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Structure of concentrated solutions of cellulose triacetate in methylenechloride and acetic acid
'Polymer Science U.8.S.R. Vol. 28, lqo. 5, pp. 1082-1089, 1081 Printed in Poland
0032-39501811081082-08S07.50/0 O,1982 Pergamon Press Ltd.
STRUCTURE OF CONCENTRATED SOLUTIONS OF CELLULOSE TRIACETATE IN METHYLENECHLORIDE AND ACETIC ACID* I. I. RYSKINA, N. A. VAKULENKO and L. I. J~HOMUTOV N. G. Chernyshevskii State University, Saratovsk
(Received 16 January 1980) The rheological behaviour Ofconcentrated solutions of cellulose triacetate in acetic acid and in methylene chloride hys been studied over a wide range of temperatures and concentrations. As the concentration is increased, the structure of the solution is described by two models of a fluctuation network, consisting of either overlapping coils or "entanglements". It is shown that the conditions of formation and the properties of the fluctuations are determined by the thermodynamic chain flexibility, the coil volume and the quality of the solvent which, for cellulose acetate, exhibit specific features as the temperature and concentration are changed. THE question of the effect of the nature of a solvent on the structure of t h e solution is one that has been little studied in the theory of concentrated solutions. A connection between 'the thermodynamic characteristics, as well as the polarizability of the solvent, and the rheological behaviour of the solutions has been established in a number of papers [1-3]. The temperature and the polymer concentration are known to affect the solvent's quality and this is reflected in t h e conformation of the macromolecules and in their degree aggregatio n. Solutions of rigid-chain polymers, which exhibit a specific s e t of viscosity properties [4], deserve special attention in this area. Solutions of Cellulose acetate, the special features of whose molecular properties distinguish them from a number of other rigid-chain polymers [5], also belong to this class of systems. On the basis of investigations [6-8] of the thermodynamic chain flexibility and the quality of the solvent in dilute solutions of the polar polymer cellulose triacetate (CTA.) in two different polar solvents, namely, methylenechloride and acetic acid, the present paper discusses the rheological properties o f concentrated solutions as the temperature and polymer concentration are changed. The structure of the highly concentrated solutions is modelled as a network with intermittent "fluctuation" nodes or "entanglements". At lower concentrations, the structure is represented b y overlapping and, finally, b y isolated macromolecular coils. Theory [9] predicts that the driving force for chain swelling should decrease as the concentration is increased, which implies a contraction of the coil. This leads to a reduction in the intensity of the intermolecular interaction and to a reduction in the rate at which the viscosity rises with an increase in concentration, * Vysokomol. soyed. ASS- No. 5, 972-977, 1981. 1082
Concentrated solutions of cellulose triacetate in methylenechloride
1083
Investigations carried out previoilsly [6] have shown that the system CTAmethylenechloride is a system a lower critical miscibility temperature for which t h e 02-point is at 27°C and is close to the boiling point of the solvent (40°0). With a low concentration of CTA in the solution, methylenechloride is a thermodynamically poor solvent but in the concentration region bounded by infinitely dilute and by moderately concentrated solutions, the polymersolvent interaction improves; a further increase in concentration leads to a reduction in this interaction [10]. Good compatibility is observed for the system CTA-acetic acid over the temperature range studied, which is bounded by the crystallization temperature (16°0) and the boiling point (118°0) of the solvent, and acetic acid is, consequently, a good solvent for OTA [7]. A phase transition is observed in this system at 53°0, the transition being accompanied by a change in the way in which the macromolecule's thermodynamic and hydrodynamic parameters depend on temperature [8]. A commercial sample of CTA with ~fv=104 and with an acetyl number of 61.5°/o was used for the present work as well as fractions with M~-----(1-20) × 104 and acetyl numbers of 60.0-62.0~/o. The fractions were obtained by fractional .precipitation [11]. The concentration of the solutions was varied in the range from 1 to 200 g/l. The concentration was limited by the possibility of obtaining homogeneous isophase solutions. The rheological properties were studied by means of the following equipment: H6ppler viscometers, an AKC-2 automatic capillary viscometer and an Ubbelohde-type capillary viscometer. The laminarity and stability of the flow were assessed before the flow curves were obtained [12]. Figure la shows the concentration dependence of the initial viscosity t/0(c) for CTA in methylenenchloride and in acetic acid. The initial viscosity increases monotonically with concentration. The positioning of the curves with respect to one another is determined by the contribution of the solvent's viscosity [2] and by the contribution of the swelling parameter of the macromolecular coil [13]. The higher value of the viscosity of acetic acid and the greater swelling parameter for CTA in it as compared with methylenechloride (r/~s'C~--l.1 and 0.4 cP, a-~l.3 and 1.0 [8] for acetic acid and methylenechloride respectively) are the reasons why the curve for CTA in acetic acid lies above the curve for CTAmethylenechloride. The curves come together at high concentrations and this occurs when a continuous fluctuation network is present in both systems. The critical concentration for the formation of a fluctuati6n network of entanglements, Cn, was determined by using the curves (tl0--t/s)----f(c) (Fig. lb); this critical concentration was found to be equal to 10 g/l. for CTA in methylenechloride and 30 g/1. for CTA-acetic acid. In the concentration region below Cn, regions are observed with a different rate of increase of viscosity. The explanation for this phenomenon may be obtained by considering the concentration dependence of the viscosity on the basis of the coil's hydrodynamic volume (14]. Figure 2 shows the reduced viscosity rlmp/c depends on c[t/]; this relationship determines
108~
I.I.
RYSXrNA et aZ.
the inspissation action of the polymer which is related to the volumetric filling of the sglution by macromolecular chains. The decrease in viscosity in the initial section of curve 2, which implies a contraction of the coil for CTA-methylenechloride at low concentrations as the concentration, is increased, extends as far as ca, that is, until a continuous fluctuation network is formed in the system. This anomaly in viscosity is observed only in the case of a poor solvent such as methylenechloride. The relationship considered gives, moreover, an idea about the change in solvent quality as the polymer concentration in the solutions is increased. The slope of this relationship is the constant KM in Martin's equation: ~/s___p= [~/] exp (KM[tl]C), o
which characterizes the interaction between the polymer and the solvent in a concentrated solution. The reduction in the absolute value of the reduced viscosity correspoflds to an improvement in the solvent's quality in the system CTA-methylenechloride as the concentration rises to ca [6]; at concentrations greater than ca, the quality deteriorates, the degree of deterioration deoreasiag as the concentration is increased. In the system CTA-acetic acid over the entire" concentration range studied, the polymer-solvent interaction deteriorates loc
5
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log(,jo-, s)EcpJ
3
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I
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!
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Fzo. 1. a - - C o n c e n t r a t i o n dependence of the logarithm of the initial viscosity, and b - - t h e logarithm of the difference in viscosities log (t/o--t/,) (~, is the viscosity of the solvent) for the systems 1 - - C T A - a c e t i c acid and g--CTA-rnethylenechloride a t 25°C.
Concentrated solutions of cellulose t r i a c e t a t e ia~Lmethylenechloride
108~
with an increase in concentration, this occurring to a great extent at low concentrations (up to c~). The structure of the solutions at concentrations lower than Cn can bg assesed from the way in which ~/0 depends on the polymer molecular weight, as s h o w n in Fig. 3. The initial viscosity increases as the molecular weight increases but, at a certain critical value of molecular weight, the exponent describing t h e increase changes abruptly: for both systems, the slope of the relationship increases from 0.3-0.4 to 1.0, that is, it takes on a value characteristic of the region
i
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FIG. 2. Dependence o f the reduced viscosity on the product c [,/] for 1--~l~A-acetic acid: a n d 2 - - f o r CTA-methylenechloride at 25°C. The arrows denote Cn. FIG. 3. Dependence of log t/0 on the logarithm of the poly~ner's molecular weight at various t e m p e r a t u r e s for CTA-methylenechloride (points) and CTA-acetic acid (triangles). 1--30; 2-- 25; 3-- 20; 4-- 15; 5-- 80; 6-- 50; 7-- 40; 8-- 30 and 9-- 20 ~C; c----4 g/1.
in which the coils overlap. The position of the point for tile change in slope of the curves, which corresponds to the critical molecular weight for the formation of a statistical network through the overlapping of the coil, Me, changes with temperature as shown in Fig. 4. This relationship is found to correlate with the temperature dependence of the equilibrium chain flexibility (the Kuhn segment, Ares), given in [8]. The values of M~ are found to be greater for the system CTA-acetic acid, in which the macromolecules have a high flexibility. The chain flexibility is, consequently, not favourable to the formation of intermolecular contacts between randomly overlapping coils. A more sparse network is found to be formed in the case of the more flexible chain. The number of intermolecular contacts in each millilitre of solution, calculated by t h e expression V-----cSTA/M~[15] (where Na is Avogadro's number and c the concentration) is equal to 18 ×10 is for CTA-acetic acid and to 26 × 1016 for CTA-methylenechlo-
I086
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RYSXI~A e~ a/.
ride, that is, the number of contacts is smaller with a high chain flexibility than with high rigidity. The structure of solutions of the two systems at concentrations greater than Ca is found to be different from a consideration of the flow curves. S t a t i s t i c a l and rheological characteristics of the structures being studied, which were represented as a network of "entanglements", were obtained as a result •Of calculations using an analytical method of treating the flow curves [16] (see Table). These characteristics reflect the kinetics of the process involved in the formation of a network of "entanglements" and they reflect the network's mechanical properties. Thus the order of the process of macromolecular ag-
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4. T e m p e r a t u r e dependence: ] a n d 2 . M ~ and 1" a n d 2 ' - - t h e f o r C T A a c e t i c a c i d (1 a n d 1') a n d C T A - m e t h y l e n e c h l o r i d e
I~HEOLOGICAL A N D
Am/[8]
STATISTICAL PROPERTIES OF THE SYSTEM C T A - I ~ E T H Y L E N E C H L O R I D E
AND C T A - A c E ~ c
7 Solvent
Kuhn segment (2 a n d 2 ' ) .
P
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~ X
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biethylenechloride
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0"89
0.44
0.8
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6.7
6.4
5.7
0.56
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Acetic acid
3.2
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0.75 0.61
0.37
0.4
0.9
53
5.0
4.9
4.9
0.31
1.6
.Vote. = - B~ate constant for the rupture of structural bonds; P - order of this process; ~= -- bounding stress for the structure disrupted to the maximum extent; ~ - shear stress at the point of inflexion of the rheological curve; r, -- Blngham flow limit; #pz -- plastic viscosity; #M -- effective viscosity of the structure disrupted to m a . l m u m extent; • -- i n ~ l specific power dissipated in flow; ~ -- mathematical expectation; ~ -- median of distribution; ~ -- mode o f distribution; f -- irregularity factor; ~ - shear stress a t the point of lnflexion on the curve of the system's flow rate.
Concentrated solutions of cellulose triacetate in methylenechloride
1087
gregation is 'one less in the system C~A-methylenechloride t h a n in the system CTA-acetic acid. The rate o f formation of the structural bonds is greater by a factor of 105 for CTA-methylenechloride, a fact which gives rise to the greater strength of the structure itself and hence to the greater (by a factor of 2) value of the integral specific power dissipated during flow, 8, as well as to the greater value of the bounding stress for the structure cLisrupetd to the m a x i m u m extent, • m, the Bingham flow limit ~0, and other characteristics. The rheologicat properties considered above have been obtained with a constant value of either concentration or temperature. Ageneralized conception of the kO
•
/(,.7
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FIG. 5. Temperature dependence of the activation parameters, ~Hv and ~ v , for the solvents and solutions of different concentrations for: ]-Z--Cr£A-methylenenohloride and
l'-5"--CTA-acetio acid. 1--Methylenecldoride; g--3.0; 3--10.0; 4--30.0; 5--B0.0; 6--100.0 a~d 7--150.0 g/l.;/'--acetic acid; 2'--5.0; 3'--30-0; 4'--50.0 and 5'--200.0 g/1.
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influence of these ~wo variables m a y be obtained by consideration of the activation parameters for viscous flow (Fig. 5). The value of the heat of activation for viscous flow, ztHv, is a measure of the strength of the structure and the activation entropy, ASv, is a measure of its ordering. I t m a y be seen from Fig. 5 t h a t the relationships AH=f(t) and also AS=f(t) exhibit different characteristics for the systems CTA-acetic acid and CTA-m~thylene chloride. Differences are, moreover, observed in the trend of the curves for concentrations greater than and less t h a n ~ . I n both systems for C>Cn, the entropy and enthalpy of activation were found to increase with an increase in concentration, t h a t is, the degree of order of the structure and the intermolecular interaction energy increase. For V~Cn, the polymer concentration is found to affect the characteristics of the temperature dependence of the thermodynamic activation parameters for viscous flow differently. For CTA-acetic acid, ASv and AHv, increase but for CTA-methylenechloride t h e y decrease with an increase in concentration. This anomaly in the system CTA-methylenechloride is connected with the effect t h a t isolated coils swell as the concentration rises in dilute solutions with a poor solvent. I t m a y also be noted t h a t the change in AHv and ASv with concentration correlates with the effect of t h e latter on the quality of the solvent. With an increase in temperature, zlSv and AHv, which have low values in the system CTA-acetic acid, do not change for concentrations greater than c~; for concentrations less t h a n Cn (curves 2' and 3'), the value of ASv depends on temperature. The smallest value of ASv is observed at 50°C. This is evidence t h a t the degree of ordering of the structure has its lowest value and is explained by the chain flexibility being greatest at the temperature of the phase transition. I n the system CTA-methylenechloride at concentrations greater t h a n cn, an abrupt decrease in ASv and AHv is observed as the temperature is increased above 20°C; this is evidence of the disruption of ordered supermolecular formations t h a t are stronger t h a n those in CTA-acetic acid. A transition at 0~----27°C is observed on the curves AHv:f(t) and ZtSv-----f(t).
Translated by G. F. M o D ~
REFERENCES , A. A. TAGER and G. V. VINOGRADOVA, Mel~anika pollmerov, 729, 1973 V. Ye. DREVAL', G. O. BOT~rINNIK, A. Ya. ~ and A. A. TAGER, Mekhanika polimerov, 1110, 1972 K. GANDHI and M. VtrILLIAMS, Vyazkouprugaya relaksat~iya v polimerakh (Visco. elastic Relaxation in Polymers), p. 214, "Mir", 1974 (Russian ~ranslation) V. G. ~VLT~V~IK;IYN, A. Ira. MALKIN, Ye. G. KOGAN and A. V. VOLOKHINA, Khimich. volokna, No. 6, 26, 1978 K. KAMIDE, J. Soc. Fiber Sci. and Teehnol. Japan 83: 3, 1977 I. I. RYSKINA~ V. P. LOZGACHEVA, Ye° D. DOKHVALENS]~II and V. M. AVER'YANOVA, VysokomoL soyed. A18: 2500, 1976 (Translated in Polymer Sci. U.S.S.R. 18:
1. V. Ye. DREVAL', A. Ya. ~
2. 3. 4.
5. 6.
11, 2854, 1976)
Connection between micro-crazing and meohauieal behaviour of glassy PETP
1089
7. L I. RYSKINA, V sb. T~L~lovaniya v oblm~i elektrokhimfi i fiziiro-khlrnll polimerov (In: Research in the Field of Electrochemi~, T and Physical Chemistry of Polymers). p. 52, Izd. Saratovskogo gos. un-ta, 1975 8. L I. RYSKINA, VI Vsesoyuznoye soveshchaniey: Khimiya i teklmologiya proizvodnykh tsellyulozy (VIth All-Union Conference: Chemistry and Technology of Cellulose I)erivatives) pt. 1, p. 76, Vladlm~r, 1980 9. M. FIXMAN, J. Chem..Phys. 25: 1656, 1955 10. W. MOORE and R. SHUTTLEWORTH, J. Polymer Sci. AI: 1985, 1963 11. N. P. ZAKURDAYEVA, E. D. DERZHAVINA and Ye. K. PODGORODETSKII, Khimich. volokna, No, 1, 28, 1963 12. G. A. LOBANOVA, Candidate's dissertation, S. V. Lebedev All-Union Scientific Reaserch Institute for Synthetic Rubber, Leningrad, 1972 13. V. I, IRZHAK, Mashiny i tekhnologiya pererabotki kauehukov, polimerov i rezinovykh smesei (Machinery and Technology for the Processing of Rubbers, Polymers and Resin Mixtures). Interuniversity collection of scientific papers, No. 2, p. 29, Yaroslav, 1978 14. R. SIMHA and L. UTRACKI, J. Polymer SCI. 5, A-2: 853, 1967 15. J. SC~URZ, Cellulose Chem. Technol. 11: 3, 1977 16. N. Ya. AVDEYEV, V sb. Matematika i nekoto~yye yeye prilozheniya v teoretieheskom i prikladnom yestsstvoznanii (In: Mathematics and Certain of its Applications in Theoretical and Applied Science), p. 24, Pedinstitut, Rostov-na-Donu, 1972
Polymer Science U.S.S.R. Vol. 23, 1~o. 5, pp.
1089-1097, 1981
Printed in Poland
0032-3950/81/051089-09507.50/0 © 1982 Pergamon Prem Ltd.
AN INVESTIGATION OF THE CONNECTION BETWEEN MICRO-CRAZING AND ~ MECHANICAL BEHAVIOUR OF GLASSY POLYETHYLENETEREPHTHALATE DURING DEFORMATION IN ADSORPTION-ACTIVE MEDIA* A. L. VOL~SK~, N. A. Sm~ov and ~. F. BAKEYEV M. V. Lomonosov State University, Moscow
(Received 21 January 1980) The mechanical properties of glassy polycthyleneterphthalatc have been investigated in a number of liquid adsorption-active media, The tensile curve of the polymer in an adsorption.active medium has been found to contain information about features of micro-cracks which determines the transition of the polymer into the oriented conditions; this enables the rate of micro-crack growth to be found directly from the polymer's tensile curves. The rate of micro-crack growth has been shown to be controlled by the surface reactivity of the liquid medium, its viscosity and molecular dimensions which determine the migration of the liquid into the active deformation zone of the polymer, as well as by the conditions of loading. * Vysokomol. soyed. A25: No. 5, 978-984, 1981.
0032-39501811081082-08S07.50/0 O,1982 Pergamon Press Ltd.
STRUCTURE OF CONCENTRATED SOLUTIONS OF CELLULOSE TRIACETATE IN METHYLENECHLORIDE AND ACETIC ACID* I. I. RYSKINA, N. A. VAKULENKO and L. I. J~HOMUTOV N. G. Chernyshevskii State University, Saratovsk
(Received 16 January 1980) The rheological behaviour Ofconcentrated solutions of cellulose triacetate in acetic acid and in methylene chloride hys been studied over a wide range of temperatures and concentrations. As the concentration is increased, the structure of the solution is described by two models of a fluctuation network, consisting of either overlapping coils or "entanglements". It is shown that the conditions of formation and the properties of the fluctuations are determined by the thermodynamic chain flexibility, the coil volume and the quality of the solvent which, for cellulose acetate, exhibit specific features as the temperature and concentration are changed. THE question of the effect of the nature of a solvent on the structure of t h e solution is one that has been little studied in the theory of concentrated solutions. A connection between 'the thermodynamic characteristics, as well as the polarizability of the solvent, and the rheological behaviour of the solutions has been established in a number of papers [1-3]. The temperature and the polymer concentration are known to affect the solvent's quality and this is reflected in t h e conformation of the macromolecules and in their degree aggregatio n. Solutions of rigid-chain polymers, which exhibit a specific s e t of viscosity properties [4], deserve special attention in this area. Solutions of Cellulose acetate, the special features of whose molecular properties distinguish them from a number of other rigid-chain polymers [5], also belong to this class of systems. On the basis of investigations [6-8] of the thermodynamic chain flexibility and the quality of the solvent in dilute solutions of the polar polymer cellulose triacetate (CTA.) in two different polar solvents, namely, methylenechloride and acetic acid, the present paper discusses the rheological properties o f concentrated solutions as the temperature and polymer concentration are changed. The structure of the highly concentrated solutions is modelled as a network with intermittent "fluctuation" nodes or "entanglements". At lower concentrations, the structure is represented b y overlapping and, finally, b y isolated macromolecular coils. Theory [9] predicts that the driving force for chain swelling should decrease as the concentration is increased, which implies a contraction of the coil. This leads to a reduction in the intensity of the intermolecular interaction and to a reduction in the rate at which the viscosity rises with an increase in concentration, * Vysokomol. soyed. ASS- No. 5, 972-977, 1981. 1082
Concentrated solutions of cellulose triacetate in methylenechloride
1083
Investigations carried out previoilsly [6] have shown that the system CTAmethylenechloride is a system a lower critical miscibility temperature for which t h e 02-point is at 27°C and is close to the boiling point of the solvent (40°0). With a low concentration of CTA in the solution, methylenechloride is a thermodynamically poor solvent but in the concentration region bounded by infinitely dilute and by moderately concentrated solutions, the polymersolvent interaction improves; a further increase in concentration leads to a reduction in this interaction [10]. Good compatibility is observed for the system CTA-acetic acid over the temperature range studied, which is bounded by the crystallization temperature (16°0) and the boiling point (118°0) of the solvent, and acetic acid is, consequently, a good solvent for OTA [7]. A phase transition is observed in this system at 53°0, the transition being accompanied by a change in the way in which the macromolecule's thermodynamic and hydrodynamic parameters depend on temperature [8]. A commercial sample of CTA with ~fv=104 and with an acetyl number of 61.5°/o was used for the present work as well as fractions with M~-----(1-20) × 104 and acetyl numbers of 60.0-62.0~/o. The fractions were obtained by fractional .precipitation [11]. The concentration of the solutions was varied in the range from 1 to 200 g/l. The concentration was limited by the possibility of obtaining homogeneous isophase solutions. The rheological properties were studied by means of the following equipment: H6ppler viscometers, an AKC-2 automatic capillary viscometer and an Ubbelohde-type capillary viscometer. The laminarity and stability of the flow were assessed before the flow curves were obtained [12]. Figure la shows the concentration dependence of the initial viscosity t/0(c) for CTA in methylenenchloride and in acetic acid. The initial viscosity increases monotonically with concentration. The positioning of the curves with respect to one another is determined by the contribution of the solvent's viscosity [2] and by the contribution of the swelling parameter of the macromolecular coil [13]. The higher value of the viscosity of acetic acid and the greater swelling parameter for CTA in it as compared with methylenechloride (r/~s'C~--l.1 and 0.4 cP, a-~l.3 and 1.0 [8] for acetic acid and methylenechloride respectively) are the reasons why the curve for CTA in acetic acid lies above the curve for CTAmethylenechloride. The curves come together at high concentrations and this occurs when a continuous fluctuation network is present in both systems. The critical concentration for the formation of a fluctuati6n network of entanglements, Cn, was determined by using the curves (tl0--t/s)----f(c) (Fig. lb); this critical concentration was found to be equal to 10 g/l. for CTA in methylenechloride and 30 g/1. for CTA-acetic acid. In the concentration region below Cn, regions are observed with a different rate of increase of viscosity. The explanation for this phenomenon may be obtained by considering the concentration dependence of the viscosity on the basis of the coil's hydrodynamic volume (14]. Figure 2 shows the reduced viscosity rlmp/c depends on c[t/]; this relationship determines
108~
I.I.
RYSXrNA et aZ.
the inspissation action of the polymer which is related to the volumetric filling of the sglution by macromolecular chains. The decrease in viscosity in the initial section of curve 2, which implies a contraction of the coil for CTA-methylenechloride at low concentrations as the concentration, is increased, extends as far as ca, that is, until a continuous fluctuation network is formed in the system. This anomaly in viscosity is observed only in the case of a poor solvent such as methylenechloride. The relationship considered gives, moreover, an idea about the change in solvent quality as the polymer concentration in the solutions is increased. The slope of this relationship is the constant KM in Martin's equation: ~/s___p= [~/] exp (KM[tl]C), o
which characterizes the interaction between the polymer and the solvent in a concentrated solution. The reduction in the absolute value of the reduced viscosity correspoflds to an improvement in the solvent's quality in the system CTA-methylenechloride as the concentration rises to ca [6]; at concentrations greater than ca, the quality deteriorates, the degree of deterioration deoreasiag as the concentration is increased. In the system CTA-acetic acid over the entire" concentration range studied, the polymer-solvent interaction deteriorates loc
5
(l
4
log(,jo-, s)EcpJ
3
b 2 1 0 I
I
1
!
2
!ogGEg/l.J IogcCg/tJ
Fzo. 1. a - - C o n c e n t r a t i o n dependence of the logarithm of the initial viscosity, and b - - t h e logarithm of the difference in viscosities log (t/o--t/,) (~, is the viscosity of the solvent) for the systems 1 - - C T A - a c e t i c acid and g--CTA-rnethylenechloride a t 25°C.
Concentrated solutions of cellulose t r i a c e t a t e ia~Lmethylenechloride
108~
with an increase in concentration, this occurring to a great extent at low concentrations (up to c~). The structure of the solutions at concentrations lower than Cn can bg assesed from the way in which ~/0 depends on the polymer molecular weight, as s h o w n in Fig. 3. The initial viscosity increases as the molecular weight increases but, at a certain critical value of molecular weight, the exponent describing t h e increase changes abruptly: for both systems, the slope of the relationship increases from 0.3-0.4 to 1.0, that is, it takes on a value characteristic of the region
i
q.5 i
1o9 H 5"5
I. V,p/C IV] 2
!
I 0 I
I
WO FIG. 2
c[~]
1
300
logr]oI FzG. 3
FIG. 2. Dependence o f the reduced viscosity on the product c [,/] for 1--~l~A-acetic acid: a n d 2 - - f o r CTA-methylenechloride at 25°C. The arrows denote Cn. FIG. 3. Dependence of log t/0 on the logarithm of the poly~ner's molecular weight at various t e m p e r a t u r e s for CTA-methylenechloride (points) and CTA-acetic acid (triangles). 1--30; 2-- 25; 3-- 20; 4-- 15; 5-- 80; 6-- 50; 7-- 40; 8-- 30 and 9-- 20 ~C; c----4 g/1.
in which the coils overlap. The position of the point for tile change in slope of the curves, which corresponds to the critical molecular weight for the formation of a statistical network through the overlapping of the coil, Me, changes with temperature as shown in Fig. 4. This relationship is found to correlate with the temperature dependence of the equilibrium chain flexibility (the Kuhn segment, Ares), given in [8]. The values of M~ are found to be greater for the system CTA-acetic acid, in which the macromolecules have a high flexibility. The chain flexibility is, consequently, not favourable to the formation of intermolecular contacts between randomly overlapping coils. A more sparse network is found to be formed in the case of the more flexible chain. The number of intermolecular contacts in each millilitre of solution, calculated by t h e expression V-----cSTA/M~[15] (where Na is Avogadro's number and c the concentration) is equal to 18 ×10 is for CTA-acetic acid and to 26 × 1016 for CTA-methylenechlo-
I086
I.I.
RYSXI~A e~ a/.
ride, that is, the number of contacts is smaller with a high chain flexibility than with high rigidity. The structure of solutions of the two systems at concentrations greater than Ca is found to be different from a consideration of the flow curves. S t a t i s t i c a l and rheological characteristics of the structures being studied, which were represented as a network of "entanglements", were obtained as a result •Of calculations using an analytical method of treating the flow curves [16] (see Table). These characteristics reflect the kinetics of the process involved in the formation of a network of "entanglements" and they reflect the network's mechanical properties. Thus the order of the process of macromolecular ag-
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10 7O
.,,,.-2, V I
I
I
20 Fzo.
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60
T°
4. T e m p e r a t u r e dependence: ] a n d 2 . M ~ and 1" a n d 2 ' - - t h e f o r C T A a c e t i c a c i d (1 a n d 1') a n d C T A - m e t h y l e n e c h l o r i d e
I~HEOLOGICAL A N D
Am/[8]
STATISTICAL PROPERTIES OF THE SYSTEM C T A - I ~ E T H Y L E N E C H L O R I D E
AND C T A - A c E ~ c
7 Solvent
Kuhn segment (2 a n d 2 ' ) .
P
X
~ X
ACID .~T 2 5 ° C
7 X
7 r/sp
t/m
X
X
x
J"
x
l~/m~
N/m s
biethylenechloride
2.2
1.7× × 10 -10
1.3
0"89
0.44
0.8
1.1
106
6.7
6.4
5.7
0.56
2.0
Acetic acid
3.2
1.1× × 10 -16
0.75 0.61
0.37
0.4
0.9
53
5.0
4.9
4.9
0.31
1.6
.Vote. = - B~ate constant for the rupture of structural bonds; P - order of this process; ~= -- bounding stress for the structure disrupted to the maximum extent; ~ - shear stress at the point of inflexion of the rheological curve; r, -- Blngham flow limit; #pz -- plastic viscosity; #M -- effective viscosity of the structure disrupted to m a . l m u m extent; • -- i n ~ l specific power dissipated in flow; ~ -- mathematical expectation; ~ -- median of distribution; ~ -- mode o f distribution; f -- irregularity factor; ~ - shear stress a t the point of lnflexion on the curve of the system's flow rate.
Concentrated solutions of cellulose triacetate in methylenechloride
1087
gregation is 'one less in the system C~A-methylenechloride t h a n in the system CTA-acetic acid. The rate o f formation of the structural bonds is greater by a factor of 105 for CTA-methylenechloride, a fact which gives rise to the greater strength of the structure itself and hence to the greater (by a factor of 2) value of the integral specific power dissipated during flow, 8, as well as to the greater value of the bounding stress for the structure cLisrupetd to the m a x i m u m extent, • m, the Bingham flow limit ~0, and other characteristics. The rheologicat properties considered above have been obtained with a constant value of either concentration or temperature. Ageneralized conception of the kO
•
/(,.7
d
,dSV, "m'oTe.deg
Hv,molJ" ]
I CZ .
qO0 -
-;
300-
/)
I00
, q,
, ,
50 I
ZO
50
I
I
I
ip
80 T °
200-
- t J
7
I
20
b
I
50
I
l
I
80 7"0
FIG. 5. Temperature dependence of the activation parameters, ~Hv and ~ v , for the solvents and solutions of different concentrations for: ]-Z--Cr£A-methylenenohloride and
l'-5"--CTA-acetio acid. 1--Methylenecldoride; g--3.0; 3--10.0; 4--30.0; 5--B0.0; 6--100.0 a~d 7--150.0 g/l.;/'--acetic acid; 2'--5.0; 3'--30-0; 4'--50.0 and 5'--200.0 g/1.
"]088
]~, I,. RYSKII~A ~ ~ .
influence of these ~wo variables m a y be obtained by consideration of the activation parameters for viscous flow (Fig. 5). The value of the heat of activation for viscous flow, ztHv, is a measure of the strength of the structure and the activation entropy, ASv, is a measure of its ordering. I t m a y be seen from Fig. 5 t h a t the relationships AH=f(t) and also AS=f(t) exhibit different characteristics for the systems CTA-acetic acid and CTA-m~thylene chloride. Differences are, moreover, observed in the trend of the curves for concentrations greater than and less t h a n ~ . I n both systems for C>Cn, the entropy and enthalpy of activation were found to increase with an increase in concentration, t h a t is, the degree of order of the structure and the intermolecular interaction energy increase. For V~Cn, the polymer concentration is found to affect the characteristics of the temperature dependence of the thermodynamic activation parameters for viscous flow differently. For CTA-acetic acid, ASv and AHv, increase but for CTA-methylenechloride t h e y decrease with an increase in concentration. This anomaly in the system CTA-methylenechloride is connected with the effect t h a t isolated coils swell as the concentration rises in dilute solutions with a poor solvent. I t m a y also be noted t h a t the change in AHv and ASv with concentration correlates with the effect of t h e latter on the quality of the solvent. With an increase in temperature, zlSv and AHv, which have low values in the system CTA-acetic acid, do not change for concentrations greater than c~; for concentrations less t h a n Cn (curves 2' and 3'), the value of ASv depends on temperature. The smallest value of ASv is observed at 50°C. This is evidence t h a t the degree of ordering of the structure has its lowest value and is explained by the chain flexibility being greatest at the temperature of the phase transition. I n the system CTA-methylenechloride at concentrations greater t h a n cn, an abrupt decrease in ASv and AHv is observed as the temperature is increased above 20°C; this is evidence of the disruption of ordered supermolecular formations t h a t are stronger t h a n those in CTA-acetic acid. A transition at 0~----27°C is observed on the curves AHv:f(t) and ZtSv-----f(t).
Translated by G. F. M o D ~
REFERENCES , A. A. TAGER and G. V. VINOGRADOVA, Mel~anika pollmerov, 729, 1973 V. Ye. DREVAL', G. O. BOT~rINNIK, A. Ya. ~ and A. A. TAGER, Mekhanika polimerov, 1110, 1972 K. GANDHI and M. VtrILLIAMS, Vyazkouprugaya relaksat~iya v polimerakh (Visco. elastic Relaxation in Polymers), p. 214, "Mir", 1974 (Russian ~ranslation) V. G. ~VLT~V~IK;IYN, A. Ira. MALKIN, Ye. G. KOGAN and A. V. VOLOKHINA, Khimich. volokna, No. 6, 26, 1978 K. KAMIDE, J. Soc. Fiber Sci. and Teehnol. Japan 83: 3, 1977 I. I. RYSKINA~ V. P. LOZGACHEVA, Ye° D. DOKHVALENS]~II and V. M. AVER'YANOVA, VysokomoL soyed. A18: 2500, 1976 (Translated in Polymer Sci. U.S.S.R. 18:
1. V. Ye. DREVAL', A. Ya. ~
2. 3. 4.
5. 6.
11, 2854, 1976)
Connection between micro-crazing and meohauieal behaviour of glassy PETP
1089
7. L I. RYSKINA, V sb. T~L~lovaniya v oblm~i elektrokhimfi i fiziiro-khlrnll polimerov (In: Research in the Field of Electrochemi~, T and Physical Chemistry of Polymers). p. 52, Izd. Saratovskogo gos. un-ta, 1975 8. L I. RYSKINA, VI Vsesoyuznoye soveshchaniey: Khimiya i teklmologiya proizvodnykh tsellyulozy (VIth All-Union Conference: Chemistry and Technology of Cellulose I)erivatives) pt. 1, p. 76, Vladlm~r, 1980 9. M. FIXMAN, J. Chem..Phys. 25: 1656, 1955 10. W. MOORE and R. SHUTTLEWORTH, J. Polymer Sci. AI: 1985, 1963 11. N. P. ZAKURDAYEVA, E. D. DERZHAVINA and Ye. K. PODGORODETSKII, Khimich. volokna, No, 1, 28, 1963 12. G. A. LOBANOVA, Candidate's dissertation, S. V. Lebedev All-Union Scientific Reaserch Institute for Synthetic Rubber, Leningrad, 1972 13. V. I, IRZHAK, Mashiny i tekhnologiya pererabotki kauehukov, polimerov i rezinovykh smesei (Machinery and Technology for the Processing of Rubbers, Polymers and Resin Mixtures). Interuniversity collection of scientific papers, No. 2, p. 29, Yaroslav, 1978 14. R. SIMHA and L. UTRACKI, J. Polymer SCI. 5, A-2: 853, 1967 15. J. SC~URZ, Cellulose Chem. Technol. 11: 3, 1977 16. N. Ya. AVDEYEV, V sb. Matematika i nekoto~yye yeye prilozheniya v teoretieheskom i prikladnom yestsstvoznanii (In: Mathematics and Certain of its Applications in Theoretical and Applied Science), p. 24, Pedinstitut, Rostov-na-Donu, 1972
Polymer Science U.S.S.R. Vol. 23, 1~o. 5, pp.
1089-1097, 1981
Printed in Poland
0032-3950/81/051089-09507.50/0 © 1982 Pergamon Prem Ltd.
AN INVESTIGATION OF THE CONNECTION BETWEEN MICRO-CRAZING AND ~ MECHANICAL BEHAVIOUR OF GLASSY POLYETHYLENETEREPHTHALATE DURING DEFORMATION IN ADSORPTION-ACTIVE MEDIA* A. L. VOL~SK~, N. A. Sm~ov and ~. F. BAKEYEV M. V. Lomonosov State University, Moscow
(Received 21 January 1980) The mechanical properties of glassy polycthyleneterphthalatc have been investigated in a number of liquid adsorption-active media, The tensile curve of the polymer in an adsorption.active medium has been found to contain information about features of micro-cracks which determines the transition of the polymer into the oriented conditions; this enables the rate of micro-crack growth to be found directly from the polymer's tensile curves. The rate of micro-crack growth has been shown to be controlled by the surface reactivity of the liquid medium, its viscosity and molecular dimensions which determine the migration of the liquid into the active deformation zone of the polymer, as well as by the conditions of loading. * Vysokomol. soyed. A25: No. 5, 978-984, 1981.