Juho Antti Sirviö

Enhancement of the Nanofibrillation of Wood Cellulose through Sequential Periodate–Chlorite Oxidation

Sequential regioselective periodate-chlorite oxidation was employed as a new and efficient pretreatment to enhance the nanofibrillation of hardwood cellulose pulp through homogenization. The oxidized celluloses with carboxyl contents ranging from 0.38 to 1.75 mmol/g could nanofibrillate to highly viscous and transparent gels with yields of 100-85% without clogging the homogenizer (one to four passes). On the basis of field-emission scanning electron microscopy images, the nanofibrils obtained were of typical widths of approximately 25 ± 6 nm. All of the nanofibrillar samples maintained their cellulose I crystalline structure according to wide-angle X-ray diffraction results, and the crystallinity index was approximately 40% for all samples.

Biocomposite cellulose-alginate films: Promising packaging materials

Biocomposite films based on cellulose and alginate were produced using unmodified birch pulp, microfibrillated cellulose (MFC), nanofibrillated cellulose (NFC) and birch pulp derivate, nanofibrillated anionic dicarboxylic acid cellulose (DCC), having widths of fibres ranging from 19.0 μm to 25 nm as cellulose fibre materials. Ionically cross-linked biocomposites were produced using Ca(2+) cross-linking. Addition of micro- and nanocelluloses as a reinforcement increased the mechanical properties of the alginate films remarkably, e.g. addition of 15% of NFC increased a tensile strength of the film from 70.02 to 97.97 MPa. After ionic cross-linking, the tensile strength of the film containing 10% of DCC was increased from 69.63 to 125.31 MPa. The biocomposite films showed excellent grease barrier properties and reduced water vapour permeability (WVP) after the addition of cellulose fibres, except when unmodified birch pulp was used.

Amphiphilic cellulose nanocrystals from acid-free oxidative treatment: physicochemical characteristics and use as an oil-water stabilizer.

A chemical pretreatment for producing cellulose nanocrystals (CNCs) with periodate oxidation and reductive amination is reported. This new functionalization of cellulose fibers dispenses an alternative method for fabricating individual CNCs without the widely used acid hydrolysis process. CNCs can be directly modified during the pretreatment step, and no additional post-treatments are required to tune the surface properties. Three butylamine isomers were tested to fabricate CNCs with amphiphilic features. After mechanical homogenization, CNCs occurred as individual crystallinities without aggregation where high uniformity in terms of shape and size was obtained. The elemental analysis and (1)H NMR measurement show that iso- and n-butylamine attach the highest number of butylamino groups to the cellulose fibers. Linking the alkyl groups increases the hydrophobic nature of the CNCs, where water contact angles from self-standing films up to 110.5° are reported. Since these butylamino-functionalized CNCs have hydrophobic characteristics in addition to the hydrophilic backbone of cellulose, the stabilization impact on oil/water emulsions is demonstrated as a potential application.

High-strength nanocellulose-talc hybrid barrier films.

Hybrid organic-inorganic films mimicking natural nacre-like composite structures were fabricated from cellulose nanofibers obtained from sequential periodate-chlorite oxidation treatment and talc platelets, using a simple vacuum-filtration method. As a pretreatment, commercial talc aggregates were individualized into well-dispersed talc platelets using a wet stirred media mill with high-shear conditions to promote the homogeneity and mechanical characteristics of hybrids. The nanofiber-talc hybrids, which had talc contents from 1 to 50 wt %, were all flexible in bending, and possessed tensile strength and Youngs modulus values up to 211 ± 3 MPa and 12 ± 1 GPa, respectively, the values being remarkably higher than those reported previously for nanofibrillated cellulose-talc films. Because of the lamellar and well-organized structure of hybrids in which the talc platelets were evenly embedded, they possessed a small pore size and good oxygen barrier properties, as indicated by the preliminary results. The talc platelets decreased the moisture adsorption of highly talc-loaded hybrids, although they still exhibited hydrophilic surface characteristics in terms of contact angles.

Deep eutectic solvent system based on choline chloride-urea as a pre-treatment for nanofibrillation of wood cellulose†

Deep eutectic solvents (DESs) are promising novel chemicals that can function as solvents, reagents, and catalysts in many applications because they are readily available, have low toxicity, are biodegradable, and exhibit negligible vapor pressure. In this study, a DES of choline chloride-urea (molar ratio of 1:2) was used as a non-hydrolytic pre-treatment media to promote nanofibrillation of birch cellulose pulp using a microfluidizer. The DES pre-treatment was conducted at 100 °C, and then DES was removed by washing with water. Three degrees of mechanical treatment with the microfluidizer for DES pre-treated cellulose pulp were conducted and their effects on the fiber properties were studied. Cellulose fibers were observed to disintegrate into nanofibril bundles with widths ranging from 15 to 200 nm and to individual cellulose nanofibrils with widths of 2–5 nm. Wide-angle X-ray diffraction (WAXD) and degree of polymerization analysis using the limiting viscosity method revealed that both the cellulose crystalline structure and the degree of polymerization of the cellulose remained intact after pre-treatment with DES.

Strong, Self-Standing Oxygen Barrier Films from Nanocelluloses Modified with Regioselective Oxidative Treatments

In this work, three self-standing nanocellulose films were produced from birch pulp using regioselective oxidation and further derivatization treatments. The modified celluloses were synthesized using periodate oxidation, followed by chlorite oxidation, bisulfite addition, or reductive amination with amino acid taurine, which resulted in dicarboxylic acid cellulose (DCC), α-hydroxy sulfonic acid cellulose (HSAC), and taurine-modified cellulose (TC), respectively. The nanocelluloses were fabricated by mechanical disintegration using high-pressure homogenization. Mechanical and barrier properties of the nanocellulose films were characterized. Two (2,2,6,6-tetramethyl-piperidin-1-yl)oxyl (TEMPO) oxidation-based nanocellulose films were also produced, and their properties were compared to the periodate-based nanocellulose films. All of the periodate-based nanocellulose films showed high tensile strength (130-163 MPa) and modulus (19-22 GPa). Oxygen barrier properties of the films were superior to many synthetic and composite materials; in particular, the nanofibrillated DCC films had oxygen permeability as low as 0.12 cm(3) μm/(m(2) d kPa) at 50% relative humidity. Compared to films of TEMPO-oxidized nanocelluloses, all of the periodate-based nanocellulose films had similar or even better mechanical and barrier properties, demonstrating versatility of periodate oxidation to obtain nanocellulose films with adjustable properties. Also, for the first time, amino-acid-based cellulose modification was used in the production of nanocellulose.

Weighing the factors behind enzymatic hydrolyzability of pretreated lignocellulose

The major factors determining enzymatic hydrolyzability of pretreated wheat straw were analyzed and their relative importance quantified. The effects of NaOH-delignification, autohydrolysis and their combination at different severities were analyzed by determining the pore size distribution (DSC-thermoporometry), the cellulose surface area and the accessible phenolic hydroxyls on the lignin surface (adsorption of Congo Red and Azure B; ATR-FTIR) and crystallinity (WAXD). The correlation of these factors with initial and overall enzymatic hydrolyzability was studied and further arranged in order through principal component analysis. The major positive factors affecting hydrolyzability were the cellulose surface area and the accessibility of the pore system, while the lignin content was the major negative factor accompanied by cellulose crystallinity. Autohydrolysis effectively increased the cellulose surface area by hemicellulose dissolution, but the high lignin content associated with small pores led to a lower hydrolyzability compared to delignified straw. Besides the removal of lignin, delignification led to a more accessible pore structure, which was supported by the remaining hemicellulose. Additionally, delignification increased the hydrophilicity of the remaining lignin, which also increased hydrolyzability. All pretreatments decreased cellulose crystallinity, which particularly increased the initial hydrolysis, and also improved the final carbohydrate conversion. The established weighed order of the factors behind enzymatic carbohydrate conversion is an important milestone in the path towards more efficient lignocellulosic sugar utilization in biorefineries.

Use of nanoparticular and soluble anionic celluloses in coagulation-flocculation treatment of kaolin suspension

In this work, the effectiveness of a novel, combined coagulation-flocculation treatment based on alum and soluble or nanoparticular anionic derivatives of dialdehyde cellulose, ADAC, was evaluated by studying the removal of colloidal material in a model suspension containing kaolin. Four different ADACs with varying degrees of substitution, size and water solubility were synthesized by periodate oxidation and sulfonation of cellulose. The effects of ADAC dosage, solution pH and temperature on flocculation were studied by measuring residual turbidity of the settled suspension. Moreover, the charge densities, sizes, ζ-potentials and stability of the ADACs in aqueous solutions were studied. The combined treatment was effective in the removal of colloidal particles, as demonstrated by reduced residual turbidity with remarkably lower total chemical consumption compared with coagulation with alum alone. Of the ADACs, samples with lower solubility that contained cellulose nanoparticles performed better than the fully water-soluble sample. Due to the restricted pH tolerance of alum, the combined treatment was effective only at acidic conditions (pH < 5), although the ADACs were found to be stable in a much broader pH range (pH of 3 to about 9). ADACs also retained strong activity at higher temperatures (30-60 °C) and after several days of storage in aqueous solution.

Flocculation performance of a cationic biopolymer derived from a cellulosic source in mild aqueous solution.

The flocculation behavior of cationic, quaternary ammonium groups containing cellulosic biopolymers, CDACs, synthesized by cationizing dialdehyde cellulose in mild aqueous solution was studied in a kaolin suspension. In particular, the role of CDAC dosage and solution pH, NaCl concentration, and temperature were clarified. In addition, the initial apparent charge densities (CDs), particle sizes, ζ-potential, and stability of CDs were determined. CDACs possessed a high flocculation activity in neutral and acidic solutions, but a significant decrease was observed in alkaline solutions (pH >9). This was also seen as a decline in the apparent CD and particle size of the CDACs in alkaline conditions. The measurements also indicated that the apparent CD decreased to a constant level of 3 mmol/g in aqueous solutions. However, no notable decrease in flocculation performance was obtained after several days of storage. Moreover, the variation of NaCl concentration and temperature did not affect the flocculation activity.

Regeneration and Recycling of Aqueous Periodate Solution in Dialdehyde Cellulose Production

Abstract The regeneration of aqueous iodate solution from the regioselective periodate oxidation of softwood cellulose pulp to dialdehyde cellulose using hypochlorite as a secondary oxidant was studied. The influence of oxidation time on the pulp dissolution and regeneration efficacy was examined in particular. In addition, the recycling of regenerated periodate solution back to oxidation was clarified. The solutions from the 10 and 15 min oxidations were regenerated with 100% conversion efficacy when 1.2–1.4 times the stoichiometric amounts of hypochlorite were used. However, the regeneration efficacy decreased when the reaction time in the oxidation increased to 30 min because the content of soluble impurities, which consumed the hypochlorite in the side-reactions, increased significantly as the oxidation reaction proceeded. The regenerated solutions possessed good oxidation performance, showing that periodate was successfully regenerated using hypochlorite and supporting the assumption that periodate can be effectively recycled in the process when short oxidation times are used.