Preparation of crosslinked chitosan/poly(vinyl alcohol) blend beads with high mechanical strength

Crosslinked chitosan beads reported in the literature have the disadvantage of high water content and thus low mechanical strength. In this paper, a chitosan/poly(vinyl alcohol) (PVA) blend aqueous solution was first suspended in toluene–chlorobenzene to form droplets. Some of the water was then distilled out as an azeotrope with the aromatic hydrocarbons to reduce the water content of the suspension droplets. Glutaraldehyde was finally added to the suspension to result in the crosslinked chitosan/PVA beads with low water content and high mechanical strength. It was found that glutaraldehyde reacted with PVA to form crosslinkage at acidic conditions (pH 1 and 2). The H+ ions act as both protection agents of amino groups of chitosan by forming salts and catalyst for the formation of acetal between aldehyde groups and hydroxyl groups of PVA. At pH 4 and 5, glutaraldehyde reacted with chitosan to form Schiff's base crosslinkage. Crosslinked chitosan/PVA beads with micron size were also prepared by the distillation method using very dilute initial polymer concentration and high stirring speed.