By
M. S. Sureshkumar (Department of Chemical Engineering, Industrial Chemistry and Material Science (DICCISM) and Giovanni Polacco (University of Pisa, Via Diotisalvi 2, Italy)
Abstract
In order to enhance its performances, asphalt is often modified with polymers. Recently, the addition of nanoclay as a third component was studied and found to further improve the asphalt properties. This results with ternary polymer/asphalt/nanoclay blends, which were termed as polymer modified asphalt nanocomposite (PMAN). In this study, PMAN were prepared by using ethylene vinyl acetate (EVA), styrene-butadiene-styrene (SBS), ethylene metha-crylate (EMA) and an organo-modified montmorillonite. Moreover, two different preparation methods were used: i) physical mixing, where polymer and nanoclay are added separately to hot asphalt and ii) nanocomposite blending, where polymer and nanoclay are previously blended in a high shear mixer. The thermal and morphological properties, as well as the fuel resistance of the obtained PMAN were studied.
Keywords: Polymer modified asphalts, Nanocomposites, Kerosene.
1. Introduction:
Asphalt is an engineering material, mainly used for pavements and, in order to enhance its performances, it is often modified with polymers. However, recent studies are focused on the addition of nanoclay as a third component, thus producing ternary blends termed as polymer modified asphalt nanocomposites (PMAN). In this case, it was found that the mixing procedure significantly affects the final rheological, thermal and morphological properties of the material.
In this study two different base asphalts were modified by the addition of a polymer (SBS, EVA or EMA) and an organo-modified montmorillonite. Then, the obtained PMANs were characterized by fluorescence microscopy, ring and ball softening point and wide angle X-ray diffraction. Moreover, the solubility of the PMANs in a jet fuel was evaluated. The later point is related to the fact that airport pavements frequently face damages due to accidental fuel spillage. This occurs due to solubility of asphalt in hydrocarbon fuels, a problem that was often solved by using fuel resistant coal-tar pitches. However, coal-tar pitch is not environmental friendly and new formulations are necessary.
2. Materials and Methods:
Base asphalts of 50/70 pen grade from two different sources referred as L and R were modified with: linear styrene-butadiene-styrene (Kraton D-1102, SBS); Ethylene vinyl acetate with 28 wt. % vinyl acetate content (Greenflex HN70, EVA) kindly provided by Polimeri Europa; Ethylene Methacrylate containing 25 wt. % methacrylate (Elvaloy-1125, EMA) provided by Dupont and Cloisite 20A® (CL), from Southern Clay Products, USA. The latter is an organoclay prepared from a sodium montmorillonite having a cation exchange capacity of 0.926 meq.g-1 by treatment with dimethyldihydrogenated-tallow ammonium chloride. Kerosene classified as jet fuel A1 was used to test the fuel resistance of base asphalts, modified asphalts and PMANs.
Calculated quantity (~ 250 g) of base asphalt was heated to 180 °C for 2 hours and then shifted to an electrical heater to maintain and control the temperature. A high speed mixer was introduced to the hot asphalt can and the polymer, polymer/clay or its nano composite were added. Mixing was carried out in the sequence 180 °C, 45 min, 4500 rpm. After 45 minutes of mixing time, 5 min were allowed for degassing with lower rotor speed. For physical mix, polymer and nanoclay were weighed and mixed manually in a small beaker for 5 minutes. Nanocomposites were prepared by adding polymer and nanoclay in the ratio 60:40 wt. % using a Brabender Plasticorder at temperatures above 120 °C. All the samples contained 6%w of polymer with respect to asphalt. Samples for various tests were collected after mixing. For morphology tests, hot asphalt mix was poured into a cylindrical mold preheated to 180 °C. For softening point, hot asphalt was poured into the preheated ring. For XRD, analysis, samples were prepared using special templates. Similarly, disc shaped samples were prepared for the kerosene solubility tests. In what follows, letters P and N indicate physical mixing and nano composite addition, respectively.
3. Results and discussion
3.1. Softening point:
Softening point values for the prepared mixes are provided in Table 1. As compared to the softening point of neat asphalt L (49 °C) and R (48 °C), a slight increase is observed when CL alone was added. Around 22 °C rise was observed with SBS and 25 °C with EMA, but EVA increased the softening point only around 11 °C. The increase in softening point found to depend on nanoclay/polymer interaction, polymer/asphalt type and modification methods. SBS and EVA showed an increasing trend from physical mixing to nano composite blending. In case of EMA and L asphalt a decreasing trend was observed, while for R asphalt, physical method has the higher softening point.
Table 1: Softening point
|
L |
Modifier |
R |
|
49.0 |
– |
48.0 |
|
52.3 |
CL |
52.3 |
|
72.7 |
SBS |
68.9 |
|
75.1 |
SBSP |
71.4 |
|
80.8 |
SBSN |
75.3 |
|
77.5 |
EMA |
74.0 |
|
76.8 |
EMAP |
76.2 |
|
72.6 |
EMAN |
71.1 |
|
60.5 |
EVA |
62.0 |
|
61.1 |
EVAP |
66.9 |
|
70.2 |
EVAN |
76.3 |
3.2 Phase morphology:
Phase morphology as obtained from optical microscopy provides a neat characteristic dark phase for asphalt and some characteristic spots were observed when nanoclay is added. Upon addition of polymer (SBS, EVA or EMA), two phases can be observed: asphalt as continuous phase and polymer as dispersed phase featured with globules. When polymer/clay physical mix is introduced into asphalt, it is quite interesting to observe a phase reversion, in which polymer becomes the continuous phase and asphaltenes found to disperse into it. This clearly shows that the clay enhances the compatibility between asphalt and polymer. In general, as compared to the physical mixing, nanoblending found to cause better dispersion of the mixes. In case of EMA & EVA with nanocomposite blending better dispersion was observed. This led to a single dispersed phase which might be probably due to the complete swelling of polymer with the asphalt components.
3.3 Fuel Resistance:
Fuel resistance of all the blends was studied by using kerosene. Disc shaped samples were prepared and then immersed in a beaker containing kerosene (jet fuel A1). The whole set-up was stirred at a rate of 30 rpm. The change in weight was recorded for two hours with an interval of 20 min. SBS modified samples showed the lowest fuel resistance. However, the introduction of SBS and CL considerably reduced the solubility. In case of EVA and EMA, swelling occurred up to 18 % from the initial value as time progressed and the swelling was not much affected with the methods of incorporation of nanoclay. EVA and EMA compositions showed excellent resistance to fuel which is in line with our earlier findings.
3.4 X-ray Diffraction:
X-ray diffraction studies with EVA/Asphalt nanocomposite confirmed the presence of coherent intercalation with sharp peaks towards lower angles. Also, the compatibility of the nanoclay with the polymer played a vital role in effective intercalation.
4. Conclusion:
Studies carried out to investigate the properties of PMAN using various polymers have brought out promising futuristic asphalt compositions. With these preliminary investigations, EVA and EMA based asphalt compositions found to possess good mechanical properties, evidenced from softening point values along with exceptional fuel resistance. Further characterizations are in progress in order to select the better composition of the blends.
Acknowledgement:
Paper presented at the International Conference on Nanoscience and Nanotechnology (ICONN 2010), SRM University, Kattankulathur, India, pp. 405-406
Sincere gratitude is offered to ‘Leonardo Da Vinci’ School of Engineering, University of Pisa, Italy for providing sufficient funding to carry out this research work and to present this research work at this international gathering.
References:
1. Polacco G., Kríž P., Filippi S., Stastna J., Biondi D. & Zanzotto L., (2008), Rheological properties of asphalt/SBS/clay blends, Eur. Poly. J., Vol. 44, 3512-3521.
2. Giuliani F., Merusi F., Filippi S., Biondi D., Finocchario M.L. & Polacco G., (2009), Effect of polymer modification on the fuel resistance of asphalt binders, Fuel, Vol. 88, pp. 1539-1546.
3. Sureshkumar M.S., Filippi S., Polacco G., Kríž P., Kachatchov I.B., Stastna J. & Zanzotto, L. (2009), Internal structure and linear visco-elastic properties of EVA/Asphalt nanocomposites, Eur. Poly. J., (Accepted).
4. Sureshkumar M.S., Filippi S., Polacco G., Wasage L.T., Kachatchov I.B., Stastna J. & Zanzotto, L., (2009), Rheological properties of EVA/Asphalt nanocomposites, J. App. Poly. Sc., (Submitted).
5. Sureshkumar M.S., Filippi S., Biondi D. & Polacco G., (2009), EVA/Asphalt Nanocomposite: Preparation and Characterization, (2010), Poly. Adv. Tech., (To be communicated).
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