ASPHALT-POLYBUTENE PAINTS
vesso 3 is required to give a con
sistency similar to 20 per cent poly
butene of 87,590 molecular weight in 73 per cent Solvesso 3. Poly
butene of this m olecular weight is also considerably less compatible w ith asphalts. T he resulting com
position should be classed as a m astic and for th a t reason a dis
cussion of com patibilities m ay be irrelevant.
T he blends of 87,590-molecular- w eight polybutene after fifty cycles have shown th e best results of any tested to date. Slight dust
ing was noticed in th e 5 and 10 per cent blends, b u t no dusting a t all w ith th e 20 per cent blend. Sam
ples form ulated w ith more than 1 per cent high-molecular-weight polymer were alm ost free from
R e d le a d p r im e r N o P rim e r
?ieure 4. Effect o f Primer on Weathered Asphalt Paint 21-A (a b o v e ) and on Asphalt-Polybutene Paint 21-J-IL ( b e lo w )
C ir c le s in d ic a t e in s p e c t io n p o in t s ; n o te r u s t in g a r o u n d ed g es o f p a n e ls w it h o u t p r im e r .
to the thixotropic char
acteristics of plastic oxi
dized asphalt and the polybutene.
In an atte m p t to im
prove th e bond of the paints to steel and to im
prove the com patibility of polybutene in asphalt, sodium sulfonate or so
dium alkyl s u l f o n a t e (molecular weight about 450),
0
R—S—0 —Na
1
was added to asphalt- p o l y b u t e n e p a i n t s
Figure 5. Weathered A sphalt-Polybutene M ica-Filled Paint
T h e t e a r o c c u r r e d in r e m o v in g t h e s a m p le fr o m th e r o o f; th e c ir c le s h o w s a s e c tio n m a g n i f ie d 2 5 t im e s .
April, 1943 I N D U S T R I A L A ND E N G I N E E R I N G C HE MI S T R Y 487 tested under norm al w eathering conditions.
Several filled asphalt-polybutene p aints were prepared in the laboratory kneader and tested for w eathering characteris
tics. Two coats of each p a in t were placed on steel, and the plates were tested in th e W eather-om eter and on th e roof of the General Engineering Building. Some tests were also con
ducted w ith th e p ain ts over steel th a t h ad been given a prim er coat of red lead. T he experim ental paints did no t brush so easily over red lead as over th e clean polished steel. Table V I lists the composition of each p a in t and results observed in the W eather-ometer. T hey indicate th a t polybutene reduces the chalking and im proves th e surface consistency of filled asphalt paints.
I t appeared desirable to com pare a filled asphalt-polybu
tene blend w ith other commercial asp h alt and coal-tar roof coat
ing. Therefore, an asphalt-polybutene mica-filled blend was formulated and placed on roofing pap er covering a portion of the Pipe Trench Building a t B ayw ay. A t th e same tim e eight other well-known com mercial products, some w ith a guarantee of ten years, were also placed on a p a r t of th e sam e building.
After • th irteen m onths th e asphalt-polybutene mica-filled product was rate d first, based on durability, application, and cost to the com pany b y a disinterested neutral observer (Figure 5). All of the products tested showed some evidence of chalking.
Of considerable interest is th e tw o-year actual w eathering te st for filled paints 91-20A to 21J + 1L, inclusive. T h e re
sults are listed in T able V II. I t is evident th a t th e presence of a red lead prim er coat gives im proved protection to m etal when asphalt-polybutene p ain ts are used. Also 5 per cent of 15,000 m olecular w eight polybutene increased th e w eathering resistance of a num ber of th e experim ental filled asphalt
lecular w eight in oxidized and steam -reduced asphalts reduced or com pletely elim inated th e tendency of th e asphalts to alli
gator, slightly reduced th e tendency to check, reduced sur
face hardness, and increased th e length of tim e before dusting began.
2. Film s having b e tte r appearance and resistance to w eathering were form ed from cutbacks containing highly arom atic solvents th a n from cutbacks containing highly paraf- finic solvents.
3. P olybutene of 6000-15,000 m olecular w eight also im proved th e w eathering resistance of in e rt filler-asphalt films.
W ith fillers steam-reduced asphalts were more favorable than oxidized asphalts; w ithout fillers the reverse was true.
4 . All coatings on red lead primer were superior to those
on polished steel. . ,
5 . In general, the improvement was proportional to the polybutene content, the polybutene film of higher molecu ar weight having better physical properties; b u t films contain
ing over 10 per cent polybutene were either too tacky, for the low-molecular-weight polybutene, or too viscous for easy application in the case of the polybutene of higher molecular weight.
488 I N D U S T R I A L a n d e n g I N E E R I N G C H E M I S T R Y Vol. 35, No. 4
a c k n o w l e d g m e n t
The advice, encouragem ent, and assistance of G. W. Oxley during the course of this work is greatly appreciated.
l i t e r a t u r e c i t e d
(1) Staudinger, H ., “ D er A ufbau der hochm olekularen organischen Verbindungen” , 1932.
(2) Thom as, R . M ., Zimmer, J. C ., Turner L R , R osen, R ., and Frölich P K ., In d. En g. Ch e m., 32, 2 9 9 -3 0 4 (1940).
(3) Traxler R N-, and Coom bs, C. E ., Proc. A m . Soc. T esting M ate
ria ls,’ 37, II, 549 (1937).
Pr e s e n t e d b e f o r e t h e D i v i s i o n o f P a i n t , V a r n i s h , a n d P l a s t i c s C h e m i s t r y a t t h e 1 0 4 t h M e e t i n g o f t h e Am e r i c a n Ch e m i c a l So c i e t y. B u f f a l o , N . Y .
B r it t le T e m p e r a t u r e o f
R u b b e r u n d e r V a r ia b le S tr e s s
A . R . K E M P , F . S . M A L M , AND G . G . W I N S P E A R
Bell Telephone Laboratories, M urray Hill, N . J.
T
H E projected use of synthetic elastomers on a large scale for outdoor service presents a pressing need for information dealing w ith their properties a t subzero tem peratures. U nder extreme cold weather conditions insulation, cable jackets, tires and tubes and m any other items m ust be capable of being (repeatedly) flexed w ithout failure a t tem peratures o f —50° C. or lower.
In a previous paper (25) a method was presented for de
term ining the critical tem perature of fracture where the sample is bent rapidly through an angle of approxim ately 90 . Although this te st provides an excellent technique for the comparison of various rubber compositions, it was realized th a t the procedure should be revised to include the effect of varying the m agnitude of stress as well as the rate of bending in order to simulate more closely certain types of service.
T he present paper does this and also reviews some of the work already carried out in the field of low-tem perature rubber
tipstme. •
E arly investigation (21) showed th a t crude rubber in
creased in tensile strength a t low tem peratures. Le Blanc
and Kroger (17) described this phenomenon as cold vulcan
ization. The observation th a t rubber which had been elongated and cooled in liquid air could be disrupted into fibrous fragments was reported by H ock (11) . M ark and Valko (19) associated this phenomenon w ith brittleness and conducted experiments which showed th a t, under given test conditions, the “critical p o in t” of raw rubber was - 6 7 ° C.
Ruhem ann and Simon (22) observed th a t a sharp rise in the specific heat of smoked sheet rubber occurred in the range
- 6 5 ° to - 7 5 ° C.
Bekkedahl (1) found th a t a t - 7 0 ° C. a sharp change of slope occurs in the tem perature-volum e curve w ith both super
cooled amorphous and crystalline raw rubbers. This observa
tion is im portant because it dem onstrates th a t th e state of brittleness develops a t th e same point independently of the existence of either physical sta te . Differences in the brittle points of crystalline and am orphous smoked sheet rubber, as determined by the fracture m ethod described in th e previous work (25), were found to be slight.
Aside from the fracture m ethod (IS, 16 ,25) other procedures used in investigations of rubber a t low tem peratures m ay be grouped according to the m ethod of te s t into three general types involving deflection (15 ,18 ), penetration (20), and elastic
T h i s p a p e r s u p p l i e s t h e n e e d f o r a m e t h o d t o d e t e r m i n e t h e t e m p e r a t u r e a t w h i c h r u b b e r a n d s i m i l a r m a t e r i a l s f r a c t u r e u n d e r v a r i a b l e b e n d i n g s t r e s s . A l t h o u g h th e b r i t t l e t e m p e r a t u r e is s h a r p l y d e f in e d u n d e r h i g h - s p e e d b e n d i n g t h r o u g h a s h a r p a n g l e , i t is lo w e r a s t h e s p e e d o f a p p l i c a t i o n o r t h e m a g n i t u d e o f t h e s t r e s s is r e d u c e d . I n s o m e i n s t a n c e s d e c r e a s e s o f m o r e t h a n 28° C . i n b r i t t l e t e m p e r a t u r e r e s u l t e d f r o m
r e d u c t i o n s i n b e n d i n g s t r e s s s u c h a s m i g h t b e e n c o u n t e r e d i n s e r v ic e .
V u l c a n i z e d p u r e g u m n a t u r a l r u b b e r a n d p l a s t i c i z e d p o l y v i n y l c h l o r i d e - a c e t a t e c o p o l y m e r s h o w e d t h e l a r g e s t c h a n g e s , w h e r e a s t h e c o m p o u n d e d a n d v u l c a n i z e d n a t u r a l a n d s y n t h e t i c r u b b e r s in v o l v e d i n t h i s s t u d y e x h i b i t e d a r e d u c t i o n i n b r i t t l e t e m p e r a t u r e f r o m 5° t o 10° C . i n g o i n g f r o m t h e h i g h e s t t o t h e lo w e s t s t r e s s e m p l o y e d .
deform ation (7, 8, 9, 14, 24, 26). The elastic deform ation and tem perature lowering on rubber. T his testing pro
cedure is sim ilar to th e T-50 m ethod (9) commonly used for determ ining the sta te of vulcanization in certain flat-curing c a rb o n -b la c k -re in -fo rc e d r u b b e r com pounds; th e in terp retatio n of th e d ata is the im p o rtan t difference.
Although th e deflection, penetration, and elastic deform ation tests detect appreciable changes in certain properties of rubber a t low tem peratures, it would increased resistance to deform ation a t tem peratures above the brittle point, b u t would n o t perm it th e prediction of how a
changeable gears to v ary the rate of deform ation. T his mechan
ism is driven by a W h o rs e p o w er squirrel-eage m otor, operating
mometer was used for tem p eratu re m easurem ents in this work.
Apparatus for D eterm ining Critical Tem perature o f Fracture on Bending
Experience in m anipulating the acetone-solid carbon dioxide conditioning b a th has shown th a t certain precautions are neces
sary to assure accurate tem perature control. T he procedure con
sists of placing 3.5 pounds (1.59 kg.) of crushed solid carbon m inutes are required to reach a condition of equilibrium where an im m ediate lowering of th e tem perature is noted upon th e addition of a small q u a n tity of the pulverized refrigerant. T he quantities of a refrigerant and liquid m entioned produce an equilibrium tem perature of approxim ately —70° C. In determ ining th e b rittle fracture point, it is stan d ard practice to establish the approxim ate tem perature of failure by prelim inary tests a t 10° C.
intervals and th en continue testing a t 1° C. ascending intervals tested after a 2-m inute immersion to minimize th e possible effects of solvent action on their structure. T he use of b o th acetone and ethyl alcohol as cooling m edia have been found to produce results which check closely w ith those from sim ilar tests con
ducted in an air atm osphere after longer conditioning periods.
B R I T T L E T E M P E R A T U R E O F R U B B E R C O M P O S I T I O N S
T able I contains b rittle fracture point d a ta for p u re gum and high-quality mechanical rubber compositions tested u nder controlled conditions of variable bending stress and ra te of deform ation. T he results as sta te d were found by num erous check te sts on th e same m aterials to be reproducible w ithin
± 0 .5 ° C. I t was shown, however, in our previous work th a t raw rubber from different sources varies in b rittle point over a range of about 4° C. which results in a wider lim it of repro
ducibility from b atch to batch.
W ith th e decreased m agnitude of th e bending stress and rate of deform ation, th e pure gum vulcanizate does no t fail a t
—78° C., b u t th e b rittle fracture p o int of th e carbon-black-
490 I N D U S T R I A L AND E N G I N E E R I N G C HE MI S T R Y Vol. 35, No. 4
B rittle fracture point d ata under variable stress for a series of reclaimed rubber compositions (Table II) showing the effects of adding semireinforcing black, clay and whiting, mineral oil, blown asphalt, and smoked sheet. The brittle point of the uncompounded reclaimed rubber was - 4 9 ° C.
These d ata show th a t the tem perature of fracture varies with both the speed and m agnitude of the bending stress.
As previously found (25), the nature of the rubber used is more im portant th a n minor changes in the composition. Un
doubtedly lower speeds or less severe bending stresses than
mediate possibility of their extensive use, the need for informa
tion pertaining to their low-tem perature properties becomes urgent. In contrast to rubber, considerable improvement m ay be effected in some of these materials by
the use of certain compounding ingredients.
W ide variations in brittle points were observed
Considerable information is available on the low-tem perature properties of polyvinyl chloride which, although a hard plastic a t room tem perature, can be converted into a flexible and elastic m aterial by the incorporation of chemi
cal plasticizers in sufficiently large quantities.
Russell (23) reported th a t the p form of perature a sudden change in m echanical and electrical proper
ties is noted. H e refers to this point a t which brittleness occurs as an internal m elting point. Since the unplasticized m aterial is in a general class of h ard plastics, includmg cellu
lose acetate and polystyrene which are also extensively used in their unplasticized form and as such are evaluated by their resistance to plastic flow, this term inology is correct. How
ever in the case of th e plasticized m aterials which are useful in their flexible and elastic condition, th e term “ brittle poin t”
is a more significant designation. Davies, Miller, and Busse (S) also studying th e electrical properties of this material, stated th a t three variables—tem perature, frequency of cur
rent, and ratio of plasticizer to polyvinyl chloride— can be made to produce roughly equivalent results. T he chemical significance of plasticizer action on these m aterials is beyond the scope of this work; however, reference m ay be made to the work of Houwink (12) who suggests th a t th e brittleness of a substance will depend upon th e distance over which the interacting molecular forces work. Considerable insight on the mechanics of plasticizer action w ith particular reference to cellulose acetate is given in a recent article b y Gloor and
G ilbert (10). . . .
Table I I I lists b rittle fracture d ata for plasticized polyvinyl chloride and polyvinyl chloride-acetate copolymers which m ay be considered average m aterials of their types. The
Some difficulty was encountered in testing these m aterials.
In the various test cycles occasional cases of nonfailure were observed as much as 10° C. lower th a n th e b rittle fracture points stated: thus there is th e possibility of a heterogeneous condition in piasticized m ixtures of th e types investigated. ^
V u i . c a n i z a b l e S y n t h e t i c E l a s t o m e r s . S ynthetic elastic polymers which more closely resemble rubber include buta
diene polymers, acrylonitrile and styrene copolymers of b u ta
diene, polychloroprene and its diolefin copolymers,
polyiso-Ta b l e I I . Br i t t l e Fr a c t u r e Po i n t s o f Al l- Re c l a i m a n d
April, 1943 I N D U S T R I A L A ND E N G I N E E R I N G CHE MI S T R Y 491 organic polysulfides. These m aterials, mixed in various proportions w ith vulcanizing agents and typical rubber com
pounding ingredients and vulcanized by heating, exhibit widely varying low -tem perature properties (25) owing to their different chemical structures. K och (15) applied his deflec
tion test to an undisclosed butadiene-styrene copolymer com
position and observed a freezing point of —66° G., which is in agreement w ith th e b rittle point range of —66° to —70° C.
for this m aterial observed in th e previous work (25). Bekke- dahl and S cott (2) recently reported a second-order transition point of - 2 3 ° C. for H ycar O R (modified butadiene-nitrile copolymer), using th e technique previously described in their work on rubber. These authors also sta te d th a t no first- stress of three butadiene-styrene copolymer compositions.
These results are sim ilar to those in T able I in respect to the
Yerzley and F raser (27) recently investigated the effects of low tem peratures on th e Shore A hardness, elastic deform a
tion, and mechanical deflection (torsion) of neoprene com
positions; they proposed th e term “freeze factor” to express the ratio of th e observed change in hardness produced by low tem peratures to th e maxim um possible increase in hardness
positions a t their respective b rittle fracture points. T he frac
ture te st indicates th a t compound 17, containing 30 p a rts of dibutyl sebacate, would be serviceable a t a tem perature 5° C.
lower th a n th e best of th e series as indicated by th e hardness observations. Composition 17, subjected to bending tests a t a q u ad ra n t speed of 37.5 r. p. m. over a 3.8-cm. radius arbor, showed no failure a t — 76° C.; com pound 14 exhibited a brittle fracture p oint under these conditions a t —67° C.
T he addition of dibutyl sebacate and diisobutyl adipate which they were used, and th a t freezing occurs well w ithin th e conditioning tim e allowed according to th e testing procedure.
Swelling tests on vulcanized base compound 19 in diisobutyl
Ta b l e V. Co m p a r i s o n o f Lo w- Te m p e r a t u r e Pr o p e r t i e s o f
adipate and dibutyl sebacate showed appreciable increases in weight after 12-hour immersion a t 60° C. The neoprene im
mersed in dibutyl sebacate increased 80 per cent by weight as com pared to a 70 per cent increase for the sample immersed in diisobutyl adipate. On the basis of these observations and the b rittle fracture te st results, it appears th a t _ increased solvent action m ay offer a better guide to the selection of ma
terials for lowering-the brittle fracture point than the freezing point observations on the plasticizers.