334
INDUSTRIAL AND ENGINEERING CHEMISTRY
the bale should be r q a i r e d (to prevent entry of water or dirt) by fixing sheets over the cut corner of the bale, as is shown in Figure 6. These samples were shown to be adequately representative by cutting opposite edges from a series of bales; it was not possible to detect, any variation between samples within bales, compared with the mixing-curing-testing error,
Rate of Cure There have been frequent coinp1:iiiits in thc literature t,hat rubber is variable in rate of cure, and attention was given to this point during the survey. It was difficult t o find a definition of rate of cure which gainrd .universal acceptance, and it v a s eventually decided to use the time of cure required to produce the minimum strain, or maximum modulus, as the measure of speed of vulcanization. It was then found that the time required to develop the minimum strain had a standard deviation of 4 minutes and was correlated with the value of the Malagan strain as is shown in Figure 7 . Moreover, the proportionate differences iri times of cure were relatively smaller than t>he differences in strain or modulus.
IntcrauticPn with A w e n a w a t e b i v s The surveys described in this paper Ivere carried out n.it,h the A.C.9. mix, but it was realized that the use of other accelerators could arrange the rubbers in different orders. In particular, the use of a basic accelerator such as diphenyl guanidine was found to produce a different order. This ivas expected, since there is good reasoii to believe that the variability in the vulcanization characteristics of ruhlic?rs in the A.C.S. mix a i k s mainly from the different effects which the nitrogenous components of the rubber have on the niercaptobenzothiazole acceleration. This interaction between accelerators d l be a complicating factor in any scheme for specifJ-ing rubber on the basis of its technical properties, but it is believed that basic accelerators are so seldom used that no confusion will arise. LIixings containing “boosted” thiazole-type accelerators generally arrange t,he rubbers in the same order as does the A.C.S. mix, although t,he relative differences between the rubbers are retluced.
Vol. 43, No. 2
Methods of Improving the Uniformity of Natural Buhlber The surveys described in this paper have shown where the variability in natural rubber lies-that is, between the produco of different estates or between output on different days from packing houses or remilling plants. It is clear that considerable improvement in the uniformity of consignments of rubber will he made possible by using only hales marked according to their inherent technical propeities, as envisaged by the French scheme of classification. In the case of estates it will be possihle to set up quality control charts and maintain output within a particular technological grade. In the case of packing houses it will bc necessary to collect several incoming lots of rubber, in each visual grade, and pack the sheets in such a manner that the difference3 between lots Tvill be averaged out. Samples draxn from a consignment of bales packed in such a manner can then be used t,o caharacterize the consignment. In the case of remilling plants it will be necessary t o find methods of blending the raw material to remove the marked day-to-day variation which exists a t p 1,esrnt. Chsignments of rul)bei~,in different visual grades and bearing t h e French technical marks, ~villbe arriving from the three major producing areas of southomtern Asia, Malaya, Indonesia, and Indochina, and users of this rubber are specially asked to coninicnt on the uniformity bet\\-een consignments.
Aekmwwlealgmeaat Aicknonledgments aie made t o the Hoard of the R U ~ ~ J P I Research Institute of llalaga for prrmission t o publish thic a ork, to the man5 eatate managers who wholeheartedly cooperated in the survey nork, and to the dealers, remillers, officials of agency houses, and others n h o have helped to ensure the w(’ces3 of the surveya
Effect of Syret erties o# H. A. Endres, R. J. Coleman, H. ,M. Pierson, and E. A. Sinelair The Goodwear T i r e & Rubber Co., Akron, O h h
P
ETItOLECbl asphalt, which is the residue obtained from the distillation of petroleum, is a complex colloidal system of indefinite composition. It can be regarded as a colloidal dispersion of highly carbonaceous matter in a medium composed of a mixture of hydrocarbons ranging from low molecular weight oils to high molecular weight resinous bitumens. Because of its waterproofness, adhesive qualities, ion price, and ready availability, pet8roleuni asphalt is used extensively as a binder in road construction and numerous other applications. The hardness and softening point of petroleum asphalt can be varied over a considerable range by variations in the manufacturing procedure, and solid as well as liquid grades are commercially available. The type normally employed in “hot mix” road construction has a softening point of 45” to 5 5 ” C. as determined by the A.S.T.M. standard ring-and-ball method. Such a material will tend to be soft and sticky under traffic conditions in hot weather and hard and brittle a t low temperatures.
T h e good durability of bituminous surfaced roads containing small amounts of natural rubber, which were constructed in Holland prior to 1939, inspired this investigation of the effect of butadiene-based synthetic rubber powders on the properties of road- type petroleum asphalts. As the properties of synthetic rubbers can be varied over a wide range they are potentially more versatile for such applications than natural rubber. Standard procedures were established for the preparation of the elastomers in powder form and for incorporation with the asphalt. Studies were then made of the effect of polymerization variables and of physical factors connected with the preparation of the powders. The
February 1951
*)
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
T h e reduction of this susceptibility t o temperature changes is of considerable interest to asphalt technologists and has been the subject of much investigation. During the 1930’s the Rubber Foundation of Delft, Holland, carried out a systematic investigation of the changes in the properties of asphalt that could be brought about b y the addition of rubber, I n this work, reported by Houwink ( 6 ) ,van Rooijen (8) and others, it was found t h a t the addition of small amounts of natural rubber, in the form of a powder, to hot asphalt reduced the temperature susceptibility while increasing the softening temperature and rendering it less brittle at temperatures of 0 ” C. and below. The effect of this treatment on other properties such as resistance to impact, penetration, plastic flow, ductility, and adhesion to concrete was also studied. The changes in the properties of the asphalt were ascribed to absorption of the more volatile constituents by the rubber, making the mixture less fluid. Concurrently, the brittleness a t low temperatures is reduced because of the presence of the highly swollen and elastic rubber particles. These changes in the properties of the asphalt brought about by the addition of natural rubber powder were considered of interest in road construction and consequently the Dutch and British investigators installed several test sections of road containing this material (6, 7 ) ; these were reported t o have been quite successful. This work inspired the investigation of the effect of synthetic elastomers on the properties of petroleum asphalts. Reference to this new potential use for synthetic rubber was made by Dinsmore (S), who discussed some of the properties obtained with synthetic rubber powder of the GR-S type, which was lightly vulcanized in latex form to prevent coalescence on drying. T h e principal purpose of the study reported here was t o make a preliminary investigation of the effects 011 the properties of petroleum asphalt of some of the variables that could easily be manipulated in the plant preparation of synthetic rubber powder. Some comparisons with natural rubber and reclaimed rubber are included. Although the factors that might weigh in favor of choosing one type over another are not discussed here in detail, i t is evident t o anyone familiar with the techniques of synthetic rubber preparation t h a t the properties and the composition of the product can be varied with a latitude not even approachable with the natural product or with reclaimed rubber. Of course, factors other than properties alone will influence the choice of polymer for a particular application. The concentrations of rubber powder that have been of interest for use in road-type asphalts have been in the range of 2 t o lo%, and generally around 4 or 5%. The ratios of asphalt t o aggregate (crushed rock and sand) are generally of the order of 1 part asphalt t o 10 to 20 parts of aggregate; hence the amount of rubber in the final mix is less than 1%. This is a n amount considerably
addition of the elastomers raises the softening point of the asphalt while cbld flow, penetration, and susceptibility to temperature changes are reduced. Polybutadiene and GR-S were found to be effective in improving asphalt properties, particularly when these were polymerized just beyond the gel point. Some comparisons were made with natural rubber and reclaimed rubber powders. The improvement in the properties of asphalt resulting from the addition of small amounts of synthetic elastomers should find many useful applications. The reduced susceptibility to temperature changes is of particular interest in road surfacing and several installations are now under test.
335
different from t h a t given in various press treatments of the subject of “rubber roads.” It should also be pointed out that because of the low concentration of the rubber only the effects of rather gross changes in the polymer can be detected.
Preparation of Rubber Powder Polymers used in this study came from various sources and include samples prepared by each of several possible methods of making powdered rubber: 1. Grinding bulk rubber which has been pretreated in some way to render it easily disintegratable; this is essentially a cutting rather than a grinding operation. 2. Spray-drying a latex to which “detackifying” stabilizers have been added to minimize cohesion of particles in the collection system; conventional spray-drying equipment is used. 3. Coagulating latex t o a fine crumb and processing the resulting slurry through the washing, dewatering, and drying operations in a manner which retains the h e particle size. detackifying agent additions or other treatments can be carried out on either the latex or the coagulated slurry.
For the purpose of evaluating polymerization variables alone on rubbers made in small bottles, it was desired t o use a single method which could be applied to polymers of widely different physical characteristics (chiefly softness) and which would have the feature of easy manipulation on a small scale without introducing excessive amounts of nonpolymer or other variables. The process finally adopted was a variation on method 3. Latex, which had been prepared in 4- or 8-ounce polymerization bottles with conventional fatty acid soap recipes similar to those used in the production plants, was further stabilized by the addition of either 5 o r 10 parts of tallow soap per 100 parts of polymer solids. One volume of latex diluted to 15% solidq was spraycd a t 20 t o 40 pounds gage pressure through a pinhole orifice noznle into 2 t o 3 volumes of rapidly stirred coagulating solution containing approximately 0.7% aluminum sulfate [AI%(S0+.18H~O], 1.0% sodium chloride, and 0.008% sodium hydroxide and having a pH around 4. The resulting fine particle size slurry was made alkaline with ammonia, a step which was essential to eliminate the tendency for particles to cohere during later processing; probably alkali soap and colloidal aluminum hydroxide are the active detackifying agents formed. Coagulum was washed on a cloth filter, dewatered to a 40 t o 60% solids cake by squeezing, broken up, force-screened through 16 mesh by hand, and tray-dried for 2 t o 3 hours in a n air oven at 160’ F. Occasionally, especially in the softer samples, some further disintegration was necessary at intervals during drying t o prevent formation of cakes. The resulting powders averaged 20 to 25 mesh in size, and were screened through 8 mesh prior to use. Several spray-dried samples were prepared by the Goodyear chemical engineering division using a small experimental Western Precipitation Co. spray dryer. This latter work has all been done on either GR-S-I latex or polybutadiene of 50-Mooney (large rotor) viscosity. The cured GR-S, from Type V latex, used in this investigation was from a large scale run of several thousand pounds made in 1947. This was prepared from a vulcanized latex t h a t was coagulated and then ground until all passed a 20-mesh sieve. The natural rubbers used were commercially available products. T h e cured sample was prepared from a lightly vulcanized latex t h a t was coagulated to give a crumb averaging 30 mesh in size. T h e reclaimed rubber, which is commercially available also, will pass a 20-mesh screen and contains 6% ash.
Mixing Procedures The mixing procedure used for the laboratory evaluation of the elastomers consisted of slowly adding the rubber powder t o the hot (150” C.) asphalt while stirring mechanically; heating was continued and t h e mix was stirred by hand every 15 to 30 minutes. Large size rubber particles tend to separate and rise to the surface more rapidly,than fine particles and have t o be Ytirred
336
INDUSTRIAL AND ENGINEERING CHEMISTRY
t; l
A
* 55
--
'Ob
A
A
1'5
I\
HEATING TIME
AT
1'8
IlO'C.,
2'1
2'4
HOURS
2'7
'
Figure 1. Effect of Heating Time on Softening Point of Asphalt Mixes 5.0 parts of various rubbers per 100 parts of asphalt
more frequently. Most mixes are near equilibrium after 5 hours, and this time was used for most of the evaluation work. This method rather closely assimilates one which has been widely used in experimental highway applications, where hot asphalt is stirred continuously with the rubber powder in conventional equipment] and the resulting hot blend is added along with aggregate to a pug mill in which the hot mix is made for highway application. An alternative laboratory procedure consists of preparing a master batch of rubber asphalt by milling 1 or 2 parte of warm liquid asphalt into 1 part of rubber on a standard rubber mill and adding this to the hot asphalt. This method has not proved satisfactory and was abandoned for the present study.
Vol. 43, No. 2
ointment can is held rigidly on the platform of a Randall and Stickney thickness gage while the */le-inch diameter plunger is allowed to push into the center of the sample under a 4-ounce load. The penetration after 1 minute is measured, the load removed, the sample allowed t o recover for 4 minutes, and the plunger again lowered carefully until it just touches but does not rest on the surface. T h e difference betwben the original and recovered distance is determined and is expressed as a percentage of the original figure. Low Temperature Susceptibility Factor (L.T.S.F.). This is a widely used measure of the resistance of asphalts t o embrittlement at low temperatures and is defined as the ratio of the penetration a t 77" F. to that a t 32' F., where the latter is measured with a 200-gram load and a 60-second penetration time: Penetration a t 77" F. (0.1 mm./5 seconds/100 grams) L'T*S'F' = Penetration a t 32 O F . (0.1 mm./60seconds/2OOgrams) Samples are conditioned for 3 days a t 32" F. before testing. A lowering of the susceptibility factor implies t h a t an improvement in the useful temperature range of the asphalt has been achieved. Cold Flow. The cold flow test is made at 77" F. by placing a sample completely filling an ointment can 2.5 inches in diameter by 3/8 inch deep on its side on a piece of graph paper and measuring the dimensions of the area covered by the portion of the asphalt which has flowed out onto the paper after 24 hours. For simplicity, only the linear forward flow, measured from the leading edge of the container, is recorded. 25
Testing of Asphalt Cements Penetration. Penetration is the principal method used for rating the consistency of semisolid asphalt and is usually measured a t room temperature (77" F.); it is also measured a t temperatures considerably above and below room temperature. The penetration is expressed as the distance in tenths of a millimeter that a tapered standard needle (0.14 to 0.16 mm. tip diameter) will penetrate the asphalt in 5 seconds with a 100-gram load (A.S.T.M. D 5-49). Asphalts for road construction are usually bought and graded by their penetration ranges a t 77" F.-that is, 40 to 50, 70 to 85, 120 to 150, and 200 to 300. The choice of a particular grade will depend on both the type construction planned and the prevailing ambient temperature range. Softening Point, A.S.T.M. E 28-421'. Softening point is determined by the ring-rand-ball method, wherein the sample contained in a flat brass cylinder, 5/8 inch inside diameter and 1/4 inch deep, is preconditioned for 15 minutes a t 5" C. prior to heating a t a controlled rate in a water bath. At the start of heating a 3/8-inch steel ball weighing 3.5 grams is placed in the center of the top surface of the sample, and the latter is positioned on a platform 1 inch above the bottom of the container in a manner which supports only the ring surrounding the sample and leaves the latter free to sag to the bottom under the weight of the ball. The bath temperature is raised without stirring a t the rate of 5 " C. (10.5') per minute. The tolerance for duplicate determinations is 1O C. Generally, the highest possible softening point for a given penetration is desired, but the relation between the two parameters is rather inflexible for standard untreated asphalts. Recovery. No applicable standard test was available for measuring one of the properties which might be expected t o benefit most from the addition of the rubber-namely] the ability of the asphalt t o retract after a n applied load. Hence a test showing this property was developed: the air-thermostatted (77" F.) sample contained in a 2.5-inch diameter by 6/8-inch deep
I
2.5
Figure 2.
Effect
I
5.0 PARTS
I
7.5 RUBBER
I
I O
~~~
of Concentration of Softening Point
Rubber
on
Drop Height. Drop height is a measure of the resistance of the asphalt t o shattering a t low temperatures and is expressed as the height, in inches, required t o fracture a sample at 35" F., completely filling an ointment can lid, measuring z3/8 inches in diameter by 3s,' inch deep, when a 67-gram steel ball is dropped from increasing heights. The lid containing the sample is inverted so that the sample rests on a wooden block and the ball strikes the metal.
Effect of Rubber Powder on Properties As the addition of rubber t o asphalt adds to its nonhomogeneous nature, i t %-asnecessary to establish early in this work that essentially equilibrium conditions in the blend were reached with respect t o the properties under consideration. Accordingly, studies were made to determine the effect of time of mixing and particle size on softening point. However, the rubbers fell into two categories as regards their effect on the viscosity of the hot asphalt: those in which the rubber-asphalt blend maintained nearly its original fluidity up to prolonged heating times, and those in which a loose gel-like structure developed in a comparatively short time-2 to 5 hours. Some nongelling rubbers on very prolonged heating-20
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1951
4
w
to 25 hours a t 150" C.-would produce a similar weak gel structure. Thus it was necessary t o compromise on a mixing time that would be feasibly short from the standpoint of commercial use, yet long enough t o approach a n equilibrium state for rubbers of differing particle size, to make the results comparable. This could not always be done with assurance, particularly since the properties of asphalt, heated alone, change on heating. A heating time of 5 hours was adopted for most of the tests reported here. Figure 1 shows the effect of heating time on the softening point of asphalt blends containing 5 parts of various rubbers. The rise in softening point of the control is evident. The very large increase with the polybutadiene is due t o the continuing formation of a gel in the blend. This particular sample was singularly slow and extensive in its gel formation, as is evident by the 9 to 10 hours required t o reach maximum softening point. The effect of gel on softening point is further demonstrated in the cured natural rubber curve, where the reversion was caused by a disappearance of a light gel structure which had developed i n the 5-hour sample. The effect of particle size was sought b y comparing softening points of samples which had been sieve-fractionated from a single master sample of a spray-dried uncured GR-S from Type I latex. These results are shown in Table I ; none of these fractions had gelled by the completion of the 5-hour heating period.
Table I.
Effect of Particle Size of GR-S-I on Attainment of Equilibrium
Particle Size, Mesh 8-20 20-35 35-48 Pass 48
.
Softening Point Rise, 1 hr. 3 hr. 1.o 2.5 6.0 7.5 8.0 6.5 6.0 6.5
C., after 5 hr. 5.0 8.5 9.0 8.0
The A.S.T.M. method for softening point determination used in these studies is more a dynamic test than an equilibrium one, in that, owing t o the comparatively rapid rate of heating, pronounced deformation is initiated a t a temperature considerably below the final recorded temperature a t which the test specimen has deformed the requisite amount. I n order to demonstrate that the increase in softening point observed with the blends was a real one and not due simply to a retardation of viscous flow undergone by the sample during the test, control asphalt and asphalt-rubber mixtures having a gel structure were heated at rates above and below the A.S.T.M. standard rate; other factors of the test were held constant (Table 11). Although the apparent softening point does depend on the rate of heating, the difference between the control and rubber-containing samples remains substantially constant.
6ot
I A.C. C O N T R O L lot
ob Figure 3.
Rate of Rise, C./hlin. 7.5 5.0 2.2 0.65
I
I
2.5
I
I
7.5
10
P k i T S RUBBER
Effect of Concentration of Rubber on Recovery
in the asphalt industry, is a useful measure of the ability of the deformed material to return t o its original shape. This property might be considered a manifestation of one of the chief benefits which the rubber could be expected to impart to a road surfaceresilience. Generally asphalts are distilled to varying degrees of "dryness" or are cut back with lighter petroleum constituents so that any desired penetration can be attained. The relationship between softening point and penetration remains a fairly constant characteristic of the source of asphalt. Hence, increasing softening of the standard asphalts can only be obtained if the user is willing t o use harder (lower penetration) material. This relation is often improved by "blowing" the asphalt with air, giving products of higher softening point for a given penetration than for standard products (1,4 ) . If comparison is made only with the asphalt which has been improved by blowing, the effect of adding rubber can be seen in the curves of Figure 4, where the slopes of 'the softening point versus penetration curve are less for asphalts containing increasing amounts of rubber than for blowing an asphalt for increasing times. These curves were obtained with several different samples of the same base asphalt having slightly different penetrations; hence comparison should be made of slopes more than of the location. If all were based on the same material the addition of rubber would give a higher softening point, for a given penetration, than blowing. This is reflected
80
Table 11.
337
i
Effect of Rate of Raising Temperature on Softening Point % of
A.S.T.M. Rate 150 100 44 13
Control 57.5 52.0 46.0 39.5
Softening Point, Rubber asphalt gel 67.0 63.0 57.0 49.5
O
C. Difference 9.5 11.o 11.0 10.0
The actual amount of a particular rubber t h a t a user might add for a given purpose would be dictated by economics, properties desired, and ease of processing (chiefly fluidity) with the asphalt to be used. T h e effects of varying amounts of several types of polymer on softening point rise and on percentage of recovery are shown in Figures 2 and 3, respectively. The percentage of recovery, although not one of the standard tests used
Figure 4. Effect of Rubber Concentration and Effect of Blowing on Relation between Softening Point1 and Penetration
INDUSTRIAL AND ENGINEERING CHEMISTRY
338
Table IV.
Effect of Varying Amounts of Kiihher on Properties of Asphalt Penetration at Sof77" F., tening O.lbIm./ RePoint, 5 see./ covery, C. 100G. % L.T.S.F.
Rubber ppel arts GR-S-VU 0 (control) S.0
7.5 10
50.5 66.5 58.5 61.0
69
50.6 56.5
74 70 66
GR-S-IIb
0 (control) 2.5 5.0 7.5 10
e'o
3%
215
3lo
LOW TEMPERATURE
3'5
4:o
SUSCEPTIBILITY
510 FACTOR
Figure 5. Effect of Rubber Concentrations and Effect of Blowing on Relation between Low Temperature Susceptibility Factor and Penetration
61.0
66.0 70.5
Polybutadienec 0 (control) 2.5 5.0 7.5
4'6
51.0 56.2
60.0 69 0
Natural rubherd 0 (control) 2.S
especia,lly in improved low temperature properbies. In Figure 5 comparison is made between the room temperature penetrat,ion of asphalt conhining varying amounts of different rubbers and the low temperature susceptibility factor or ratio of penetrat,ion a t 77" F. to penetration at 32" F. Of course, it is desirable to keep this ratio as lorn as possible for a given rootn temperature penetration. The properties of blown asphalt are shown in Table 111. The decrease in low temperature suscept,ihilit,yis due to a greater decrease in penetration a t 77" F. thari at, 32" F. whereas the addition of rubber usually increa,scs the penetration a t 32" P.
A.C. Control
l'olybutndienr
C,
Pol, hutndiene S
Figure 6. Cold Flov of Asphalt Alone and \sphaltRitbber Blends after 48 Hours at 77" P.
D a t a comparing t h e eff'ect s of increasing anlou~itsof different rubbers 0x1 a number of properties are shown in Table I\-. An interesting demonst,ration of one of the chief benefits of the rubber, retardation of cold flow, is shown here. The phenoinenoti of cold flow is of part#icularconcern when steep grades are t.o be surfaced. I3ow greatly cold flow is retarded is shorn-n in Figure 6 , where asphalt containing 5 parts of each of t,ao polybutadiene samples-one which gels the mix (G) a!id one which does not (S)-are compared with a coiitrol. Although cold flow, which is chiefly a problem during hot weather, can be minitnixcd either by use of a higher eoft,ening point asphalt or 1 . 3 ~ changing t'he type and amount, of aggregate, ncithcr of these approaches is
Vol. 43, No. 2
5.0 7.5 10
Reclaime 0 (control) 5.0 7.5 10
k? 46 %
6Q
69 57 49
7.5 7.5 7 5 7.5
1.0 0 35 0.25 0 10
10 23 37 45 55
4.3 4.0 3.4 3.0 2.7
3-7 5 1.1 7.5 0.6 10 0.2 1F 0.08 25 Negligible
11
3.6 3.1 3.0 2.0
5 7.5 17.5
4.23 4.15 3.65 3.25 2,8-4.0
7.5 5 17.5 10 25
0.2 0.1 0.1
1.25
7 5 7.5 10 7.5
1.0 0.5 0.45 0,30
32
%
50.0 .57.0 07.0 58.0
24
55
(1 D a y ) , Inches Forward
46
39 46
70
Drop Height, Inches
3.6 2.9 2.8 2.7
11 35 40
50.0 70 54.5 62 59.0 62 64.5 65 67 , i T'aiiahlo
60 58
Cold
Flow at 77O F.
10
19 48
10 29 33
4.08
3.75 3.55
R
1 .OR 0.60 0.25 Negligible
GR-6-V cured pass 40-mesh sureen. GR-S-If, latex'cured, spray-dried.
Polybuiadiene spray-dried 40% pass 16 mesh. Natural rubbe;, latex mired, 50% pass 32 mesh. Reclaim, 6 . 5 % ash and 10% acetone extract, pass 20 inesh
considered &isfactory: in the first case because of the surfacts being too brittle in cold weather and in the second becmse of the necessity of making up separate mixes for grades and for level swetches of road. Polymerization variables whose effect on asphalt properties might profitably be studied are: the nature of the monoiners, ratio of olefin t o diolefin, sol-gel properties (related i o plasticity), conversion, and 1,emperature of polymerization. 1-nless polar monomers such as acryloniti4e imparted some special prope not ot,herwjse obtainable, which has so far not, proved to be the case, butadiene and styrene seemed the only representatives of the diolefin and olefin classes that seemed worth investigating: these are the least expensive of the common moiiomers. T h c effect of aft,ertreatnients, such 9 s curing, c m be cwneidered in thc category of sol-gel properties. Butadiene to Styrene Ratio. Figures 7 and 8 shon- the effect of varying butadiene to st.yrene ratios on the rise in softening point above the control, atid on percentage recovery, respec-
a
~~
Table 111. Properties of Blown .4sphalt Blowing Time, Hours
0 2 4.5
6 9 12
~ ~ Penetration, f ~ ~ ~ iCold ~ Point 0 . 1 mm.1 0.1 mn1.i Flow a t 5 see / 60 see./ Re77' F'. (Ring and Ball), 100 g a t 200 e. a t covery, ( 1 n a y ) , C. 77' F'. .7Z0 F. L.T.S.F." o/c Inch 20 70 19.5 3.6 1.0 51.5 3 .43 21 0.85 62 18 53.5 3.45 15 31 56-57 52 0.45 3.05 35 0.30 46 15 58 -59 47 2 9 0.10 13.5 39 62 2.75 64 .Negligible 12 33 66
Low temperature susceptibility factor.
~
I
I
20
STYRERE
Figure 7.
40
I
I
60 80 CHARGED, PERCENT
I
