Ind. Eng. Chem. Prod. Res. Dev. 1982, 21, 76-79
78
hydrazones are formed in the bubblers. The corresponding carbonyl compounds were identified as formaldehyde, acetaldehyde, glyoxal, and n-butyraldehyde in the case of butyl ethers. Conclusion Glycol and diglycol monoethers are thermally stable organic compounds since they begin to decompose at about 400 "C. This temperature corresponds with the values given by Wolf and Rosie (1967) for aliphatic alcohols and ethylene glycol monomethyl ether. The presence of oxygen lessens the temperature of the beginning of decomposition. The compounds resulting from thermal degradation above 400 "C consist essentially of gaseous hydrocarbons, hydrogen, and carbon monoxide. In both cases (pyrolysis and combustion), the importance of the CO release and the
toxicity of the effluent must be pointed out. Literature Cited Anderson, K. R.; Benson, S. W. J . Chem. Phys. 1962, 36, 2320. Bruneau, C.; Soyer, N.; BrauR, A.; Kerfanto, M. J . Anal. Appl. mol. 1961, 3, 71. Cathonnet, M.; Boeltner, J. C.; James, H. J . Chlm. phys. 1979, 76, 183. Chevalier, G.; Dupoux, N. "Epuratlon par traltement thermique des atmosphhs charQ6es de poiluants organlques volatils"; rapport C.E.A.R4 7 3 2 Servlce de documentation du C.E.N. Saclay, B.P. No. 2 91190 Glf sur Yvette, France, 1976. FouceuR, J. F.; Martin. R. J . Chem. Phys. 1978, 75, 132. Groenendyk, H.; Levy, E. J.; Samer, S. F. J . Chmmfogr. Sci. 1970. 6, 401. Hagemann, R.; Virelirier, H.; Gaudin, D. A/ta/usIs, 1978, 6, 401. Levy, E. J.; Paul. D. G. J . Gas. Chromtogr. 1967, 5 , 136. Wolf, T.; Rosle, D. M. Anal. Chem. 1967, 39, 725.
Received for review July 6 , 1981 Accepted October 15, 1981
Plasticized Sulfur Asphalt Replacements Allen C. Ludwlg Southwest Research Institute, Sen Antonio, Texas 78284
Sulfur, a bright yetlow brittle crystalline solld, has been chemically modified to produce a material with physical properties approaching those of asphalt. Sulphlex is the name used to describe these highly plasticized sulfur composltions. Sulphlex has been successfully demonstrated as an alternate to asphalt as a binder and seal coat material in several publlc highway applications. To better understand the chemistry of Sulphlex, infrared, molecular weight distribution, X-ray dtffractbn, and dlfferential scanning calorimetry were used for three different Sulphlex formulations. This paper reports on thelr findings as well as the Ames Bioassay for the potential mutagenicity of Sulphlex vapor.
Sulphlex is the name used to describe a family of highly plasticized sulfur compositions. Developed originaUy under a contract to the Federal Highway Administration, these materials have demonstrated the potential of replacing asphalt or Portland cement as binders for pavements or as sealants (Ludwig, 1980). Figure 1shows the manufacture of Sulphlex. In developing Sulphlex, it was thought desirable to try to duplicate the properties of asphalt. As a result, the principal properties used to evaluate the various Sulphlex formulations were penetration, ductility, softening point, and viscosity. This approach was fruitful in that the resultant formulations were subsequently found to act similar to asphalt and as a result were ultimately substituted for asphalt in conventional commercial equipment. For example, Sulphlex was hauled in asphalt trailers, pumped into the asphalt storage tanks, and ultimately mixed with aggregate in the batch plant to produce the hot mix product. Thephot mix was delivered in open dump trucks and laid with conventional laying machines such as a Barber-Greene. Figure 2 shows a Sulphlex pavement being placed in a manner identical with asphaltic concrete, but this particular mix will become rigid after several days to have properties more comparable to a Portland cement concrete. In other words, asphaltic concrete laying machines place all the Sulphlex mixes, but the particular Sulphlex binder that is selected determines if the pavement will be flexible like asphaltic concrete, rigid like
Portland cement concrete, or intermediate between these extremes. In December 1978 a 620-ft experimental roadway was constructed on the grounds of SwRI in San Antonio. Based on ita performance, FHWA negotiated with seven states to place Sulphlex pavements under varying traffic and climatic conditions. Texas was the first state to install a mile and a half of a nominal 1 in. thick overlay of hot mix in August 1980. Five other states have installed test sections as well. The last state is scheduled to install its section in the fall of 1981. In addition to the hot mix material, Texas also chose to lay a 3OOO-ft section using Sulphlex as a seal coat parallel to an asphalt seal coat. By October 1980 (less than 2 months after installation) there was evidence of bleeding or flushing of the asphalt in the wheel paths and particularly at intersections due to the turning action of the tires. By April 1981, the flushing was very pronounced with the asphalt, whereas the Sulphlex material is virtually unchanged. Thus it appears that this is one application where there could be a decided advantage of Sulphlex over asphalt. The question arises: what is Sulphlex chemically that it should be so drastically different from sulfur or even other modified sulfur formulations? Since this fell outside the scope of the FHWA program, Southwest Research Institute initiated a small program with ita OWTI funds to study it. Four principal techniques were selected for
0196-43211821l22l-0O76$01.25/0 0 1982 American Chemical Society
Ind. EN. Chem. Rod. Res. Dev.. Vol. 21, No. 1. 1982 77
Table 1. Chemical Compositions of Formulations no. 233 no. 230 no. 126 70%sulfur 70%sulfur 61%sulfur 12% dicyclo15%dicyclo- 13%dicycloDentadiene
16% dipentene
8%vinyl toluene
Figure I. Sulphlex flow chart.
i
.
Figure 2.
..
. . .. Installing a rigid Sulphlex pavement with asphalt tech. .
nology.
studying three of the more promising formulations at that time. These were infrared, molecular weight distribution, X-ray diffraction, and differential scanning calorimetry. The infrared technique was discontinued after only a cursory investigation because the hydrocarbons used to m o d i the sulfur "swamped" any sulfur compounds. Had the program been more extensive, this area might have proven more fruitful and it probably will in any future endeavors. The other three systems, however, furnished considerable information about the Sulphlex formulations. Three promising Sulphlex formulations were selected for thia work. Formulation no. 233 has physical properties very similar to a road grade asphalt, no. 230 gives a concrete with properties similar to rigid Portland cement
hi
96 To>. Y I
Figure 3. Molecular weight distribution of elemental sulfur.
Dentadiene
~
~~
Dentadiene
lg% dipentene 13'% vinyl toluene 13%coal tar
concrete, and no. 126 was termed an intermediate formulation since it produced concretes with properties intermediate between the other two. The chemical compositions for these three formulations are listed in Table 1. The molecular weight distribution data for these Sulphlex formulations are interesting when compared to that of elemental sulfur (Figures 3 4 ) . It would appear that approximately 30% of formulation no. 233 is unreacted sulfur while approximately 50% of formulation no. 126 and no. 230 is unreacted. For all three formulations, however, the bulk of the material is relatively low molecular weight, ranging from approximately 250 to 2500 with some evidence of molecular weights as high as loo00 to 2Oo00. The data from the differential scanning calorimeter, however, when compared to elemental sulfur, shows the Sulphlex formulations to be substantially different from crystalline sulfur (Figures 7-10). For these formulations the distinct peaks a t 95 "C, the S-.S, transition temperature, and 120 "C, the melting point of s,, have been eliminated. Before jumping to too many conclusions as to what is happening a t 95 "C for the no. 230 and 233 materials. one should examine the data for AC-20, a typical road grade asphalt, which also shows a similar depression a t 95 "C (Figure 11). X-ray diffraction was the final technique used in the evaluation of the Sulphlex formulations. We were somewhat skeptical of the value of this technique as a result of trying to distinguish between S, and S, samples a number of years ago. When S, samples were subjected to the X-ray, the data indicated S, and when the specimens were viewed, the surface had indeed been converted to S, by the X-rays, although the bulk of the sample remained as Sp The data from the Sulphlex formulations, however, indicated that there was essentially no crystalline sulfur in the three Sulphlex formulations. A question then arises: if the unreacted sulfur is not crystalline, but perhaps supercooled liquid, how stable will it be? Long-term studies with various Sulphlex formulations should ultimately answer this question, for there is considerable evidence that crystallization does occur. When Sulphlex pavements are
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 1, 1982
7
>
Figure 5. Molecular weight distribution of Sulphlex no. 230. I
6;
9c
?4D
Mc'
3'0
769
2300 10,030
.
?0,000
hlt
Figure 6. Molecular weight distribution of Sulphlex no. 233.
placed, reflective crystals can be seen in the pavement. Recent photomicrographs made available to use also indicated the presence of sulfur crystals. In addition, it has long been observed that there is a hardening effect encountered in some Sulphlex formulations which would easily be explained by crystallization of the unreacted sulfur. However, easy or simple explanations are not necessarily always correct. For example, Figures 12 and 13, are DSC's of 126 and 233 that were two years old when tested. Neither of these are significantly different from the DSC's of the freshly prepared material of Figures 8 and 10, respectively. To say that any particular Sulphlex formulation is a complex mixture would be an understatement. A GC/MS
analysis has indicated that it could consist of hundreds of compounds-if not thousands! From a practical point of view, however, no major problems are envisioned as long as Sulphlex can be manufactured to meet performance specifications similar to asphalt. One detrimental property of formulations 230 and 233 is what many people find to be a very disagreeable odor. Dipentene is believed to be the cause since both of these formulations contain it. Southwest Research Institute conducted an Ames Bioassay for the potential mutagenicity of Sulphlex vapor when the decision was made to use this material in the various states. The results of the Ames test were negative for formulation 233 which was the material chosen for the construction work. The odor, plus
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 1, 1982 70
r i
Elemental S u l f u r E
AC-20 A s p h a l t Y
Y
z I
95
250
0”
Figure 11. DSC thermogram for AC-20 grade asphalt. 95
120
160
250
OC
Figure 7. DSC thermogram for elemental sulfur.
E
u c Y
E
S u l p h l e x NO. 126
Y
253
80
0°C
Figure 12. DSC thermogram for two year old Sulphlex no. 126. Figure 8. DSC thermogram for Sulphlex no. 126.
S u l p h l e x 1;0. 2 3 3 (2 yrs O l d )
S u l p h l e x ElO. 230
95 250
95
250
Figure 13. DSC thermogram for two year old Sulphlex no. 233.
7C
Figure 9. DSC thermogram for Sulphlex no. 230.
lations for less than $200 per ton can be manufactured. Should the price of sulfur ultimately fall, it is not impossible to foresee Sulphlex prices at or near $120 per ton. Sulphlex is a Trademark of Southwest Research Institute, which owns title to U.S.Patents (Ludwig et al., 1981).
Acknowledgment S u l p h l e x No. 2 3 3
Thanks are due to Mr. Frank Newman and his staff for the molecular weight distribution work, Dr. George Lee for the DSC data, Mr. Jim Barbee for the X-ray diffraction, Drs.Leon Adams and Carter Nulton for the infrared and GC/MS, and Dr. Nathan Greene and his staff for the performance of the Ames tests. 250
95
“C
Figure 10. DSC thermogram for Sulphlex no. 233.
the fact that dipentene is expected to be in short supply for the foreseeable future, have made formulations 230 and 233 obsolete and work is already progressing on other, lower cost formulations. The possibilities are good that even if sulfur remains at $loo+ per ton, Sulphlex formu-
Literature Cited Ludwig, A. C.; Gerhardt. B. B.; Dale, J. M. “Materials and Techniques for Improving the Engineering Properties of Sulfur” Interim Report No. FHWA/RD80/023, NTIS, SprlngfieM, Va., June 1 b O . Ludwig, A. C.; Dale, J. M.; Frazler, H. F. U S . Patent 4290818, 1981.
Received for review July 22, 1981 Accepted September 18,1981
