Browsing by Author "Ahvenainen, Patrik"
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Item Birch wood pre-hydrolysis vs pulp post-hydrolysis for the production of xylan-based compounds and cellulose for viscose application(2018-06-15) Borrega, Marc; Larsson, Per Tomas; Ahvenainen, Patrik; Ceccherini, Sara; Maloney, Thaddeus; Rautkari, Lauri; Sixta, Herbert; Department of Forest Products Technology; Department of Bioproducts and Biosystems; Bio-based Materials; Wood Material Science; Biorefineries; RISE Bioeconomy; University of HelsinkiHydrothermal treatments of birch wood and kraft pulp were compared for their ability to extract the xylan and produce viscose-grade pulp. Water post-hydrolysis of kraft pulp produced a high-purity cellulosic pulp with lower viscosity but higher cellulose yield than traditional pre-hydrolysis kraft pulping of wood. Post-hydrolysis of pulp also increased the crystallite dimensions and degree of crystallinity in cellulose, and promoted a higher extent of fibril aggregation. The lower specific surface area in post-hydrolyzed pulps, derived from their larger fibril aggregates, decreased the accessibility of –OH groups. However, this lower accessibility did not seem to decrease the pulp reactivity to derivatizing chemicals. In the aqueous side-stream, the xylose yield was similar in both pre- and post-hydrolysates, although conducting post-hydrolysis of pulp in a flow-through system enabled the recovery of high purity and molar mass (∼10 kDa) xylan for high-value applications.Item Characterisation of lignin microparticle size with static light scattering(2024-08-29) Makkonen, Janita; Penttilä, Paavo; Ahvenainen, Patrik; Kemian tekniikan korkeakoulu; Österberg, MonikaThe complex nature of lignin is one of the main issues hindering its use in high-value applications. Incomplete knowledge of the structure and lack of efficient and accurate structural analysis methods make it challenging to use lignin in large scale. Obtaining knowledge of the size and shape of lignin particles is important for application development since they affect the material properties. This work was conducted to examine static light scattering techniques on lignin microparticle size characterisation. Static light scattering methods are based on complex mathematical theory that typically assumes that particles are spherical and homogeneous, even though the shape is often overlooked. Hence, the effects of the particle shape on the measured particle sizes were studied. Organosolv and kraft lignin particles in suspension were measured with laser diffraction and small-angle light scattering. The particle sizes obtained from the light scattering measurements were compared to results from microscopy and static image analysis. Results showed that particle concentration and used absorption coefficient affected the measured sizes obtained from laser diffraction. For large particles, the most important aspect was the sampling whereas for the finer particles choosing the right refractive index became the most important parameter. For the spherical lignin particles, results from the laser diffraction corresponded to sizes obtained from microscopy images whereas for arbitrary shaped particles there was more variability in the results. The small-angle light scattering experiments showed that for the samples more homogeneous in shape and size, simple sphere model fits decently and obtained sizes were consistent with those from other methods. For the samples with wider size distribution and irregularly shaped particles, fitting a simple model was challenging and more complex models should be used.Item Effect of chemical composition of tropical tree species on durability, usage and mechanical properties(2023-01-14) Nguyen, Tam; Ahvenainen, Patrik; Kemiantekniikan korkeakoulu; Kontturi, EeroItem Kevyen ja tiheän puulajin vertailu(2022-12-20) Paukku, Sander; Ahvenainen, Patrik; Kemiantekniikan korkeakoulu; Kontturi, EeroItem Structural analysis of Ioncell-F fibres from birch wood(ELSEVIER SCI LTD, 2018-02-01) Asaadi, Shirin; Hummel, Michael; Ahvenainen, Patrik; Gubitosi, Marta; Olsson, Ulf; Sixta, Herbert; Department of Bioproducts and Biosystems; Biorefineries; University of Helsinki; Lund UniversityQuite recently, the Ioncell-F process, a novel and promising Lyocell fibre process, has been developed. The ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) utilized in this process, was identified as an excellent cellulose solvent for dry-jet wet fibre spinning. Fibres spun from cellulose-[DBNH]OAc solution have shown excellent mechanical properties. Herein, various structural features of these ionic liquid-based fibres were analyzed and correlated with their mechanical properties. The highest slope of tenacity increase of these Ioncell-F fibres (from birch wood) observed at low draw ratios (DRs), while a continuous but slower increase occurs to partly very high draws. The improvements in the mechanical properties do not seem to correlate with changes in the crystallite size or the crystalline orientation based on wide-angle X-ray scattering (WAXS) results. More significant differences were seen for the sample crystallinity, the amorphous orientation (measured by birefringence), the orientation of the voids, the specific surface (measured by small-angle X-ray scattering (SAXS)), and the sorption/desorption properties of the fibres.Item Supercritical water hydrolysis: a green pathway for producing low-molecular-weight cellulose(2016) Buffiere, Jean; Ahvenainen, Patrik; Borrega Sabate, Marc; Svedström, Kirsi; Sixta, Herbert; Department of Forest Products Technology; University of Helsinki; Department of Bioproducts and BiosystemsThis work discusses the suitability of supercritical water treatment (SCWT) for depolymerising microcrystalline cellulose in a controlled way. The SCWT partially hydrolysed cellulose down to a mixture of three valuable products: water-insoluble low-molecular-weight cellulose (WI-LMWC) precipitate, water-soluble low-molecular-weight cellulose (WS-LMWC) oligomers, and glucose. The conditions under which the energy demand for obtaining these products is minimised were identified by adjusting the reaction time inside the continuous reactor and the temperature around the critical point. The optimum conditions were 370 °C and 0.4 seconds for producing WI-LMWC and 360 °C and 0.5 seconds for producing WS-LMWC, with maximum yields of 19 wt% and 50 wt%, respectively. This work also shows that the water-insoluble product precipitates into crystalline cellulose II arrangements. This precipitation phenomenon enabled isolation of cellulose chains of different lengths according to their respective solubilities in ambient water. The results show that SCWT is a relevant process for producing narrowly distributed fractions of low-molecular-weight cellulose using water and heat only.Item Tailoring the Structure and Morphology of Low-Molecular-Weight Cellulose Produced during Supercritical Water Hydrolysis(AMER CHEMICAL SOC, 2018) Buffiere, Jean; Abad, Nerea; Ahvenainen, Patrik; Dou, Jinze; Cocero, María José; Sixta, Herbert; Department of Bioproducts and Biosystems; Biorefineries; Wood Chemistry; University of Valladolid; University of HelsinkiThis paper discusses the influence of reactor design and initial consistency when partially hydrolyzing microcrystalline cellulose (MCC) in supercritical water. Experiments conducted on two pilot reactors located in Finland and in Spain showed that stopping the reaction using depressurization instead of quenching, combined with a sufficiently high MCC consistency, led to significant change in reaction kinetics. A complete particle size reduction was achieved after 50 ms only due to additional shear-induced degradation, with a low-molecular-weight product yield above 50 wt % and an average DP of 25. In addition, gradually increasing the MCC consistency triggered precipitation under higher apparent temperature, which affected both the morphology and structure of the product. A range of particles from ribbon-like cellulose II to shish-kebab structures to lamellar cellulose IVII crystals was obtained. Furthermore, heat requirements as low as 66 kJ·g-1 of product confirm the high potential and versatility of this process for refining MCC into colloidal low-molecular-weight cellulose with different particle shapes and structural properties.Item Ultrastructural X-ray scattering studies of tropical and temperate hardwoods used as tonewoods(International Association of Wood Anatomists, 2020-07-01) Viljanen, Mira; Ahvenainen, Patrik; Penttilä, Paavo; Help, Hanna; Svedström, Kirsi J.; Department of Bioproducts and Biosystems; Wood Material Science; University of HelsinkiThe structure of hardwoods representing eight tropical and five temperate species was characterized from the atomistic level up to the cellular level using X-ray scattering, X-ray microtomography and light microscopy. The species were chosen for this study based on their popularity as tonewoods. The ultrastructure of wood cell walls, including crystallite size, orientation and close-range order of cellulose microfibrils were determined by small- and wide-angle X-ray scattering (SAXS, WAXS). The SAXS patterns were interpreted by using an analytical model of cylinders packed in a hexagonal close-range order with paracrystalline distortion. The values for the cylinder diameters given by this model were compared to the average crystallite widths obtained by WAXS using the Scherrer equation. In six out of 26 samples, all of these representing tropical species used especially in fretboard parts of electric guitars, large differences between these two sizes were obtained. The WAXS and microscopy results of these samples corresponded to tension wood structures. These comparisons and interpretations of SAXS results have not been previously presented for any tropical hardwoods, especially related to those containing tension wood tissue. The importance of the ultrastructural characterization was highlighted in this study in the case of tropical hardwood samples.Item Water-induced crystallization and nano-scale spinodal decomposition of cellulose in NMMO and ionic liquid dope(SPRINGER, 2019-01-15) Nishiyama, Yoshiharu; Asaadi, Shirin; Ahvenainen, Patrik; Sixta, Herbert; Department of Bioproducts and Biosystems; Biohybrid Materials; Biorefineries; Institut national de physique nucléaire et de physique des particules; University of HelsinkiWe followed the cellulose structure formation induced by water diffusion into Lyocell dopes based on both N-Methylmorpholine N-oxide (NMMO) and 1,5-diazabicyclo[4.3.0]non-5-ene acetate ([DBNH][OAc], by using scanning simultaneous small- and wide-angle scattering (SAXS-WAXS) experiment along the diffusion gradient. The water content at each point was estimated from the wide-angle scattering profile, giving a binary diffusion constant of the order of 5 × 10−10 m2/sec. In the case of the cellulose solution in NMMO monohydrate, diffraction peaks corresponding to cellulose II appeared concomitantly with the increase in small angle scattering features indicative of nanofibril formation. In the cellulose solution in the ionic liquid, an increase in small angle scattering intensity with the progression of water content appeared at scattering vector q = 0.015 Å−1 corresponding to a correlation length of about 40 nm, indicative of nanometric spinodal decomposition preceding the coagulation process, though no crystalline peak appeared in the wide-angle scattering. Graphical Abstract: [Figure not available: see fulltext.].
