Characterization of chitosan. Influence of ionic strength and degree of acetylation on chain expansion (original) (raw)
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Biomacromolecules, 2004
Physicochemical properties of four different homogeneous series of chitosans with degrees of acetylation (DA) and weight-average degrees of polymerization (DP w) ranging from 0 to 70% and 650 to 2600, respectively, were characterized in an ammonium acetate buffer (pH 4.5). Then, the intrinsic viscosity ([η] 0), the root-mean-square z-average of the gyration radius (R G,z), and the second virial coefficient (A 2) were studied by viscometry and static light scattering. The conformation of chitosan, according to DA and DP w , was highlighted through the variations of R and ν parameters, deduced from the scale laws [η] 0) K w M w R and R G,z) K′M w ν , respectively, and the total persistence length (L p,tot). In relation with the different behaviors of chitosan in solution, the conformation varied according to two distinct domains versus DA with a transition range in between. Then, (i) for DA < 25%, chitosan exhibited a flexible conformation; (ii) a transition domain for 25 < DA < 50%, where the chitosan conformation became slightly stiffer and, (iii) for DA > 50%, on increasing DP w and DA, the participation of the excluded volume effect became preponderant and counterbalanced the depletion of the chains by steric effects and long-distance interactions. It was also highlighted that below and beyond a critical DP w,c (ranging from 1 300 to 1 800 for DAs from 70 to 0%, respectively) the flexibility of chitosan chains markedly increased then decreased (for DA > 50%) or became more or less constant (DA < 50%). All the conformations of chitosan with regards to DA and DP w were described in terms of short-distance interactions and excluded volume effect.
Typical Physicochemical Behaviors of Chitosan in Aqueous Solution
Biomacromolecules, 2003
Physicochemical properties of a homogeneous series of chitosans with different degrees of acetylation and almost the same degree of polymerization were investigated in an ammonium acetate buffer. Techniques such as interferometry, static light scattering (in batch or coupled on line with a chromatographic system), and viscometry were processed. All of the results agree with a unique law of behavior only depending on the degree of acetylation of the polymer. Indeed, values of the refractive index increment, radius of gyration, second virial coefficient, and intrinsic viscosity are decreasing in the same way as DA is increasing. Three distinct domains of DA were defined and correlated to the different behaviors of chitosans: (i) a polyeletrolyte domain for DA below 20%; (ii) a transition domain between DA ) 20% and 50% where chitosan loses its hydrophilicity; (iii) a hydrophobic domain for DAs over 50% where polymer associations can arise. Conformations of chitosan chains were studied by the calculations of the persistence lengths (L p ). The average value was found to be close to 5 nm, in agreement with the wormlike chain model, but no significant variation of L p with the degree of acetylation was noticed.
On the preparation and characterization of chitosan hydrochloride
Polymer Bulletin, 1999
The procedures for the purification of commercial chitosan samples as hydrochlorides and in the neutralized form are described. Thermal analysis reveals that, independently of the purification method, all samples are highly pure. The agreement between values of degrees of acetylation determined by conductimetric titrations and by 1 H nmr spectroscopy is very good. The aqueous solutions of both forms of purified chitosan were free of aggregation as evaluated by their Huggins constants. The potential use of solutions of chitosan hydrochloride in acid-free aqueous NaCl for the studies aiming to characterize the solution behavior of chitosan is demonstrated.
Carbohydrate Polymers, 2015
A viscometric study was carried out at 25 • C to assess the physical-chemical behavior in solution and the mean viscometric molar mass (M v) of chitosan solutions with different deacetylation degrees, in two solvent mixtures: medium 1-acetic acid 0.3 mol/L and sodium acetate 0.2 mol/L; and medium 2-acetic acid 0.1 mol/L and sodium chloride 0.2 mol/L. Different equations were employed, by graphical extrapolation, to calculate the intrinsic viscosities [Á] and the viscometric constants, to reveal the solvent's quality: Huggins (H), Kraemer (K) and Schulz-Blaschke (SB). For single-point determination, the equations used were SB, Solomon-Ciuta (SC) and Deb-Chanterjee (DC), resulting in a faster form of analysis. The values of −M v were calculated by applying the equation of Mark-Houwink-Sakurada. The SB and SC equations were most suitable for single-point determination of [Á] and −M v and the Schulz-Blachke constant (k SB), equal to 0.28, already utilized for various systems, can also be employed to analyze chitosan solutions under the conditions studied.
Chitosan: An Overview of Its Properties and Applications
Polymers
Chitosan has garnered much interest due to its properties and possible applications. Every year the number of publications and patents based on this polymer increase. Chitosan exhibits poor solubility in neutral and basic media, limiting its use in such conditions. Another serious obstacle is directly related to its natural origin. Chitosan is not a single polymer with a defined structure but a family of molecules with differences in their composition, size, and monomer distribution. These properties have a fundamental effect on the biological and technological performance of the polymer. Moreover, some of the biological properties claimed are discrete. In this review, we discuss how chitosan chemistry can solve the problems related to its poor solubility and can boost the polymer properties. We focus on some of the main biological properties of chitosan and the relationship with the physicochemical properties of the polymer. Then, we review two polymer applications related to green...
Some physical properties of chitosan in propionic acid solutions
2000
Surface tensions, contact angles and conductivities of propionic acid solutions containing different amounts of chitosan were measured at a room temperature to a temperature accuracy of ± 0.20o. The value of critical coagulation concentration (CCC) was then obtained from the plots of contact angle and conductivity versus concentration. Viscosity of the solutions with different concentrations was also measured in this
e-Polymers, 2008
Two salts of the biopolymer chitosan were prepared in aqueous medium by employing an excess of HCl or HNO 3 in order to ensure neutralization of all NH 2 -chitosan groups. Chitosan salts were extensively dialyzed in dionised water and dried at 40 ºC until film formation. The films were characterized by thermogravimetry, FTIR and conductimetric tritration. QH + Cl − and QH + NO 3 − salts were viscosimetrically evaluated in free acid aqueous solutions in the presence of NaCl to control ionic strength of the medium. Unexpected high intrinsic viscosity values were obtained at low ionic strength when QH + NO 3 − salt were evaluated.
Journal of Applied Polymer Science, 2002
Materials and methods Medium molecular weight chitosan [product batch #9012-76-4] with 75-85 % dcacetylated chitosan was purchased from Aldrich, Milwaukee, WI. Acetic acid [product batch #5-0994-494-138931J was purchased from s.d. fine Chemicals Ltd., Mumbai, India. The acetic acid purity, as assayed by gas chromatography, was 99.7 mol %, and its density was 1.0490 g/cnr1 at 293.15 K. Double-distilled deionized water was used throughout the research. Acetic acid-water mixtures were prepared by mass within an uncertainty of ±0.01 mg using an electronic single pan Mettler balance (A£ 240, Switzerland). Four chitosan con
Characterisation of chitosan solubilised in aqueous formic and acetic acids
2009
The intrinsic viscosity of chitosan (MW 7.9 x 10(5) g mol(-1)) having a high degree of deacetylation and solubilised in aqueous formic and acetic acids was determined at room temperature. Contact angle and conductivity of the chitosan solutions were also studied. The values of critical coagulation concentration (CCC) were then obtained from the plots of contact angle or conductivity versus concentration.
The degree of deacetylation (DDA) of various low molecular weight chitosan (LMWC) species as the hydrochloride and free base (amine form) was determined by direct and back potentiometric titration,respectively. The DDA values obtained for the chitosan hydrochloride by direct titration were greater than 93% for all oligomers tested (Molecular weight (Mwt) between about 1.3 to 30.0 kDa). However, the DDA values obtained for chitosan amine oligomers using back titration were significantly lower, especially for the relatively high molecular weight (30.0 kDa) chitosan amine oligomers. Furthermore, after using the back titration method, greater DDA values were obtained for the same samples of chitosan amine after the chitosan solution had been heated to 60EC before titration. In addition, the DDA values showed a significant decrease with increased concentration for a given chitosan oligomer. Although the effects of hydration time,ionic strength and method specific behavior were not explic...