 1).</li>
	<li>Separate the supernatant carefully and weigh it (A).</li>
	<li>Add 1.7(A) g propanol to the supernatant obtained in 2.6 while stirring to precipitate SNCC. Details about the separated SNCC and added propanol is available in Figure 1.</li>
	<li>Centrifuge the biphasic solution at 3,000 x g for 10 min, and separate the resulted gel-like precipitate (second fraction, SNCC) by decantation, which is ready to be redispersed and dialyzed for further purification (section 4) and characterization (section 5).</li>
	<li>To the supernatant obtained in 2.8, add 3.5(A) g propanol to yield a white precipitate (third fraction, DAMC).</li>
	<li>Centrifuge the solution of 2.9 at 3,000 x g for 10 min, and collect the gel-like DAMC precipitate (by pouring the supernatant in a separate beaker) ready to be redispersed in water, purified by dialysis (details available in section 4), and characterized (section 5).</li>
</ol>
3. Synthesis of ENCC and DCC
<ol>
	<li>Prepare a solution of 0.5 M sodium hydroxide (NaOH) by dissolving ~ 2 g NaOH in 100 ml water and keep it aside. This will be used in step 3.7.</li>
	<li>Divide the wet oxidized pulp, obtained in 1.11, by four: m3 = m1/4, and measure the weight of absorbed water: mw,3 = m3 - 1.</li>
	<li>Separately, add 2.93 g sodium chloride (NaCl) and 1.41 sodium chlorite (NaClO2) to (50 - mw,3) ml water and stir to dissolve.</li>
	<li>Suspend m3 gram of wet oxidized pulp (containing ~ 1 g dry oxidized pulp) in the solution obtained in 3.3. Note that the final pulp concentration is 1 g in 50 ml total available water (free and absorbed water).</li>
	<li>Place a pH meter in the solution of 3.4.</li>
	<li>Add 1.41 g hydrogen peroxide (H2O2) to the mixture of step 3.4 dropwise.</li>
	<li>Stir the suspension of 3.6 for 24 hr in RT at 105 rpm while maintaining the pH ~ 5 by gradually adding 0.5 M sodium hydroxide (NaOH) prepared in step 3.1. 
	Note: The pH starts decreasing rapidly after ~ 15 min from the beginning of reaction, and it should be kept constant at 5 for at least the first 4 hr of the reaction. For convenience, it is suggested that the reaction is started at 1 PM and the pH is controlled until 5 PM, then the reaction is left O/N and early in the morning the pH is increased to 5 again. After such a long time, pH drop will not be significant, indicating that most of the conversion is achieved. Now, almost no solid can be observed in the solution (large fibers are broken down into nanoparticles). Note that if the reaction is left for a longer time, the crystalline part may be disrupted.</li>
	<li>Divide the suspension obtained from 3.7 into equally weighted centrifuge tubes and centrifuge at 27,000 x g for 10 min, and separate the supernatant (ENCC + DCC) from the micro-fibrous precipitate.</li>
	<li>Weigh the supernatant obtained from 3.8 and call the solution mass (B).</li>
	<li>Slowly add 0.16(B) g ethanol to the solution of 3.9 while stirring to form a white precipitate (second fraction, ENCC).</li>
	<li>Centrifuge the solution of 3.10 at 3,000 x g for 10 min, and separate the resulted gel-like ENCC precipitate by decantation. ENCC is ready to be redispersed in water, purified by dialysis (details available in section 4), and characterized (section 5).</li>
	<li>To the supernatant obtained in 3.11, add equal mass of ethanol as the solution mass to yield a white precipitate (third fraction, DCC).</li>
	<li>Centrifuge the solution of 3.12 at 3,000 x g for 10 min, and separate the gel-like DCC precipitate ready to be redispersed in water, purified by dialysis (details available in section 4), and characterized.</li>
</ol>
4. Dialysis Procedure to Purify SNCC, DAMC, ENCC or DCC
<ol>
	<li>Redisperse the gel-like precipitate obtained in any steps of 2.8 (SNCC), 2.10 (DAMC), 3.11 (ENCC), or 3.13 (DCC) in 10 ml water by vigorous stirring for 1 hr.</li>
	<li>Place the dispersion in a dialysis tubing (MW Cutoff = 12-14 kDa, Length ~ 30 cm, width ~ 4.5 cm) and secure the top and bottom by clipping.</li>
	<li>Place the filled dialysis bag in ~ 4 L of distilled water and stir for 24 hr to eject the salts.</li>
	<li>Collect the dialyzed solution in a container and store in a cold (4 &#176;C) place.</li>
</ol>
5. Post-purification Characterization: Solid Phase and Charge Concentrations Measurement
<ol>
	<li>Concentration measurement
	<ol>
		<li>Weigh 3 ml of a desired dispersion in a weighting dish (Aluminum cup, 57 mm).</li>
		<li>Place the weighing dish containing the dispersion in an oven (50 &#176;C) O/N.</li>
		<li>Weigh the dry film and calculate the concentration of nanoparticles or polymers in the dispersion: 
		Concentration (w/v%) = 100 x mass of dry film / 3, or 
		Concentration (w/w%) = 100 x mass of dry film / mass of dispersion</li>
	</ol>
	</li>
	<li>Conductometric titration
	<ol>
		<li>Conductometric titration of SNCC or DAMC to determine aldehyde content
		<ol>
			<li>Prepare 0.1 M hydrochloric acid (HCl) by adding 0.82 ml HCl to 25 ml water followed by adjusting the final volume to 100 ml.</li>
			<li>Separately, prepare NaOH 0.1 M by adding 0.4 g sodium hydroxide to distilled water to achieve 100 ml final solution.</li>
			<li>Following the hydroxylamine hydrochloride method24, add a known amount of a desired dispersion to a desired amount of water (e.g., 0.02 g in 50 ml H2O).</li>
			<li>Adjust the pH to 3.5 using dilute HCl (0.1 M).</li>
			<li>Add 10 ml hydroxylamine hydrochloride solution (5% w/w) to the dispersion.</li>
			<li>Monitor the pH and keep it at 3.5 by adding 0.1 M NaOH until pH becomes stable at 3.5.</li>
			<li>Using the consumed volume of NaOH to neutralize the H+ released from the reaction of aldehyde groups and NH2OH&#183;HCl, measure the aldehyde concentration (mole of consumed NaOH = mole of produced HCl during the reaction = mole of aldehyde groups on SNCC).</li>
		</ol>
		</li>
		<li>Conductometric titration of ENCC or DCC to determine carboxyl content
		<ol>
			<li>Following literature25, add enough amount of a desired dispersion to have 0.02 g of solid in 140 ml distilled water.</li>
			<li>Separately, prepare 20 mM NaCl by dissolving 0.117 g NaCl in distilled water to achieve 100 ml final solution. Add 2 ml of 20 mM NaCl to 5.2.2.1.</li>
			<li>Reduce the pH to about 3 using dilute HCl (0.1 M).</li>
			<li>Perform the conductometric titration by adding standard sodium hydroxide (NaOH, 10 mM) in 0.1 ml/min increments up to pH ~ 11.</li>
			<li>Using the consumed volume of NaOH to neutralize charged groups (details in Figure 2), measure the surface charge concentration (1 mole of consumed base equals to one mole COOH on the particle surface).</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

Following the chemistry discussed in this visual paper, a spectrum of highly stable cellulose-based nanoparticles with tunable charge bearing both crystalline and amorphous phases (hairy nanocrystalline celluloses) are produced. Depending on the periodate oxidation time, as shown in Table 1, various products are yielded: oxidized fibers (fraction 1), SNCC (fraction 2), and DAMC (fraction 3) each of which providing unique properties, such as defined size, morphology, crystallinity, and aldehyde content. F...

Cellulose, as the most abundant biopolymer in the world, has been served recently as a key raw material to yield crystalline nanoparticles named nanocrystalline cellulose (NCC, also known as cellulose nanocrystals CNC)1. To understand the mechanism of NCC synthesis, the structure of cellulose fibers needs to be explored. Cellulose is a linear and polydispersed polymer comprising poly-beta(1,4)-D-glucose residues2. The sugar rings in each monomer are connected through glycosidic oxygen to form chains of (1-1.5) x 104 glucopyranose units2,3, introducing alternating crystalline parts and disordered, amorphous regions, first reported by Nageli and Schwendener2,4. Depending on the source, crystalline parts of cellulose can adopt various polymorphs5.
If a cellulose fiber is treated with a strong acid, such as sulfuric acid, the amorphous phase can be completely hydrolyzed away to disrupt the polymer and produce crystalline particles of various aspect ratio depending on the source (e.g., wood and cotton yield more than 90% crystalline nanorods of width ~ 5-10 nm and length ~ 100-300 nm, whereas tunicin, bacteria, and algae produce 5-60 nm wide and 100 nm to several micrometer long NCCs)6. Readers are referred to the vast amount of literature available on the scientific and engineering aspects of these nanomaterials2,5,7-16. Despite numerous interesting properties of these nanoparticles, their colloidal stability has always been an issue at high salt concentrations and high/low pH due to their relatively low surface charge content (less than 1 mmol/g)17.
Instead of strong acid hydrolysis, cellulose fibers can be treated with an oxidizing agent (periodate), cleaving C2-C3 linkage in the anhydro D-glucopyranose residues to form 2,3-dialdehyde units with no significant side reactions18,19. These partially oxidized fibers can be used as a valuable intermediate material to produce nanoparticles bearing both amorphous and crystalline regions (hairy nanocrystalline celluloses) using solely chemical reactions without any mechanical shear or ultrasonication20. When the partial oxidation degree DS &#60; 2, heating oxidized fibers results in three batches of products, namely fibrous cellulose, water dispersible dialdehyde cellulose nanowhiskers called sterically stabilized nanocrystalline cellulose (SNCC), and dissolved dialdehyde modified cellulose (DAMC), which can be isolated by precise control over the co-solvent addition and intermittent centrifugation21.
Performing controlled chlorite oxidation on the partially oxidized fibers converts almost all the aldehyde groups to carboxyl units, which can introduce as high as 7 mmol COOH groups per gram of nanocrystalline cellulose depending on the aldehyde content18, acting as stabilizers. These nanoparticles are called electrosterically stabilized nanocrystalline cellulose (ENCC). Furthermore, it has been confirmed that soft layers of charged hair-like protruding chains exist on ENCC17. This material has been used as a highly efficient adsorbent to scavenge heavy metal ions22. The charge of these nanoparticles can be precisely controlled by controlling the periodate reaction time23.
Despite known oxidation reactions of cellulose, the production of SNCC and ENCC has never been reported by any other research groups most probably due to the separation challenges. We have been able to successfully synthesize and isolate various fractions of nanoproducts by precisely designing the reaction and separation steps. This visual article demonstrates with complete detail how to reproducibly prepare and characterize the aforementioned novel nanowhiskers bearing both amorphous and crystalline parts from wood fibers. This tutorial may be an asset for active researchers in the fields of soft material, biological, and medicinal sciences, nanotechnology and nanophotonics, environmental science and engineering, and physics.

<table><tbody><tr><td>Q-90 softwood pulp</td><td>FPInnovations</td><td>-</td><td>-</td></tr><tr><td>Sodium periodate</td><td>Sigma-Aldrich</td><td>S1878-500G/CAS7790-28-5</td><td>Light sensitive, strong oxidizer, must be kept away from flammable materials</td></tr><tr><td>Sodium chloride</td><td>ACP Chemicals</td><td>S2830-3kg/7647-14-5</td><td>-</td></tr><tr><td>2-Propanol</td><td>Fisher</td><td>L-13597/67-63-0</td><td>Flammable</td></tr><tr><td>Ethylene glycol</td><td>Sigma-Aldrich</td><td>102466-1L/107-21-1</td><td>-</td></tr><tr><td>Sodium hydroxide</td><td>Fisher</td><td>L-19234/1310-73-2</td><td>Strong base, causes serious health effects</td></tr><tr><td>Sodium chlorite</td><td>Sigma-Aldrich</td><td>71388-250G/7758-19-2</td><td>Reactive with reducing agents and combustible materials</td></tr><tr><td>Hydrogen peroxide</td><td>Fisher</td><td>H325-500/7722-84-1</td><td>Corrosive and oxidizing agent, keep in a cool and dark place</td></tr><tr><td>Ethanol</td><td>Commercial alcohols</td><td>P016EAAN</td><td>Flammable</td></tr><tr><td>Hydrochloric acid</td><td>ACP Chemicals</td><td>H-6100-500mL/7647-01-0</td><td>Strong acid, causes serious health effects</td></tr><tr><td>Hydroxylamine hydrochloride</td><td>Sigma-Aldrich</td><td>159417-100G/5470-11-1</td><td>Unstable at high temperature and humidity, mutagenic</td></tr><tr><td>Centrifuge</td><td>Beckman Coulter</td><td>J2</td><td>High rotary speed</td></tr><tr><td>Fixed angle rotor</td><td>Beckman Coulter</td><td>JA-25.50</td><td>Tighten the lid carefully</td></tr><tr><td>Dialysis tubing</td><td>Spectrum Labs</td><td>Spectra (Part No. 132676)</td><td>Cutoff Mw = 12-14 kD, Length ~ 30 cm, width ~ 4.5 cm</td></tr><tr><td>Aluminum cup</td><td>VWR</td><td>611-1371</td><td>57 mm</td></tr><tr><td>Titrator</td><td>Metrohm</td><td>836 Titrando</td><td>-</td></tr></tbody></table>

highly stable, functional hairy nanoparticles and biopolymers from wood fibers: towards sustainable nanotechnology

Nanoparticles, as one of the key materials in nanotechnology and nanomedicine, have gained significant importance during the past decade. While metal-based nanoparticles are associated with synthetic and environmental hassles, cellulose introduces a green, sustainable alternative for nanoparticle synthesis. Here, we present the chemical synthesis and separation procedures to produce new classes of hairy nanoparticles (bearing both amorphous and crystalline regions) and biopolymers based on wood fibers. Through periodate oxidation of soft wood pulp, the glucose ring of cellulose is opened at the C2-C3 bond to form 2,3-dialdehyde groups. Further heating of the partially oxidized fibers (e.g., T = 80 &#176;C) results in three products, namely fibrous oxidized cellulose, sterically stabilized nanocrystalline cellulose (SNCC), and dissolved dialdehyde modified cellulose (DAMC), which are well separated by intermittent centrifugation and co-solvent addition. The partially oxidized fibers (without heating) were used as a highly reactive intermediate to react with chlorite for converting almost all aldehyde to carboxyl groups. Co-solvent precipitation and centrifugation resulted in electrosterically stabilized nanocrystalline cellulose (ENCC) and dicarboxylated cellulose (DCC). The aldehyde content of SNCC and consequently surface charge of ENCC (carboxyl content) were precisely controlled by controlling the periodate oxidation reaction time, resulting in highly stable nanoparticles bearing more than 7 mmol functional groups per gram of nanoparticles (e.g., as compared to conventional NCC bearing &#60;&#60; 1 mmol functional group/g). Atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) attested to the rod-like morphology. Conductometric titration, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), dynamic light scattering (DLS), electrokinetic-sonic-amplitude (ESA) and acoustic attenuation spectroscopy shed light on the superior properties of these nanomaterials.

The mass portion and charge content of each fraction during the periodate and chlorite oxidation of pulp depends on the reaction time (Table 1). Moreover, DAC molecular weight depends on heating condition and residence time (Table 2). Once SNCC and DAMC are made, they precipitate out by adding propanol (Figure 1). To measure the charge content of ENCC, conductometric titration is performed (Figure 2). NCC and ENCC colloid...

Watch this Scientific Journal Video about Highly Stable, Functional Hairy Nanoparticles and Biopolymers from Wood Fibers: Towards Sustainable Nanotechnology at JoVE.com

Highly Stable, Functional Hairy Nanoparticles and Biopolymers from Wood Fibers: Towards Sustainable Nanotechnology

Synthesis schemes to prepare highly stable wood fiber-based hairy nanoparticles and functional cellulose-based biopolymers have been detailed.

Nanoparticles, as one of the key materials in nanotechnology and nanomedicine, have gained significant importance during the past decade. While ...

highly-stable-functional-hairy-nanoparticles-biopolymers-from-wood

Research

JoVE Journal

Chemistry

11.9K Views.  McGill University. Synthesis schemes to prepare highly stable wood fiber-based hairy nanoparticles and functional cellulose-based biopolymers have been detailed. 

Video: Highly Stable, Functional Hairy Nanoparticles and Biopolymers from Wood Fibers: Towards Sustainable Nanotechnology

Towards Biomimicking Wood: Fabricated Free-standing Films of Nanocellulose, Lignin, and a Synthetic Polycation

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and lignin. Layer-by-layer (LbL) assembly process which relies on the assembly of oppositely charged molecules from aqueous solutions was used to build a freestanding composite film of isolated wood polymers of lignin and oxidized nanofibril cellulose (NFC). To facilitate the assembly of these negatively charged polymers, a positively charged polyelectrolyte, poly(diallyldimethylammomium chloride) (PDDA), was used as a linking layer to create this simplified model cell wall. The layered adsorption process was studied quantitatively using quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry. The results showed that layer mass/thickness per adsorbed layer increased as a function of total number of layers. The surface coverage of the adsorbed layers was studied with atomic force microscopy (AFM). Complete coverage of the surface with lignin in all the deposition cycles was found for the system, however, surface coverage by NFC increased with the number of layers. The adsorption process was carried out for 250 cycles (500 bilayers) on a cellulose acetate (CA) substrate. Transparent free-standing LBL assembled nanocomposite films were obtained when the CA substrate was later dissolved in acetone. Scanning electron microscopy (SEM) of the fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle (PDDA-Lignin-PDDA-NC) was estimated to be 17 nm for two different lignin types used in the study. The data indicates a film with highly controlled architecture where nanocellulose and lignin are spatially deposited on the nanoscale (a polymer-polymer nanocomposites), similar to what is observed in the native cell wall.

The objective of this research was to form synthetic plant cell wall tissue using layer-by-layer assembly of nanocellulose fibrils and isolated lignin assembled from dilute aqueous suspensions.&#160; Surface measurement techniques of quartz crystal microbalance and atomic force microscopy were used to monitor the formation of the polymer-polymer nanocomposite material.

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and ...

Functionalization and Dispersion of Carbon Nanomaterials Using an Environmentally Friendly Ultrasonicated Ozonolysis Process

Functionalization of carbon nanomaterials is often a critical step that facilitates their integration into larger material systems and devices. In the as-received form, carbon nanomaterials, such as carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs), may contain large agglomerates. Both agglomerates and impurities will diminish the benefits of the unique electrical and mechanical properties offered when CNTs or GNPs are incorporated into polymers or composite material systems. Whilst a variety of methods exist to functionalize carbon nanomaterials and to create stable dispersions, many the processes use harsh chemicals, organic solvents, or surfactants, which are environmentally unfriendly and may increase the processing burden when isolating the nanomaterials for subsequent use. The current research details the use of an alternative, environmentally friendly technique for functionalizing CNTs and GNPs. It produces stable, aqueous dispersions free of harmful chemicals. Both CNTs and GNPs can be added to water at concentrations up to 5 g/L and can be recirculated through a high-powered ultrasonic cell. The simultaneous injection of ozone into the cell progressively oxidizes the carbon nanomaterials, and the combined ultrasonication breaks down agglomerates and immediately exposes fresh material for functionalization. The prepared dispersions are ideally suited for the deposition of thin films onto solid substrates using electrophoretic deposition (EPD). CNTs and GNPs from the aqueous dispersions can be readily used to coat carbon- and glass-reinforcing fibers using EPD for the preparation of hierarchical composite materials.

Here, a novel method for the functionalization and stable dispersion of carbon nanomaterials in aqueous environments is described. Ozone is injected directly into an aqueous dispersion of carbon nanomaterial that is continuously recirculated through a high-powered ultrasonic cell.

Functionalization of carbon nanomaterials is often a critical step that facilitates their integration into larger material systems and devices. In the ...

Environment

Functionalization of Single-walled Carbon Nanotubes with Thermo-reversible Block Copolymers and Characterization by Small-angle Neutron Scattering

We demonstrate a protocol for single-walled carbon nanotube functionalization using thermo-sensitive PEO-PPO-PEO triblock copolymers in an aqueous solution. In a carbon nanotube/PEO105-PPO70-PEO105 (poloxamer 407) aqueous solution, the amphiphilic poloxamer 407 adsorbs onto the carbon nanotube surfaces and self-assembles into continuous layers, driven by intermolecular interactions between constituent molecules. The addition of 5-methylsalicylic acid changes the self-assembled structure from spherical-micellar to a cylindrical morphology. The fabricated poloxamer 407/carbon nanotube hybrid particles exhibit thermo-responsive structural features so that the density and thickness of poloxamer 407 layers are also reversibly controllable by varying temperature. The detailed structural properties of the poloxamer 407/carbon nanotube particles in suspension can be characterized by small-angle neutron scattering experiments and model fit analyses. The distinct curve shapes of the scattering intensities depending on temperature control or addition of aromatic additives are well described by a modified core-shell cylinder model consisting of a carbon nanotube core cylinder, a hydrophobic shell, and a hydrated polymer layer. This method can provide a simple but efficient way for the fabrication and in-situ characterization of carbon nanotube-based nano particles with a structure-tunable encapsulation.

A method for the functionalization of carbon nanotubes with structure-tunable polymeric encapsulation layers and structural characterization using small-angle neutron scattering is presented.

We demonstrate a protocol for single-walled carbon nanotube functionalization using thermo-sensitive PEO-PPO-PEO triblock copolymers in an aqueous ...

Nanosponge Tunability in Size and Crosslinking Density

We describe a protocol for the synthesis of linear polyesters containing pendant epoxide functionality and their incorporation into a nanosponge with controlled dimensions. This approach begins with synthesis of a functionalized lactone which is key to the pendant functionalization of the resulting polymer. Valerolactone (VL) and allyl-valerolactone (AVL) are then copolymerized using ring-opening polymerization. Post-polymerization modification is then used to install an epoxide moiety on some or all of the pendant allyl groups. Epoxy-amine chemistry is employed to form nanoparticles in a dilute solution of both polymer and small molecule diamine crosslinker based on the desired nanosponge size and crosslinking density. Nanosponge sizes can be characterized by transmission electron microscopy (TEM) imaging to determine the dimension and distribution. This method provides a pathway by which highly tunable polyesters can create tunable nanoparticles, which can be used for small molecule drug encapsulation. Due to the nature of the backbone, these particles are hydrolytically and enzymatically degradable for a controlled release of a wide range of hydrophobic small molecules.

This article describes a process for tuning the size and crosslinking density of covalently crosslinked nanoparticles from linear polyesters containing pendant functionality. By tailoring synthesis parameters (polymer molecular weight, pendant functionality incorporation, and crosslinker equivalents), a desired nanoparticle size and crosslinking density can be achieved for drug delivery applications.

We describe a protocol for the synthesis of linear polyesters containing pendant epoxide functionality and their incorporation into a nanosponge with ...

Manufacturing Of Robust Natural Fiber Preforms Utilizing Bacterial Cellulose as Binder

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose and short sisal fibers are dispersed into a water suspension containing bacterial cellulose. The fiber and nanocellulose suspension is then filtered (using vacuum or gravity) and the wet filter cake pressed to squeeze out any excess water, followed by a drying step. This will result in the hornification of the bacterial cellulose network, holding the loose natural fibers together.
Our method is specially suited for the manufacturing of rigid and robust preforms of hydrophilic fibers. The porous and hydrophilic nature of such fibers results in significant water uptake, drawing in the bacterial cellulose dispersed in the suspension. The bacterial cellulose will then be filtered against the surface of these fibers, forming a bacterial cellulose coating. When the loose fiber-bacterial cellulose suspension is filtered and dried, the adjacent bacterial cellulose forms a network and hornified to hold the otherwise loose fibers together.
The introduction of bacterial cellulose into the preform resulted in a significant increase of the mechanical properties of the fiber preforms. This can be attributed to the high stiffness and strength of the bacterial cellulose network. With this preform, renewable high performance hierarchical composites can also be manufactured by using conventional composite production methods, such as resin film infusion (RFI) or resin transfer molding (RTM). Here, we also describe the manufacturing of renewable hierarchical composites using double bag vacuum assisted resin infusion.

We present a novel method of manufacturing rigid and robust short natural fiber preforms using a papermaking process. Bacterial cellulose acts simultaneously as the binder for the loose fibers and provides rigidity to the fiber preforms. These preforms can be infused with a resin to produce truly green hierarchical composites.

A novel method of manufacturing rigid and robust natural fiber preforms is presented here. This method is based on a papermaking process, whereby loose ...

Bioengineering

Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial applications. Here we describe how electrospinning or electrospraying a polymer mixture containing a biodegradable, biocompatible aliphatic polyester (e.g., polycaprolactone and poly(lactide-co-glycolide)), as the major component, doped with a hydrophobic copolymer composed of the polyester and a stearate-modified poly(glycerol carbonate) affords a superhydrophobic biomaterial. The fabrication techniques of electrospinning or electrospraying provide the enhanced surface roughness and porosity on and within the fibers or the particles, respectively. The use of a low surface energy copolymer dopant that blends with the polyester and can be stably electrospun or electrosprayed affords these superhydrophobic materials. Important parameters such as fiber size, copolymer dopant composition and/or concentration, and their effects on wettability are discussed. This combination of polymer chemistry and process engineering affords a versatile approach to develop application-specific materials using scalable techniques, which are likely generalizable to a wider class of polymers for a variety of applications.

Two- and three-dimensional superhydrophobic polymeric materials are prepared by electrospinning or electrospraying biodegradable polymers blended with a lower surface energy polymer of similar composition.

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial ...

Synthesis of Keratin-based Nanofiber for Biomedical Engineering

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of these porous nanofibers is of great interest due to their unique physiochemical properties. Here we elaborate on the fabrication of keratin containing poly (&#949;-caprolactone) (PCL) nanofibers (i.e., PCL/keratin composite fiber). Water soluble keratin was first extracted from human hair and mixed with PCL in different ratios. The blended solution of PCL/keratin was transformed into nanofibrous membranes using a laboratory designed electrospinning set up. Fiber morphology and mechanical properties of the obtained nanofiber were observed and measured using scanning electron microscopy and tensile tester. Furthermore, degradability and chemical properties of the nanofiber were studied by FTIR. SEM images showed uniform surface morphology for PCL/keratin fibers of different compositions. These PCL/keratin fibers also showed excellent mechanical properties such as Young&#39;s modulus and failure point. Fibroblast cells were able to attach and proliferate thus proving good cell viability. Based on the characteristics discussed above, we can strongly argue that the blended nanofibers of natural and synthetic polymers can represent an excellent development of composite materials that can be used for different biomedical applications.

Electrospun nanofibers have a high surface area to weight ratio, excellent mechanical integrity, and support cell growth and proliferation. These nanofibers have a wide range of biomedical applications. Here we fabricate keratin/ PCL nanofibers, using the electrospinning technique, and characterize the fibers for possible applications in tissue engineering.

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of ...

Fabrication and Design of Wood-Based High-Performance Composites

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber reinforced composites, due to its excellent mechanical properties. Delignified wood, however, is rather fragile in a wet state, which makes handling and shaping challenging. Here we present two fabrication processes, closed-mold densification and vacuum densification, to produce high-performance cellulose composites based on delignified wood, including an assessment of their advantages and limitations. Further, we suggest strategies for how the composites can be re-used or decomposed at the end-of-life cycle. Closed-mold densification has the advantage that no elaborate lab equipment is needed. Simple screw clamps or a press can be used for densification. We recommend this method for small parts with simple geometries and large radii of curvature. Vacuum densification in an open-mold process is suitable for larger objects and complex geometries, including small radii of curvature. Compared to the closed-mold process, the open-mold vacuum approach only needs the manufacture of a single mold cavity.

Delignified densified wood represents a new promising lightweight, high-performance and bio-based material with great potential to partially substitute natural fiber reinforced- or glass fiber reinforced composites in the future. We here present two versatile fabrication routes and demonstrate the possibility to create complex composite parts.

Delignified densified wood is a new promising and sustainable material that possesses the potential to replace synthetic materials, such as glass fiber ...

Engineering

Designed for Molecular Recycling: A Lignin-Derived Semi-aromatic Biobased Polymer

The development of chemically recyclable biopolymers offers opportunities within the pursuit of a circular economy. Chemically recyclable biopolymers make a positive effort to solve the issue of polymer materials in the disposal phase after the use phase. In this paper, the production of biobased semi-aromatic polyesters, which can be extracted entirely from biomass such as lignin, is described and visualized. The polymer poly-S described in this paper has thermal properties similar to certain commonly used plastics, such as PET. We developed a Green Knoevenagel reaction, which can efficiently produce monomers from aromatic aldehydes and malonic acid. This reaction has been proven to be scalable and has a remarkably low calculated E-factor. These polyesters with ligno-phytochemicals as a starting point show an efficient molecular recycling with minimal losses. The polyester poly(dihydrosinapinic acid) (poly-S) is presented as an example of these semi-aromatic polyesters, and the polymerization, depolymerization, and re-polymerization are described.

An example of a closed-loop approach towards a circular materials economy is described here. A whole sustainable cycle is presented where biobased semi-aromatic polyesters are designed by polymerization, depolymerization, and then re-polymerized with only slight changes in their yields or final properties.

The development of chemically recyclable biopolymers offers opportunities within the pursuit of a circular economy. Chemically recyclable biopolymers make ...

Lignin Micro-/Submicron Particle Synthesis for Bioflavonoid Release

Green Synthesis, Characterization, Encapsulation, and Measurement of the Release Potential of Novel Alkali Lignin Micro-/Submicron Particles

The applicability of biopolymer micro-/nano- technology in human, veterinary medicine, pharmaceutical, and food technology is rapidly growing due to the great potential of biopolymer-based particles as effective carrier systems. The use of lignin as a basic heteropolymer biomatrix for the design of innovative micro-/submicron formulations allows the achievement of increased biocompatibility and offers various active functional groups presenting opportunities for customization of the physicochemical properties and bioactivities of the formulations for diverse applications. The aim of the present study was to develop a simple and ecofriendly methodology for the synthesis of lignin particles with micro- and submicron size; to evaluate their physicochemical, spectral, and structural characteristics; and to examine their capacity for encapsulation of biologically active molecules and potential for in vitro release of bioflavonoids in simulated gastrointestinal media. The presented methodologies apply cheap and green solvents; easy, straightforward, quick, and sensitive processes requiring little equipment, non-toxic substances, and simple methods for their characterization, the determination of encapsulation capacity towards the poorly water-soluble bioactive compounds morin and quercetin, and the in vitro release potential of the lignin matrices.

Author Spotlight: Development and Characterization of Eco-Friendly Lignin-Based Microparticles for Enhanced Delivery of Bioflavonoids

We describe novel, simple methodologies of synthesis and characterization of biocompatible lignin micro- and submicron particles. These formulations provide a facile approach for the utilization of the heteropolymer, as well as an alternative for the rational design of multifunctional carrier matrices with potential applicability in biomedicine, pharmaceutical technology, and the food industry.

The applicability of biopolymer micro-/nano- technology in human, veterinary medicine, pharmaceutical, and food technology is rapidly growing due to the ...