Studies On The Degradation Of Chitosan And Intrinsic Viscosity Determination Of Polymer Solution

1. Study on the Degradation of Chitosan by Using FeCl₃ as catalystChitosan and its derivatives are broad used, but the molecular weight of coarse products of chitosan is very large, usually from several hundred thousand to several million, and chitosan can not dissolve in water but only dissolve in acid or acidic liquor, thus the application of chitosan is mostly limited, so it is very important to change the dissolving ability and the molecular weight of chitosan, low and water soluble chitosan can usually prepared by degradation. at present, there are some method on the degradation of chitosan including acid degradation , enzymes degradation, oxidation degradation and physical degradation.Now the society put more and more importance on environment, chemists aim to make chemistry reaction not only economy but also environmental conservation, considering above factor and controllability of speed on chitosan degradation, we put a little amount of ferric salt into chitosan solution dissolved by 0.5% HAc solution. the degradation in this system the best conditions of the reaction are studied. The results show that the kinds of anion in ferric salt act little, the best conditions of the reaction by the catalysis of FeCl₃ are as follows: the temperature is 75℃; n (FeCl₃):n (CS)=1:5; c(CS)=1 mmol/100 mL; c(CS)=0.5%. we can get different molecular weight of chitosan by controlling reaction time on the best condition. chitosan can be degraded from 1.46 million to 0.6 million by reacting 10 hours under the best condition.This method is mild with controllable molecular weight of the production, besides, it is economical and environmental because ferric saults are cheap and less contaminative.2. Study on the oxidative degradation of chitosan with Hydrogen Peroxide Catalized by Keggin-structure heteropolymolybdovanadophosphate.In recent years, there are many studies on the oxidative degradation of chitosan, among which hydrogen peroxide is studied most, the strongpoints of this method there is no residual poison of the reaction with hydrogen peroxide, and the reaction is easy to dealt with, so this method has been applied to produce chitosan with lowmolecular weight. degradation with hydrogen peroxide can react both in acidic and basic condition, and neutral condition is also ok. This chapter aims to improve the degradation efficiency by speeding the degradation, cutting degradation time and amount of hydrogen peroxide, thereby finding a green method to prepare low molecular weight with high efficient. We studied the oxidative degradation with hydrogen peroxide catalized by heteropolymolybdovanadophosphate both in homogeneous and heterogeneous condition by adding a little amount of heteropolymolybdovanadophosphate into chitosan solution, and the impact factors of the degradation under two different case were discussed.The results show that a little amount of heteropolymolybdovanadophosphate can remarkably speed the degradation, the best conditions of the oxidative degradation of chitosan with hydrogen peroxide catalized by heteropolymolybdovanadophosphate in homogeneous condition are as follows: the ratio of catalyst and chitosan is 1 to 10, concentration of hydrogen peroxide is 0.15%, the temperature is 80℃, reaction time is 2h. 0.2g chitosan was degraded under the best condition and the molecular weight by viscometry was degraded from 1460000 to 7812. then water-soluble chitosan was obtained by this method; The heterogeneous method is a high efficient way, the best condition of this method are as follows: the ratio of catalyst and chitosan is 2 to 100, the volume of 30% hydrogen peroxide is about 3mL, the temperature is 90℃, reaction time is 5min～30min. low molecular weight by viscometry from 2000 to 9000 can be prepared by degrading 1 g chitosan under this condition. degradation of chitosan by this method is simple and convenient with fewer dosage of catalyst and hydrogen peroxide, besides, the reaction time is very short.3. A Novel Method for Intrinsic Viscosity Determination of Polymer SolutionThere are many methods for molecular weight determination of polymers, among which viscometry is used most, it has been broad applied both in production and scientific research. This method is easy to operate with simple instruments and is applicable for broad-range molecular weight, additionally, it has high precision.In many conditions, the intrinsic viscosity of homogeneous polymers should be determined repeatedly, it is very inconvenient and time-consuming to do the determination by extrapolation for more than three relative viscosity of the sample should be determined, especially it is difficult to determine the intrinsic viscosity ofpolymers when there is little amount of sample. Therefore, a shortcut namely one point method was found by which only one relative viscosity should be determined, then intrinsic viscosity of polymer solution can be calculated by one point method equation. There are many literatures about one point method equations, those equations have some disadvantages such as complicated to calculate, too much parameters and low accuracy. as a result of this, we put forward a novel empirical equation for intrinsic viscosity determination of polymer solution by one point method, and the equation was testified by using the data reported in the literatures, the results indicate that new one point method equation for intrinsic viscosity determination of polymer solution possesses high accuracy and broad applicability, and it is simple and easy for operation.