Agnes Stépán

Corncob arabinoxylan for new materials

Corncob agricultural waste was used as a source of arabinoxylan for preparation of films. Three arabinoxylan samples were prepared: crude extract (CCAX), purified by a washing step, and purified by bleaching CCAX. Films prepared with untreated CCAX were water soluble, yellowish in color and had poor mechanical properties. After the purification processes the Youngs modulus increased from ∼ 293 MPa to ∼ 1400-1600 MPa, and strength was improved from ∼ 9 MPa to around 53 MPa, while the strain at break was kept at ∼ 8% both in untreated and purified CCAX. The contact angle was increased from ∼ 21.3° to 67-74° after washing or bleaching CCAX. Acetylation of bleached CCAX showed the highest thermal resistance (325 °C), had low Tg (125°C) and a high contact angle (80°), and its films were stronger (strength ∼ 67 MPa; Youngs modulus ∼ 2241 MPa) and more flexible (∼ 13%). These characteristics make purified CCAX a suitable material to be used as a matrix for film applications.

Assembly of Debranched Xylan from Solution and on Nanocellulosic Surfaces

This study focused on the assembly characteristics of debranched xylan onto cellulose surfaces. A rye arabinoxylan polymer with an initial arabinose/xylose ratio of 0.53 was debranched with an oxalic acid treatment as a function of time. The resulting samples contained reduced arabinose/xylose ratios significantly affecting the molecular architecture and solution behavior of the biopolymer. With this treatment, an almost linear xylan with arabinose DS of only 0.04 was obtained. The removal of arabinose units resulted in the self-assembly of the debranched polymer in water into stable nanoparticle aggregates with a size around 300 nm with a gradual increase in crystallinity of the isolated xylan. Using quartz crystal microbalance with dissipation monitoring, the adsorption of xylan onto model cellulose surfaces was quantified. Compared to the nonmodified xylan, the adsorption of debranched xylan increased from 0.6 to 5.5 mg m(-2). Additionally, adsorption kinetics suggest that the nanoparticles rapidly adsorbed to the cellulose surfaces compared to the arabinoxylan. In summary, a control of the molecular structure of xylan influences its ability to form a new class of polysaccharide nanoparticles in aqueous suspensions and its interaction with nanocellulose surfaces.

Lipases efficiently stearate and cutinases acetylate the surface of arabinoxylan films.

This is the first report on successful enzyme catalyzed surface esterification of hemicellulose films. Enzyme catalyzed surface acetylation with vinyl acetate and stearation with vinyl stearate were studied on rye arabinoxylan (AX) films. Different surface analytical techniques (FT-IR, TOF-SIMS, ESCA, CA) show that lipases from Mucor javanicus, Rhizopus oryzae and Candida rugosa successfully surface stearate AX films and that a cutinase from Fusarium solani pisi surface acetylates these films. The specificities of cutinase and lipases were also compared, and higher activity was observed for lipases utilizing long alkyl chain substrates while higher activity was observed for cutinase utilizing shorter alkyl chain substrates. The contact angle analysis showed films with increased initial hydrophobicity on the surfaces.