Determination of surface-accessible acidic hydroxyls and surface area of lignin by cationic dye adsorption

A new colorimetric method for determining the surface-accessible acidic lignin hydroxyl groups in lignocellulose solid fractions was developed. The method is based on selective adsorption of Azure B, a basic dye, onto acidic hydroxyl groups of lignin. Selectivity of adsorption of Azure B on lignin was demonstrated using lignin and cellulose materials as adsorbents. Adsorption isotherms of Azure B on wheat straw (WS), sugarcane bagasse (SGB), oat husk, and isolated lignin materials were determined. The maximum adsorption capacities predicted by the Langmuir isotherms were used to calculate the amounts of surface-accessible acidic hydroxyl groups. WS contained 1.7-times more acidic hydroxyls (0.21 mmol/g) and higher surface area of lignin (84 m2/g) than SGB or oat husk materials. Equations for determining the amount of surface-accessible acidic hydroxyls in solid fractions of the three plant materials by a single point measurement were developed. A method for high-throughput characterization of lignocellulosic materials is now available

Nanoselluloosan ja ksylaanin oksastuskopolymerointi redox-initiaattorilla vesiliuoksissa

Aqueous graft copolymerization of nanofibrillated cellulose (NFC) and different xylans with several acrylates and methacrylates, was studied using cerium(IV) initiated free radical method. The most important reaction parameters affecting the yield were the monomer type and concentration. The selectivity of monomers with higher homopolymerization tendency was improved by a higher initiator concentration. Grafting patterns obtained with different monomers differed significantly in graft length and density. Thermoplastic behavior was observed in NFC copolymers with more than 50% of synthetic polymer. The composition of the xylan substrate also had a high impact on the yield and selectivity. The branching degree of 4-O-methylglucuronic acid was the most important reactivity-increasing factor, probably both by solubilizing xylan and attracting the positively charged cerium ion. High lignin content was found to hinder the reaction, most likely due to decreased solubility and radical scavenging by the phenolic hydroxyl groups in lignin. The graft yield was especially poor with xylan having very low molecular weight, apparently because short polysaccharide chains prevented the successful separation of the copolymer by precipitation. Polymer grafting reduced the affinity of arabinoxylan towards cellulose surface. The affinity of glucuronoxylan was slightly increased, most likely due to the grafted polymer screening the negative charge of the xylan, and hence decreasing the electrostatic repulsion and compensating for weaker hydrogen bonding. Nanocomposites were prepared by solution casting from poly(methyl methacrylate) (PMMA) and NFC grafted with the same polymer. Formation of a percolating NFC network took place between 1 and 5 wt% NFC loading. Elastic moduli of the composites increased and strain at break decreased with increasing NFC content. Tensile strength also decreased at all NFC concentrations between 0.5 and 5 wt%, which was the maximum processable NFC loading. Using grafted NFC instead of unmodified NFC did not improve the mechanical properties, suggesting negligible entanglement formation between grafted polymer and matrix. Cationic NFC was synthesized by grafting NFC with a monomer containing a quaternary ammonium group. The product exhibited limited antimicrobial properties against Gram positive and negative bacteria and a type of yeast. Comparison to another NFC derivative, cationized by etherification, showed that the etherified product was more antimicrobial, most likely due to its higher charge density. Preliminary cytotoxicity screening showed that neither NFC derivative released soluble chemicals harmful to human cells.Nanofibrilloidun selluloosan (NFC) ja eri kasveista eristettyjen ksylaanien oksastuskopolymerointia tutkittiin käyttäen cerium(IV)-initioitua vapaaradikaalimenetelmää vesiliuoksessa. Tärkeimmät saantoon vaikuttavat parametrit olivat käytetty monomeeri ja sen konsentraatio. Selektiivisyyttä voitiin parantaa lisäämällä initiaattoripitoisuutta käytettäessä helposti homopolymeroituvia monomeerejä. Eri monomeereillä saavutettava oksastustiheys ja polymeerihaarojen pituus vaihteli suuresti. Kopolymeerit olivat termoplastisia synteettisen polymeerin osuuden ylittäessä 50 p-%. Ksylaanin sivuhaaroina olevat 4-O-metyyliglukuronihapporyhmät olivat tärkein reaktiivisuutta lisäävä tekijä, jotka paransivat ksylaanin vesiliukoisuutta ja vetivät puoleensa cerium-ioneja. Korkean ligniinipitoisuuden todettiin haittaavan reaktiota, koska se luultavasti alensi ksylaanin vesiliukoisuutta ja ligniinin fenoliset hydroksyyliryhmät toimivat radikaalisieppareina. Lyhytketjuisen ksylaanin oksastussaanto oli hyvin alhainen. Todennäköisesti lyhyet polysakkaridiketjut vaikeuttivat kopolymeerin erotusta homopolymeeristä. Polymeerillä oksastus pienensi arabinoksylaanin affiniteettia selluloosaan. Sen sijaan glukuronoksylaanin affiniteetti kasvoi hieman, koska todennäköisesti oksastettu polymeerikerros heikensi varautuneiden ksylaaniketjujen välistä poistovoimaa ja kompensoi siten heikompaa vetysidosten muodostumista. Nanokomposiitteja valmistettiin sekoittamalla polymetyylimetakrylaattiin (PMMA) liuoksessa samalla polymeerillä oksastettua NFC:aa. Perkoloivan NFC-verkon havaittiin muodostuvan 1 ja 5 p-% NFC-pitoisuuksien välillä. Vetolujuusmittaukset osoittivat kimmokertoimen kasvavan ja murtovenymän pienenevän NFC-pitoisuuden kasvaessa. Vetolujuus ei kasvanut 0,5-5 p-% NFC-pitoisuuksilla, ja tätä korkeammalla pitoisuudella seos ei ollut sulatyöstettävä. Oksastetun NFC:n käyttäminen lujitteena ei parantanut mekaanisia ominaisuuksia verrattuna muokkaamattomaan NFC:aan, mikä viittasi vähäiseen polymeeriketjujen kietoutumiseen oksastetun ja matriisipolymeerin välillä. Kationisoitu NFC-johdannainen syntetisoitiin oksastamalla NFC:aa kvaternäärisen ammoniumryhmän sisältävällä monomeerillä. Tuote kykeni rajallisesti tuhoamaan Gram-positiivisia ja –negatiivisia bakteereja sekä hiivasientä. Vertailu toiseen, eetteröimällä valmistettuun NFC-johdannaiseen paljasti eetteröidyn tuotteen paremmat antimikrobiset ominaisuudet, johtuen luultavasti korkeammasta varaustiheydestä. Kummastakaan NFC-johdannaisesta ei liuennut ihmissoluille haitallisia yhdisteitä

Enzymatically Debranched Xylans in Graft Copolymerization

| openaire: EC/H2020/648925/EU//BHIVEWheat arabinoxylan was treated with two α-arabinofuranosidases exhibiting different mode of action to create three different polymeric substrates. These three substrate preparations were characterized by xylopyranose backbone sugars that are (1) singly substituted by arabinose at C2 or C3, (2) doubly substituted by arabinose at C2 and C3, and (3) largely unsubstituted. All xylan preparations were grafted with glycidyl methacrylate using cerium ammonium nitrate and then evaluated in terms of graft yield and adsorption to cellulose surfaces. The highest graft yield was observed for the xylan preparation characterized by a largely unsubstituted xylopyranose backbone. Furthermore, QCM-D analyses revealed that grafted xylans exhibited a two-stage desorption pattern, which was not seen with the ungrafted xylans and was consistent with increased water sorption. Accordingly, this study demonstrates the potential of arabinofuranosidases to increase the yield and influence the viscoelastic properties of grafted xylans used as biobased cellulose coatings.Peer reviewe

Determination of surface-accessible acidic hydroxyls and surface area of lignin by cationic dye adsorption Determination of surface-accessible acidic hydroxyls and surface area of lignin by cationic dye adsorption

Abstract A new colorimetric method for determining the surface-accessible acidic lignin hydroxyl groups in lignocellulose solid fractions was developed. The method is based on selective adsorption of Azure B, a basic dye, onto acidic hydroxyl groups of lignin. Selectivity of adsorption of Azure B on lignin was demonstrated using lignin and cellulose materials as adsorbents. Adsorption isotherms of Azure B on wheat straw (WS), sugarcane bagasse (SGB), oat husk, and isolated lignin materials were determined. The maximum adsorption capacities predicted by the Langmuir isotherms were used to calculate the amounts of surface-accessible acidic hydroxyl groups. WS contained 1.7-times more acidic hydroxyls (0.21 mmol/g) and higher surface area of lignin (84 m 2 /g) than SGB or oat husk materials. Equations for determining the amount of surface-accessible acidic hydroxyls in solid fractions of the three plant materials by a single point measurement were developed. A method for high-throughput characterization of lignocellulosic materials is now available.

Effect of xylan structure on reactivity in graft copolymerization and subsequent binding to cellulose

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