| Chitosan(CS),poly(?-(1?4)-N-acetyl-D-glucosanmine),is a natural polysaccharide.Due to its intrinsic properties including biocompatibility,biodegradability,biological activity and abundance in nature,CS was enabled in a wide range of applications,such as in food industry,water treatment,tissue engineering,and cosmetic so on.There are abundance of active groups easily to be modified,such as-NH2,-OH and so on,thus many chitosan derivatives were developed.Much attention was paid to the foundational study and applications of chitosan derivatives in the past decades.Because of a higher melting temperature than the decomposition temperature,most of researches about chitosan and its derivatives were conducted in solution state.In this work,The solutions properties and thermal-responsible rheology behavior of CS modified by hydrophilic side chains of PAM,CS-graft-PAM(GPAM),in aqueous solution were investigated,the main content of this paper include:1.The formation of aggregations and stability of GPAM solution were examined.The water solubility of GPAM is improved than CS.GPAM solution appears an excellent shear resistance and low temperature stability.2.Thermo-thickening behavior of GPAM solutions were explored in the presence of HAc.The GPAM has an irreversible thermo-thickening phenomenon.Armed with dynamic laser scattering(DLS),rheological test,the mechanism of the formation of lager aggregations induced by HAc in thermo-thickening process is proposed.Based on molecular structure,HAc can promote the degree of protonation-NH2,causing the enhancement of hydrophilic and electrostatic repulsion,and it would result the formation of larger aggregations.3.The influence factors of thermo-thickening were investigated systematically,include concentration and graft ration of GPAM,shear stress,and the kinds of acid.A critical temperature and concentration of GPAM,appearing thermo-thickening,are put forward.With increasing concentration of GPAM,shear stress or in the strong acid,the larger aggregations is unstable,resulting weakness even disappearance of thermo-thickening.4.The rheological behaviors for binary system of GPAM/?-CD and CS/?-CD was studied preliminarily.Shearing induced thickening both existed in them,which has obvious dependence on the concentration of ?-CD.The discovery of thermo-thickening for GPAM provided a new view to prepare CS-based functional materials and enrich potential application and other similar system.The understanding based on its molecular mechanism can be extended to similar systems,providing a new way to prepare polymer rheological modulators and profile control agents based on thermal viscosity.In addition,binary system of GPAM/?-CD and CS/?-CD shows an unique shear induced thickening through combined with ?-CD,it provides another way in the research of polysaccharide. |
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