ISSN 1070-4272. Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 5, pp. 806 !810. + Pleiades Publishing, Inc., 2006. Original Russian Text + E.S. Sashina, A.V. Vnuchkin, N.P. Novoselov, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 5, pp. 816 !820.

ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ

MACROMOLECULAR CHEMISTRY ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ AND POLYMERIC MATERIALS

Properties of Films Prepared from Solutions of Fibroin!Cellulose Blends in N-Methylmorpholine N-Oxide E. S. Sashina, A. V. Vnuchkin, and N. P. Novoselov St. Petersburg State University of Technology and Design, St. Petersburg, Russia Received January 17, 2006

-

Abstract The physicomechanical properties and thermal stability of films prepared from solutions of fibroin3cellulose blends in N-methylmorpholine N-oxide were studied. DOI: 10.1134/S1070427206050211

The unique physicomechanical properties of fibroin, a natural polymer, are well known [1]. This polypeptide is the main component of silk threads and cobweb and consists to more than 80% of the simplest amino acids (glycine, alanine, serine). The content of crystalline fraction of the polymer can be as high as 70%. In this fraction, the macromolecules form antiparallel b-folded structure and a-spiral secondary structure.

eral compounds) and wood sulfite pulp with the degree of polymerization of 495. The polymers were dissolved in NMMO at 95oC for 235 h. The resulting solutions with the polymer concentration of 4% were mixed to obtain solutions with the fibroin/cellulose ratios of 90/10, 50/50, 30/70, and 10/90. The films were prepared by application of these solutions to glass plates with subsequent coagulation with aqueous alcohol. After coagulation, the films were washed with distilled water to completely remove the solvent and were dried in air. The film thickness was 10 3 30 mm.

The possibility of using fibroin in the form of powders, gels, and films for biotechnological and biomedical purposes was studied in [23 4]. Fibroin membranes can be used to separate aqueous alcoholic solutions and to immobilize enzymes. Fibroin is a biocompatible compound suitable for preparing contact lenses.

The physicomechanical properties of the films were studied on an Instron tensile-testing machine in accordance with DIN EN ISO 527-3. The IR spectra were recorded on a IFS25 IR spectrometer. Thermal gravimetric analysis was performed in air on a MOM Q-1500D derivatograph (Hungary) in the temperature range 233500oC. The heating rate was 2.5 deg min31.

The main disadvantage of films prepared from fibroin solutions is their high brittleness. Dry films are virtually unsuitable for practical purposes. Fibroin in natural silk threads is plasticized with natural sericin, which imparts strength and elasticity to silk. Therefore, we studied blends of fibroin with other polymers [5, 6] with the aim to improve the film properties. Taking into account the possible applications of the films, we used natural and biodegradable polymers as the second component.

The IR spectra of recovered fibroin, cellulose, and their blends with different ratios of the components are shown in Fig. 1. The band assignment is given in Table 1. According to the published IR data, the crystalline fraction with the b-structure has particular spectrum, whereas the IR spectra of the a-spiral crystal structure are similar to those of the amorphous random globules [9313]. Therefore, we could not distinguish the a-structure and the amorphous fraction by IR spectroscopy. The bands at 1624 (Amide I), 1521 (Amide II), and 671 cm31 (Amide V) in the spectrum of fibroin (curve 6) can be assigned to the crystalline b-structure. The band at 1230 cm31 (Amide III) in the spectrum of pure fibroin suggests that a part of the macrololecues has the a-spiral or random globule conformation. The cellulose spectrum (curve 1) is typical of cellulose II [14].

In this study we examined properties of films prepared from solutions of fibroin3cellulose blends. N-Methylmorpholine N-oxide (NMMO) readily dissolving cellulose [7] and fibroin [8] was used as the solvent. EXPERIMENTAL We used the following polymers: fibroin of Bombyx mori silk (washed to remove fat, wax, and min806

PROPERTIES OF FILMS PREPARED FROM SOLUTIONS

807

n, cm!1 Fig. 1. IR spectra of the films of (1) 100% cellulose, fibroin3cellulose [component ratio: (2) 10/90, (3) 30/70, (4) 50/50, (5) 90/10], and (6) 100% fibroin; the same for Fig. 2. (A) absorption and (n) wavenumber. The same for Fig. 2. RUSSIAN JOURNAL OF APPLIED CHEMISTRY

Vol. 79

No. 5

2006

808

SASHINA et al.

Table 1. Assignment of the absorption bands in the IR spectra of the films of fibroin3cellulose blends to various fibroin conformations

ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ ³ Frequency, cm!1 Absorption band ÃÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄ ³ 100% fibroin ³ 90 : 10 ³ 50 : 50 ³ 30 : 70 ³ 10 : 90 ³ 100% cellulose ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄ Characteristic fibroin bands Amid I (C=O) Amid II (N3H bound, C3N) Amid III (C3N, N3H bound) Amid V Gly3Gly Gly3Ala

³ ³ ³ ³ ³ ³ ³ ³

1624 (b) ³ 1652 (a) 1521 (b) ³ 1560 (a), ³ 1521 (b) 1230 (a) ³ 1265 (b), ³ 1232 (a) 671 (b) ³ 669 (b) 1014 ³ 1020 987 ³ 987

³ 1627 (b) ³1654 (a), 1629 (b)³ 1635 (b) ³ ³ 1521 (b) ³ 1521 (b) ³ 1558 (a), ³ ³ ³ ³ 1531 (b) ³ ³ 1232 (a) ³ 1234 (a) ³ 1232 ³ ³ ³ ³ ³ ³669 (b), 628 (a)³ 669 (b), 617 (a) ³667 (b), 630 (a)³ ³ 1018 ³ 1020 ³ 1020 ³ ³ 987 ³ 987 ³ 987 ³

1637 1541 1232 673, 605 1028 997

Characteristic cellulose bands

³ 3417 ³ 3371 ³ 3400 ³ 3400 ³ 3417 ³ 3384 ³ 3 ³ 1419 ³ 1425 ³ 1423 ³ 1423 ³ 1419 ³ 1375 ³ 1375 ³ 1373 ³ 1375 ³ 1371 ³ 1375 ³ 671 ³ 669 ³ 669 ³ 669 ³ 667 ³ 673 ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄ

O...H OH CH2 OH

The IR spectra of the films of fibroin3cellulose blends (curves 2!5) contain the typical bands of the components and new bands assigned to the spiral and random conformations of fibroin macromolecules (printed italic in Table 1). The spectrum in the range 1250 3800 cm31 characterizing the primary polypeptide structure changes. The bands of the Gly3Gly units at 1014 cm31 change to the greatest extent. The frequency and the intensity of the bands of H-bonded hydroxy groups of cellulose at 3384, 1419, and 673 cm31 change in the spectra of the films of the blends. These data suggest that the hydroxy groups of cellulose macromolecules form intermolecular hydrogen bonds with the amide groups of fibroin and prevent b-folding of the polypeptide macromolecules. Table 2. Physicomechanical properties of films of fibroin3 cellulose blends

ÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄ Fibroin content ³ Tensile strength, ³ Elongation ³ at break, % in the blend, % ³ N mm!2 ÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ 100 ³ 31.1 ³ 2.9 90 ³ 31.2 ³ 3.1 50 ³ 35.0 ³ 9.5 30 ³ 47.5 ³ 10.4 10 ³ 45.3 ³ 10.3 3 ³ 50.1 ³ 10.4 ÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄ

The TG curves of the films are shown in Fig. 2. The samples undergo stepwise thermal oxidative degradation accompanied by weight loss. The weight loss of the fibroin in air at 130oC (curve 6) is due to vaporization of adsorbed water. On further heating, gradual weight loss owing to transformations of the amorphous fractions is observed. The thermolysis rate increases at 250oC and reaches a maximum at 278oC. At this temperature, the H bonds of nonoriented b-crystalline fractions of the polymer start to rupture [15318]. The weight loss at 500oC is 77%. The TG curve of the cellulose film (curve 1) contains a step at 105oC with a weight loss of 11.2%, caused by vaporization of adsorbed water. The thermolysis sharply accelerates on heating above 157oC. The maximal rate of the weight loss is observed at 190oC. The total weight loss at this temperature is 43%. On further heating, the thermolysis rate decreases and then increases again, reaching a maximum at 349oC (weight loss 73.5%). This can be due to dehydroxylation of cellulose units mainly in the amorphous fractions and then, at higher temperatures, to depolymerization of the crystalline fraction of the polymer [19, 20]. The weight loss at 500oC is 96%, owing to liberation of volatile thermolysis products. The temperature of the intense weight loss of the cellulose film containing 10% fibroin (curve 2) is 10oC higher than that of the pure cellulose film. With increasing fibroin concentration, this temperature in-

RUSSIAN JOURNAL OF APPLIED CHEMISTRY

Vol. 79

No. 5

2006

PROPERTIES OF FILMS PREPARED FROM SOLUTIONS

809

T, oC Fig. 2. TG curves of the films (Dm) Weight loss and (T) heating temperature. Heating temperature (oC), weight loss (%): (1) (I) 105, 11.2; (II) 157, 17; (III) 197.5, 47.5; (IV) 349, 73.5; (V) 500, 96; (2) (I) 120, 6; (II) 167, 12; (III) 192, 28.5; (IV) 347, 71; (V) 500, 95; (3) (I) 81, 3; (II) 252, 9; (III) 345, 22.5; (IV) 500, 67.5; (4) (I) 105, 4.8; (II) 180, 6; (III) 254, 11; (IV) 350, 40; (V) 500, 74.2; (5) (I) 100, 6, 245, 12; (III) 280, 26; (IV) 500, 70; (6) (I) 130, 6; (II) 250, 11; (III) 278, 26; (IV) 500, 77.

creases, approaching the thermolysis temperature of fibroin (curves 3!5). The weight loss of these samples at 500oC decreases to 70 374%. The film with a fibroin3cellulose ratio of 30/70 is the most stable at temperatures of up to 500oC. Thus, addition of fibroin increases the heat resistance of cellulose. Nishioka et al. [21] showed that the heat resistance of cellulose in blends with synthetic polymers decreases or reRUSSIAN JOURNAL OF APPLIED CHEMISTRY

Vol. 79

mains virtually the same depending on the type of the synthetic polymer. The tensile strength and elongation at break of the films with different component ratios are presented in Table 2. As seen from Table 2, the sample containing 30% fibroin and 70% cellulose has the best combination of the tensile strength and elongation. No. 5

2006

810

SASHINA et al.

CONCLUSIONS (1) An IR study of the films of fibroin3cellulose blends revealed intermolecular interaction between the components. (2) The fibroin3cellulose films are characterized by good physicomechanical properties and high heat resistance. REFERENCES 1. Silk Polymers: Material Science and Biotechnology, Kaplan, D., Ed., Washington: Am. Chem. Soc., 1994. 2. Asakura, T., Kitaguchi, M., Demura, M., et al., J. Appl. Polym. Sci., 1992, vol. 46, no. 1, pp. 49353. 3. Minoura, N., Tsukada, M., and Nagura, M., Biomaterials, 1990, vol. 11, no. 3, pp. 430 3 435. 4. Minoura, N., Tsukada, M. and Magura, M., Polymer, 1990, vol. 31, no. 3, pp. 2653269. 5. Sashina, E.S. and Novoselov, N.P., Zh. Prikl. Khim., 2005, vol. 78, no. 3, pp. 4933498. 6. Sashina, E.S., Novoselov, N.P., and Heinemann, K., Zh. Prikl. Khim., 2005, vol. 78, no. 1, pp. 1553160. 7. Philipp, B., Polym. News, 1990, vol. 15, no. 6, pp. 170 3175. 8. RF Patent 2 002 107 622. 9. Miyazawa, T., Shimanouchi, T., and Mizuchima, S.,

J. Chem. Phys., 1958, vol. 29, no. 3, pp. 6113 616. 10. Asai, M., Tsuboi, M., Shimanouchi, T., and Mizushima, S., J. Phys. Chem., 1955, vol. 59, no. 3, pp. 3223 325. 11. Venyaminov, S.Yu. and Kalnin, N.N., Biopolymers, 1990, vol. 30, no. 6, pp. 125931271. 12. Magoshi, J., Mizuide, M., and Magoshi, Y., J. Polym. Sci., Polym. Phys. Ed., 1979, vol. 17, no. 3, pp. 5153 520. 13. Freddi, G., Pessina, G., and Tsukada, M., Int. J. Biol. Macromol., 1999, vol. 24, no. 2, pp. 2513263. 14. Asai, M., Tsuboi, M., and Shimanouchi, T., J. Phys. Chem., 1955, vol. 59, no. 3, pp. 3223326. 15. Kweon, H., Woo, S.O., and Park, Y.H., J. Appl. Polym. Sci., 2001, vol. 81, no. 13, pp. 227132276. 16. Nam, J. and Park, Y.H., J. Appl. Polym. Sci., 2001, vol. 81, no. 15, pp. 300833021. 17. Motta, A., Fambri, L., and Migliaresi, C., Macromol. Chem. Phys., 2002, vol. 203, no. 9, pp. 165831665. 18. Kweon, H. and Park, Y.H., J. Appl. Polym. Sci., 2001, vol. 82, no. 5, pp. 750 3758. 19. Milosavljevic, I. and Snuberg, E.M., Ind. Eng. Chem. Res., 1995, vol. 34, no. 4, pp. 108131091. 20. Rubtsov, Yu.I., Kazakov, A.I., Andrienko, L.P., and Manelis, G.B., Fiz. Goren. Vzryva, 1993, vol. 29, no. 6, pp. 49353. 21. Nishioka, N., Hamabe, S., et al., J. Appl. Polym. Sci., 1998, vol. 69, no. 11, pp. 213332137.

RUSSIAN JOURNAL OF APPLIED CHEMISTRY

Vol. 79

No. 5

2006