Rheological Properties Of Xanthan/Guar Gum Mixture And Its Borax-Crosslinking Solutions

In this study,the rheological properties of xanthan(XG)/guar gum(GG)mixture and its borax-crosslinking solutions were investigated under the influences of solution composition,pH,temperature and electrolyte(NaCl and CaCl2).Besides,the synergistic interaction between XG and GG was also examined.We expect this study could deepen the understanding of the rheological characteristics of XG/GG mixed solution,and also provide the basis for its practical application.The main conclusions of this thesis are as follows:(1)The XG or GG pure solution and their mixed solution(the concentration of CP = 0.20%)were pseudoplastic fluids.The flow pattern system(except the GG solution can form gel after crosslinked at CP = 0.20%,)was not affected by pH,temperature,electrolyte and borax crosslinker on the given conditions of the study.The rheological curves could be described by the Herschel-Bulkley and Casson models.(2)The mixture solutions of XG and GG showed significant synergistic interaction,and their strength were related to the XG/GG mass ratios.The strongest synergistic interaction was reached at a XG(FXG)mass fraction of 0.20 and 0.90.On the basis of the apparent viscosity(?105)variations at the shear rate of 105.1 s'1,the calculated value of "synergistic interaction ratio"(Rm)is about 42%and 34%,which is great significance for the practical application of the XG/GG mixed solution.(3)Borax can be crosslinked with the XG/GG in the mixed solution,and its crosslinked effect was enhanced by either the decreasing of FXG or the increasing of borax concentration(CB).The crosslinking viscosity increasing rate is up to 85%at the shear rate of 105.1 s-1 when the mass fraction of XG(FXG)is 0.50 and the concentration of XG/GG mixed solution(CP)is 0.20%and the concentration of borax concentration(CB)is 1.00 g/L.It indicates that borax crosslinking with the XG/GG mixed solution prompts their application values.(4)The rheological properties of the XG/GG mixed solution showed no significant change at the pH in the range of 6.2 to 10.0.Differently,the apparent viscosity of the XG/GG/B crosslinked system(CP = 0.20%,FXG = 0.50,CB =0.75-1.00 g/L)increased with increasing pH at beginning and decreased subsequently.The maximum value of apparent viscosity was reached at pH 9.0,meanwhile,crosslinking viscosity increasing rate was up to 107%.The apparent viscosity of the XG/GG mixed solution(CP = 0.20%,FXG = 0.50)was increased significantly after preheating at 40.0 0C and 60.0 ?,respectively.The ?105 value of it was 22%higher than the one without preheating.These results provide important information for their application.(5)The viscosity of the XG/GG/B crosslinked solution(CP = 0.20%,FXG = 0.10,CB = 0.50 g/L)decreased significantly in the presence of electrolyte NaCl and CaCl2,respectively.The weak salt resistance was exhibited from the given system,and the effect of CaCl2 was more notable than the one of NaCl.The improvements of its salt resistance remain to be addressed.In addition,we also explored the possibility of crosslinking between polyacrylamide grafted xanthan gum(PAM-g-XG)and alginate dialdehyde,which was based on Schiff-base.Unfortunately,it was not successful.The one possibility is that the two cannot react with each other(so far,it has not been reported that the amide participates in the Schiff-base reaction).The other is the fact that we may not find the appropriate reaction conditions.However,these preliminary exploratory findings are written in Appendix I as a reference for related study.