September, 1946
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
with elasticity; the narrower distribution yields a greater decrease in elasticity when the temperature is increased. Therefore, it can be postulated from the standpoint of equal processing qualities that a narrower distribution of molecular neight can tolerate a higher average molecular weight. .4 mcthod has been developed for isolating the elastic and plastic or viscous components of deformation under constant load. Under specific conditions of constant load a t 40” C. variations in molecular weight distribution, for a given average molecular weight, result in variations in high elastic deformat,ion while the viscous component remains constant. Thus, increasing thc molecular weight distribution for a given viscosity-average molccdar w i g h t tends to yield a softer, more elastic polymer. Sinct. t>heviscous component of deformation is independent of molecular weight distribution and dependent only on averagts constant 16ad deformation test described of estimating average molecular weight. hich is independent of time if precautions erved in the testing procedures, has been tietcrmined for individual fractions as well as for blends of varying molecular weight distribution. The logarithm of flow rat(’ the square root of the viscosity-avetxpc, -uggcsted by Flory’s viscosity eqiiatioii. .iCKNOW LEDGMENT
Thcs authors \vis11 t o thank J. Rehner, Jr., for :t constructive revielv of this paper and for permission to use the mathematical expression derived for the propagation of elastic deformation with time. For the layout and construction of the finished graphs JVC arc indebted to C. IT. Haemrr.
955
LITERATURE CITED
6. S.,Acta Physicochin. I‘.R.S.S., 12, ti47 (1940). ( 2 ) CtLinpbell, H., arid Johnson. l’., Tmtw.. Faraday Soc., 40, ‘ 2 1 (1) Alexairdrw, .A, l ’ ~ ,a n d Laziirkin,
(1944). (3) Diene arid KI(WIIII, paper presented before Soc. of Rheolorz.. O r t . 24, 1945. (4) I)unstsn, A . E., Z . j ~ h y s i k Chaui., . 56, 370 (1906). ( 5 ) Flory, P. J., J . Am. Chem. Yoc., 62, 1057 (1940). (ti) Ibid.. 65, 372 (1943); Rubhel- (’hem. Tech., 16, 493 (1943). ( 7 ) Gee, G., and Melville, H. W., Trnns. Faraday Soc., 40, 2 4 ) (1944); Rubbe,. C‘hem. Tech., 18, 223 (1945); Herringtoit, E.F. G., T r a m . Faraday SOC.,40, 236 (1944). (8)Kernp., A. R., and Straitiff, IT.L., IND. ENG.CHEM.,36, 707 (1944); Rubber Chem. Tech., 18, 41 (1945). ( 9 ) Kehner, J., Jr., IND.ENG.CHEM..36, 46 (1944): Ktrhhev C‘hvni. Tech., 17, 346 (1944). (10) Rehner, J., Jr., to be published. i l l ) Rehner, J., Jr., unpublished data. (12) Sookne, .4. M., and Harris, XI., I s u . Esu. CHERI.. 37. 4 i S (1946). (13) Spurlin, H. M., Ibid., 30, 538 (l93X). (14) Stefan, h1. .J., Sitzber. A k a d . Wiss. W’I.’~~/L., .1Jathitntiirw, Klasae 36, Abt., 69, 713 (1874); Foote. N. 51.. ISD. ENG.CHWY., 244 (1944). (15) Tuckett, R. F., Chemistry & I n d u s t ~ . y /62, , 130 (1943). (16) Wall, F. T., J . Am. Chem. Soc., 67, 1939 (1945). (17) Zapp, R. L., and Gessler, A. Xl., h n . EXG.CHEY.,35, 666 (1944); Rubber Chem. Tech.. 17, 88% (1944). PRESENTED before the Division of Rubher Chemistry a t t h e 109th \Iret,ioa the .%\fERICAX C F i E J r l C A L SOCIETY, .Atlnlltir City, N. .I.
Of
Styrene-Diene Resins in Rubber Compounding \. 34.
BORDERS, R. D. JUVN,
AND
L. D. HESS
Goodyear Tire & Rubber Cornpart.v, Akron, Ohio
A copolymer of approximately 15 parts butadieiie and 85 parts styrene (Pliolite S-3) is a thermoplastic resin with excellent oiygen and chemical resistance. It is compatible with natural rubber and with most synthetic rubbers. I11 mixtures with rubbers as a reinforcing resin, it is valuable for improvement of smoothness during extrusion or calendering and for reduction of shrinkage. Although Pliolite S-3 alone is brittle at room temperatures, in mixtures w ith rubber (up to 50-50), it does not increase the rate at w hich the mixture stiffens with reduction in temperature. Data are tabulated H hich illustrate the effect of 15 butadiene85 styrene copolymer in GR-S or natural rubber compounds upon hardness, stiffness, extrudability, tenbile strength, and impact resistance. The low moisture absorption and excellent electrical propertiek ha\e encouraged the use of the copolymer in rubber rompoundk for elevtriral insulation.
E
ARLl- in the investigation of butadiene-styreric copolymeIs
‘
as synthet,ic rubbers, this laboratory became interested in copolymers containing much more styrene than ally of the American or German synthetics. This interest was soon directed to the resinous copolymers obt.ained when styrene content is increased beyond the range in which rubberlike properties are observed a t room temperature. The exploratory work, therefore, involved preparation and evaluation of butadiene-styrene copolymers containing from 65 to 98% st,yrc!nc>. No description of similar polymers has bwn
found. Konrad and Ludivig ( 4 ) claimed the improvtxnrnt of rubberlike properties of butadiene-styrene copolymers by increasing the styrene content from the normal range to “between about 47.5 and about 70%”. The claims and examples of this patent emphasize the improvement of rubberlike properties, such as tensile, elongation, and rebound, a t high temperatiires. It is well known in this country, however, that increase in styrene content beyond a certain point, perhaps 50-55%, is accompanied by a loss of over-all balance of rubber characteristics. Therefore, the copolymers a t the upper end of the range described by Korirad and Ludwig have definite limitations for rubber iiscsfor example, low rebound, high brit,tle point, shortness, et,c. In the writers’ laboratory useful resins have been propared From dienes and vinyl aryl hydrocarbons in the range 5 to 2094 diene and 80 t,o 9570 vinyl aryl hydrocarbon. This papw doscribes the properties and certain uses of one of these copolynir~n containing approximately 15 parts of butadiene and &5 parts of styrene. This material possesses a combination of physical and chemical properties which permit its use in several applications where cyclized natural or synthtxtic rubbers are commonly tmiployed. Cyclized natural rubber has been described by Rruson (f), Endres (S), and Thies and Clifford ( 5 ) . Cyclized synthetic rubbers were described recontly by Endres ( 2 ) . One product of this type is made from a special synthetic rubber. The new 15 butadiene45 styrene copolymer is now identified as Pliolite 5-3, since i t may be used in many Pliolite applications, often with distinct advant,agcs ovrr either t,he natural or synthotic rubber derivat.ives.
I N D U S T R I A L A N D EN G I N E E R I N G C H E M I S T R Y
956
Vol. 38, No. 9
PROPERTIES
Pliolite S-3 is a white thermoplastic crumb or powder with a heat distortion point of 40-45" C. I t is practically odorless and is nontoxic in normal handling and processing. Only a small amount of nonhydrocarbon is present in the resin, including 0.5$ antioxidant. The resin has a specific gravity of approximatel) I .os.
TIFILEI. HARDSE~S OF PLIOLITE S-3 BLEXDSWITH GI 100 55 > 100 75 > 100 .. R 28 55 12 75 22 m, .a 32 100 75 > 100 .. 25 5 6 3i!n 13 35 > 100 70 > 100 80 22 .. 45 5 75 18 100 45 > 100 75 > 100 8(1
Rockuell XI-Scale
4 .i 68
43 6Y
52 72
*
.5 72
thc first addition is not made slowly, the band will shred and cauw difficulty in mixing. .\mong the synthetic rubbers which are mechanically compatible with Pliolite S-3 are GR-S, neoprene, C'heniigum S-1, Chemiguni 5 - 2 , Chemigum Pi-3, Butyl, polyisoprene, 1,utadicne-chlorostyrene, Vistanex, and polyethylene. S a t u r a l rubber is also compatible with the resin. The various synthetic rubbers and natural rubber can be admixed with Pliolitc S-3 in any proportions. T h e 50-50 resin-rubber blsntis of Comparison of Shrinkage and Smoothness of Equal 15 butadiene-85 styrene copolymrr with GR-S, Butyl, butadicneWeights of GR-S ( r i g h t ) and of a 50-50 Blend of G R - S chloroetyrene, and polyisoprene are rather stiff and display white with Pliolite S - 3 ( / e f t ) Taken from a Cool \rill cracks when bent on a 180" angle. After cold remilling, these Iilends become smoother and more flexible. The smoothness of GR-S and other synthetic rubbers during Aliphatic solvents have only a moderate effect on this c ~ p ~ l y [iroces~ingis improved by the presence of Pliolite 8-3. lIillctl mer, but the resin is much less resistant to aromatics and chloshrets, such as 50-50 GR-R-Pliolitc S-3 have unusually low rinated solvents. By hot milling it can be made soluble in such 5hrinkage hen removed from thc mill. T o obtain particularly solvents as benzene, toluene, ethylene dichloride, and methyl -mooth processing stock for wire insulation, etc., thc GR-8 has ethyl kctone. Low viscosity solutions uf greater than 20 1)cSc;n pcLptized to l o x lIooncy viscosity prior t o the blending can be made in these solvents. operation. The reduccd nerve of peptized GR-S allows Pliolitr Resistance of the resin t o acids and alkalies is excellent. I t is S-3-GR-S blends t o rxtrudr smoothly even in the absence of any more resistant t o oxidation than cyclized natural or synthetic, c.onipouni1 loading. rubbers. Prolonged exposure t o air even a t elevated tenipcw-
tures does not cause appreciable change. 'I-nder severe conditions, solubility of the resin may decrease slightly, but no effect upon the stiffening action of the resin in ruhber compounds hay been observed. The moisture absorption of Pliolite 5-3 is very low. .liter 20hour immersion a t 70" C.. the molded resin absorbs only a h i t 3.0 to 6.0 mg. of water per'square inch of surface. The electrical properties of Pliolite 5-3 are typical of those of hydrocarbon polymers. The folloxing ranges of valurs have 1)et.n ohtnined on testing a t one kilocycle a t 35' C. : Dielectric constant P o a e r factor, % Loss factor Specific resistivity, olini-riii.
2 , .>-2,Li 0-0.02
0--0.004 0 . 8 - 1 . 6 X 10'5
Pliolite 5-3 can be handlrd in an open niill, internal in-ixer, calender, or extruder, and ran be molded readily. For Banbury mixing with GR-S, the usual proccdure ii: t o add GR-S first, t h m the 15 butadiene-85 styrene ropolymw. PROCESS ABILITY AYD COnIPATIBlLITY
Pliolitc S-3 can be banded readily on a hot mill. A nnll t t m perature of approximately 215' F. is satisfactory. Iluhber a i d various types of synthetic rubber can then be added to the band. T h e addition must be rather slow a t first, but the increments can be larger after the first additions have been well tiiqpcrsed. If
COMPOUh DIh C,
For natural rub1x.r and the variou9 synthetic rubbers thr I.? 8.i ropolymrr behavrq a? a mffrning agent somea hat bimilarly
rr.%HI,L
11. TESSILE STRESGTH BLESDSWITH GR-S
Krsin-Rubber Ratio 11)I'liolite S-3-90 GR-S 30 Pliolite S-3-70 G R S .XIPliolite 5-3-50 GR-S 7 0 Pliolite 5-3-30 G R - 6 YO Pliolite S-3--10 GR-S 10 Pliolite J-3-90 pale crepe 30 Pliolite 5-3-70 pale crepe 50 Pliolite 5-3-50 pale crepe 70 Pliolite Y-3-30 pale crepe !I0 Pliolite S-3-10 pale c r e w Pliolite-90 Pliolite-70 Pliolite-50 Pliolite-30 Pliolite-10 Pliolite-90 Pliolite-70 50 Pliolite-50 70 Pliolite-30 90 Pliolite-10
10 30 .i0 70 90 10 30
GR-S GR-S GR-5 GR-8 GR-S pale crepe pale crepe pale crepe pale crepe pale crepe
A S D STIFFNESS O F P L I O L I T E ASD CREPERUBBER
Tensile, T,b. 'Sa. I n . 60 60 550 1900 4350
"i I I
300 530 1590 3700 30
,
m .a -
3 20 800 2310
iUu
810 2350 3880
Elongation, 9% 925 385 70 20 5 780 420 180 50 3 350 290 60 0 0
j'i5
235 15 3
Relative Torsion Modulus 0.023 0.023 0.50 22 44
0.023 0.233 0.73 8.0 89.0 0.023 0.023 1.09 89.0 89.0 0.023 0.023 0.50 89.0 29.0
8-3
Ohen Stiffness. Inrh-Lb. 0.016 0.021 0.215 0 . 90
2.41 0.0'23 0 058 0.205 0.61 2.61 0.015 0.018 0.25 Broke Broke 0.019 0.012 0.143 0.73 Broke
INDUSTRIAL AND ENGINEERING CHEMISTRY
September, 1946
t o the way shellac or Pliolite was used before the start of Korld War 11. .is little as 5 or 10 parts gives some stiffness to GR-S compounds. This amount can be increased as much as desired with a n attendant increase in stiffness and hardness. Compounds containing as high as 50 parts of the resin per 100 parts of GR-5 appear quite rubberlike after cure and retain considerable resilience. Ordinary fillers and softeners may be used in Pliolite S-3 blends with rubber and synthetic rubbers. S o distortion during cure is caused by the prcwnce of the 1.5-5.5 copolymer in synthetic rubber stocks, and articles may be removed from lint molds in the normal manner xithout change in size or shape. The rate of vulcanization of GR-S i,s not retarded by the presence of Pliolite S-3. Sormal sulfur and accelerator ratios such as are required for GR-S are satisfactory for Pliolite S-3 blends with GR-S. The res& itself can be vulcanized in the following recipe: Pliolite 5-3, 100 parts by w i g h t ; zinc oxide, 5 ; stearic acid, 0.5; sulfur, 2.5; santocure, l.i; total, 109.5 parts. The Shore hardness of the vulcanizate (D-scale) is 70-80; the Rockwell hardness (AI-scale) is 70-75. Heat distortion and benzene solubility data follon.: Heat Distortion Puint. C. 43 47 .5 3
Soly. in Benzene, 70 100 2 3 , .5 0 3
In mill mixing it is advisablr to introduce the sulfur and accelerator last, at a mill temperature as lon- as xi11 permit the particular stock t o stay smooth Thii: procedure tends to prevent scorching. BLENDS WITH GR-S AIVD CREPE RUBBER
The data in Table I indicate the degree of stiffening caused in GR-S and crepe rubber by the addition of increment amounts of Pliolite S-3 and the ordinary Pliolite which is cyclized rubher. Both of the resins behave similarly in increasing the hardness of uncured stocks. Table I1 shows that the increase in tensile strength and stiffness with increase in resin content ie accompanied by a loss of extensibility. Over the range of composition shown, uncured blends of Pliolite 5-3 with GR-S have higher tensile strength, higher elongation, but, lower stiffness than the corresponding blends of natural rubber Pliolite with GR-S. I n uncured blends with pale crepe, the 15-85 copolymer exhibits tensile and elongation characteristics similar t,o those of similar blends containing the cyclized Pliolite.
TABLE 111. FLOWCHSRACTERISTICS WITH
Resin-Rubber Ratio 70 90 70 90
Pliolite S-3-30 GR-S Pliolite S-3-10 GR-S Pliolite-30 GR-S Pliolite-10 GR-S
OF PLIOLITE
5-3 BLENDS
GR-S
212' F.
F l o w Test, Sec I n c h 220' F. 240' F.
17 40 42 203
13 19 31 1.50
2
5 9 60
The data of Table I11 shovi that blends of Pliolitc S-3 and GRS flow more readily a t 212 220 and 2-10 F. than do similar O,
O
blends of Pliolite and GR-S. The impact resistance of Pliolite 5-3 resin is somewhat better t h a n the impact resistance of the cyclized rubber Pliolite. Likewise, blends of Pliolite S-3 with GR-S and with pale crepe, with no other compounding ingredients, have somewhat greater impact resistance than similar blends containing regular Pliolite. Milled sheets of Pliolite S-3 alone are fragile, but the addition of 10 parts of GR-S renders the resin more resistant t o fracture on impact. T e n parts of palp
957
crepe in Pliolite S-3 also impart excellent rceistnnce t o impact, despite its high hardness. Since Pliolite S-3 has very low moisture absorption, blends o f unusually low Tyater absorption can be prepared by using cieproteinized rubber or special GR-S types of low water absorptivc characteristics. Typical master batches of 50 parts of Pliolito 5-3 and 50 part;? of special GR-S have a moisture absorption of approsimately 2 mg. per square inch after 4-hour soaking a t 70" C., 5 to 8 mg. after 20 hours, 12 my. after 48 hours, ant1 15 mg. per square inch after 96 hours in water a t 70" C.
TABLE IV, IMPACT RESSTASCEO F PLIOLITE S-3 BLESDYwrrR GR-S A X D CREPERVBBER Resin-Rubber Ratio
Izoil Impact. Inch-Lb.
!I0 Pliolite S-3-10 GR-S 00 Pliolite S-3-10 pale crepe
100 Pliolite 9-3
90 Pliolite-10 GR-S PO Pliolite-10 pale crepp 100 Pliolite
3.0 4.6 2.2
1.9 3.9 1.5
The electrical properties of Pliolitc S-3 were described carlicr in the paper. I n admixture with special types of GR-S of lo^ water ahsorption, this 15-55 copolymer is used as electrical insulation. Table 1 ' lists the brittle points measured for mixtures of Pliolite S-3 with pale crepe and with GR-S. Incorporation of as much as 50 parts Pliolite S-3 per 100 part of total stock raises the brittle point only slightly in either GR-S or natural rubber blends. Vulcanization raises the brittle point o n l y . a little. Blends of 70 parts resin with 30 paits rubber display much higher brittle points, cured or uncured. T o determine the effect of reduced teniperatures upon the $tiffness of Pliolite S-3 blends with rubber, torsional modulus of wveral stocks Jyas measured (Figure 1). Although increasing amounts of Pliolite 5-3 increase the stiffness of rubber stocks at room temperature, the rate a t which the relative modulus inrreases with lair-ered temperature is no greater for stocks containing larger amounts of Pliolite S-3. I n agreement FT-ith the brittlo point data, the temperature a t which the relative modulus curve rises abruptly 'is not greatly different for blends containing 10 to 50 parts of resin in 100 parts of blend. APPLICATIONS
The effectiveness of Pliolite 5-3 as a st,iffening agent for rubber and synthetic rubbers encourages its general use for increasing the hardness and rigidity of stocks and, a t the same time, retaining a certain amount of resilience. This resin has been found useful as a stiffening and reinforcing agent in rubber and synthetic rubber footwear. Because of its processing characteristics, dielectric properties, and low moisture absorption, 15-85 copolymer has found application in T7ii-e insulation. The reduction in t'he amount of shrinkage caused by the presence of the resin allows close control of thc gage of extruded wire insulation and permits accurate centering of the conductor. Blends of Pliolite S-3 in certain proportions with synthetic rubbers have unique balatalike properties and have been used to replace costly balata for certain articles such as golf ball covers. I n most uses Pliolite 5-3 serves equally as well as Pliolite and in many instances offers definite advantages to the cyclized rubber derivative. Pliolite 9-3 is of particular interest in applications where ease of processing, resistance t o oxidation, and uniformity are required beyond those offered by the older product. EXPERIMENTAL PROCEDURES
The moisture absorption d a t a were obtained by immersing inch samples in water at 70" C. for 20 hours. T h e 1x 4 x water ahsorption in milligrams per square inch was determined.
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
958
F
\
Vol. 38, No. 9
L
RATIO
PLIOLITE S-3 / PALE CREPE
PP
PLIOLITE S-3 / GR-S 1000-
-
70130
-
30170
ti
I
I
-60
-40
I
'-20
I
0
I
I
20
I
II
40
I
I
-60
-40
TEMPERATURE PC$ Figure 1.
I
I
I
-20
0
20
40
TEMPERATURE ("C.)
'I'orsioiial ~ l o d i i l u sData o n Bleiiclb of I'liolitt. $ 4 M i t h Yatural Kubher and GH-S
For cl(~terminutioiiof lic':it distc~i.ti1111 poiiitx, moldcd strips, I X 10 X 0.05 inch, \vc'i'tB siisj)endtd kit, thc, c,tltls iii :i watc'r bath. T t i ( b middle of the strip x i s pvriodically ticfl(a(.tcd am1 hcld for 15 s~,i*oiids at various tenipc,r:itures. Aftvr thcl p lii.vcd :md the strip removed from thc water bath, the pc~r~ni:inciit oc't \vas chcckcd by measuring the ho\v :it the ccntrr. The temitirli nxs said to hc! the I)i'r;itiirt' at which the bow i,c.:iched Ili,:tt distortion point. St iti'itess tests were run 011 the Olsen stiflnws ti:sttJr oii 0.5'10 x 3.5 inrh samples after 24-hour conditioning at 77" P. arid 50C;b Iiumidi?y. The stiffnoss was recorded as the bending moment i i i i ri c.li-pouiids. I z o d impact, values \ k x e determiiitd o i l iiotchthd bars. The t i t i i t s : i r t s inch-pounds prr inch of fncc.
l ' l i t ~ Horv c1iar:ictc:riutic:s ~verestudied in t: floiv tester rnade by 'l'iniiis Olsen Testing Machine Company. A pressure of I500 quare inch \vas used :it three diffcrrnt temperatures
ecorded as the seconds required For one inch of f l ~ ~ . the torsion cold test five strips were mounted on a rack in :in iiisulatcd cylindricd container. The temperature in the cylinder w:is controlled by regulating the volume of an air stream u-hicli blew across the dry ice in the bottom of the cylinder. 1iip1i.h were attached in succession to a torsion wire and torsioil 1ii.atl. The twist of each sample for a 90" twist of t h e torioii hixtl was recordcd as a function of temper:iture. It slioiild be understood that minor changes in the data of T:it)lcx I\-, ns ~vcllas in the other tables of test resiilts, rould result from v:tri:ttioiis in the techniquc used in mising the* htchi's. 111
LITERATURE CITED ( 1 1 1 3 i , u w i i , H. .\., Brit,. Patent
18s (1931).
- 57 - 5; - 41i
-, a
306,390 (1923); U. H. Patelit
l,i'!li,-
K u f j f i c rA U e ( S .Y.), 55, 301 (19.14).
U. 8.Patent 2,062,391 (1936). Ludwig, I b i d . , 2,335,124 (194,3). ( 5 ) Thies. H. I < . . and Clifford, -4.M , , Isu. ICsc;. CHEW.,26, l"8 (1934). (4) Koirrad
Pale crepe in this a e r i w iiutP:i(I of GR--:
'L F D
,,f the
iiiid
hefirw tile 1)iviriun of Riibbei ('lieiiiistlj a t tlir 100th lleetini. SOCIETY, htlantic r i t s , S . J.
: A ~ i ~ i i r c . (
