Name: green and low-cost production of thermally stable and carboxylated cellulose nanocrystals and nanofibrils using highly recyclable dicarboxylic acids
Uploaded: 2017-01-09T14:00:00.000+00:00
Duration: 7 min 25 s
Description: Watch this Scientific Journal Video about Green and Low-cost Production of Thermally Stable and Carboxylated Cellulose Nanocrystals and Nanofibrils Using Highly Recyclable Dicarboxylic Acids at JoVE.c

This work was conducted while Bian, Chen, and Wang were visiting Ph.D. students at the US Forest Service, Forest Products Laboratory (FPL), Madison, WI, and on official government time of Zhu. This work was partially supported by the USDA Agriculture and Food Research Initiative (AFRI) Competitive Grant (No. 2011-67009-20056), the Chinese State Forestry Administration (Project No. 2015-4-54), the National Natural Science Foundation of China (Project No. 31470599), Guangzhou Elite Project of China, and China Scholarship Fund. Funding from these programs made the visiting appointments of Bian, Chen, and Wang at FPL possible.

NOTE: Bleached eucalyptus kraft pulp (BEP) and unbleached mixed hardwood kraft pulp (UMHP) fibers from commercial sources were used as feedstock for producing CNC and CNF. Commercial maleic acids purchased were used for hydrolysis. Hydrolysis conditions were acid concentrations of 60 wt% at 100 &#176;C for 60 min and 120 &#176;C (no boiling at atmospheric pressure) for 120 min, for BEP and UMHP, respectively.
1. Preparation of Concentrated Dicarboxylic Acid Solution
<ol>
	<li>Heat 40 mL deionized (DI) water in a multiple-neck flask in a liquid glycerol bath on a heating plate to approximately 85 &#176;C.</li>
	<li>Add 60 g anhydrous maleic acid into the flask to make a 60 wt% solution with magnetic stirring. Using the densities of the acid solutions reported previously 15, calculate the required amount of water and acid for making the acid solution at the specified mass concentration.</li>
	<li>Heat the solution to the desired hydrolysis temperature of 100 or 120 &#176;C (no boiling due to high dicarboxylic acid concentrations).</li>
</ol>
2. Hydrolysis Reaction
<ol>
	<li>Once the acid solution is at temperature, add 10 g oven dried (OD) of BEP or UMHP fibers into 80 mL dicarboxylic acid solution (1.1) with continuous stirring.
	<ol>
		<li>Take an aliquot of the acid hydrolysate (approximately 2 mL) at the end of the predetermined reaction time of 60 min before terminating hydrolysis by adding 160 mL of 80 &#176;C DI water.</li>
	</ol>
	</li>
	<li>Dilute 0.5 mL of the sampled hydrolysate for sugar and acid concentration analyses. 15 Observe the remaining hydrolysate sample for crystallization taking place while cooing down to room temperature.</li>
	<li>Separate the hydrolysate from the hydrolyzed pulp by vacuum filtration using a filter paper in a Buchner funnel. 
	NOTE: This separation needs to occur rather quickly before the temperature drops and the acid begins to crystallize out of solution. Due to high ionic strength from the acid solution, the CNC&#39;s generated in hydrolysis agglomerate and stay with the FCSR residuals. Approximately 80-90% of the acid will be removed with the filtrate.</li>
</ol>
3. CNC Separation
<ol>
	<li>Wash the filtered solids from section 2 using DI water and dilute to approximately 1% total solids with DI water. Centrifuge the filtrate at 11,960 x g for 10 min.</li>
	<li>Decant off the supernatant. Repeat the washing and filtration process using fresh DI water until the supernatant is turbid. The turbidity indicates that the ionic strength of the solution has fallen enough for the CNC to disperse and start to become colloidal.</li>
	<li>Mix the turbid supernatant with the settled hydrolyzed pulp (2.3). Dialyze the mixture in a dialysis bag (MWCO 14 kDa) using DI water until the conductivity of the liquid approaches that of DI water. Measure the conductivity using a conductance meter.</li>
	<li>Centrifuge the dialyzed sample at 3,500 x g for 10 min to obtain a CNC dispersion in the aqueous phase. Retain the precipitate phase, i.e., FCSR, for CNF production.</li>
	<li>Determine CNC yield from the measured amount of CNC in the dispersion using a COD method described previously 3, 18.</li>
</ol>
4. CNF Production
<ol>
	<li>Determine the yield of precipitated FCSR by gravimetric measurements after separating the CNC dispersion. Dry the FCSR at 105 &#176;C and measure the oven dry weight of the FCSR relative to the initial oven dry weight of BEP or UMHP fibers used.</li>
	<li>Mechanically fibrillate the FCSR at fiber suspension of 0.5% by consecutively passing the suspension 3 times through a 200 &#181;m orifice chamber followed by 2 times through an 87 &#181;m orifice chamber, all at 100 MPa.</li>
</ol>
5. Atomic Force Microscopy (AFM) Imaging
<ol>
	<li>Sonicate approximately 0.01 wt% CNC or CNF suspensions for 2 min. Deposit a drop of the dispersed suspension on a mica substrate. Air-dry the deposited suspension at ambient temperature.</li>
	<li>Take AFM images of the air-dried CNCs and CNFs in vibrating tapping mode using manufacturer&#39;s protocol. Analyze the AFM images of approximately 100 individual CNCs or CNFs using commercial software to obtain diameter and length distributions.</li>
</ol>
6. Fourier Transform Inferred (FTIR) Measurements
<ol>
	<li>Use a commercial FTIR spectrophotometer with a universal attenuated-total-reflection (ATR) probe to analyze the resultant CNC and CNF samples along with the original BEP and UMHP fibers to identify ester groups.</li>
	<li>Record the absorption spectra of the samples in a wavelength range between 450 - 4,000 cm-1 with a resolution of 4 cm-1 and 4 scans for each sample.</li>
</ol>
7. Conductometric Titration
<ol>
	<li>Use conductometric titration to quantify the carboxyl group contents of samples resulted from esterification by the dicarboxylic acid.</li>
	<li>Add CNC or CNF suspension with 50 mg (OD) of CNCs or CNFs into 120 mL of 1 mM NaCl solution. Titrate the mixture by adding approximately 0.2 mL of 2 mM NaOH solution at 30 s intervals.</li>
	<li>Measure the conductivity using a conductance meter. Find the inflection point (the lowest point) on the conductivity curve during the course of adding NaOH.</li>
	<li>Calculate the amount of carboxyl groups (mmol/L) based on the consumed NaOH relative to the inflection point using the following equation in which c is the concentration of NaOH solution (mol/L), v is the volume of added NaOH solution (mL), m is the mass of CNCs or CNFs in OD weight (g). 
	<img alt="Equation" src="/files/ftp_upload/55079/55079eq1.jpg" /></li>
</ol>
8. CNC and CNF Thermal Stability Determination
<ol>
	<li>Conduct thermal degradation measurements of the CNC and CNF samples by thermogravimetric analysis (TGA).</li>
	<li>Purge the furnace using a high purity nitrogen flow at 20 mL/min to prevent any unwanted oxidative decomposition. Dry the samples at 50 &#176;C for 4 h before testing. Use a sample size of 5 mg in dry weight.</li>
	<li>Record the weight of the sample as the furnace temperature is increased from ambient to 600 &#176;C at a heating rate of 10 &#176;C/min.</li>
	<li>Normalize the measured weight loss by the initial weight.</li>
	<li>Conduct separate thermal stability tests of CNC and CNF samples in an oven at 105 &#176;C. Record the color change of the samples after 4 and 24 h by conventional photography.</li>
</ol>
9. X-ray Diffraction
<ol>
	<li>Press freeze-dried CNC or CNF samples at 180 MPa to make pellets as described previously. 5 Conduct wide angle X-ray diffraction measurements of the pellet using Cu-K&#945; radiation on an X-ray diffractometer in the 2&#952; range of 10 - 38&#176; in steps of 0.02&#176;.</li>
	<li>Calculate the crystallinity index (CrI) of a pellet using the Segal method 19 (without base line subtraction).</li>
</ol>

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Chen and Zhu are co-inventors of a US patent application using dicarboxylic acids for CNC and CNF production.

The thicker CNC diameters of the CNC samples from maleic acid hydrolysis resulted in a moderate average aspect ratio 7.24 and 8.53, for the CNCs from BEP and UMHP, respectively, despite their long lengths as discussed above. The CNFs had a longer length and a thinner diameter, which resulted in a large aspect ratio of 13.9 and 19.0, for the CNCs from BEP and UMHP, respectively, both greater than their respective CNCs. It is possible to use severe mechanical fibrillation to reduce CNF diameter to improve the aspect ratio as the pressure used in microfluidization in the present study was quite low.
Lignin particles were visible on the CNC sample from UMHP. Lignin should also chemically bound to CNC particles. It will be interesting to see the effect of lignin on surface hydrophobicity in future studies for a variety of applications.
Due to the presence of carboxyl group, the CNC samples were easily dispersible as shown in Figures 1c and 2c, which facilitates aqueous processing. The surface charges measured by zeta potential were -13 and -34 mV, for the CNCs from BEP and UMHP, respectively.
Thermal stability of the CNC and CNF samples were similar to those found in the feed fibers. This is important for applications requiring thermal processing at elevated temperatures such as extrusion for composite production. The improved thermal stability was attributed to the improved crystallinity.
Critical steps in the protocol are as follows. With the preparation of acid solution of desired concentration (section 1), one needs to use the density data presented in our early work 15 to calculate the amount of salt needed to make the acid solution of desired concentration. For CNC separation (section 3), multiple steps of centrifugation and filtration may be needed. Dialysis is needed to separate CNC particles.
The presented process for producing cellulose nanomaterials is also suitable for nonwoody lignocellulosic materials. The method is relatively straightforward. Troubleshooting should be focused on making sure that the critical steps described above are carried out correctly.
The significance of the present process compared with traditional mineral acid hydrolysis or oxidation processes are (1) the resultant CNC and CNF are thermally stable and (2) the minimal loss of cellulose top sugars. Also, the acid can be easily recycled to achieve environmental sustainability and reduce production cost. There are no potential harmful products to be produced as the acid is used as a catalyst when compared with oxidation method.

Sustainable economic development requires not only using feedstocks that are renewable and biodegradable but also uses green and environmental friendly manufacturing technologies to produce a variety of bioproducts and biochemicals from these renewable feedstocks. Cellulose nanomaterials, such as cellulose nanocrystals (CNC) and cellulose nanofibrils (CNF), produced from renewable lignocelluloses are biodegradable and have unique mechanical and optical properties suitable for developing a range of bioproducts 1, 2. Unfortunately, existing technologies for producing cellulose nanomaterials are either energy intensive when using pure mechanical fibrillation or environmentally unsustainable due to non-recycling or insufficient recycling of processing chemicals, such as when using the concentrated mineral acid hydrolysis process 3-8 or oxidation methods 9-11. Furthermore, oxidation methods may also produce environmentally toxic compounds by reacting with lignocelluloses. Therefore, developing green manufacturing technologies for producing cellulose nanomaterials is critically important to make full use of the abundant and renewable material - lignocelluloses.
Using acid hydrolysis to dissolve hemicellulose and depolymerize cellulose is an effective approach for producing cellulose nanomaterials. Solid acids have been used for sugar production from cellulose with the advantage of easing acid recovery 12, 13. Previous studies using concentrated mineral acids indicated that a lower acid concentration improved CNC yield and crystallinity 3, 5. This suggests that a strong acid may damage cellulose crystals while a milder acid hydrolysis might improve the properties and yield of cellulose nanomaterials through the approach of integrated production and CNC with CNF 3, 14. Here we document a method using concentrated solid dicarboxylic acids hydrolysis to produce CNC along with CNF 15. These dicarboxylic acids have low solubility at low or ambient temperatures, and therefore they can be easily recovered through the mature crystallization technology. They also have good solubility at elevated temperatures which facilitates concentrated acid hydrolysis without boiling or using pressure vessels. Since these acids also have a higher pKa than typical mineral acids used for CNC production, their use results in good CNC crystallinity, and despite lower CNC yields, with a substantial amount of fibrous cellulosic solid residue (FCSR or partially hydrolyzed fibers) remaining due to incomplete cellulose depolymerization. The FCSR can be used to produce CNF through subsequent mechanical fibrillation using low energy inputs. Therefore, cellulose loss to sugars is minimal as compared to using mineral acids.
It is well known that carboxylic acids can esterify cellulose through Fisher-Speier esterification 16. Applying dicarboxylic acids to cellulose can result in semi-acid un-crosslinked esters 17 (or carboxylation), to produce carboxylated CNC and CNF as we demonstrated 15 previously. The method documented here can produce carboxylated and thermally stable CNF and CNC that is also highly crystalline from either bleached or unbleached pulps while having relatively simple and high chemical recovery and using low energy inputs.

<table><tbody><tr><td>Bleached eucalypus pulp&amp;nbsp;</td><td>Aracruz Cellulose</td><td></td><td></td></tr><tr><td>Unbleached mixed hardwood kraft pulp&amp;nbsp;</td><td>International Paper&amp;nbsp;</td><td></td><td></td></tr><tr><td>Maleic acid</td><td>Sigma-Aldrich</td><td>M0375-1KG/CAS110-16-7</td><td>Powder; assay: 99.0% (HPLC)</td></tr><tr><td>Glycerol</td><td>Sigma-Aldrich</td><td>G5516-4L/CAS56-81-5</td><td></td></tr><tr><td>Sodium hydroxide</td><td>Fisher Scientific</td><td>S318-500/CAS1310-73-2, 497-19-8</td><td>Certified ACS</td></tr><tr><td>Sodium chloride</td><td>Mallinckrodt</td><td>7581-12/CAS7647-14-5</td><td>Crystal,AR</td></tr><tr><td>Cupriethylenediamine solution</td><td>GFS Chemicals</td><td>E32103-1L/CAS14552-35-3</td><td>1 M, for determination of solution viscosity of pulps</td></tr><tr><td>Acetone</td><td>Fisher Scientific</td><td>A18-500/CAS67-64-1</td><td>Certified ACS</td></tr><tr><td>Accu-Test&lt;sup&gt;TM&lt;/sup&gt; Vials for COD Testing</td><td>Bioscience,Inc.</td><td>01-215-28</td><td>COD testing for 20 to 900&amp;nbsp;mg/L standard range concentration</td></tr><tr><td>Heating plate</td><td>IKA</td><td></td><td>Mode: C-MAD HS7 digital</td></tr><tr><td>Magnetic stir bar</td><td>ACE Glass</td><td></td><td></td></tr><tr><td>Pyrex three-neck round-bottom flask</td><td>Sigma-Aldrich</td><td>CLS4965B500-1EA</td><td></td></tr><tr><td>Dialysis tubing cellulose membrane</td><td>Sigma-Aldrich</td><td>D9402-100FT</td><td>Typical molecular weight cut-off = 14,000 kDa</td></tr><tr><td>Disposable aluminum dishes</td><td>Sigma-Aldrich</td><td>Z154857-1PAK</td><td>Circles, 60 mm</td></tr><tr><td>Disintegrator</td><td>Testing Machines Inc.(TMI)</td><td></td><td></td></tr><tr><td>Microfluidizer</td><td>Microfluidics Corporation</td><td></td><td></td></tr><tr><td>Sonicator</td><td>Qsonica LLC.</td><td></td><td>Mode: 3510R-MT, 50-60&amp;nbsp;Hz, 180&amp;nbsp;W</td></tr><tr><td>Zeta potential analyzer</td><td>Brookhaven Instruments Corporation</td><td></td><td></td></tr><tr><td>FTIR</td><td>PerkinElmer</td><td></td><td></td></tr><tr><td>Conductometric titrator</td><td>Yellow Springs Instrument (YSI)</td><td></td><td></td></tr><tr><td>TGA analyzer</td><td>PerkinElmer</td><td></td><td></td></tr><tr><td>X-ray diffractometer</td><td>Bruker Corporation</td><td></td><td></td></tr><tr><td>AFM imging&amp;nbsp;</td><td>AFM Workshop</td><td></td><td></td></tr><tr><td>SEM imaging</td><td>Carl Zeiss</td><td></td><td></td></tr></tbody></table>

green and low-cost production of thermally stable and carboxylated cellulose nanocrystals and nanofibrils using highly recyclable dicarboxylic acids

Here we demonstrate potentially low cost and green productions of high thermally stable and carboxylated cellulose nanocrystals (CNCs) and nanofibrils (CNF) from bleached eucalyptus pulp (BEP) and unbleached mixed hardwood kraft pulp (UMHP) fibers using highly recyclable dicarboxylic solid acids. Typical operating conditions were acid concentrations of 50 - 70 wt% at 100 &#176;C for 60 min and 120 &#176;C (no boiling at atmospheric pressure) for 120 min, for BEP and UMHP, respectively. The resultant CNCs have a higher thermal degradation temperature than their corresponding feed fibers and carboxylic acid group content from 0.2 - 0.4 mmol/g. The low strength (high pKa of 1.0 - 3.0) of organic acids also resulted in CNCs with both longer lengths of approximately 239 - 336 nm and higher crystallinity than CNCs produced using mineral acids. Cellulose loss to sugar was minimal. Fibrous cellulosic solid residue (FCSR) from the dicarboxylic acid hydrolysis was used to produce carboxylated CNFs through subsequent mechanical fibrillation with low energy input.

Typical AFM images of the CNC and CNF from BEP and UMHP along with corresponding SEM images of the feed acid hydrolyzed fibers are shown in Figures 1 and 2. The images clearly show the substantial reductions in fiber length by acid hydrolysis with minimal change in fiber diameters (comparing Figure 1a with 1b, and 2a with 2b). The shortened fiber length was also reflected by the measured cellulose degree of polymerization (DP) of the hydrolyzed fibers. DP was reduced from 1,021 and 806 to 319 and 342, for the BEP and UMHP, respectively. CNCs isolated from the hydrolyzed fiber had relatively longer lengths and thicker diameters compared with the typical length and diameter of concentrated sulfuric acid produced CNCs cited in the literature 5; this is perhaps due to the weak strength of maleic acid. The mean CNC lengths and diameters measured by AFM image were 239 and 33 nm, 336 and 39 nm for the two samples shown in Figures 1c and 2c, respectively.
The weak strength of maleic acid also resulted in a substantially low CNC yield of 1.8% and 5.5% from BEP and UMHP, respectively. However, the remaining solids, i.e., FCSR, still have utility and were used to produce CNF through subsequent mechanical fibrillation to achieve the integrated production of CNC with CNF. CNC yield can be increased by using more severe reaction conditions as demonstrated previously 15. Depending on the application and economics, the severity can be adjusted to accommodate the desired CNC to CNF ratio.
The CNFs had a very long lengths based on AFM image measurements while actually having thinner diameters than their corresponding CNCs as (comparing Figure 1c with 1d, and 2c with 2d). It is felt these CNF&#39;s would be ideal for polymer reinforcement in composite applications.
<img alt="Figure 1" src="/files/ftp_upload/55079/55079fig1.jpg" /> 
Figure 1: SEM and AFM images of the bleached kraft Eucalyptus pulp (BEP) fibers and cellulose nanomaterials produced. (a) SEM image of BEP fibers; (b) SEM image of the acid hydrolyzed BEP fibrous cellulosic solid residues (FCSR); (c) AFM image of the BEP nanocrystals (CNCs); (d) AFM image of the BEP cellulose nanofibrils (CNFs). <a href="https://cloudflare-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/55079/55079fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55079/55079fig2.jpg" /> 
Figure 2: SEM and AFM images of the unbleached kraft mixed hardwood Pulp (UMHP) fibers and cellulose nanomaterials produced. (a) SEM image of UMHP fibers; (b) SEM image of the acid hydrolyzed UMHP fibrous cellulosic solid residues (FCSR); (c) AFM image of the UMHP nanocrystals (CNCs); (d) AFM image of the UMHP cellulose nanofibrils (CNFs). <a href="https://cloudflare-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/55079/55079fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Green and Low-cost Production of Thermally Stable and Carboxylated Cellulose Nanocrystals and Nanofibrils Using Highly Recyclable Dicarboxylic Acids at JoVE.c

Green and Low-cost Production of Thermally Stable and Carboxylated Cellulose Nanocrystals and Nanofibrils Using Highly Recyclable Dicarboxylic Acids

Here we demonstrate a novel method for green and sustainable productions of highly thermally stable and carboxylated cellulose nanocrystals (CNC) and nanofibrils (CNF) using highly recyclable solid dicarboxylic acids.

Here we demonstrate potentially low cost and green productions of high thermally stable and carboxylated cellulose nanocrystals (CNCs) and nanofibrils ...

green-low-cost-production-thermally-stable-carboxylated-cellulose

Nanyang Technological University

Research

JoVE Journal

Chemistry

11.8K Views.  Nanjing Forestry University. Here we demonstrate a novel method for green and sustainable productions of highly thermally stable and carboxylated cellulose nanocrystals (CNC) and nanofibrils (CNF) using highly recyclable solid dicarboxylic acids.

Video: Green and Low-cost Production of Thermally Stable and Carboxylated Cellulose Nanocrystals and Nanofibrils Using Highly Recyclable Dicarboxylic Acids

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 ...

Pretreatment of Lignocellulosic Biomass with Low-cost Ionic Liquids

A number of ionic liquids (ILs) with economically attractive production costs have recently received growing interest as media for the delignification of a variety of lignocellulosic feedstocks. Here we demonstrate the use of these low-cost protic ILs in the deconstruction of lignocellulosic biomass (Ionosolv pretreatment), yielding cellulose and a purified lignin. In the most generic process, the protic ionic liquid is synthesized by accurate combination of aqueous acid and amine base. The water content is adjusted subsequently. For the delignification, the biomass is placed into a vessel with IL solution at elevated temperatures to dissolve the lignin and hemicellulose, leaving a cellulose-rich pulp ready for saccharification (hydrolysis to fermentable sugars). The lignin is later precipitated from the IL by the addition of water and recovered as a solid. The removal of the added water regenerates the ionic liquid, which can be reused multiple times. This protocol is useful to investigate the significant potential of protic ILs for use in commercial biomass pretreatment/lignin fractionation for producing biofuels or renewable chemicals and materials.

The pretreatment of lignocellulosic biomass with protic low-cost ionic liquids is shown, resulting in a delignified cellulose-rich pulp and a purified lignin. The pulp gives rise to high glucose yields after enzymatic saccharification.

A number of ionic liquids (ILs) with economically attractive production costs have recently received growing interest as media for the delignification of ...

Environment

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.

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 ...

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

Estimation of Crystalline Cellulose Content of Plant Biomass using the Updegraff Method

Cellulose is the most abundant polymer on Earth generated by photosynthesis and the main load-bearing component of cell walls. The cell wall plays a significant role in plant growth and development by providing strength, rigidity, rate and direction of cell growth, cell shape maintenance, and protection from biotic and abiotic stressors. The cell wall is primarily composed of cellulose, lignin, hemicellulose and pectin. Recently plant cell walls have been targeted for the second-generation biofuel and bioenergy production. Specifically, the cellulose component of the plant cell wall is used for the production of cellulosic ethanol. Estimation of cellulose content of biomass is critical for fundamental and applied cell wall research. The Updegraff method is simple, robust, and the most widely used method for the estimation of crystalline cellulose content of plant biomass. The alcohol insoluble crude cell wall fraction upon treatment with Updegraff reagent eliminates the hemicellulose and lignin fractions. Later, the Updegraff reagent resistant cellulose fraction is subjected to sulfuric acid treatment to hydrolyze the cellulose homopolymer into monomeric glucose units. A regression line is developed using various concentrations of glucose and used to estimate the amount of the glucose released upon cellulose hydrolysis in the experimental samples. Finally, the cellulose content is estimated based on the amount of glucose monomers by colorimetric anthrone assay.

The Updegraff method is the most widely used method for the cellulose estimation. The main purpose of this demonstration is to provide a detailed Updegraff protocol for estimation of cellulose content in plant biomass samples.

Cellulose is the most abundant polymer on Earth generated by photosynthesis and the main load-bearing component of cell walls. The cell wall plays a ...

Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often result in fragile aerogels with poor shape control. The use of carboxymethylated cellulose nanofibers (CNFs) to form a covalently bonded hydrogel allows for the reduction of metal ions such as palladium on the CNFs with control over both nanostructure and macroscopic aerogel monolith shape after supercritical drying. Crosslinking the carboxymethylated cellulose nanofibers is achieved using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in the presence of ethylenediamine. The CNF hydrogels maintain their shape throughout synthesis steps including covalent crosslinking, equilibration with precursor ions, metal reduction with high concentration reducing agent, rinsing in water, ethanol solvent exchange, and CO2 supercritical drying. Varying the precursor palladium ion concentration allows for control over the metal content in the final aerogel composite through a direct ion chemical reduction rather than relying on the relatively slow coalescence of pre-formed nanoparticles used in other sol-gel techniques. With diffusion as the basis to introduce and remove chemical species into and out of the hydrogel, this method is suitable for smaller bulk geometries and thin films. Characterization of the cellulose nanofiber-palladium composite aerogels with scanning electron microscopy, X-ray diffractometry, thermal gravimetric analysis, nitrogen gas adsorption, electrochemical impedance spectroscopy, and cyclic voltammetry indicates a high surface area, metallized palladium porous structure.

A synthesis method for cellulose nanofiber biotemplated palladium composite aerogels is presented.The resulting composite aerogel materials offer potential for catalysis, sensing, and hydrogen gas storage applications.

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often ...

Fractionation of Lignocellulosic Biomass using the OrganoCat Process

The shift from a petroleum-based to a more sustainable and bio-based economy requires the development of new refinery concepts to maintain the supply of raw materials and energy. For these novel and sustainable biorefinery concepts, it is important to use catalysts and solvents that are aligned with the principles of Green Chemistry. Therefore, the implementation of biogenic alternatives can be a promising solution. The lignocellulose pretreatment and fractionation process presented herein-OrganoCat-is an integrated fractionation of lignocellulose into its main components using biogenic acids such as 2,5-furandicarboxylic acid as catalyst. Hemicelluloses and other non-cellulosic polysaccharides are selectively depolymerized by the diluted acid and dissolved, while the crystalline cellulose remains in the solid pulp. In the presence of a second organic phase consisting of biogenic 2-methyltetrahydrofuran, disentangled lignin is extracted in situ. The process allows for the efficient fractionation of the three main components-lignin, cellulose, and non-cellulosic sugars. This helps to focus on the quality of the lignin, the improvement of enzymatic hydrolysis of the cellulose-enriched pulp, and the mild non-cellulosic sugar extraction with low degradation.

OrganoCat is a method for the pretreatment and fractionation of lignocellulose under mild conditions into lignin, fermentable sugars, and cellulose pulp. In a biogenic, biphasic solvent system of water and 2-methyltetrahydrofuran with 2,5-furancarboxylic acid as catalyst, the OrganoCat products are separated in situ for straightforward product recovery.

The shift from a petroleum-based to a more sustainable and bio-based economy requires the development of new refinery concepts to maintain the supply of ...

Bacterial Cellulose Spheres that Encapsulate Solid Materials

Bacterial cellulose (BC) spheres have been increasingly researched since the popularization of BC as a novel material. This protocol presents an affordable and simple method for BC sphere production. In addition to producing these spheres, an encapsulation method for solid particles has also been identified. To produce BC spheres, water, black tea, sugar, vinegar, and bacterial culture are combined in a baffled flask and the contents are agitated. After determining the proper culture conditions for BC sphere formation, their ability to encapsulate solid particles was tested using biochar, polymer beads, and mine waste. Spheres were characterized using ImageJ software and thermal gravimetric analysis (TGA). Results indicate that spheres with 7.5 mm diameters can be made in 7 days. Adding various particles increases the average size range of the BC capsules. The spheres encapsulated 10 - 20% of their dry mass. This method shows low-cost sphere production and encapsulation that is possible with easily obtainable materials. BC spheres may be used in the future as a contaminant removal aid, controlled release fertilizer coating, or soil amendment.

This protocol presents an easy, inexpensive method of forming bacterial cellulose (BC) spheres. This biomaterial can function as an encapsulation medium for solid materials, including biochar, polymer spheres, and mine waste.

Bacterial cellulose (BC) spheres have been increasingly researched since the popularization of BC as a novel material. This protocol presents an ...

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 ...