Influence of homogenization and drying on the thermal stability of microfibrillated cellulose

Homogenization has been used to release microfibrils from cellulose fibres to produce microfibrillated cellulose (MFC). Oven drying, atomization or freeze-drying were used to dry MFC. Morphological differences were observed linked to the compaction of the system and the formation of microfibril agglomerates. Thermal stability of the dried MFC, checked by TGA, decreased after homogenization and drying. Char level at the end of the pyrolysis was higher than for cellulose fibres. Derivative TGA (dTGA) showed a shoulder around 250 °C for the dried MFC. Volatile degradation product detection by FTIR spectroscopy (FTIR) coupled to TGA and DSC showed that the shoulder corresponds to expected dehydration reactions of the cellulose. Increasing the contacts between microfibril(s) (bundles) and agglomerates of the freeze-dried MFC by compression promoted dehydration reactions. Homogenization and drying modified the thermal properties of the MFC. No significant influence of freeze-drying kinetics on the thermal behaviour of the MFC was observed.     

Chemical surface modifications of microfibrillated cellulose

Microfibrillated cellulose (MFC) was prepared by disintegration of bleached softwood sulphite pulp through mechanical homogenization. The surface of the MFC was modified using different chemical treatments, using reactions both in aqueous- and organic solvents. The modified MFC was characterized with fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Epoxy functionality was introduced onto the MFC surface by oxidation with cerium (IV) followed by grafting of glycidyl methacrylate. The length of the polymer chains could be varied by regulating the amount of glycidyl methacrylate added. Positive charge was introduced to the MFC surface through grafting of hexamethylene diisocyanate, followed by reaction with the amines. Succinic and maleic acid groups could be introduced directly onto the MFC surface as a monolayer by a reaction between the corresponding anhydrides and the surface hydroxyl groups of the MFC.     

Different types of microfibrillated cellulose as filler materials in polysodium acrylate superabsorbents

Three types of microfibrillated cellulose(MFC)with differences in structure and surface charge were used at low concentration as filler materials in polysodium acrylate superabsorbents(SAPs).The swelling of the composite hydrogels was determined in 0.9%NaCl solution as well as in deionized water.The shear modulus of the samples was determined through uniaxial compression analysis after synthesis and after swelling in 0.9%NaCl solution.Furthermore,the ability to retain filler effects after washing was investigated.The results showed that all of the investigated MFCs had a strong reinforcing effect on the shear modulus after synthesis.The filler effect on swelling and on the associated shear modulus of swollen samples showed a more complicated dependence on structure and surface charge.Finally,it was found that the filler effects were reasonably retained after washing and subsequent drying.The results confirm that MFC holds great potential as a filler material in superabsorbent applications.Furthermore,the results provide some insight on how the structural properties and surface charge of MFC will affect gel properties depending on swelling conditions.This information should be useful in evaluating the use of different types of MFC in future applications.     

Gas-phase esterification of microfibrillated cellulose (MFC) films

The barrier properties of microfibrillated cellulose (MFC) films were improved by heterogeneous gas-phase esterification using various combinations of trifluoroacetic acid anhydride, acetic acid and acetic anhydride. The temperature, reagent ratio and reaction time were varied in the experimental design. The effects of two different purification procedures on the barrier properties of esterified MFC films were investigated. Washing with water did not affect the barrier properties compared to those of the films that were not washed, while the use of diethyl ether led to improved barrier properties as measured by the contact angle (CA) of water. The chemical composition of the modified films was studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Alterations in hydrophobicity and oxygen permeability were evaluated using dynamic CA and oxygen transmission rate measurements, respectively.     

Properties and characterization of hydrophobized microfibrillated cellulose

Microfibrillated cellulose (MFC) obtained by disintegration of bleached softwood sulphite pulp in a homogenizer, was hydrophobically modified by surface silylation with chlorodimethyl isopropylsilane (CDMIPS). The silylated MFC was characterized by Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), transmission electron spectroscopy (TEM), X-ray photoelectron spectroscopy (XPS) and white light interferometry (WLI). The degree of surface substitution (DSS) was determined using Si concentrations from XPS survey scans, as well as deconvoluted peaks in high-resolution C1s XPS spectra. The DSS values obtained by the two methods were found to be in good agreement. MFC with DSS between 0.6 and 1 could be dispersed in a non-flocculating manner into non-polar solvents, TEM observations showing that the material had kept its initial morphological integrity. However, when CDMIPS in excess of 5 mol CDMIPS/glucose unit in the MFC was used, partial solubilization of the MFC occurred, resulting in a drop in the observed DSS and a loss of the microfibrillar character of the material. The wetting properties of films cast from suspension of the silylated MFC were also investigated. The contact angles of water on the films increased with increasing DSS of the MFC, approaching the contact angles observed on super hydrophobic surfaces for the MFC with the highest degree of substitution. This is believed to originate from a combination of low surface energy and surface microstructure in the films.     

Toughness enhancement of cellulose nanocomposites by alkali treatment of the reinforcing cellulose nanofibers

Nanocomposites were produced with NaOH aqueous solution-treated microfibrillated cellulose (MFC) and phenolic resin, and the mechanical properties were compared with their microcomposite counterparts based on pulp fiber. Tensile tests showed that strong alkali-treated MFC nanocomposites with resin content around 20 wt.% achieved strain at fracture values two times higher than those of untreated MFC nanocomposites and five times higher than those of untreated pulp microcomposites. The improvement in work of fracture of alkali-treated MFC nanocomposites was attributed to the ductility of the nanofibers caused by transformations in the amorphous regions along the cellulose microfibrils.     

The effect of fiber content on the mechanical and thermal expansion properties of biocomposites based on microfibrillated cellulose

A new method to obtain composites of phenolic resin reinforced with microfibrillated cellulose with a wide fiber content was established and the mechanical properties were evaluated by tensile test. A linear increase in Young’s modulus was observed at fiber contents up to 40 wt%, with a stabilizing tendency for higher fiber percentages. These results were ratified by measurements of the coefficient of thermal expansion (CTE) relative to fiber content, which indicated a strong thermal expansion restriction rate below 60 wt% fiber content, indicating the effective reinforcement attained by the cellulose microfibrils. The low CTE achieved of 10 ppm/K is one of the important properties of cellulose composites.     

Effect of tethered and free microfibrillated cellulose (MFC) on the properties of paper composites

High strength and low gas permeability cellulosic composites were produced using the papermaking technology with a commercial microfibrillated cellulose (MFC). The effect of blending MFC with hardwood fibers was compared to the direct refining of the fibers with and without polyamideamine-epichlorohydrin (PAE) addition. The addition of MFC, free or tethered, to pulp fibers combined with PAE can increase the dry strength and wet strength of cellulosic materials by an order of magnitude. Air permeability of the composites decreases by up to orders four of magnitude with MFC addition. The hypothesis that refining wood fibers can produce tethered MFC which provides equivalent strength properties but significant drainage benefits was proven. Furthermore, major benefits in paper formation uniformity (fiber distribution homogeneity) were achieved with refined fibers.     

An environmentally friendly electrochemical method for synthesis of benzofuranoquinone derivatives

Electrochemical oxidation of catechols (1a-c) has been studied in the presence of 2-hydroxy-1,4-naphtoquinone (3b) in aqueous solutions, using cyclic voltammetry and controlled-potential coulometry. The results indicated that the electrochemically generated o-benzoquinones (2a-c) participate in Michael addition reaction with 3b to the corresponding benzofuranoquinones (8a-c, 10a-c). The electrochemical synthesis of these compounds has been successfully preformed at a carbon rod electrode with good yields using an environmentally friendly method.     

Titrimetric methods for the determination of surface and total charge of functionalized nanofibrillated/microfibrillated cellulose (NFC/MFC)

Total and surface charge of three different carboxymethylated nanofibrillated/microfibrillated cellulose (NFC/MFC) samples were investigated by using titrimetric methods (conductometric and polyelectrolyte (PE) titrations). Conductometric titration was found to be suitable method for the NFC total charge measurements when the back titration with HCl was applied. Surface charge measurements of NFC/MFC were conducted by using both indirect and direct PE titrations. The direct PE titration was found to be a more suitable method for the surface charge determination of NFC/MFC whereas the indirect PE titration produced too high surface charge values. This is presumably due to kinetically locked polyelectrolyte conformations on the NFC/MFC surfaces or entrapment of residual polymer after adsorption onto the NFC/MFC gel network. Finally, NFC was propargyl-functionalized and the changes in surface and total charge were successfully monitored and compared to those of propargyl-functionalized pulp. A good correlation between the titrimetric methods and elemental analysis was observed.     

Development and validation of a capillary electrophoresis method for the characterization of sulfoethyl cellulose

To characterize sulfoethyl cellulose el samples, a capillary electrophoresis method was developed and validated sulfoethyl cellulose el was hydrolyzed, and the resulting d ‐glucose derivatives were analyzed after reductive amination with 4‐aminobenzoic acid using 150 mM boric acid, pH 9.5, as background electrolyte at 20°C and a voltage of 28 kV. Peak identification was derived from capillary electrophoresis with mass spectrometry using 25 mM ammonia adjusted to pH 6.2 by acetic acid as electrolyte. Besides mono‐, di‐, and trisulfoethyl d ‐glucose small amounts of disaccharides could be identified resulting from incomplete hydrolysis. The linearity of the borate buffer‐based capillary electrophoresis method was evaluated using d ‐glucose in the concentration range of 3.9–97.5 μg/mL, while limits of detection and quantification derived from the signal‐to‐noise ratio of 3 and 10 were 0.4 ± 0.1 and 1.2 ± 0.3 μg/mL, respectively. Reproducibility and intermediate precision were determined using a hydrolyzed sulfoethyl cellulose el sample and ranged between 0.2 and 8.8% for migration times and between 0.3 and 10.4% for peak area. The method was applied to the analysis of the degree of substitution of synthetic sulfoethyl cellulose el samples obtained by variation of the synthetic process and compared to data obtained by elemental analysis.     

An environmentally friendly multicommutated alternative to the reference method for anionic surfactant determination in water

It has been developed a fully mechanized procedure for the spectrophotometric determination of anionic surfactants in water expressed in terms of SDS concentration. The reference method, based on the reaction of SDS with methylene blue (MB) followed by extraction in chloroform, was mechanized in order to reduce the consumption of organic solvents. The system was based on the multicommutation approach and provided a 35 times reduction of the waste production without sacrificing the figures of merit of the method in terms of sensitivity and repeatability, for a dynamic linear range from 0.2 to 1.7 mg l⁻¹. Results obtained for washing water samples were comparable with those obtained using the reference method and no significant differences, at 95% confidence level, were observed. Other useful characteristics are a solvent consumption of 0.7 ml per determination, a sampling throughput of 40 determinations per hour, a relative standard deviation of 5.9% (n = 10) for a sample containing 2 × 10⁻⁶ mol l⁻¹ (576 μg l⁻¹) surfactant and a limit of detection of 6.1 × 10⁻⁹ mol l⁻¹ (1.7 μg l⁻¹).     

Localized hydrogels based on cellulose nanofibers and wood pulp for rapid removal of methylene blue

Access to clean water has become increasingly difficult, motivating the need for materials that can efficiently remove pollutants. Hydrogels have been explored for remediation, but they often require long times to reach high levels of adsorption. To overcome this limitation, we developed a rapid, locally formed hydrogel that adsorbs dye during gelation. These hydrogels are derived from cellulose—a renewable, nontoxic, and biodegradable resource. More specifically, we found that sulfated cellulose nanofibers or sulfated wood pulps, when mixed with a water-soluble, cationic cellulose derivative, efficiently remove methylene blue (a cationic dye) within seconds. The maximum adsorption capacity was found to be 340 ± 40 mg methylene blue/g cellulose. As such, these localized hydrogels (and structural analogues) may be useful for remediating other pollutants.     

Novel cellulose derivatives. II. synthesis and characteristics of mono-functional cellulose propionate segments

Mono-functional cellulose propionate segments for use in ter- or star-block polymers have been prepared by the depolymerization (step 1) of cellulose propionate in homogeneous phase using a mixture of HBr and propionic anhydride in methylene chloride solution. The anomeric mixture of glycosyl bromide has subsequently (step 2) been hydrolyzed in aqueous acetone. Functionality was determined by H-NMR spectroscopy of triethyl silane derivatives in combination with gel permeation chromatography. The cellulose ester segments were semi-rigid, highly crystalline materials with melting points between 180° and 250°C. The lowest useful segment size, based on crystallinity and Mark-Houwink-Sakurada exponential factor, appeared to be DP 20, with an optimum around DP 40 to 50.Part I has been published in theJ. Appl. Polym. Sci.,49, 1671 (1993).     

Chiral separation abilities of homogeneously synthesized cellulose 3,5-dimethylphenylcarbamates: Influences of degree of substitution and molecular weight

A series of cellulose 3,5-dimethylphenylcarbamates(CDMPCs) with different degrees of substitution(DS) and degrees of polymerization(DP) were homogeneously synthesized in 1-allyl-3-methylimidazolium chloride(Amim Cl). Then, the CDMPCs were coated on silica gel and used as chiral stationary phases(CSPs), and their chiral recognition abilities for seven racemates were evaluated by high performance liquid chromatography. The results showed that DS and DP of CDMPCs had a great influence on chiral recognition abilities of the CSPs. The CSPs with the DS ≈ 1 gives a low chiral recognition to most racemates. On the contrast, the CSPs with the DS ? 2 exhibited high chiral separation abilities. For example, six racemates could be separated on the CSP with CDMPC of DS ≈ 2(CSP-2). Especially, for the enantioseparation of 1-(2-naphthyl) ethanol and Tr?ger's base, CSP-2 gave the highest separation ability in all of CSPs. On the other hand, when the DP of cellulose was in a range from 39 to 220, the chiral separation abilities of CDMPCs increased as the DP increased. This work demonstrates that the structure of cellulose esters such as DS and DP has important effect on their chiral separation ability, and therefore provides a practical method to design and prepare desirable CSPs for different racemates.     

One-dimensional GdVO4:Ln (Ln=Eu, Dy, Sm) nanofibers: Electrospinning preparation and luminescence properties

One-dimensional GdVO₄:Ln³⁺ (Ln=Eu, Dy, Sm) nanofibers have been prepared by a combination method of sol-gel process and electrospinning technology. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL), quantum efficiency (QE), and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The XRD, FT-IR, and TG-DTA results show that GdVO₄:Ln³⁺ nanofibers samples crystallize at 700 °C. SEM images indicate that the as prepared precursor fibers are smooth. After being calcined at 700 °C for 4 h, the fibers still maintain their fiberlike morphology with rough surface. TEM image further manifests that the GdVO₄:Ln³⁺ nanofibers consist of nanoparticles. Under ultraviolet excitation and low-voltage electron beam excitation, GdVO₄:Ln³⁺ phosphors showed their strong characteristic emission due to an efficient energy transfer from vanadate groups to dopants. The optimum doping concentration of Ln³⁺ in the GdVO₄ nanofibers also has been investigated.     

An environmentally friendly method for the extraction and determination of priority phenols in soils using microwave-assisted micellar extraction

A non-ionic surfactant, polyoxyethylene 10 lauryl ether (POLE), was used for the microwave-assisted extraction (MAE) of priority phenolic compounds from soil samples. A central composite design was applied to optimize the extraction parameters, namely, time and power. Under the optimized conditions, the method was applied to different soil samples in order to analyze the influence of soil characteristics on the phenol extraction. Results demonstrated that most of these compounds can be recovered from the soils investigated in good yields (higher than 80%). The standard deviation is lower than 9% (n = 6) for most analytes. Validation of the method by analyzing a reference soil sample containing eight phenols and a comparison with Soxhlet extraction are also reported.     

Hydroxypropyl cellulose (HPC)-stabilized dispersion polymerization of styrene in polar solvents: Effect of reaction parameters

Dispersion polymerization of styrene in polar solvents in the presence of hydroxypropyl cellulose (HPC) produces latex particles from ca. 1 to 26 μm depending on reaction parameters. Increasing the initiator concentration or temperature decreases the molecular weight, but increases the particle size and breadth of the size distribution. The decrease in molecular weight with increasing R_i, caused by larger initiator concentration or higher temperature, is expected based of fundamental kinetic relationships. The inverse correlation between size and rate of initiation is rationalized by polarity (stabilizing ability) of the grafted HPC-polystyrene formed in situ. High polar HPC-g-PS, which contains shorter graft polystyrene chain, stabilizes particles less effectively and this leads to larger particles. The primary influence of initial styrene concentration is a solvent effect: larger particles are obtained at high styrene concentration due to high solubility of polystyrene during the initial part of the reaction. The influence of the molecular weight of HPC is to change the polarity of the HPC-g-PS stabilizer. Comparison of particle growth of three critical polymerization systems suggests that the favorable continuous-phase solubility parameter for dispersion polymerization of styrene is around 11.6 (cal/mL)^1/2. Too high or too low polarity generates particles with broad size distribution because large particles are formed during the initial stage and nucleation continues as the polymerization proceeds. © 1992 John Wiley & Sons, Inc.     

Preparation of amidoxime-modified polyacrylonitrile (PAN-oxime) nanofibers and their applications to metal ions adsorption

Polyacrylonitrile (PAN) nanofibers were applied to metal adsorption. PAN nanofibers (prepared by an electrospinning technique) were chemically modified with amidoxime groups, which are suitable for metal adsorption due to their high adsorption affinity for metal ions. The adsorption of the amidoxime-modified PAN (PAN-oxime) (25% conversion) nanofibers followed Langmuir isotherm. The saturation adsorption capacities for Cu(II) and Pb(II) of 52.70 and 263.45 mg/g (0.83 and 1.27 mmol/g), respectively, indicating that the monolayer adsorption occurred on the nanofiber mats. In addition, over 90% of metals were recovered from the metal-loaded PAN-oxime nanofibers in a 1 mol/L HNO₃ solution after 1 h.