Thermal stability of carboxymethyl chitosan varying the degree of substitution

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Chitosan is a cationic copolymer of glucosamine and N-acetylglucosamine (Mourya, Inamdar,&Tiwari, 2010).Due toits non-toxicity, biodegradability, biocompatibility, bioadhesivity, antimicrobial activity and physicochemical and biological properties, chitosan can be applied in a variety of fields. However, the poor solubility in water and most common organic solvents limits its applications (Dash, Chiellini, Ottenbrite, &Chiellini, 2011).According to the literature (Du & Hsieh, 2008; Mourya, Inamdar, &Tiwari, 2010; Rinaudo, 2006) carboxymethylation is one of the chemical modification methods that increase the water solubility of chitosan. The carboxymethylation of chitosan enhances moisture retention and adsorption properties, chelating and sorption properties, antioxidant activity, antimicrobial activity, apoptosis inhibitory activity, etc.Among the applications of CM-chitosan, sustained or controlled release drug delivery, pH responsive drug delivery and DNA delivery as permeation enhancer (Mourya, Inamdar, &Tiwari, 2010) are important. Literature(Chen et al. 2004; Yu et al., 2006) showed that the location of substitution or type of CM-chitosan(N-, O-, N,O-, N,N-) in Scheme 1 and DS depend on the parent chitosan, reaction conditions and reaction reagents and their stoichiometry. Numerous works (Abreu &Campana-Filho, 2009; An, Dung, Thien, Dong, &Nhi, 2008; Anitha et al., 2009; Ge&Luo, 2005; Hjerde, Varum, Grasdalen, Tokura, &Smidsrod, 1997; Kittur, Harish Prashanth, UdayaSankar, &Tharanathan, 2002; Mourya, Inamdar, &Tiwari, 2010; Muzzarelli, Tanfani, &Emanuelli, 1984; Rinaudo, Dung, Gey, &Milas, 1992; Xu, Xin, Li, Huang, & Zhou, 2010) have been carried out on CM-chitosan. Du &Hsieh(2008) showed that longer alkalization and ca... ... middle of paper ... ... spacing) of CM-chitosan was different from chitosan. According to Fig.5, X-ray diffractograms, ordered arrangement of CM-chitosan was decreased with increase of DS. Therefore the crystallinityof CM-chitosan decreased with increaseof DS. 4. Conclusion CM-chitosan with different DS (53.4%, 62.0% and 72.5%) were synthesized by the reaction of chitosan with monochloroacetic acid. The structure was confirmed by FTIR and 1H NMR spectroscopy. According to TGA data, the onset of degradation occurred ~ 251.5 °C, 189.9 °C, 169.5 °C and 166 °C for native chitosan, DS 53.4% CM-chitosan, DS 62.0% CM-chitosan and DS 72.5% CM-chitosan, respectively. Therefore, thethermal stability of CM-chitosan decreased with increase of DS. The CM-chitosan had a different crystallinity compared to that of chitosan. Also less ordered arrangement was resulted with increase of DS of CM-chitosan.

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