Adhesion Enhancers for Anionic Bituminous Emulsions

This invention relates to rapid set, medium set, and slow set anionic emulsions prepared from straight bitumen or bitumen modified by the incorporation of polymers such as styrene butadiene rubbers (SBR), styrene block copolymers (SBS), ethylene vinyl acetate copolymers (EVA), and other suitable modifiers. The invention also relates to emulsions modified by the incorporation of solvents (such as diesel oil or kerosene) or by the addition of polymer latices (such as SBR-latex or natural rubber latex). More particularly, the invention relates to improved methods for enhancing adhesion between asphalt and aggregate in anionic solventless and solvent-containing bituminous emulsions wherein the emulsifiers are alkali earth salts of tall oil fatty acids, fortified tall oil fatty acids, tall oil rosin and fortified rosin as well as combinations of kraft lignin and nonionic emulsifiers. The novel adhesion enhancers utilized in these improved methods are the condensation reaction products of polyalkylene polyamines with a blend of polymerized linoleic acids and styrene (.alpha.-methyl styrene)-acrylic (metacrylic) acid copolymers.

In paving operations, three main practices are employed to achieve thorough mixing of bitumen and aggregate:

(1) mixing of free flowing heated asphalt (asphalt cement) with pre-dried aggregate,

(2) mixing pre-dried aggregate with asphalt diluted with a hydrocarbon solvent (cutback asphalt, cutter stock) at ambient or slightly elevated temperatures, and

(3) mixing aggregate with asphalt emulsions (e.g., oil in water emulsions) obtained by vigorous agitation of asphalt and water in the presence of an emulsifying agent.

The escalating costs of energy and hydrocarbon solvents coupled with a heightened environmental awareness have stimulated increased usage of emulsified asphalts in the road paving industry. The type of emulsifier employed is determined by the desired application of the asphalt emulsion. For rapid set emulsions (mainly used for chip sealing) sodium soaps of tall oil are commonly utilized. For medium set emulsions (applied in cold mixes of virgin aggregate or reclaimed asphalt pavement) higher concentrations of tall oil or modified tall oil soaps are generally being used with and without the addition of moderate amounts of hydrocarbon solvent. Slow set emulsions with good mix stability in the presence of fine graded aggregate are usually based on vinsol (a by-product of the wood rosin manufacture), or fortified tall oil rosin in combination with kraft lignin or lignosulfonates, and combinations of kraft lignin or lignosulfonates with nonionic emulsifiers from the class of ethoxylated alkylphenols, ethoxylated linear or branched fatty alcohols, and of ethylene oxide-propylene oxide-block co-polymers. In anionic emulsions the asphalt droplets are stabilized by anionic surfactants (wherein their negatively-charged surface migrates to the anode when an electric field is applied).

In the case of rapid set emulsions (mainly used for repair work of old wearing courses) the emulsion is applied on the existing surface and aggregate is spread on top. After the water of the emulsion has evaporated, an intimate matrix of asphalt and stone with good load beating capacity is formed. The road can be re-opened to traffic shortly after application of the seal. Medium set emulsions are commonly being mixed with aggregate in a pug mill prior to being used in road construction. The incorporation of solvent allows the mixes to be stockpiled prior to use. The mixes are prepared in central mixing plants and transported to the job sites or are generated "in-place". Slow set emulsions are being applied where good penetration and wetting is necessary. Mixes with high loadings of fines, base stabilization and tack coat are the main applications.

Anionic emulsions are taught by Mertens in U.S. Pat. No. 3,062,829 to be prepared via the use of alkali hydroxide which saponify the surface active acids naturally occurring in asphalt. These emulsions contain high molecular weight polyamides (Versene) as viscosity reducers and adhesion promoters. In U.S. Pat. No. 3,108,971 to Mertens anionic emulsions of the same type are improved with the addition of alkanol amines lacking lipophilic characteristics. Lignin amines are taught by Borgfeldt in U.S. Pat. No. 3,123,569. Quick setting emulsions obtained from highly acidic asphalts using lithium hydroxide are disclosed by Mertens in U.S. Pat. No. 3,240,716. Montgomery and Pitchford teach the alkali metal salts of complex polynuclear aromatic polycarboxylic acids as anionic emulsifiers in U.S. Pat. No. 3,344,082. Heinz in U.S. Pat. No. 3,006,860 employs alkali metal soaps of higher fatty acids such as those found in tall oil. In U.S. Pat. Nos. 3,956,002 and 4,088,505 Moorer teaches anionic emulsifiers consisting of alkali lignin or oxygenated alkali lignin, an ethylene oxide adduct of alkylphenol and up to 10% by weight of sodium borate. Detroit describes in U.S. Pat. No. 4,293,459 combinations of partially desulfonated oxygenated lignosulfonates and nonionic surfactants. Schilling et al. disclose the alkali soaps of maleated or fumarated tall oil fatty acids or rosin, of DIACID.RTM. 1550 and of sulfonated tall oil fatty acid as emulsifiers for anionic high float emulsions in U.S. Pat. No. 4,676,927 and the use of carboxyethylated modified tall oil amidoamines as emulsifiers for anionic slurry seals in U.S. Pat. No. 4,561,901. Ferm in U.S. Pat. No. 3,740,344 teaches the preparation of quick set anionic slurry seal compositions by applying a combination of aryl alkyl sulfonates and ethylene oxide adducts of alkyl phenols and of fatty alcohols. Schreuders in U.S. Pat. No. 3,615,796 teaches the use of petroleum sulfonates. A combination of sodium lignate or lignosulfonate and saponified tall oil or rosin is disclosed in U.S. Pat. No. 3,594,201 by Sommer and Evans. In U.S. Pat. No. 3,350,321 Conn describes the use of alkyl or alkoxy alkyl phosphoric acid salts as emulsifiers for asphalt.

Anionic emulsions are generally prepared at emulsifier concentrations of 0.2-10.0% based on 100% activity, preferentially at 0.2 to 2.0%. The pH range is 7 to 14, preferentially at 10 to 12 in the case of tall oil and rosin soaps. The advantage of anionic emulsions lies in the relatively low cost of tall oil based emulsifiers. The disadvantage is the low bond strength of asphalt to aggregate once the emulsion has dried and formed a film of asphalt on the surface of the aggregate. As most of the aggregates are negatively charged, the electrostatic repulsion between the negatively charged asphalt and the negatively charged stones causes inferior adhesion. Highly acidic aggregates such as quartzite, granite, rhyolite and many of the sedimentary, metamorphic and igneous rocks are considered responsible for the existing bitumen-stripping problem. This problem is also encountered in hot mix applications and when cut back asphalts are being used.

The quality of the road surface is generally dependent upon the strength of the bonds between the asphalt and the aggregate after curing of the composition. Poor service performance is due to poor adhesion, which results in asphalt stripping off the aggregate surface. Asphalt compositions also have relatively poor adhesion to aggregate in the presence of water. Since the aggregate is preferentially wetted by water, the eventual penetration of water into the composition reaches the aggregate and interferes with the bond between aggregate and asphalt. The result of this stripping is flaked pavement and the formation of pot holes.

To reduce water-induced debonding of asphalt from the stone surface, in many cases surface-active amines or diamines are added to the asphalt. Generally, anti-stripping agents or adhesion promoters are introduced into the asphalt prior to the asphalt being mixed with the aggregate. In the case of anionic asphalt emulsions it is advantageous to add the additive to the emulsion to prevent degradation at the high pH values. The patent literature sets forth a large number of compounds which can be used to improve adhesion of asphalt to aggregate. These include ethylene oxide condensates of long chain alkyl triamines (U.S. Pat. No. 3,615,797), alkoxylated amines and their salts (U.S. Pat. No. 3,347,690), and reaction products of ozonized unsaturated fatty acids with polyalkylene amines (U.S. Pat. Nos. 3,246,008 and 3,245,451). Other additives are based on fatty carboxylic chromites (U.S. Pat. No. 3,963,509), on combinations of epoxy resins and onium borates (U.S. Pat. No. 3,947,395), on tall oil alkanol amines and amido mines (U.S. Pat. Nos. 2,679,462 and 4,806,166), on fatty ether amines in combination with alkanol amines (U.S. Pat. No. 3,928,061), and on fatty acid amido amine soaps (U.S. Pat. Nos. 2,426,220, 2,891,872 and 3,230,104). Aminoalkyl polyalkoxysilanes are disclosed in U.S. Pat. No. 3,861,933; and condensation products of amines, polyamines, and amides with formaldehyde are taught in U.S. Pat. No. 4,639,273. Mannich reaction products of polyamines with formaldehyde and alkylphenols are described in U.S. Pat. No. 4,789,402, and ethoxylated hexamethylenediamines and their derivatives are taught in European Pat. Application No. 0 077 632 (82305420.0). Fatty primary, secondary and tertiary amines and imidazolines, their reaction products with various acids (including fatty acids), metal soaps, and several other compounds including rosin reaction products are described in U.S. Pat. No. 3,868,263.

Despite these developments, there exists a long felt need in the paving industry for relatively inexpensive adhesion enhancers for use in hot mix and in cut back asphalts which are effective even when employed in anionic emulsions. It is, therefore, an object of this invention to disclose an improved method for enhancing adhesion between asphalt and aggregate in anionic bituminous emulsions. A further object of this invention is to disclose improved adhesion enhancers for use in bituminous emulsions.

The objectives of this invention are met by adding polyamidoamine adhesion enhancers to anionic bituminous emulsion. These adhesion promoting compositions are produced by reacting a blend of polymerized linoleic acids and styrene-acrylic acid copolymers in a condensation reaction with polyalkylene polyamines.

These products for enhancing adhesion between asphalt and aggregate are effective even when employed with traditionally recalcitrant, highly acidic aggregates. The adhesion promoting effects produced via the addition of these compositions are primarily due to their ability to migrate to the asphalt/aggregate interphase, where the compositions hydrophobize the aggregate surface and render it water repellent. In addition, these compositions also increase adhesion by neutralizing some of the negative charges introduced into the asphalt by the anionic character of the emulsifier.

The polyamidoamine compositions which are effective in enhancing adhesion between asphalt and aggregate in anionic bituminous (asphalt) emulsions are reaction products formed by the condensation reaction of:

A) 50-80 percent by weight (wt. %) of a mixture comprising:

1) 50-95 wt. % of a blend consisting essentially of

a) 50-70 wt. % C-36 dimer acid and

b) 50-30 wt. % of a member selected from the group consisting of C-54 trimer, higher molecular weight polycarboxylic homologues, and combinations thereof, and

2) 50-5 wt. % of the styrene-acrylic acid copolymer reaction product formed by reacting in a radical polymerization reaction

a) 1-99 wt. % of a member selected from the group consisting of .alpha.-methyl styrene, styrene, and combinations thereof,

b) 99-1 wt. % of a member selected from the group consisting of acrylic acid, metacrylic acid, alkyl esters of acrylic acid, alkylesters of metacrylic acid, and combinations thereof, and

c) a catalytic amount of a radical polymerization initiator; with

B) 50-20 wt. % of polyalkylene polyamine.

Preferred polyamidoamine compositions which are effective in enhancing adhesion between asphalt and aggregate in anionic bituminous emulsions are reaction products formed by the condensation reaction of:

A) 50-70 percent by weight (wt. %) of a mixture comprising:

1) 70-90 wt. % of a blend consisting essentially of

a) 60-65 wt. % C-36 dimer acid and

b) 40-35 wt. % of a member selected from the group consisting of C-54 trimer, higher molecular weight polycarboxylic homologues, and combinations thereof, and

2) 30-10 wt. % of the styrene-acrylic acid copolymer reaction product formed by reacting in a radical polymerization reaction

a) 10-90 wt. % of a member selected from the group consisting of .alpha.-methyl styrene, styrene, and combinations thereof,

b) 90-10 wt. % of a member selected from the group consisting of acrylic acid, metacrylic acid, alkyl esters of acrylic acid, alkylesters of metacrylic acid, and combinations thereof, and

c) a catalytic amount of a radical polymerization initiator; with

B) 50-30 wt. % of polyalkylene polyamine.

Improved methods for enhancing adhesion between asphalt and aggregate in anionic bituminous emulsions may be achieved via adding these polyamidoamine compositions to the emulsions.

The term "tall oil fatty acid" refers generally to the class of products containing 90% or more fatty acids which are obtained by fractionation of crude tall oil. These fatty acids are primarily a combination of oleic and linoleic acids, with small amounts of saturated and other unsaturated fatty acids. Common impurities include rosin and neutral materials.

The various processes for producing polymerized linoleic acids are well known to those skilled in the art. The book Tall Oil and Its Uses II by E. E. McSweeney et al. (published in 1987 by the Pulp Chemicals Association) is an excellent source of reference concerning these processes.

Polymerized linoleic acids which are suitable for the practice of this invention include C-36 dimer acids, higher molecular weight polycarboxylic homologues (such as C-54 trimer acids, C-72 tetramer acids, etc.), and combinations thereof. In that portion of the polymerized linoleic acid blend not comprising C-36 dimer acids, it is preferred to primarily utilize C-54 trimer acids and correspondingly spolycarbmounts of the higher molecular weight polycarboxylic homologues.

The ratio of .alpha.-methyl) styrene to acrylic acid (or metacrylic acid) required to yield the desired styrene -acrylic acid copolymers ranges from about 1:1 to 3:1. These copolymers are produced by heating in the presence of a suitable radical initiator the desired mixture of (.alpha.-methyl)styrene and acrylic acid (or metacrylic acid) to a temperature in the range of about 180.degree.-270.degree. C. for a time sufficient for the polymerization reaction to occur (usually about 1 to 20 min). This polymerization reaction is described in U.S. Pat. No. 4,546,160 by Brand et al. (which is hereby incorporated by reference). Styrene-acrylic acid copolymers suitable for the practice of this invention have number average molecular weights in the range of about 1,000 to about 10,000.

Radical initiators which are suitable for the use in the above noted polymerization reactions include heat sensitive organic peroxides and azo compounds, and the like. These include, but are not limited to, members selected from the group consisting of azo-bis-isobutyonitrile, benzoyl peroxide, t-butyl peroctoate, t-butyl peroxybenzoate, and combinations thereof.

Polyalkylene polyamines which are suitable for the use in these methods have a number average molecular weight in the range of about 60 to about 500. Such polyalkylene polyamines include, but are not limited to, the following: aminoethylethanolamine, aminoethylpiperazine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, hexaethyleneheptamine, bis-aminopropylamine, pentamethylenediamine, hydroxyethylpiperazine, bis-hexamethylenetriamine, higher molecular weight homologues, and combinations thereof.

For application purposes it is preferred to produce adhesion promoters which are liquid in form. Therefore it may be necessary to adjust the viscosities of certain formulations by the addition of a solvent (a process well within the ability of a skilled artisan). Solvents which are suitable for use in the present methods include, but are not limited to, the following: ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, alkanolamines, and combinations thereof. Preferred alkanolamines suitable for use as a solvent include monoethanolamine, diethanolamine, triethanolamine, combinations thereof, and the like.

The following examples are provided to further illustrate the present invention and are not to be construed as limiting the invention in any manner.

A polyamidoamine adhesion promoter was produced via the following method. A clean 2 L three-necked flask equipped with agitator, thermometer, and reflux condenser with Dean-Stark trap was charged with 100 parts by weight of a polyalkylene polyamine blend (mainly consisting of triethylene tetramine and aminoethyl piperazine). The amine blend was heated to 100.degree. C. and 30 parts by weight of a styrene-acrylic acid copolymer (JONCRYL 680 manufactured by S. C. Johnson) was added in small increments. After a homogeneous solution had formed, 120 parts by weight of DIMER 1500 (a polymerized linoleic acid manufactured by Westvaco) was added slowly while the polyamine/styrene-acrylic acid copolymer blend was agitated. The resulting mixture was heated to 240.degree.-260.degree. C. and kept at this temperature until all water of condensation had been collected (about 4-6 hrs). The product was cooled to 120.degree. C. and discharged. Ethylene glycol or diethylene glycol was added when a less viscous adhesion promoter formulation was desired. The resulting adhesion promoter is hereafter referred to as AP#1.

A polyamidoamine adhesion promoter was produced via the following method. A clean 2 L three-necked flask equipped with agitator, thermometer, and reflux condenser with Dean-Stark trap was charged with 100 parts by weight of a polyalkylene polyamine blend (mainly consisting of triethylene tetramine and aminoethyl piperazine). The amine blend was heated to 100.degree. C. and 30 parts by weight of a styrene-acrylic acid copolymer (VANCRYL 64 manufactured by Air Products) was added in small increments. After a homogeneous solution had formed, 120 parts by weight of DIMER 1500 (a polymerized linoleic acid manufactured by Westvaco) was added slowly while the polyamine/styrene-acrylic acid copolymer blend was agitated. The resulting mixture was heated to 240.degree.-260.degree. C. and kept at this temperature until all water of condensation had been collected (about 4-6 hrs). The product was cooled to 120.degree. C. and discharged. Ethylene glycol or diethylene glycol was added when a less viscous adhesion promoter formulation was desired. The resulting adhesion promoter is hereafter referred to as AP#2.

A polyamidoamine adhesion promoter was produced via the following method. A clean 2 L three-necked flask equipped with agitator, thermometer, and reflux condenser with Dean-Stark trap was charged with 100 parts by weight of a polyalkylene polyamine blend (mainly consisting of triethylene tetramine and aminoethyl piperazine). The amine blend was heated to 100.degree. C. and 30 parts by weight of a styrene-acrylic acid copolymer (VANCRYL 65 manufactured by Air Products) was added in small increments. After a homogeneous solution had formed, 120 parts by weight of DIMER 1500 (a polymerized linoleic acid manufactured by Westvaco) was added slowly while the polyamine/styrene-acrylic acid copolymer blend was agitated. The resulting mixture was heated to 240.degree.-260.degree. C. and kept at this temperature until all water of condensation had been collected (about 4-6 hrs). The product was cooled to 120.degree. C. and discharged. Ethylene glycol or diethylene glycol was added when a less viscous adhesion promoter formulation was desired. The resulting adhesion promoter is hereafter referred to as AP#3.

This example illustrates the invention methods utilizing the adhesion promoters in anionic asphalt emulsions prepared with a sodium soap of tall oil (M28B) which were combined with granite aggregate from Georgia or quartzite river gravel from South Carolina. An emulsion was prepared from Amoco EB-20 asphalt or Exxon 120/150 penetration asphalt at 65% asphalt residue using 0.8% tall oil soap (based on the weight of the emulsion) at pH 11.5. The emulsion was allowed to cool to 140.degree. F. at which temperature the adhesion promoter (generally 0.3% based on the weight of the emulsion) was added to the emulsion and held at this temperature for at least one hour. Then, it was mixed with aggregate retained on U.S. standard sieve No. 4 or No. 8. Sufficient emulsion was used to achieve uniform coating of the aggregate. The mixes were allowed to dry two days at ambient temperature. To determine the performance of the respective adhesion promoters, the cured mixes were placed in a basket which was introduced into boiling water for ten minutes. After the basket was removed, the aggregate was spread on an absorbent paper towel and allowed to cool. The percent of retained asphalt coat on the aggregate was judged visually after placing the sample in a shallow glass pan filled with cold water and by illuminating the coated aggregate surfaces with a 60 watt lamp. The evaluation results are listed in Table 1 below.

The results noted in Table I above clearly show the increased efficiency of the methods utilizing the novel adhesion promoters disclosed herein, especially when compared to conventional adhesion promoters.

It is clear that the novel adhesion promoter compositions taught herein achieved superior results when compared to conventional adhesion promoters used for asphalt/aggregate compositions. Many modifications and variations of the present invention will be apparent to one skilled in the art in light of the above teaching. It is understood therefore that the scope of the invention is not to be limited by the foregoing description, but rather is to be defined by the claims appended hereto.