Continuous Process for GR-S Master Batches with Nonblack Pigments E. L. Borg, J. C. Madigan, R. L. Provost, and R. E. Meeker L-nited States Rubber Company, Institute, R. F'u.
By a new technique, Buca A clay has been successfully incorporated into GR-S latex. Specially designed equipment has adapted this process to the standard GR-S plant. A highly concentrated latex-clay mixture allows good retention of the pigment after coagulation with hydrochloric acid. A small amount of sodium hydroside permits the preparation of a high-solids clay slurry. Based on gra\imetric principles, the plant proportioning equipment has eliminated serious measuring difficulties and resulted in excellent uniformity of pigment loading. Phqsical properties are superior to those of a mill-mixed master batch at equiFalent polymer plasticity. Improted
processing results when %->Iooney latex is used. Incorporation of the pigment facilitates handling of this polymer of lower plasticity in the copolymer plant and even permits "bareback" shipment. Other good features for the user are reduction of mixing power costs and elimination of pigment handling. Various pigments, such as other clays, Silene, and Kalvan, are susceptible of similar treatment. ,The master batches obtained should enjoy TI ide application because of their escellent processing and physical properties and their compatibility with nonstaining, nondiscoloring stabilizers such as experimental stabilizer 401.
T
I t 11-asnoted early that, because of the hydrophilic character of Buca A clay, dispersing agents were not necessary in preparing a slurry in Tvater. Cpon standing or mild agitation in water, the clay particles swelled to form a uniform dispersion. Actually, from a practical standpoint, dispersing agents are undesirable because the crumb obtained upon Coagulation from systems in which they are present is too small to permit effective filtration and drying. The dispersions of Buca A clay in water used in experimental work were a t first limited in concentration to about 157, because of their high viscosities. Table I gives data on the effect of clay conrentration on slurry viscosity. Upon mixing a l5yOclay slurry with latex and coagulating with acid, only about 80% of the clay was retained by the rubber. (Clay loading is measured by determining the ash content of the master batch and correcting for the volatile constituents of the clay.) The importance of concentration of clay-latex mixture was not realized until some experiments mere made during which dry clay Tvas added directly to the latex prior to coagulation. This procedure increased the clay retention to approximately 95% and it became apparent that, although complete retention could probably not be attained in actual process operation, a satisfactory compromise might be made if a concentrated system could be devised. I n order to determine the optimum practical total solids, a series of master batches vas prepared experimentally in which the solids was varied by diluting in steps a mixture of dry clay and latex. Figure 1 gives the (lata on clay retention, which indicate that total solids of the mixture prior to coagulation should be kept above 3770 in order to minimize variation in clay retention Jvith change of solids. Means of preparing concentrated slurries of Buca A clay with relatively low viscosity were then sought. I t \vas known that the addition of small amounts of electrolyte to concentrated mixtures greatly reduces viscosity (3). In the case of Buca A clay it was found that the presence of less than O.lyo sodium hydroxide, based on the clay, makes possible the preparation of low-viscosity clay slurries of 65 to 70y0solids. The prcsence of the sodium hydroxide does not affect coagulation in so far as clay retention and crumb size are concerned. In a study of various latices it w.s found that fatty acid soap is the most desirable emulsifier. Other soaps gave latices which yielded master batches of much 1011-er clay retention. The effect of polymer plasticity has not been fully investigated, but
HE extensive use of GR-S stocks reinforced with pigments other than carbon black suggested an investigation of the
incorporation of the pigment in the GR-S latex and subsequent coprecipitation of the GR-S and the pigment in the form of a master batch. It m-as thought that this method of incorporating the pigment would result in a better dispersion with consequent ,improved physical properties over those obtained with the conventional dry-mixing process. Laboratory work on several nonblack reinforcing pigments confirmed this belief, and led to an extensive investigation and, ultimately to large-scale plant production of a GR-$clay master batch. Early in the w-ork it was recognized that uniform loading of the pigment would require the use of specially designed proportioning equipment in plant production. Such equipment was designed and installed a t the GR-S plant operated for Office of Rubber Reserve by United States Rubber Company. It is now known that a GR-S-clay master batch can be made on the installed equipment using a low plasticity (35-Mooney) polymer. I n this way an additional advantage in improved processibility is obtained over master batches made on the conventional 50-Mooney GR-S. Without the stiffening effect of the pigment it would not be possible to produce a polymer at plasticity as low as 35 Mooney on existing GR-S plant finishing equipment. The experimental work leading to the production of GR-S X-283 (a 100-100 GR-S-clay master batch) and a brief description of the properties of this polymer are used as examples. Many of the techniques described are applicable to master batches of other pigments, but since clay systems have been most thoroughly investigated and a full-scale run utilizing a clay has been successfully completed, it was thought best to limit the discussion to the development of a clay master batch. LABORATORY INVESTIGATION
When the problem of developing a continuous process for the production of a master batch containing 100 parts Buca A clay (Moore and hlunger) was first approached, a few preliminary experiments showed that conventional methods of preparation such as those used in the commercial production of carbon black master batches ( 2 ) could not be employed. The major difficulties were that the clay was not completely incorporated into the rubber and that the coagulated crumb was extremely fine.
10 13
1014
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 38, No. 10
MO-,
TABLEI. EFFECTOF CLAYCONCENTRATION ON SLURRY VISCOSITY AT 25"
clay,
% 6
2
6
10 12
Viscosity. Centipoiseq N o X a O H 0.075% NaOH
60 140 270 440
.. ..
.. ..
c.
clay,
%
Viscosity. Centipoiees 0.075% NaOH
No NaOH
14 16 18 50
..
720 1220 1740
..
...
5
9 0-
TABLE'11. COMPARATIVE DRYINGRATES O F BUCA A CLAY MASTERBATCHASD STAXDARD GR-S AT 175' F. Time, Min. 0 3 6 10 15
0
80-
Grams \Vater/100 G. Dry Polymer Master Standard batch GR-S 44 0 41 0
35 0
28.0 21.0
35.0 31 0 27 0 22.0 16 0
G r a m Water/100 G. Dry Polymer
Time, Min.
Maiter batch
Standard GR-9
25
8.0 1.3
10,o
40 60
0 3
1.5 0.5
80
...
5.0
I
35
40
45 I
MASTCRBATCH SOLIDS IN PERCENT
Figure 1. Effect of Total Solids on Clay Retention
100 -
+ y
95-
a a
EXPERIMENTAL STABILIZER
0.5
Figure 2.
1.0 PERCENT STABILIZER
2.0
1-5
Effect of Stabilizer on Clay Retention
GRAVIMETRIC MEASURING TOWERS DISPERSION
L
TO COAGU LATlON
I
I
I
BLENDING TANK
Figure 3.
do
I
FIGURE
ID
RIaster Batch Proportioning Equipment
there h:ivc: bceu indications that high-plasticity polymers retain more filler on coagulation than do polymers prepared to the standard Mooney viscosity of 50. By decreasing the water content of the emulsion or by allonkg the reaction to proceed to higher conversion, a latex of relatively highsolidscontent may be prepared and a contribution to higher total solids coiitent of thc lates-clay mixture made. Thc t,ypc of stabilizer employed has a pronounced effect 011 both crumb size and clay retention. Figure 2 illustrates the effect of four standard GR-S stabilizers on clay retention. Of these four, only experimcntnl stabilizer 401 (Saugatuck Chemical Division, Ts. S. Rubber Company) provided both good retention and large crumb size. Antioxidant A (BLE) had practically no effect on retention, but, a marked decrease in size of the coagulated crumb accompanied an increase in stabilizer content. At the required concentration of 1.5%, both B (PBS.4) and C (Stalite) reduced retention below a practical value. An additional advantage of experimental stabilizer 401 is that it gives a nondiscoloring, nonstaining product. Before the importance of solids content of the latex-clay mixture was recognized, some experimental n-ork was performed viith divalent and trivalent salts as coagulants. I n general, complete rctention of the clay was obtained, but crumb size was too small to permit washing, filtering, :md drying on existing plant equipment, The high cl:ty retention made possible by the use of a concentrated system allowed practical cmploymerit of acids alone as coagulants. Hydrochloric acid has proved more satisfactory than sulfuric acid in that higher loading and larger more uniform crumb size are obtained. Agitation plays an important part in the coagulation process. Relatively mild agitation is essential since the crumb as it is formed is very friable because of the higher filler content. To provide low shear and mild agitation and still obtain sufficient action to hold the heavy crumb (specific gravity of about 1.35) in suspension, a curved paddle impeller operated at comparatively slow speed \vas tested for performance on a pilot plant scale, and good results were obtained, Under these conditions crumb size was larger and clay retention was 3 to 5% higher than when
+
and pilot plant work, a SI$',, solids clay slurTy was used in actual production. A lkitr'x a t 31Y0 solids was used. After mixing of the clay and latex, coagulation was carried out with 0.70% hydrochloric acid. A c t u d losses during coagulation amounted t o about 8% of thc clay used or almost exactly that predicted from 1dx)rutory
(20-
2
-
z 0 z n
100-
0 0 .
~ - o ~ ~ - ~ - o - o - 0 2 ~ o ~ o , o ~ o ~ o ~ o ~ 0 2 0
-
4
s
80-
form loading. I n actual operation this was done by equipment dcsigned to proportion ingredients gravimetrically. Essentially t h e equipment consisted of four gravimetric measuring towers (Figure 3), operating on an automatically timed cycle which allows filling and draining of two units simultaneously; one unit 611s viith latex and one with pigment dispersion while the corresponding two are draining. This provides a semicontinuous flow t o a mixing tank where blending takes place. ilccurate measurement is attained through actuation of the i n k t valves by contact bubbler manometers recording static head of the material in each of the units. Such a gravimetric measurement has been found t o be more accurate and more reproduciblr than proportioning by means o i weir boxes, orifice boxes, etc., whose calibration is strictly volumetric. This is particularly true for those dispersions n-hich show a tendency to foam and incorporate air during preparation or agitation. Operation of the proportioning equipment was considered highly successful during the plant run of GR-S X-283. .4s Figure 4 shows, the maximum range of loading was =t4parts with about half the total production within * 1 part. T o obtain uniformity of loading within narrow limits, it was essential t h a t the coagulation step be controlled closely since losses of pigment must remain constant throughout. As recommended from laboratory
TABLEIv.
PHYSIC41, 4YD P R O C E R S I X G
Cure, llin. lliidulus.ct 3 0 0 7 , , Ib./ bq.
111.
2.5 30
430 410 -1'30 1310 1430
90
14-10
25 30
90 Teysile btrength, ih. sq. 111.
DATAFOR
50-Mooney PlasticityGR-S lIiL1S-283 mixed
CLAY SrOCK
3i-llooney Plasticity ~ _ Latex\Iillmixed itiixed
-_ 0'0 220
320 340 330
250 310 310
1200 1020 930
1150
I on0
1310
!J80 7dO
ieno
_
230
Elongation, rG Hardness Rebound Tear, lh./O.l in.
25
: 0 90
Extrusion r a t e a , grams/ l0sec. Tubing index ( 1 ) Swello. %
15 4 15.6 15.0
13 2 6 (2112)
14.0 9 (2322) 25
Measured on sample extruded through
190' F.
11 3 13 6 15.4
31 3
1: 4 13 5 14 2
I1 9 11 8 '38
17 5 1 1 (3823)
15.0 10 (2323)
33
33
w i n c h die in a KO.I / ? Kohle a t
INDUSTRIAL AND ENGINEERING CHEMISTRY
1016
The stiffening effect of pigment in the polymer is sufficient to permit the storage and shipment of bales without packaging in conventional paper bags.
Vol. 38, No. 10
cooperation and interest of Rubber Reserve in the work and the permission to present this paper are greatly appreciated. LlTERATURE CITED
ACKNOWLEDGMENT
The authors wish to acknowledge the assistance of their associates in this work, H. J. E. Segrave, R. J. Meyer, H. Z. Hurlburt, F. Price. The proportioning equipment was designed and installed under the direction of C. G. StronTe. The funds for carrying Out this program were appropriated the Office Of .. . Rubber- Reserve, keconstruction Finance Corporation. The
(1) Garvey, Whitlock, and Freese, IND. ENQ.CHEM.,34,1309 (1942). (2) Rongone, Frost, and Swart, Rubber A g e (N. Y . ) , 55, 577-82 (1944); Rubber Chem. Tech., 18, 130-40 (1945). (3) Smothers and Herold, Univ. ilfo. School Mines Minerd. Pub., 15,N o . 3 (Sept., 1944). PRESENTED before the Division of Rubber Chemistry at the 109th Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantic City, N. J.
Melting Points of N-Substituted Polyamides
B. S. BIGGS, C. J. FROSCH, AND R. H. ERICKSON
J
Bell Teleph,one Laboratories, Murray Hill, N . J .
L
INEAR polyamides, it is generally known, may be made by
Melting point curvee are presented for several families
condensation of a dibasic acid with a diprimary diamine (6). If a portion of the diprimary diamine is replaced by a primary-secondary diamine or a disecondary diamine, the resulting product is a partially substituted polyamide. Unsubstituted and partially substituted chains are compared in formulas 1 and 2. I n this paper the preparation of a number of such substituted polyamides is reported, and the correlation of their melting points with the degree and type of substitution is discussed. Unmodified polyamides, whether of the 6-6, 6-10, or 10-10 series, are high melting crystalline compounds insoluble in the usual solvents; when allowed to cool slowly from a melt, they are very brittle. As the hydrogen atoms of the amide groups are progressivrly replaced by alkyl radicals, these original properties are modified in the direction of lower melting point, greater flexibility, and greater solubility in ordinary solvents. I n general it has been noted that, in a slowly cooled sample of a n N-substituted polyamide, there is good correlation between flexibility and melting point, As a matter of fact, in any given series the melting point is a better criterion of how much flexibility is to be expected than is the percentage substitution, since it makes a difference whether the substitution is furnished by a primary-
of polyamides in which the amide hydrogen atoms are
0
0
0
--N-(CH,)
I
H
/I
,-N-c-(CH,)
I
CHs
0
0
0
/I
Ii
n-C-A%--(~~2) ,--N--c(cH,)
I
H
I
H
progressively replaced with alkyl substituents. Lowered melting point, increased solubility, and greater flexibility are correlated with increased substitution, and it is suggested that these effects are due to a large extent to elimination of the hydrogen bonds between the chains.
secondary diamine or a secondary-secondary diamine, or both. For example, a 10-10 polyamide of 35Yc methylation prepared from a mixture of primary-primary diamine and secondarysecondary diamine melts a t about 170' C., whereas one of equal degree of methylation prepared from a mixture of primaryprimary and primary-secondary diamines melts a t about 133" C. These differences in structure are shown by formulas 3 and 4. I n a sample of the type of formula 4 only 17V0 methylation would be required to lower the melting point to 170" C. It thus appears that, for a given number of substituents, the maximum effect on the properties of the polymer is obtained when the substituents are as far apart as possible. The differences in melting point are well illustrated by the melting p o i n t-com p o s i t i o n curves of Figure 1. The area bounded by these curves includes all the melting- -points possible for substituted polyamides of the 10-10 series in which the substituent.is methyl. The boundary to the right (curve 1) is the melting pointcomposition curve for sebacamides prepared from mixtures of decamethylene diamine with pure N,N'-dimethyldecamethylene diamine. The boundary to the left (curve 4) is the analogous curve for mixtures of decamethylene diamine with N0 methyldecamethylene diamine. I1 The straight line a t the bottom (4) .-C-X-( CHJ,,-N(curve 5 ) is the curve for all mixi I turesof N-methyl decameth ylene H CHa
