Study On The Synthesis Of Rosin/hydrogenated Rosin Xylitol Ester By Subcritical CO₂-hot Compressed Water And Its Surface/emulsification Properties

Rosin/hydrogenated rosin is a high-quality renewable forest resource in China,which mainly contains abietic resin acid and sea pine resin acid.Xylitol is a kind of sweetener widely used in the food industry,which has the advantages of high sweetness,anti caries,not easy to cause fat,not easy to combine with amino acids to produce browning reaction.Supercritical/subcritical CO₂as a green catalyst and extractant has been widely used in industrial production.With the depletion of fossil resources,the development and preparation of green fine chemicals have important research value and broad application prospects.In this paper,rosin/hydrogenated rosin and xylitol were used as raw materials for the synthesis of xylitol resinate catalyzed by subcritical CO₂-hot compressed water and its surface/emulsion properties were studied.The main contents are as follows:In the solvent-free system,subcritical CO₂-hot compressed water was used as catalyst,rosin and hydrogenated rosin were used as raw materials,and single factor experiment was designed to optimize the synthesis process of Rosin/hydrogenated rosin resin acid xylitol ester.The results showed that the optimum reaction conditions for the synthesis of RXE were:temperature 250℃,CO₂pressure 4 MPa,the ratio of rosin to xylitol 1:1,reaction time 4 h,the conversion rate of rosin acid reached 90.30%;the optimum reaction conditions for the synthesis of XEHR were:temperature 250℃,CO₂pressure 4 MPa,reaction time 4 h.The conversion rate of hydrogenated rosin resin was 91.54%.ICP-AES was used to determine the content of heavy metals in the products.It was found that the residues of copper,iron,nickel,lead and zinc in RXE and XEHR were lower than those in the same products using traditional Zn O as catalyst.The structure and molecular weight of RXE and XEHR were characterized by FTIR,NMR and GPC.The results showed that rosin/hydrogenated rosin xylitol monoester and diester were formed.The content of monoester and diester in the two products accounted for 50%respectively.The surface tension and interfacial tension of six organic solvents（DMSO,n-butanol,ethyl acetate,dichloromethane,turpentine and carbon tetrachloride）with RXE added were studied by ring method.The results show that RXE can effectively reduce the surface tension of six polar organic solvents,among which,RXE has the strongest ability to reduce the surface tension of DMSO,andγcmc is as low as 36.26 m N/m;RXE has the strongest ability to reduce the interfacial tension between turpentine and water,andγcmc is as low as 1.51m N/m.For the micelles formed in solution,the particle size distribution of micelles in carbon tetrachloride is the smallest,7-20 nm,and that in dichloromethane is the largest,20-100 nm.When the solution concentration is10.4 m M,the particle size of aggregates in carbon tetrachloride is 26-90 nm,and that in dichloromethane is 196-700 nm.The results of TEM showed that RXE was self-assembled successfully and could be transformed from micelle to vesicle in organic solvent according to the change of concentration.Draw cmc curves at different temperatures,and calculate the thermodynamic parameters of aggregate formation.From the surface tension curve of the solution at 25-55℃,it can be concluded that the change value of△G_agg⁰is negative,indicating that the aggregation process of RXE in organic solvent is spontaneous;the value of△H_agg⁰is negative,indicating that the aggregation process is exothermic,and the increase of temperature is not conducive to the aggregation process.The surface properties and oil-water interface properties of XEHR in soybean oil were studied by ring method and rotating drop method.The relationship between emulsification ability and p H（4,6.86,10）,salt types（Na Cl,KCl,Mg Cl₂,Ca Cl₂）was studied.The results show that under different p H and salt concentration,XEHR can reduce the interfacial tension of oil and water to less than 2 m N/m,showing a good ability to reduce the interfacial tension of oil and water.2%XEHR oil in water emulsion was prepared by high-pressure homogenization.All XEHR containing emulsions had strong emulsifying activity.The emulsifying activity and emulsion stability of the emulsion were tested by ultraviolet spectrophotometer.The results showed that when the emulsion contained Mg Cl₂（100 m M）,its emulsifying activity index（9.52 m²/g）and emulsion stability index（94.53%）were the best.The droplet structure was observed by dynamic light scattering and confocal microscopy under different p H values,different salts and different salt concentrations.The presence of salt made the emulsion form a more uniform droplet size and a more fine emulsion structure.The viscosity of the emulsion was tested by rheometer under different p H values,different salts and different salt concentrations.The results showed that the higher the salt content and the greater the viscosity,the stronger the emulsion droplet network.