Energy & Fuels 2004, 18, 63-67
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Characterization of Glass Transition Temperature and Surface Energy of Bituminous Binders by Inverse Gas Chromatography C. C. Puig* and H. E. H. Meijer Section Materials Technology, Faculty of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
M. A. J. Michels Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
L. H. G. J. Segeren and G. J. Vancso Department of Materials Science and Technology of Polymers and MESA+ Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands, and Dutch Polymer Institute, P.O. Box 902, 5600 AX Eindhoven, The Netherlands Received March 20, 2003. Revised Manuscript Received September 23, 2003
Inverse gas chromatography (IGC) was used to characterize two bituminous binders (A and B) of different origin. Glass transition temperatures (Tg) were determined by constructing van’t Hoff plots using n-pentane probes in a temperature range between -50 °C and +120 °C. Tg values were specified using the first deviations from linearity observed in the adsorption zone of the plots. A 6 °C difference in Tg was found between the two different specimens. Retention measurements using n-alkane probes, carried out at -30 °C, revealed a higher dispersive surface 2 energy term (γD s ) for bituminous binder A than for B, with values of 59.3 and 50.6 mJ/m , respectively. Binder A was composed of a higher asphaltenes content compared to binder B. This difference in chemical composition accounted for the different surface energy values.
Introduction Bitumens are complex mixtures of different molecular species originating from oil refinery residues. Their constituents are classified according to their solubility in given solvents. If the bitumen is diluted with certain n-alkanes such as n-heptane or n-pentane, a precipitate known as “asphaltenes” is formed. It is possible to separate the diluted part known as “maltenes” into different fractions using chromatographic techniques.1 The most common use of bitumens is for the construction of pavement roads, serving as binder for mineral aggregates. Recently, their use to dispose of troublesome waste plastics within road bitumens was investigated by Fawcett et al.2 We applied inverse gas chromatography (IGC) to study the glass transition temperature (Tg) of two bituminous binders. Knowledge of Tg is essential for their application, e.g., because of its close relation to brittle behavior. Tg data are also needed when the * Author to whom correspondence should be addressed at Departamento de Ciencias de los Materiales, Universidad Simo´n Bolı´var, Apartado 89000, Caracas 1080-A, Venezuela. Phone: +58 (212) 9063389. Fax: +58 (212) 9063932. E-mail:
[email protected]. (1) Redelius, P. G. Fuel 2000, 79, 27-35. (2) Fawcett, A. H.; McNally, T.; McNally, G. M.; Andrews, F.; Clarke, J. Polymer 1999, 40, 6337-6349.
surface energy of the stationary phase is determined by IGC. The accurate determination of phase transitions in liquid-crystalline materials using IGC was described first by Price and Shillcock.3 In the present study we show how IGC can be applied to study the glass transition of bituminous binder. Numerous articles have been written on IGC and its application to fundamental scientific studies and to applied studies on surface and bulk properties of materials.4-9 The large variety of applications includes studies of minerals,10 pigments,11,12 composite materials,13-16 wood and pulp fibers,17-20 industrial fibers,21-24 (3) Price, G. J.; Shillcock, M. Polymer 1993, 34, 85-89. (4) Martin, A. J. P. Analyst (London) 1956, 81, 52-53. (5) Purnell, H. Gas Chromatography; Wiley & Sons: New York, 1962. (6) Kiselev, A. V. In Advances in Chromatography; Giddings, J. C., Keller, R. A., Eds.; Marcel Dekker: New York, 1967; pp 113-196. (7) Guillet, J. E.; Wooten, W. C.; Combs, R. L. J. Appl. Polym. Sci. 1960, 3, 61-64. (8) Smidsrød, A.; Guillet, J. E. Macromolecules 1969, 2, 272277. (9) Guillet, J. E.; Stein, A. N. Macromolecules 1970, 3, 102-105. (10) Balard, H.; Saade, A.; Siffert, B.; Papirer, E. Clays Clay Miner. 1997, 45, 489-495. (11) Hegedus, C. R.; Kamel, I. L. J. Coatings Technol. 1993, 650, 31-43. (12) Lundqvist, Å.; O ¨ dberg, L. J. Pulp Paper Sci. 1997, 23, 298303.
10.1021/ef030062l CCC: $27.50 © 2004 American Chemical Society Published on Web 12/05/2003
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cross-linked systems,25-27 polymer blends,28-31 steel tubing,32 etc. Several reviews of specialized topics have been published.28,33-39 Bitumen-related materials have also been studied by IGC.40-42 Davis et al. showed that differences in asphalt samples of various origins can be detected by IGC using a series of test probes.40 These authors carried out retention time measurements at a high temperature, 130 °C. The authors also fractionated one asphalt sample into its different constituents and found strong differences in retention time among these.40 The surface properties of an asphalt specimen and its asphaltene fraction were investigated by IGC as a function of temperature in the range between 50 and 130 °C, and a higher dispersive surface energy term at room temperature was found for the asphaltene fraction than for the parent asphalt.42 Glass transition temperatures of bitumens are usually determined using differential thermal analysis (DTA) or differential scanning calorimetry (DSC). These studies revealed that the secondary phase transition is usually found for these materials at subambient temperatures. The early study by Connor and Spiro using DTA showed the dependence of Tg on asphaltenes and paraffins contents in asphalts.43 The authors compared (13) Ahsan, T.; Taylor, D. A. J. Adhes. 1998, 67, 69-79. (14) Borges, J. P.; Godinho, M. H.; Belgacem, M. N.; Martins, A. F. Presented at the EURO-FILLERS 99, September 1999, Lyon-Villeurbanne, France. (15) Godinho, M. H.; Martins, A. F.; Belgacem, M. N.; Gil, L.; Cordeiro, N. Presented at the EURO-FILLERS 99, September 1999, Lyon-Villeurbanne, France. (16) Schultz, J.; Lavielle, L.; Martin, C. J. Adhes. 1987, 23, 45-60. (17) Shen, W.; Parker, I. H.; Sheng, Y. J. J. Adhes. Sci. Technol. 1998, 12, 161-174. (18) Riedl, B.; Kamdem, P. D. J. Adhes. Sci. Technol. 1992, 6, 10531067. (19) Jacob, P. N.; Berg, J. C. Langmuir 1994, 10, 3086-3093. (20) Dorris, G. M.; Gray, D. G. J. Colloid Interface Sci. 1980, 77, 353-362. (21) Saint Flour, C.; Papirer, E. J. Colloid Interface Sci. 1983, 91, 69-75. (22) Park, S.-J.; Donnet, J.-B. J. Adhes. Sci. Technol. 1998, 206, 2932. (23) Asten, A.; van Veenendaal, N.; Koster, S. J. Chromatogr., A 2000, 888, 175-196. (24) Rebouillat, S.; Donnet, J.-B.; Guo, H.; Wang, T. K. J. Appl. Polym. Sci. 1998, 67, 487-500. (25) Price, G. J.; Siow, K. S.; Guillet, J. E. Macromolecules 1989, 22, 3116-3119. (26) Tan, Z.; Jaeger, R.; Vancso, G. J. Polymer 1994, 35, 3230-3236. (27) Tan, Z.; Vancso, G. J. Macromolecules 1997, 30, 4665-4673. (28) Al-Saigh, Z. Y. Int. J. Polym. Anal. Charact. 1997, 3, 249-291. (29) Etxeberria, A.; Uriarte, C.; Fernandez-Berridi, M. J.; Iruin, J. J. Macromolecules 1994, 27, 1245-1248. (30) Murakami, Y.; Enoki, R.; Ogoma, Y.; Kondo, Y. Polym. J. 1998, 30, 520-525. (31) Du, Q.; Chen, W.; Munk, P. Macromolecules 1999, 32, 15141518. (32) Papirer, E.; Balard, H.; Brendle, E.; Lignieres, J. J. Adh. Sci. Technol. 1996, 10, 1401-1411. (33) Braun, J. M.; Guillet, J. E. Adv. Polym. Sci. 1976, 21, 108145. (34) Li, B. C. Rubber Chem. Technol. 1996, 69, 347-376. (35) Hegedus, C. R.; Kamel, I. L. J. Coatings Technol. 1993, 65, 2330. (36) Mukhopadhyay, P.; Schreiber, H. P. Colloids Surf., A 1995, 100, 47-71. (37) Al-Saigh, Z. Y.; Guillet, J. Inverse Gas Chromatography in Analysis of Polymers and Rubbers. In Encyclopedia of Analytical Chemistry: Applications, Theory, and Instrumentation; Meyer, R. A., Ed.; Wiley & Sons: Chichester, 2000; Vol. 9, pp 7759-7792. (38) Belgacem, M. N. Cellulose Chem. Technol. 2000, 34, 357-384. (39) Charmas, B.; Leboda, R. J. Chromatogr. A 2000, 886, 133152. (40) Davis, T. C.; Petersen, J. C.; Haines, W. E. Anal. Chem. 1966, 38, 241-243. (41) Davis, T. C.; Petersen, J. C. Anal. Chem. 1967, 39, 1852-1857. (42) Papirer, E.; Kuczinski, J.; Siffert, B. Chromatographia 1987, 23, 401-406.
Puig et al.
the values obtained by DTA and those obtained by dilatometric measurements, and observed a good agreement. Later, DSC was used by Noel and Corbett to study the presence of paraffin waxes in asphalts as well as to identify which asphalt components were mainly responsible for the observed secondary phase transition.44 The authors showed that apparently only saturates and naphthene aromatic fractions underwent glass phase transitions, as was also later demonstrated by Claudy et al.45 Giavarini and Pochetti studied the effect of oxidation on the thermal behavior of asphalts by DSC through changes in Tg. The authors indicated the difficulties in determining the glass transition temperatures of asphalts from DSC traces.46 In the present work we use IGC at subambient temperaturessfirst, to gain knowledge on the glass transition temperature of two bituminous binders having two different origins and, second, to carry out surface energy determinations of these materials. Theory Probe Retention Determination. In an IGC experiment the stationary phase is investigated by injecting vapors of pure and known liquids or gases (“probes”) and the primarily result is the retention volume, VP.7 The value of VP is calculated from the first moment of the elution peak, tP, multiplied by the carrier gas flow rate, F. A marker, i.e., a probe that does not significantly interact with the stationary phase and elutes at tM, is used to correct for the intrinsic gas hold-up (dead volume) of the system. VM is the corresponding value of the retention volume of the marker. A correction factor J32 is introduced to account for gas compressibility. The so-called net retention volume, which is related to thermodynamic properties of the stationary phase, is calculated using eq 1:47,48
VN ) (tP - tM)FJ32 ) (VP - VM)J32
(1)
Van’t Hoff Plot. The sorption of a probe on the stationary phase consists of two parts: (a) the adsorption on the surface, and (b) the absorption into the bulk of the material. Depending on the permeability of the probe into the stationary phase (“unknown”) one of the two mechanisms dominates. A “van’t Hoff plot” shows the relation of the logarithm of the net retention volume as a function of the reciprocal absolute temperature.49-51 The individual mechanisms show a linear relation in the van’t Hoff plot. From the slope, the adsorption or absorption enthalpy of the probe at the surface, or in the bulk, of the stationary phase can be calculated, respectively. Retention of the probe in the region below the glass transition temperature of the material making (43) Connor, H. J.; Spiro, J. G. J. Inst. Pet. 1968, 54, 137-139. (44) Noel, F.; Corbett, L. W. J. Inst. Pet. 1970, 56, 261-268. (45) Claudy, P.; Le´toffe, J. M.; King, G. N.; Planche, J. P.; Brule, B. Fuel Sci. Technol. INT’L 1991, 9, 71-92. (46) Giavarini, C.; Pochetti, F. J. Thermal Anal. 1973, 5, 83-94. (47) Price, G. J.; Guillet, J. E. J. Macromol. Sci. 1986, A23, 14871502. (48) Conder, J. R.; Young, C. L. Physicochemical Measurements by Chromatography; Wiley & Sons: New York, 1979. (49) Braun, J.-M.; Guillet, J. E. Macromolecules 1975, 8, 882-888. (50) Panda, S.; Bu, S.; Huang, B.; Edwards, R. R.; Liao, Q.; Yun, K. S.; Parcher, J. F. Anal. Chem. 1997, 69, 2485-2495. (51) Parcher, J. F.; Edwards, R. R.; Yun, K. S. Anal. Chem. News Features 1997, 69, 229A-234A.
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up the stationary phase arises from condensation and adsorption onto the surface, since the probe is unable to diffuse into the bulk of the material at the corresponding temperatures.52 Near the glass transition temperatures of the stationary phase, both mechanisms contribute significantly to the net retention volume, which is reflected in the plot by a nonlinear behavior. The onset of the deviation from the nonlinear behavior is considered to coincide with the glass transition temperature.33,49,53 The degree of interaction between a solid and its environment is of great importance in applications such as composite materials. The interaction is given by surface properties, which in turn is described by the value of the materials’ surface energy. It is usually considered that the surface energy (γs) of a solid can be understood as the result of the contribution of two parts, a dispersp 54 sive (γD s ) and a specific (γs ) energy component: sp γ ) γD s + γs
(2)
γD s expresses the contributions of London- or dispersive -type of interactions. These interactions are also termed “nonspecific” because they always take place between two species that are brought into contact. In practice, n-alkanes (C2-C11) are used to obtain the dispersive component for a solid by injecting them in the gas chromatograph column filled with the unknown specimen.55 The value of the dispersive component of the unknown can be determined from the surface area of the n-alkane molecules, a, and the dispersive component of the surface tension of the probe (γD L ) using eq 3: 1/2 D 1/2 + Cst RT ln(VN) ) 2NAV(γD s ) a(γL )
(3)
where NAV is Avogadro constant and Cst is an additive constant. By plotting RT ln(VN) of the n-alkane probes versus D 1/2 a(γD L ) , the γs can be obtained directly from the slope of the straight line fitted to the data points.16 On the other hand, γsp s describes specific interactions of the stationary phase, such as polar, acid/base, hydrogen bonding, etc.55 If a polar probe is injected, an increase of VN is expected. This difference of ordinates between RT ln(VN) value of a polar probe and the “nalkane reference line” observed is attributed to specific interactions. Experimental Section Equipment. A Shimadzu GC-14B equipped with a flame ionization detector and an AOC-20i autoinjector was used. A CRG-15 cryogenic attachment was added in order to control the inlet of liquid nitrogen, which was fed from an Apollo liquid nitrogen tank (Messer Griesheim, Krefeld, Germany). Measurements below ambient conditions were established and a large temperature window could be covered, within the range (52) Lipson, J. E. G.; Guillet, J. E. Study of Structure and Interactions in Polymers by Inverse Gas Chromatography. In Developments in Polymer Characterisation; Dawkins, J. V., Ed.; Applied Science Publishers: Barking, 1982; pp 33-74. (53) Lavoie, A.; Guillet, J. E. Macromolecules 1969, 2, 443-446. (54) Fowkes, F. M. Ind. Eng. Chem. 1964, 56, 40-52. (55) Papirer, E.; Lacroix, R.; Donnet, J.-B. Carbon 1996, 34, 15211529.
of -80 °C to 400 °C. Liquid nitrogen was directly sprayed into the oven at a pressure of 1.5 bar. Additionally, a Brooks mass flow controller 5850S together with a 0152 Brooks Microprocessor control & read out unit was integrated in the carrier gas stream. The pressure was measured by a Druck PDCR911 pressure sensor (0-4.0 × 105 Pa absolute), connected to a DPI 281 digital read-out unit. A computer with a custom-made software program, developed in our laboratory, was used to run the experiments automatically and to process the data.56 The injector and detector temperature was kept at 100 °C. The SGE 0.5 µL autosampler syringe used enabled injection volumes between 0.01 µL and 0.45 µL of liquid or vapor. In our IGC determinations, we used infinite dilution conditions, i.e., at effectively near-zero surface coverage, allowing us to determine the interactions between the probes and the solid in the absence of interactions between the probe molecules themselves.16 Differential scanning calorimetry experiments were performed on a Perkin-Elmer Pyris 1, using a 10° C/min heating rate within a temperature range between -50 and 170 °C. Runs were carried out under inert atmosphere and using liquid nitrogen as coolant. Materials. Two bituminous binders A and B of asphaltenes content 24.9% and 13.2%, respectively, determined through heptane precipitation, were supplied by the Shell Research and Technology Center Amsterdam (The Netherlands). For the IGC experiments, the bitumen was coated to a loading percentage of approximately 5.9 wt % onto Chromosorb G 60/ 80 AW DMCS (Alltech, The Netherlands). The bituminous binder was first dissolved into high-grade toluene, mixed with the Chromosorb, and subsequently a gentle evaporation of toluene was established in a rotary evaporator. Copper tubes of 1/4′′ outer diameter (Alltech) were pre-cleaned with toluene, 2-propanol, and acetone. The columns were cut to a length of approximately 0.80 m and filled with the different specimens using a mechanical vibrator and applying vacuum. Both ends of the columns were loosely plugged with quartz wool (Chrompack Nederland B. V., Bergen op Zoom, The Netherlands). The carrier gas used was helium-5.0, and the flow rate was kept at 30 mL/min. The columns were conditioned for 2 days at 30 °C prior to the experiments. The “dead volume” of the system was determined by the injection of methane-5.5 (Praxair, Oevel, Belgium). The retention times were taken from the point of injection to the maximum peak height at infinite dilution conditions. In this case, VN was practically independent of the probe concentration. All nonpolar probes were high-grade n-alkanes obtained from Aldrich. The gas n-butane was obtained from Praxair. Polar probes such as diethyl ether, acetone, ethyl acetate, dichloromethane, and chloroform were also obtained from Aldrich. Small injection volumes were ensured by sampling from the gaseous phase on top of the liquid probes in the vials. An average of five injections was recorded per probe.
Results and Discussion The use of IGC to determine the glass transition of polymers, pioneered by Guillet and co-workers,7 is conducted by measuring VN as a function of column temperature. To our knowledge, no previous IGC work has been carried out to determine glass transition temperatures at subambient temperatures. Asphalts are semisolid materials at room temperature and show glass transition temperatures below room temperature. Under cryogenic conditions, IGC is a suitable technique to study such materials with respect to their surface properties (surface tension). Figure 1 shows van’t Hoff (56) Segeren, L. H. G. J.; Wouters, M. E. L.; Bos, M.; van den Berg, J. W. A.; Vancso, G. J. J. Chromatogr., A 2002, 969, 215-227.
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Puig et al. Table 1. Parameters Used for the Determination of Dispersive Surface Energya
a
Figure 1. Van’t Hoff plots for both bituminous binders used as stationary phases. Binder A (9). Binder B (b).
Figure 2. DSC thermograms (heating curves) for both bituminous binders at 10 °C/min heating rate. (‚‚‚) Binder A. (-) Binder B.
plots for both bituminous binders using n-pentane as a molecular probe. A z-shaped curve is observed in both cases as described in an earlier section. As one can see, the reversal from the normal linear behavior is more pronounced for binder A. For both bituminous binders, the right-hand side of the curve, i.e., retention data obtained at low temperatures, shows a well-defined linear behavior. This region is solely associated with surface adsorption of the pentane probe. It is usually assumed that the temperature of the onset of deviation from linearity corresponds to the glass transition temperature of the stationary phase.49 At this temperature the first detectable contribution from bulk absorption to the total retention volume occurs. It is attributed to the interaction of the probe with the bulk polymer due to the increase in free volume.52 From the van’t Hoff plots shown in Figure 1, deviation from the linear behavior for bituminous binder A occurs at -27 °C, whereas the glass transition temperature for bituminous binder B is estimated at -21 °C. Figure 2 shows the thermograms on heating obtained by DSC for both bituminous binders (A and B). Baseline subtraction is required in order to obtain DSC traces in which their more prominent features can be observed.
probe
1/2 a(γD L) (nm2 mJ1/2 m-1)
n-butane n-pentane n-hexane n-heptane n-octane n-nonane
1.50b 1.86b 2.21 2.57 2.90 3.28
Ref 24. b Extrapolated values.
The DSC traces in Figure 2 show close resemblance to those previously reported by Claudy and co-workers.57 Differences in thermal behavior between binders A and B are characteristic of their different origin. The presence of multiple endothermic processes in the DSC traces was previously assigned to the existence of some paraffins in asphalts as well as naphthene aromatics which crystallize on cooling from high temperatures, melting later on subsequent heating.44 No clear step in the heat flow located at subambient temperatures is observed in the DSC traces for bituminous binders A and B. The presence of multiple features and the absence of a unique and clear step on the DSC curve make thermal analysis inconclusive for Tg determination of asphalts in our case. However, due to the high sensitivity and clear sorption behavior, IGC is well suited for this purpose. It can be mentioned at this juncture that due to enhanced sensitivity, IGC has been proved to be the method of choice in other cases of phase transition studies due to enhanced sensitivity when compared to DSC.3 A region of nonequilibrium probe sorption follows the linear behavior found in the right part of the retention diagram with increasing temperature in Figure 1. The region extends over a 50 °C temperature range for bituminous binder A and 65 °C for binder B. At temperatures above 55 °C, the retention behavior of both bituminous binders are already following the equilibrium absorption line of the probe absorption into the bulk of the material. The more pronounced reversal behavior found for binder A, despite having the same percentage loading as for the binder B (5.9 wt %), may be attributed to differences in chemical composition (e.g., asphaltenes content). The slope of the linear plot of log(VN) versus 1/T results in the enthalpy of adsorption. For both bituminous binders a straight line is found. However, the slope is higher for binder B than for A, which reflects the greater affinity of the n-pentane probe to interact with binder B. We have determined the dispersive energy term for bituminous binders A and B using eq 2 and 1/2 values shown in Table 1. the a(γD L) Having determined previously the glass transition temperatures of both bituminous binders, a temperature of -30 °C was chosen to carry out surface energy determination in order to exclude bulk absorption of probe molecules. Oven temperatures below the glass transition of the bituminous binders ensure a sufficiently impermeable material, such that retention times are not affected by absorption mechanisms. (57) Claudy, P. M.; Le´toffe, J. M.; Martin, D.; Planche, J. P. Thermochim. Acta 1998, 324, 203-213.
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1/2 Figure 3. Plot of RT ln(VN) vs a(γD (see eq 3) for both s) bituminous binders. Binder A (9). Binder B (b).
Figure 3 shows the plots of RT ln(VN) as a function of 1/2 for both binders, using n-butane, n-pentane, a(γD s) n-hexane, and n-heptane as probes, respectively. A linear behavior is found for both materials studied. Derivations from the slope yielded values of γD s at -30 °C for binder A of 59.3 mJ/m2 and 50.6 mJ/m2 for binder B. In the work of Papirer et al. the determination of the dispersive surface energy of asphalt and its asphaltene fraction as a function of temperature were carried out within the range between 50 °C and 130 °C.42 The results showed that a higher dispersive surface energy was found for the asphaltene fraction. The values obtained by Papirer et al., when extrapolated to -30 °C, agree very well with those reported in the present work. Plots that relate RT ln(VN) to the vapor pressure at saturation of the injected polar probe for both bituminous binders are shown in Figure 4. The resulting interaction of both stationary phases with polar probes, of various specific characters, and the values of the specific interaction parameters (Isp) are shown in Table 2. The Isp values are given by the differences of ordinates (RT ln(VN) in Figure 4 between the n-alkane line and the corresponding polar probe (having the same vapor pressure as a hypothetical value n-alkane). According to Schultz et al., the specific interactions are essentially Lewis acid-base interactions or electron acceptordonor interactions. Strong interactions develop only between an acid and a base.16 Results show that both bituminous binders have a strong acidic character and a rather low basic character. Bituminous binder B exhibits a slightly higher acidic character than bituminous binder A does, whereas binder A has a slightly higher basic character. Siffert et al. showed using electrokinetic measurements in organic media, that the ratio of the electron donor and acceptor numbers of different asphaltenes obtained from Safaniya heavy oil residues is given by the ratio of the number of acid surface groups to that of the base groups.58 Bituminous binders of different origin may show acid and base groups of different ratio content as well as of different nature. (58) Siffert, B.; Rageul, P.; Papirer, E. Fuel 1996, 75, 1625-1628.
Figure 4. Plot relating RT ln(VN) to the vapor pressure at saturation of the injected probes (P0) -30 °C. (a) Bituminous binder A. (b) Bituminous binder B. Table 2. Specific Interaction Parameters (Isp) for Bituminous Binders A and B probe
specific character
Isp (kJ/mol) Binder A
Isp (kJ/mol) Binder B
diethyl ether acetone ethyl acetate dichloromethane chloroform
base amphoteric amphoteric acid acid
7.91 6.96 4.72 4.43 2.75
8.70 8.36 6.25 4.29 2.65
Conclusions The Inverse gas chromatography technique was sensitive and successful to determine the glass transition in bituminous binders by constructing van’t Hoff plots. Due to the semisolid character of bituminous binders at room temperature, retention measurements, using n-pentane as probe, were carried out from below ambient conditions to 100 °C. Determinations of the dispersive surface energy term for both bituminous binders at -30 °C reveal a higher value for the binder of higher asphaltenes content. Acknowledgment. The authors acknowledge financial support by the Subsidiary Program for Economy, Ecology and Technology from the Ministry of Economic Affairs The Netherlands under the project number EETK99029/39510-0710. EF030062L
