2186
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 1 has been constructed from the charts of Su ( 2 ) and Dodge (1) and the ideal reduced volume defined by Equation 3; t,he compressibility factor from the chart will correlate experimental values for most gases within a n average deviation of 2%. This chart is useful because trial and error solutions can be eliminated and, also, interpolation of the chart is improved. For example, an intermediate T’, line can be added to the chart by finding tho intersections Of this line with the 2.r‘ and Pr lines* The accuracy of t.he construction is adequate for most purposes.
urfural
Vol. 40, No. 11.
Interpolation between w lines is made by select,ing various points along the T , line until Equation 3 is satisfied. LITERATURE ClTED
(1) D o d g e , B. F.. “Chemical Engineering T h e r m o d y n a m i c s , ” g g . 161. 162, Kew York. McCran~-HillBook Co., 1944. ( 2 ) Su,G. J., IXD. ENG.CIIEM.,38,803 (1946). RECEIVED September 11, 1947. -4 copy of Figure 1 (11 X 17 inches) and a similar print of the high pressure region can be obtained by x\.rriting t o the author.
enyhydrazone as Chemical oftener for GR-S d
J
J . C. AJIBELASG, G. E. P. S\IITM, J R . , h N D G. W. GOTTSCHALK Firestone Tire & Rubber Company, Akron, Ohio
In the development of new processing aids for synthetic rubbers, it has been discovered that the phenylhydrazones of furfural and of certain aromatic aldehydes show high activitj as chemical softeners for GR-S. The p-bromophenylhydrazone and the 1-naphthylhydrazone of furfural are also active softeners. while thep-nitrophenylhydrazone is not. The phenylhydrazones of various additional aldehides and ketones are either inert or show a stiffening action under comparable conditions. Furfural phenylhydrazone may be used effectively in two general procedures, (a)by incorporating the hydrazone into the GR-S polymer on the mill and either storing for 2 weeks a t room temperature or by oven heating for a shorter period of time, or (b) by dispersing the furfural phenjlhydrazone in G K - S latex so that, after coagulation, drying of the polymer and softening take place simultaneously. Air appears necessar) for the softener to function. No softening was
observed w-hen the polymer-hydrazone mixture was dried in vacuo after coagulation of the latex. Tread compounds of increased plasticity ma> be prepared from the furfurai phenylhydrazone-softened polymers, especially after the furfural phenj lhydrazone has been incorporated into the latex and the softening obtained during the suhsequent drying period. It has been found that stiff, nonprocesbible, high Mooney polymers (ML4/212 = 75 to 180) may be softened to equal regular GR-S of specification Mooney (\IL4/212 = 45 t o 5 5 ) in processing characteristics, yet the v ulcaniaates retain many of the superior properties of the high-hZooney rubber, such as higher aged tensile, elongation, and crack-growth resistance. Thus plasticization and improved processibility of these polymers and stocks have been achieved without any additional operation other than t h a t of mixing the furfural phenylhydrazone dispersion into the latex.
d.
Most chemical softcners are thought to be either oxidizing agents or oxidation catalysts which promote the specific oxidation reactions of rubber so important in the breakdown of rubber on thc mill. The subject has been reviewed recently by Davis (3,4 ) , in describing a new class of catalytic plasticizers for GR-S and natural rubber-via., the o,o’-diaeylaminodiphenyl disulfides. GR-S, being less reactive t.han natural rubber toward oxygen (25) might be expected to require more active chemical softeners, higher concentrations, or more severe working condit,ions. Thus, while hydrazones in general have been reported to have weak to moderately strong plasticizing action (55) in natural rubber, the authors found that only a few monoarylhydrazones of certain aromatic and heterocyclic aldehydes were effective in GR-S. While p-nitrophenylhydrazine and as-phenylmethylhydrasine were reported to be plasticizers for natural rubber (Sf?), their furfural derivatives proved to be inert in GR-S. Ketone phenylhydrazones appeared to be either inert in GR-S, as in the case of benzophenone phenylhgdrazone, or t o be stiffeners, as, for example, acetophenone phenylhydrazone. Both of t’hese were mentioned by Gumlich (16) as softeners for a butadiene-styrene copolymer, which, however, might not show all the properties o f GR-S. Furfural phenylhydrazone in the aut’hors’ investigations proved to be one 01 the most active chemical soft.eners for GR-S.
YXCDk: rubber,, nst,ui’al or syiithetic, before mixing with pigments or fabrication into useful articles, must be plasticized. While natural rubber is readily plasticized by a milling operation, GR-S type synthetic rubber does not respond as readily to mechanical breakdown. Hence, the synthetic rubber must be modified during polymerization to give a relatively soft polymer with some loss of properties in the vulcanized product, or else the tough unmodified polymer must be: (a) mixed with rehtively large amounts of plasticizing oils in compounding, ( b ) plasticized thermally, or (c) plasticized by chemical means. Substances m-hich, when added in low concentrations to a polymer, bring about a marked increase in plasticity may be defined as “chemical softeners.” They are distinguished from solvent and lubricant type plasticizers by the characteristic that much smaller amounts of the chemical type are required for a given degree of plasticization. Their activity is assumed to be due to chemical reaction with the polymer or t’o a catalysis of t h e , breakdown reactions of the polymer molecules. Chemical softeners for natural rubber have been known for some time (2f) ; these include hydrazine derivatives, especially phenylhydrazine (a, 6, 10, 28, 3-5, 36, 38), aromatic and heterocyclic thiols (9, 16, 18, 37, 40) and their salts (3f, S 2 ) , monothiocarboxylic acids and their derivatives (5, 19, 23, 24, $7, ,$I), aromatic nitroso compounds (12, 39),and acyl peroxides (SO).
November 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
2187
TABLE I. FCRFURAL PHEA-YLHYDRAZONE AS A HEAT-SOFTENINQ CATALYST FOR DRY-MILLED GR-S POLYMER Softene Added on t h e Mill Initial Extrusion* Plasticity Values 1
2
GR-S Blank
S CR-S 4 Blank
5 GR-S
+
Polymer 2% furfural phenylhydrazone
+ 2% furfural phenylhydrazone +
T-41/r. . -,
Extrusion Plasticity Values" after 18 Hr. a t 185O F.
Bec.
Softening, %
59 65
10
-,-.
T-- 4 1 / ' .
67 182 In press
33 56
Softening, %
seo.
41
After 10 Min. a t 325' F. SoftenIn Softenoven ing, % ing, %
30 53
..
63
13 49
9
..
73
..
Softener Added in Banburv. _ . 10 Min. a t 280° F. Initial Extrusion Plasticity Values Final Banbury Temp., OF. T-41/4,sec. Softening, 2% furfural phenylhydrazone 291 20 40 ~
6 Blank 7 Untreated GR-S a Firestone plastometer (7,8).
273
33 66
..
FURFURAL PHENYLHYDRAZONE AS A CHEMICAL SOFTENER FOR GR-S TYPE POLYMERS
Under certain conditions i t was even more effective than an equal weight of phenylhydrazine. Benzaldehyde phenylhydrazone has been reported from abroad in recent years as a softener for Buna S and GR-S (14,10,26).Furfural phenylhydrazone compares favorabIy with the benzaldehyde derivative in activity and also has advantages in availability, cost, and lower melting point.
Furfural phenylhydrazone softened GFbS effectively after either of the two methods of addition-that is, to the dried polymer or to the latex.
EXPERIMENTAL
The softeners were tested in the dried polymer by milling into the rubber according to a standard procedure, the batch size, gage, time, and number of cuts being the same in all cases. The batches were started at a roll temperature of 55" to 80" F. and the cooling water was run through the rolls throughout the mixing. The relative plasticities of these samples were evaluated by the determination of extrusion times with the Firestone extrusion plastometer ( 7 , 8 ) . On this instrument, the T-41/4 value is the number of seconds required for 5 ml. of sample to be extruded under 4.25 pounds per square inch pressure, while the T-81/r value is the extrusion time for the same volume of sample under 8.25 pounds per square inch pressure. Plasticities were determined immediately after mixing and after 18 hours' heating in a n oven a t 185" F. The softeners were added to the latex usually by preparing a n aqueous dispersion and stirring it into the latex. The most frequently used dispersion of furfural phenylhydrazone was prepared by grinding the solid hydrazone in a pebble mill with 300% water, 2.0% Darvan No. 1, and 0.2% Aquarex D. Three coagulation procedures were followed: 1. Four per cent or stronger aluniinum sulfate solution was poured into the latex until coagulation was complete. The coagulum was WILLIAMS 7 washed on the mill, six passes with wash water turned on and three without. The slabs were then dried 20 hours at 150"F. 2. The latex was poured slowly into a PLASTICITY 6 rapidly stirred 2% aluminum sulfate solution. The resulting crumb was filtered off and dried 2.5 hours at 22O'F. VALUES 5 3. The latex was poured slowly into a rapidly stirred solution containing 10 parts of sodium chloride and 5 parts of acetic acid in 100 parts Y, at 212.4 of water. The resulting crumb was washed twice IN MM. by mechanical stirring with water and dried 2.5 hours at 240' F. The relative plasticities of the resulting polymers were determined with the M ooney plastometer. I n the study of thermal softening, the Williams plastometer (34) was used because of the necessarily small size of the samples dried in t h e Abderhalden dryer.
TABLE 11. EFFECT O F AIR ON THE SOFTENINffA ~ C T I O NOF FURFURAL PHENYLHYDRAZONE ADDEDT O GR-S L.4TEX" Plasticity Williams Values
Ya a t 212O F.,Mm. Dried Dried in air in vacuob
High iMooney GR-S
(ML4/212 = 136)
Polymer I1 1.6% furfural phenylhydrazone
8 Blank
1.6% furfural phenylhydrazone
11
+ 5%
3.83 3.75 A v . 3.79
5.09 5.45 5.27
5.10 5.09 Av. 5.10
5.70 5.47 5.59
pyrogallol
4.50 4.83
Av. 4.57 10
5% pyrogallol
7.01 6.84 Av. 6.92
5.12
5.40 6.26 6.65 6.70 6.68
Furfural phenylhydrazone was added as a n aqueous dispersion, pyrog+llol as an aqueous solution, to the latex. The latexes were then ooagulated with 2% alurmnum sulfate solution and dried 2.5 hr. a t 240' F. 6 Dried in vacuo in a n Abderhalden dryer at 1- t o 2-mm. pressure. Q
AIR
0
VACUUM
3 BLANK
POLYMER 6
1.6%FURFURAL 5% PYROGALLOL PHENYLHYDRAZONE POLYMER 9
POLYMER
IO
G% PYROGALLOL 1.6%FURFURAL PHENYLHYDRAZONE POLYMER I I
Figure 1. Effect of Air on Softening Action of Furfural Phenylhydrazone
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
2188
t
2o
4
tI
u
\
0 ,
, 1 0
I
0
2
I
4
5
PER CENT FURFLiRAL PHENYLHYDRAZONE
Figure 2. EEect of Concentration of Furfural Phenylhydrazone of the Elasticity of GR- s Contact between dry-milled polymer and air appeared to be necessary in order for the softener t o function propcrly. The plasticizing action occurred slowly during storage of the polymerhydrazone mixture at room temperature for 2 t o 4 weeks. Softening was produced much more rapidly during heating in a forced-
circulation air oven or during mastication in a heated Banbury, but very little softening action was observed if the mixture was heated in a press (Table I). TTOper cent of furfural phenylhydrazone, milled into the polymer, decreased the extrusion time over 60% after 18 hours' oven heating at 185" F. or after 10 minutes in the oven a t 325 F. TWOper cent of the hydrazone decreased the extrusion time by 4OY0 after hot mastication in a Banbury mixer. Although hot mast'ication was shown to soften the polymer, the resulting improvement in plasticity obtained by this method was lost in subsequent compounding; hence this t,reatment was not considered advantageous. The activity of this sofbener at temperatures as low as room temperature was in marked contrast with the activity of 0'0'diacylaminodiphenyl disulfides which seem to function slightly around 240' F., and rapidly around 300" F. ( 3 ' 4 ) . The low temperature activity of furfural phenylhydrazone made possible another more advantageous method of mixing and heat softening. The hydrazone was dispersed in t,he polymer latex and the softening act'ion then took place in tJheoven during the drying of the polymer. Air again appeared to be necessary, as no softening could be observed when the samples were dried in vacuo (Table 11, Figure I). Gunilich, who previously reported the use of benzaldehyde phenylhydrazone (24, 15) in Buna S latex, aerated the latex-phenylhydrazone mixture. I n the present work with furfural phen>-lhydrazone, the aeration st,ep appeared to be unnecessary when the coagulum was dried in air. The plasticity of the polynier in most cases increased with tlie concentration of softener up to 47, on the rubber. IfigIi(1i
TABLE 111. EFFECT OF COXCENTRATION OF FURFURAL PHDSYLHYDRAZONE ON THE PLASTICITY OF GR-8 POLYMERS OF VARYIXG
WlLLIAMS PLAST!UTY
I N I T I A L PL.4STICITYa
Polymer 12 13 14 15 16
Polsmerization Conversion,
%
72 60 77.6 73 75
0 130 136 87 72 52
VALES
% of Furfural Phenylhydrazone Added t o L a t e x 1.0 1.5 2.0
0.5
Vol. 40, No. 11
Y3 A? 2 P F
3.0
4.0
N o o n e y Plasticity Values, ML4/212 .. 158 .. 110 83 61 ,. 36 21 70 .. 41 .. 60 45 32 24 , . 45 38 32 26 ..
..
H MM.
I
01
,
1
1
15 30 45 60 MINUTES HEATED IN AIR AT 280-F
63 12 ,.
Figure 3. Thermal Softening of High Mooney GR-S Containing Furfural
, ,
..
Phenylhydrazone
Coagulated with 2 % aluminum sulfate and dried 2 . 5 hr. a t 240' F.
0 Polymer 20, GR-S b l a n k
alum aoagulated 0 Polymer 19, GR-S with 1%f u r f u r a l phenylhydrazone alum coagulated A Polymer 18, GR-S b l a n k salt-acid coagulated 0 Polymer 17, GR-S with 1 Q f u r f u r a l phenylhydrazone salt-acid coagulated
TABLEIV. THERXAL SOFTENING OF HIGH MOONEY GR-Sa C O N T . 4 I N I N G FURFCRAL PHCIiYLHYDRAZOXE Furfural PhenylhydraPolynier zone,
18 17 19 20 a
1 0
1 0
Initial
O m n Heated a t 280° F., 1RIin. 0 15 30 45 60
hi00ney
Coagulant
S.h.6 P.A.b
A1um.C
Value, ILIL4/212
Williams Plasticity Valuee, Y Bat 212' F.,A l r n 2 . 5 6 2 . 0 9 1 . 5 8 1.5.5 1 . 4 7 4.33 2.26 1.54 1.53 1.38 3 . 4 9 2 . 8 1 2 . 2 7 1 . 9 3 1.66 5 . 3 3 5.09 4 . 3 0 3 . 5 0 3 . 0 3
39 63 65
130
All samples from same latex, 60% conversion, crumb, dried 2 . 5 hr. a t
240° F. b c
Coagulated with 10% sodium chloride and 5 % acetic acid. Coagulated with 2% aluminum sulfate.
140 U
3
n
U
120 MOONEY
23 100
n
HIGH MWNEY
-
22 A
PLAS~UTY
PI
80-
0
'
'
OR-s
"
+ 1.6% FURFURAL MNYLHYDR4ZW-E
"
*25%FWINRAL M N n H Y W d Z O N
VALUES TABLE V. EFFECT OF AGINGo s PLASTICITY OF HIGH~ T O O N E Y GR-S POLYMER SOFTENED WITH FURFURAL PHENYLHYDRAZOSF
(>looney plasticity Furfural Phenylhydrazone Added to Polymer Polymer as Latex, %" Initial 21 2.5 30 22 1.6 44 138 23 ., 5
values, RIL4/212) 3 Days 32 49
138
1 2 4 8 Week Weeks Weeks TTeeks 28 33 34 42 50 50 57 66 133 134 135 133
Coagulated with 2% aluminurnsulfate and dried 2 . 5 hr. a t 240° I?.
20 I
Figure 4.
,
I
I 2 3 4 s WEEK5 STORED AT ROWI TEMPERATURE
I
I
6
7
I
8
Effect of Aging on Plasticity of GR-S Softened with Furfural Phenylhydrazone
November 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
concentrations were not run as the polymers then tended to become too sticky for convenient handling. The softener was found t o be effective in all samples of GR-S tested, although for s, given Mooney value a low conversion polymer (60%) was softened more easily than a high (72y0) conversion polymer (Table 111,and Figure 2, polymers 12 and 13). When furfural phenylhydrazone was added t o the latex, the softening action produced by the chemical softener appeared to be substantially completed by the time the coagulated polymer was dried. Samples of high Mooney GR-S latex, both with and without furfural phenylhydrazone, were coagulated, both with aluminum sulfate and with sodium chloride and acetic acid. After drying 2.5 hours at 240' F., the polymers were subjected to a thermal plasticization treatment by heating in an oven at 280" F. The behavior of the samples was followed by means of the Williams plastometer (Table IV and Figure 3). It appeared that, after t h e initial chemically catalyzed softening was complete, the furfural phenylhydrazone did not catalyze the subsequent thermal softening of the dried polymer. I n the alum coagulated polymer, the rate of thermal plasticization was unaffected by the hydrazone although the polymer containing it was softer than the blank before and after the high temperature heating. I n the salt-acid coagulated polymer, the hydrazonecontaining sample appeared to have been rapidly softened during the drying period of 2.5 hours at 240' F. The salt-acid coagulated blank softened only slightly during the drying period, but was thermally softened during subsequent heating at 280" F., so t h a t both salt-acid coagulated samples reached the same ultimate plasticity after half a n hour at 280' F. The initial Williams plasticity values indicated t h a t 1% of furfural phenylhydrazone lowered the Ya value about 1.8 mm. during the drying period of 2.5 hours at 240' F. with either alum or salt-acid coagulation. WhiIe i t was difficult t o dissociate the chemical and heat softening in a single sample, the data indicated t h a t the furfural phenylhydrazone was about equally effective with alum and salt-acid coagulation although the saltacid polymer was the softer, all other conditions being the same. This statement should be considered valid only for the type of polymer used in the above experiment. Certain special types of polymers were not softened by furfural phenylhydrazone unless the polymer was coagulated by salt-acid. However, these were exceptional, and alum coagulation was used throughout this study unless otherwise indicated. It has been reported t h a t the German heat-softened Buna S had to be compounded within 24 hours, or a t most within a week of the softening operation, or the thermal plasticization had to be repeated (33). However, polymers softened with furfural phenylhydrazone retained their plasticities for a much longer period. D a t a in Table V and Figure 4 indicated that 3 to 4 weeks elapsed before a measurable stiffening was observed. CHEMICAL NATURE OF T H E REACTION PRODUCING SOFTENING O F G R - S T Y P E POLYMERS
The cause of the high softening action of aromatic and heterocyclic aldehyde monoarylhydrazones is not yet clear. This type of compound, such as furfural phenylhydrazone, is more effective in latex than is phenylhydrazine itself (Table VI) hence, the softening action probably cannot be attributed to phenylhydrazine released by hydrolysis. The greater solubility of the hydrazone softener in the rubber hydrocarbon may be a partial explanation for its greater activity as compared with phenylhydrazine. Phenylhydrazine itself would be more soluble in water and have a less favorable distribution coefficient and hence might be lost partially to the serum during coagulation of the latex. Also its greater volatility would mean that it would tend to evaporate during drying of the coagulum. From Table VI1 it appears that the crystalline p-nitrophenylhydrazone, which is difficultly soluble in organic solvents,
.
2189
TABLE VI. PHENYLHYDRAZINE AND FURFURAL PHENYLHYDRAZONE A S CHEMICALSOFTENERS I N HIGHM O O N E Y GR-S Mooney Plastioitv Values SoftML4/212 MS4/212 ening, "/c.
Softener Per 100 Grams of Polymer Po1y m er Added t o Latexa 24 2.0 g. (0.019 mole) phenylhydrazine b 25 2.0 g. (0.011 mole) furfural phenylhydrazone b 26 Blank
95
..
21
31
67
74
121c
..
..
27
1.2 g. (0.011 mole) phenylhydra2.0 g. (0.011 mole) furfural phenylhydrazoned Blank
77 0
43
28
41
22 130C
..
83
1.2 g. (0.011 mole) phenylhydra. zine e 1.2 g. (0.009 mole) p-nitrophenylhydrazinef 2.0 P. (0.011. mole) 'furfural ph>nylhydraaone e Blank
121
29 30 31 32 33
zinw
72
82
40
11
..
67 136
51
..
,.
Coagulated with 2% aluminum sulfate and dried 2.5 hr. a t 240' F. b Added as an emulsion containing toluene as solvent for softener.
a
0
d e
Calculated f r o m MR4/212.
Added-&
.ii;Gis-'sGpknsion. Added as a n alcohol solution, some precoagulation observed.
f Added as a dioxane solution, some precoagulation observed.
TABLE VII. FURFURAL ARYLHYDRAZONES IN GR-Sa Mole of Hydrazone in 100 G. Polymer 0.011 0.0076
Polymer Hydrazone 34 Furfural phenylhydrazone 35 Furfural p-bromophenylhydrazone 36 Furfural 1-naphthylhydraeone 37 Furfural phenylmethylhydraaone 38 Blank 39 Furfural phenylhydrazone 40 Furfural p-nitrophenylhydrazone 41 Blank
'rABLE
VIII. AND
44
45
0,0085
0.010
60
....
60 26 67 66
0.011 0,0087
....
PHENYLHYDRAZONES O F VARIOUS ALDEHYDES KETONESAS SOFTENERS IN GR-Sa
PhenylPolymer hydrazone 42 Furfural 43 Benzophenone 44 Acetophenone 45 Blank
46 47
Mooney Plasticity Values, ML4/2 12 38
.
48
Salicylaldehyde (Phenylhydrazine) Blank
49 50 51
hIL4/212 initial
25 25
Mooney Plasticity Values SoftML4/212 ening, after 18 hr. % a t 185" F. 0 6 0 26 36 45 .. 27
-
34 25
T-4'/4, inital, see. 16
Softening,
% '
78
4
- 67
..
Extrusion Plasticity Valuesb T-41/4, Softafter 18 hr. Softening, a t 185' F., enlng
%
see.
%
27
39
59
35
..
39 98
58
22
Furfural Blank
59 65
10
67 182
63
29 26
-5 7
39
53
Butyraldehyde Benzaldehyde Blank
..
23
- 40 53 ..
54 55 56 57
Crotonaldehyde Acetone Furfural Blank
25 212
40 -410 -3
93 479 45 53
52
14
1
28
43
.
..
41
13
..
- 76
- 800
14
..
a 2 grams of each hydrazone milled into 100 grams of regular GR-S, each.
mixing according t o a standard milling procedure. b Firestone extrusion plastometer (7, 8). -
-
__
is inert, while the more soluble, difficult to crystallize p-bromophenylhydrazone and I-naphthylhydrazone are very active. The failure of furfural phenylmethylhydrazone to soften t h e polymer is assumed to indicate t h a t only mono-substituted hydrazine derivatives are capable of bringing about the plasticization of GR-S type polymers. From Table VI11 it is apparent that:
INDUSTRIAL AND ENGINEERING CHEMISTRY
2190
PHENYLHYDRAZOXE AS A SOFTEYER FOR TABLE IX. FURFURAL GR-S TREAD STOCKS (Furfural phenylhydrazone added to dried GR-S polymer) ABCEFH D G I
GR-S E P C black Zinc oxide Bulfur Accelerator (N-cyclohexylbenzothiazole Antioxidant (phenyl-%naphthylamine) Softener oils Furfural phenylhydrazone
100.0 45.0
2.4 1.7 1.2 0.6 8.9 0.0 159.8
_ I
Extrusion Plasticity Values Compound, Polymer, T-8114, see. T-4114, see. 3.6 ..
Straight mix Polymer plus furfural phenylhydrazone aged 14 days G Polymer plus furfural phenylhydrazone milled 5 minutes a t 260' F. I) Control E Polymer plus furfural phenylhydrazone, mill mixed, aged 14 days B Polymer plus furfural phenylhydraaone, Banbury mixed, aged 14 days Q Control El Polymer plus furfural phenylhydrazone, hot Banbury mixed, 10 minutes a t 280' F. Control A
B
1.8
4.0 3.8
..
3.4 3.0
5.4
.. ..
3 2
19 8 66 1
Vol. 40, No. 11
latex or when mixed into the dried polymer and heated; however. the term monoarylhydrazones must be qualified to exclude derivat,ives of p-nitrophenylhydrazine. The data in Table I1 and Figure 1 indicate that the furfural phenylhydrazone funct,ions as a softner only in the presence of oxygen. The plasticization then is probably attributable to selective oxidation of the polymer, catalyzed by the phenylhydrazone. The differences observed between phenylhydrazones, some of which are stiffeners rather than softeners, can be explained only after further study. Selective oxidation may produce oxygen-catalyzed polymerization and cross linking, a? well as dissociation and chain scission (9%). The mechanism of peptization of natural rubber by hydrazines has been discussed by \T7illiams (3.5). The activity of' phenylhydrazine was attributed to chemical activity, part' of which involved oxidation catalysis. Both chain scission and molecular dissociation were proposed as results of oxidation leading to softening of thc polymer. FURFURAL PHENYLHYDRAZONE A S A CHEIIICAL SOFTENER FOR GR-S TREAD STOCKS
The technological int'erest of furfural phenylhydrazone depends as much on its ability t o improve the processing qualities of a compounded rubber as on its ability to soften the crude polymer. Certain other chemical and physical treatments were Aliphatic aldehyde phenylhydrazones have a stiffening action found t o increase the plasticity of the GR-S t'ype polymers, but after heating of the polymer-phenylhydrazone mixture. after the reinforcing and curing ingredients had been incorporKetone phenylhgdrazones are either inert or have a definite stiffening action. ated the measured plast,icities in many instances were no better Aromatic and heterocyclic aldehyde phenylhydraaones generthan the control value for the stock prepared from untreated ally soften the polymer during the application of heat. GR-S, similarly compounded. The monoarylhydrazones of aromatic and heterocyclic aldeFurfural phenylhydrazone has been used t o produce an uncuwd CR-S tread compound of marke$ly improved plasticity. Two hydes appear to be effective softeners for GR-S when added to the methods of bringing about this effect were found, aF follows : TABLE x. PROPERTIES O F VCLCAKIZ.4TES (Polymer containing 2% furfural phenylhydranone aged 2 weeks before compounding) 1. Approximately 2 7 , of Kormal Properties --Oven Aged 4 Days at 2 1 2 O F.-lurfural phcnylhydrazone Cured a t Cured at Cured a t was incorporated into the 280,' F., D 280: F., G 280'. F., G polymer on the mill or in min. B control min. min. E F control E F control an internal mixer. The Modulus a t 300%, hlodulus a t 300%, LIodulus at 300% polymer was then st'ored Lb./Sq. In. Lb./Sq. In. Lb./Sq. In. for 2 weeks at ordinary tcm875 30 675 275 20 828 580 20 2200 2100 2000 peratures before adding the 60 850 675 40 1100 1100 1025 .. 2275 40 other pigments. 2280 80 90 950 8ZC5 80 1000 1000 900 120 900 900 160 1050 1025 980 160 2300 2100 2 . One to 47, of furfural phenylhydrazone was Tensile Strength, Tensile Strength, dispersedin the latex, which Lb./Sq. In. Lb./Sq. In. was then coagulated and 2300 2100 30 2650 1800 20 20 2100 2750 2700 40 2000 2200 2150 60 40 the polymer dried in thcJ 90 2525 2650 2250 2123 2000 80 80 iisual wa;v. 2728 2440 160 160 120 2450 2178 2100 3.2
-
7
Elongation a t Break.
Elongation a t Break,
735 645 580 610
Elongation at Break.
w,
,"
07-
30 60 90 120
,"
07.
/"
810 620 610 560
20 40 80 160
Cured a t : 280" F. for 80 ~ i i i n . 298O F. for 80 min.
570 460 480 490
670 440 540 500
600 550 530 550
20 40 80 60
310 240 300 315
Xormal Properties Cut Growth ( B ) ,Inch A Setting 30 Min. a t Room TCIIIP. E F c: control 0.55 0.73
0.71 0.83
0.55 0.57
3-Lb. Penetration, Inch Firestone Flexometer ( I ) , 250-lb. load, 0.3-inch throw, cured a t 280' F. for 80 min Cold Hot
0.51 0.75
21.3
0.51 0.71 DrAection, 20.0
0.49 0.70
70
Running Temp., 274 271
20.0 OF.
272
300 270 260 280
315 290 240 300
Polymers softcncd by other methods 'generally were found to be ineffective in producing tread compounds of improvccl plasticities. The second niethod was the more advantageous as the only added operation involved was the dispcrsion of furlural phenvlhydrazone in the latex, while the first involved an addit'ional milling or mixing operation and a storage period, both of which would be objectionable in large scale practice. Furthermore, t h r sccond
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1948
T4BLE
XI,
F U R F U R A L P H E N Y L H Y D R A Z O N E AS A SOFTEXER F O R
GR-S TREAD STOCKB
[Furfural uhenylhydrasone added to regular GR-S latexa)
Sulfur Accelerator (S-cyclohexylbenaothiazole sulfenamide) Antioxidant (phenyl-%naphthylamine) Softeners Furfural phenylhydrazone Extrusion plasticity values, seconds
T-81/4,
K
J 100.0 45.0 2.4 1.7
100.0 45.0 2.4 1.7
M Control 100.0 45.0 2.4 1.7
L 100,o 45.0 2.4 1.7
1.2
1.2
1.2
1.2
0.6 7.1 2.0
0.6 8.1 1.0
0.6 8.6 0.5
0.6 9.1
160.0
160.0
160.0
160.0
15.4
19.2
25.4
26.2
...
Properties of Vulcaniaates
Normal properties
Cured a t hl 280' F., Min. J Control Modulus a t 300%, Lb./Sq. In. 20 725 575 40 775 500 80 800 895 160 975 975 Tensile Strength, Lb./Sq. 20 1800 40 1600 80 1875 160 1550 Elongation 20 40 80 160
Oven aged 4 days a t 212' F.
Tensile Strength, Lb./Sq. 40 1425 80 1575 160 1450
Firestone Flexoineter ( I ) , 250-lb. load, 0.3-inch throw, cured a t 280° F. for 80 min. Cold Hot
+
a
1 .o 0.6 7.6
1. o 0.6 7.6
__
166.3
47.5
71.8
50
Mooney plasticity value for oompound ML4/212
61
75
55
Tubing test, Royle Tuber Garvey rating (15)
13
1.5
13
Properties of the Vuloaniaates High50Mooney Mooney Control Control N 0 P Modulus a t 300%, Lb./Sq. In.
Cured a t 280° F., Min. Normal properties
30 60
90
950 1150 1250
Tensile 30 60 90
Strength, Lb./Sq. 2350 2425 2425 2525 2525 2625
30 60 90 Oven aged 4 days a t 212' F.
975 1450 1550
326 900 107:; In. 1250 2325 2300
Elongation a t Break, YG 620 550 740 550 500 640 540 470 570
Tensile Strength, Lb./Sq. In. 2000 1925 1550 2050 1950 1750 2000 1950 1850
30 60 90
Elongation a t 240 260 270 90 GO 30
Break, % 240 220 250 230 240 260
Cut growth ( 2 2 ) , Inch
0.45 0.77
Normal properties Cured a t 280' F., for 60 min.
B Setting, 60 Min. a t Room Temp.
21.3
Aged 4 days a t 212' F. Cured at 280° F., for GO min.
B Setting 10 Min. a t Room Temp. 0.24 0.43 0.41
yo
Running Temp., 288
0.0 0.0 100.0 53.0 2.4 1.7
hlooney plasticity value for polymer ML~/ZE
3-Lb. Penetration, Inch
Deflection, 24.0
0.0 100 .o 0.0 53.0 2.4 1.7
166.3
0.31 0.55
0.48' 0.80
50Mooney Control P
166.3
Cut Growth (&), Inch A Setting, 30 Min. a t Room Temp. 0.20 0.23
N
HighMooney Control 0
High Mooney OR-8 1% furfural 100.0 phenylhydrazone 0.0 High Nooney GR-S 0.0 Regular GR-S 53.0 IiMF black 2.4 Zinc oxide 1.7 Sulfur Accelerator (Ar-cyclohexylbenzothiaaole 1 .o sulfenamide) 0.6 Antioxidant (phenyl-2-naphthylamine) 7.6 Softener oils
In. 1475 1250 1300
Elongation a t Break, % 40 190 220 80 220 220 160 220 220
Normal properties Cured a t 280° F. for 80 nun. 298O F. for 80 min.
TABLE XII. LABORATORY PROCESSIXO TESTO N HIGHMOONBY GR-S SOFTENED WITH FURFURAL PHENYLHYDRAZONE ADDEDTO T H E LATEX"
In. 1400 1725 1475 1500
a t Break, % 560 550 510 600 540 640 460 450
2191
F. 276
a Coagulated with aluminum sulfate, washed and sheeted on the laboratory rnill, and dried 20 hr. a t 160" F.
Firestone Flexometer ( I ) , 250-lb. load, 0.3-inch throw, cured a t 280° F. for 80 min. Cold Hot
0.55
0.63
3-lb. Penetration, Inch 0.47 0 62 19.3
prl,crduia \$a\ ab ieadilj adaptable to high Mooney polymers
as to regular GR-S so that they could be softened to equal the plasticity and processibility of the latter, while retaining most of the superior vulcanixate properties of high molecular weight polymers (11, 17, 26, 4 2 ) . The results of various mixing procedures for furfural phenylhydrazone in standard 50 Mooney GR-S are presented in Table IX and Table X. I t was apparent from a comparison of stocks A , B, and D that addition of furfural phenylhydrazone without aging the polymer-softener mixture had no effect on the plasticity of the compound, while a 14-day aging period reduced the extrusion time of this compound by 50%. From stocks B and C it appeared that hot milling could not be substituted for aging, and from stocks H and Z t h a t hot mastication of the GR-S polvmer containing furfural phenylhydrazone in a Banbury mixer
0.47
265
0.47 0.57
0.54 0.72
Deflection, % 17.3 23.3
Running Temp., OF. 258 280
a Coagulated with aluminum sulfate and dried 2.5 hr. a t 230' to 240° F. both processes in factory equipment.
was likewise ineffective in increasing the plasticity of the compound. Extrusion plasticities of the polymers here illustrate that a softened polymer does not necessarily yield a softened compound. The plasticities of stocks E and F indicated that furfural phenylhydrazone could be added either on the mill or in a Banbury mixer with equally good results if the mixed polymer was allowed to stand 14 days before complete compounding. Physical properties of the vuicanizates showed that apart from a slight acceleration of the cure, no great alteration had occurred.
2192
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
The second method of adding furfural phenylhydrazonethat is, by dispersing in the latex-gave comparable results. The softening action occurred during the drying of the coagulum rather than during the 2-week storage period required when the softener was mixed into the dried polymer. In this method, as in the first, 296 of the phenylhydrazone in regular alum-coagulated GR-S increased the plasticity of the compounded stock from that of the standard GR-S control by about 40%. One per cent of softener had a scarcely measurable effect. The softener was found to increase the rate of cure but had no great effect on the normal properties of the vulcanizate (Table XI), The superior vulcanizate properties of high molecular weight rubbers were known a t an early date but the difficulties in processing high molecular xeight butadiene-styrene copolymers led to the adoption of 45-55 llooney as the specification plasticity for GR-S. This represents nearly the maximum molecular weight polymer r h o s e workability permits rapid processing in the tire plant. If, however, an initially high molecular weight polymer can be made processible by mechanical, chcmical, or thermal plasticization, a part at least, o€ the advantageous properties of the high molecular weight polymer may be obtained. Mechanical plasticization, while an effective process with natural rubber, is not practical in the factory with GR-S type synthetic rubbers. Thermal plasticization was the means employed by tho Germans to make B u m S processible. Furfural phenylhydrazone is a chemical plasticizer which can be used in high hlooney GR-S or &una S for this purpose. By adding furfural phenylhydrazone to the latex, the softening and drying are effected simultaneouqly, no separate plasticizing operation being involved. I n this wav. 72 Alooney alum-coagulated GR-S was softened to 47-48 illooney in a plant run by addition of 1%furfural phenylhydrazone. Laboratory processing tests indicated that the polymer checked closely with GR-8 in plasticity and tubing characteristics. The polymer was satisfactorily processed in the factory and made into tire treads. Vulcanizate properties were intermediate between those of regular GR-S and unsoftened 72 &looney GR-S. The rcsult was a rubber equal to regular GR-6 in processing characteristics but higher in modulus, in normal and aged tensiles, in aged elongation, and in aged crack-growLh resistance. Data are presented in Table XII. Higher molecular weight GR-S type polymers have been shown to give better tread wear (11) b u t have not come into general use in this country because of processing difficulties and the impracticability of heat-softening on a large scale. The addition of the chemical softener, furfural phenylhydrazone, is a means of obtaining EL high molecular weight polymer in a state of processibility comparable to that of regular GR-S. SUMMARY
Alonoarylhydrazones of aromatic and heterocyclic aldehydes corresponding to the Following formula have been found to be effective chemical softeners for GR-3:
ilr--?;H--S-CH-X nhere Ar = arvl, exclusive of nitro substituted aryl iadicals, and X = furyl, phenyl, or o-hydrouvphenpl. Furfural phenylhydrazone has been shown t o be one of thc most active softeners for GR-S, as well as one of the most readily available materials of this type. Softening of GR-S type polymers has been accompliihed by several different methods: by incorporating the hydrazone into the dried polymer and either aging or baking the mixture in air, and by dispersing the hydrazone in the latex, whereby softening and drying may be effected simultaneouolr. The method of adding thc hydrazone t o the latex has been found satisfactory for all polymers examined of normal plasticity varying from 50 to 180 Mooney (ML4/212), and can be used n ith either salt-acid or alum coagulation in most cases.
Vol. 40, No. 11
The effects of plasticization have been shown to persist from
3 to 4 weeks before stiffening of the polymer becomes apparent. The softening of GR-S polymers carried out in either of these two ways persists throughout compounding so that tread stocks of improved plasticity arc obtained. High AIooney GR-S type polymers softened to a Mooney value of 80 (ML4/212) process about as readily as standard 50 Mooney GR-S, yet the vulcanizates approach more closely in properties the high Mooney GR-S vulcanizates-that is, they possess higher aged tensile and elongation, higher aged crackgrowth resistance, and lower running temperature. ACKNOWLEDGMENT
The writers gratefully acknowledge the encouragement and assistance of F. W. Stavely and R. F. Dunbrook in this investigation and the permission of the Firestone Tire & Rubber Company for its publication. LITERATURE CITED
(1) Allen, It. IT7., U. S. P a t e n t 2,048,314 (1930). (2) BBchle, O., Ger. P a t e n t 702,209 (1941).
( 3 ) D a v i s , A. R., I n d i a Rubbei. W o d d , 113,814 (1946). (4) D a v i s , A. R . , IND.E N G .CHEM,, 39, 94 (19.47). (5) D a v i s , A. R . , U. S. Pittent 2,366,316 (1945).
(6) Deutsche Dunlop Gummi Co., A.G., F r . Patent 845,203 (1939). (7) Dillon, J. H., P h y s i c s , 7, 73 (1936). ( 8 ) Dillon, J. II., a n d J o h n s t o n , N., I b i d . , 4,225 (1933). (9) E. I. du P o n t de Semours & Co., Brit. P a t e n t 490.292 (1938). (10) E. I. d u P o n t d e Nemours & Go., Fr. P a t e n t 791,321 (1935): a d d i t i o n 47,789 (1937). (11) Firestone T i r e & R u b b e r Co., p r i v a t e communication t o Office of R u b b e r Reserve, M a r c h 4, 1946. (12) Fisher, H. L., U. S. P a t e n t 2,035,698 (1936). (13) G a r v e y , B . S., Jr., ISD.ENG.CHEN., 34,1309 (1942). (14) Gumlich, W., Ger. P a t e n t 715,228 (1931). (15) Gumlich, W., U. S. P a t e n t 2,230,894 (1941). (16) Harman, M .W., U. S. P a t e n t 2,303,691 (1942). ESG. CHEW 40, 35 (1948). (17) Johnson, B. L., IND., (18) Jones, hl., and F l i n t , C., B r i t . P a t e n t 520,653 (1940). (19) M o n s a n t o Chemical Co., I b i d . , 562,199 (1944). (20) Mueller, H. J., I n d i a Rubber World, 107, 35 (Octoker 1942). (21) Neal, A. M., I b i d . , 104, 39 ( J u n e 1941). ENG. CHEX.,36, 29 (1944). (22) P r e t t y m a n , I. E., IND. (23) Roblin, R. O., Jr., U. S.P a t e n t 2,332,401 (1943). (24) Ibid., 2;347,966 (1944). (25) S a n d s , G. D., and Johnson, B. L., A n a l . C h e m . , 19, 261 (1947). (26) Schidrowitz, P., I n d i a - R u b b e r J., 107, 492 (1944). (27) Sibley, R . L., U. S. P a t e n t 2,339,033 (1944). (28) Spirk, L., C h e m . Listy, 35, 214 (1941); C h e m . Zentr., 1942, 11, 107. (29) Tobolsky, A. V., P r e t t y m a n , I. B., and Dillon, J . H., J. Applied P h a s . , 15, 380 (1944). (30) T u l e y , W.F.. U. 3. P a t e n t 2,016,403 (1935). (31) Vincent, J. R., Ibid., 2,378,519 (1945). (32) Ibid., 2,394,952 (1946). (33) Weidlein, E. R., Jr.,and KixMiller, R. W., p r i v a t e communicstion t o Rubber Reserve Co., W a r Production B o a r d , April 21., 1945. (34) Williams, I., IXD. EKG.CHEX., 16, 362 (1924). (35) Williams, I., a n d S m i t h , C. C., I b i d . , 27, 1317 (1935). (36) Williams, I., a n d S m i t h , C. C., U. R. P a t e n t s 2,018,643-4 a n d 6 (1935). (37) I b i d . , 2,064,580 (1936). (38) I b i d . , 2,132,506 (1938). (39) I b i d . , 2,183,342 (1939). (40) I b i d . , 2,190,587 (1940). (41) I b i d . , 2,191,266 (1940). (42) Y a n k o , J. A , , “Physical Properties of F r a c t i o n s of G R - 3 and Their Vulcanizates,” presented at 112th Meeting of AMERICAN CHE&iICXL SOCIETY, New York, N . Y., sop%.1s to 19, 1947.
RECEIVED June 10, 1947. Presented before the Division of Rubber Clit~mi s t r y of the AMERICAX CHEWICAL Socmrs, Cleveland, Ohio, M a y 26. 1047.
