Stability and efficiency improvement of ASA in internal sizing of cellulosic paper by using cationically modified cellulose nanocrystals

Alkenyl succinic anhydride (ASA) is a reactive sizing agent that can impart good water repellence to paper by decreasing the wettability of the cellulose fibers. However, ASA can undergo hydrolysis, which is detrimental to the ASA sizing efficiency. In order to improve the ASA emulsion stability and ASA sizing efficiency, we used cationically modified cellulose nanocrystals (CNCs) to stabilize the cationic starch-emulsified ASA. Transmission electron microscope observation revealed that ASA droplets were well shielded by both the cationic CNCs and cationic starch, which may be responsible for the improved stabilization of ASA. The Hercules size test sizing degree, contact angle and particle size measurements demonstrated that cationic CNCs–ASA sized paper exhibited improved results in comparison with the control (without cationic CNCs under otherwise the same conditions). Furthermore, the resulting cationic CNCs–ASA system can improve the tensile index and burst index of the sized paper.     

A study on the interaction of cationized chitosan with cellulose surfaces

This investigation describes the interaction of trimethyl chitosans (TMCs) with surfaces of cellulose thin films. The irreversible deposition/adsorption of TMCs with different degrees of cationization was studied with regards to the salt concentration and pH. As substrates, cellulose thin films were prepared by spin coating from trimethylsilyl cellulose and subsequent regeneration to pure cellulose. The pH-dependent zeta potential of cellulose thin films and the charge of TMCs were determined by streaming potential and potentiometric charge titration methods. A quartz crystal microbalance with dissipation monitoring was further used as a nanogram sensitive balance to detect the amount of deposited TMCs and the swelling of the bound layers. The morphology of the coatings was additionally characterized by atomic force microscopy and related to the adsorption results. A lower degree of cationization leads to higher amounts of deposited TMCs at all salt concentrations. Higher amounts of salt increase the deposition of TMCs. Protonation of primary amino groups results in the immobilization of less material at lower pH values. The results from this work can further be extended to the modification of regenerated cellulosic materials to obtain surfaces, with amino- and trimethylammonium moieties.     

Charge remote fragmentation of fatty acids cationized with alkaline earth metal ions

Fatty acids can be collisionally activated as [M ? H + Cat]⁺, where Cat is an alkaline earth metal, by using tandem mass spectrometry. High-energy collisional activation induces charge remote fragmentation to give structural information. In the full scan mass spectra molecular ions are easily identified, particularly when barium is used as a cationizing agent; ions are shifted to a higher mass, lower chemical noise region of the mass spectrum. Moreover, the isotopic pattern of barium is characteristic, and the high mass defect of barium allows an easy separation of the cationized analyte from any remaining interfering ions (chemical noise), provided medium mass-resolving power is available. An additional advantage is that most of the ion current is localized in [M ? H + Cat]⁺ species. Structural analysis of fatty acids can be performed when the sample size is as low as 1 ng.     

Effect of fiber modification with carboxymethyl cellulose on the efficiency of a microparticle flocculation system

Carboxymethyl cellulose (CMC) has been used widely to enhance dry strength of paper and uniformity of sheet in the papermaking industry. Besides these positive effects, it may affect the fines retention and dewatering processes negatively. These negative effects are mainly seen when fiber modifications with high CMC dosages are studied in laboratory scale. In this paper, the effect of fiber modification with CMC on the deposition of precipitated calcium carbonate (PCC) and on the dewatering process in the presence of cationic polyacrylamide (CPAM)/bentonite microparticle flocculation system is examined. It was determined that fiber modification with 10 mg g⁻¹ of CMC decreased PCC deposition at the initial addition of CPAM and gave better PCC deposition at 2 mg g⁻¹ of CPAM. It was also observed that PCC deposition on unmodified fibers is higher at lower CPAM concentration. PCC deposition was found as almost stable after a maximum value obtained at 0.5 mg g⁻¹ of bentonite concentration for fiber modified with 40 mg g⁻¹ of CMC. This indicates that interaction between CPAM and bentonite particles changed due to higher surface charge and CMC conformation on fibers. Results of the dewatering experiments showed that CMC modification increased the drainage time due to a denser and more plugged sheet. This negative effect was compensated with higher concentrations of CPAM and bentonite. On the other hand, dewatering is also affected by the mass ratio of CMC and CPAM, which was not the optimum one in this study at lower of CPAM. Thus, the increase in the drainage time in the presence of CMC on the fiber surface could be also caused by incorrect ratios of chemicals because the effect of CMC on the drainage time was not observed at higher concentrations of CPAM.     

One-pot functionalization of cellulose nanocrystals with various cationic groups

After successful cationization of cellulose nanocrystals (CNCs) to produce pyridinium-grafted-CNCs, a variety of different cationic CNCs were prepared using a similar procedure, thus unlocking access to a wide variety of cationized cellulose nanocrystals through a simple one-pot reaction. In this study, cationic CNCs were prepared through the use of 4-(1-bromoethyl)benzoic acid or 4-bromomethylbenzoic acid, p-toluenesulfonyl chloride, CNCs, and two different amines, 1-methylimidazole and 4-dimethylaminopyridine. The amines acted as both the base catalyst for the esterification and the nucleophile to form the cationic charge. This method offers a versatile and straightforward route to prepare a variety of different cationic nanocrystals and therefore tailor their interaction with their environment.     

Charge separation in heterostructures of InP nanocrystals with metal particles

The optical and electron paramagnetic resonance (EPR) properties of InP nanocrystals, in which metallic gold or indium is present as an incorporated part of the nanocrystals, have been studied. A study of Au/InP quantum rods supports different carrier localization regimes compared to metal-free quantum rods, including the charge-separated state for which the electron and hole are located in different parts of the heterostructure. They also show that elongated semiconductors that grow on metallic catalysts have electronic properties that are different from those of pure semiconductor nanocrystals of the same shape. We have also developed a simple method for growing melted indium particles on the surface of colloidal spherical InP nanocrystals, and in these In/InP nanocrystals the emission is completely quenched while the absorption spectrum moves to red due to the strong mixing of the semiconductor and metal electronic states.     

Thermally-activated shape memory behaviour of bionanocomposites reinforced with cellulose nanocrystals

Bionanocomposites with thermally-activated shape memory ability have been designed based on a synthesized poly(ester-urethane) matrix reinforced with both neat and functionalized cellulose nanocrystals. The functionalization of the cellulose nanocrystals was performed by grafting poly(l-lactic acid) (PLLA) chains onto their surface. The matrix has a block copolymer structure of two biodegradable and biocompatible polymers, poly(ε-caprolactone) (PCL) and PLLA. This research is focused on the effects of cellulose nanofillers on the thermally-activated shape memory response of the neat matrix confirming that the bionanocomposites are able to show shape memory effects at 35 °C, close to the human body temperature, making these materials good candidates for biomedical applications. Three thermo-mechanical cycles at 50 % of deformation were performed in order to check the thermally-activated shape memory ability of the bionanocomposites and to determine the shape memory parameters, namely the strain fixity (R_f), and the strain recovery (R_r) ratio. Both bionanocomposites, with neat and functionalized cellulose nanocrystals, present excellent shape memory behaviour maintaining the recovery behaviour at values of about 90 % as measured previously for the pure matrix, indicating that the addition of the nanofiller maintains the good ability to recover the initial shape of the matrix. The cellulose nanofillers clearly improve the ability of the polymer to fix the temporary shape. In fact, the bionanocomposites show R_f at about 90 %. Moreover, bionanocomposites reinforced with the functionalized cellulose nanocrystals maintain constant their performance during all the thermo-mechanical cycles thus confirming that the improvement in the shape memory behaviour can be mainly attributed to the increase of the interactions between the functionalized cellulose nanocrystals with the polymeric matrix.     

Photooxidative degradation of cellulose: Reactions of the cellulosic free radicals with oxygen

Photooxidative degradation of cellulose resulted in decreases of degree of polymerization (DP) and α-cellulose content, concurrently producing chromophoric groups; namely, carbonyl, carboxyl, and hydroperoxide groups within the polymer. Electron spin resonance (ESR) studies revealed that cellulosic carbon free radicals readily reacted with oxygen molecules at 143–160 K to produce peroxy radicals, whereas cellulosic oxygen free radicals were inert toward oxygen molecules throughout the photooxygenation reactions. At 77 K it is feasible that only photoexcited oxygen molecules reacted with cellulosic carbon free radicals to produce peroxide radicals. These radicals were themselves stabilized at 273 K by abstraction of hydrogen atoms from cellulose to produce polymer hydroperoxides. Simultaneously, new radical sites, which exhibited three-line ESR spectra, were generated in cellulose.     

Effect of fiber drying on properties of lignin containing cellulose nanocrystals and nanofibrils produced through maleic acid hydrolysis

The effect of fiber drying on the properties of lignin containing cellulose nanocrystals (LCNC) and nanofibrils (LCNF) produced using concentrated maleic acid hydrolysis of a never dried unbleached mixed hardwood kraft pulp was evaluated. Two drying conditions, i.e., air drying and heat drying at 105 °C were employed. It was found that drying (both air and heat) enhanced acid hydrolysis to result in slightly improved LCNC yields and less entangled LCNF. This is perhaps due to the fact that drying modified the cellulose supermolecular structure to become more susceptible to acid hydrolysis and the enhanced hydrolysis severity at the fiber surface when using dried fibers. Drying substantially improved LCNC crystallinity and LCNF suspension viscoelastic behavior. The present study quantitatively elucidated the effect of pulp drying (either air or heat) on producing cellulose nanomaterials and has practical importance because commercial market pulp (heat dried) is most likely to be used commercially.     

Isolation of a novel,crystalline cellulose material from the spent liquor of cellulose nanocrystals (CNCs)

We have modified the standard sulphuric acid hydrolysis method for the production of cellulose nanocrystals (CNCs) to successfully isolate a novel, highly crystalline cellulose material from the spent liquor of CNCs. The novel material has a cellulose II crystal structure that is distinctly different from the cellulose I crystal structure of CNCs. The modified method uses a shorter time for the hydrolysis, followed by maintaining a high residual acid concentration for the separation of the spent liquor and CNCs, and by adding the spent liquor to water. The modified method offers an opportunity to concurrently produce CNCs in up to ~40 % yield and the novel, highly crystalline, sulphated cellulose II in ~15 % yield in separate and pure forms from sulphuric acid hydrolysis of a commercial northern bleached softwood kraft pulp. It can potentially reduce the production cost of CNCs, allow easier downstream processing of CNCs and recovery of sulphuric acid, and generate a new cellulose bio-material for product development.     

Effective diffusivities of BSA in cellulosic fiber beds measured with magnetic resonance imaging

The temporal and spatial evolution of concentration profiles of bovine serum albumin (BSA) in various cellulosic fiber beds is measured using magnetic resonance imaging. Effective diffusivities are calculated using a numerical one dimensional Fickian model to match experimental concentration profiles. Experimental values of the diffusivities are compared with predictions from a simple diffusion-adsorption model which accounts for porosity, tortuosity, and surface adsorption. BSA was found to have negligible adsorption in the concentration range studied, resulting in a simplified diffusion model based on fiber characteristics and geometry. Effective diffusivities agreed well with the predicted values and were within an order of magnitude of the estimated bulk diffusivity of BSA.     

Carboxymethyl cellulose on a fiber substrate: the interactions with cationic polyelectrolytes

High and low molecular weight (M_w) carboxymethyl celluloses (CMC) were adsorbed on a well-characterized fiber substrate (long fibers of a commercial bleached birch kraft pulp with the carboxylic acid groups in Na-form) to increase the charge of the fibers in a controlled fashion. The M_w played a role in the utilization of CMCs as a strength additive in paper sheets nearly doubling the tensile strength with the high M_w CMC. Swelling properties of the CMC treated fibers were measured with water retention value (WRV). The WRV increased more with the high M_w CMC. The swelling was further tuned by two highly cationic polyelectrolytes; high M_w poly(diallyldimethyl ammonium chloride) (PDADMAC) and low M_w polybrene (hexadimethrine bromide, [3,6]-ionene). They were chosen because of their known ability to neutralize the anionic charge either exclusively on the surface or in the whole fiber, respectively. Adsorption of PDADMAC could reduce WRV of the CMC pre-treated fibers to the level of the untreated reference, while polybrene adsorbed pulps with 3–10 times more cationic polyelectrolyte deswelled the fibers only slightly more than the surface neutralized fibers. These results indicated surface conformation differences with low and high M_w CMCs. While the conformation did play a role after physical alteration (drying and rewetting) of the fibers, the paper sheets produced from these fibers showed remarkable differences. In extreme cases, the strength of the paper could be retained after drying (low M_w CMC + PDADMAC) or paper, resistant to disintegration, could be achieved (CMC + polybrene).     

Resonant electron transfer and luminescent enhancement in a toluene suspension of Si nanocrystals

Efficient resonant electron transfer from the surface bonding structure to the conduction band of quantum confined Si nanocrystals is observed by Si nanocrystals in a toluene suspension. Based on the electron transfer mechanism, the enhancement of photoluminescence originates from the band-to-band recombination in the p-type Si nanocrystals suspended in a toluene solution. The energy levels of the electrons in the Si nanocrystals chemisorbed with toluene molecules are calculated using the method of linear combination of atomic orbitals, and the characteristics of the obtained density of states is in good agreement with the observed photoluminescence properties.     

Magnetic alignment of the chiral nematic phase of a cellulose microfibril suspension

Stable suspensions of tunicate cellulose microfibrils were prepared by acid hydrolysis of the cellulosic mantles of tunicin. They formed a chiral nematic phase above a critical concentration. External magnetic fields were applied to the chiral nematic phase in two different manners to control its phase structure. (i) Static magnetic fields ranging 1-28 T were used to align the chiral nematic axis (helical axis) in the field direction. (ii) A rotating magnetic field (5 T, 10 rpm) was applied to unwind the helices and to form a nematic phase. These phenomena were interpreted in terms of the anisotropic diamagnetic susceptibility of the cellulose microfibril. The diamagnetic susceptibility of the microfibril is smaller in the direction parallel (chi( parallel)) to the fiber axis than in the direction perpendicular (chi( perpendicular)) to the fiber axis, that is, chi( parallel) < chi( perpendicular) < 0. Because the helical axis coincides with the direction normal ( perpendicular) to the fiber axis, the helical axis aligned parallel to the applied field. On the other hand, the rotating magnetic field induced the uniaxial alignment of the smallest susceptibility axis, that is, chi( parallel) in the present case, and brought about unwinding of the helices.     

Acryloyl-modified cellulose nanocrystals: effects of substitution on crystallinity and copolymerization with acrylic monomers

Cellulose nanocrystals (CNCs) are crystalline nano-rods that have high specific strength with hydroxyl surface chemistry. A wide range of chemical modifications have been performed on the surface of CNCs to increase their potential to be used in applications where compatibilization with other materials is required. Understanding the surface chemistry of CNCs and critically examining the functionalization technique are crucial to enable control over the extent of modification and the properties of CNCs. This work aims to optimize the surface modification of wood-derived CNCs with isocyanatoethyl methacrylate (IEM), a bifunctional molecule carrying both isocyanate and vinyl functional groups. We studied the effect of modification reaction time and temperature on the degree of substitution, crystallinity, and morphology of the CNCs. We found that the degree of modification is a strong and increasing function of reaction temperature over the range studied. However, the highest temperature (65 °C) and the longest time of reaction (6 h) resulted in shorter, thinner, and less crystalline CNCs. We obtained surface hydroxyl conversion of 60.1?±?6% and percent crystallinity of 84% by keeping the reaction shorter (30 min) at 65 ºC. Also, the copolymerization ability of modified CNCs was verified by polymerizing attached IEM groups with acrylic monomers via solution polymerization. The polymer-grafted CNCs (6% w/w) dispersed better in an acrylic polymer matrix compared to unmodified CNCs (umCNCs), resulting in approximately 100% improvement in the tensile strength and about 53% enhancement in the hardness of the acrylic, whereas addition of 6% w/w umCNCs did not influence the strength and hardness.

Graphic abstract