Showing papers in "Cellulose in 2014"

Idealized powder diffraction patterns for cellulose polymorphs

Abstract: Cellulose samples are routinely analyzed by X-ray diffraction to determine their crystal type (polymorph) and crystallinity. However, the connection is seldom made between those efforts and the crystal structures of cellulose that have been proposed with synchrotron X-radiation and neutron diffraction over the past decade or so. In part, this desirable connection is thwarted by the use of different conventions for description of the unit cells of the crystal structures. In the present work, powder diffraction patterns from cellulose Iα, Iβ, II, IIII, and IIIII were calculated based on the published atomic coordinates and unit cell dimensions contained in modified “crystal information files” (.cif) that are supplied in the Supplementary Information. The calculations used peak widths at half maximum height of both 0.1 and 1.5° 2θ, providing both highly resolved indications of the contributions of each contributing reflection to the observable diffraction peaks as well as intensity profiles that more closely resemble those from practical cellulose samples. Miller indices are shown for each contributing peak that conform to the convention with c as the fiber axis, a right-handed relationship among the axes and the length of a < b. Adoption of this convention, already used for crystal structure determinations, is also urged for routine studies of polymorph and crystallinity. The calculated patterns are shown with and without preferred orientation along the fiber axis. Diffraction intensities, output by the Mercury program from the Cambridge Crystallographic Data Centre, have several uses including comparisons with experimental data. Calculated intensities from different polymorphs can be added in varying proportions using a spreadsheet program to simulate patterns such as those from partially mercerized cellulose or various composites.

Recent advances in bacterial cellulose

Abstract: Bacterial cellulose (BC) produced by some microorganisms has been widely accepted as a multifunctional nano-biomaterial. It is composed of linear glucan molecules attached with hydrogen bonds, which appears similar to plant cellulose. However, when compared with other conventional natural or synthesized counterparts, BC performs better in areas such as biomedicine, functional devices, water treatment, nanofillers, etc. for its distinct superior chemical purity, crystallinity, biocompatibility, and ultrafine network architecture. When BC is incorporated in a material or used as a scaffold, novel features result that are related to BC’s intrinsic characteristics mentioned above. This review mainly summarizes the recent developments of the functional products fabricated with BC. Besides, the controllable cultivation conditions should also be discussed for expecting to make a breakthrough in its productivity. We highlight the literatures mainly in last 5 years, exerting ourselves to provide the state-of-the-art opinions in areas wherever are focused on for BC researching.

Cellulose nanocrystals as promising adsorbents for the removal of cationic dyes

Abstract: Cellulose nanocrystals (CNCs) prepared from cellulose fibre via sulfuric acid hydrolysis was used as an adsorbent for the removal of methylene blue (MB) from aqueous solution. The effects of pH, adsorbent dosage, temperature, ionic strength, initial dye concentration were studied to optimize the conditions for the maximum adsorption of dye. Adsorption equilibrium data was fitted to both Langmuir and Freundlich isotherm models, where the Langmuir model better described the adsorption process. The maximum adsorption capacity was 118 mg dye/g CNC at 25 °C and pH 9. Calculated thermodynamic parameters, such as free energy change (ΔG = −20.8 kJ/mol), enthalpy change (ΔH = −3.45 kJ/mol), and entropy change (ΔS = 0.58 kJ/mol K) indicates that MB adsorption on CNCs is a spontaneous exothermic process. Tunability of the adsorption capacity by surface modification of CNCs was shown by oxidizing the primary hydroxyl groups on the CNC surface with TEMPO reagent and the adsorption capacity was increased from 118 to 769 mg dye/g CNC.

Preparation and characterization of nanocrystalline cellulose via low-intensity ultrasonic-assisted sulfuric acid hydrolysis

Abstract: Nanocrystalline cellulose (NCC) was extracted from microcrystalline cellulose via low-intensity ultrasonic-assisted sulfuric acid hydrolysis process. NCC samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size distribution (PSD) analysis, Fourier-transformed infrared spectra (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and rheological measurement. It was found that NCC yield reached 40.4 % under the optimum process of low-intensity ultrasonic-assisted sulfuric acid hydrolysis, while it was only 33.0 % in the absence of ultrasonic treatment. Furthermore, the results showed that the two NCC samples obtained from ultrasonic-assisted hydrolysis and conventional hydrolysis were very similar in morphology, both exhibiting rod-like structures with widths and lengths of 10–20 and 50–150 nm, respectively. XRD result revealed that the NCC sample from ultrasonic-assisted hydrolysis contained a small amount of cellulose II and possessed a Segal Crystallinity Index of 90.38 % and a crystallite size of 58.99 A, higher than those of the NCC sample from conventional hydrolysis. Moreover, PSD analysis demonstrated that the former exhibited a smaller value in average particle size than the latter. In addition, rheological measurements showed that the NCC suspensions from the ultrasonic-assisted process exhibited a lower viscosity over the range of shear rate from 0.1 to 100 s−1 in comparison with that prepared in the absence of ultrasonic treatment.

Adsorption of Ni(II), Cu(II) and Cd(II) from aqueous solutions by amino modified nanostructured microfibrillated cellulose

Abstract: The aim of the present study was to investigate the adsorption properties of aminopropyltriethoxysilane (APS) modified microfibrillated cellulose (MFC) in aqueous solutions containing Ni(II), Cu(II) and Cd(II) ions. The modified adsorbents were characterized using elemental analysis, Fourier transform infrared spectroscopy, SEM and zeta potential analysis. The adsorption and regeneration studies were conducted in batch mode using various different pH values and contact times. The maximum removal capacities of the APS/MFC adsorbent for Ni(II), Cu(II), and Cd(II) ions were 2.734, 3.150 and 4.195 mmol/g, respectively. The Langmuir, Sips and Dubinin-Radushkevich models were representative to simulate adsorption isotherms. The adsorption kinetics of Ni(II) Cu(II), and Cd(II) adsorption by APS/MFC data were modeled using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics equations. The results indicate that the pseudo-second-order kinetic equation and intra-particle diffusion model were adequate to describe the adsorption kinetics.

Cellulose and chitin nanomaterials for capturing silver ions (Ag + ) from water via surface adsorption

Abstract: The study explores the potential of cellulose nanocrystals (CNC), cellulose nanofibers (CNF) and chitin nanocrystals (ChNC) isolated from bioresidues to remove silver ions from contaminated water. Zeta sizer studies showed negatively charged surfaces for CNC and CNF isolated from cellulose sludge in the acidic and alkaline pHs, whereas ChNC isolated from crab shell residue showed either positive or negative charges depending on pH conditions. Model water containing silver ions showed a decrease in Ag+ ion concentration (measured by inductively coupled plasma-optical emission spectrometer; inductively coupled plasma mass spectrometry), after treatment with CNC, CNF and ChNC suspensions. The highest Ag+ ion removal was measured near neutral pH for CNC, being 34.4 mg/g, corresponding to 64 % removal. ChNC showed 37 % and CNF showed 27 % removal of silver ions. The WDX (wavelength dispersive X-ray analysis) and XPS (X-ray photoelectron spectroscopy) analysis confirmed the presence of silver ions on the surface of the nanocellulose and nanochitin after adsorption. Surface adsorption on the nanoparticles via electrostatic interactions is considered to be the prominent mechanism of heavy metal ion capture from aqueous medium, with CNC with negative surface charge and negatively charged functional groups being most favourable for the adsorption of positively charged Ag+ ions compared to other native bionanomaterials.

Enhancing adsorption of heavy metal ions onto biobased nanofibers from waste pulp residues for application in wastewater treatment

Abstract: Biobased nanofibers are increasingly considered in purification technologies due to their high mechanical properties, high specific surface area, versatile surface chemistry and natural abundance In this work, cellulose and chitin nanofibers functionalized with carboxylate entities have been prepared from pulp residue (ie, a waste product from the pulp and paper production) and crab shells, respectively, by chemically modifying the initial raw materials with the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) mediated oxidation reaction followed by mechanical disintegration A thorough investigation has first been carried out in order to evaluate the copper(II) adsorption capacity of the oxidized nanofibers UV spectrophotometry, X-ray photoelectron spectroscopy and wavelength dispersive X-rays analysis have been employed as characterization tools for this purpose Pristine nanofibers presented a relatively low content of negative charges on their surface thus adsorbing a low amount of copper(II) The copper adsorption capacity of the nanofibers was enhanced due to the oxidation treatment since the carboxylate groups introduced on the nanofibers surface constituted negative sites for electrostatic attraction of copper ions (Cu2+) The increase in copper adsorption on the nanofibers correlated both with the pH and carboxylate content and reached maximum values of 135 and 55 mg g−1 for highly oxidized cellulose and chitin nanofibers, respectively Furthermore, the metal ions could be easily removed from the contaminated nanofibers through a washing procedure in acidic water Finally, the adsorption capacity of oxidized cellulose nanofibers for other metal ions, such as nickel(II), chromium(III) and zinc(II), was also demonstrated We conclude that TEMPO oxidized biobased nanofibers from waste resources represent an inexpensive and efficient alternative to classical sorbents for heavy metal ions removal from contaminated water

Synthesis of regenerated bacterial cellulose-zinc oxide nanocomposite films for biomedical applications

Abstract: Regenerated bacterial cellulose (RBC) composites with zinc-oxide nanoparticles (ZnO) were prepared using a new strategy for enhanced biomedical applications of BC. Powdered BC was dissolved in N-methylmorpholine-N-oxide, and different concentrations of ZnO nanoparticles were mixed into the BC solution. RBC, RBC-ZnO1 (1 % ZnO) and ZnO-RBC2 (2 % ZnO) nanocomposite films were prepared by casting the solutions through an applicator. FE-SEM images confirmed the structural features and impregnation of the RBC films by nanoparticles. XRD analysis indicated the presence of specific peaks for RBC and ZnO in the composites. The RBC nanocomposites were found to have greatly enhanced thermal, mechanical and biological properties. Specifically, the degradation temperatures were improved from 334 °C for RBC to 339 and 344 °C for RBC-ZnO1 and RBC-ZnO2, respectively. The mechanical strength and Young’s modulus of the composites were also higher than those of pure RBC. The greatly improved antibacterial properties of the RBC-ZnO nanocomposites are the most striking feature of the present study. The bacterial growth inhibition measured for the RBC was zero, but reached up to 34 and 41 mm for RBC-ZnO1 and RBC-ZnO2, respectively. In addition to their antibacterial properties, the RBC-ZnO nanocomposites were found to be nontoxic and biocompatible with impressive cell adhesion capabilities. These RBC-ZnO nanocomposites can be used for different biomedical applications and have the potential for use in bioelectroanalysis.

Dissolution of cellulose in aqueous NaOH/urea solution: role of urea

Abstract: Urea can improve the solubility and stability of cellulose in aqueous alkali solution, while its role has not come to a conclusion. To reveal the role of urea in solution, NMR was introduced to investigate the interaction between urea and the other components in solution. Results from chemical shifts and longitudinal relaxation times show that: (1) urea has no strong direct interaction with cellulose as well as NaOH; (2) urea does not have much influence on the structural dynamics of water. Urea may play its role through van der Waals force. It may accumulate on the cellulose hydrophobic region to prevent dissolved cellulose molecules from re-gathering. The driving force for the self-assembly of cellulose and urea molecules might be hydrophobic interaction. In the process of cellulose dissolution, OH− breaks the hydrogen bonds, Na+ hydrations stabilize the hydrophilic hydroxyl groups and urea stabilizes the hydrophobic part of cellulose.

Using graphene/TiO2 nanocomposite as a new route for preparation of electroconductive, self-cleaning, antibacterial and antifungal cotton fabric without toxicity

Abstract: A novel and efficient process is reported for fabrication of electroconductive, self-cleaning, antibacterial and antifungal cellulose textiles using a graphene/titanium dioxide nanocomposite. Cotton fabric was loaded with graphene oxide using a simple dipping coating method. The graphene oxide-coated cotton fabrics were then immersed in TiCl3 aqueous solution as both a reducing agent and a precursor to yield a fabric coated with graphene/titanium dioxide nanocomposite. The crystal phase, morphology, microstructure and other physicochemical properties of the as-prepared samples were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and UV-Vis reflectance spectroscopy. Electrical resistance, self-cleaning performance, antimicrobial activity and cytotoxicity of treated fabrics were also assessed. The electrical conductivity of the graphene/titanium dioxide nanocomposite-coated fabrics was improved significantly by the presence of graphene on the surface of cotton fabrics. The self-cleaning efficiency of the treated fabrics was tested by degradation of methylene blue in aqueous solution under UV and sunlight irradiations. The results indicated that the decomposition rates of methylene blue were improved by the addition of graphene to the TiO2 treatment on fabrics. Moreover, the graphene/titanium dioxide nanocomposite-coated cotton samples had negligible toxicity and possessed excellent antimicrobial activity.

Ionic strength effects on the microstructure and shear rheology of cellulose nanocrystal suspensions

Abstract: The effect of ionic strength on the rheology and microstructure of Cellulose nanocrystals (CNC) aqueous suspensions are studied over a broad range of CNC (3–15 wt%) and NaCl concentrations (0–15 mM), using polarized optical microscopy combined with rheometry. The CNC suspensions are isotropic at low concentration and form chiral nematic liquid crystalline structure above a first critical concentration and gel above a second critical one. It has been shown that for isotropic CNC suspensions, increasing the ionic strength of the system up to 5 mM NaCl concentration weakens the electro-viscous effects and thus reduces the viscosity of these suspensions. For biphasic samples, which contain chiral nematic liquid crystal domains, increasing the ionic strength up to 5 mM NaCl concentration decreases the size of the chiral nematic domains, and leads the viscosity of the samples at low shear rates to increase. On the other hand, at high shear rates, where all the ordered domains are broken, the viscosity decreases with NaCl addition. For gels, the addition of NaCl up to 5 mM weakens the gel structure and decreases the viscosity. Further addition of NaCl (10 and 15 mM NaCl concentrations) results in extensive aggregation and de-stabilizes the CNC suspensions.

Comparison of nano- and microfibrillated cellulose films

Abstract: Nanocellulose is an interesting building block for functional materials and has gained considerable interest due to its mechanical robustness, large surface area and biodegradability. It can be formed into various structures such as solids, films and gels such as hydrogels and aerogels and combined with polymers or other materials to form composites. Mechanical, optical and barrier properties of nanofibrillated cellulose (NFC) and microfibrillated cellulose (MFC) films were studied in order to understand their potential for packaging and functional printing applications. Impact of raw material choice and nanocellulose production process on these properties was evaluated. MFC and NFC were produced following two different routes. NFC was produced using a chemical pretreatment followed by a high pressure homogenization, whereas MFC was produced using a mechanical treatment only. TEMPO-mediated oxidation followed by one step of high pressure (2,000 bar) homogenization seems to produce a similar type of NFC from both hardwood and softwood. NFC films showed superior mechanical and optical properties compared with MFC films; however, MFC films demonstrated better barrier properties against oxygen and water vapor. Both the MFC and NFC films were excellent barriers against mineral oil used in ordinary printing inks and dichlorobenzene, a common solvent used in functional printing inks. Barrier properties against vegetable oil were also found to be exceptionally good for both the NFC and MFC films.

Carboxymethylated nanofibrillated cellulose: rheological studies

Abstract: The rheological properties of carboxymethylated nanofibrillated cellulose (NFC), investigated with controlled shear rate- and oscillatory measurements, are reported for the first time. It was shown that the rheological properties of the studied system are similar to those reported for other NFC systems. The carboxymethylated NFC systems showed among other things high elasticity and a shear thinning behaviour when subjected to increasing shear rates. Further, the shear viscosity and storage modulus of the system displayed power-law relations with respect to the dry content of the NFC suspension. The exponential values, 2 and 2.4 respectively, were found to be in good agreement with both theoretical predictions and published experimental work. Furthermore, it was found that the pulp consistency at which NFC is produced affects the properties of the system. The rheological studies imply that there exists a critical pulp concentration below which the efficiency of the delamination process diminishes; the same adverse effect is also observed when the critical concentration is significantly exceeded due to a lower energy input during delamination.

Antimicrobial nanocomposite films made of poly(lactic acid)-cellulose nanocrystals (PLA-CNC) in food applications-part B: effect of oregano essential oil release on the inactivation of Listeria monocytogenes in mixed vegetables

Abstract: Antimicrobial nanocomposite films containing oregano essential oil (EO) were prepared by solvent casting. Film matrix was composed of supramolecular poly(lactic acid)–cellulose nanocrystals (PLA–CNC) nanocomposite. Bioactive PLA–CNC–oregano films were prepared by incorporating oregano EO as an antimicrobial agent. Resulting films were then converted into packaging applied on mixed vegetables as a food model and stored for 14 days at 4 °C to determine their antimicrobial capacity against Listeria monocytogenes, their physico-chemical/structural properties and their total phenols (TP) release during storage, in order to evaluate the effect of oregano EO. It was observed the addition of oregano EO did not affect the water vapor permeability (WVP) of films, but increased their elongation at break (Eb) and reduced their tensile strength (TS) and tensile modulus (TM) at day 0. However, TS, TM, Eb and WVP values of control and bioactive films were increased slightly after 14 days of storage. FTIR analysis allowed characterizing the molecular interactions of oregano EO with PLA–CNC matrix via the identification and interpretation of their respective vibration bands. Microbiological analysis of mixed vegetables inoculated with L. monocytogenes (3 log CFU g−1) indicated that PLA–CNC–oregano films induced a quasi-total inhibition of bacteria in vegetables at day 14 and therefore demonstrated a strong antimicrobial capacity in situ. The percentage of TP release from bioactive films was determined by Folin–Ciocalteu’s method and results showed that TP release increased continuously from day 0 to day 14, up to 16.6 % at day 14. These results allowed demonstrating the strong antimicrobial capacity of PLA–CNC–oregano films for food packaging applications in vegetable produce.

Microstructural and mechanical properties of porous biocomposite scaffolds based on polyvinyl alcohol, nano-hydroxyapatite and cellulose nanocrystals

Abstract: In this study, in situ synthesis of polyvinyl alcohol (PVA)/nano-hydroxyapatite (n-HA)/cellulose nanocrystals (CNC) organic–inorganic biocomposite porous scaffolds is reported. The effect of the CNC content on the properties of the biocomposite scaffold was investigated and characterized using field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis, porosity and compressive strength measurements, thermal studies, and in vitro biomineralization and degradation studies. The morphological study showed highly porous structures with good pore interconnectivity in which n-HA was homogeneously dispersed. XRD analysis showed a decrease in the crystalline fraction and crystallite size of nano-hydroxyapatite with introduction of PVA and with increasing content of CNC. It was observed that the porosity decreased to some extent with increasing CNC content, while increases in the compressive strength (from 0.85 to 2.09 MPa) and elastic modulus (from 4.68 to 16.01 MPa) were found as the CNC content was increased. In vitro biomineralization study revealed the formation of apatite on PVA/n-HA/CNC biocomposite scaffolds when soaked for 7 and 14 days in simulated body fluid (SBF) solution. The obtained porous scaffolds offering good mechanical performance may provide a promising alternative scaffolding matrix for use in the field of bone tissue engineering.

Hydrophobic cellulose nanopaper through a mild esterification procedure

Abstract: Films of cellulose nanofibrils (CNF) (referred to as nanopaper) present a great potential in many applications due to the abundance, low environmental impact, excellent oxygen barrier properties and good mechanical performance of CNF. However, the strong hygroscopic character of the natural nanofibers limits their use in environments with high relative humidity. In this paper, we introduce a simple route for the esterification and processing of CNF with the aim of reducing their hydrophilicity, and producing hydrophobic cellulose nanopaper with reduced moisture sensitivity. The preparation steps of hydrophobic nanopapers involve vacuum filtration, solvent exchange from water to acetone, and reaction with anhydride molecules bearing different hydrophobic alkyl chains by hot pressing. Porous films having a surface area between 38 and 47 g/m2 and pore sizes in the 3–200 nm range are obtained. This method preserves the crystalline structure of native cellulose, and successfully introduces hydrophobic moieties on CNF surface as confirmed by FTIR, XPS and elemental analysis. As a result, modified nanopapers have a reduced moisture uptake, both higher surface water contact angle and wet tensile properties as compared with reference non-modified nanopaper, thus illustrating the benefit of the modification for the use of cellulose nanopaper in humid environments.

Dry-jet wet spinning of strong cellulose filaments from ionic liquid solution

Abstract: Considerable growth is expected in the production of man-made cellulose textile fibers, which are commercially produced either via derivatization to form cellulose xanthate (viscose) or via direct dissolution in N-methylmorpholine N-oxide (Lyocell). In the study at hand, cellulosic fibers are spun from a solution in the ionic liquid [DBNH] [OAc] into water, resulting in properties equal or better than Lyocell (tensile strength 37 cN tex−1 or 550 MPa). Spinning stability is explored, and the effects of extrusion velocity, draw ratio, spinneret aspect ratio and bath temperature on mechanical properties and orientation are discussed. With the given set-up, tenacities and moduli are improved with higher draw ratios, while elongation at break, the ratio of wet to dry strength, modulus of resilience and birefringence depend little on draw ratio or extrusion velocity, elastic limit not at all. We find the process robust and simple, with stretching to a draw ratio of 5 effecting most improvement, explained by the orientation of amorphous domains along the fiber axis.

Dispersion stability and aggregation behavior of TEMPO-oxidized cellulose nanofibrils in water as a function of salt addition

Abstract: Dispersion stability of TEMPO-oxidized cellulose nanofibrils (TOCNs) in water was investigated through both experimental and theoretical analyses to elucidate the critical aggregation concentration of different salts. The 0.1 wt% TOCN/water dispersions with various NaCl concentrations were evaluated by measuring light transmittance, viscosity under steady-shear flow, and the weight fraction of TOCN that had aggregated. Homogeneous TOCN/water dispersion turned to gel as the NaCl concentration increased. The TOCN dispersion maintained its homogeneous state up to 50 mM NaCl, but aggregated gel particles were formed at 100 mM NaCl. The mixture became separated into two phases (gel and supernatant) at ≥200 mM NaCl. Theoretical analysis using ζ-potentials of TOCN elements in the dispersions revealed that the aggregation behavior upon NaCl addition could be explained well in terms of the interaction potential energy between two cylindrical rods based on the Derjaguin–Landau–Verwey–Overbeek theory. The experiments were extended to analyze critical aggregation concentrations of MgCl2 and CaCl2 for the 0.1 wt% TOCN dispersion. In the case of divalent electrolytes, TOCN elements began to form aggregated gel particles at salt concentrations of 2–4 mM, corresponding to the critical aggregation concentration predicted by the empirical Schultz-Hardy rule.

From paper to nanopaper: evolution of mechanical and physical properties

Abstract: In the present work the evolution of physical and mechanical properties of papers and nanopapers is studied. Handsheets made of eucalyptus fibres reinforced with 0, 25, 50, 75 and 100 wt% of nanofibrillated cellulose (NFC) content were fabricated using a Rapid Kothen-like equipment. The obtained papers and nanopapers were physical- and mechanically-characterized. The results showed a significant increase in density and a reduction of porosity in the samples during their transition from paper to nanopaper; besides, nanopapers were more transparent and smoother than normal papers. These physical changes where more evident with increasing amounts of NFC. Regarding mechanical properties, nanopapers with a 100 wt% content of NFC improved their strength and rigidity in 228 and 317 %, respectively, in comparison with normal papers. The evolution of strength and rigidity from paper to nanopaper was linear in relation to the amount of NFC, which means that the ultimate tensile strength was mainly dependant on nanofibril failure.

Excellent chemical and material cellulose from tunicates: diversity in cellulose production yield and chemical and morphological structures from different tunicate species

Abstract: The high crystallinity and the high microfibrils aspect ratio of tunicate cellulose (TC) indicate TC's excellent chemical and material applications. However, its quantity and quality from different ...

Visualization of the nanoscale pattern of recently-deposited cellulose microfibrils and matrix materials in never-dried primary walls of the onion epidermis

Abstract: For more than 10 years epidermal cell layers from onion scales have been used as a model system to study the relationship between cellulose orientation, cell growth and tissue mechanics To bring such analyses to the nanoscale, we have developed a procedure for preparing epidermal peels of onion scales for atomic force microscopy to visualize the inner surface (closest to the plasma membrane) of the outer epidermal wall, with minimal disturbance and under conditions very close to the native state of the cell wall The oriented, multilayer distribution of cellulose microfibrils, approximately ~3 nm wide, is readily observed over extended lengths, along with other features such as the distribution of matrix substances between and on top of microfibrils The microfibril orientation and alignment appear more dispersed in younger scales compared with older scales, consistent with reported values for mechanical and growth anisotropy of whole epidermal sheets These results open the door to future work to relate cell wall structure at the nm scale with larger-scale tissue properties such as growth and mechanical behaviors and the action of cell wall loosening agents to induce creep of primary cell walls

A comparative molecular dynamics study of crystalline, paracrystalline and amorphous states of cellulose

Abstract: The quintessential form of cellulose in wood consists of microfibrils that have high aspect ratio crystalline domains embedded within an amorphous cellulose domain. In this study, we apply united-atom molecular dynamics simulations to quantify changes in different morphologies of cellulose. We compare the structure of crystalline cellulose with paracrystalline and amorphous phases that are both obtained by high temperature equilibration followed by quenching at room temperature. Our study reveals that the paracrystalline phase may be an intermediate, kinetically arrested phase formed upon amorphisation of crystalline cellulose. The quenched structures yield isotropic amorphous polymer domains consistent with experimental results, thereby validating a new computational protocol for achieving amorphous cellulose structure. The non-crystalline cellulose compared to crystalline structure is characterized by a dramatic decrease in elastic modulus, thermal expansion coefficient, bond energies, and number of hydrogen bonds. Analysis of the lattice parameters shows that Iβ cellulose undergoes a phase transition into high-temperature phase in the range of 450–550 K. The mechanisms of the phase transition elucidated here present an atomistic view of the temperature dependent dynamic structure and mechanical properties of cellulose. The paracrystalline state of cellulose exhibits intermediate mechanical properties, between crystalline and amorphous phases, that can be assigned to the physical properties of the interphase regions between crystalline and amorphous cellulose in wood microfibrils. Our results suggest an atomistic structural view of amorphous cellulose which is consistent with experimental data available up to date and provide a basis for future multi-scale models for wood microfibrils and all-cellulose nanocomposites.

Preparation of cellulose nanocrystals and carboxylated cellulose nanocrystals from borer powder of bamboo

Abstract: Carboxylated cellulose nanocrystals (CCN) and cellulose nanocrystals (CNC) were prepared from borer powder of bamboo by two different kinds of procedures: one-step approach with ammonium persulfate for CCN and two-step approach with sulfuric acid for CNC. The obtained samples were characterizated by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. The results show that the particles of CCN and CNC present spherical shape with diameters of 20–50 and 20–70 nm, respectively. The crystallinity of CCN and CNC is significantly improved after a series of chemical treatment, which is up to 62.75 and 69.84 %, respectively. The research indicates that the borer powder from bamboo could be an excellent raw material for manufacturing CNC in a low-cost and environmental-friendly way. Rational and sustainable utilization of the bamboo borer powder to develop new bioproducts holds great potential value for industry and offers many benefits and opportunities.

Tensile strength of Iβ crystalline cellulose predicted by molecular dynamics simulation

Abstract: The mechanical properties of Iβ crystalline cellulose are studied using molecular dynamics simulation. A model Iβ crystal is deformed in the three orthogonal directions at three different strain rates. The stress–strain behaviors for each case are analyzed and then used to calculate mechanical properties. The results show that the elastic modulus, Poisson’s ratio, yield stress and strain, and ultimate stress and strain are highly anisotropic. In addition, while the properties that describe the elastic behavior of the material are independent of strain rate, the yield and ultimate properties increase with increasing strain rate. The deformation and failure modes associated with these properties and the relationships between the material’s response to tension and the evolution of the crystal structure are analyzed.

Poly(ε-caprolactone) (PCL)/cellulose nano-crystal (CNC) nanocomposites and foams

Abstract: Poly(e-caprolactone) (PCL)/cellulose nanocrystal (CNC) nanocomposites were produced via twin-screw extrusion. Microcellular nanocomposite samples were produced with microcellular injection molding using carbon dioxide (CO2) as physical blowing agent. The foaming behavior, physical properties, thermal properties, crystallization behavior, and biocompatibility were investigated. It was found that the CNCs interacted with the PCL matrix which led to a strong interface. The CNCs effectively acted as nucleation agents in microcellular injection molding. Both solid and foamed samples with higher levels of CNC content showed higher tensile moduli, complex viscosities, and storage moduli due to the reinforcement effects of CNCs. Furthermore, improvement in the foamed samples was more significant due to their fine cell structure. The addition of CNCs caused a reduction of the decomposition temperature and an increase in the glass transition temperature, crystallization temperature, and crystallinity of PCL. Moreover, the biocompatibility of the foamed nanocomposites with low CNC content was verified by 3T3 fibroblast cell culture.

Size, shape, and arrangement of native cellulose fibrils in maize cell walls

Abstract: Higher plant cell walls are the major source of the cellulose used in a variety of industries. Cellulose in plant forms nanoscale fibrils that are embedded in non-cellulosic matrix polymers in the cell walls. The morphological features of plant cellulose fibrils such as the size, shape, and arrangement, are still poorly understood due to its inhomogeneous nature and the limited resolution of the characterization techniques used. Here, we sketch out a proposed model of plant cellulose fibril and its arrangement that is based primarily on review of direct visualizations of different types of cell walls in maize using atomic force microscopy at sub-nanometer scale, and is also inspired by recent advances in understanding of cellulose biosynthesis and biodegradation. We propose that the principal unit of plant cellulose fibril is a 36-chain cellulose elementary fibril (CEF), which is hexagonally shaped and 3.2 × 5.3 nm in cross-section. Macrofibrils are ribbon-like bundles containing variable numbers of CEFs associated through their hydrophilic faces. As the cell expands and/or elongates, large macrofibril may split to become smaller bundles or individual CEFs, which are simultaneously coated with hemicelluloses to form microfibrils of variable sizes during biosynthesis. The microfibrils that contain one CEF are arranged nearly parallel, and the hydrophobic faces of the CEF are perpendicular to the cell wall surface. Structural disordering of the CEF may occur during plant development while cells expand, elongate, dehydrate, and die, as well as during the processing to prepare cellulose materials.

Physical structure and thermal behavior of ethylcellulose

Abstract: The physical structure and properties of ethylcellulose (EC) powders of different molecular weights were examined. A molecular weight in the range of 20–144 kDa with a large polydispersity was determined. EC thermal analysis revealed a glass transition at ~130 °C and a melting temperature at ~180 °C. Glass transition temperatures increased with polymer molecular weight. Wide angle (WAXS) analysis detected an amorphous broad peak at q = 1.5 A−1 and a distinct Bragg’s peak at 12.6 A, which seems to be related to a supramolecular ordered structure of the polymer. These observations were confirmed using high temperature powder X-ray diffraction analysis where the crystalline peak disappeared above the melting temperature of the polymer. Ultra-small angle (USAXS) results were fitted to the Bouacage fractal unified model and fractals with an average size of 100–600 nm with a relatively smooth surface were predicted. This prediction was confirmed by transmission electron microscopy (TEM) images. According to our results, the EC polymer has a semi-crystalline structure, with crystalline domains within an amorphous background.

Antimicrobial nanocomposite films made of poly(lactic acid)-cellulose nanocrystals (PLA-CNC) in food applications: part A—effect of nisin release on the inactivation of Listeria monocytogenes in ham

Abstract: New bioactive nanocomposite films were prepared by compression molding method for food applications. Film matrix was composed of poly(lactic acid) containing cellulose nanocrystals (PLA-CNC). Nanocomposite films were converted to bioactive films using nisin as an antimicrobial agent by an adsorption coating method. Resulting antimicrobial films were then introduced in packages containing sliced cooked ham as a food model and stored for 14 days at 4 °C to determine their inhibiting capacity against Listeria monocytogenes and their physicochemical and structural properties. The study also focused on the nisin release from the films by using an agar diffusion bioassay. It was observed that mechanical properties such as tensile strength, tensile modulus, elongation at break and water vapor permeability values of the bioactive films were stable after 14 days of storage. Fourier transform infrared spectroscopy analysis allowed characterizing the adsorption of nisin onto PLA-CNC surface. Microbiological analysis of sliced cooked ham inoculated with L. monocytogenes (3 log CFU/g) allowed determining the potentiality of nisin as a strong antimicrobial agent in PLA-CNC-based films. Bioactive PLA-CNC-nisin films showed a significant reduction of L. monocytogenes in ham from day 1 and a total inhibition from day 3. The percentage of nisin release increased continuously from day 0 to day 14, up to 21 % at day 14. These results demonstrated the potential application of PLA-CNC-nisin films on controlling the growth of food pathogens in meat products.

Determination of nanocellulose fibril length by shear viscosity measurement

Abstract: The lengths of ten types of cellulose nanofibrils were evaluated by shear viscosity measurement of their dilute dispersions. Aqueous dispersions of surface-carboxylated cellulose nanofibrils with a uniform width of ~3 nm were prepared from wood cellulose by 2,2,6,6-tetramethylpiperidine-1-oxyl-mediated oxidation and successive mechanical treatment. Cellulose nanofibril samples with different average lengths were prepared by controlling the conditions of the oxidation or mechanical treatment. The viscosity-average lengths, L visc, of the nanofibrils were calculated by applying the shear viscosities of the dilute dispersions to an equation for the dilute region flow behavior of rod-like polymer molecules. The obtained L visc values ranged from 1,100 to 2,500 nm and showed a linear relationship to the length-weighted average length, L w, measured by microscopic observation; the relation was described as L visc = 1.764 × L w + 764. The influences of the electric double-layer of the nanofibrils and surface-carboxylate content on the value of L visc were also investigated.

Preparation and characterization of cellulose nanocrystals via ultrasonication-assisted FeCl 3 -catalyzed hydrolysis

Abstract: Cellulose nanocrystals (CNC) was obtained from bamboo pulp via ultrasonication-assisted FeCl3-catalyzed hydrolysis process, with parameters optimized by response surface methodology. The optimal parameters were reaction temperature: 107 °C, reaction time: 58 min, ultrasonication time: 186 min. The morphological, crystal structural, chemical structural and thermal features of the prepared cellulose nanocrystals were analyzed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), Fourier transfer infrared (FTIR) and thermogravimetric analysis. The results showed that the cellulose nanocrystals formed an interconnected network structure and CNC was rod-like with the length of 100–200 nm and the width of 10–20 nm. XRD result revealed that, compared with cellulose pulp, the crystallinity index of CNC increased from 69.5 to 79.4 %, while the cellulose I crystal structure remained. FTIR analysis demonstrated that CNC had the similar chemical structures to that of cellulose pulp, which indicated that the chemical structures of CNC remained unchanged in the presence of FeCl3-catalyzed hydrolysis process and ultrasonication treatment. Thermogravimetric analysis revealed that the resulting CNC exhibited relatively high thermal stability. The research shows that ultrasonication-assisted FeCl3-catalyzed hydrolysis could be a highly efficient method for preparing CNC.