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Sorption of solvents by cellulose and cellulose materials from the liquid phase
Sorption of solvents by cellulose and cellulose materials from liquid phase
2285
3. M. M. KOTON, V. V. KUDRYAVTSEV, V. P. SKLIZKOVA, M . 1. BYESSONOV, V. Ye. SMIRNOVA, B. G. BYELEN'KII and V. I. KOLEGOV, Zh. prikl, khim. 49: 387, 1976 4. V. Ye. ESKIN, Rasseyaniye sveta rastvorami polimerov i svoistva makromolekul (Light Scatter by Polymer Solutions and the Properties of Macromoleenles). Leningrad, 1986 5. V. N. TSVETKOV, V. Ye. ESKIN and S. Ya. FRENKEL', Struktura makromolekul v rastvorakh (Structure of Macromolecules in Solution). Moscow, 1964 6. S. Ya. MAGARIK, G. E. TIMOFEYEVA and M. I. BYESSONOV, Vysokomol. soyed. A23: 581, 1981 (Translated in Polymer Sci. U.S.S.R. 23: 3, 650, 1981) 7. V. A. ZUBKOV, T. M. BIRSHTEIN and I. S. MILEVSKAYA, Ibid. AI7: 1955, 1975 (Translated in Polymer Sci. U.S.S.R. 17: 9, 2252, 1975) 8. V. M. DENISOV, V. M. SVETLICHNYI, V. A. GINDIN, V. A. ZUBKOV, A. I. KOL'TSOV, M. M. KOTON and V. V. KUDRYAVTSEV, Ibid. 21: 1948, 1979 (Not translated in Polymer Sci. U.S.S.R.) 9. G . L . WALLACH, J. Polymer Sci., 5, 653, 1967 10. V. Ye. ESKIN, I. A. BARANOVSKAYA, M. M. KOTON, V. V. KUDRYAVTSEV and V. P. SKLIZKOVA, Vysokomol. soyed. A18: 2362, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 10, 2699, 1976) 11. m. M. KOTON, O. V. KALLISTOV, V. V. KUDRYAVTSEV, V. P. SKLIZKOVA and I. G. SlLINSKAYA, Ibid. A21: 532, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 3, 583, 1979) 12. I. A. BARANOVSKAYA, V. V. KUDRYAVTSEV, N. V. D'YAKONOVA, V. P. SKLIZKOVA, V. Ye. ESKIN and M. M. KOTON, Ibid. 27: 604, 1985 (Not translated in Polymer Sci. U.S.S.R.) 13. V. N. TSVETKOV, Zhestotsepnye polimernye molekuly (Rigid Chain Polymeric Molecules). Leningrad, 1986 14. H. YAMAKAWA, Modern Theory of Polymer Solution, N. Y., 1971 15. A. PERICO and C. CUNIBERTI, Macromolecules 8: 823, 1975 16. I. A. BARANOVSKAYA, L. A. VOLKOVA, N. V. D'YAKONOVA, S. Ya. MAGARIK, G. D. RUDKOVSKAYA ~nd V. Ye. ESKIN, Vysokomol. soyed. A25: 2108, 1983 (Translated in Polymer Sci. U.S.S.R. 25: 10, 2448, 1983) 17. C. W. TSIMPRIS and K. G. MAYHAN, J. Polymer Sci. 11: 1151, 1973
Polymer Science UIS.S.R. Vol. 31, No. 10, pp. 2285-2291, 1989 Printed in Poland
0032-3950/89 $10.00+.00 © 1990 Pergamon Press pie
SORPTION OF SOLVENTS BY CEIJ,ULOSE AND CELLULOSE MATERIALS FROM THE LIQUID PHASE* YE. A. CHIRKOVA a n d A. E. KREITUS Institute of Wood Chemistry, Latvian S.S.R. Academy of Sciences (Received 1 April 1988)
The interaction of wood fibre cellulose with 20 solvents has been studied. The total sorption of the solvent by the cellulose material and equilibrium swelling of the cellulose fibre wall have been determined. A correlation has been established between these magnitades and the * Vysokomol, soyed. A31: No, 10, 2079-2083, 1989.
2286
YE. A. CmRKOVAand A. E. KI~EITUS
component of the parameter of solubility corresponding to the hydrogen bonds. Solvents entering into chemical reaction with cellulose are not subject to these laws. Hydrogen bonds are also chiefly responsible for the other physicochemical properties of cellulose-solvent systems.
SYNTHESIS,isolation and processing of cellulose and also different areas of
the application of cellulose materials are connected with contact of cellulose with liquid media. In the literature much attention is paid to the problems of the interaction of cellulose with water and aqueous solutions of salts and hydroxides [1]. The behaviour of cellulose in organic solvents has been far less studied. The lack of experimental data makes it difficult to systematize them and, therefore, so far no success has attended attempts to find a correlation between the sorption of solvents by cellulose and their physicochemical properties. F r o m investigations the qualitative conclusion has been drawn that an essentim role in the interaction with cellulose is played by the ability of the solvent to form hydrogen bonds [2, 3]. Within one homologous series the dependence of sorption on the size of the solvent molecules has been established [2-5]. The sorption of liquid media by cellulose materials comes about in two stages: 1) capillary suction of the liquid into the interfibre spaces and domains of the f i b r e s - at this stage occurring at a fast rate, the values of sorption reach hundreds o f percentages; a n d 2) sorption of the liquid by the cellulose fibre wall, i.e. directly by the substance cellulose accounting for only a few percent. The rate of the last stage is lower by several orders than that o f the first, the sorption process is accompanied by separation of the fibre into structural elements and hence by increase in its volume (swelling). We studied sorption at both stages of a series of solvents by Taircell pulped wood cellulose sulphate (content of ~-cellulose 98~o, degree of polymerization 1200). The solvents are specified in the Table. The global absorption of the liquid by the cellulose material was determined by the traditional method: a sample measuring 10x 15 x2 ram was dried for 20 hr at I05°C, vacuum treated for 0-5 hr at a residual pressure 1 Pa and in vacuo wetted with degassed liquid. The sample was held in the liquid for seven days at 23 _+1°C and the excess liquid removed with a Bt~ehner funnel. The global absorption (cma/g) mend ~ m o mo
Pllquid
where m0 and m,.d are the initial and final mass to the sample respectively; Pll~u~d is the density of the liquid. Equilibrimn swelling of the wall of an individual cellulose fibre was determined by kinetic densitometry [8] by measuring on analytical scales the change with time in the mass of the initially dried and vacuum treated sample, then lowered into the test liquid. According to Archimedes law the mass of the sample in liquid m l i q u l d ~- m a l r ~ ~ / P l l q u i d
where m,~r is the mass of the sample in air; Vis the volume of the sample. If the material of the sample does not dissolve in the liquid medium and does not enter into chemical reaction with it mm remains constant and assmning p,qu in--const change in m~Q~doccurs only as a result of change in the volume of the sample. As the liquid penetrates into the sample its volume decreases changing from apparent to true (volume of structural elements). However, for non-rigid materials exposure to adsorption forces may increase the volu~e with the formation of an
Sorption of solvents by cellulose and cellulose materials from liquid phase
2287
CHARACTERISTICS OF THE SWELLING OF WOOD CELLULOSE IN LIQUID SOLVENTS
Sample No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Solvent
Parameter of solubility and its components,* (J/m3) ~ J
Water Methanol Ethanol 1-Propanol 1-Butanol 1-Pentanal Benzyl alcohol n-Pentane n-Hexane n-Heptane Benzene Acetone Dioxane Diethyl ether Ethyl acetate Ethylene glycol DMSO Acetic anhydride Acetic acid Formic acid DMFA DMAA Glycerine
Jdt
Jvt
12.3 15-1 15.8
31.3 12.2 8"8 6.7 5.7 4.5
J~, 34"1
0 0 0 1"0 10.4 1-8 2.9 5.3 11.0 16.3 11.0 8"0 11.8 13-7 11.5 12
Density of cellulose
1/'t'o. 5 X
x 104,
Po 1"560 1"544 1"541 1"558 1- 527 1"543 1"550 1"574 1"540 1"546 1"552 1"541 I" 566 1"563
Pead
sec- 1
1"629 1"593 1-570 1"573 1"577 1"597 1-628 1"675 1"656 1"596 1.623 1.626 1-626
0"08
1.505 1' 540 1"537 1.543 1.684
1"597 1-679 1-566 1.647 1.715
10"25 2"61 0"96
1>28 0-73 0.06 0"04 3"08 0"91 2"40 6"14 1.18
*The values o f 6 and its components are taken from references [6, 7]. t Jd and d~p are the dispersion and polarization components respectively.
ultraporous structure inaccessible for the liquid molecules. By measuring the ml~quid values with time one may judge the kinetics and character of the processes occurring in the polymer-liquid" system. Equilibrium swelling of the fibre wall (cm3/g) was calculated as ztmllquid m o fil Iquld
1
1
,190 fiend
where AmHq,,d is the difference between the final and initial mass of the sample in the liquid; the initial mass was found by extrapolating the initial portion of the kinetic curve to ~=0; Po and P©nd are respectively the initial and final (equilibrium) densities of the sample. The rate of reaching equilibrium swelling (equilibrium density) was characterized by the magnitude l/to.5 (ro.s is the time taken to reach half the value of change in mass) proportional to ttte diffusion coefficient. The limiting absolute error of determining Q~ and Qwatt was 0.0005 cma/g. The divergence between parallel measurements did not exceed 0.15 for Q~ and 0.003 cmS/g for Qwau. The initial density of the cellulose in most cases is 1-547 + 0.020 g/cm 3 (Table) which corresponds to the apparent density of the cellulose fibre wall determined from helium [9]. Consequently, filling of the interfibre spaces and domains of the fibres on initial vacuum treatment occurs almost instantaneously and the method of kinetic densitometry helps to determine the swelling of the wall of the
2288
YE. A. CmggovA and A. E. Ird~rrtrs
individual fibre. The po values in ethylene glycol differ significantly from the mean which is connecte.d with its high viscosity exceeding 20 times that of water and with formic acid which rapidly enters into a chemical reaction with cellulose [10]. Examples of the kinetic curves are given in Fig. 1. The rate at which equilibrium swelling (equilibrium density) of cellulose is reached in the solvents studied differs by three orders (Table). Sorption equilibrium is established at the fastest rate in the alcohols, the rate of diffusion of alcohol into cellulose decreasing with increase in the size of the molecules. The rate of penetration into cellulose of normal hydrocarbons is lower by an order and of water and acetone by two orders than for the alcohols. For most of the solvents studied a mutual link exists between the rate of diffusion into cellulose and the constant a / 4 t / o f the Washburn equation (~r and r/are the surface tension and viscosity of the liquid respectively) describing the speed of movement of the liquid in the capillaries [12] (Fig. 2).
~'d'5"1°4,sec-' I o 18 6 19 " p,g/cm 3
/-74~
2
1.6
2
5 11
• 2
I
50
I00 150 Time,hr,
200
16o
9
lO
O'/#r2
20
Fro. 1 Fie. 2 Fxo. 1. Kinetics of change in the density of cellulose fibre in benzene (1), n-hexane (2) and dioxane (3). FIo. 2. Dependence of the rate of diffusion of solvents into cellulose on the constant of the Washburn equation. Here, and in Figs. 3 and 4, the point numbers correspond to the sample numbers in the Table. With the variety of solvents studied it appears possible to identify the factors which exert the main influence on the interaction of solvents wih cellulose. Earlier it was shown that for many polymer-solvent systems extremal dependence of some properties (equilibrium swelling, intrinsic viscosity, etc.) on the solubility parameter 6 is observed, the position of the extreme corresponding to the solubility parameter of the polymer [13]. For cellulose in the series of solvents studied a mutual link between swelling and the solubility parameter is absent. However, a good correlation is found between Qr and Qw,Jl (or the specific volume V,p), on the one hand, and the component of the solubility parameter 6h corresponding to the contribution of the energy of the hydrogen bonds [6], on the other (Fig. 3).
Sorption of solvents by cellulose and cellulose materials from liquid phase
2289
The dependence of the specific volume (equilibrium swelling of the wall) on 8h represents a curve with a maximum the abscissa of which is close to the @value of cellulose equal to 15.6 (J/m3) °'s [14]. The largest specific volume (least density) is shown by cellulose fibre in alcohols. Apparently the alcohols 5h of which is close to the solubility parameter of cellulose activity loosen the fibre wall but the resulting ultraporous structure is inaccessible for the molecules of the alcohols. At the same time, the energy of adsorption interaction is insufficient for the fuller separation of the structural elements of cellulose which would ensure penetration of the solvent molecules into the interstructural intervals. Qwall cm3/g mZj/g
"17
VsP'Sm
0.08
'i\
200 0.06
?.6#
0.00
7.52
0.02
l oj"
\'x " o17"-
I
I
10
zx ..~'"-
0.60
~.-." o20 1
I
20
30
FIG. 3
o-
~,(Olm a)
|
19 ~ o s
I 7o. 10
30
& (j/,.,,,)o 5 Fro. 4
FIo. 3. Specific volume (1) and equilibrium swelling (2) of the cellulose fibre wall and the total sorption of the solvent by the cellulose material (3) as a function of the component of the solubility parameter &h. FIo. 4. Glass transition temperature of plasticized cellulose (accolding to reference II 5l) as a function of the compon ent of the solubility parameter &h. As may be seen from the Table in some cases Pend values are obtained exceeding the X-ray density of cellulose (1.63-1,64 g/cma). Particularly high is the density of cellulose in normal hydrocarbons which are inert in respect of cellulose [11]. In our view the X-ray density of non-rigid hydrophilic materials to which cellulose belongs is not maximally possible for the given structure since the roentgenograms are obtained as a rule for air-dry samples and deformation of the all-sided stretching of the crystallites in the field of adsorption forces is not excluded. The saturated hydrocarbons the energy of interaction of which with the surface of cellulose is low do not deform the crystalline cell which is expressed in high Pc,a values apparently close to the true density of cellulose. It should be noted that the Q~a~zvalues are quite small (Fig. 3) and several times lower than the sorption values obtained in saturated vapours (in particular, for water). The reason for these discrepancies probably lies in the fact that in saturated vapours the liquid with capillary condensation at the sites of contacts of the structural elements
2290
YE. A. CrtmKOVhand A. E. KREITUS
makes a large contribution to the sorption values. With the method of kinetic densitometry this liquid is regarded as a dispersion medium. The dependence of the global absorption of the liquid by the cellulose material cn Jh with the probability 0-95 is described by the polynomial Qz = 1.1087 + 0"127Jn + 0'0012J~ The contribution of the absorption o f the solvent by the fibre wall to the global sorption (Fig. 3) does not exceed a few percent, i.e. Q2 is essentially determined by the capillary suction of the liquid into the cellulose material. The mutual link between Qz and Jh may be due to different factors. With increase in the ability of the solvent to form hydrogen bonds the energy of its interaction with cellulose increases. Since we are dealing with a swelling sorbent, on sorption there is increase not only in the volume of the individual fibres but also the interfibre distances. As Jh increases the wettability of the surface of the cellulose with solvent improves and the cohesion energy of the solvent increases. All these factors directly depending on 3h lead to rise in Qz. Figure 4 presents the dependence of the glass transition temperature of cellulose plasticized by solvents on Jh. With the probability 0.96 this dependence is described by the equation Tg= (231 + 15)-(35"1 _ 3.6)c5°'5 It is known that the plasticization effect is chiefly determined by the thermodynamic affinity of a solvent for a polymer [16] expressed by the Flory-Huggins interaction parameter which is proportional to the difference in the squares of the solubility parameters of the polymer and solvent. Therefore, not surprising is the mutual link between Tg and the solubility parameter of the plasticizer which, as shown above, is best expressed with the use not o f total J but its component Jh. Thus, hydrogen bonds play a decisive role in shaping the physicochemical properties of cellulose materials in contact with liquid media. The use of a three-dimensional model of the solubility parameter allows these properties to be described and hence predicted. Translated by A. CRozY REFERENCES
1. R. E. REIZIN'SH, Strukturoobrazovaniye v suspenziyakh tsellyuloznykh volokon (Structuring in Cellulose Fibre Suspensions). 208 pp., Riga, 1987 2. A.J. STAMM and X. H. TARKOW, J. Phys. Colloid. Chem. 54: 745, 1950 3. E.A. COLOMBO and E. H. IMMERGUT, J. Polymer Sci. C, 31,137, 1970 4. R. K. S. BHATIA, Indian J. Chem. 9: 1279, 1971 5. O. G. TARAKANOV, S. Yu. KHOVRYAKOV, Z. A. BYELOVA and T. N. GVOZDOVICH, Vysokomol. soyed. B21: 435, 1979 (Not translated in Polymer Sci. U.S.S.R.) 6. S. HANSEN, Industr. Engn. Chem. Product Res. Development 8: 2, 1969 7. S. A. DRINBYERG and E. F. ITSKO, Rastvoriteli dlya lakokrasochnykh materialov. Spravoehnoye posobiye (Solvents for Paint-Varnish Materials. Reference Guide). 206 pp., Leningrad, 1986 8. Ye. A. CHIRKOVA, G. P. VEVERIS and A. P. VEVERIS, Khim. drevesiny, 3, 28, 1985 9. P. H. HERMANS, Physics and Chemistry of Cellulose, 543 pp., N.Y., 1949
Diffusion and sorption of water vapour in polyurethane foam
2291
10. Z. A. ROGOVIN, Khimiya tsellyulozy (Chemistry of Cellulose). 519 pp., Moscow, 1972 11. N. I. KLENKOVA, Struktura i reaRtsionnaya sposobnost' tsellyulozy (Structure and Reactivity of Cellulose). 367 pp., Leningrad, 1967 12. A. ADAMSON, Fizicheskaya khimiya poverkhnostei (Physical Chemistry of Surfaces). 568 pp., Moscow, 1979 13. A. A. TAGER and L. K. KOLMAKOVA, Vysokomol. soyed. A22: 483, 1980 (Translated in Polymer Sci. U.S.S.R. 22: 3, 533, 1980) 14. Entsiklopediya polimerov (Polymer Encyclopaedia), Vol. 1, 1224 pp., Moscow, 1972 15. E. L. AKIM, N. I. NAIMARK, B. V. VASIL'EV, B. A. FOMENKO, E. V. IGNAT'EVA and N. N. ZHEGALOVA, Vysokomol. soyed. A13: 2244, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 10, 2522, 1971) 16. P. V. KOZLOV and S. P. PAPKOV, Fiziko-khimicheskiye osnovy plastifikatsii polimerov (Physicochemical Bases of Polymer Plasticization). 223 pp., Moscow, 1982
Polymer Science U.S.S.R. Vol. 31, No. 10, pp. 2291-2296~ 1989 Printed in Poland
0032-3950/89 $10,00+ .00 © 1990 Pergamon Press ple
DIFFUSION AND SORPTION OF WATER VAPOUR IN POLYURETHANE FOAM* A. G. DEMENT'EV, T. K. KHLYSTALOVAand I. I. MIKHEYWgA "Polimersintez" Science-Production Association
(Received 6 April 1988) The diffusion and sorption patterns of water vapour in rigid polyurethane foam have been studied. A technique is proposed and the activity of the water vapour PIPs determined for its different states: bound, clustered a n d free. The link between the water sorbed by the
polymer and its state and thermophysical and mechanical properties of the foam plastic is considered. THE diffusion and sorption patterns of water vapour by polymers, the state of sorbed water and its link with the physicomechanical properties of monolithic polymeric materials form the subject of quite a number of studies [1-4]. This attention is primarily due to practical requirements since polymeric materials are usually used and stored in conditions with wide limits of change in humidity. Rigid polyurethane foams (PUP') used in refrigerating technology, for heat insulation of heating networks and main pipelines, in building and many other branches of m o d e m technology may be used in humid media. However, the data on the behaviour of foam plastics for raised humidity are limited in the literature [5]. Therefore, we studied the diffusion and sorption of water vapottr in P U F s and their links with the thermophysical and mechanical properties of the f o a m plastic. * Vysokomol. soyed. A31: No. 10, 2084-2088, 1989.
2285
3. M. M. KOTON, V. V. KUDRYAVTSEV, V. P. SKLIZKOVA, M . 1. BYESSONOV, V. Ye. SMIRNOVA, B. G. BYELEN'KII and V. I. KOLEGOV, Zh. prikl, khim. 49: 387, 1976 4. V. Ye. ESKIN, Rasseyaniye sveta rastvorami polimerov i svoistva makromolekul (Light Scatter by Polymer Solutions and the Properties of Macromoleenles). Leningrad, 1986 5. V. N. TSVETKOV, V. Ye. ESKIN and S. Ya. FRENKEL', Struktura makromolekul v rastvorakh (Structure of Macromolecules in Solution). Moscow, 1964 6. S. Ya. MAGARIK, G. E. TIMOFEYEVA and M. I. BYESSONOV, Vysokomol. soyed. A23: 581, 1981 (Translated in Polymer Sci. U.S.S.R. 23: 3, 650, 1981) 7. V. A. ZUBKOV, T. M. BIRSHTEIN and I. S. MILEVSKAYA, Ibid. AI7: 1955, 1975 (Translated in Polymer Sci. U.S.S.R. 17: 9, 2252, 1975) 8. V. M. DENISOV, V. M. SVETLICHNYI, V. A. GINDIN, V. A. ZUBKOV, A. I. KOL'TSOV, M. M. KOTON and V. V. KUDRYAVTSEV, Ibid. 21: 1948, 1979 (Not translated in Polymer Sci. U.S.S.R.) 9. G . L . WALLACH, J. Polymer Sci., 5, 653, 1967 10. V. Ye. ESKIN, I. A. BARANOVSKAYA, M. M. KOTON, V. V. KUDRYAVTSEV and V. P. SKLIZKOVA, Vysokomol. soyed. A18: 2362, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 10, 2699, 1976) 11. m. M. KOTON, O. V. KALLISTOV, V. V. KUDRYAVTSEV, V. P. SKLIZKOVA and I. G. SlLINSKAYA, Ibid. A21: 532, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 3, 583, 1979) 12. I. A. BARANOVSKAYA, V. V. KUDRYAVTSEV, N. V. D'YAKONOVA, V. P. SKLIZKOVA, V. Ye. ESKIN and M. M. KOTON, Ibid. 27: 604, 1985 (Not translated in Polymer Sci. U.S.S.R.) 13. V. N. TSVETKOV, Zhestotsepnye polimernye molekuly (Rigid Chain Polymeric Molecules). Leningrad, 1986 14. H. YAMAKAWA, Modern Theory of Polymer Solution, N. Y., 1971 15. A. PERICO and C. CUNIBERTI, Macromolecules 8: 823, 1975 16. I. A. BARANOVSKAYA, L. A. VOLKOVA, N. V. D'YAKONOVA, S. Ya. MAGARIK, G. D. RUDKOVSKAYA ~nd V. Ye. ESKIN, Vysokomol. soyed. A25: 2108, 1983 (Translated in Polymer Sci. U.S.S.R. 25: 10, 2448, 1983) 17. C. W. TSIMPRIS and K. G. MAYHAN, J. Polymer Sci. 11: 1151, 1973
Polymer Science UIS.S.R. Vol. 31, No. 10, pp. 2285-2291, 1989 Printed in Poland
0032-3950/89 $10.00+.00 © 1990 Pergamon Press pie
SORPTION OF SOLVENTS BY CEIJ,ULOSE AND CELLULOSE MATERIALS FROM THE LIQUID PHASE* YE. A. CHIRKOVA a n d A. E. KREITUS Institute of Wood Chemistry, Latvian S.S.R. Academy of Sciences (Received 1 April 1988)
The interaction of wood fibre cellulose with 20 solvents has been studied. The total sorption of the solvent by the cellulose material and equilibrium swelling of the cellulose fibre wall have been determined. A correlation has been established between these magnitades and the * Vysokomol, soyed. A31: No, 10, 2079-2083, 1989.
2286
YE. A. CmRKOVAand A. E. KI~EITUS
component of the parameter of solubility corresponding to the hydrogen bonds. Solvents entering into chemical reaction with cellulose are not subject to these laws. Hydrogen bonds are also chiefly responsible for the other physicochemical properties of cellulose-solvent systems.
SYNTHESIS,isolation and processing of cellulose and also different areas of
the application of cellulose materials are connected with contact of cellulose with liquid media. In the literature much attention is paid to the problems of the interaction of cellulose with water and aqueous solutions of salts and hydroxides [1]. The behaviour of cellulose in organic solvents has been far less studied. The lack of experimental data makes it difficult to systematize them and, therefore, so far no success has attended attempts to find a correlation between the sorption of solvents by cellulose and their physicochemical properties. F r o m investigations the qualitative conclusion has been drawn that an essentim role in the interaction with cellulose is played by the ability of the solvent to form hydrogen bonds [2, 3]. Within one homologous series the dependence of sorption on the size of the solvent molecules has been established [2-5]. The sorption of liquid media by cellulose materials comes about in two stages: 1) capillary suction of the liquid into the interfibre spaces and domains of the f i b r e s - at this stage occurring at a fast rate, the values of sorption reach hundreds o f percentages; a n d 2) sorption of the liquid by the cellulose fibre wall, i.e. directly by the substance cellulose accounting for only a few percent. The rate of the last stage is lower by several orders than that o f the first, the sorption process is accompanied by separation of the fibre into structural elements and hence by increase in its volume (swelling). We studied sorption at both stages of a series of solvents by Taircell pulped wood cellulose sulphate (content of ~-cellulose 98~o, degree of polymerization 1200). The solvents are specified in the Table. The global absorption of the liquid by the cellulose material was determined by the traditional method: a sample measuring 10x 15 x2 ram was dried for 20 hr at I05°C, vacuum treated for 0-5 hr at a residual pressure 1 Pa and in vacuo wetted with degassed liquid. The sample was held in the liquid for seven days at 23 _+1°C and the excess liquid removed with a Bt~ehner funnel. The global absorption (cma/g) mend ~ m o mo
Pllquid
where m0 and m,.d are the initial and final mass to the sample respectively; Pll~u~d is the density of the liquid. Equilibrimn swelling of the wall of an individual cellulose fibre was determined by kinetic densitometry [8] by measuring on analytical scales the change with time in the mass of the initially dried and vacuum treated sample, then lowered into the test liquid. According to Archimedes law the mass of the sample in liquid m l i q u l d ~- m a l r ~ ~ / P l l q u i d
where m,~r is the mass of the sample in air; Vis the volume of the sample. If the material of the sample does not dissolve in the liquid medium and does not enter into chemical reaction with it mm remains constant and assmning p,qu in--const change in m~Q~doccurs only as a result of change in the volume of the sample. As the liquid penetrates into the sample its volume decreases changing from apparent to true (volume of structural elements). However, for non-rigid materials exposure to adsorption forces may increase the volu~e with the formation of an
Sorption of solvents by cellulose and cellulose materials from liquid phase
2287
CHARACTERISTICS OF THE SWELLING OF WOOD CELLULOSE IN LIQUID SOLVENTS
Sample No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Solvent
Parameter of solubility and its components,* (J/m3) ~ J
Water Methanol Ethanol 1-Propanol 1-Butanol 1-Pentanal Benzyl alcohol n-Pentane n-Hexane n-Heptane Benzene Acetone Dioxane Diethyl ether Ethyl acetate Ethylene glycol DMSO Acetic anhydride Acetic acid Formic acid DMFA DMAA Glycerine
Jdt
Jvt
12.3 15-1 15.8
31.3 12.2 8"8 6.7 5.7 4.5
J~, 34"1
0 0 0 1"0 10.4 1-8 2.9 5.3 11.0 16.3 11.0 8"0 11.8 13-7 11.5 12
Density of cellulose
1/'t'o. 5 X
x 104,
Po 1"560 1"544 1"541 1"558 1- 527 1"543 1"550 1"574 1"540 1"546 1"552 1"541 I" 566 1"563
Pead
sec- 1
1"629 1"593 1-570 1"573 1"577 1"597 1-628 1"675 1"656 1"596 1.623 1.626 1-626
0"08
1.505 1' 540 1"537 1.543 1.684
1"597 1-679 1-566 1.647 1.715
10"25 2"61 0"96
1>28 0-73 0.06 0"04 3"08 0"91 2"40 6"14 1.18
*The values o f 6 and its components are taken from references [6, 7]. t Jd and d~p are the dispersion and polarization components respectively.
ultraporous structure inaccessible for the liquid molecules. By measuring the ml~quid values with time one may judge the kinetics and character of the processes occurring in the polymer-liquid" system. Equilibrium swelling of the fibre wall (cm3/g) was calculated as ztmllquid m o fil Iquld
1
1
,190 fiend
where AmHq,,d is the difference between the final and initial mass of the sample in the liquid; the initial mass was found by extrapolating the initial portion of the kinetic curve to ~=0; Po and P©nd are respectively the initial and final (equilibrium) densities of the sample. The rate of reaching equilibrium swelling (equilibrium density) was characterized by the magnitude l/to.5 (ro.s is the time taken to reach half the value of change in mass) proportional to ttte diffusion coefficient. The limiting absolute error of determining Q~ and Qwatt was 0.0005 cma/g. The divergence between parallel measurements did not exceed 0.15 for Q~ and 0.003 cmS/g for Qwau. The initial density of the cellulose in most cases is 1-547 + 0.020 g/cm 3 (Table) which corresponds to the apparent density of the cellulose fibre wall determined from helium [9]. Consequently, filling of the interfibre spaces and domains of the fibres on initial vacuum treatment occurs almost instantaneously and the method of kinetic densitometry helps to determine the swelling of the wall of the
2288
YE. A. CmggovA and A. E. Ird~rrtrs
individual fibre. The po values in ethylene glycol differ significantly from the mean which is connecte.d with its high viscosity exceeding 20 times that of water and with formic acid which rapidly enters into a chemical reaction with cellulose [10]. Examples of the kinetic curves are given in Fig. 1. The rate at which equilibrium swelling (equilibrium density) of cellulose is reached in the solvents studied differs by three orders (Table). Sorption equilibrium is established at the fastest rate in the alcohols, the rate of diffusion of alcohol into cellulose decreasing with increase in the size of the molecules. The rate of penetration into cellulose of normal hydrocarbons is lower by an order and of water and acetone by two orders than for the alcohols. For most of the solvents studied a mutual link exists between the rate of diffusion into cellulose and the constant a / 4 t / o f the Washburn equation (~r and r/are the surface tension and viscosity of the liquid respectively) describing the speed of movement of the liquid in the capillaries [12] (Fig. 2).
~'d'5"1°4,sec-' I o 18 6 19 " p,g/cm 3
/-74~
2
1.6
2
5 11
• 2
I
50
I00 150 Time,hr,
200
16o
9
lO
O'/#r2
20
Fro. 1 Fie. 2 Fxo. 1. Kinetics of change in the density of cellulose fibre in benzene (1), n-hexane (2) and dioxane (3). FIo. 2. Dependence of the rate of diffusion of solvents into cellulose on the constant of the Washburn equation. Here, and in Figs. 3 and 4, the point numbers correspond to the sample numbers in the Table. With the variety of solvents studied it appears possible to identify the factors which exert the main influence on the interaction of solvents wih cellulose. Earlier it was shown that for many polymer-solvent systems extremal dependence of some properties (equilibrium swelling, intrinsic viscosity, etc.) on the solubility parameter 6 is observed, the position of the extreme corresponding to the solubility parameter of the polymer [13]. For cellulose in the series of solvents studied a mutual link between swelling and the solubility parameter is absent. However, a good correlation is found between Qr and Qw,Jl (or the specific volume V,p), on the one hand, and the component of the solubility parameter 6h corresponding to the contribution of the energy of the hydrogen bonds [6], on the other (Fig. 3).
Sorption of solvents by cellulose and cellulose materials from liquid phase
2289
The dependence of the specific volume (equilibrium swelling of the wall) on 8h represents a curve with a maximum the abscissa of which is close to the @value of cellulose equal to 15.6 (J/m3) °'s [14]. The largest specific volume (least density) is shown by cellulose fibre in alcohols. Apparently the alcohols 5h of which is close to the solubility parameter of cellulose activity loosen the fibre wall but the resulting ultraporous structure is inaccessible for the molecules of the alcohols. At the same time, the energy of adsorption interaction is insufficient for the fuller separation of the structural elements of cellulose which would ensure penetration of the solvent molecules into the interstructural intervals. Qwall cm3/g mZj/g
"17
VsP'Sm
0.08
'i\
200 0.06
?.6#
0.00
7.52
0.02
l oj"
\'x " o17"-
I
I
10
zx ..~'"-
0.60
~.-." o20 1
I
20
30
FIG. 3
o-
~,(Olm a)
|
19 ~ o s
I 7o. 10
30
& (j/,.,,,)o 5 Fro. 4
FIo. 3. Specific volume (1) and equilibrium swelling (2) of the cellulose fibre wall and the total sorption of the solvent by the cellulose material (3) as a function of the component of the solubility parameter &h. FIo. 4. Glass transition temperature of plasticized cellulose (accolding to reference II 5l) as a function of the compon ent of the solubility parameter &h. As may be seen from the Table in some cases Pend values are obtained exceeding the X-ray density of cellulose (1.63-1,64 g/cma). Particularly high is the density of cellulose in normal hydrocarbons which are inert in respect of cellulose [11]. In our view the X-ray density of non-rigid hydrophilic materials to which cellulose belongs is not maximally possible for the given structure since the roentgenograms are obtained as a rule for air-dry samples and deformation of the all-sided stretching of the crystallites in the field of adsorption forces is not excluded. The saturated hydrocarbons the energy of interaction of which with the surface of cellulose is low do not deform the crystalline cell which is expressed in high Pc,a values apparently close to the true density of cellulose. It should be noted that the Q~a~zvalues are quite small (Fig. 3) and several times lower than the sorption values obtained in saturated vapours (in particular, for water). The reason for these discrepancies probably lies in the fact that in saturated vapours the liquid with capillary condensation at the sites of contacts of the structural elements
2290
YE. A. CrtmKOVhand A. E. KREITUS
makes a large contribution to the sorption values. With the method of kinetic densitometry this liquid is regarded as a dispersion medium. The dependence of the global absorption of the liquid by the cellulose material cn Jh with the probability 0-95 is described by the polynomial Qz = 1.1087 + 0"127Jn + 0'0012J~ The contribution of the absorption o f the solvent by the fibre wall to the global sorption (Fig. 3) does not exceed a few percent, i.e. Q2 is essentially determined by the capillary suction of the liquid into the cellulose material. The mutual link between Qz and Jh may be due to different factors. With increase in the ability of the solvent to form hydrogen bonds the energy of its interaction with cellulose increases. Since we are dealing with a swelling sorbent, on sorption there is increase not only in the volume of the individual fibres but also the interfibre distances. As Jh increases the wettability of the surface of the cellulose with solvent improves and the cohesion energy of the solvent increases. All these factors directly depending on 3h lead to rise in Qz. Figure 4 presents the dependence of the glass transition temperature of cellulose plasticized by solvents on Jh. With the probability 0.96 this dependence is described by the equation Tg= (231 + 15)-(35"1 _ 3.6)c5°'5 It is known that the plasticization effect is chiefly determined by the thermodynamic affinity of a solvent for a polymer [16] expressed by the Flory-Huggins interaction parameter which is proportional to the difference in the squares of the solubility parameters of the polymer and solvent. Therefore, not surprising is the mutual link between Tg and the solubility parameter of the plasticizer which, as shown above, is best expressed with the use not o f total J but its component Jh. Thus, hydrogen bonds play a decisive role in shaping the physicochemical properties of cellulose materials in contact with liquid media. The use of a three-dimensional model of the solubility parameter allows these properties to be described and hence predicted. Translated by A. CRozY REFERENCES
1. R. E. REIZIN'SH, Strukturoobrazovaniye v suspenziyakh tsellyuloznykh volokon (Structuring in Cellulose Fibre Suspensions). 208 pp., Riga, 1987 2. A.J. STAMM and X. H. TARKOW, J. Phys. Colloid. Chem. 54: 745, 1950 3. E.A. COLOMBO and E. H. IMMERGUT, J. Polymer Sci. C, 31,137, 1970 4. R. K. S. BHATIA, Indian J. Chem. 9: 1279, 1971 5. O. G. TARAKANOV, S. Yu. KHOVRYAKOV, Z. A. BYELOVA and T. N. GVOZDOVICH, Vysokomol. soyed. B21: 435, 1979 (Not translated in Polymer Sci. U.S.S.R.) 6. S. HANSEN, Industr. Engn. Chem. Product Res. Development 8: 2, 1969 7. S. A. DRINBYERG and E. F. ITSKO, Rastvoriteli dlya lakokrasochnykh materialov. Spravoehnoye posobiye (Solvents for Paint-Varnish Materials. Reference Guide). 206 pp., Leningrad, 1986 8. Ye. A. CHIRKOVA, G. P. VEVERIS and A. P. VEVERIS, Khim. drevesiny, 3, 28, 1985 9. P. H. HERMANS, Physics and Chemistry of Cellulose, 543 pp., N.Y., 1949
Diffusion and sorption of water vapour in polyurethane foam
2291
10. Z. A. ROGOVIN, Khimiya tsellyulozy (Chemistry of Cellulose). 519 pp., Moscow, 1972 11. N. I. KLENKOVA, Struktura i reaRtsionnaya sposobnost' tsellyulozy (Structure and Reactivity of Cellulose). 367 pp., Leningrad, 1967 12. A. ADAMSON, Fizicheskaya khimiya poverkhnostei (Physical Chemistry of Surfaces). 568 pp., Moscow, 1979 13. A. A. TAGER and L. K. KOLMAKOVA, Vysokomol. soyed. A22: 483, 1980 (Translated in Polymer Sci. U.S.S.R. 22: 3, 533, 1980) 14. Entsiklopediya polimerov (Polymer Encyclopaedia), Vol. 1, 1224 pp., Moscow, 1972 15. E. L. AKIM, N. I. NAIMARK, B. V. VASIL'EV, B. A. FOMENKO, E. V. IGNAT'EVA and N. N. ZHEGALOVA, Vysokomol. soyed. A13: 2244, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 10, 2522, 1971) 16. P. V. KOZLOV and S. P. PAPKOV, Fiziko-khimicheskiye osnovy plastifikatsii polimerov (Physicochemical Bases of Polymer Plasticization). 223 pp., Moscow, 1982
Polymer Science U.S.S.R. Vol. 31, No. 10, pp. 2291-2296~ 1989 Printed in Poland
0032-3950/89 $10,00+ .00 © 1990 Pergamon Press ple
DIFFUSION AND SORPTION OF WATER VAPOUR IN POLYURETHANE FOAM* A. G. DEMENT'EV, T. K. KHLYSTALOVAand I. I. MIKHEYWgA "Polimersintez" Science-Production Association
(Received 6 April 1988) The diffusion and sorption patterns of water vapour in rigid polyurethane foam have been studied. A technique is proposed and the activity of the water vapour PIPs determined for its different states: bound, clustered a n d free. The link between the water sorbed by the
polymer and its state and thermophysical and mechanical properties of the foam plastic is considered. THE diffusion and sorption patterns of water vapour by polymers, the state of sorbed water and its link with the physicomechanical properties of monolithic polymeric materials form the subject of quite a number of studies [1-4]. This attention is primarily due to practical requirements since polymeric materials are usually used and stored in conditions with wide limits of change in humidity. Rigid polyurethane foams (PUP') used in refrigerating technology, for heat insulation of heating networks and main pipelines, in building and many other branches of m o d e m technology may be used in humid media. However, the data on the behaviour of foam plastics for raised humidity are limited in the literature [5]. Therefore, we studied the diffusion and sorption of water vapottr in P U F s and their links with the thermophysical and mechanical properties of the f o a m plastic. * Vysokomol. soyed. A31: No. 10, 2084-2088, 1989.