All-cellulose nanocomposite fibers produced by melt spinning cellulose acetate butyrate and cellulose nanocrystals

Bio-based continuous fibers were prepared by melt spinning cellulose acetate butyrate (CAB), cellulose nanocrystals (CNC) and triethyl citrate. A CNC organo-gel dispersion technique was used and the prepared materials (2 and 10 wt% CNC) were melt spun using a twin-screw micro-compounder and drawn to a ratio of 1.5. The microscopy studies showed that the addition of CNC in CAB resulted in defect-free and smooth fiber surfaces. An addition of 10 wt% CNC enhanced the storage modulus and increased the tensile strength and Young’s modulus. Fiber drawing improved the mechanical properties further. In addition, a micromechanical model of the composite material was used to estimate the stiffness and showed that theoretical values were exceeded for the lower concentration of CNC but not reached for the higher concentration. In conclusion, this dispersion technique combined with melt spinning can be used to produce all-cellulose nanocomposites fibers and that both the increase in CNC volume fraction and the fiber drawing increased the mechanical performance.     

Aligned cellulose nanocrystals and directed nanoscale deposition of colloidal spheres

Cellulose nanocrystals are aligned in wrinkled polydimethylsiloxane templates and transferred to polyethyleneimine-coated silica surfaces in a printing process similar to microcontact printing. The highly aligned nanorods were deposited onto the surfaces with a line-to-line distance of 225–600 nm without loss of alignment. It was also possible to repeat the transfer process on the same surface at a 90-degree angle to create a network structure. This demonstrates the versatility of the technique and creates more options for advanced multilayering of materials. To demonstrate that the surface properties of the anionic cellulose nanorods were unaffected by the transfer process and to prove the concept of functionalizing transferred particles, cationic latex particles were electrostatically self-assembled onto the cellulose nanorods. The directed deposition of these particles resulted in excellent site specificity and the highest resolution to date for controlled deposition of colloids on an electrostatically patterned surface.     

Chiral separation of trans-stilbene oxide through cellulose acetate butyrate membrane

An enantioselective membrane was prepared using cellulose acetate butyrate as a membrane material. The flux and permselective properties of membrane using 50% ethanol solution of (R,S)-trans-stilbene oxide as feed solution were studied. The top surface and cross-section morphology of the resulting membrane were examined by scanning electron microscopy. The resolution of over 92% enantiomeric excess was achieved when the enantioselective membrane was prepared with 15 wt % cellulose acetate butyrate and 30 wt % N,N-dimethylformamide in the casting solution of acetone, 10 °C temperature of water bath for the gelation of the membrane, and the operating pressure and the feed concentration of the trans-stilbene oxide were 3 kgf/cm² and 5.2 mmol/L, respectively. Since the cellulose acetate butyrate contained a large amount of asymmetric carbons on the backbone structure, it was possible to form helical structure, this was considered to be the reason for the enantioselectivity of the membrane.     

Thermal stability of cellulose acetate urethanes

The thermal degradation of isocyanate modified cellulose acetate has been studied by dynamic thermogravimetric analysis in air. The activation energy of decomposition of these modified polymers has also been determined from differential thermal analysis thermograms. The data indicate that the cellulose acetate urethane polymers are thermally stable.     

Combined sorption/transport of sodium dodecyl sulfate and hydrochloric acid in a blend of cellulose acetate butyrate with cellulose acetate hydrogen phthalate

The transport of hydrochloric acid (0.001-0.1 M) and sodium dodecyl sulfate (0.001-0.1 M) has been measured through a membrane consisting of a blend of cellulose acetate butyrate and cellulose acetate hydrogen phthalate. The cellulose derivative blend is suggested to suffer an alteration in the degree of hydrophobicity when in equilibrium with sodium dodecyl sulfate (SDS) through hemimicelle formation. An increase in surface hydrophobicity of the blend when in equilibrium with SDS solution was observed by fluorescence measurements using the vibronic bands of the probe pyrene, as well as by water desorption kinetics; a decrease of the effective diffusion coefficients from 1.2 × 10⁻¹¹ m² s⁻¹ in the absence of SDS to approximately 2 × 10⁻¹³ m² s⁻¹ in its presence was found. The value obtained for the mutual diffusion coefficient of HCl in the concentration range 0.001-0.1 M (D=4.2×10⁻¹⁴ m² s⁻¹) shows also that the membrane presents hydrophobic features. The flux of SDS in the blend membrane at different pH values shows two distinct permeation rates depending on the cmc. However, from the calculation of permeability coefficients at SDS concentrations below the cmc a clear decrease in P is found, whilst, at concentrations above the cmc the permeability coefficients are nearly constant, only showing a slightly increase. The diffusion coefficients of SDS in the blend increase over the whole SDS concentration range analysed and show an effective diffusion coefficient 2-3 orders of magnitude below the diffusion coefficients of SDS in aqueous solutions. This fact suggests that the only diffusing species are SDS unimers. The presence of HCl in the SDS bulk solution has the effect of increasing the permeability and diffusion coefficients. Mutual analysis of permeation and diffusion coefficients and sorption isotherms shows that, on decreasing the pH, the interactions between SDS and the polymer network decrease. This is also reflected in a clear decrease of the hydrophobic interactions between the diffusing and polymeric species, provoked by a decrease in the unimer-unimer association.     

Uniaxial drawing of poly[(R)-3-hydroxybutyrate]/cellulose acetate butyrate blends and their orientation behavior

Miscible blends of PHB and CAB were prepared by the solvent-casting method with various blend compositions, and their orientation behavior was investigated during uniaxial drawing. X-ray analysis revealed that the orientation of the crystallizable PHB component in the drawn PHB/CAB blends was changed from c-axis-orientation to a-axis-orientation with increasing CAB content. The a-axis-orientation was a result from the a-axis-oriented crystal growth caused by the intramolecular nucleation and the confined crystal growth. For quantitative assessment of the chain orientation, the Hermans orientation functions of the two respective components were obtained from the polarized FT-IR measurements. The orientation function of pure PHB stretched to 5 times of its initial length was approximately 0.8. However the value decreased rapidly with increasing CAB content, and it turned to a negative value from 30 wt.-% CAB content. This indicates that the PHB chains were aligned perpendicular to the drawing direction. On the contrary, the value of the CAB component remained almost unchanged at about 0.1 regardless of the blend composition and the annealing time, indicating that the CAB chains were constantly oriented parallel to the drawing direction without any chain relaxation. In addition, SAXS analysis suggested that the lamellar stacking direction also changed from parallel to perpendicular in the stretching direction with increasing CAB content.     

Synthesis and characterization of photosensitive cinnamate-modified cellulose acetate butyrate spin-coated or network derivatives

The photochemical behavior of photosensitive materials obtained by spin-coating or network synthesis of a cellulosic polymer bearing photo-cross-linkable cinnamate groups was investigated. First, cinnamate groups were grafted on a cellulose acetate butyrate polymer, with different grafting densities. The photochemical properties of the polymers were studied in solution by UV–visible and ¹H NMR spectroscopy. Then spin-coated films and networks were prepared and characterized as a function of the number of cinnamate groups per cellulosic unit. The water-wetting properties of both surfaces were studied by dynamic contact angle measurements, before and after photoirradiation, and subsequent heating. The surfaces obtained by the two methods have significantly different behaviors that can be assigned to the distinct photochemical pathways of the cinnamate groups upon irradiation depending on the sample preparation. Indeed, dimerization reaction is evidenced as the main process in the spin-coated films while the expected isomerization is predominant at the surface of the polymer networks.     

Two-phase synthesis of shape-controlled colloidal zirconia nanocrystals and their characterization

We have developed a two-phase approach for the synthesis of shape-controlled colloidal zirconia nanocrystals, including spherical-, teardrop-, rod-, and rice grain-shaped particles. We found that the key factors for controlling the shape were the reaction time, the nature of the capping agent, and the monomer concentration. We have analyzed the morphologies, crystallinity, optical properties, and structural features of the as-prepared ZrO2 nanoparticles by using transmission electron microscopy (TEM), high-resolution TEM, X-ray powder diffraction, and UV-vis absorption and fluorescence spectroscopy. The possible nucleation and growth process is also discussed.     

Effect of microcrystalline and nanocrystals cellulose fillers in materials based on PLA matrix

The aim of this work was to compare the effects of microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC) addition on the properties of PLA matrix. The CNC were obtained by acid hydrolysis of the MCC. Both MCC and CNC were separately incorporated in PLA at ratios of 3, 5 and 7 wt%. In some compositions, organophilic silica (R972) was added to improve the cellulose-matrix compatibility. The properties of the materials were evaluated by FTIR, XRD, NMR and mechanical tests. Functional groups and crystalline structure of MCC and CNC were determined by FTIR and XRD, respectively. NMR T₁H values showed that films containing CNC presented better interfacial interaction than those containing MCC, and indicated that R972 acts as compatibilizer. MCC and CNC acted as nucleating agents for PLA crystallization and there was an improvement in the mechanical performance of materials with the addition of CNC.     

Phase behavior and crystallization of a poly(ethylene oxide)/cellulose acetate butyrate blend

The phase behavior of a partially miscible blend of poly(ethylene oxide) (PEO) and cellulose acetate butyrate (CAB) and the crystalline microstructure of PEO in the blend were studied with differential scanning calorimetry (DSC), optical microscopy, and synchrotron small‐angle X‐ray scattering (SAXS) methods. PEO/CAB showed a lower critical solution temperature (LCST) of 168 °C at the critical composition of PEO of 60 wt %. All blend compositions showed a single glass‐transition temperature (T_g) when they were prepared at temperatures lower than the LCST. However, with increasing CAB content, T_g of the blend changed abruptly at 70 wt % CAB; that is, a cusp existed. Below 70 wt % CAB, the change in T_g with blend composition was predicted by the Brau–Kovacs equation, whereas this change was predicted by the Fox equation at higher CAB contents. A gradual but small depression of the melting point of PEO in the blend with an increasing amount of CAB suggested that the PEO/CAB blends exhibited a weak intermolecular interaction. From DSC and SAXS experiments, it was found that amorphous CAB was incorporated into the interlamellar region of PEO for blends with less than 20 wt % CAB, whereas it was segregated to exist in the interfibrillar region in PEO for other blends with larger amounts of CAB. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1673–1681, 2002     

Lewis acid‐base properties of cellulose acetate butyrate by inverse gas chromatography

The dispersive component of the surface‐free energy, , of cellulose acetate butyrate (CAB) has been determined using the net retention volume, V_N, of n‐alkanes (C₅? C₈) probes in the temperature range 323.15–393.15 K. The values decrease nonlinearly with increase in temperature, and the temperature coefficients of are ? 0.32 (mJ/m²K) and ? 0.10 (mJ/m²K) in the range 323.15–353.15 K and 353.15–393.15 K, respectively. This variation in has been attributed to the structural changes that take place on the surface of CAB at ～353.15 K. The specific components of the enthalpy of adsorption, , and entropy of adsorption, , calculated using V_N of polar solutes are negative. The values are used to evaluate Lewis acidity constant, K_a, and Lewis basicity constant, K_b, for the CAB surface. The K_a and K_b values are found to be 0.126 and 1.109, respectively, which suggest that the surface is predominantly basic. The K_a and K_b results indicate for the necessary surface modifications of CAB which act as biodegradable adsorbent material. Copyright © 2010 John Wiley & Sons, Ltd.     

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

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.     

Synthesis of colloidal uranium-dioxide nanocrystals

In this paper, we have developed an organic-phase synthesis method for producing size-controlled, nearly monodispersed, colloidal uranium-dioxide nanocrystals. These UO2 nanocrystals are potentially important to applications such as nuclear fuel materials, catalysts, and thermopower materials. In addition, we have systematically mapped out the functions of the solvents (oleic acid, oleylamine, and 1-octadecene) in the synthesis, and we found that N-(cis-9-octadecenyl)oleamide-a product of the condensation of oleic acid and oleylamine-can substantially affect the formation of UO2 nanocrystals. Importantly, these results provide fundamental insight into the mechanisms of UO2 nanocrystal synthesis. Moreover, because a mixture of oleic acid and oleylamine has been widely used in synthesizing a variety of high-quality metal or metal-oxide nanocrystals, the results herein should also be important for understanding the detailed mechanisms of these syntheses.     

Luminescence in colloidal Mn-doped semiconductor nanocrystals

Recent advances in nanocrystal doping chemistries have substantially broadened the variety of photophysical properties that can be observed in colloidal Mn²⁺-doped semiconductor nanocrystals. A brief overview is provided, focusing on Mn²⁺-doped II–VI semiconductor nanocrystals prepared by direct chemical synthesis and capped with coordinating surface ligands. These Mn²⁺-doped semiconductor nanocrystals are organized into three major groups according to the location of various Mn²⁺-related excited states relative to the energy gap of the host semiconductor nanocrystals. The positioning of these excited states gives rise to three distinct relaxation scenarios following photoexcitation. A brief outlook on future research directions is provided.     

Side reactions in controlling the quality, yield, and stability of high quality colloidal nanocrystals

Effects of side reactions during the formation of high quality colloidal nanocrystals were studied using ZnO as a model system. In this case, an irreversible side reaction, formation of esters, was identified to accompany formation of ZnO nanocrystals through the chemical reaction between zinc stearate and an excess amount of alcohols in hydrocarbon solvents at elevated temperatures. This irreversible side reaction made the resulting nanocrystals stable and with nearly unity yield regardless of their size, shape, and size/shape distribution. Ostwald ripening and intraparticle ripening were stopped due to the extremely low solubility/stability of the possible monomers because all free ligands in the solution were consumed by the side reaction. However, focusing on size distribution and 1D growth that are needed for the growth of high quality nanocrystals could still occur for high yield reactions. Upon the addition of a small amount of stearic acid or phosphonic acid, immediate partial dissolution of ZnO nanocrystals took place. Although the excess alcohol could not react with the resulting zinc phosphonic acid salt, it could force the newly formed zinc stearate gradually but completely back onto the existing nanocrystals. The results in this report indicate that side reactions are extremely important for the formation of high quality nanocrystals by affecting their quality, yield, and stability under growth conditions. Due to their lack of information in the literature and obvious practical advantages, studies of side reactions accompanying formation of nanocrystals are important for both fundamental science related to crystallization and industrial production of high quality nanocrystals.     

Microwave-assisted synthesis of colloidal inorganic nanocrystals

Colloidal inorganic nanocrystals stand out as an important class of advanced nanomaterials owing to the flexibility with which their physical-chemical properties can be controlled through size, shape, and compositional engineering in the synthesis stage and the versatility with which they can be implemented into technological applications in fields as diverse as optoelectronics, energy conversion/production, catalysis, and biomedicine. The use of microwave irradiation as a non-classical energy source has become increasingly popular in the preparation of nanocrystals (which generally involves complex and time-consuming processing of molecular precursors in the presence of solvents, ligands and/or surfactants at elevated temperatures). Similar to its now widespread use in organic chemistry, the efficiency of "microwave flash heating" in dramatically reducing overall processing times is one of the main advantages associated with this technique. This Review illustrates microwave-assisted methods that have been developed to synthesize colloidal inorganic nanocrystals and critically evaluates the specific roles that microwave irradiation may play in the formation of these nanomaterials.     

Thermal stability of surface-esterified cellulose and its composite with polyolefinic matrix

Thermal stability of hydrophobized cellulose powders was investigated from the perspective of potential use as filler in non-polar polyolefinic matrix. The hydrophobization was done by heterogeneous esterification with three carboxylic acids which differ in chain length (3, 10 and 18 carbons). Data measured by means of thermogravimetry (TG) were recalculated according to model-free isoconversional method to construct time–temperature plots. It was demonstrated that the esterification significantly decreases thermal stability of the material, which reduces feasible processing window. Under non-oxidative atmosphere, the single-step decomposition of materials is prevailing, while the process is more complex in air. In both cases the oleic acid esters showed the lowest stability and the original cellulose was the most stable. Finally, all powders were compounded with polyethylene or polypropylene. Obtained composites were then subjected to color measurement and TG. Even though the materials were partly degraded, which was indicated by the yellowish hue of the composites, virtually no impact of the filler pyrolysis on the polymer matrix decomposition was observed, particularly in case of decanoyl esters.     

Surface chemistry of colloidal PbSe nanocrystals

Solution nuclear magnetic resonance spectroscopy (NMR) is used to identify and quantify the organic capping of colloidal PbSe nanocrystals (Q-PbSe). We find that the capping consists primarily of tightly bound oleic acid ligands. Only a minor part of the ligand shell (0-5% with respect to the number of oleic acid ligands) is composed of tri- n-octylphosphine. As a result, tuning of the Q-PbSe size during synthesis is achieved by varying the oleic acid concentration. By combining the NMR results with inductively coupled plasma mass spectrometry, a complete Q-PbSe structural model of semiconductor core and organic ligands is constructed. The nanocrystals are nonstoichiometric, with a surface that is composed of lead atoms. The absence of surface selenium atoms is in accordance with an oleic acid ligand shell. NMR results on a Q-PbSe suspension, stored under ambient conditions, suggest that oxidation leads to the loss of oleic acid ligands and surface Pb atoms, forming dissolved lead oleate.     

Role of membrane surface morphology in colloidal fouling of cellulose acetate and composite aromatic polyamide reverse osmosis membranes

Laboratory-scale colloidal fouling tests, comparing the fouling behavior of cellulose acetate and aromatic polyamide thin-film composite reverse osmosis (RO) membranes, are reported. Fouling of both membranes was studied at identical initial permeation rates so that the effect of the transverse hydrodynamic force (permeation drag) on the fouling of both membranes is comparable. Results showed a significantly higher fouling rate for the thin-film composite membranes compared to that for the cellulose acetate membranes. Addition of an anionic surfactant (sodium dodecyl sulfate, SDS) to mask variations in chemical and electrokinetic surface characteristics of the cellulose acetate and aromatic polyamide membranes resulted in only a small change in the fouling behavior. The higher fouling rate for the thin-film composite membranes is attributed to surface roughness which is inherent in interfacially polymerized aromatic polyamide composite membranes. AFM and SEM images of the two membrane surfaces strongly support this conclusion. These surface images reveal that the thin-film composite membrane exhibits large-scale surface roughness of ridge-and-valley structure, while the cellulose acetate membrane surface is relatively smooth.     

FTIR imaging coupled with multivariate analysis for study of initial diffusion of different solvents in cellulose acetate butyrate films

Fourier transform infrared (FTIR) spectroscopic imaging was used to study the initial diffusion of different solvents in cellulose acetate butyrate (CAB) films containing different amounts of acetyl and butyryl substituents. Different solvents and solvent/non-solvent mixtures were also studied. The FTIR imaging system allowed acquisition of sequential images of the CAB films as solvent penetration proceeded without disturbing the system. The interface between the non-swollen polymer and the initial swelling front could be identified using multivariate data analysis tools. For a series of ketone solvents the initial diffusion coefficients and diffusion rates could be quantified and were found to be related to the polar and hydrogen interaction parameters in the Hansen solubility parameters of the solvents. For the solvent/non-solvent system the initial diffusion rate decreased less than linearly with the weight-percent of non-solvent present in the solution, which probably was due to the swelling characteristic of the non-solvent. For a given solvent, increasing the butyryl content of the CAB increased the initial diffusion rate. Increasing the butyryl content from 17 wt.% butyryl to 37 wt.% butyryl produced a considerably larger increase in initial diffusion rate compared to an increase in butyryl content from 37 wt.% to 50 wt.% butyryl.