| Cellulose is a kind of innoxious natural polymer material with abundant natural resources, polymerization degree, molecule orientation degree and chemical stability. It is distinguished from many synthesized polymers by the excellent biological compatibility and biological degradation property. Through chemical reactions with the active hydroxyl groups in its molecules, a series of modified polymers can be prepared, which can be widely used in the fields of oil recovery, construction, coating, polymerization, food, medicine, cosmetic and so on.In this study, the hydrophobic monomers, such as 1-Bromododecane, 1,2-Epoxydecane, 1,2-Epoxyhexadecane and 1,2-Epoxyoctadecane, were applied to the hydrophobic modification of a class of nonionic cellulose ether derivative-hydroxyethyl cellulose (HEC). Through the macromolecule reaction method, the hydrophobically-modified hydroxyethyl cellulose (HAHEC) was prepared, which aimed to improve the viscosification property of HEC, endow it with unique rheological behavior and make researches on the supramolecular structure and the viscosification mechanism, which could provide the theory basis for the further application of HEC as fluidity-controlling agent.Accessibility and the activation degree of hydroxyl groups of cellulose are significant factors that influence its chemical reaction and the properties of the product. The effect of synthesis technique parameters, such as activating agent concentration, HEC concentration, hydrophobic monomer content, reactionLiterature and reaction time, on the rheological behavior of HAHEC wassystematically studied. The optimum parameters were determined to assure that the cellulose molecules can achieve proper activation degree and accessibility, and the reaction system can be situated in the most proper swelling and dispersing state. A series of HAHEC with excellent rheological behavior, including BD-HAHEC, EP10-HAHEC, EP16-HAHEC and EP18-HAHEC, were synthesized. The apparent viscosity of BD-HAHEC reached 450mPa s at 0.45g/dl polymer concentration, while for the same kind of HAHEC as reported in the literature, the same apparent viscosity can be achieved at 2g/dl polymer concentration. EP16-HAHEC even has the lower critical associating concentration and the better viscosification property than BD-HAHEC.The solution properties of HAHEC were comprehensively studied. The effect of different kinds of hydrophobic monomers on the viscosification property was investigated, which showed that HEC modified by hydrophobic monomers with 12-16 hydrophobic carbon chain length displayed excellent rheological behavior. Addition of electrolyte led to the much stronger hydrophobic association of the polymer molecules and the viscosification performance of HAHEC was greatly enhanced due to the increase of the polarity of the polymer aqueous solution. With asc uf NaCl concentration, the apparent viscosity of HAHEC got to the climax at 5-6%(wt%) NaCl concentration and then decreased due to the phase separation caused by the too strong inter-molecule hydrophobic association. HAHEC also exhibited complex rheological behaviors under shearing application. At a specific shear rate, the apparent viscosity of EP16-HAHEC initially decreased with time and then increased to a certain value due to the reformation of supramolecular network led by the orientation of the polymer molecules under shearing fields, while such phenomenon was not observed for BD-HAHEC solution. Amphiphilic structure of HAHEC molecules contributes to the surface activity of HAHEC, which led to the decrease of surface tension with the increase of the polymer concentration. Near the critical association concentration (Cp*) of HAHEC,however, the surface tension increased to some degree. Good thermal stability of HAHEC was confirmed by thermal aging measurements and the 30% of initial apparent viscosity of BD-HAHEC was maintained after aging at 70℃ for 20 days. Through forming complex micelles with hydrophobic groups, surfactants could cross-link polymer molecules of HAHEC and led to the...
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