US3395110A - Asphalt compositions - Google Patents

Description

Unite ABSTRACT OF THE DISCLOSURE An improved asphalt composition comprising 1 to 20 weight percent atactic propylene-ethylene copolymer containing 1 to 30 Weight percent ethylene and having a molecular weight in the range of 10,000 to 40,000 and 80 to 99 weight percent asphalt.

This invention relates to improved asphalt compositions and particularly to paving asphalt containing a small but effective amount of amorphous low molecular weight propylene-ethylene copolymer. Paving grade asphalt is made from residuum stocks originating with such crudes as Mid- Continent, Wyoming, West Texas, Mexican, Middle East and Venezuelan. At the present time, the majority of asphalt crudes are treated by either of two processes, i.e., straight vacuum reduction and vacuum reduction followed by air blowing to produce suitable residuum. The method used is dependent on the source and nature of the crude. For example, most Venezuelan crudes are treated by vacuum distillation alone whereas Middle East crudes generally require vacuum distillation followed by an air blowing treatment.

State and federal governments have derived paving asphalt specifications which must be met where the material is to be used in public road building programs. The requirements vary in the different jurisdictions but all require a certain specification to be met for penetration. In the broadest sense, paving asphalt may have a penetration range of 40 to 300 but the great majority of asphalt paving put down has a penetration of 70 to 120 at 77 F. Over 40% of the asphalt used in the Middle Atlantic States is 85/100 penetration grade. This means that the penetration at 77 F. must fall Within the range of 85 to 100.

The penetration test determines the hardness or softness of the material. Degrees penetration means the distance (in of a centimeter) a standard needle will penetrate into the asphalt when loaded to 100 grams for five seconds at 77 F. Penetration is also measured at 39.2 F. with a 200 gram weight and a time of 60 seconds. These tests are made according to ASTM D561 procedure. Another specification that ordinarily must be met by paving grade asphalt compositions is penetration ratio. Penetration ratio is Pen. 392 F.

Pen. 77.0 F.

and is multiplied by 100 to express the value as a percentage. Normally most states and federal specifications require paving grade asphalt to have a penetration ratio of at least 30 percent.

It is necessary to exercise very careful control in the reduction of crude to a certain percentage residual bottoms and in air blowing to meet these paving grade specifications.

A number of polymers and copolymers have been added to asphalts to improve such properties as softening point, penetration, penetration ratio, and ductility. The success of these materials has been limited. The chief reasons for lack of success are high cost, poor dispersibility States Patent 3,395,110 Patented July 30, 1968 employing conventional blending equipment, and poor low temperature performance.

It has recently been discovered that by the addition of certain olefin homopolymers asphalt can be produced which will meet the above penetration requirements without subjecting the asphalt to the costly air blowing treatment. However, all of these improved asphalt compositions suffer from the inherent defect of poor low temperature flexibility. It has been found that at sub-freezing temperatures, particularly in moisture-rich areas, most of the presently used asphalt compositions become brittle and are subject to cracking and crumbling, consequently permitting only a limited period of use before repairs or replacement is necessary.

It is an object of this invention to provide an improved asphalt composition having superior low temperature flexibility.

It is a particular object of this invention to provide an improved paving grade asphalt composition which meets all the requirements of paving grade asphalts while exhibiting superior sub-freezing wear-lift qualities due to its improved low temperature flexibility.

I have found that certain amorphous copolymers of propylene provide the qualities lacking in other polyolefinasphalt compositions. These copolymers are the soluble by-products produced in the preparation of propylene ethylene copolymers.

It is known that some of the deficiencies of isotactic polypropylene, which is highly crystalline, can be overcome by inserting ethylene segments of limited size and quantity in the propylene polymer chain. During the preparation of the crystalline propylene high molecular weight polymers and copolymers a certain amount of substantially amorphous low molecular weight material is produced. This material is normally soluble in the inert hydrocarbon polymerization medium and is normally considered an undesirable by-product of the process. The polymerization process from which the low molecular weight amorphous propylene-ethylene copolymer by-product useful in the present invention is obtained is as follows:

A highly crystalline propylene-ethylene copolymer is prepared by contacting under temperatures, pressures, polymerizing conditions, and in the presence of coordinate complex catalyst systems such as those disclosed in British Patents 889,230 and 889,659, an olefin mixture consisting of a major amount of propylene (i.e., -99 wt. percent) and a minor amount of ethylene (i.e., 1-20 wt. percent). Polymers having highly crystalline structure by X-ray analysis can be prepared in the above-described manner. The polymerization product generally contains some amount of predominately low molecular weight amorphous or atactic polymers which are more soluble in hydrocarbon solvents than the crystalline polymers and hence can be separated therefrom, for example, by extraction with pentane at room temperature. This hydrocarbon soluble by-product of the above disclosed copolymer process which usually comprises 2 to 30% of the total polymer product and normally has an average molecular weight in the range of 10,000 to 40,000 as measured by intrinsic viscosity is recovered from the insoluble product by various means. In one known process the total polymerization product and catalyst in the hydrocarbon polymerization medium is contacted with a solvent consisting of methanol and water to kill the catalyst. The catalyst is then removed in solution with the methanol and water'leaving behind a hydrocarbon slurry of soluble and insoluble polymer product. The soluble copolymer and hydrocarbon are removed from the insoluble copolymer product by filtering or centrifuging. The soluble copolymer is recovered from the hydrocarbon solvent which is subsequently recycled. The

material which remains is the predominately low molecular weight (10,000 to 40,000) substantially amorphous propylene-ethylene copolymer employed in the composition of this invention. For purposes of this invention this hydrocarbon soluble propylene-ethylene copolymer is hereinafter referred to as atactic propylene-ethylene copolymer or as the heptane soluble fraction of the propylene-ethylene copolymer.

The atactic propylene-ethylene copolymer used in the present invention is predominately propylene having short segments of ethylene randomly dispersed within the propylene polymer chain. The copolymer is normally soluble in heptane and is predominately amorphous although it is synthesized using a stereospecific catalyst system.

Because of the fact that lower molecular weight fractions of propylene-ethylene copolymers have higher concentrations of ethylene than the higher molecular weight fractions of the same copolymer, the heptane soluble fraction can contain as much as 30 weight percent ethylene even though the weight percent ethylene in the monomer feed during polymerization is much lower. For present purposes the atactic copolymer should contain from 1 to 30 weight percent ethylene.

The copolymer product of the present invention is termed propylene-ethylene copolymer to denote the fact that the polymer is predominately polypropylene with short segments of ethylene randomly dispersed in the propylene polymer chain. The copolymers of the present invention may be readily distinguished from ethylenepropylene block copolymers which are characterized as high molecular weight copolymers synthesized by nonstereospecific catalyst systems which copolymers have high concentrations of long ethylene sequences in the copolymer chain. These block ethylene-propylene copolymers, because of their distinct diflerences in molecular structure, weight and high ethylene concentration, are readily distinguished from the copolymers of the present invention.

The coordinate complex catalyst referred to in the copolymer polymerization above can be a metal subhalide of a Group IVa, Va, or VIa (of the periodic table as set out on page 411 of the Partingtons Textbook of Inorganic Chemistry, MacMillan & Co., Ltd., London, 1937) metal in combination with a polymerization activator. By the term activator is intended a co-catalyst as shown in Table XII-2 and Table XII-4 in Linear and Stereo Regular Addition Polymers, by Norman G. Gaylord and Herman F. Mark, copyrighted in 1959 by Interscience Publishers, Inc.

In the present invention the amount of atactic propylene-ethylene copolymer mixed with the asphalt is small, preferably in the range of from about 1 to by Weight. Any suitable mixing method can be used which results in good distribution of the polymer in the asphalt.

A coordinated catalyst system comprising titanium trichloride and diethyl aluminum chloride was used in the synthesis of the atactic propylene-ethylene copolymer which forms a part of the specific embodiments of the present invention disclosed below. For use in the present invention, the heptane soluble fraction of the propyleneethylene copolymer obtained by contacting under anhydrous conditions a monomer mixture of 3.5 weight percent ethylene and 96.5 weight percent propylene with the above mentioned coordinate complex catalyst dispersed in heptane at a temperature of 150 F. and at a pressure of 65 p.s.i.g. is recovered by previously discussed methods.

This atactic propylene-ethylene copolymer is typically characterized as being white and translucent having a specific gravity of 0.86 (ASTM D162259T), a ring and ball softening point at 120 C. (ASTM D28*58T), a brittle point of C. (ASTM D-146-58T), and molecular weight of about 25,000 as determined by intrinsic viscosity measurements.

The above described propylene-ethylene copolymer is blended with Lagomedio asphalt bottoms in the concentration range of 2 to 10 weight percent copolymer to form a paving grade asphalt.

In Table I is demonstrated the improvements in penetration properties of Lagomedio asphalt that are achieved by addition of incremental amounts of atactic propyleneethylene copolymer.

As is readily apparent from the data of Table I, the most stringent penetration specifications of paving grade asphalt can be easily met by the practice of the present invention.

However, the most significant improvement realized by the paving asphalt compositions of the present invention lie in the superior low temperature flexing properties as demonstrated by the data presented in Table II. A paving asphalt composition having 10 weight percent atactic propylene-ethylene copolymer blended therein is shown to have superior low temperature flexing properties when compared with two presently known paving asphalt compositions.

A new asphalt composition having a flexural modulus at 20 F. in the range of 300-1500 p.s.i. has been discovered. This new composition comprises a blend of asphalt and substantially amorphous atactic propyleneethylene copolymer containing 1-30 weight percent polymerized ethylene and 99-70 weight percent polymerized propylene. The copolymer is obtained as the heptane soluble fraction of the stereospecific polymerization of a propylene-ethylene monomer mixture. The content of the copolymer in the asphalt-copolymer composition can be in the range of 1-20 weight percent of the blend.

This improved low temperature flexibility of the compositions of the present invention is totally unexpected in view of the results noted when the atactic homopolymer of propylene is blended with asphalt. As is clearly demonstrated by the results in Table II, the addition of atactic polypropylene to asphalt results in an asphalt composition having a higher resistance to flexing at 20 F. than unadulterated asphalt. Poor low temperature flexing properties render the atactic polypropylene, asphalt composition undesirable for many applications, particularly in cold climates. However, an asphalt containing atactic propylene-ethylene copolymer is found to have superior low temperature flexing properties over both unadulterated asphalt and an atactic polypropylene-asphalt composition.

Low temperature stiffness or lack of flexibility is a primary contributor to cracking and subsequent deterioration of roads, particularly in areas subject to colder climates. Thus it can be seen that the paving compositions of the present invention by their superior flexibility at low temperatures are more resistant to cracking and resulting deterioration of asphalt road surfaces than other presently used asphalt paving compositions. The asphalt paving compositions of the present invention by virtue of their superior flexibility properties inherently possess superior wear properties, particularly in colder climates.

The atactic propylene-ethylene copolymer can be used according to the present invention in conjunction with any crude asphaltic residium. The invention is particularly useful for those residuua which are diflicult to bring into paving grade specifications by conventional procedures.

The invention has been described primarily with references to asphalts for use in paving; however, the composition of the present invention may find equal utility where an asphalt having particular penetration characteristics is required. For example, the asphalt compositions of the present invention may be used in soil stabilization, protection of banks and canals by asphalt linings, pipe coating and coating of metals which are to be buried in soil, and moulded articles such as battery boxes and tiles.

Obvious modifications such as blending of the asphalt composition of the invention with mineral aggregates,

6 cement, sand, asbestos, vermiculite, fiber glass and the 5. A blend according to claim 3 having a flexural modlike are included in the scope of the invention. ulus at 20 F. in the range of 300 to 1500 p.s.i.

TABLE I 6. A method for improving low temperature properties of asphalt which comprises blending with said asphalt Lagornedio Bottoms, Weight Percent 100 98 94 92 90 Awctichpligpymggthylene copolymer, 6 8 10 5 from 1 to weight percent atactic propylene-ethylene eig t ercent 0 2 penetration 3 F dmm 24 33 34 35 34 copolyl'nier contan'llng to 30 welght Rel-cent ethylene llzenegragon t 1%, g n m. 1% polymerized therem, Said copolymer having been recovene a M ered from the stereospecific polymerization of a propylene- TABLE II ASTM D-28-58'l ASTM D790-61 Paving Composition Pen. at Pen. at Pen. Duct. Softening Point, 77 F. 39.2 F. Ratio at 77 F. Flexural Modulu F, psi. at 20 F.

100% Lagomedio Bottoms 106-110 131 24 18 100+ 1, 779 10 Wt. fiercent Atactic Polypropy ene 90 Wt. Percent Lagomedio 138 57 19 33 21 747 Bottoms 10 X5 liercegt Atlactic Propyleney ene opo ymer 90 Wt. Percent Lagomedio 142 62 34 54 58 689 Bottoms l l i ethylene monomer mix and having a molecular weight in 1. A composition comprising 1 to 20 weight percent th rang ilf1 fl atactic propylene-ethylene copolymer having 1 to 30 7. A method for improving penetration properties of weight percent ethylene therein and having a molecular asphalt which comprises blending with said asphalt from weight in the range of 10,000 to 40,000, and 80 to 99 l to 20 weight percent atactic propylene-ethylene copolyi h percent h lt, mer containing 1 to weight percent ethylene polymer- 2. As a new composition a blend of asphalt and atactic ized therein, said copolymer having been recovered from propylene-ethylene copolymer recovered from a stereothe stereospecific polymerization of a propylene-ethylene specific polymerization of a propylene-ethylene monomer 30 monomer mix.

mixture said propylene being in the range of 70-99 weight 8. A composition according to claim 1 having a flexpercent and said ethylene being in the range of 1 to 30 ural modulus at 20 F. in the range of 300 to 1500 psi.

weight percent of the polymerized copolymer product, 9. A composition according to claim 2 having a flexural said copolymer having a molecular weight in the range of modulus at 20 F. in the range of 300 to 1500 psi.

10,000 to 40,000 and said blend containing 1 to 20 weight 10. A method according to claim 9 wherein the impercent copolymer therein. provement in penetration properties comprises lowering 3. As a new composition, a blend of asphalt and subthe penetration value of the asphalt composition at 77 stantially amorphous atactic propylene-ethylene copoly- F. and raising the penetration value of the asphalt commer containing 1 to 30 weight percent polymerized ethylposition at 392 F.

ene and 99 to 70 weight percent propylene polymerized therein obtained as the heptane soluble fraction of the References fiited stereospecific polymerization off a propyltlene-ethglene UNITED STATES PA ENTS monomer mixture, the content 0 said copo ymer eing in the range of 1 to 20 weight percent of the blend and g g et figg ggg ggg a molecular Weght the range 3:154:508 10/1964 Clelland 260-28:5

4. A paving composition comprising 80 to 99% asphalt and 1 to 20% of a substantially amorphous atactic propylene-ethylene copolymer having 1 to 3 0 weight percent JULIUS FROME Primary Examiner. ethylene polymerized therem and having a molecular weight in the range of 10,000 to 40,000. H. S. KAPLAN, Assistant Examiner.