INDUSTRIAL AND ENGINEERING CHEMISTRY
2748
Vol. 45, No. 12
CONCLUSIONS
The strong dependence of ultrasonic propagation parameters on the extent of cure of phenolic molding resins suggests that they may be used as criteria for the extent of polymerization of phenolic and other thermosetting molding resins. Measurement of these parameters can be made while the resin is undergoing cure in a typical compression mold, thus providing instantaneous information regarding the progress of cure. The technique also seems capable of providing useful indication of the rate of cure. This method, however, will not furnish absolute information relative to the extent or rate of reaction, but may be calibrated against any technique which might yield such information. LITERATURE CITED
(1) Adams, J. H., Bakelite Co., Union Carbide &- Carbon Corp.,
personal communication, July 24, 1952. Auerbach, V., Bakelite Co., Union Carbide & Carbon Corp., personal communication, Dee. 3, 1952. (3) Green, R. B., Barrett. Division, Allied Chemical & Dye Corp., personal communication, Dee. 22, 1952. (4)Mikhailov, I. G., and Gurevich, S. R., Zhur. Eksptl. i Teort. Fiz., 19, 193-201 (1949). (5) Nielson, L. E., Am. SOC.Testing Materials Bull., 165, 48-52 (1950). ( 6 ) Xolle, A. W,, and Rlowry, S. L., J . Acoust. SOC.Am., 20, 432 (1948). ( 7 ) Sofer, G . A., and Hauser, E. A., J . P o l y n w Sci.. 8, 611 (1952).
(2)
1000/T*K
Figure 16.
Relation of Maximum Slope of Attenuation t o Cure Temperature
Data plotted against reciprocal of absolute temperature
tained from the Arrhenius equation, using t h e rate of change of viscosity of polymer solutions, reacting under alkaline conditions ( p H 7.0 to 8.5) a t a series of different temperatures, as an index for the rate of reaction.
RECEIVF for ~ reriew March 30, 1953. ACCEPTED August 15, 1963. Work descrihed is one aspect of the research which constit,uted a doctor of science thesis in the Department of Chemical Enginearing a t the Massachusetts Institute of Technology, Cambridge, llass., under the supervision of E. A. Hauser. Work sponsored by the Plastics Group, Manufacturing Chemists’ .4ssociation, Washington, D. C., under the general direction of Albert G. H. Dietz. professor of structural engineering and director of the Plastics Research Laboratory, RIassachusetts Institute of Technology, Cambridge, Mass.
Viscosity Changes in Thermosetting Resins I
D. I. MARSHALL Development Laboratories, Bakelite Co., Division of Union Carbide 6% Carbon Corp., Bound Brook, N. J .
S
OLID thermosetting resins have been manufactured and
used for many years for molding material and bonding applications in which performance is related to viscosity and reaction speed. Therefore, viscosity-temperature relations up to fabricating temperatures and viscosity-time curves in the fabricating temperature range are of primary concern to the thermosetting plastics industry. However, serious attempts to measure the properties effectively have been announced only recently. The standard test methods used by the industry, such as the hot-plate gel time test, have been useful for production control but have not yielded fundamental data. Recently published work on flow properties of phenolic resins has included three papers dealing with the viscosity of the Novolak (nonsetting) type of resin (2, 4,&). The work included no results on reactive phenolic resins, however. Two methods have been announced for measuring the viscosity of thermosetting resins and following viscosit,y change during reaction, but data had not appeared a t this writing. The methods include a rotating shearing disk viscosity method by Sontag ( 7 ) and an ultrasonic viscosity method by Roth and Rich (6). This paper describes the procedure and presents results obtained using a third method of measuring rapid viscosity changes -namely, the parallel plate plastometer method. Results ob-
tained on several phenolic resins and a silicone resin are presented. The method is not continuous and is not applicable to materials departing appreciably from Newtonian behavior. However, it has the very desirable features of using layers of resin thin enough for rapid temperature equilibrium, no cleaning problem, and an extremely wide viscosity range. THEORY OF METHOD
The theory of the parallel plate plastometer and the application of the device to the measurement of the viscosity of Novolak resins have been described by Dienes (3, 3 ) . Briefly, a test specimen is squeezed between two parallel plane surfaces, causing radial flow, and the distance between the planes, h, is measured as a function of time. I n accordance with the theory, a plot of l / h 4 versus time, equivalent to a deformation-time curve, is constructed and the slope determined. The equation for viscosity is 1 7 =
8.21 X 1 0 W mV2
where 7 = viscosity, poises; W = load on sample, kg.; V = volume of sample, cc.; ?n = slope of the plot, cm.? sec.-l
December 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
2749
NEWTONIAN BEHAVIOR OF THERMOSETTING RESINS
The papers previously cited on flow properties of Novolak resins are in agreement on the Newtonian character of these substances. Data on the reactive resins were lacking, however. Experiments were carried out, therefore, to confirm the Newtonian character of some reactive resins. Figures 1 and 2 show the deformationtime curves obtained. The fast deformations recorded in Figure 1 were recorded with a photographic technique, whereas the curve shown in Figure 2 was obtained by reading the dial micrometer at %second intervals. The linear nature of these plots shows the two-stage resin with hardener, the self-hardening resol resin, and the silicone resin to be essentially Newtonian under the condi- . tions of the tests. With most phenolic resin samples this behavior holds true until the viscosity a t 140” C. has increased by a factor of approximately 100, at which point non-Newtonian behavior commonly appears as a result of increased molecular weight and increased cross linking. Further indication of whether a material is Newtonian can be had by carrying out repeated parallel plate viscosity tests using different loads and sample sizes. Variations in viscosity results greater than those obtained under constant loads and sample sizes are an indication of anomalous flow properties. Many resins show this behavior in the later portions of the viscositytime curves, but in the initial portions the method revealed no anomalous flow properties.
6
TWO-STAGE RESIN WITH HARDENER 910 POISES
2
PROCEDURE
Some simplification of the viscosity measurement is possible where linear deformation-time plots such as those shown in Figures 1 and 2 are obtained. I n this case two points only are required to determine the slope. The curves will be concave toward the time axis if the resin is hardening during the test
0
TIME IN SECONDS
Figure 1. Deformation-Time Curves on PhenolFormaldehyde Resins at 140’ C.
Equation 1 is the basic equation by which viscosity values are determined and used to construct viscosity-temperature curves or viscosity-time curves on thermosetting resins. I
I
I
10
20
30
40
50
TIME IN SECONOS
Figure 2.
Deformation-Time Curve on Silicone Resin at 150’ C. Viscosity 3 X lo6 Poises
Figure 3. Viscosity-Temperature Curve and Viscosity-Time Curve on Resol Phenolic Resin
INDUSTRIAL AND ENGINEERING CHEMISTRY
2750
VOI.
45, No. 12
i
6
,/
%w I
0
C. T~~r,STfiGE--PH_ENOLIC
D. SILICONE
/0
40
8. RESOL PHENOLIC RESIN AT 140' C.
eo
120
TIME
Figure 4.
i 6 0 ° C.
RESIN AT
200
160 IN SECONDS
2,
0
Yiscosity-Time Curves on Three Different Types of Thermosetting Resins
or if the resin has advanced to a point where non-Newtonian flow becomes noticeable. The effect of hardening may be minimized by speeding up the test, but anomalous flow is more troublesome. 6
I
I
I
5
30
60
90
120
150
180
TIME I N SECONDS AT 14OOC.
Figure 5 .
Yiscosi ty-Time Curves on Three Different Two Stage Phenolic Resins
When the curvature is not too pronounced, the slope of a secant to the curve, which approximates the slope of the tangent a t a point midway between the two time values, may be used as the measure of viscosity. With resinous materials that already are non-Newtonian in the initial melts, the parallel plate method i9 of very limited usefulness. Its use is further limited to conditions under which foaming is not severe. Equation 1 was made more convenient by representing the proportionality constant and normalization factor by s ingle quantity, 8'. Equation 1 then becomes
4
120. G= H *
3 u) W
c.
RESOL RESIN TWO-STAGE RESIN
-
SECONDS
9
100
2
200
300
400
500
6
f F
3' 3
140' C. A= RESOL RESIN I = TWO-STAGE RESIN
2
I
I
30
60
I
90
I
120
I
150
TIME IN SECONDS
Figure 6.
Viscosity-Time Curves at Two Different Temperatures
By setting up a chart indicating F values for practical loads and specimen sizes, and a table of Allh4 values for practical intervals of h , the calculations are reduced to a minimum. The need for cleaning the testing apparatus is eliminated by using 0.001-inch aluminum foil to separate the resin from the metal plates. The test samples are pressed into pellet form from pulverized or granulated resin. A series of tests is carried out a t different temperatures to construct a viscosity-temperature curve, and at different heating times to construct a viscosity-time curve. For the latter, each test pellet is rapidly pressed to a thickness of about 0.8 mm., where effective temperature equilibrium requires approximately 3 seconds' time, and the position is held for the desired heating time. A4tthe end of the heating time the force is applied to squeeze the sample and a specified interval of thickness is timed. The viscosity value is computed and plotted a t the time value obtained by adding the heating period to one half the time required for the viscosity reading. Two viscosity values may be obtained in a single test by timing two thickness intervals. In cases where it is desired to extend a viscosity-time curve into the region of anomalous flow properties it is helpful to plat de-
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1953
275 1
Applying the analysis to curve A (Figure 3) one finds that t h e resin had a n initial viscosity of 80 poises, required 112 seconds for viscosity to increase by a factor of 100, required 141 seconds for viscosity to reach 106 poises, and had a fluidity-time integral of 0.475 sq. cm./dynes (0.475 strain per unit of stress).
I
6
5RESULTS ON SEVERAL RESINS
4TWO-STAGE RESIN K = I.l%WATER J * .3% WATER
Z
Viscosity-time curves are shown in Figures 3 to 7 on several phenol-formaldehyde resins and a silicone resin. The data obtained from the curves are listed in Table I. These results illustrate the wide ranges of viscosity and reaction speed that a r e found among thermosetting resins. Curves A and B represent base-catalyzed resol type resins. Curves C, E, and F show a, wide range of behavior found in three two-stage resinsNovolak resins with hardener. The hardener for the two-stage resins was hexamethylenetetramine added in the amount of approximately 10% by weight. The differences in initial viscosity found among the two-stage resins represent differences in the mole ratio of formaldehyde to phenol, the ratios ranging in this case approximately from 0.80 to 0.86. Curve F represents a fastrcuring, two-stage phenolic resin (11. Curve D is that obtained on a thermosetting silicone resin of the methyl phenyl polysiloxane type catalyzed with 0.25% triethanolamine. The silicone resin was much slower in its reaction a t 150 C. than any of the phenolic resins a t 140 C.
-
6-
P
4-
RESOL RESIN
O
B*
L* II
0
2% WATER I %WATER I
60
30
90
120
T I M E I N SECONDS AT
150
I
180
-
140. G.
.4 W
z
*n ai
z 0
.e-
: I-
*
-
:
li 0 20
IO
INCLINED-PLATE
I
I
I
40
50
60
FLOW AT
125'C.
30
IN MM.
Figure 8. Correlation between Fluidity-Time Integral and Inclined-Plate Flow
The effect of temperature on the viscosity-time curve is illustrated by the curves shown in Figure 6. T h e reaction of the two-stage resin (curves H and I ) was more sensitive to temperature than that of the resol (curves A and G ) .
TABLE I. DATAFROM VISCOSITY-TIME CURVES
Curve A C
It gives a measure of the maximum shear strain theoretically obtainable per unit of stress. I n other words, i t is a measure of the amount of flow t h a t will be experienced in an idealized situation.
I
0
B
(3)
.I-
G
METHOD O F ANALYZING THE VISCOSITY-TIME CURVE
Neither a theoretical nor an empirical relation for fitting the the viscosity-time curves has been found. One has several choices for obtaining useful quantities from the curves, however. The initial viscosity may be selected as a measure of how soft the resin will become. As a measure of reaction speed, the time required for viscosity t o change by a factor of 100 was chosen. A third property, which perhaps is of more interest to the fabricator, is the time required to reach a certain viscosity level. Still a fourth property was obtained by plotting the reciprocal viscosity against time and measuring the area under the curve. T h e integral so obtained, which may be termed the fluidity-time integral (FTI), is further defined as
.3-
-z
formation-time curves from readings taken a t several time values. Anomalous flow curves so obtained can be used t o draw tangents a t different points, thereby yielding two or more viscosity values per curve. While laborious, this procedure improves accuracy where anomalous flow is encountered. A sample result combining a viscosity-temperature curve and a viscosity-time curve is shown in Figure 3. This plot serves to illustrate the tremendous viscosity range available. Such a combination curve offers a picture of the viscosity changes that take place when the resin is carried through an idealized melting and curing cycle. I n this paper the melting portion is not taken up in detail; rather attention is focused on the hardening portion.
= Jrn
-
u)
Figure 7. Viscosity-Time Curves at Different Values of iMoisture Content
FTI
O
D E
F
a
H I J K L
Resin Type Resol Resol Two-stage Silioone Two-stage Two-stage Resol Two-stage Two-stage Two-stage Two-stage Resol
C. 140 140 140 O
150 140 140 120 120 140 140 140 140
Initial See. to See. to Viscosity, Increase Reach Poises X 100 106 Poises 112 80 141 21 118 92 320 95 101 25tiO 350 250 2050 88 93 48 56 38 600 420 393 4200 520 ,586 320 97 104 250 111 95 170 135 96 81 30 96
FluidityTime Integral S Cm 1 8yni 0.475 1.73 0.149 0.032 0.020 0,400 0.227 0.056 0.116 0,194 0.239 1.16
2752
INDUSTRIAL AND ENGINEERING CHEMISTRY
Viscosity and reaction speed were both very sensitive to temperature in a compensating manner, but with the examples given, the viscosity effect predominated, resulting in a net increase in flow with increasing temperature (compare curves H and I or curves A and G ) . However, the fact that the temperature sensitivity of viscosity becomes smaller a t higher temperatures (6) leads to the conclusion that a temperature of maximum flow exists. This checks with the experience of the thermosetting plastics industry where temperatures of maximum flow are commonly encountered. Moisture plasticizes phenolic resins (a). The effect of moisture on the viscosity-time curves is shown by Figure 7 . The results indicate that moisture not only plasticized the two-stage resin, but increased its initial reaction rat& The acceleration was not large, however, and later became of no consequence when the wetter sample failed to harden to the degree that the dryer one did. This result brings out the inadequacy of a single-point test for hardening speed, indicating that the complete viscosity-time curve is needed for interpreting flow- behavior. I n the case of the resol the effect of moisture was somewhat different, the wetter sample remaining softer throughout. The explanation for the difference probably lies in the fact that water is a reaction product in the resol; therefore, the presence of water may tend t o retard t h e reaction through the influence of an equilibrium effect. The results obtained at different levels of moisture content indicate that moisture tends to cause the viscosity to level off a t a lower plateau, indicating a lowering of the rigidity of a cured article. High moisture content, therefore, while giving rise t o greater flow, may be a disadvantage in applications requiring high rigidity a t the end of the curing cycle. It is interesting to compare the fluidity-time integral with the inclined-plate flow teet commonly used in the grinding wheel industry. The inclined-plate flow test uses a pellet of resin placed on an inclined glass plate a t 125" C. to determine how far
Vol. 45, No. 12
the resin will flow, which is a crude approach to the property represented by the fluidity-time integral. Figure 8 shows graphically the degree of correlation obtained between fluiditytime integral a t 140' C. and inclined-plate flow at 125" C. for several phenolic resins covering wide ranges of viscosity and reaction speed. The correlation between the two properties is not bad in spite of the temperature difference and the crudeness of the inclined-plate flow test. The parallel plate plastometer was found useful for measuring rapid ViscoEity changes. Although it has not been applied to other types of thermosetting resins, it should be applicable except where departure from Newtonian behavior is appreciable or where foaming is severe. ACKNOV('LEDGMF,YT
The author wishes to acknowledge the assistance and helpful criticisms from his associates a t Bakelite Co., particularly F. D. Dexter, V. E. Meharg, W-. A. Zinzow, and H. M. Quackenbos, Jr. LITERATURE CITED
(1) Bender, H. L., a n d F a r n h a m , A. G., U. S. P a t e n t 2,475,587 ( J u l y 12, 1949). (2) Dienes, G. J., J . Colloid Sci., 4, 257-64 (1949). (3) Dienes, G. J., a n d Klemm, H. F.. J . A p p l . P h y s . , 17, 4 3 - 7 1 (1946). (4) Guzzetti, A. J., Dienes, G. J., a n d Alfrey, T., J . Colloid Sci., 5, 202-17 (1950). ( 5 ) Jones, T. T., J . A p p l . Chem., 2, 1 3 4 4 9 (1952). (6) Rqth, W., a n d Rich, S.R., J . A p p l . Phys., 24, 940-50 (1953). (7) Sontag, L. A,, U. 3. P a t e n t 2,574,715 (Nov. 13, 1951). RECEIVED for review June 4 , l K 3 . ACCEPTEDAugust 13, 1953. Presented before the Division of Polymer Chemistry at the 124th Jfeeting of the z h E R I C A X CHEMICAL SOCIETY, Chicago, 111.
Rosin Acid-Rubber Master A STUDY OF COMPOUNDING VARIABLES J. F. SVETLIIL AND R. S. HANRIER Research Disisian, Phillips Petroleum Co., Phillips, Tex.
T
HE use of relatively large amounts of rosin acids as extenders
for synthetic elastomers of high Mooney viscosity is a comparatively recent outgrowth of oil extension of similar types of polymers. Earlier work had been carried out on latex masterbatching of moderate quantities of rosin soaps ( 6 ) . Rosin and other organic acids \?-ere also evaluated by other investigators (8) in amounts up t o 9 parts based on the elastomer. These investigations showed that certain vulcanizate properties were improved by the addition of rosin, especially tensile strength, heat generation, and processability. Howland et al. (5) reported that an elastomer of high Mooney viscosity masterbatched with up to 33 parts of rosin acids gave vulcanizates having excellent tensile strength, heat generation, tear strength, abrasion resistance, and resistance to flex-crack growth. These properties were observed both before and after accelerated oven aging. These same investigators reported that latex masterbatches gave superior products compared t o those prepared by addition of the rosin acid during compounding, that masterbatching with black aided in overcoming processing problems of the rubber-rosin acid crumb, and that coagulation with various metallic salts offered little advantage over conventional brine-acid techniques. Other groups active in the development of rosin acid masterbatches have shown
substantially the same trends in improvements from extension with rosin acids (i-4, 7 ) . Only very limited information has been disclosed for masterbatches containing larger amounts of rosin. I n view of this, masterbatches containing variable amounts of rosin were studied systematically t o establish the maximum amount of this extender that can be utilized without causing serious degradation of vulcanizate properties. It was also believed that higher zinc oxide levels might be desirable, especially in the masterbatches containing the larger quantities of rosin acid, in view of the possible formation of zinc rosinate during vulcanization. Accordingly, a systematic stiidy has been made of a series of masterbatches of 150-Mooney GR-S-1500 in which the rosin acid content was varied from 0 to 200 parts per 100 parts of rubber. Zinc oxide levels of 3, 5 , 10, 15, and 20 parts per 100 parts of masterbatch were evaluated a t each rosin level. To establish the optimum compounding formulation for use with a rosin acid-extended elastomer, other compounding variables were investigated. The masterbatch selected for this portion of the work contained 100 parts of rosin acid per 100 parts of rubber. The effects of varying the pigments, softener level, and curatives were evaluated.
