Absolute viscosities of semi-dilute solutions of polytethylene.
glycol) and poly(vinyl alcohol) and their mixtures in water and of
poly(ethylene glycol) and poly(vinyl chloride) and the ir mixtures
in chlorobenzene have been measured at 30 C C. The viscosities
of poly(vinyl alcohol) and poly(vinyl chloride) increase sharply
with concentration. The plots of viscosity of polymer mixtures
against composition deviate from linearity. The effect of total
polymer content on the viscosity of mixtures has also been
studied. The\u27 results are discussed in terms of the association of
similar type macromolecules and compatibility between dissimilar
types of macromolecules. Theoretical predictions of compatibility/
incompatibility have also been made for these systems.
It appears that poly(viniy alcohol) and poly(vinyl chloride) macromolecules associate at higher concentrations and poly(ethylene glycol) is incompatible with poly(vinyl alcohol), but compatible with poly(vinyl chloride) in water and chlorobenzene, respectively

Harun Ur Rashid

English

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CROATICA CHEMICA ACTACCA-1839CCACAA 62 (1) 57-65 (1989)YU ISSN 0011-1643UDC 532.13Original Scientific PaperViscometric Studies of Poly(ethylene glycol), Poly(vinyl alcohol)and Poly(vinyl chloride) and Their Mixtures in Water andChlorobenzeneBarun Ur Rashid20, Carpenter Court, Markharn, Ontario, Canada L3P 6W2Received October 7, 1987Absolute viscosities of semi-đilute solutions of polytethylene.glycol) and poly(vinyl alcohol) and their mixtures in water and ofpoly(ethylene glycol) and poly(vinyl chloride) and the ir mixturesin chlorobenzene have been measured at 30 C C. The viscositiesof poly(vinyl alcohol) and poly(vinyl chloride) increase sharplywith concentration. The plots of viscosity of polymer mixturesagainst composition deviate from linearity. The effect of totalpolymer content on the viscosity of mixtures has also beenstudied. The' results are discussed in terms of the association ofsimilar type macromolecules and compatibility between dis-similar types of macromo1ecu1es. Theoretical predictions of com-patibility/incompatibility have also been made for these systems.It appears that poly(viniy alcoho1) and po1y(viny1 chloride) mac-romolecules associate at higher concentrations and po1y(ethy1eneglycol) is incompatib1e with polytvinyl alcohol), but compatiblewith po1y(viny1 chloride) in water and chlorobenzene, respective1y.INTRODUCTIONMacromolecules remain isolated in polymer solution of infinite dilutionwithout interacting with one another. As the concentration of the solutionincreases, the macromolecules come into contact with each other formingassociates'! The higher the molecular mass of the polymer, the smaller is theconcentration at which they come into contact. The attractive interactionbetween polymer chains is enhanced in a poor solvent and if the polymerchains have capability of forming hydrogen bonds with each other. Theassociation of macromolecules may result in an increase of viscosity of thesystem.Viscometric results of polymer mixtures in a common solvent have beeninterpreted in terms of compatibility between polymers. The nonlinear plotof viscosity against composition has been considered as the indication ofincompatibility between polymers.F" Other works", however, have concludedthat the deviation of the values of viscosity from additivity should not beregarded as a measure of incompatibility.The full address of the author to wnom correspondence should be sent: De-partment of Chernistry, Bayero University, P. M. B. 3011, Kano, Nigeria.r58 H. U. RASHIDIn the present work we have used the viscometry method to study semi--dilute aqueous solution of a low molar mass polymer, poly(ethylene glycol),and its high mol ar mass isomer, poly(vinyl alcohol). We have also presentedthe viscometric data of a mixture of poly(ethylene glycol) and poly(vinylalcohol) in water and a mixture of poly(ethylene glycol) and poly(vinyl chlo-ride) in chlorobenzene. Attempts have been made to explain the results interms of the association of similar type macromolecules and compatibilitybetween dissimilar types of macromolecules. Attempts have also been madeto estimate roughly the extent of compatibility between the macromoleculesthrough theoretical approach.EXPERIMENTALMate1'ialsCornmercial samples of poly(vinyl alcohol) (PVA), poly(vinyl chloride) (PVC)and poly(ethylene glycol) (PEG) were us ed in this work. The molecular weights ofthe samples as indicated by the supplier, BDH Ltd., England are PVA, 125000(Degree of hydrolysis: 87-89~/0) and PVC, 100000. The molecular weight of PEG1000, also supplied by BDH, was determined by end group analysis" as 995.Chlorobenzene and water were fractionaUy distilled. Only middle fractions wereused.Preparation of SolutionsAccurately weighed amounts of polymers were simultaneously dissolved in thesolvent. For PEG/PVA/water system, the range of polymer composition and thetotal polymer concentrations studied were 0-100% and 2-8% (w/v), respectively.For PEG/PVC/chlorobenzene system, solutions of 2% total polymer concentrationwere prepared from a whole range of composition. But clear, homogeneous solutionsof 8% total polymer content were obtained only from 10, 20 and 40% of PVC.Gelation was observed in solutions of higher proportions of PVC. At least 24 hourswere allowed (for the polymers to dissolve completely) before the solutions werefiltered using sintered glass filters.Measurement of Absolute Viscosity of SolutionsThe absolute viscosity, 'Y}, of solutions was evaluated from the following wellknown equation(3f)'>1=ant---., - t (1)where f} and t are the density and flow time of the solution, respectively. AnUbbelohde suspended level type viscometer was used to measure the flow timeof solutions at 30CC. The viscometer constants, et and fJ were determined by mea-suring the flow time of water at different temperatures. The absolute viscosityvalues of water at various temperatures were taken from literature."Measurement of Densities of Polymers and Thei1' SolutionsThe densities of polymers were determined using the Archimedes principleand those of solvents and solutions by pyknometer.RESULTS AND DISCUSSIONPEG/PV.4./Water SystemThe absolute viscosities of aqueous solutions of PEG and PVA at differentconcentrations are given in Table I. As expected, the viscosity increases withan increase in concentration for both systems. For PEG!water system theincrease is not very significant owing to the low molar mass of PEG andVISCOMETRIC STUDIES 59TABLE IAbsoLute viscosities of aqueous soLutions of poLy(ethyLene gLycoL) and poLy(vinyLatcohol) at different concentrations measured at 30 ce% Concentration 'YI (PEG) X 103 'YI (PVA) X 103(w/v) (N s m") (N s m-2)2 1.04 4.094 1.16 23.346 1.19 146.008 1.28 226.20its incapacity of associating intermolecularly. On the other hand, in thePVA/water system an increase of concentration by 400 percent has increasedthe viscosity by about 5500 percent. The higher molar mass of PVA and itscapability of associating through hydrogen bonds has resulted in this massiveincrease of viscosity.The absolute viscosity of the mixture of PEG and PVA in water hasbeen plotted against weight percentage of PVA for various total polymerconcentrations in Figures 1 and 2. Non-linear plots are obtained for datapoints above 200/0 PVA./:; 2',. Polymer mixtureo 4 'I.Polymer eit x tu re3.5 --- From eqn. (II) 25NNI IE Eul ulZ----;. Z<, <,,...,(y) OO 15x 2.5 / x~ / ~/ul / ulO / OU / Uul / ·Ul> / 5 >1.5 /////40 60 O 100WtOfo PVAFigure 1. Absolute viscosity of 2% and 4% PEG - PVA mixture in water versusweight percent of PVA.Absolute viscosity valu.es have been calculated using additivity rule fromthe following equation for 2 and 60/0 solutions:(2)where XI and X2 are the weight fraction of the component polymers in themixture and 7]1 and 7]2 are the measured viscosities of the individual polymersolutions. These values have also been plotted against composition, as shown60 H. U. RASHIDo 6% Pol y rn er mi xtureO 8% Polymer mi x t u r e--- F eo m eq n. (i i)40 60Wt % PVA80 100Figure 2. Absolute viscosity of 6% and 8% PEG - PVA mixture in water versusweight percent of PVA.by dotted lines in Figures 1 and 2. The measured viscosity values of themixtures deviate negatively from the dotted lines and the deviation is morepronounced in the case of a higher concentrated solution.The effect of PVA on the viscosity of PEG solutions is more revealingin the plots of absolute viscosity against the weight percent of total polymerin the solution (Figure 3) at various weight percentage of PVA. Addition/1r I/I/ / iJ/ ,1.1~~;=q=-~;;, _-!:-I .J2 1.-'---'--6-- 8 1CWt % Polymer rn i x t ureFigure 3. Absolute viscosity of PEG - PVA mixture verS1ts weight percent ofpolymer mixture at different PVA concentrations; 6. O~/o,D 10%, Il 20%, O 40%and X 60% PVA.35N,Eul~J>-.•..25ulouul> 5oVISCOMETRIC STUDIES 61of 10, 200/0 of PVA does not alter much the viscosity of the solution. Wemay observe a rapid increase of viscosity in solutions containing more than200/0PVA and a total polymer content higher than 4010.In solution of a lower concentration of PVA, isolated PVA moleculesmay interact with isolated PEG molecules forming polycomplexes throughhydrogen bonds (Illustration 1).-CH,-~H-CH,-~H-o oI IH HI .;- (CH,J,-O-(CH,),.o-(CH,J,-O-Illustration 1. Polycomplex formation through hydrogen bonds between PVA andPEG macromolecules.When the concentration of a solution increases, macromolecules beginto come into contact with one another, forming associates. The higher themolecular mass of a dissolved polymer, the lower is the concentration atwhich they come into contact. In solutions of higher concentration of PVAand also due to larger PVA molecular size, contacts among PVA moleculesare more likely than those between PVA and PEG molecules. Association ofPVA is formed also through hydrogen bonds between hydroxyl groups (Illu-stration 2). Association is enhanced in poor solvents like water where thepolymer contacts are more likely to predominate. Single polymer moleculesno longer diffuse separately, but drag along neighbours. This leads to alarger dissipation of energy and a higher viscosity.-CH,-~H- -~H-CH,-O_H······O_H······O_H.....··O_HI I-CH-CH,- -CH-CH,-Illustration 2. Intermolecular association of PVA.The non-linear behaviour of viscosity with composition has been consi-dered as the indication of incompatibility between polymers.š" In PEG/PVAI/water system, the incompatibility between PEG and PVA at higher eon-centrations mayarise due to this tendency of PVA molecules to associate.Deviation from the linear behaviour of viscosity with composition, however,may not be considered as an unambiguous measure of incompatibility betweenpolyrners.?Methods are available which may be used to predict the extent of corn-patibility between polymers. One of the methods is to ca1culate the heat ofmixing, tJ. Hm for the whole range of composition of the polymer mixtureand compare the values with 42 X 10-3 J mol-i, which has been regardedas the uper limit for a polymer pair to be compatible.l? Schneier-? deducedthe following equation for the heat of mixing for two component polymerblends. .(3)where X, M, p and o are the weight fraction, repe at unit molecular weight,density and the solubility parameter, respectively. tJ,. Hm has been ca1culatedusing equation (3) for PEG/PVA mixture and plotted against the composition62 H. U. RASHIDTABLE IIDensity and solubiLity parameters of polymers and solvents*Density(kg m=)Solubility ParameterX 10-3 (J m-3)1/2PVAPVCPEGChlorobenzeneWater12701350ll50ll7299525.8"19.4"18.8c19.6"48.1"* Measured at 30 cC.n J. B r U n d r u p and E. H. E m m e r g u t, Eds., Polymer fIandbook, 2nd Ed.,New York, Wiley - Interscience, 1975, pp. IV-354.h C. M. Han s e n, J. Paint Tech. 39 (1967) 505.c H. U. R ash i d and S. C. Z a k k a, unpublished work.'I..oE-, 65"-NoxE 40I<l9010Figure 4. Heat of mixing, !J.Hm (equation 3) of PEG and PVA versus weight fractionof component 1; O PVA component 1 and x PEG component 1.00Wto fraction of component 1(Figure 4). Density and solubility parameters of polymers which have beenused to evaluate A Hm are shown in Table II. According to Schneier's criterion,incompatibility may be predicted in the present system as all A Hm valuesare above the limit of 42 X 10-3 J mol:". The maximum points of the curvesare independent of the choice of polymer as component 1.Another method of estimating the extent of compatibility is to comparethe values of X12 and (XI2)(cr),the interaction parameter and the critical inter-action parameters between polymers. The interaction parameter betweenpolymers is related to their solubility parameters by equation (4).11,12V1.:12 = _r_ (OI - (2)2RT(4)where V, is the molar volume of repe at unit. The critical inter action para-meter is given by equation (5).13VISCOMETRIC STUDIES 63( 1 1)2(Zul (er) = 1/2 -- +--X//2 X2'/2 (5)XI and X2 are the degrees of polymerization of polymers 1 and 2, respeetively.In general, if X12> (X12)(er),then the two polymers should be incompa-tible. The greater the difference between Xl2 and (X12)(cr),the more incompa-tible should the polymers be. If X12s (XI2)(er), then the two polymers maybe expected to be compatible. The ca1culated valu es of X12and (XI2)(cr)aregiven in Table nr. lVIolar volumes of repeat units of both polymers have beenused to calculate X12. For the PEG!PVA system, extensive incompatibility maybe envisaged.TABLE IIIInteraction parameters ealeulated from equaiions (4) and (5)System X12 X12 (er)PEG/PVA 0.818 0.0260.753PEG/PVC 0.076 X 10-2 2.8 X 10-20.092 X 102Although both of these theoretical methods indicate incompatibility bet-ween PEG and PVA, one must realize the limitation of these methods.Equation (3) and (4) contain solubility parameters of polymers. The conceptof solubility parameters is usually useful in the case of polymeric systemswhere specific interactions are negligible. Hydrogen bonds are present in PVA.Therefore, the prediction of incompatibility in PEG!PV A (and compatibi1ityin PEG!PVC as predicted below) by these methods must be confirmed bydefinitive experimental methods such as dynamic mechanical analysis anddifferential scanning calorimetry. Rough estimations of compatibility!incom-patibility by these methods have also been made for other polymer pairswith specific interactions.š+'."PEGIPVC/ChloTobenzene SystemThe absolute viseosity of the solution of PEG and PVC in chlorobenzeneis plotted as a function of weight percent PVC in Figure 5. The shapes ofthe plots are distinctly different from those obtained for the PEG/PV A/watersystem for which we can see' elongated S-type curves in Figures 1 and 2.The viscosity values have also been calculated using equation (2) for 20/0solution. The dotted line in Figure 5 represents this valu es against compo-sition. The measured viscosity valu es of the mixture for this system alsodeviate negatively from the additive values.The plot in Figure 5 for 20f0 polymer is linear up to about 600f0 of PVC.For a higher concentrated solution (80f0), the plot is line ar only about 100/0of PVC.The heat of mixing, A Hm of the PEG/PVC system has also been calculatedusing equation (3) and plotted against the composition in Figure 6. It may64 H. U. RASHIDN 3·5IEVIz<,(")Sx 2·5>-.•..VI .....o •.•..•u oVI•.•..•>o 100Figure 5. Absolute viscosity of PEG - PVC mixture in chlorobenzene versus weightpercent of PVC; O 2% polymer mixture, O 8% polymer mixture and --- datacalculated from equation (2).20 40 60 80W t of. P VCbe seen that all t::. Hm values are below the upper limit 42 X 10-3 J mol:'indicating compatibility between PEG and PVC in all proportions. Themaximum points of the curves are not, however, independent of the choiceof polymer as component 1. The XI2 values are lower than the (X12)(cr) (TableIII) for this system, also predicting compatibility. The nearly equal solubil.ityparameters of PEG and PVC (Table II) may also suggest compatibility betweenthem. It has been suggested-" that PVC is a weak proton donor and, therefore,PVC is capable of forming polycomplexes with the oxygen atom of PEGthrough hydrogen bonds. At a higher concentration (e. g. 8% solution), this25r---------------------------~l-oE2010Wto f rn ct io n of c o rnpon e n t 1Figure 6. Heat of rmxmg, fo.H m (equation 3) of PEG and PVC versus weight frac-tion of component 1; O PVC component 1 and O PEG component 1.15xE 10:r:<l50·0 0·2 0·4VISCOMETRIC STUDIES 65capacity of forming hydrogen bonds may also result in association of PVCmacromolecules'" causing a sharp increase in viscosity.Thus, it follows from the presented viscometric data that poly-(vinylalcohol) and poly(vinyl chloride) macromolecules tend to associate at higherconcentrations in water and chlorobenzene, respectively. Poly(ethylene glycol)does not associate appreciably in water. The incompatibility of poly(ethyleneglycol) with poly(vinyl alcohol) in water and its limited compatibility withpoly(vinyl chloride) in chlorobenzene may also be predicted from these dataand from theoretical calculations.REFERENCES1. A. Ta g e r, Phsjsica; Chemistry of PoLymers, Translated from the Russian byD. S o b ole v and N. B o b r o v, Moscow, Mir Publishers, 1978, Ch. 17.2. G. R. W i Il i a m s and B. W r i g h t, J. Polym. Sci. A3 (1965) 3885.3. D. F e 1d man and M. R u s u, Eur. Polym. J. 6 (1970) 627.4. C. H u g eli n and A. D o n d o s, Nlakromolek. Chem. 126 (1969) 206.5. V. E. Gul, E. A. Penskaya, and V. N. Kuleznev, CoHoid J. USSR27 (1965) 283.6. Y. P. S i n g h and R. P. S i n g h, Eur. Polym. J. 19 (1983) 535.7. O. Qua d rat, Makromol. Chem., Rapid Commun. 1 (1980) 651.8. C. L. Og g and W. L. P ort e r, Ind. Eng. Chem .• 4nal. Ed. 17 (1945) 394.9. R. C. W e a s t (Ed.), Handbook of Chemistry and Physics, 58th Edn., Ohio,CRC Press Inc., 1977-1978, F-51.10. B. O. S c h n e i e r, J. Appl. Polym. Sci. 17 (1973) 3175.11. J. H. Hil d e bra n d and R. L. S c o t t, The Solubility of Non-electrolytes,3rd Edn., New York, Dover Publications, 1964.12. J. H. Hil d e bra n d and R. L. S c o t t, Requuir Solutions, New Jersey,Prentice-Hall, Englewood Cliffs, 1962.13. R. L. S c o t t, J. Chem. Phys. 17 (1949) 279.14. D. J. H o u r s t o n and I. D. H u g h es, Polymer 19 (1978) 1181.15. S. P. M i shr a and B. L. Deo p ura, Polym. Commun. 26 (1985) 5.16. P. A. S mall, J. Appl. Chem. 3 (1953) 71.17. J. S p e v ii ček and B. Sc h n e ide r, IVIakromol. Chem. 176 (1975) 3409.SAŽETAKStudij viskoznosti poli(etilen-glikola), poli(vinil-alkohola) i poJi(vinil-klorida)i njihovih smjesa u vodi i klorbenzenuH. U. RashidMjerena je apsolutna viskoznost polurazrijeđenih otopina poli(etilen-glikola) ipoli(vinil-alkohola) i njihovih smjesa u vodi, te poli(etilen-glikola) i poli(vinil-klo-rida) i njihovih smjesa u klorbenzenu pri 30oC. Viskoznost poli (vinil-alkohola) ipoli(vinil-klorida) naglo raste s koncentracijom. Ovisnost viskoznosti polimernihsmjesa o sastavu odstupa od linearnosti. Također je proučavan i utjecaj ukupnogsadržaja polimera na viskoznost smjesa. Rezultati su razmatrani u smislu asocija-cije makromolekula iste vrste i kompatibilnosti između makromolekula nejednakihvrsta. Dane su i teorijske pretpostavke o kompatibilnosti i nekompatibilnosti. Proiz-lazi da se molekule poli(vinil-alkohola) i poli(vinil-klorida) asociraju pri višim kon-centracijama, te da je poli(etilen-glikol) nekompatibilan s poli(vinil-alkoholom), akompatibilan s poli(vinil-kloridom) u vodi i klorbenzenu.

Viscometric Studies of Poly(ethylene glycol), Poly(vinyl alcohol) and Poly(vinyl chloride) and Their Mixtures in Water and Chlorobenzene

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