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Ind. Eng. Chem. Res. 1990, 29, 800-805
MATERIALS AND INTERFACES Biodegradable Film Derived from Chitosan and Homogenized Cellulose Jun Hosokawa,* Masashi Nishiyama, Kazutoshi Yoshihara, and Takamasa Kubo Government Industrial Research Institute, Shikoku. 2-3-3 Hananomiya-cho, Takamatsu 761, Japan
A novel composite film derived from chitosan and fine cellulosic fiber has been developed. Its general characteristics are discussed. The composite film obtained by cast drying is hydrophilic but insoluble in water. It has a high oxygen-gas barrier capacity. T h e strength of the composite film changes with chitosan content, and the maximum tensile strength (more than 1000 kg/cm2) has been attained a t 10-20 w/w '70chitosan on cellulose. T h e composite film is assumed t o have chemical bonds between chitosan and the cellulosic material. T h e flexibility of the composite film can be improved by t h e addition of glycerol as a plasticizer. T h e composite film is degraded t o fine fragments by cellulase and a ubiquitous chitosan-degrading bacterium isolated from soils in Japan. T h e period of its biodegradation can be controlled by the conditions during film formation, such as temperature and the functional groups of cellulose. film from fine cellulosic fiber shows no water resistance. A composite film can be expected to be biodegradable, and further, there is a possibility to control the period of degradation. Therefore, the preparation conditions of this composite film and its properties (including biodegradation) are discussed in this report.
We have studied complex compounds between chitosan and cellulose and have found that a combination of chitosan and fine cellulosic fiber produces a useful material that can be used to form biodegradable film and moldings. Plastic films made from petroleum have come into wide use throughout the world. With an increase in their applications, the treatment of waste plastics has become a serious problem because of the difficulty of ensuring reclaimed land and burning in incinerators. Therefore, the development of new plastics that can be degraded by microorganisms in soil and seawater has recently started. Some famous plastics of this type are hydroxybutyratevalerate copolyester (which is accumulated in a special bacterium (Doi et al., 1988)), polyethylene containing starch (Otey et al., 19801, and so on. Chitosan is one of a few natural cationic polysaccharides that can be derived from crustaceans or various fungi. Fine cellulosic fiber, which is a gellike suspension in water. can be produced from pulp by the use of such pulp-beating machines as a Niagara beater, a refiner, or a highly pressurized homogenizer. Techniques involving the utilization of chitosan for cellulose pulp have mainly been mentioned in publications with respect to improvements in the surface strength of paper (Allan et al., 1975, 1977). In this report they mentioned that pulp treated with chitosan resulted in the production of paper having a high wet strength (Allan et al., 1975). Nishiyama (1983) demonstrated the improvement in printing quality of Japanese traditional paper by the addition of chitosan to pulp. These effects reported so far all concern the application of chitosan to paper or pulp sheet. Tokura et al. (1987) presented a method for producing various fibrous chitin-chitosan derivatives. Nishiyama et al. (1982) made paper sheet from such fibrous chitin derivatives. However, this was not film. but paper. We have found that the combination of chitosan and fine cellulosic fiber results in the formation of various kinds of strong, gas-barrier, and water-resistant composite films by only cast drying the material without any complicated treatment. On the other hand, chitosan film formed by cast drying requires the involvement of an alkali treatment in order to prepare a film that is insoluble in water Sheet 0888-5885/90/ 2329-0800$02.5010
Experimental Section A. Materials. Commercial-grade chitosan (Chitosan 10B, Katokichi Co., Japan; origin, prawn; degree of deacetylation, 99.8%; viscosity (0.5% concentrated in 0.5% acetic acid a t 25 "C), 200 cP) was used to prepare the composite film used in this study. Fine cellulosic fiber (homogenized cellulose) was made by using a Niagara beater from bleached softwood pulp or was obtained from Dice11 Co., Japan. The homogenized cellulose named Micro-fibril-celluloseof Dice11 Co. was made from bleached pulp and was offered as a 4% suspension in water. Micro-fibril-cellulosehas a diameter of
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103
Glycerol C o n t e n t ( S )
Figure 3. Relation between the glycerol content as a plasticizer and the tensile strength of a composite film at a chitosan content of 20%.
of the composite film. Though the composite films containing 10070glycerol were too soft and weak, composite films of 75% glycerol had suitable flexibility to make wrapping film. The tensile strength of a composite film containing 7570 glycerol is lower than that without glycerol (Figure 2) but almost the same as those of general plastic films. In both cases of 0% and 75% glycerol, the maxima of the wet tensile strength have occurred at 10-30% chitosan content on cellulose. A composite film was also prepared from homogenized cellulose (52 mL of CSF), which was obtained by beating with a Niagara beater. The appearance of the film was very similar to that from Micro-fibril-cellulose, but its strength was 7040% of that. It was therefore decided to adopt Micro-fibril-cellulose in subsequent studies. Effect of Glycerol on Strength. The relationship between the glycerol content and the tensile strength of composite film is shown in Figure 3. The tensile strength per cross-sectional area of test pieces decreases with an increase in the glycerol content. This is mainly attributable to an increment in the thickness of the composite film absorbing glycerol. However, the strength dropped slightly with an increase in the glycerol content, even though the thickness was assumed to remain unchanged upon the addition of glycerol (Figure 4). This fact shows that glycerol inhibits the bonding, namely, the complexing of cellulose and chitosan. The main factor for the inhibition is presumably a lack of ac-
Figure 4. Estimated tensile strength of a composite film containing glycerol on the condition that the thickness of all films was assumed to be 62 um.
cessibility between the cellulose and chitosan due to the presence of glycerol. Though the elongation of the composite film increased with glycerol content, the value of elongation, 10-20%, was not high in comparison with general plastic films. O t h e r Properties of t h e Composite Film. From the data mentioned above, the composite film is found to be formed attractively under the following conditions: 20% chitosan, 75% glycerol on homogenized cellulose, and a drying temperature of 70 OC. Therefore, the various properties of the composite film formed under these conditions are discussed. The film (80-pm thick) showed a low oxygen-gas permeability of 2-8 mL/ (m2.24h-atm) (ASTM 1434-661'). This value is much lower than that of polyethylene but comparable to that of nylon and P E T films, which are known as oxygen barrier films. However, the permeability of our film for oxygen gas increased under the circumstances of high humidity. Bai et al. (1988) found that chitosan-acetic acid complex membrane has low permeabilities for oxygen and especially for carbon dioxide and proposed using it as a preservation membrane for fruits. The structure of our composite film would be similar to that of the chitosan-acetic acid membrane. The composite film (80-pm thick) showed a high water-vapor transmission rate of 6500 g/(m2.24 h) according to the Japanese Industrial Standard 2-0208. This rate is higher than those of general cellophane films. The liquid water transmission of the composite film was 0.88 L/(m2-h) a t a pressure of 4.0 atm. A thermal analysis of the composite film, which does not contain glycerol, is shown in Figure 5. The exothermic peak at 330 " C can be attributed to the carbonization accompanying combustion. Except for vaporization at 70 "C of the absorbed water, TG and DTA of the composite film did not exhibit any detectable change below 280 "C. Effect of T e m p e r a t u r e on Film Properties. The effect of the heat treatment temperature is discussed regarding the strength and water absorption of the composite film. As shown in Figure 6, the tensile strength did not increase with a rise in temperature of the heat treatment. Films formed at high temperatures absorb less water than those formed a t low temperatures (Figure 7 ) . This fact suggests that the bonding points in the film increase with increasing temperature and that the obtained film has difficulty swelling. The reason that the increase in the number of bonding points did not effect the strength of film is not vet clear.
Ind. Eng. Chem. Res., Vol. 29, No. 5, 1990 803 600
TG-DT h d r Stre8.UI.
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Temperature ( "C) F i g u r e 5. Thermal analysis of a composite film composed of 20% chitosan and 0% glycerol.
Carbonyl groups ( m m l / k g cell u l o s e ) Figure 8. Relation between the oxidation degree of cellulose and the tensile strength of the prepared composite film. G75Ch20
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Carbonyl groups (mmol/kg c e l l u l o s e )
Figure 9. Relation between the oxidation degree of cellulose and the swelling of a composite film in water.
OC
Figure 6. Relation between the temperature of the heat treatment and the tensile strength of a composite film composed of 20% chitosan and 75% glycerol.
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.3
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T e m p e r a t u r e ( OC
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Figure 7. Effect of a heat treatment on the swelling of a composite film in water.
Effect of Carbonyl a n d Carboxyl Groups of Cellulose on Film Properties. The effects of carbonyl and carboxyl groups of cellulosic fiber on the strength and water absorption of a composite film are shown in Figures 8 and 9. It is well-known that carbonyl groups form Schiff-base compounds with amino groups of chitosan and carboxyl
groups form ionic bonds with the amino groups of chitosan. After such bonds form, they tend to rearrange through Amadori transition and produce more complex bonds (Isbell and Frush, 1958). We therefore had expected that an increase in the number of carbonyl or carboxyl groups in cellulose would result in an increase in the number of bridging bonds between chitosan and cellulose and would enhance the strength of the composite film. However, the strength became lower with an increase in such functional groups of cellulosic fiber (Figure 8). The intrinsic strength of cellulosic fiber deteriorates after an ozone treatment (Soteland, 1974; Secrist and Singh, 1971). This is presumably the reason why the strength of the composite film prepared from cellulose having many carbonyl and carboxyl groups was weak. The degree of swelling of the composite film decreases with an increase in the number of functional groups of cellulose (Figure 9), suggesting that the number of bridging points is large when the composite film is prepared from cellulose having many carboxyl and carbonyl groups. Biodegradation of Composite Films. The accelerating biodegradability test was performed for the various composite films. Sharp degradation behavior of the films to fine fragments made it possible to observe their degradation points in the accelerating test. These composite films except for 0% chitosan film were not degraded a t all for over 3 weeks in pure water and in the media without the bacterium and cellulase. The biodegradability of various composite films is shown in Figures 10 and 11. The increase in the chitosan content,
804 Ind. Eng. Chem. Res., Vol. 29, No. 5 , 1990
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Conclusions Complexing of chitosan and fine cellulosic fiber can be successfully completed by drying, and results in the formation of nonthermoplastic composite films having good
3,0q
0
Temperature of Heat T r e a t men t ( O C )
Figure 10. Period of degradation of a composite film in bacterium and cellulase solutions
carboxyl content, and temperature prolongs the degradation periods for the attack of the bacterium and cellulase. On the other hand, an increase in the glycerol content shortens the degradation periods. The effect of the chitosan content on the biodegradation is reasonably understandable, since the high content of chitosan may prolong the degradation periods of the composite film by the bacterium; further, cellulose fully coated with chitosan may be resistant against cellulase. The effect of the glycerol content on biodegradation could be explained by the fact that glycerol is a kind of swelling reagent. A composite film containing a high glycerol content is fully swollen, and its polymer-chain network would be so loose that enzymes easily invade into the film. Concerning the effect of temperature, it is assumed that an increase in the number of bridging points in the polymer chain prevents the attack of enzymes. This is the same situation as in the case of carbonyl- and carboxyl-rich homogenized cellulose. Composite films made from cellulose of high carbonyl and carboxyl content must possess many chemical bonds, namely, bridging points in polymer chains. Though the increase of carbonyl and carboxyl contents of cellulose decreased the strength of the film (as mentioned in the former section), it prolongs the biodegradation period. This fact shows that bridging points of specific chemical bonds are formed in the film, and that such bridging would prevent an?; attack by bacteria or enzymes on the film. Since cellulose is known to form carboxyl and carbonyl (both keto and aldehyde types) groups in its polymer chain by oxidation, mechanically damaged cellulose like homogenized cellulose would have small amounts of such functional groups. We are now attempting to make s w e which functional groups play an important role on the film formation and the biodegradability.
100 1 3 0 160 19C
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F u n c t i o n a l Groups i n c e l l u l o s e (mmol/kg)
F i g u r e 11. Period of degradation of a composite film in bacterium and cellulase solutions.
wet strength, gas shielding, and biodegradability. The combination of the two materials is essential to form a film that is insoluble in water. The composite film has a maximum wet strength (600 kg/cm2) at 10-2070 chitosan on cellulose and is softened by the use of a plasticizer, glycerol. The biodegradability can be controlled by adjusting the complexing condition, e.g., the temperature a t film formation. Changing the amounts of carbonyl or carboxyl groups in cellulose is also effective in controlling the biodegradability of the composite film.
Literature Cited Allan, G. G.; Friedhoff, J. F.; Korpela, M.; Laine, J. E.; Powell, J. C. Marine Polymers, V. Modification of Paper with Partially Deacetylated Chitin. 4CS Symp. Ser. 1975, 10, 172. Allan, G. G.; Fox, J. R.; Crosby, G. D.; Sarkanen, K. V. Chitosan, A. Mediator for Fiber-Water Interactions in Paper. Trans. BPBlF Symp. Fiber-Water Interact. Papermaking (Oxford) 1977,2,765. Bai. R. K.; Huang, M. Y.; Jiang, Y. Y.Selective permeabilities of chitosan-acetic acid complex membrane and chitosan-polymer complex membranes for Oxvgen and Carbon dioxide. Polym. HuiL 1988, 20. 83. Doi. Y.: Tamaki. A.: Kunioka. M.: Sopa. K. Production of C O D O ~ V esters of 3-hydroxy butyrate and 3-hybroxwalerate by Alcaligenes rutrophus from butyric and pentamic acids. Appi. Microbiol. Hiutechnoi. 1988, 28, 330. Fukui, T.Microfibrillated Cellulose. Ann. High Perform. Pap. SOC. 1985, 2.3, 5 . Hosokawa. .J.; Kubo, T. Color Reversion of Ozone-bleached Kraft Pulp VII. Mokuzai Gakkaishi 1987, 33, 660. Ishell, H. S.; Frush, H. L. Mutarotation, Hydrolysis, and Rearrangement Reactions of Glycosylamines. J . Org. Chem. 1958, 23, _
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Mattisson, M. F.; Legendre, K. A. Determination of the Carboxyl Content of Oxidized Starches. Anal. Chem. 1952, 24, 1942. Miya, M.; Iwamoto, R.; Mima, S.; Yamashita, S.; Mochizuki, A.; Tanaka, 1..Chitosan Membrane for Separation of Water-Ethanol by Pervaporization. Kobunsi Ronbunsyu 1985, 42, 139. Nishiyama, M. Application of Chitin and Chitosan to Paper Technology as High Performance Material. Ann. High Perform. Pap. Soc. 1983. 22. 11. Nishiyama, hl.; Kobayashi. Y.; Tokura, S.: Nishi, N. Paper from Regenerated Chitin Fiber. Jap. Patent Kokai, 16999, 1982. Otev, F H.: Westhoff. R. P.; Doane, W. M. Starch-Rased Blown
I n d . Eng. C h e m . Res. 1990, 29, 805-818 Films. Ind. Eng. Chem. Prod. Res. Deu. 1980, 19, 592. Samuelson, 0.;Soderholm, I. Determination of Carbonyl Groups in Cellulose by the Hydrazine Method. Suen. Papperstidn. 1963,66, 833. Secrist, R. B.; Singh, R. P. Kraft Pulp Bleaching 11. Studies on the Ozonation of Chemical Pulps. Tappi 1971, 54, 581. Soteland, N. Bleaching of Chemical Pulps with Oxygen and Ozone. Pulp Pap. Mag. Can. 1974, 75, T153.
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Tokura, S.; Nishimura, S.; Nishi, N.; Nakamura, K.; Hasegawa, 0.; Sashiwa, H.; Seo, H. Preparation and Some Properties of Variously Deacetylated Chitin Fibers. J. SOC.Fiber Sci. Technol., J p n . 1987, 43, 288.
Received for review August 28, 1989 Revised manuscript received January 2, 1990 Accepted January 29, 1990
PROCESS ENGINEERING AND DESIGN Nonlinear Analysis in Process Design. Why Overdesign To Avoid Complex Nonlinearities? Warren D. Seider,* David D. Brengel, and Alden M. Provost Department o f Chemical Engineering, University o f Pennsylvania, Philadelphia, Pennsylvania 19104
Soemantri Widagdo Chemistry and Chemical Engineering Department, Stevens I n s t i t u t e of Technology, Hoboken, N e u Jersey 07030
Overdesigns are believed t o be commonplace in the chemical industry. Usually they compensate for uncertainties in the model, allow for increases in capacity, and provide margins of safe operation. In some cases, they involve elements of conservatism to protect against regimes of complex nonlinear operation t h a t can occur in exothermic and isothermal reactors, thermally coupled and azeotropic distillation towers, supercritical extractors, and other processes, as illustrated in this paper. T h e illustrated examples have their key parameters constrained and the degree of back-mixing reduced to avoid operation near or within regimes having multiple steady states and periodic or chaotic behavior. In designing these processes, it is important t o locate the range of the design parameters over which complex operating regimes may occur. Bifurcation analysis and singularity theory are potentially helpful, but these tools have not been used often. Hence, this paper briefly reviews these areas and focuses on the roles they could assume in the design of nonlinear processes. A related focus is on algorithms for flexibility and resiliency analysis and model predictive control, which when applied t o nonlinear processes may permit operation closer to the steady-state economic optimum, even when near or within complex regimes. This paper argues for the coordination of design, operations, and control optimizations t o reduce the instances of overdesign. Many recent advances in the analysis of nonlinear systems are leading to better modeling of processes and, in turn, improved operations. Examples of the use of bifurcation analysis and singularity theory to characterize the steady state and dynamic performance of chemical reactors are now widespread, with applications to physical processes and recycle systems gaining in importance. It is noted, however, that bifurcation analysis and singularity theory are not often used in process design. Similarly, many new applications of mathematical programming for multiobjective and multilevel optimization are permitting much improved process identification and the location of local and global optima of systems subject to nonlinear algebraic and differential constraints. These applications often arise in process design. Although examples of nonlinear programs (NLPs) abound in the literature on design, key parameters are *Author t o whom correspondence should be addressed.
often constrained, and the degree of back-mixing is reduced to keep the processes from operating near or within regimes characterized by hysteresis and periodic or chaotic behavior. This may prevent operation near steady-state economic optima. However, with new nonlinear programming strategies being developed to permit more reliable m o d e l predictive control (MPC) near or within these operating regimes, an important opportunity and challenge faces process designers: how to utilize nonlinear analysis to obtain more economical designs that are flexible and controllable in regimes characterized by greater sensitivities to modeling errors (process/model mismatch) and changes in set points and in which good servo-control and the rejection of disturbances are more difficult to achieve. With innovative applications of nonlinear programming for multiobjective design, operations, and control optimizations, it should be possible to reduce sharply the instances of overdesign in the process industries. This paper begins with a brief review of nonlinear analysis, placing emphasis on the new developments and
C 1990 American Chemical Society 08S~-SSSS/9Q~2S29-0S05$02.50/0
