Preparation And Study Of Performance Of Thermal Induced HPMC Hydrogel

A new-style hydrogel were prepared by hydroxypropyl methyl cellulose in thermal induced way, after reviewing the solution property of cellulose ethers (hydroxypropyl cellulose HPC and hydroxypropyl methyl cellulose HPMC) and process of sol-gel transition of HPMC. The intelligent responding behaviors of this hydrogel were studied as well.The viscosity of HPC and HPMC solutions with different solvents were tested by Ubbelohde viscosity meter, and its intrinsic viscosity were calculated by a traditional way. Subsequent investigations about properties of dilute solution were carried out with intrinsic viscosity and the following findings can be concluded: first, in the solvents with strong polarity such as DMF, molecular chains show a curly state because of the presence of stronger hydrogen bond. Addition of Cl" will lead to weaken of hydrogen bond and molecular chains become more relaxed. At the same time, the reciprocity of short range between macromolecules declined due to the static repulsion of Cl^-. Critical overlap concentration (C^*) of different solution systems were estimated from experiential formula by intrinsic viscosity. The influence of molecular weight on C^* is remarkable, while solvent property has a weak effect. Fall of C^* can be observed after adding ions, as a result of the relaxation of molecular chains led by the static repulsion between ions.Rheological property of HPMC solutions were studied by rotary viscosity meter. The flow behavior is much more influenced by molecular weight than degree of substitution. Critical overlap concentration can be concluded from the rheological test. By fitting the curves of studied solutions, a mathematical model was established which show there is a coincident function relationship between flow behavior index and concentration: n=k^*exp(-C/t₀)+b.Thermoreversible gelation process of HPMC samples were reviewed on dynamic rheometer by analyzing the change of visco-elastic mechanical behavior. This process can be divided in two stages: pre-gel stage and gel stage. The hydrophobic association in heating process is not the same as the disassociation in cooling. Thermal gelation behavior is strongly influenced by the degree of substitution. More methoxy content and lower hydroxypropyl content is easier to form a gel at lower temperature. But the effect of molecular weight is different for two sample series. The sample with higher molecular weight gels easily for HF series whose thermal behavior is mostly controlled by methoxy groups while there is an opposite trend for HK series because of the predominant inhibition of hydroxypropyl groups.HPMC hydrogel were prepared by thermal induced way using different MW and DS samples and its swelling kinetics were researched at the same time. It was found that HPMC hydrogel has a good absorbency. Its swelling behavior processed in three steps and was accordant with Schott mode, namely, the relationship between the swelling ration and times follow the equation as: t/SR=A+Bt.Intellective responsive behavior of HPMC hydrogel has been investigated: equilibrium swelling ration decrease with the increase of temperature. The sensitivity of effect of temperature on equilibrium swelling ratio is different. Relationship between ESR and temperature for HK series display a square relation, while show linearity for HF series. Swelling behavior of HPMC hydrogel were also greatly influenced by solvents. Swelling ratio increase in strong polarity solvents because of the enhancement of hydrogen bond, while descend rapidly in weak polarity solvents. It is not very obvious for the effect of change of pH on swelling ability, but there are different reductions of absorbency due to salt-out action brought by the addition of ions from acid or base.The results of research about effect of MW and DS on swelling behavior are as following: owing to more hydrogen bond action between macromolecules, HK hydrogel which has higher hydroxypropyl and lower methoxy content get a better swelling ability than HF series. Equilibrium swelling ratio of HK series hydrogel increases with the augment of MW, while a contrast influencing trend can be observed for HF series hydrogel.