Terhi Suopajärvi

Hydrophobic, Superabsorbing Aerogels from Choline Chloride-Based Deep Eutectic Solvent Pretreated and Silylated Cellulose Nanofibrils for Selective Oil Removal

Superabsorbents are highly appealing materials for use in cleaning up oil and chemical spills. However, the development of a low-cost, highly efficient superabsorbent remains a major challenge. This paper demonstrates a straightforward method of producing a cellulose nanofibril aerogel that is low-cost, ultralight, highly porous, hydrophobic, and reusable superabsorbing cellulose nanofibril aerogel from recycled waste fibers using a simple, environmentally friendly nanofibrillation treatment involving deep eutectic solvent and freeze-drying. Nanofibrillation and hydrophobic modification (silylation) of waste cellulose fibers resulted in nanofibril sponges with ultralow density (0.0029 g/cm3) and high porosity (up to 99.81%) after freeze-drying. These sponges exhibited excellent absorption performances for various oils and organic solvents and were reusable. In particular, the nanofibril aerogels showed selectivity in absorbing marine diesel oil from an oil-water mixture and possessed ultrahigh absorption capacities of up to 142.9 g/g, much higher than those of the commercial absorbent materials (i.e., polypropylene-based material) (8.1-24.6 g/g) that were used as references. The absorbed oil could easily be recovered by means of simple mechanical squeezing. In addition, the nanofibril sponges exhibited excellent reusability, maintaining a high capacity to absorb diesel oil for at least 30 cycles at 71.4-81.0% of capacity compared to a fresh absorbent. The above-mentioned advantages make cellulose nanofibril superabsorbents created from recycled waste cellulose fibers promising material for cleaning oil and chemical spills.

Nanofibrillation of deep eutectic solvent-treated paper and board cellulose pulps

In this work, several cellulose board grades, including waste board, fluting, and waste milk container board, were pretreated with green choline chloride-urea deep eutectic solvent (DES) and nanofibrillated using a Masuko grinder. DES-treated bleached chemical birch pulp, NaOH-swollen waste board, and bleached chemical birch pulp were used as reference materials. The properties of the nanofibrils after disc grinding were compared with those obtained through microfluidization. Overall, the choline chloride-urea DES pretreatment significantly enhanced the nanofibrillation of the board pulps in both nanofibrillation methods-as compared with NaOH-treated pulps-and resulted in fine and long individual nanofibrils and some larger nanofibril bunches, as determined by field emission scanning electron microscopy and transmission electron microscopy. The nanofibril suspensions obtained from the DES pretreatment had a viscous, gel-like appearance with shear thinning behavior. The nanofibrils maintained their initial crystalline structure with a crystallinity index of 61%-47%. Improved board handsheet properties also showed that DES-treated and Masuko-ground waste board and paper nanocellulose can potentially enhance the strength of the board. Consequently, the DES chemical pretreatment appears to be a promising route to obtain cellulose nanofibrils from waste board and paper.

Distinctive green recovery of silver species from modified cellulose: Mechanism and spectroscopic studies

The present study aimed to recover precious silver in order to identify the adsorption coupled reduction pathways that determine this process. A combination technique of adsorption and nanocrystallization was used to investigate the recovery of silver species from taurine-cellulose (T-DAC) samples. The non-synthetic route of nanocrystallization yielded spherical zero-valent silver sized ∼ 18 nm. Rate-controlling steps were modeled by adsorption parameters by the best fit of Langmuir capacity (55 mg/g), pseudo-second order curves, and exothermic chemical reactions. The T-DAC was an excellent sorbing phase for the treatment of silver-polluted waters over a broad range of pH (2.1-10.1) and varying ionic strengths (8.5-850 mM, as NaCl), which are the conditions often encountered in industrial and mining effluents. A good recovery of silver (40-65%) was also obtained in the presence of Cd(II), Co(II), Cr(VI), Ni(II), and As(V) at lower or equivalent concentrations with Ag(I), either from individually added metals or from all metal ions mixed together. Desorption was compared with a series of five eluents including complexing agents. In these experiments acidified thiourea yielded 86% desorption of Ag(I). Aqueous silver reduced to metallic silver on the surface of the T-DAC samples, which was confirmed by X-ray photo electron spectroscopy.

Fragment analysis of different size-reduced lignocellulosic pulps by hydrodynamic fractionation

Micro- and nanocelluloses are typically produced using intensive mechanical treatments such as grinding, milling or refining followed by high-pressure homogenization to liberate individual nano- and microcellulose fragments. Even though chemical and enzymatic pretreatments can be used to promote fiber disintegration, the required mechanical treatments are still highly energy consuming and very costly. Therefore, it is important to understand the kinetics and factors affecting the disintegration tendency of cellulose. In this study, the disintegration tendency of three different wood cellulose pulps with varying chemical composition processed in a PFI mill was examined by analyzing the fractional composition of the microparticles formed. The fractional compositions of the microfibrils and microparticles formed were measured with novel analyzers, which fractionated particles using a continuous water flow in a long tube. The hydrodynamic fractionators used in this study gave valuable information about different size of particles. Results showed that the amount of lignin and hemicelluloses clearly affected the kinetics and the mechanics of cellulose degradation. The P and S1 layers were peeled off from the Kraft fibers, causing the S2 layer to be cropped out. The thermomechanical pulp (TMP) fibers were first degraded by comminution and delamination from the middle lamella and the primary wall. As the refining process progressed, the fibers and fiber fragments began to unravel. Surprisingly, the semi-chemical pulp (SCP) fibers degraded more like Kraft fibers than TMP fibers despite their high lignin and extractive content.

Use of Optical Monitoring to Assess the Breakage of Activated Sludge Flocs

Optical monitoring with a charge-coupled device camera was used to assess the breakage of activated sludge flocs obtained from three different activated sludge plants: two municipal and one industrial. In this method, the samples were processed through the imaging unit and recycled back to a beaker using a centrifugal pump which causes the breakage of flocs together with hydrodynamics forces. Based on the image analysis results, the breakage models of the activated sludge flocs vary between the plants. The major breakage model in the two municipal plants was surface erosion whereas it was large-scale fragmentation in the industrial plant. A larger amount of filaments in the industrial plant most likely caused the large-scale fragmentation. Furthermore, the effect of the addition of a cationic polymer on the strength of activated sludge floc was studied in one sample. When the cationic polymer was used, the flocs started to grow at the start of the breakage process. However, they broke up at the end of the process and remained small, as found in flocs not exposed to any chemical treatment. Based on the results, the optical monitoring seems to be suitable for analyzing the breakage of flocs.

Morphological Analyses of Some Micro- and Nanofibrils from Birch and Wheat Straw Sources

The morphological properties of nano- and microcellulose depend on the source of the particles, the preparation methods, and the processing conditions. In this study, two different kinds of microfibrillated (MFC) and nanofibrillated (NFC) celluloses were produced from wood and non-wood cellulose pulps through mechanical methods without using any chemicals. The morphological properties of the samples and feasibility of different analysis methods were investigated using a novel chromatographic washer, a field emission scanning electron microscope (FESEM), a laser diffractometer (LS), a rotational viscometer, X-ray diffractometry (WAXD) and, additionally, the degree of polymerization (DP) was assessed. The analyses showed that the formed non-wood cellulose fibrils were shorter than the wood cellulose fibrils, but wheat straw pulp comminuted to nanofibrils more easily. The low hemicelluloses content of wheat straw pulp caused the flocculation of the nanofibrils formed in homogenization. All of the analytical methods reflect morphological differences between the micro- and nanocellulose materials.

The effect of seasonal variations on floc morphology in the activated sludge process

ABSTRACT The effect of seasonal variations on floc formation in the activated sludge process (ASP) was studied in a municipal wastewater treatment plant in Finland nearly 16 months. Floc formation was measured with an online optical monitoring device, and results were correlated with the temperature of the upcoming wastewater and the treatment efficiency of the ASP. Results showed that floc formation has a clear, seasonal pattern, with flocs in summer being larger and rounder and having fewer filaments and small particles. In addition, treatment efficiency increased in summer. The study correlated the results of image analysis with the composition (chemical oxygen demand and suspended solids content) and temperature of the wastewater before and after the ASP. Results showed that the composition of upcoming wastewater has no clear correlation with floc morphological parameters. However, the wastewater temperature clearly correlated with floc formation. Results indicated that cold winter conditions enhanced the growth of filamentous bacteria in wastewater, decreasing treatment efficiency. Furthermore, these results confirmed that floc formation has seasonal variations.