Abstract:
This invention relates to a composition and method for improving the storage stability of polymer modified asphalts. More specifically, the storage stability of an asphalt which contains greater than 1.0 wt. % polymer can be improved by adding the polymer to an asphalt which has previously been reacted with an inorganic acid. The storage stable acid treated polymer modified asphalt thus produced is particularly well suited for use as a binder in paving materials and as a coating or saturant for roofing shingles.

Description:
CROSS REF. TO RELATED APPLICATIONS 
     This is a continuation of U.S. Ser. No. 237,028, filed Aug. 29, 1988 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a composition and method for improving the storage stability of polymer modified asphalts. 
     2. Discussion of Related Art 
     Asphalt is a bituminous material resulting from the distillation of crude oil. Typically, asphalt is derived from the bottoms of a vacuum distillation tower and has an atmospheric boiling point of at least 380° C. Because it is hydrophobic and has good adhesiveness and weatherability, asphalt has been used widely as a binder in paving materials and as a coating for roofing shingles. 
     Frequently, polymeric materials have been added to asphalt to enhance its rheological properties, i.e., to improve its creep resistance above about 20° C. Polymer modified asphalts must also have good phase compatibility between the asphalt and polymer, and be storage stable at high temperatures for ease of handling and application. Compatibility between the polymer and asphalt is very important to ensure that the properties of both are transferred to the finished product for good long term performance. Poor storage stability will render the polymer modified asphalt unsuitable for use in paving binder applications, roofing applications, and other industrial specialty products. Accordingly, various methods have been suggested for maintaining storage stability. 
     One method requires continuous mixing of the asphalt/polymer mixture to avoid phase separation (See, for example, U.S. Pat. Nos. 4,240,946 and 4,314,921, which require high shear mixing to obtain physical dispersion of a polyolefin in bitumen. See also Transportation and Road Research Laboratory Report 1101 by J. H. Denning et. al., Highways and Structures Department, Crowthorne, Berkshire, England (1983)). Another method discloses adding one or more dispersants to a polyethylene modified asphalt to avoid phase separation (See Jew et al., Journal of Applied Polymer Science, 31, pp.2685-2704 (1986)). 
     In yet another method, the composition of the asphalt is tailored to ensure compatibility with the polymer used or the polymer is selected to be compatible with the asphalt (See U.S. Serial Nos. 073,813 filed June 15, 1987 and 134,954 filed Dec. 18, 1987). 
     In still another method, polymer modified asphalt is stabilized by the addition of an acid after the polymer has been added to the asphalt (See, for example, German patent DE 22 55 173 C3 which discloses stabilizing mixtures of asphalt and styrenic thermoplastic elastomers (styrene-butadiene-styrene) by adding small amounts of 85% o-phosphoric acid or 36% hydrochloric acid to the asphalt/SBS mixture). 
     However, none of these methods, alone or in combination, teach or suggest the specific method for improving the storage stability of polymer modified asphalts described hereinafter. 
     SUMMARY OF THE INVENTION 
     This invention relates to a composition and method for improving the storage stability of polymer modified asphalts. More specifically, the storage stability of an asphalt that contains greater than 1.0 wt.% of a polymer can be enhanced if the asphalt is contacted with an inorganic acid prior to adding the polymer. The resulting acid treated polymer modified product will have enhanced storage stability relative to that obtained had the acid been added with or after the polymer. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The asphalt used in this invention may be obtained from a variety of sources including straight-run vacuum residue; mixtures of vacuum residue with diluents such as vacuum tower wash oil, paraffin distillate, aromatic and naphthenic oils, and mixtures thereof; oxidized vacuum residues or oxidized mixtures of vacuum residues and diluent oils; and the like. Other asphaltic materials such as coal tar pitch, rock asphalt, and naturally occurring asphalt may also be used. Typically, the asphalt will have an atmospheric boiling point of at least 380° C., more typically of at least 440° C., and an asphaltene content of between about 5 and about 30 wt.% as determined by ASTM D4124. In paving binder applications, the asphalt will typically comprise 85, preferably 90, wt.% or more of the acid treated polymer modified product (i.e., the final product). The asphalt will typically comprise 80, preferably 85, wt.% or more of the final product when it is used in roofing applications. 
     An inorganic acid is then contacted with, or added to, the asphalt to form an acid treated asphalt. In general, acid addition improves the temperature susceptibility of the asphalt and the stability of the acid treated polymer modified blend. However, it is critical to obtaining a product having improved storage stability that the acid not be added to the asphalt after or with the polymer. Preferably, the inorganic acid is added slowly to the asphalt to avoid foaming which may occur if all the acid were added at one time. The inorganic acid content of the asphalt is not critical, but normally should range between about 0.2 and about 5.0 wt.%, preferably between about 0.25 and about 3.0 wt.%, of the asphalt. Although a wide variety of inorganic acids can be used, the inorganic acid will preferably be selected from the group consisting of hydrochloric acid, phosphoric acid, phosphorus pentoxide, sulfuric acid, and mixtures thereof. The term &#34;inorganic acid&#34; is meant to include compounds that are capable of forming an inorganic acid when contacted with the asphalt (e.g., chlorinated paraffin wax and polyvinyl chloride release hydrochloric acid when contacted with hot asphalt). Hydrochloric acid, phosphoric acid, phosphorus pentoxide, and mixtures thereof are preferred inorganic acids, with phosphoric acid being particularly preferred. 
     Following acid addition, the polymer is then added to the acid treated asphalt to form an acid treated polymer modified asphalt that has enhanced storage stability relative to the storage stability obtained if the polymer were added prior to or concurrent with the inorganic acid. However, the asphalt must contain greater than 1.0 wt.% (preferably at least 1.5 wt.% and more preferably at least 2.0 wt.%) of the polymer for the storage stability to be enhanced by acid addition. At polymer concentrations of 1.0 wt.% or less, polymer modified asphalts appear to be storage stable without acid addition. Conversely, polymer modified asphalts are believed to become increasingly less stable as the polymer concentration in the asphalt increases above 1.0 wt.%. However, the upper limit on the amount of polymer in the asphalt is not critical and can range up to 15 wt.% or more based on weight percent of the acid treated asphalt, although amounts below 15 wt.% are preferred. Therefore, the amount of polymer in the asphalt will typically range from above 1.0 to about 15 wt.% based on weight of the acid treated asphalt. Preferably, the amount of polymer in the asphalt will range from about 1.5 to about 15 wt.% and more preferably from about 2.0 to about 15 wt.%. When used as a paving binder, the acid treated polymer modified asphalt normally contains from about 4 to about 8 wt.% polymer. When used for roofing applications, the acid treated polymer modified asphalt normally contains from about 8 to about 15 wt.% polymer. 
     A wide variety of polymers may be used in this invention. Suitable polymers include both thermoplastics and thermosets, as defined by ASTM D 883-69 Standard Definitions of Terms Relating to Plastics, the disclosure of which is incorporated herein by reference. ASTM D 883-69 defines a thermoplastic as a polymer that can be repeatedly softened when heated and hardened when cooled. A thermoset is defined as a polymer that can be changed into a substantially infusible or insoluble product when cured by heat or by chemical means. 
     Examples of suitable thermoplastics include acetals (e.g., polymers and copolymers of formaldehyde), acrylics, acrylonitrile-butadiene-styrene plastics, cellulosics (such as cellulose acetate, propionate and acetate-butyrate), chlorinated polyethylene, fluorocarbons, nylon, polycarbonates, polyethylenes, polyphenylene oxides, polyphenylene sulfides, polypropylene, polystryene, polysulfone, polyvinyl acetates, polyvinyl alcohols, polyvinyl chlorides, polyvinylidine chloride, styrene-acrylonitrile plastics, saturated polyesters, and thermoplastic elastomers of all classes including urethanes, polyesters, styrenics and olefinics. Preferred thermoplastics are polyethylene, ethylene methacrylate, ethylene-propylene elastomer, ethylene-vinyl acetate, nylon, uncured ethylene-propylene-diene terpolymers, and uncured thermoplastic styrenic elastomers (e.g., styrene-butadiene-styrene block copolymers), with ethylene methacrylate, ethylene-vinyl acetate, or their mixtures being most preferred. 
     Examples of suitable thermosets include amino resins (e.g., melamine-formaldehyde, urea-formaldehyde, and mixtures thereof), phenolics, polyimides, polyuretyanes, polysulfides, silicone rubbers, unsaturated polyesters, and vulcanized (i.e., cured) rubbers (e.g., natural rubbers and cured elastomers such as ethylene-propylene-diene terpolymers and styrene-butadiene-styrene block copolymers). Preferred thermosets are polyimides, polyurethanes, and vulcanized rubbers. Most preferred are polyurethanes, cured elastomers, or their mixtures. 
     The particular polymers used may be readily obtained in the marketplace from various chemical suppliers. Accordingly, their methods of preparation are well known to those skilled in the art (See Encycolpedia of Polymer Science and Technology, Interscience Publishers, New York (1971); Kirk-Othmer Encyclopedia of Chemical Technology, Wiley-Interscience, 3rd Ed., New York (1981); G. L. Kinney, Engineering Properties and Applications of Plastics, John Wiley &amp; Sons, New York (1957); and Plastics in Building, edited by Irving Skeist, Reinhold Publishing Corporation, New York (1966), the disclosures of which are incorporated herein by reference). 
     The conditions at which the acid and polymer are added to the asphalt are not critical and will vary with the particular asphalt and polymer used. However, the conditions will be within the ranges normally used for acid or polymer addition to asphalt. For example, acid is normally added slowly to the asphalt (typically, over a period of from about 1 to about 3 hours) at a temperature of from about 150° C. to about 250° C., preferably from about 180° C. to about 210° C. Once a substantial amount (preferably all) of the acid has been added, the acid treated asphalt is mixed for an additional period of time (typically from about 0.5 to about 1 hour, although longer times could be used because no further reaction is likely to occur once all of the acid has been reacted or depleted). The polymer is then added to the acid treated asphalt at a temperature of from about 150° to about 300° C., preferably from about 175° to about  230° C. Typically, the polymer will be added over a period of from about 1.5 to about 3 hours to ensure adequate dispersal of the polymer. Although the polymer can be added over a longer period of time, it is important not to add the polymer over too short a period because the polymer could then melt and coalesce when contacted by the hot acid treated asphalt. This would slow dispersal of the polymer in the asphalt. Once polymer addition is complete, the acid treated polymer modified asphalt is mixed for an additional 0.5 to 1.5 hours or more. 
     The asphalt may be mixed or blended with the acid and polymer in any number of ways that can readily be selected by one skilled in the art. Suitable means include external mixers, roll mills, internal mixers, Banbury mixers, screw extruders, augers, and the like. Normally, the mixing or blending during acid and polymer addition will be at ambient pressure. 
     An oxygen-containing gas (such as air) may be added to the asphalt before or during acid and polymer addition if desired. However, in a preferred embodiment of this invention, the gas is not added before or during either step because it would tend to produce asphaltenes, which would have a detrimental effect on the storage stability of the final product. 
     The acid treated polymer modified asphalt thus formed may be employed in essentially any application requiring asphalt-based products with superior storage stability. Examples of such applications include adhesives, coatings, fabricated products, road and roofing applications, sealants, sound and vibration dampening products, water proofing membranes and the like. However, the final product is particularly well suited for use as a paving binder, particularly a binder in the load bearing course as well as the top or surface course of hot mix pavement structures. 
     The present invention will be further understood by reference to the following Examples which are not intended to restrict the scope of the claims appended hereto. In the Examples, the storage stability of the acid treated polymer modified asphalts tested was measured by placing a 200 gram sample in a copper tube (10 inches high and 1 inch in diameter) and heating it to 160° C. for 5 days. Then the sample was removed from the tube and divided into top and bottom fractions. The viscosity of each fraction was measured at 135° C. and then used to calculate the ratio of the top to the bottom viscosity. A ratio of 1.0 is considered as optimum storage stability, with ratios above or below 1.0 representing mixtures that are increasingly less storage stable. 
    
    
     EXAMPLE 1 
     Addition of Phosphoric Acid and Ethylene - Vinyl Acetate to Asphalt 
     Tests were performed on several samples of a 300/400 penetration straight-run asphalt obtained from vacuum distillation. Phosphoric acid (85 wt.%) and ethylene-vinyl acetate (EVA) polymer, each alone or in combination, were added to the samples. The temperature of the samples ranged between 190° and 200° C. at all times during the tests. The order and conditions of acid and polymer addition were varied as follows: 
     When acid addition preceded polymer addition, the acid was added to the asphalt over approximately a twenty minute period followed by reaction with the asphalt for about an additional thirty minutes. Polymer was then added over approximately a two to three minute period and mixed with the acid modified asphalt for from about one to about two hours. 
     When polymer addition preceded acid addition, the polymer was added to the asphalt over from about two to about three minutes and the mixture mixed for from about one to about two hours. Acid was then added over approximately a twenty minute period followed by reaction with the polymer modified asphalt for about an additional thirty minutes. 
     When the acid and polymer are added together, both were added over about a five minute period and then reacted with the asphalt for an additional hour and a half. 
     The asphalt was stirred during acid and polymer addition. The properties of the samples tested were determined and are shown in Table 1. 
     
                                           TABLE 1__________________________________________________________________________         Sample No.         1     2      3       4         Unmodified               Acid Added                      Polymer Added                              Acid &amp; Polymer         Asphalt               First  First   Added Together__________________________________________________________________________Feedstock InspectionsPolymer             EVAwt. %         0     5.0melt index, g/10 mins         --    10vinyl acetate, wt. %         --    12Asphalt, wt. %         100   94.5Penetration at 25° C.,         318   318    318     304mm/10H.sub.3 PO.sub.4 (85%), wt. %         0     0.5Product InspectionsSoftening Point, °C.         31    53     52      46Penetration at 25° C., mm/10         318   95     108     123Viscosity at 60° C., Pa · S         34.4  373    381     166at 135° C., cSt         171   1111   862     619Storage Stability         1.0   1.3    2.2     4.2__________________________________________________________________________ 
    
     The data in Table 1 show that the mineral acid must be reacted with the asphalt prior to addition of the polymer (Sample No. 2) to obtain the most storage stable product. If the acid is added after or with the polymer (Sample Nos. 3 and 4), the product is less storage stable. 
     EXAMPLE 2 
     Addition of Phosphoric Acid and Styrene-Butadiene-Styrene to Asphalt 
     Example 1 was repeated using styrene-butadiene-styrene as the polymer except that when the acid and polymer were added together, both were added over about a twenty minute period followed by reaction with the asphalt for about an additional two hours. The properties of the samples tested were determined and are summarized in Table 2. 
     
                                           TABLE 2__________________________________________________________________________         Sample No.         1     2      3       4         Unmodified               Acid Added                      Polymer Added                              Acid &amp; Polymer         Asphalt               First  First   Added Together__________________________________________________________________________Feedstock InspectionsPolymer             SBSwt. %         0     5.0    5.0     5.0molecular weight         --    300 × 10.sup.6wt % styrene  --    30wt % butadiene         --    70Asphalt, wt. %         100   93.2Penetration at 25° C.,         318   302    302     304mm/10H.sub.3 PO.sub.4 (85%), wt. %         0     1.8Product InspectionsSoftening Point, °C.         31    77     75      79Penetration at 25° C., mm/10         318   59     68      64Viscosity at 135° C., cSt         171   8640   3917    6317Storage Stability         1.0   1.2    3.6     2.3__________________________________________________________________________ 
    
     The data in Table 2 confirm that the storage stability of acid stabilized polymer modified asphalts can be further enhanced if the acid is added before the polymer. 
     EXAMPLE 3 
     Addition of Hydrochloric Acid or its and Ethylene-Vinyl Acetate to Asphalt 
     Using the procedure of Example 1, tests were performed on samples of a 150/200 straight-run asphalt. In one sample, only polymer was added. In two other samples, HCl (or Chlorez 760, a chlorinated wax available from Dover Chemical Corp.) was added before addition of ethylene-vinyl acetate. The properties of the samples tested were determined and are shown in Table 3. 
     
                                           TABLE 3__________________________________________________________________________         Sample No.         1     2    3     4         Unmodified               Polymer                    HCl Added                          Chlorez 760         Asphalt               No Acid                    First Added First__________________________________________________________________________Feedstock InspectionsPolymer             EVAwt. %         0     5.0melt index, g/10 mins         --    10vinyl acetate, wt. %         --    12Asphalt, wt. %         100   95.0 91.2  93.76Penetration at 25° C., mm/10         165   180  169   1696N HCl, wt. % 0     0    3.8   0Chlorez 760, wt. %         0     0    0     1.24HCl Equivalent, wt. %         0     0    0.91  0.92Product InspectionsSoftening Point, °C.         38    55   61    61Penetration at 25° C., mm/10         165   79   57    44Viscosity at 60° C., Pa · S         79.5  537  1848  1951at 135° C., cSt         254   896  1993  2066Storage Stability         1.0   2.4  1.1   0.8__________________________________________________________________________ 
    
     The results in Table 3 show that adding hydrochloric acid or compounds that form hydrochloric acid (e.g., Chlorez 760) to the asphalt before the polymer produces a product having enhanced storage stability relative to that obtained if no acid were added. 
     EXAMPLE 4 
     Addition of Hydrochloric Acid or its Precursors and Linear Low Density Polyethylene to Asphalt 
     Using the procedure of Example 1, linear low density polyethylene, alone or after hydrochloric acid or Chlorez 760, was added to samples of a 100/200 penetration straight-run asphalt. The properties of the samples tested were determined and are shown in Table 4. 
     
                       TABLE 4______________________________________       Sample No.       1      2          3       Polymer              HCl        Chlorez 760       No Acid              Added First                         Added First______________________________________Feedstock InspectionsPolymer       Linear Low Density Polyethylenewt. %         5melt index, g/10 mins         20density, g/cm.sup.3         0.924Asphalt, wt. %         95       93.76      88.2Penetration at 25° C.,         160      158        168mm/106N HCl, wt. % 0        0          6.8Chlorez 760, wt. %         0        1.24       0HCl Equivalent, wt. %         0        0.92       1.64Product InspectionsSoftening Point, °C.         49       57         61Penetration at 25° C.,         97       55         43mm/10Viscosity at 60° C.,         3338     2207       3779Pa · Sat 135° C., cSt         786      1989       2651Storage Stability         (1)      2.3        3.1______________________________________ (1) Viscosity of top phase too high to measure. 
    
     The results in Table 4 show that the addition of hydrochloric acid or Chlorez 760 (which produces HCl at the blending conditions) to the asphalt before polyethylene addition forms a product having enhanced storage stability relative to that obtained if no acid were added. 
     EXAMPLE 5 
     Addition of Hydrochloric Acid Precursor and Ethylene-Vinyl Acetate to Asphalt 
     Using the procedure of Example 1, Chlorez 760 and a different grade of ethylene-vinyl acetate were added to samples of a 100/200 penetration straight-run asphalt, the Chlorez 760 being added before the polymer. The properties of the samples tested were then determined and the results shown in Table 5. 
     
                       TABLE 5______________________________________            Sample No.            1      2            Polymer                   Chlorez 760            No Acid                   Added First______________________________________Feedstock InspectionsPolymer            EVA      EVAwt. %              5        5melt index, g/10 mins.              3        3vinyl acetate, wt. %              9        9Asphalt, wt. %     95       93.76Penetration at 25° C., mm/10              190      168Chlorez 760, wt. % 0        1.24HCl Equivalent, wt. %              0        0.92Product InspectionsSoftening Point, °C.              47       61Penetration at 25° C., mm/10              99       60Viscosity at 60° C., Pa · S              (1)      3511at 135° C., cSt              997      2335Storage Stability  4.9      1.4______________________________________ (1) Too high to measure. 
    
     The results in Table 5 show that an asphalt modified with other grades of EVA also has improved storage stability provided the asphalt has first been reacted with a mineral acid (HCl from degradation of the chlorinated wax at the blending temperature). 
     EXAMPLE 6 
     Addition of Hydrochloric Acid or its Precursors and Ethylene-Vinyl Acetate to Asphalt 
     Using the procedure of Example 1, hydrochloric acid (or Chlorez 760) and the ethylene-vinyl acetate of Example 1 were added to samples of a 100/200 penetration straight-run asphalt, with the acid (or Chlorez 760) being added first. The properties of the samples tested were then determined and the results shown in Table 6. 
     
                                           TABLE 6__________________________________________________________________________         Sample No.         1      2      3      4      5         Chlorez 760                HCl    Chlorez 760                              HCl    Chlorez 760         Added First                Added First                       Added First                              Added First                                     Added First__________________________________________________________________________Feedstock InspectionsPolymer       EVAwt. %         5melt index, g/10 mins.         10vinyl acetate, wt. %         12Asphalt, wt. %         94.8   94.0   94.5   91.2   93.76Penetration at 25° C.,         168mm/10Chlorez 760 wt. %         0.2    0      0.5    0      1.246N HCl, wt. % 0      1.0    0      3.8    0HCl Equivalent, wt. %         0.15   0.24   0.37   0.91   0.92Product InspectionsSoftening Point, °C.         54     55     57     61     61Penetration at 25° C., mm/10         66     63     60     57     44Viscosity at 60° C., Pa · S         698    794    1090   1848   1951at 135° C., cSt         1321   1464   1589   1993   2066Storage Stability         2.0    1.8    1.7    1.1    0.8__________________________________________________________________________ 
    
     The results in Table 6 show that as the percent of acid reacted with the asphalt is increased (on an equivalent HCl basis), the storage stability is improved. 
     EXAMPLE 7 
     Effect of Polymer Concentration on Storage Stability 
     Example 1 was repeated at different concentrations of phosphoric acid and ethylene-vinyl acetate in which the acid was added to the asphalt before the polymer. The results obtained are shown in Table 7. 
     
                                           TABLE 7__________________________________________________________________________         Sample No.         1   2   3     4     5   6__________________________________________________________________________Feedstock InspectionsPolymer       EVAwt. %         0.5 0.5 1.0   1.0   2.0 2.0melt index, g/10 mins         10vinyl acetate, wt. %         12Asphalt, wt. %         99.5             99  99    98.5  98  97.5Penetration at 25° C.,         309mm/10H.sub.3 PO.sub.4 (85%), wt. %         --  0.5 --    0.5   --  0.5Product InspectionsSoftening Point, °C.         34  40  33    38    38  48Penetration at 25° C., mm/10         288 188 271   182   216 115Viscosity at 60° C., Pa · S         40  82  44    91    74  209at 135° C., cSt         195 294 220   324   321 648Storage Stability         1.0 1.0 1.2 (1)                       1.2 (1)                             1.9 1.2__________________________________________________________________________ (1) An average of three measurements. 
    
     The data in Table 7 show that the storage stability of a polymer modified asphalt is not enhanced by acid addition at polymer concentrations of 1.0 wt.% or less. The data also show that at polymer concentrations greater than 1.0 wt.%, acid addition prior to polymer addition enhances the storage stability of polymer modified asphalts.