Preparation, Optimization And Properties Of Dialdehyde Crosslinked Sesbania Gum

Sesbania gum is a kind of natural polymers which is extensively used in many fields due to its good properties. However, the native sesbania gum has the poor compatibility with electrolytes, high content of the insoluble substance, and poor heat resistance so that its application is limited. Therefore, it is necessary for sesbania gum being modified to improve its properties.The preparation and properties of dialdehyde cross-linked sesbania gum were studied by using sesbania gum as a raw material, ethanol as a solvent, glutaraldehyde as a cross-linking reagent, and sodium periodate as a oxidation reagent in this paper. The sedimentation volume was used to measure the cross-linking degree of the cross-linked sesbania gum. The aldehyde content was determined by the method of the acid base titrations. The effects of the reaction time, reaction temperature, amount of ethanol, amount of glutaraldehyde and amount of sodium periodate on the sedimentation volume of cross-linked sesbania gum and the aldehyde content of dialdehyde cross-linked sesbania gum were investigated. The reaction conditions for preparing cross-linked sesbania gum and dialdehyde cross-linked sesbania gum were optimized with the response surface methodology on the basis of the single factor. The surface modification mechanism of sesbania gum was further discussed through the variation of the numbers of the surface hydroxyl groups on the granules and the Schiff’s reagent coloration of the aldehyde groups by means of fourier transform infrared spectrometer(FTIR), X-ray powder diffractometer(XRD), scanning electron microscope(SEM), polarized optical microscope(POM).The thermal properties of sesbania gum, cross-linked sesbania gum and dialdehyde cross-linked sesbania gum were compared and analyzed by differential scanning calorimeter(DSC) and simultaneous thermal analyzer. The effects of cross-linking and oxidation on the acid resistance, alkali resistance, cold and hot viscosity, separated water, swelling power and retrogradation of SG were also investigated.The optimum conditions for preparing cross-linked sesbania gum were: reaction time 1.5 h, reaction temperature 50 ℃, pH 4.0, amount of glutaraldehyde 10%, amount of ethanol 80%. And the optimum conditions for preparing dialdehyde cross-linked sesbania gum were: reaction time 2.5 h, reaction temperature 40 ℃, pH 4.0, amount of sodium periodate 30%, amount of ethanol 70%.The results showed that the intensity of the hydroxyl stretching vibration decreased after cross-linking through FTIR analysis of sesbania gum, cross-linked sesbania gum and dialdehyde cross-linked sesbania gum. The carbonyl peak at the wave numbers of 1760 cm-1 proved that the aldehyde groups were introduced into the molecules of SG owing to the oxidation. After the sesbania gum was cross-linked, its onset decomposition temperature and end decomposition temperature increased. However, after the cross-linked sesbania gum was oxidized, its onset decomposition temperature and end decomposition temperature decreased. After the SG was cross-linked and oxidized, its acid resistance, alkali resistance, cold and hot viscosity, freeze-thawed stability, swelling power decreased, but its retrogradation increased.The results showed that and the number of hydroxyl groups decreased with the increasing of cross-linking degree by determining the numbers of surface hydroxyl groups and dyeing by the Schiff’s reagent. The hydroxyl groups were consumed by the oxidation, but the expansion of sesbania gum granules occurred after the sodium periodate oxidation, which made the numbers of the hydroxyl groups increased with increasing the oxidation degree. The aldehyde groups produced by the oxidation were mainly located on the edge of the SG particles. The better conditions for L-asparagine adsorbed by dialdehyde cross-linked sesbania gum were: reaction time 1.5 h, reaction temperature 70 ℃, p H 3.0, amount of L-asparagine 20%, amount of ethanol 70%. The maximum adsorption capacity for L-asparagine adsorbed by dialdehyde cross-linked sesbania gum could be 40.73 mg/g under the better adsorption conditions.