Cellulose fibrillation and interaction with psyllium seed husk heteroxylan

Fibrillated cellulose (FC) and its mixture with psyllium seed husk powder (PSY) were investigated to broaden the applications of these two materials by a novel combination. Purified cellulose was processed by a colloid mill and relatively stable suspensions were obtained. An FC suspension shows localised concentrations appearing as flocculates, which can be promoted by heating or centrifugation. The structures of unheated mixtures of FC and PSY appear to be binary phase dispersions while, after heat treatment, FC fibres were incorporated into PSY gels and form composites. Fibrillation on the FC surface does not influence the structure and rheological property of the composite mixtures while fibre disintegration contributes to a denser structure and higher moduli. Fluorescent images show the attachment of PSY heteroxylan aggregates on cellulose and fibrillated cellulose fibres. The interaction is weak and time-dependent because G' during cooling was higher than that during heating, and declined back to the same value as the start of heating during an isothermal test at 20 degrees C. PSY was fractionated according to temperature and only F60 (fraction at 60 degrees C) clearly associates with the unfibrillated cellulose fibres, possibly via long arabinan sidechains (similar to hairy pectin) or/and backbone (via interaction with helical domains or/and conformational compatibility). The interaction was promoted by fibrillation, potentially trapping PSY heteroxylan aggregates within the cellulose dispersion. With further fibrillation, smaller FC fibres were generated and form interpenetrating particles with whole PSY or PSY fractions. Highly fibrillated cellulose has a higher surface area and smaller fibrils, which significantly increased the interaction resulting in a clumped structure.