Study On Preparation, Structure And Properties Of Quaternized Carboxyalkyl Chitosans

Chitosan(CTS) is a natural macromolecular compound from the deacetylation of chitin,which is about multibillion tons synthesized by biology annually.Chemical modification and embellishment for CTS is one of important way to improve its applying property.Quaternizing modification of carboxyalkylation chitosans(CA-CTSs) for preparing quaternized CA-CTSs (amphoteric chitosan),which has zwitterionic characterization as polymeric electrolyte,has been put forward in this dissertation.This is of great signification in development of potential applying value of chitosan.Steamy distillation combined with extraction and recrystallization using complex solvents is brought forward innovately to treat the products synthesized by reaction between trialkylamine or its hydrochloride salt and epichlorodrin.Four active quaternary salts including 3-chloro-2-hydroxypropyl tripropyl ammonium chloride(CHPTPA),3-chloro-2-hydroxypropyl dimethylbenzyl ammonium chloride(CHPDMBA),glycidyl tripropyl ammonium chloride(GTPA) and glycidyl tributyl ammonium chloride(GTBA) in which the content of quaterary salt is up to 98%were obtained firstly.CA-CTSs including N,O-carboxymethyl chitosan(N,O-CMC),N,O-1-carboxyethyl chitosan (N,O-1-CEC),N,O-2-carboxyethyl chltosan(N,O-2-CEC),N-carboxymethyl chitosan (N-CMC) and N-1-carboxyethyl chitosan(N-1-CEC) are quaternized using active quaternary salts prepared in laboratory.5 series including 25 kinds amphoteric chitosans characterized with polymeric ampholyte,in which 24 kinds are synthesized firstly,are obtained, 2-Hydroxypropyl dimethylbenzyl ammonium N,O-(1-carboxyethyl) chitosan chloride (GDMBA-N,O-1-CEC) is hydrolyzed into serial low molecular weight(Mw) GDMBA-N, O-1-CEC with acid as catalyst and microwave as assistant instrumentality innovately. A coagulant composed QCMC,which is the product of N,O-CMC quaternized by 3-chloro-2-hydroxypropyl trimethyl ammonium chloride(CHPTMA),with bentonite is brought forward innovately.This coagulant has a upstanding property to removal COD of print waste-water.The flocculating properties of QCMC are investigated systematically using print waste-water and simulating waste-water containing Cd(Ⅱ) or Cr(Ⅵ) as evaluating object.Results about studies of the dissolving behaviour of CA-CTSs and their quaternizing product using spectrophotometry method indicate there is affinity between their solvency and the pH of solution,and exist a pH(pH_iep or pI value) in which the water-solubility of quatemized CA-CTSs is the lowest.Different quaternized CA-CTSs possess different pI value.The increase of substituted degree of carboxyalkylation(DS) of quaternized CA-CTSs results in the decrease of their pI value while the increase of substituted degree of quaternization(DQ) results in the increase of pI value.When carboxyalkyl group and quaternary group are same, and the ratio of DQ to DS is similar,the pI values of amphoteric chitosans also are similar. The argar plate method is utilized to determine the minimum inhibitory concentrations(MICs) of amphoteric chitosans against Escherichia coli(E.coli) and Staphylococcus aureus(S. aureus).The relation between the antibacterial activity of quaternized CA-CTSs and their structure is investigated systematically.The results indicate that all of them have antimicrobial ability against E.coli and S.aureus,and the activities against S.aureus are much better than that against E.coli.When DS is similar,the antibacterial activity of N,O-1-CEC against the tested bacteria is higher than that of N,O-2-CEC.When the carboxyalkyl group is same and the DS is similar,the antibacterial ability of N,O-CA-CTS and N-CA-CTS also is similar.The antimicrobial activities of amphoteric chitosans against the tested bacteria are much stronger than that of CA-CTSs and quatermized CTS(QCTSs).The increase of carbon numbers of carboxyalkyl and quaternary group could result in the improvement of antibacterial activity of amphoteric chitosans,and the existence of dimethylbenzyl in quaternary group could endow amphoteric chitosans with much better antibacterial activity.The decrease of Mw and the increase of DQ of GDMBA-N,O-1-CEC could improve its antibacterial activity against E.coli and S.aureus.When the DS is 0.837,the DQ is 0.537 and the Mw is 3300,the MICs of GDMBA-N,O-1-CEC against E.coli and S.aureus are 25μg/mL and 12.5μg/mL,its antibacterial activities are better than that of Bromo-Geramium(the MICs of Bromo-Geramium against E.coli and S.aureus are 31.3μg/mL and 15.6μg/mL,respectively).Study on the flocculating properties of QCMC shows it has a good removal ability to Cd(Ⅱ) and Cr(Ⅵ) in simulating waste-water and dyestuff in industrial waste-water.The utilization of assistant flocculant could improve the ability of QCMC to remove dye.When the substitution degree of carboxymethylation(DS of CM) is 0.856 and DQ is 0.614,the appropriate pH of QCMC for removal of Cd(Ⅱ) and Cr(Ⅵ) are ca 8.5 and 5.0,and the appropriate mass concentrations of flocculant are 140mg/L and 120.0mg/L,respectively.Under these conditions, the removal ratio of Cd(Ⅱ) and Cr(Ⅵ) may reach 99.7%and 94.4%,respectively.When the pH is 5.0-6.0,bentonite is utilized as assistant flocculant and the m_Bentonite/m_QCMC=40,and the utilizing amount of complex flocculant composed of bentonite and QCMC is 2500-3000 mg/L, the COD removal ratio of wastewater treated in study is above 80%.This value is much higher than that of PAC and PAM to the test waste-waters.