2). Due to the incomplete deacetylation of CTS, absorption bands of the C=O group were identified at 1750 and 1650 cm-1 superimposed on the band of an NH.
Fibre Chemistry, Vol. 40, No. 1, 2008
PHYSICOCHEMICAL PROPERTIES OF CHITOSAN FROM DIFFERENT RAW MATERIAL SOURCES V. F. Abdullin,* A. B. Shipovskaya,** V. I. Fomina,*** S. E. Artemenko,* G. P. Ovchinnikova,* and E. V. Pchelintseva*
UDC 547.1.002.61:547.995
A microelemental, thermal, and IR spectroscopic analysis of samples of chitosan separated from fresh- and salt-water crustaceans was performed. The viscometric and optical properties of the solutions made from them freshly prepared and during storage were investigated. It was found that the physicochemical characteristics of crayfish shell chitosan almost do not differ from the indexes for the industrial polymer prepared from a traditional source of raw material crab shells. This allows considering crayfish shells as an alternative raw material resource for obtaining chitosan.
The natural polysaccharide chitosan (CTS) is used in the chemical, cosmetics, and food industries, in agriculture, and in human and veterinary medicine [1-3]. Commercial marine crustacean shells are the basic raw material source in industrial production of CTS. In view of the cost and uniqueness of this product and the enormous area of practical application, searching for different accessible resources capable of ensuring wide production of CTS is pressing. For regions distant from the sea, this problem can be solved by using objects from our own industry, for example, crayfish shells. Not only will the raw material base for CTS technology expand significantly, but the cost of the final product will decrease significantly. The possibility of obtaining chitin and CTS from crayfish shells was reported earlier [4-7]. A comparative analysis of the physicochemical properties of CTS obtained from different raw-material sources is reported here: salt-water crab and fresh-water crayfish shells. Samples of CTS obtained from crab shells (CrS) in industrial conditions at Bioprogress AOZT and from crayfish shells (CS) in laboratory conditions with our technology [5] and from solutions and films were investigated. The samples are characterized in Table 1. The samples of CTS investigated had a similar degree of deacetylation, almost did not differ in molecular mass (except for CTS-1), and did not dissolve in distilled water. The viscosity-average molecular weight of the polysaccharide was determined viscometrically by the standard method and calculated with the MarkKuhnHouwink equation with the constants from [8]. The viscosity was measured in a Ubbelohde viscometer with a 0.54-mm capillary diameter at 25°C. Solutions of 0.05 and 0.5 g/dl concentration were prepared by dissolving a weighed portion of polymer powder in CH3COOH (0.33 mole) + CH3COONa (0.2 mole) acetate buffer for several days. Cp glacial acetic acid and sodium acetate were used. The degree of deacetylation of the samples was determined by potentiometric titration. The optical rotation spectra of the CTS solutions were made on a SPU-E automatic spectropolarimeter in the wavelength range of λ = 300-710 nm at t = 25°C. A high-pressure DRSh-250 mercury lamp was the light source. Glass thermostated cuvettes 1 dm long with quartz windows were used. The specific optical rotation [α] was determined according to the recommendations in [9]. The concentration of the solutions was 0.2-0.5 g/dl. Acetate buffer and an aqueous solution of acetic acid with a concentration of 2 and 4% were used as the solvent. Before the study, the solutions were filtered through a Schott No. 160 filter. The optical rotation scattering curve (ORS) was plotted with data from three parallel experiments. *Engels Institute of Technology, SSTU; **N. G. Chernyshevskii Saratov State University; ***Scientific-Research Institute of Natural Sciences, Saratov State University. Translated from Khimicheskie Volokna, No. 1, pp. 33-36, JanuaryFebruary, 2008. 40
0015-0541/08/4001-0040 © 2008 Springer Science+Business Media, Inc.
TABLE 1. Characterization of Chitosan Samples Source of raw material
Moisture content, %
CTS-1
CrS
CTS-2 CTS-3
Molecular weight, M ç ⋅ 10−5
Degree of deacetylation, mole %
10.5
6.4
82.6
CrS
10.8
2.8
80.8
CS
9.6
2.7
89.6
CTS-4
CS
7.8
2.6
89.6
CTS-5
CS
8.5
3.5
86.1
CTS-6
CS
8.5
2.2
91.4
Sample name
TABLE 2. Qualitative Mineral Composition of Chitosan Samples Element
Source of raw material CrS
CS
+
+
Si
+
tr
Fe
tr
tr
Mg
bas
bas
Na
tr
tr
Ti
+
+
Al
+
+
Ca
bas
bas
B
______________
Notation: bas basic element; + element detected; tr element present in trace amounts.
The turbidity spectrum method was used to determine the parameters of supramolecular formations such as the average particle diameter ( rë ) and the number (N2) and weight (C2) concentration in solutions of CTS with a concentration of C = 0.5 g/dl [10, 11]. The optical density was measured on a KFK-2 photocolorimeter in the wavelength range of λ = 400-590 nm at t = 20°C. The value at λ = 490 nm was used for comparative characterization of the turbidity (τλ) of the investigated systems. The conditions of preparing the solutions and the time of beginning measurements of the physicochemical properties were the same in all experiments. The limiting viscosity number [η] of freshly prepared solutions used to calculate M ç and the specific optical rotation [α], τλ, rë , N2, and C2, determined in the first days after preparation were used as the initial values. Samples were collected as the systems were held in static conditions at t = 20±2°C to study the hydrodynamic and optical properties of the CTS solutions during storage. The elemental composition of the mineral constituent of the polymer was investigated by atomic emission spectral analysis on a setup consisting of a PGS-2 spectrograph, HFI-1 high-voltage pulsed spark generator, and 32-G368 spark frame. The samples of CTS from different raw material sources were incinerated in a furnace at 300°C for 4 h, ground to the consistency of fine powder in an agate mortar, mixed with carbon powder in the ratio of 2:1, and placed in the cavity of carbon electrodes. Parallel spectra were recorded for each sample. The structure of the CTS samples was investigated by IR spectroscopy on an Infralum FT-801 Fourier spectrometer. The differential thermal (DTA) and thermogravimetric analysis (TGA) curves were made on a Derivatograf at a heating rate of 10°/min in air medium in the 20-700°C temperature range until the products of thermolysis had totally burned up. The samples were prepared in the form of films by molding them from CTS solutions with a concentration of 0.5 g/dl in an aqueous solution of acetic acid (C = 2%) in standard conditions by pouring on a horizontal polyethylene support with a round glass die. Molding took place for 72-96 h. Elimination of the solvent was monitored by the change in weight and the films did not undergo additional drying. The thickness of the dry films, measured with a micrometer, was 150 μm. The results of studying the qualitative mineral composition of the CTS samples obtained from salt-water crab and crayfish are presented in Table 2. Note that the elemental composition of the samples did not differ. Calcium and magnesium 41
Endo ΔT Exo
I 1
2 1 200
400
600
800 T
20
2
40 60 80 Δm
4
3
2000
1500
Fig.1
1000
500 ν
Fig.2
Fig. 1. DTA (1, 2) and TGA curves (3, 4) of film samples of CTS-2 (1, 3) and CTS-3 (2, 4): Δm weight loss, %; T temperature, °C. Fig. 2. IR spectra of samples of chitosan obtained from salt-water crab (1) and crayfish shells (2): I transmission, %; ν wavenumber, cm-1.
TABLE 3. Dependence of the Limiting Viscosity Number of Solutions of Chitosan in Acetate Buffer on the Duration of Storage 25 Ñ [η] ° , dl/g
Sample
C, g/dl
Δ[η], % storage time, days
0
14
21
14
21
CTS-1
0.05
11.9
11.7
10.8
1.7
9.2
CTS-2
0.05
5.8
5.3
5.1
8.6
12.1
CTS-3
0.5
5.6
5.4
⎯
3.6
⎯
CTS-4
0.5
5.4
5.2
5.1
3.7
5.6
CTS-5
0.5
6.9
6.7
⎯
2.9
⎯
CTS-6
0.5
4.8
4.7
4.5
2.1
6.3
are the basic trace elements in CTS from both sources. Boron, aluminum, and titanium were also present in all samples, while silicon was present in CrS CTS. Iron and sodium were found in trace amounts and silicon was found in the samples of CTS from CS. The raw material used for industrial production of CTS salt-water crab shells contains a certain amount of mineral contaminants based on calcium and magnesium carbonates [1-3]. The mineral constituent is not totally removed even after severe chemical treatment, so that the final product always contains a small amount of these elements. The comparative analysis of the qualitative mineral composition of samples of CrS and CS (see Table 2) suggest that the elements found in CS CTS accumulate in the shells of the crayfish, as they do in salt-water crab shells, during vital activity as a result of different metabolic processes. This is in particular confirmed by the low ability of CTS (and in many cases the absence of this ability) to sorb the metals indicated in Table 2 [12]. The thermoanalytical study of polymer films made from both types of raw material indicate the similar behavior of CTS samples from CrS and CS in polythermal conditions (Fig. 1). A broad endothermic peak with a minimum at 118-120°C (curves 1 and 2) is observed on the DTA curves of CTS-2 and CTS-3 films in the 60-160°C temperature region. This effect is accompanied by 10-15% weight loss (curves 3 and 4) due to breaking of a salt bond, evaporation of acetic acid, and desorption of moisture. In the 240-300°C range, destructive processes evolve in both samples, and on attaining 300°C, the total weight loss is greater than 50%. In the 300-460°C region, further slow weight loss takes place, constituting almost 70% at 460°C. No 42
TABLE 4. Dependence of Turbidity and Supramolecular Particle Parameters of Solutions of Chitosan in Acetate Buffer on the Duration of Storage -1
τλ , cm
rë , nm
Sample
N2⋅10
-10
-3
5
, cm
-3
C2⋅10 , g⋅cm
storage time, days 0
14
21
0
14
21
CTS-1
0.09
CTS-2
0.04
CTS-3 CTS-4 CTS-5 CTS-6
0.09
0.08
130
125
100
0.12
0.14
1.10
1.2
1.2
2.4
0.04
0.04
30
25
35
64.3
77.1
56.7
2.9
2.4
5.4
0.21
0.21
0.19
150
150
135
8.42
9.12
15.4
4.2
4.1
4.3
0.18
0.17
0.17
140
135
120
0.14
0.19
0.95
2.6
2.6
2.7
0.11
0.11
0.11
90
90
80
1.27
1.31
1.84
5.2
5.2
5.8
0.14
0.14
0.13
150
150
125
0.12
0.13
0.10
2.7
2.8
3.1
300
400
500
0
600
14
700
21
0
14
21
λ
[α]tλ -20 -40 -60
1 2 3 4
-80
Fig. 3. ORS curves of solutions of CTS-1 (1, 2) and CTS-5 (3, 4) in acetate buffer (1, 3) and acetic thermal effects were identified on the DTA curves. In the 460-700°C region, the products of decomposition burn up, and an exothermic peak with a maximum at 550-570°C appears on the DTA curves. The IR spectroscopic study of the samples of CTS obtained from crayfish and marine crab shells showed the identity of their chemical structure. Absorption bands characteristic of CTS in the 1650-1560 cm -1 (absorption of primary amino groups), 2890, 1460, and 1300-1150 cm-1 (absorption of the CH2 group), 1380 cm-1 (absorption of the CH2CO) bond, and 1150-1000 cm-1 (absorption of the COC glycoside bond) are present in the IR spectra of samples from both sources (Fig. 2). Due to the incomplete deacetylation of CTS, absorption bands of the C=O group were identified at 1750 and 1650 cm-1 superimposed on the band of an NH 2 group. In addition, there are weak absorption bands at 890-880 and 800-790 cm-1 responsible for the deformation vibrations of the C1H group and pulsing vibrations of the pyranose ring in β-sugars. The weak band at 1540-1550 cm -1 present in the IR spectra of all of the samples which corresponds to stretching vibrations of COH groups bound by hydrogen bonds with metal atoms should also be noted. This is in agreement with the respects of the microelemental analysis reported in Table 2. The scattering of the characteristic bands by wavenumbers observed in the IR spectra of the CTS sample from CS and CrS (see Fig. 2) is comparatively small. It could be due to structural-molecular inhomogeneity caused by the different degree of deacetylation of the samples, their polydispersity with respect to the molecular weight, etc. These circumstances are not only characteristic of the samples investigated here. They reflect a specific feature of production of CTS in heterogeneous conditions as a result of uncompleted polymer-analog transformations and correspondingly, the block structure of this polymer [13]. Since processing and use of CTS involve conversion of the CTS to the viscous-flow state, we investigated the hydrodynamic and optical properties of the solutions. The viscometric parameters of freshly prepared solutions of CTS in acetate buffer and solutions stored for different times are reported in Table 3. The concentration dependence of the reduced specific viscosity, used in determining [η], had an unusual linear character for the solutions of all of the samples. Table 3 shows that the limiting viscosity number [η] regularly decreases in holding these 43
systems in time. For example, the decrease in the viscosity Δ[η] of solutions of CTS-1 and CTS-2 from CrS was 9-12% over 21 days, while it was approximately 6% for solutions of CTS-4 and CTS-6 from CS in the same conditions. The effect of the instability of CTS solutions in acid and buffer media is well known [14-16]. Despite the higher values of Δ[η] for solutions of CrS CTS, the irreversible decrease in the viscosity of all systems investigated when they were held in time in the absence of an external field was almost the same. The higher values of Δ[η] of solutions of CS CTS are probably due to their lower concentration, since the decrease in the viscosity of solutions of CTS in acetone buffer are more pronounced in time the lower the concentration of the polymer in the solution [16]. The study of the supramolecular order of CTS solutions by the turbidity spectrum method (Table 4) showed that the experimentally established turbidity level τλ of solutions of both samples was low. The value of τλ of solutions of CrS CTS was slightly lower than for CS CTS, which could be due to the different degree of purification of the samples. There was no clear correlation between the particle size and number and weight concentration with the type of raw material. No significant variation in the supramolecular parameters of the solutions of CTS of different origin was found during storage. A weak dependence of τλ rë , N2, and C2 on the storage time for at least 14 days was characteristic of all of the systems. CTS, like other polysaccharides, is an optically active polymer due to the presence of chiral centers in the glucopyranose rings. Since optical activity is extremely sensitive to fine structural changes in a substance [8], the ORS of solutions of CTS of different origin was measured in different media and in time. As Fig. 3 shows, the scattering curves for solutions of CTS-1 and CTS-5 are identical in both acetate buffer and in aqueous solution of acetic acid. In addition, these systems are characterized by the stability of the optical activity in time: in prolonged storage of the solutions (for up to 1 month), neither the specific optical rotation [α] nor the shape of the ORS curves change very much. All of the above also holds for the other samples investigated. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
44
R. A. A. Muzzarelli, Chitin, Pergamon Press, Oxford (1977). K. G. Skryabin, G. A. Vikhorevaya, and V. P. Varlamov (eds.), Chitin and Chitosan: Fabrication, Properties, and Use [in Russian], Nauka, Moscow (2002). L. S. Galbraikh, Sorosovsk. Obrazovat. Zh., 7, No. 1, 51-56 (2001). R. R. Uteushev and M. D. Mukatova, in: Proceedings of the 8th International Conf. Current Prospects in Chitin and Chitosan Research [in Russian], Kazan (2006), pp. 64-68. RF Patent No. 2277543, Int. Cl. C 08 B 37/08, Method of Fabrication of Chitosan. V. F. Abdullin, A. B. Shipovskaya, and O. A. Suraeva, in: Proceedings of the V All-Russian Conference of Young Scientists Current Problems in Theoretical and Experimental Chemistry [in Russian], Saratov (2005), pp. 218-219. V. F. Abdullin, S. E. Artemenko, et al., in: Proceedings of the 8th International Conference Current Prospects in Chitin and Chitosan Research [in Russian], Kazan (2006), pp. 7-10. A. I. Gamzazade, V. M. Shlimak, et al., Acta Polym., 36, No. 8, 420-424 (1985). Ch. F. Kettering, Newer Methods of Polymer Characterization, Wiley, New York, London, Sydney (1964). V. I. Klenin, Thermodynamics of Systems with Flexible-Chain Polymers [in Russian], SGU, Saratov (1983). V. I. Klenin, S. Yu. Shchegolev, and V. I. Lavrushin, Characteristic Light-Scattering Functions of Disperse Systems [in Russian], SGU, Saratov (1977). L. F. Gorovoi and V. N. Kosyakov, in: Chitin and Chitosan: Fabrication, Properties, and Use [in Russian], Nauka, Moscow (2002), pp. 217-246. A. I. Gamzazade, Ibid., 112-118. A. M. Sklyar, A. I. Gamzazade, et al., Vysokomolek. Soedin., 23A, No. 6, 1396-1403 (1981). L. A. Nudga, A. M. Bochek, et al., Zh. Prikl. Khim., 66, No. 1, 198-202 (1993). V. I. Fomina, N. A. Solonina, et al., in: Proceedings of the 7th International Conference Current Prospects in Chitin and Chitosan Research [in Russian], Repino, St. Petersburg (2003), pp. 367-371.
