Study On Preparation,Property And Application Of Cross-linked Oxidized Sesbania Gum

Sesbania gum?SG?,as a kind of natural plant gums,was categorized as a galactomannan polysaccharide produced only in china,and widely used in many areas owing to its properties of flocculation,thickening and flotation.However,there were some questions in the application of SG because of its low viscosity stability,high water solublility and poor electrolyte compatibility.The chemical modification could be used to make for the performance deficiencies of natural sesbania gum.The preparation and properties of cross-linked oxidized sesbania gum were studied using SG as a material,ethanol as a solvent,phosphorus oxychloride as a cross-linking agent,hydrogen peroxide as an oxidant in this paper,The cross-linking degree of sesbania gum was evaluated by sedimentation volume and combined phosphorus content.The effect of cross-linking temperature,cross-linking time,p H,dosage of ethanol,and dosage of phosphorus oxychloride on the sedimentation volume of cross-linked sesbania gum were investagated.The oxidation degree of sesbania gum was evaluated according to the viscosity change rate.The influence of oxidation temperature,oxidation time,p H,dosage o f ethanol,dosage of hydrogen peroxide and dosage of copper sulfate on the viscos ity change rate of cross-linked oxidized sesbania gum were discussed.O n the basis of single factor,the cross-linking conditions of sesbania gum and oxidation conditions of cross-linked sesbania gum were further optimized by the response surface method.The surface modification mechanism of sesbania gum was discussed by means of FTIR,XRD,SEM,POM,and variation of the surface hydroxyl number.The thermal properties of sesbania gum,cross-linked sesbania gum and cross-linked oxidized sesbania gum were compared and analyzed by DSC,TGA.The influence of crosslinking and oxidation on the resistance to acid and alkaline,hot and cold viscosity stability,freeze-thaw stability,swelling capacity and retrogradation of sesbania gum were studied.The best cross-linkingconditions of sesbania gum were as follows: cross-linking temperature 30?,cross-linking time 70 min,p H 10,dosage of phosphorus oxychloride 1.0%,dosage of alcohol 67%.The best oxidation conditions of cross-linkedsesbania gum were as follows: oxidation temperature 40?,oxidation time 2h,p H 6,dosage of hydrogen peroxide 24%,dosage of alcohol 68%.The freeze-thaw stability of sesbania gum was improved after the crosslinking,but the freeze-thaw stability of cross-linked sesbania gum was decreased after the oxidation.The surface hydroxyl numbers of sesbania gum particles decreased after cross-linking,and reduced with increasing the crosslinking degree.After the cross-linked sesbania gum being oxidized,its surface hydroxyl numbers increased.The viscosity of cross-linked sesbania gum paste and surface hydroxyl numbers also decreased with increasing the oxidization degree.The FTIR spectra showed that no new groups were introduced into the molecules of cross-linked sesbania gum or sesbania gum by hydrogen peroxide oxidation.The main reason of the reduction in viscosity was from breakage of sesbania gum molecule chains.After sesbania gum being modified by cross-linking,its onset temperature,the peak temperature and the enthalpy change increased,but end temperature,onset decomposition temperature,end decomposition temperature and weight loss rate decreased.After cross-linked sesbania gum being oxidized,its onset temperature,onset decomposition temperature and weight loss rate decreased,but the peak temperature,end temperature,end decomposition temperature and enthalpy changeincreased.The crystallinity degree of sesbania gum was reduced by cross-linking and oxidation.The surface structure of sesbania gum was compact,rough and bumpy before modification.Many small grooves onto the particles of cross-linked sesbania gum existed after the cross-linking.It proved that cross-linking was unevenly carried out.After sesbania gum was further oxidized on the base of cross-linking,most of the particle surfaces were eroded so that the surface of cross-linked oxidized sesbania gum became more rough than cross-linked sesbania gum.For sesbania gum grains,the damage caused by oxidation was more than that caused by cross-linking.The effect of Cu²⁺ adsorpted by sesbania gum and cross-linked oxidized sesbania gum were discussed using removal rate of C u²⁺ as a evaluation criteria,and changing the conditions such as adsorption temperature,adsorption time,dosage of adsorbent and so on,.The experiment results showed that the removal rate of C u²⁺ for sesbania gum could reach 33.1% under adsorption temperature 45?,dosage of sesbania gum 0.3mg/100 m L simulating waste water,adsorption time 2h.The removal rate of C u²⁺ for cross-linked oxidized sesbania gum would reach 64.9% under adsorption temperature 30 ?,dosage of sesbania gum 1mg/100 m L simulating waste water,adsorption time 1.5 h.The effect of removing C u²⁺ was superior to that of sesbania gum.