Unblown ethylene-vinyl acetate copolymer treated asphalt and its method of preparation

A method is provided for improving high temperature performance grade properties of unblown asphalt by i) heating an asphalt cement to 200.degree. F. to 500.degree. F. (93.degree. C. to 260.degree. C.), ii) adding 0.1 wt. % to 10 wt. % ethylene-vinyl acetate copolymer based on weight of said asphalt cement to the heated asphalt cement, iii) adding 0.05 wt. % to 1.0 wt. % phosphorus-containing acid, e.g., polyphosphoric acid, based on weight of said asphalt cement and iv) mixing the resulting blend, thereby providing an unblown asphalt composition of greater useful temperature index (UTI). The invention further relates to asphalt compositions thus made and paving compositions containing these asphalt compositions.

BACKGROUND OF THE INVENTION 
I Field of the Invention 
The invention relates to unblown polymer modified asphalt compositions that 
exhibit improved performance grade specifications for high temperature 
properties. The invention further relates to a method of improving 
ethylene-vinyl acetate copolymer efficiency in polymer-modified asphalts. 
II. Description of the Prior Art 
It is known that adding polymer to asphalt improves the high temperature 
performance grade (PG) of paving asphalt cements as defined under the test 
methods established by the Strategic Highway Research Program (SHRP). 
Commonly used polymers include ethylene-vinyl acetate (EVA) copolymers and 
styrene-butadiene-styrene triblock (SBS) copolymer. These polymers are 
blended into the asphalt using high shear mix conditions to ensure proper 
dispersion of the polymer. Of the polymers used, SBS polymers are 
preferred because of their compatibility with a large number of asphalts. 
In addition, they can be crosslinked using vulcanizing agents such as 
sulfur. 
Blending polymers with paving asphalts produces a change in the 
viscoelastic behavior of the asphalt. The change in viscoelastic 
properties is attributed to an increase in viscosity and elasticity and 
the formation of a network structure. The change in viscoelastic 
properties is related to the amount of polymer added, with network 
formation occurring above some finite polymer concentration. The amount of 
polymer needed can be reduced by adding a vulcanizing (crosslinking) agent 
such as sulfur. The crosslinking reaction allows the network structure to 
form at a lower polymer concentration. This improves polymer efficiency, 
reducing the amount of polymer needed to make a specific grade of asphalt 
cement. Unsaturated polymers such as SBS copolymers are easily 
crosslinked, but EVA copolymers which lack the requisite unsaturation are 
not. 
Crosslinking enhances the efficiency of the polymer so that a lower 
concentration can give the desired improvement in the SHRP high 
temperature performance grade. The crosslinking is believed to occur 
through the reaction of sulfur with residual double bonds of the butadiene 
portion of the polymer. Unfortunately, the unsaturation in the SBS 
copolymer makes it more susceptible to degradation by atmospheric oxygen. 
EVA copolymers do not contain residual unsaturation and are not so easily 
degraded; however, the lack of unsaturation makes it difficult to 
crosslink these polymers. 
U.S. Pat. No. 4,454,269 to Goodrich teaches the use of phosphoric acid and 
P.sub.2 O.sub.5 as a catalyst for air-blowing of asphalt/EVA copolymer 
blends. The purpose of the air blowing step is to improve the 
compatibility of the EVA copolymer. Simply blending the EVA copolymer into 
an airblown asphalt leads to incompatibility of the polymer. In contrast, 
the present invention relates to improving high temperature properties for 
unblown asphalts. 
SUMMARY OF THE INVENTION 
I. General Statement of the Invention 
In one aspect, the present invention relates to a method for improving high 
temperature performance grade properties of unblown asphalt which 
comprises i) heating an asphalt cement to 200.degree. F. to 500.degree. F. 
(93.degree. C. to 260.degree. C.), ii) adding 0.1 wt. % to 10 wt. % 
ethylene-vinyl acetate copolymer based on weight of said asphalt cement, 
iii) adding a useful temperature index (UTI) improving amount of 
phosphorus-containing acid, and iv) mixing the resulting blend, thereby 
providing an unblown asphalt having a greater useful temperature index 
(UTI) than a corresponding blend to which no phosphorus-containing acid is 
added. 
In another aspect, the invention relates to an unblown asphalt composition 
comprising a mixture containing a) at least 80 wt. % of an asphalt cement, 
b) 0.1 wt. % to 10 wt. % ethylene-vinyl acetate copolymer, and c) 
polyphosphoric acid added in an amount sufficient to improve useful 
temperature index (UTI) relative to a corresponding mixture free of said 
polyphosphoric acid. 
In still another aspect, the invention relates to a method for improving 
the effectiveness of ethylene-vinyl acetate copolymer modifier in unblown 
asphalt compositions containing a) at least 80 wt. % asphalt cement and b) 
0.1 wt. % to 10 wt. % ethylene-vinyl acetate copolymer by adding a useful 
temperature index (UTI) improving amount of polyphosphoric acid. 
In yet another aspect, the invention relates to a pavement composition 
comprising an aggregate or aggregate material and from 1.0 wt. % to 10.0 
wt. % of an unblown paving asphalt composition containing a) at least 80 
wt. % of a paving asphalt cement, b) 0.1 wt. % to 10 wt. % ethylene-vinyl 
acetate copolymer, and c) phosphorus-containing acid added in an amount 
sufficient to improve useful temperature index (UTI) relative to a 
corresponding mixture free of said phosphorus-containing acid. 
Although the mechanism of the present invention is not known, it can be 
postulated that the addition of phosphorus-containing acid, e.g., 
polyphosphoric acid, to an EVA-containing asphalt mixture causes an acid 
induced elimination of the acetate group, thereby creating unsaturated 
sites having potential for crosslinking reactions. Alternatively, the acid 
groups in the asphalt could transesterify, forming crosslinks within the 
asphalt. The present invention is of particular utility in applications 
where the presence of sulfur is to be avoided or minimized, inasmuch as 
the crosslinking associated with the present invention can occur in 
sulfur's absence. The use of sulfur has some major drawbacks. In 
particular, adding sulfur to asphalt produces hydrogen sulfide gas as a 
byproduct. Hydrogen sulfide is extremely poisonous and must be properly 
removed and treated. This requires the installation and maintenance of 
special equipment which increases capital and operating costs. 
The present invention can be used to prepare a wide variety of asphalt 
materials including asphalt pavement compositions, asphalt emulsions, 
modified asphalt emulsions, roofing asphalt compositions, coatings, 
sealants, adhesives, and sound deadeners. 
ASPHALT CEMENT (PETROLEUM BITUMENS) 
The asphalt composition of the present invention contains an unblown 
natural or synthetic asphalt cement component. Such asphalt cement 
component can have a viscosity of 100 to 5000 poise at 60.degree. C. 
(140.degree. F.), preferably 250 to 4000 poise, e.g., 2000 poise for AC20 
asphalt cement, and 500 poise for AC5 asphalt cement. The asphalt cement 
component is added in amounts sufficient to provide the resulting asphalt 
composition with the desired viscosity for the intended application, e.g., 
2000 poise at 60.degree. C. (140.degree. F.) for various applications, 
e.g., paving applications. For Performance Graded Applications, the 
asphalt compositions can have a G*/sin delta value in excess of 1.0 kPa at 
temperatures ranging from 46.degree. C. to 82.degree. C., preferably 
52.degree. C. to 76.degree. C. Generally, the asphalt compositions of the 
present invention contain at least 80 wt. %, preferably from 80 wt. % to 
98.9 wt. %, e.g., 90 wt. % to 95 wt. %, of such asphalt cement component. 
The asphalt cement component of reduced viscosity can be obtained from any 
suitable source, e.g., atmospheric distillation bottoms or vacuum tower 
bottoms. The asphalt used in the present invention can be a natural 
asphalt or a synthetic asphalt. 
Natural asphalt can be obtained from crude petroleum, bituminous schists, 
heavy oils, bituminous sands or coal. Natural asphalt can be, for example: 
a) the heaviest fraction obtained by direct distillation of crude 
petroleum at atmospheric or reduced pressure; b) the heavy phase obtained 
by solvent-deasphalting a heavy fraction as obtained under a); c) the 
product of oxidation, in the presence or absence of a catalyst, of a heavy 
fraction as obtained under a) or of a heavy phase as obtained under b); d) 
the product of oxidation, in the presence or absence of a catalyst, of a 
blend of a heavy fraction as obtained under a) or of a heavy phase as 
obtained under b) and a distillate, or an aromatic extract obtained in the 
dearomatization of lubricating oils, or a deasphalting pitch; e) a blend 
of an oxidized product obtained as under c) and d) or of a hard phase, and 
a distillate, or an aromatic extract obtained in the dearomatization of 
lubricating oils, or a deasphalting pitch, or a heavy fraction as obtained 
under a) or a heavy phase as obtained under b); f) a visbroken base, alone 
or in admixture with one or more of the above said products; g) one of the 
products as obtained under a) to f) in admixture with a distillate, or an 
aromatic extract obtained in the dearomatization of lubricating oils, or a 
deasphalting pitch, or a heavy aromatic fraction (catalytic slurry) 
obtained from a catalytic cracking process. 
Suitable synthetic asphalts have properties similar to those of the 
above-described natural asphalts, for example, clear synthetic binders 
that can be colored by addition of pigments. Such asphalts can consist, 
for example, of petroleum resins or indeno-coumarone resins blended with 
aromatic and/or paraffinic hydrocarbons. Such petroleum resins can be 
prepared by polymerization of unsaturated hydrocarbons present in 
unsaturated petroleum fractions, such as the fractions obtained by thermal 
or steam cracking or by pyrolysis. The indene-coumarone resins are 
generally obtained from coal tars. 
As used herein, the terms "asphalt composition," "asphalt cement" or 
"asphalt binder" are understood to refer to any of a variety of organic 
materials, solid or semi-solid at room temperature, which gradually 
liquefy when heated, and in which the predominate constituents are 
naturally occurring bitumens, e.g., Trinidad Lake, or residues commonly 
obtained in petroleum, synthetic petroleum, or shale oil refining, or from 
coal tar or the like. A "paving asphalt composition," "paving asphalt 
cement," or "paving asphalt binder," accordingly is an asphalt composition 
or asphalt cement having characteristics which dispose the composition to 
use as a paving material, as contrasted, for example, with an asphalt 
composition suited for use as a roofing material. "Roofing asphalts," for 
example, usually have a higher softening point, and are thus more 
resistant to flow from heat on roofs. Paving asphalt mixtures may be 
formed and applied in a variety of ways, as well understood by those 
skilled in the art. For example, the paving asphalt composition and the 
aggregate can be mixed and applied at elevated temperatures at the fluid 
state of the paving asphalt composition to form the pavement or road 
surface. 
POLYMER ADDITIVES 
The polymers finding particular use in this application are 
ethylene-vinyl-acetate (EVA) copolymers. The preferred copolymer is 
tradenamed Polybilt 152.TM. and is available from Exxon Chemical Company, 
Houston, Tex. Another suitable EVA copolymer is trade named ELVAX.RTM.40P 
and manufactured by the E. I. DuPont de Nemours Corporation of Wilmington, 
Del. EVA describes a family of thermoplastic polymers ordinarily ranging 
from 5 to 50 percent by weight of vinyl acetate incorporated into an 
ethylene chain. The EVA ELVAX.RTM.40P contains approximately 39-42 weight 
percent of vinyl acetate and has a melt index of 48-66 g/10 minutes g/10 
minutes (ASTM D1238). It is a medium low viscosity resin showing excellent 
solubility in many organic solvents and is ordinarily used to improve 
flexibility and adhesion of lacquers and inks and in pressure-sensitive 
hot melt or solvent-applied adhesives. The preferred amount of EVA 
introduced into the asphalt ranges from about 0.1 wt. % to 10 wt. %, 
preferably 2 wt. % to 5 wt. %, for example 3 wt. % based on asphalt cement 
content. 
Optionally, compositions of the present invention may contain other 
polymers in addition to ethylene-vinyl acetate copolymer. Such polymers 
include ethylene butylacrylate copolymer, ethylene butylacrylate glycidyl 
methacrylate copolymer such as those known as ELVALOY.RTM. AM, available 
from E. I. DuPont. Other suitable polymers include, styrene-butadiene (SB) 
diblocks, styrene-isoprene-styrene (SIS) triblocks, and 
styrene-butadienestyrene (SBS) triblocks, such as those taught in U.S. 
Pat. No. 3,238,173 to Bailey (assigned Shell); U.S. Pat. No. 4,145,322 to 
Maldonado et al. (Elf) (block copolymer with an average molecular weight 
between 30,000 and 300,000 having the theoretical formula S.sub.x -B.sub.y 
in which S corresponds to styrene structure groups, and B corresponds to 
conjugated diene structure groups and x and y are integers); U.S. Pat. No. 
4,154,710 to Maldonado et al. (Elf) (thermoplastic elastomer having a 
molecular weight between 100,000 and 2,000,000, e.g. polyisobutenes, 
styrene-butadiene rubber (SBR), polychloroprene, isobutene-isoprene 
copolymers, halogenated or non-halogenated, ethylene-propylene-diene 
terpolymers (EPDM), ethylene-propylene copolymers (EPR), 
ethylene-cyclopentadiene copolymers, polybutadienes, and polynorbornenes); 
U.S. Pat. No. 4,162,999 to Bohemen (British Petroleum); U.S. Pat. No. 
4,237,052 to Fitoussi et al. (Elf) (dihalopolybutadiene polymer and 
tri-block copolymer with a linear or cyclic structure of a molecular 
weight within the range of 100,000 and 300,000); U.S. Pat. No. 4,242,246 
to Maldonado (Elf) (polystyrene-polydiene disequenced, multisequenced, or 
statistical copolymer); U.S. Pat. No. 4,330,449 to Maldonado et al. (Elf) 
(polyblock copolymer of a styrene-carboxylated conjugated diene having a 
mean molecular weight of 30,000 to 300,000); U.S. Pat. No. 4,554,313 to 
Hagenbach (Elf) (styrene-conjugated diene copolymer); U.S. Pat. No. 
4,567,222 to Hagenbach (Elf); U.S. Pat. No. 4,585,816 to Vitkuske (Dow 
Chemical); U.S. Pat. No. 5,023,282 to Neubert (GenCorp); U.S. Pat. No. 
5,039,342 to Jelling (National Patent Development); U.S. Pat. No. 
5,118,733 to Gelles (Shell); and U.S. Pat. No. 5,120,777 to Chaverot 
(Elf); (diene/vinyl aromatic block copolymers, e.g. methylstyrene, 
tertiary butyl styrene, etc.). It is especially preferred to add 
styrene-butadiene (SB) diblock copolymers or styrene-butadiene-styrene 
(SBS) triblock copolymers to the blended asphalt products of the present 
invention. The preferred amount of the additional polymer introduced into 
the asphalt ranges from about 0.5 wt. % to 10 wt. %, preferably 2 wt. % to 
5 wt. %, for example, 3 wt. % to 4 wt. % based on asphalt cement content. 
PHOSPHORUS-CONTAINING ACIDS 
Phosphorus-containing acids suited to use in the present invention include 
P.sub.2 O.sub.3, P.sub.2 O.sub.5, P.sub.4 O.sub.6, P.sub.4 O.sub.7, 
phosphorous acid, phosphoric acid, and polyphosphoric acid (phospholeum). 
The term "phosphorus-containing acids" includes precursors of phosphorus 
acids, e.g., oxides of phosphorus which can form acids by reacting with 
water derived from various sources, e.g., asphalt dehydration reactions. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As a result of the 1987 Intermodal Surface Transportation Efficiency Act 
(ISTEA), a $150 million research study was commissioned in which $50 
million was spent towards asphalt research for improving asphalt 
pavements. As a product of that research which was concluded in 1992, the 
Strategic Highway Research Program (SHRP) produced what is now known as 
the Superpave.RTM. Performance Graded Binder Specification in which 
asphaltic binders are graded or characterized according to their relative 
performance in resistance to rutting, shoving or deformation at high 
temperatures, fatigue at intermediate temperatures, and thermal cracking 
resistance at low temperatures. Asphalts which normally would be graded 
either under the penetration or viscosity specifications will now be 
graded as PG or Performance Graded binders. As such, their designation 
will be representative of their resistance at both high and low 
temperature, indicating their useful temperature range as a PG AA-BB where 
AA=high temperature resistance in degrees Celsius and BB is low 
temperature cracking resistance in minus degrees Celsius, i.e., PG 64-22 
would prevent rutting up to 64.degree. C. (147.degree. F.) and low 
temperature cracking to a minus 22.degree. C. (-7.6.degree. F.). Useful 
temperature index (UTI) is the difference between AA and BB such that a PG 
64-22 material would have a UTI of 64-(-22), i.e., 86. 
Areas of high loading or slow or standing traffic as well as areas where 
temperature extremes can be experienced in excess of 86.degree. C. 
(155.degree. F.) between high and low temperature levels will require the 
use of modifiers to obtain the increased useful temperature range. As a 
result, it has been common to add or start with softer asphalts to reach 
low temperature properties while adding modifiers such as polymers to 
achieve high temperature rutting resistance. The present invention 
provides a method for providing improved paving asphalt compositions by 
providing asphalts of increased useful temperature index (UTI) as a result 
of improving polymer efficiency. 
In the process of the invention asphalt cements, e.g., petroleum bitumens, 
are heated to a temperature in the range of 200.degree. F. to 500.degree. 
F. (93.degree. C. to 260.degree. C.), preferably 300.degree. F. to 
400.degree. F. (149.degree. C. to 204.degree. C.). In those embodiments 
employing the addition of other polymers in addition to ethylene-vinyl 
acetate copolymer, the other polymers are preferably added and dispersed 
in the asphalt prior to the addition of ethylene-vinyl acetate copolymer. 
The ethylene-vinyl acetate copolymer added in amounts ranging from 0.1 wt. 
% to 10 wt. % of the asphalt cement (petroleum bitumen) component is 
dispersed in the asphalt using a high or low shear mixer. Mixing time is 
adjusted to ensure complete dispersion of the polymer. The mixer speed is 
reduced and the polyphosphoric acid (0.05 to 1.0 parts based on 100 parts 
of asphalt) is added. Mixing may be continued for 30 to 60 minutes. The 
asphalt is then kept at 300.degree. F. to 400.degree. F. (149.degree. C. 
to 204.degree. C.) for an additional 4 to 240 hours with or without 
stirring. Finally, the polymer modified asphalt is graded using the test 
procedures outlined in SHRP and adopted by American Association of State 
Highway and Transportation Officials, AASHTO, in their MP-1 Standard Test 
Method, "Superpave.RTM./Performance Graded Asphalt Binder Specification 
and Testing," Superpave.RTM. Series No. 1 (SP-1), available from Asphalt 
Institute, Lexington, Ky. (1997). The specifications are also set out in 
U.S. Pat. No. 5,601,697 to Miller. 
COMATIVE EXAMPLE 1 
A sample of AC-20 was SHRP graded. The sample had an actual SHRP grade of 
65.2-25.3 (UTI=90.5) and was rated as a PG64-22.

EXAMPLE 1 
A mixture of the AC-20 of Comparative Example 1 and 3 wt. % Polybilt 
152.TM. (EVA copolymer) available from Exxon Corporation was mixed at 
330.degree. F. (166.degree. C.) for 30 minutes using a Ross high speed 
mixer available from Charles Ross & Son Co., Hauppage, N.Y., operating at 
3000 rpm. The speed was reduced to 1000 rpm and 0.20 parts per hundred 
parts asphalt (pha) polyphosphoric acid obtained from Aldrich were added. 
Stirring was maintained for thirty minutes. Next, the mixture was placed 
in an oven set at 330.degree. F. (166.degree. C.) for 24 hours without 
stirring. This sample had an actual SHRP grade of 75.5-24.6 (UTI=100.1) 
and was rated as a PG70-22. 
COMATIVE EXAMPLE 2 
A sample of AC-20 was SHRP graded. The sample had an actual SHRP grade of 
64.5-23.5 (UTI=88.0) and was rated as a PG64-22. 
COMATIVE EXAMPLE 2A 
A mixture of the AC-20 of Comparative Example 2 and 3 wt. % Polybilt 
152.TM. (EVA copolymer) available from Exxon Corporation was mixed at 
330.degree. F. (166.degree. C.) for 30 minutes using a Ross high speed 
mixer operating at 3000 rpm. The speed was reduced to 1000 rpm and 
stirring continued for thirty minutes. The mixture was placed in an oven 
set at 330.degree. F. (166.degree. C.) for 24 hours without stirring. This 
sample had an actual SHRP grade of 75.8-27.3 (UTI=103.1) and was rated as 
a PG70-22. 
EXAMPLE 2 
A mixture of the AC-20 of Comparative Example 2 and 3 wt. % Polybilt 
152.TM. (EVA copolymer) available from Exxon Corporation was mixed at 
330.degree. F. (166.degree. C.) for 30 minutes using a Ross high speed 
mixer operating at 3000 rpm. The speed was reduced to 1000 rpm and 0.20 
pha (parts per hundred parts asphalt) polyphosphoric acid obtained from 
Aldrich were added. Stirring was maintained for thirty minutes. Next, the 
mixture was placed in an oven set at 330.degree. F. (166.degree. C.) for 
24 hours without stirring. This sample had an actual SHRP grade of 
79.2-26.1 (UTI=105.3) and was rated as a PG76-22. 
Comparing Example 1 and 2 with Comparative Examples 1 and 2 shows that the 
process of this invention significantly improves the UTI of the asphalt 
cements and raises the high temperature performance grade by one or two 
grades. Furthermore, the results of Example 2 and Comparative Example 2A 
show that the process of the present invention improves the efficiency of 
the EVA copolymer allowing 3 wt. % EVA to give the higher PG76-22 grade of 
asphalt. Asphalt paving compositions of the present invention exhibit a 
distinct improvement in useful temperature index (UTI) as defined by the 
Superpave.RTM. Performance Graded (PG) Asphalt Binder Specifications, 
AASHTO MP 1. 
MODIFICATIONS 
Specific compositions, methods, or embodiments discussed are intended to be 
only illustrative of the invention disclosed by this specification. 
Variations on these compositions, methods, or embodiments are readily 
apparent to a person of skill in the art based upon the teachings of this 
specification and are therefore intended to be included as part of the 
inventions disclosed herein. 
Reference to documents made in the specification is intended to result in 
such patents or literature being expressly incorporated herein by 
reference including any patents or other literature references cited 
within such documents.