FINITE ELEMENT ANALYSIS OF THE FATIGUE BEHAVIOR OF WOOD FIBER CELL WALLS

The fatigue behavior of the wood fiber cell wall under mechanical treatment in refining was simulated dynamically using a finite element method. The effect of the amplitude and frequency of impacts on the mechanical breakdown of the fiber wall structure was examined. The proposed model of the fiber cell wall was constructed from elementary microfibrils in various orientations embedded in isotropic lignin. The fatigue of the cell wall was simulated under normal refiner mechanical pulping conditions. A cyclic load was applied on the model fiber through a hemispherical grit proposed to be applied on the surface on refiner segments. Changes in the elastic modulus of the cell wall were analyzed to determine the potential for cell wall breakdown. An increase in the amplitude of applied forces and frequency of impacts was found to have a significant influence on the reduction of the elastic modulus of the wall structure. A high frequency of impacts increased the stiffness of the cell wall, but resulted in faster reduction of the elastic modulus. At a lower amplitude of impacts, efficient breakdown of the cell wall using grits was achieved with a high frequency of impacts or a high rotational speed of refiners

Profiles of alkali concentration and galactoglucomannan degradation in kraft impregnation of Scots pine wood: Experimental observations and modeling

A deep understanding of alkali impregnation including the profiles of alkali concentration and hemicellulose degradation is necessary to analyze the optimization of current and innovative processes. In this paper, the impregnation of Scots pine (Pinus sylvestris L.) wood is analyzed and modeled under consideration of deacetylation, reactions of acidic group, and galactoglucomannan (GGM) degradation. The immobile anionic groups activated by the ionization of lignin-derived OH groups are also considered for the assessment of the Donnan effect. Predicted profiles of sodium and hydroxide ions and acetyl group concentrations are compared to experimental results. The balance between impregnation and hemicellulose degradation levels is discussed based on the developed models. Expectedly, higher concentrations and temperatures speed up the impregnation process. Nevertheless, a higher OH-concentration has two benefits for the same impregnation front position – the alkali charge inside the chip is higher and the GGM degradation is lower.Fil: Montagna, Pablo Nicolás. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulosica; ArgentinaFil: Nieminen, Kaarlo. Alto University.; FinlandiaFil: Inalbon, Maria Cristina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulosica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; ArgentinaFil: Sixta, Herbert. Alto University; FinlandiaFil: Zanuttini, Miguel Angel Mario. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulosica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

Filament spinning of unbleached birch kraft pulps : Effect of pulping intensity on the processability and the fiber properties

Man-made lignocellulosic fibres were successfully prepared from unbleached birch kraft pulps by using the Ioncell-F technology. Pulps with different lignin content were produced by tailored kraft pulping with varying intensity. The degree of polymerization of the pulps was adjusted by acid-catalyzed hydrolysis and electron beam treatment. All substrates were completely soluble in 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH] OAc) and the respective solutions were spinnable to yield fibres with good to excellent mechanical properties despite the use of only mildly refined wood pulp. The tensile properties decreased gradually as the lignin concentration in the fibres increased. Changes in the chemical composition also affected the structure and morphology of the fibres. Both the molecular orientation and the crystallinity decreased while the presence of lignin enhanced the water accessibility. The effects of the crystallite size and lignin content on monolayer water adsorption are discussed.Peer reviewe

I. K. Inha Kalevalan laulumailta

Kirja-arvioInha, I. K.: Kalevalan laulumailt

Keittoprosessien kattavan mallin kehittäminen

The objective of this study was to develop mathematical models that describe the course of delignification and carbohydrate degradation during cooking processes as a function of cooking temperature and cooking chemicals concentrations. The cooking processes investigated in this work were the kraft and the autohydrolysis processes. In the case of kraft cooking different existing delignification models were fitted to experimental data from both soft- and hardwood cooks. The fact that data with different temperatures were present enabled the estimation of the activation energies for the reactions associated with the models. For the available data it turned out that a model containing two lignin components of differing reactivities was sufficient for a satisfactory description of the observed delignification. Furthermore, two modifications aimed at augmenting the authenticity of the model were conducted. First, Donnan theory, accounting for the time development of the chemical concentrations at the actual location of the delignification reactions, was incorporated to the model. Second, the rate constants in the model were calculated according to the real temperature during heating and cooling instead of resorting to the computation simplifying concept of isothermal time. Moreover, the square root relationship between the reciprocal lignin content and the anthraquinone charge earlier established for soda-anthraquinone cooks was confirmed in the kraft-anthraquinone context. For carbohydrate degradation during kraft cooking a model based on the endwise reactions peeling, stopping and alkaline hydrolysis was developed. The model provided satisfactory fits to the yield data of all the three carbohydrates (cellulose, glucomannan and xylan) under scrutiny. The portions of material degraded by the different reactions present in the model were calculated based on the parameter estimates obtained from the fits. Furthermore, the impact of dissolution was compared to that of the endwise reactions; for glucomannan and cellulose the endwise reactions degrade more material than does the dissolution, whereas the opposite is true for xylan. The yield loss model for the carbohydrates was also combined with a model for the decrease in the degree of polymerization. By performing a simultaneous fit of the two models an enhanced estimate of the model parameters was obtained. For the autohydrolysis cooks reaction schemes for the delignification and the degradation of xylan and glucan were developed and the corresponding kinetic models were fitted to the data resulting in estimates for the kinetic parameters. The kinetic models were combined with the diffusion equation resulting in a simulation program for the effect of cooking on the wood components on chip level. Furthermore, the kinetic models together with the Ergun equation for the forced flow of the heated cooking liquor through the packed bed led to a simulation program of the spatial developments of delignification and carbohydrate degradation on reactor level.Tämän työn tavoitteena oli kehittää matemaattinen malli kuvaamaan keiton aikana tapahtuvaa puun ligniinin ja hiilihydraattien hajoamista sekä hajoamisnopeuksien riippuvuutta keittolämpötilasta ja keittokemikaalien konsentraatioista. Sulfaattimenetelmä ja kuumavesiuutto olivat tutkimuksen kohteina. Sulfaattikeiton tapauksessa olemassa olevia ligniinin hajoamisen kineettisiä malleja sovitettiin sekä lehtipuu- että havupuukeitoista saatuun kokeelliseen dataan. Koska keittoja oli suoritettu eri lämpötiloilla, oli mahdollista arvioida malliin liittyvien reaktioiden aktivointienergiat. Saatavilla olevan datan tapauksessa malli, jossa oli kaksi eri reaktionopeudet omaavaa ligniinin lajia, osoittautui riittäväksi kuvaamaan tyydyttävästi havaittua ligniinin määrän vähenemistä. Tämän lisäksi kaksi eri tapaa lisätä mallin todenmukaisuutta otettiin käyttöön. Ensinnäkin Donnanin teoria, jonka avulla voidaan laskea kemikaalien konsentraatiot siinä kohdin missä varsinainen reaktio tapahtuu, liitettiin malliin. Toiseksi mallin reaktiokertoimet laskettiin käyttäen kuumennus-ja jäähdytysaikajaksojen todellisia lämpötiloja laskuja yksinkertaistavaan isotermiseen aikaan liittyvän kuvitteellisen vakiolämpötilan asemesta. Lisäksi vahvistettiin sooda-AQ keitosta tutun ligniinimäärän käänteisarvon ja antrakinonimäärän neliöjuuren välisen riippuvuuden pätevyys myös sulfaattikeiton tapauksessa. Hiilihydraattien hajoamiselle sulfaattikeitossa kehitettiin polymeeriketjujen reunayksikköihin kohdistuviin reaktioihin (peeling, stopping, alkaline hydrolysis) perustuva malli. Malli sopi hyvin yhteen kaikkien kolmen puun tärkeimpien hiilihydraattien selluloosan, glukomannaanin ja ksylaanin kokeellisten saantoarvojen kanssa. Mallin eri reaktioiden kautta hajoavan materiaalin osuus laskettiin sovituksista saatujen parametriestimaattien avulla. Tämän lisäksi vertailtiin polymeerien liukenemisen merkitys suhteessa polymeeriketjujen reunayksikköihin kohdistuvien reaktioiden merkitykseen; glukomannaanin ja selluloosan tapauksessa päätyreaktiot hävittävät enemmän ainetta kun liukeneminen, kun taas ksylaanin tapauksessa tilanne on käänteinen. Hiilihydraattien saantohävikin malli yhdistettiin myös polymerisaatioasteen vähenemistä kuvaavaan malliin. Mainittujen kahden mallien samanaikainen sovitus vahvisti kineettisten parametrien estimaatit. Kuumavesiuutolle kehitettiin ligniinin, ksylaanin ja glukaanin hajoamisen reaktiokaaviot ja niihin liittyvät kineettiset mallit sovitettiin dataan tuloksena kineettisten parametrien estimaatit. Kineettiset mallit yhdistettynä diffuusioyhtälön kanssa mahdollistivat keiton simulointiohjelman hakepalasen tasolla. Lisäksi kineettiset mallit yhdessä hakepedin läpi kulkevan keittonesteen virtauksen kuvaavan Ergunin yhtälön kanssa johtivat ligniinin ja hiilihydraattien hajoamisen reaktoritason simulointiohjelmaan

Suomen kansalliskirjallisuus I, VII ja VIII. Toim. E. N. Setälä, V. Tarkiainen ja Vihtori Laurila

Kirja-arvioSetälä, E. N. & Tarkiainen, V. & Laurila, Vihtori (toim.): Suomen kansalliskirjallisuus I, VII ja VIII

Eräs karsittava germanismi

Kielenaineksetkokonaan (kieli: suomi, sivulla: 269)täysin (kieli: suomi, sivulla: 269