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Ind. Eng. Chem. Prod. Res. Dev. 1005, 2 4 , 473-478 Edeieanu, C.; Evans, V. R. Trans. Faraday SOC. 1951, 4 7 , 1121. El-Nokaiy, M. A.; Huseuh-Ler, L.; Friberg, S. E.; Yasuda, H. K. J . Dlsp. Sci. Tech. 1985. in press. Foiey, R. T. Corrosion 1970, 26, 58. Heaiy, T. W.; Wiese, 0. R.; Yates, D. W.; Kavanaugh, 8. V. J . ColloM Interface Sci. 1973, 4 2 , 647. Iier, R. K. “The Chemistry of Silica”; Wiley: New York, 1979; p 97. Iler, R. K. J . Co//oMInterface Sci. 1973, 4 3 , 399. Liss, P. S. I n “Chemical Oceanography”; Riley, J. P.; Skirrow, G., Ed.; Academic Press: London, 1975; Vol. 11, p 193. Mansfeld, F.; Kenkei, J. V. I n “Galvanic Pitting and Corrosion-Field and Laboratory Studies”, ASTM STP576; American Society for Testing and Materiais: Philadelphia, 1976; p 20. Marion, S. P.; Thomas, A. W. J . Colloid Sci. 1946, 7 , 21. Miller, L. B. U S . Pub. Health Servlce, Pub. Health Report 1924, 3 9 , 1502. Okamoto, G.; Morozumi, T. J . Nectrochem. SOC.Jpn. 1953a, 2 1 , 512.
Okamoto, G.; Mororumi, T. J . Electrochem. SOC.Jpn. 1953b, 21, 573. Okamoto, G.; Morozumi, T.; Sato, N.; Hachiya, M.; Nagayama, M. J . Electrochem. SOC. Jpn. 1956, 2 4 , 269. Okamoto, G.; Okura, T.; Sudo,N. J . Nectrochem. Soc.Jpn. 1950, 19, 289. Packham, R. F. R o c . Soc.Water Treat. Exam. 1982a, 7 1 , 50. Packham, R. F. Proc. SOC. Water Treat. Exam. 1962b, 7 1 , 602. Packham, R. F. Proc. SOC. Water Treat. Exam. 1963, 12, 15. Peterson, B. H.; Bartow, E. Ind. Eng. Chem. 1928, 2 0 , 51. Powell, S. T. “Water Conditioning for Industry”; McGraw-Hili: New York, 1954; Chapter 3. Vogel, A. I. “A Textbook of Quantitative Inorganic Analysis”; Wiiey: New York, 1961; pp 425-436.
Received for review November 1, 1984 Accepted March 8, 1985
Solubility, Solvency, and Solubility Parameters John W. Van Dyk,” Harry L. Frlsch,t and Dao T. Wu Marshall R&D Laboratory, E. I. du Pont de Nemours and Co., Inc., Philadelphia, Pennsylvania 19146
Three-component solubility parameter envelopes have been useful in predicting the solubility/nonsolubility of polymers. The use of threecomponent solubility parameters in predicting both degree of solvency (as measured by inherent viscosity) and solubility/nonsolubility is demonstrated. Predictability is significantly worse if the total solubility parameter is substituted for the three-component parameters. Predictability is significantly improved if the effect of solvent molar volume on solubility is included. These conclusions are based on data for the solubility of three methacrylate polymers in 34 potential solvents, Inherent viscosity data for each of the polymers (for those solvents in which they are soluble) are also given. Three equations (two of which are based on available theory) are used to correlate inherent viscosity with solubility parameter.
Introduction In spite of its many theoretical limitations (Burrell, 1968; Nelson et al., 1970) the three-component solubility parameter approach has been very useful in dealing with problems of polymer solubility. Although many other approaches (Drago et al., 1977; Flory, 1953a; Fowkes and Mostafa, 1978; Gutman, 1977; Huggins, 1972) have been suggested, the use of solubility parameters is, at the moment, the only practical way of predicting polymer solubility. Unlike other approaches, solubility parameters give the ability to predict the solubility of a polymer in a mixture of solvents from two sets of parameters, where one set is specific to individual pure solvents and independent of the polymer and the other set is specific to the polymer and independent of the solvent mixture. Although other systems (Crowley et al., 1966; Nelson et al., 1970)are available, we chose Hansen’s three-component solubility approach (Hansen, 1967a) because (1)reliable “experimental” values are available for many solvents (Hansen and Beerbower, 1971), (2) reliable methods are available for calculating values of solvents having no experimental values (Hansen, 1967a,c; Hoy, 1970; Rheineck and Lin, 1968; Van Krevelen and Hoftyzer, 1976),and (3) the solubility envelope of many polymers can be represented by a sphere in Hansen solubility space if the nonpolar parameter is suitably scaled (Hansen, 1967b). The usual method of determining the solubility envelope of a polymer involves measuring the solubility of a polymer (at a fixed concentration) in a series of solvents having known solubility parameters. From the positions of the solvents in solubility space and from a knowledge of those solvents in which the polymer Suny, Albany, NY 12222. 0196-4321/85/1224-0473$01.50/0
is soluble, an envelope in solubility space, which surrounds the soluble region, is deduced. The location of this envelope is determined by the change from soluble to insoluble. Within the envelope most of the solvents will dissolve the polymer; outside the envelope most of the solvents will not dissolve the polymer. If the solubility region is spherical, it can be represented by four parameters-the three solubility parameters corresponding to the center of the sphere and the sphere radius. It should be noted that this approach locates the center of the sphere on the basis of the location of its boundaries. All solvents are given the same weight. Good solvents are not differentiated from poor solvents. In this paper we have subjected the three-component solubility parameter approach to a more critical test by assessing its ability to predict both degree of solvency [via inherent viscosity (Ahmad and Yaseen, 1978; Bristow and Watson, 195813; Cowie, 1968; Mangaraj et al., 1963; Sosa et al., 1977)] and solubility/nonsolubility. The solubilities of three methacrylate polymers (methyl, ethyl, and butyl) were determined by using 34 potential solvents. In addition, the inherent viscosities (at 0.5 g/dL) for all the resulting solutions (12 for PMMA and 16 for PEMA and PBMA) were measured. Three equations (two of which are based on available theory) were used to correlate the inherent viscosities and solubility/nonsolubility with three-component solubility parameters. Theoretical Considerations A. Solubility Parameter. The Hansen system consists of three parameters: 6,, nonpolar; 6,, polar; and bh, hydrogen bonding. These three parameters are related to the total solubility parameter (6,) by the following equation. 6, = (6,2 + 6; + 8h2)1/* (1) 0 1985 American Chemical Society
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Chem. Prod. Res. Dev., Vol.
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Hansen (1967b) has found empirically that if the distance along the 6, axis is doubled, most polymer solubility regions can be represented by a sphere in three-dimensional solubility space. This region can be characterized by four parameters: bnp,aPp, and bhp, the coordinates of the center of the sphere, and R, the radius of the sphere. On the basis of the above the distance in three-dimensional solubility space between a polymer and a solvent can be calculated from A6 = {[2(6np- ‘%,)I2
+ [6pp - 6ps12 + [ahp - 6h8]2\1/2
(2)
The subscript “p” in an, refers to polymer and “s” refers to solvent. The 2 in the above equation is the result of doubling the 6n axis. If A6 C R the solvent should dissolve the polymer, and if A6 > R the solvent should not dissolve the polymer. If the solvent is a mixture of pure solvents, the solubility parameters of the mixtures can be calculated by m
(3) I$~is the volume fraction of the j t h component, 6ij is the solubility parameter of the jth component, i = n, p, h, and m = the number of components in the mixture. B. Intrinsic Viscosity Equations. From Flory (19534
[n] = KW12a3 where M = molecular weight and factor. Also from Flory (195313)
CY
(4) = chain expansion
(5) which can also be expressed as a3 z
[
K
cy2 -
2
X)
(2d-1)
~
(6)
]
where X = Flory interaction parameter, V, = solvent molar volume, and d = average value of the exponent in the Mark-Houwink equation. From Bristow and Watson (1958a) X = K3 + K4VmAA2 (7) Combining (4), (6), and (7) gives
]
(26-1)
[n] = KIW/z[ fVl ml ( 1 / 2 - K3 - K4VmA62)
(8)
Rearranging and collecting constants gives Vm[n]1/(2a-1) = KI - KIIVmA62
[n] = KI - KIIVm1/2A8
(13)
In using these equations for our data correlation we have assumed that intrinsic viscosity can be replaced by inherent viscosity at 0.5 g/dL. Experimental Section The polymers used were high molecular weight methacrylates, commercially available from Du Pont. The grades used were Elvacite Acrylic Resin 2041 (methyl methacrylate), 2042 (ethyl methacrylate), and 2044 butyl methacrylate). Solvents were reagent grade and were used without further purification. Viscosities were measured at 25 f 0.01 OC by using a polymer concentration of 0.5 g/dL and a Ubbelohde viscometer. Inherent viscosities were calculated as follows:
nrel= relative viscosity and C = polymer concentration (g/dL). Solubilities were determined by mixing 1mL of each of the 34 solvents with 0.1 g of polymer. Those mixtures giving clear, noncloudy solutions after 1 week at room temperature were rated as soluble. All others were rated as nonsoluble. Results and Discussion The three-component solubility parameters and the molar volume of the 34 solvents used in this study are listed in Table 1. The solvents in this set were selected because they cover most of the accessible regions of solubility space. As such they represent a set of solvents having widely different solvency characteristics. The measured inherent viscosities of those solvent/ polymer pairs that gave solutions are given in Table 11. In order to test correlatability the best values of the parameters and constants in the three equations must be determined. This was done by using the following procedure: (1) The initial values of the three polymer solubility parameters were set equal to those of methylene chloride (the solvent giving the highest inherent viscosity). (2) The initial value of d was set equal to 0.65 (the middle of the range of 0.5-0.8 found experimentally). (3) VMAS2 was calculated for each solvent and V&inh1i(2h-1) for each solvent/polymer pair. (4) The available viscosity data and calculated values were used to make plots to determine the initial values of KI and KII for each of the equations. (5) The data along with the initial parameter and constant values were input to a computer program that measured goodness-of-fitby calculating root mean square error (RMSE).
(9)
which we have called eq I. Alternatively we can use the Stockmayer-Fixman (1963) equation:
Combining (4), (7), and (10) gives
1
- K3 - VmAS2)
(11)
Assuming K z / V, N constant and combining constants give (Matsuo, 1979) [n]= KI - KIIVmA6’ (12) which we have called eq 11. Equation I11 is empirical
In making these calculations nonsolvents were assigned a measured inherent viscosity of 0, and negative calculated inherent viscosities (corresponding to nonsolvents) were also set equal to 0. (6) Optimum values of the parameters and constants were obtained via computer by an iterative process in which the values were varied until a minimum in RMSE was obtained. Iteration was stopped when the change in RMSE was C 0.002. Also, the minimum variation in “a” was set at 0.05. It should be noted that the above procedure gives the best fit for both the solvency and the solubility/nonsolubility data.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 3, 1985
Table I. Solvent Properties solvent butyl carbitol acetone aniline carbon disulfide cyclohexane nitrobenzene diisobutyl ketone acetonitrile isophorone toluene chlorobenzene bromobenzene methylene chloride N-methylpyrrolidinone butyrolactone formic acid methyl isobutyl ketone propionitrile tetrahydrofuran heptane cyclohexanol dimethyl sulfoxide diacetone alcohol 2-propanol 1-octanol ethylenediamine tetrabromoethane propylene carbonate methanol ethylene glycol ethanolamine formamide dipropylene glycol diethylenetriamine
6x1 7.8 7.6 9.5 10.0 8.2 9.8 7.8 7.5 8.1 8.8 9.3 10.0 8.9 8.8 9.3 7.0 7.5 7.5 8.2 7.5 8.5 9.0 7.7 7.7 8.3 8.1 11.1 9.8 7.4 8.3 8.4 8.4 7.8 8.2
6p
dh
vm
3.4 5.1 2.5 0 0 4.2 1.8 8.8 4.0 0.7 2.1 2.7 3.1 6.0 8.1 5.8 3.0 7.0 2.8 0 2.0 8.0 4.0 3.0 1.6 4.3 2.5 8.8 6.0 5.4 7.6 12.8 9.9 6.5
5.2 3.4 5.0 0 0.1 2.0 2.0 3.0 3.6 1.0 1.0 2.0 3.0 3.5 3.6 8.1 2.0 2.7 3.9 0 6.6 5.0 5.3 8.0 5.8 8.3 4.0 2.0 10.9 12.7 10.4 9.3 9.0 7.0
170.3 73.0 90.8 60.1 107.6 101.8 176.0 52.2 149.0 106.0 101.3 104.6 63.8 96.1 76.2 37.6 125.3 70.1 81.7 144.6 103.7 60.0 124.3 76.8 157.7 67.3 116.8 84.3 40.3 55.6 59.5 39.8 130.4 108.0
Table 11. Inherent Viscosities of Poly(methy1 methacrylate), Poly(ethy1 methacrylate), and Poly(buty1 methacrylate) in Various Solvents aolvmer solvent PMMA PEMA PBMA butyl carbitol 0.39 0.82 0.75 0.43 acetone 1.28 0.91 0.47 aniline carbon disulfide 0.36 cyclohexane 0.25 1.45 0.85 0.40 nitrobenzene 0.61 0.50 diisobutyl ketone acetonitrile 0.35 isophorone 0.80 0.34 toluene 1.41 1.12 0.61 chlorobenzene 1.48 0.98 0.62 bromobenzene 1.26 0.91 0.55 1.92 1.32 0.81 methylene chloride 1.39 0.68 0.36 N-methylpyrrolidinone 0.49 0.24 y-butyrolactone 1.27 0.35 formic acid methyl isobutyl ketone 0.73 0.32 propionitrile 0.68 0.70 0.32 tetrahydrofuran 1.32 1.00 0.66
It is also possible to separate out just the goodness-of-fit of the solubility/nonsolubility aspect of the correlation. To do this it is necessary to calculate a parameter analogous to the radius (R) of the solubility envelope. If solvent molar volume is included in the equation, this parameter ( R9 is related to V,'12A6. R 'can be calculated from the best fit equation and is equal to Vm112A6for the case where ninh = 0. Using eq I1 as an example, we see 0 = KI - KIIRr2or R'=
[ 2 1"'
(16)
We can now compare observed solubility/nonsolubility
475
Table 111. Effect-of Using One vs. Three Solubility Parameters on the Degree of Correlation solubility parameters polymer criterion one three PMMA error, RMSE 0.51 0.22 anomalous solvents 10 3 PEMA error, RMSE 0.29 0.11 anomalous solvents 8 3 PBMA error, RMSE 0.16 0.05 anomalous solvents 5 1
with that predicted. If V,'I2A6 I R ', solubility is predicted; if Vm1/2A6> R', nonsolubility is predicted. In his study of polymer solubility Hansen (1967b) found a shell of uncertain solubility lying between 0.9R and 1.1R. Assuming this uncertainty shell also applies to our solubility space, we can define anomalous solvents as solvents having Vm'12A6 > 1.1R'and nonsolvents having V,'12A6 < 0.9R'. Therefore, the fewer the anomalous solvents the better the fit for solubility/nonsolubility. We are now in a position to compare the correlatability obtained by using different ways of treating the data. Over all goodness-of-fit can be compared via RMSE, and solubility/nonsolubility goodness-of-fit can be compared by using the number of anomalous solvents. One- vs. Three-Component Solubility Parameters. Because of the criticisms of the three-component approach we have compared its correlatability with that of the single, total solubility parameter approach. In this comparison we have used correlating eq I1 and have calculated the total solubility parameter from eq 1. The solubility parameter difference (A6) for the total solubility parameter was calculated as The results for the three polymers are summarized in Table 111. They clearly show that the three-component approach gives significantly better correlation than the single-parameter approach. In view of this it is imperative that criticisms of the inadequacies of solubility parameters be based on the three-component approach. This has not always been the case (Fowkes, 1984). It should be noted that in this comparison, as well as those that follow, four solvents were, for certain solvent/polymer combinations, omitted from the calculation of RMSE, because they were anomalous even in the best cases. These combinations were butyl carbitol/PBMA, carbon disulfide/PMMA and PEMA, cyclohexane/PEMA, and formic acid/PMMA. For a graphical description of the effect of using one vs. three solubility parameters, Figures 1 and 2 should be compared. Inclusion of Solvent Molar Volume. All three of our correlating equations contain solvent molar volume ( V,) as well as solubility parameter difference (A6). In contrast, most methods for correlating solubility/nonsolubility via solubility envelope do not take V, into account. In this comparison we have determined the effect of including a molar volume term on the degree of correlation. Three-component Solubility parameters and eq 11,with and without the molar volume term, were used to get the results summarized in Table IV. They show that including the molar volume term significantly improves the correlation. This effect can be seen graphically by comparing Figures 1 and 3. These results also show that improved correlatability will be obtained by including a solvent molar volume term in the estimation of solubility envelope via solubility/non-
478
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 3, 1985
1
Pdyethylmethacrylate 100
1 25
Polyethylmethacrylate
0.75
c
c
050
\
I
\
0 25
0
0
1oM)
2033
3 m
4000
m
6
M
X
)
0
10
20
30
40
60
50
70
A62
V, A82
Figure I. Plot of measured inherent viscosity vs. V, (solvent molar volume) times A6* (see eq 2 for definition). Line is a plot of eq 12 using the best values of KIand Kp (A) Data points excluded in the determination of KI and KII. I
I
Polyethylmethacrylate
1i
Figure 3. Plot of measured inherent viscosity vs. A62 (see eq 2 for definition). Line is a plot of eq 12 (excluding V,) using the best values of KI and KII. (A) Data points excluded in the determination of K,and KI,. Table V. Effect of t h e Viscosity Equation Used on t h e Degree of Correlation viscosity equation polymer criterion IQ I1 I11 PMMA error, RMSE 0.12 0.22 0.25 anomalous solvents 2 3 5 PEMA error, RMSE 0.10 0.11 0.12 anomalous solvents 2 3 4 PBMA error, RMSE 0.05 0.05 0.05 anomalous solvents 1 1 1 = 0.70.
200
400
600
800
1 m
1xx)
V&:
Figure 2. Plot of measured inherent viscosity vs. V, (solvent molar volume) times A6: (see eq 17 for definition). Line is a plot of eq 12 . Data points excluded in the using the best values of KI and K I ~ (A) determination of KI and Klp Table IV. Effect of Including Molar Volume on t h e Degree of Correlation molar volume Dolvmer criterion no ves error, RMSE 0.34 0.22 PMMA anomalous solvents 6 3 error, RMSE 0.18 0.11 PEMA anomalous solvents 6 3 PBMA error, RMSE 0.09 0.05 anomalous solvents 4 1
solubility. This can easily be done if a computer is used to calculate the envelope parameters. Goodness-of-fitcan be based on minimizing the number of anomalous solvents and minimizing the distance between the anomalous solvents and the envelope boundary. The effect of including the solvent molar volume term can be represented geometrically as transformation from A6 space to Vm1I2A6 space. In the latter space the center of the envelope (the three solubility parameters of the polymer) will be positioned at the origin (O,O,O) of the three-dimensional space. The position of a solvent in this space will be determined by increasing the length of the vector A6 by the factor Vm1/2.
Table VI. Effect of "a on Error, RMS error, RMS polymer a = 0.75 a = 0.70 PMMA 0.138 0.121 PEMA 0.108 0.100 PBMA 0.061 0.053
0.65 0.180 0.121 0.078
a =
It is evident from the above geometric description of the new space that it will not be possible to determine quantitatively the position of the center of the envelope by the usual method of plotting the data (Hansen, 1967b). Effect of Correlation Equation. In the preceding comparisons correlation eq I1 has been used. The results of a comparison of the three equations, using the threecomponent parameters and including the solvent molar volume term, are given in Table V. The results for two of the polymers (PEMA and PBMA) show little difference among the three equations. Only for PMMA are the results for eq I significantly better than for the other two equations. This is possibly due to the firmer theoretical basis of eq I. These differences among the three equations are shown graphically in Figure 4. It should be noted that the results for eq I in Table V are based on the use of a value of 0.70 for the parameter 8. This value was selected because it gave the lowest RMSE for each of the three polymers (see Table VI). It should be noted that this value is within the range of 0.5-0.8 found experimentally. Solubility Envelopes. The coordinates of the solubility envelopes of the three polymers as determined by the three viscosity equations as well as a solubility/nonsolubility method are summarized in Table VII. The following observations can be made: (1)Most of the center coor-
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24,
Table VII. Effect of t h e Method Used on t h e Coordinates of t h e Solubility Envelope Dolvmer method 6, 6, bh 3.7 0.9 9.5 PMMA viscosity I 2.3 2.9 9.3 viscosity I1 2.6 9.3 3.0 viscosity I11 0.5 9.5 5.2 solubility 1.3 8.8 2.9 PEMA viscosity I 1.7 8.9 3.0 viscosity I1 1.8 8.8 3.0 viscosity I11 4.7 1.2 8.8. solubility 2.0 8.5 2.9 PBMA viscosity I 1.9 8.7 2.9 viscosity I1 8.7 2.7 2.0 viscosity I11 1.5 8.8 4.1 solubility
bt 10.2 10.0 10.1 10.8 9.4 9.5 9.5 10.0 9.2 9.4 9.3 9.8
No. 3, 1985 477
R' 46.4 43.9 51.2 a
48.8 52.3 54.9 a
40.1 46.9 50.4 a
"Solvent molar volume term not used (Van Dyk, 1978). 2
.P ' 5 -f
1.6
-
1.2
-
I
/I
I
I
I
1
I
Acknowledgment
0.4
0.8
1.2
1.6
2
We wish to acknowledge Albert R. Marchetti for his measurement of inherent viscosity, Thomas P. O'Brien and William E. Schoellkopf for their help with computer programming, and Patricia Goodrich and Jean T. McFarlin for typing the manuscript. Registry No. PMMA, 9011-14-7; PEMA, 9003-42-3; PBMA,
I
B ".I 0.4
I1
0
anomalous behavior of two can be rationalized on the basis of inter- or intramolecular hydrogen bonding. For a given polymer a maximum of two solvents were anomalous. The good correlation that was obtained may be due to the relatively small role that hydrogen bonding plays in the solvation of the polymers we have used. Additional work is needed using polymers that are more dependent on hydrogen bonding for solvation. Such work would help define the types of polymers whose solubility behavior can be successfully treated by using three-component solubility parameters. This work also shows the importance of including a solvent molar volume term in correlating both solvency and solubility.
I
Measured Inherent Viscosity Figure 4. Plot of calculated viscosity (Ab defined by eq 2) vs. Equation 9 used; (A) eq 12 used; (+) eq 13 measured viscosity. (0) used.
dinates of PEMA and PBMA are the same with the exception of the 6, from solubility,which are higher. (2) The radii of PEMA and PBMA increase in going from eq I to 111. (3) For PMMA, 6, is similar for all four methods, 6 and 6h are similar for both eq I1 and 111and for eq I anc! solubility, and 6, is the highest for solubility. Exceptional Solvents. It was noted above that the behavior of four of the solvents in combination with some of polymers cannot be explained by any of the correlation equations. Two of these solvents, butyl carbitol and formic acid, exhibit greater solvency than predicted. In both cases the low predicted solvency results from too high a value of 6b It is interesting to note that formic acid can dimerize via hydrogen bonding and butyl carbitol can internally hydrogen bond to form a ring structure. To the extent that the dimer or ring structure is present the effective 6 h of both solvents will be less than the literature values we used. This lower effective may be the reason for the better observed solvency of these two solvents. The other two solvents that are exceptions are carbon disulfide and cyclohexane. These solvents are poorer solvents than predicted. Both have essentially no polar or hydrogen bonding component. We have no rationalization for exceptional performance of these two solvents.
Conclusions The results show very good correlation of solvency and solubility (for methacrylate polymers) with three component solubility parameters. Of the 34 widely different solvents used, only four showed anomalous behavior when the best correlating equation was used. Of these four, the
9003-63-8; carbon disulfide, 75-15-0; cyclohexane, 110-82-7; nitrobenzene, 98-95-3; diisobutyl ketone, 108-83-8; acetonitrile, 75-05-8; isophorone, 78-59-1; toluene, 108-88-3; chlorobenzene, 108-90-7; bromobenzene, 108-86-1; methylene chloride, 75-09-2; N-methylpyrrolidinone, 872-50-4; butyrolactone, 96-48-0; formic acid, 64-18-6; methyl isobutyl ketone, 108-10-1; propionitrile, 107-12-0; tetrahydrofuran, 109-99-9; heptane, 142-82-5; cyclohexanol, 108-93-0; dimethyl sulfoxide, 67-68-5; diacetone alcohol, 123-42-2; 2-propanol, 67-63-0; 1-octanol,111-87-5; ethylenediamine, 107-15-3; tetrabromoethanone, 25167-20-8; propylene carbonate, 108-32-7; methanol, 67-56-1; ethylene glycol, 107-21-1; ethanolamine, 141-43-5; formamide, 75-12-7; dipropylene glycol, 2526571-8; diethylenetriamine, 111-40-0; butyl carbitol, 112-34-5; acetone, 67-64-1; aniline, 62-53-3.
Literature Cited Ahmad, Y.; Yaseen, M. J . Coat. Techno/. 1978,5 0 , 66. Bristow, 0. M.;Watson, W. F. Trans. Faraday SOC. 1958a,5 4 , 1731. Bristow, 0. M.;Watson, W. F. Trans. Faraday SOC. 1958b,5 4 , 1742. Burrell, H. J . faint Technol. 1988, 4 0 , 203. Cowie, J. M. 0. J . fo/ym. Sci., Part C 1968,267. Crowley, J. D. et al. J . faint Techno/. 1988,3 8 , 269. Drago, R. S.et al. J . Am. Chem. SOC. 1977,99, 3203. Flory, P. J. "Principles of Polymer Chemistry"; Corneli Unlversity Press: Ithaca,NY, 1953; (a) p 502; (b) p 600; ( c ) p 612. Fowkes. F. M. frepr. Pap. Am. Chem. SOC.Div. Poly" Mater. Sci. Eng. 1984,5 1 , 522.
Fowkes, F. M.; Mostafa, M. A. Ind. Eng. Chem. Rod. Res. Dev. 1978, 17, 3.
Gutman, V. CHEMTECH 1877, 7 , 255. Hansen, C. M. J . felnt Technol. 1987a,3 9 , 104. Hansen, C. M. J . faint Technol. 1987b,39, 505. Hansen, C. M. J . faint Techno/. 1967c,3 9 , 51 1. Hansen, C. M.;Beerbower, A. "Kirk-0th" Encyclopedia of Chemical Tech-
nology, Supplementary Volume"; Intersclence: New York, 1971; p 892. Hoy, K. L. J . faint Technol. 1970,42, 115. Hugglns, M. L. J . faint Techno/. 1972,4 4 , 55. Mangaraj, D. et ai. Makromol. Chem. 1983, 6 5 , 39. Matsuo. T. Preprints ASCIJCS 1979,20,895.
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478
Nelson, R. C. et ai. J . faint Technol. 1070, 42, 636. Rhelneck, A. E.; Lin, K. F. J . faint Technol. 1068, 4 0 , 811. Sosa, J. M. "Structure-Solubility Relationships in Polymers"; Academy Press: New York, 1977; p 89. Stockmayer, W. H.; Fixman, M. J . folym. Sei., Part C 1063, 137. Van Dyk, J. W., unpublished data, 1978. Van Kreveien, D.w.; ~oftyzer,P. J. "Properties of Polymers"; Elsevier: AI-+ sterdam, 1976; p 152.
Received for review February 4, 1985 Revised manuscript received April 3, 1985 Accepted April 29, 1985 F"3ented a t the 188th National Meeting of the American Chemical Society, Philadelphia, PA, Aug 26-31, 1984.
Thermomechanical Behavior of Modified Asphalts' Vlkas M. Nadkarnl,' Arun V. Shenoy, and Johnson Mathew Polymer Science and Engineering Group, Chemical Engineering Division, National Chemical Laboratory, Pune 4 1 1 008, India
The thermomechanical properties of a variety of modified asphalts have been investigated by using dynamic mechanical characterization, melt viscosity determination, and softening point measurements. The asphalt modifications studied include chemical reaction of the asphalt flux with maleic anhydride, physical blending with styrene-butadiene-styrene rubber, air blowing, and use of inorganic fillers. The results indicate that chemical modification of asphatt flux with maleic anhydride significantly improves both the low-temperature cracking resistance and the hlghtemperature cohesive strength. The optimum amount of maleic anhydride has been found to be 10% on a weight basis. Whereas conventional air blowing improves the softening point and the modulus at elevated temperatures, it does so at the expense of the low-temperature flexibility. On the other hand, blending with an elastomer improves the low-temperature crack resistance, but it does not enhance the high-temperature cohesive strength and flow resistance. The effective use of cashew nut shell liquid, an agro-based raw material, as a chemical modifier for asphatt to improve the low and high temperature performance has also been demonstrated.
Introduction Asphalt-based materials are used extensively as binders, sealants, and waterproof coatings in diverse applications because of their low cost, inherent cohesive nature, weather-resistant properties, and ease of processing in the molten state. In a number of these applications, such as in road construction and in coatings on railwagon undercarriages, the materials are exposed to a wide range of temperature and load conditions. The temperature of the surface, coated or paved with asphalt, could reach 60 "C on a hot summer day and could drop well below 0 "C in winter in certain climatic zones. The material also has to sustain the stresses generated by the thermal expansion and contraction. A combination of high-temperature and low-temperature performance is therefore required from end use considerations. The critical properties include high softening point, good tracking and flow resistance at elevated temperatures (60-70 "C), high elastic modulus and cohesive strength at use temperatures, coupled with good impact strength and crack resistance at low temperatures. A low melt viscosity at the application temperatures (120-200 " C ) is also desirable for ease of spreading. Asphalt is represented as asphaltene micelles in a hydrocarbon solvent consisting of saturated and unsaturated paraffins, cycloparaffins, and aromatic structures. Asphaltenes are the high molecular weight constituents with molecular weight varying from 1000 to 2500 and are dark brown or black solids. The maltenes are the dark brown oil which comprise the low molecular weight portions of the micelles and the intermicellar phase. Studies based on X-ray diffraction by Yen et al. (1961) confirm that asphalt structure consists of stacks of up to five condensed NCL Communication No. 3498.
aromatic rings surrounded by cyclic and paraffinic substituents. Electron microscopic studies by Winniford (1983) show that asphaltene clusters of varying size are present and the clustering is more pronounced in the high molecular weight fractions. In addition, asphalt contains varying amounts of sulfur, oxygen, nitrogen, metals, etc. The asphalt flux as obtained from refinery bottoms is a thermoplastic with softening point in the range of 30-45 O C , and little cohesive strength at elevated temperatures, thus limiting its usefulness. However, the thermomechanical properties can be improved by choice of base stocks and by processing. One of the most widely used modifications of asphalt is air blowing. This process consists of blowing air into asphalt at temperatures up to 230 " C to harden the asphalt by polymerization of the asphaltenes. As a result of further fusion of the condensed aromatic rings in the blowing process, the softening point and the cohesive strength at elevated temperatures are improved. However, the low-temperature impact and crack resistance are not improved. The low-temperature performance of asphalt can be improved by physical blending with rubber crumbs (Dempster, 1978, 1979; McDonald, 1980; Shim-Ton et al., 1980) or with elastomers such as block copolymers of styrene and butadiene (Blanken and Van Gooswilligen, 1980; De Bats et al., 1981; Kraus and Rollmann, 1981; Kraus, 1981; Meynard, 1981). Although the property modifications achieved by rubber incorporation have been found to be specific to the interactions between the particular grades of asphalt and rubber (Ohta, 1983), generally this modification method does not lead to improvement in the high-temperature performance. In order to achieve a balanced improvement in both the low- and high-temperature properties of asphalt, chemical modification of asphalt via reactions with vinyl monomers has been found to be effective. Maleic
0196-4321/85/1224-0478$01.50/00 1985 American Chemical Society
