Jouko Niinimäki

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.

Recognition of highly overlapping ellipse-like bubble images

This study describes a robust bubble image recognition algorithm that detects the in-focus, ellipse-like bubble images from experimental images with heavily overlapping bubbles. The principle of the overlapping object recognition (OOR) algorithm is that it calculates the overall perimeter of a segment, finds the points at the perimeter that represent the connecting points of overlapping objects, clusters the perimeter arcs that belong to the same object and fits ellipses on the clustered arcs of the perimeter. The accuracy of the algorithm is studied with simulated images of overlapping ellipses, providing an RMS error of 0.9 pixels in size measurement. The algorithm is utilized in measurements of bubble size distributions with a direct imaging (DI) technique in which a digital camera and a pulsed back light are used to detect bubble outlines. The measurement system is calibrated with stagnant bubbles in a gel in order to define the bubble size dependent effective thickness of the measurement volume and the grey scale gradient threshold as a focus criterion. The described concept with a novel bubble recognition algorithm enables DI measurements in denser bubbly flows with increased reliability and accuracy of the measurement results. The measurement technique is applied to the study of the turbulent bubbly flow in a papermaking machine, in the outlet pipe of a centrifugal pump.

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.

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.

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.

Tall oil/water – emulsions as water repellents for Scots pine sapwood

Abstract Like classic wood preservatives, many water repellents have the drawback of being detrimental to the environment. Hence interest in environment-friendly, even biodegradable, substances has increased. Natural oils (e.g. tall oil, linseed oil) appear to be capable of preventing water uptake by wood. However, in order to achieve total sapwood penetration, the amount of oil needed is high. The aim of this study was to investigate the water repellent efficiency of crude tall oil and crude tall oil water emulsions (oil-in-water and water-in-oil emulsions), and the possibilities of reducing the amount of oil needed with the emulsion technique. Scots pine sapwood samples were impregnated with tall oil formulations. The levels of water absorption and the degree of water repellent efficiency were determined with cyclical wetting and drying tests. The results showed that tall oil treatments reduce the water uptake of pine sapwood. With tall oil emulsion treatments almost equal water repellent efficiencies were reached as with pure tall oil, even when the oil retentions were considerably lower. The total amount of oil required could be halved. The emulsion technique is a potential method of decreasing the amount of oil needed in order to protect wood from water uptake. Zusammenfassung Wie viele klassische Holzschutzmittel haben auch viele Hydrophobierungsmittel den Nachteil, dass sie umweltschädlich sind. Deshalb ist das Interesse an umweltfreundlichen, insbesondere biologisch abbaubaren, Mitteln gestiegen. Natürliche Öle (wie z.B. Tallöl, Leinöl) haben grundsätzlich eine hydrophobierende Wirkung. Um jedoch eine vollständige Imprägnierung des Splintholzes zu erreichen, ist eine grosse Ölmenge erforderlich. Ziel dieser Arbeit war es, die hydrophobierende Wirkung von Tallöl sowie von Tallöl-Wasseremulsionen (Öl-in-Wasser- und Wasser-in-Öl-Emulsionen) zu untersuchen sowie festzustellen, in welchem Umfang die benötigte Ölmenge durch das Emulgieren reduziert werden kann. Kiefernsplintholzproben wurden mit Tallölgemischen imprägniert. Der Grad der Wasseraufnahme und der Hydrophobierungsgrad wurden mittels zyklischer Befeuchtungs- und Trocknungsversuche bestimmt. Die Ergebnisse zeigten, dass eine Behandlung mit Tallöl die Wasseraufnahme von Kiefernsplintholz reduziert. Behandlungen mit Tallölemulsionen erbrachten annähernd die gleiche Wasser abweisende Wirkung wie solche mit reinem Tallöl, obwohl dabei die eingebrachte Ölmenge deutlich niedriger war. Die erforderliche Ölmenge konnte auf die Hälfte reduziert werden. Die Emulsionstechnik ist eine potenzielle Methode um die Ölmenge, die zum Feuchteschutz von Holz benötigt wird, zu reduzieren.

A model of conditioning in the flotation of a mixture of pyrite and chalcopyrite ores

Abstract Collector control in flotation plants is an important factor, which affects recovery and grade. The performance of a control system can be improved by calculating the collector requirement using a kinetic model of conditioning, which is capable of predicting the adsorption density of the collector on the surfaces of ores. In this paper, a semi-empirical model for the kinetics of conditioning of pyrite–chalcopyrite ore was suggested and tested. The suggested model for conditioning fits well the experimental data. The model is based on an electrochemical mechanism, and it also takes into account the effect of the degree of conditioning. Experiments with batch conditioning of a mixture of high-content chalcopyrite and pyrite ores sieved to a certain particle size class were carried out at pH 9. The dissolved oxygen concentration and the pulp potential were varied in the conditioning, which resulted in different rates of xanthate adsorption. The flotation was started immediately after the conditioning. The flotation model based on first order kinetics gave an excellent fit to the experimental data. The effects of the degree of conditioning on the kinetics and efficiency of flotation were also shown. It was noted that the higher the degree of conditioning with moderate conditioning times, the better the recovery of chalcopyrite and the greater the rate of chalcopyrite flotation. Long conditioning times were found to deteriorate the grade, although the high level of chalcopyrite recovery was maintained.

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.