Table IV.
'l
Effects of Molecular Weight and Structure of Diol on MOCA-MDI Urea-Urethane Elastomersa Shore d Tensile 700y0Modulus Elongation, 7, Graves Tear Hardness
Pluracol P-2010 1480 2400 PPG-1527 Poly(ethyleneadipate) 2000 5050 Based on formulation in Table I with 0.200p.p.h. ( N H ?
+
650 1060 880 O H ) stannous octoate.
cster, in the latter cases: considerable improvement of properties occurred. This, perhaps. may be due to a better balance of reactions during chain buildup and to an increase in intermolecular forces. literature Cited (1) Xxelrood, S. L.! Hamilton, C . LV.. Frisch, K. C.. Itid. Eng. Chem. 53, 889 (1961).
( 2 ) Bennet, Mi. B., Saunders, J. H., Hardy, E. E., AlabamaXcad. Sci. Meeting, Tuscaloosa, Ala., April 1954. (3) Blaich, C. F., Sampson, A. J., Division of Rubber Chemistry, 138th Meeting, XCS, New York, September 1960. (4) Britain, J. LV., Gemeinhardt, P. G.. J . Appl. Polymer Sci. 4, 207 (1960). (5) Dirkinson, I>..I.. Rubher Aqe 82, 96 (1958).
290 453 455
5 60 690 930
83 86 88
(6) Heiss, H. L., Zbid., 88, 89 (1960). 17) Hostettler, F., Cox, E. F.. Znd. Ene. Chem. 52, 609 (1960). . . (8) Kogan, I. C.,.J. Org. Chem. 26, 3504 (1961). (9) Morton, M., Deisz: M. A , , 130th Meeting, ACS, =\tlantic City, N. J., September 1956. (10) Morton, M., Deisz, M. A , . Ohta, M., U. S.Dept. Commerce Rept. PB-131795 (March 1957). (11) Smith, T. L., Magnusson! A . B., Jet Propulsion Lab.. Calif. Inst. Technol., External Publ. No. 598, May 12, 1960. (12) Smith, T. L., Magnusson, A . B., J . Polymer Sci. 42, 391 (1960). (13) Ll.-olfe. H. I\., Jr., E. I. du Pont de Nemours Sr Co., "Catalyst Activity in One-Shot Urethane Foam," March 16, 1960. Feb. 24. 1961. RECEIVED for review December 16, 1963 ACCEPTED March 16. 1964
HIGH-PERFORMANCE T O L U E N E DIISOCYANATE-POLYPROPYLENE
GLYCOL CASTABLE ELASTO PLASTICS S.
E D M U N D BERGER AND WACLAW SZUKIEWICZ
Research CY Deuelopment Department, National Aniline Division, Allied Chemical Cor$., Buffalo, IV. Y .
This paper deals with relatively inexpensive castable polymers based on toluene diisocyanate and polypropylene glycol and having mechanical characteristics of both elastomers and plastics. Formulation changes that increase strength and hardness have an unfavorable effect on elasticity. Generally, the described polymers have better mechanical properties than similar known materials. Polymers produced b y the one-shot method seem to exhibit better heat-aging properties than prepolymer-derived analogs. A range of applications i s suggested. HE USE of cast urethane polymers in mechanical applicaTtions is rapidly gaining momentum, as indicated by their increasing acceptance in areas where conventional rubbers, plastics, and metals were previously used. Generally, cast urethane polymers show outstanding strength, flexibility, toughness, and abrasion resistance combined with high load-bearing and good low-temperature properties, elasticity, and resistance to oil, chemicals, and oxidation. However, as in other polymer systems, a single composition usually does not exhibit. all these desirable characteristics; furthermore, some combinations of properties can be achieved more economically than others. The most economical polymers can usually be formulated with toluene diisocyanate (TDI) and a polypropylene glycol. Such systems have found application as sealants, adhesives, potting compounds, etc. In general, however, much of the published literature describing polymers of this type deals with soft materials of relatively low strength (7, 2, 4, 7 7 ) . Work in our laboratories has shown that excellent, low-cost, hard TDI-polypropylene glycol cast urethane polymers of high strength are also feasible.
The principles governing urethane polymerization are well known. Processing can be stepwise (prepolymer method) or by the one-shot procedure. In the prepolymer process, a polyol reacts with excess diisocyanate to form an NCOterminated, low molecular weight, liquid prepolymer which, in a second step, is cured with a polyamine or a polyol, usually a t elevated temperature. By the one-shot process, all ingredients, including the curing agent, are mixed just before casting and the mixture is then cured. In either process the amount of diisocyanate used may be equal to or greater than that stoichiometrically required to react with the active hydrogen-containing components (polyols or polyamine). In the first case, an essentially linear polymer will result; in the second, the polymer will be cross-linked. The polymers discussed herein are of the one-shot, cross-linked type. Preliminary Work
The system based on T D I , polypropylene glycol (mol. wt.
1000) (PPG), 1,4-butanediol (BD), and 4,4'-methylenebis(ochloroaniline) (MOCA) was subjected to a preliminary study. statistically designed to determine the effects of these four components on polymer characteristics. VOL. 3
NO. 2 J U N E 1 9 6 4
129
VARIABLE
levels of Variables Studied
[iYCO] [OH f NH?]
Lower Level
Center Paint
Cpper Level
1.05
1.10
1.15
0.33
0.45
0.69
0.05
0.12
0.20
The results? summarized in Figure 1> are based on a regression equation of the folloiving form, calculated for each dependent variable ( 5 ): 60
80
+ 61x1 f bzx: -t
where Y = dependent variable (response) ho = mean value of response 61: 6 2 , . = coefficients showing effect of individual variable on mean value .
,
-
X 100
where b i = b l . 6 2 . , . . For simplicity, interactions between variables are neglected. The horizontal bars shown in Figure 1 are proportional to the expected change in the individual responses when the independent variable is increased from the center point to the upper level. These results show that, in the system studied, a change in composition designed to increase strength (tensile strength. tear strength, hardness, etc.) will have an unfavorable effect on elasticity properties (decreased true elasticity and elongation, increased hysteresis loss). Similar trends have been observed previously for both polyester- and polyether-based urethanes (7. 2, 4, 70, 7 7 ) . This early work? however, also indicated the possibility of designing interesting, tough. strong elastoplastics (polymers having both elastomeric and plastic properties). In the follo\i-ing, the more significant aspects of our research on such polymers to date are discussed. Experimental
Materials. Actol 22-1 10 Diol (Allied Chemical Corp.) (polypropylene oxide diol, mol. wt. 1000) and 1,4-butanediol, anhydrous grade (Akron Chemical Co.), were used without
Table I. Composition of Polypropylene Glycol-TDI Elastoplastics Process
Prepolymer Formulation
A
B
C
D
___~
E
Parts by Weight
Actol22-110Diol 1,4-Butanediol MOCR
Nacconate 80 Dibutyltin dilaurate Raw material cost/ pound, 8
130
42.7 10.7 8.5 38.1 0.020 0.50
48.1 55.5 54.4 12.0 6.9 ... 2.3 6.8 20.7 37.6 30.8 24.9 0.012 0.012 . .. 0.44
0.44
20
40
€0
80
TENSILE MODULUS TEAR STRENGTH ABRASION RESISTANCE HARDNESS ELONGATION COMPRESSION SET HYSTERESIS LOSS ELASTIC RECOVERY TENSILE STRENGTH TENSILE MODULUS TEAR STRENGTH ABRASION RESISTANCE HARDNESS ELONGATION COMPRESSION SET HYSTERESIS LOSS ELASTIC RECOVERY
0.53
€0
40 20 0 20 40 RELATIVE LINEAR l
60 E
80 E
Figure 1. Per cent mean linear effect of individual variables based on mean value of response
60
One-Shot
0
TENSILE STRENGTH
(BD]
E -D
Per cent mean linear effect =
20
[z]
= independent variables
bi
40
TENSILE STRENGTH TENSILE MODULUS TEAR STRENGTH ABRASION RESISTANCE HARDNESS ELONGATION COMPRESSION SET HYSTERESIS LOSS ELASTIC RECOVERY
80 .XI,1 2
60
I
Dibutyltin dilaurate (0.012 % by weight) was used as the catalyst, and the polymers were cured 15 minutes a t 130" C. followed by 16 hours a t 100' C .
I' =
RESPONSE
63.5
...
14.7 21.8
...
0.47
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
further modification. These materials contained less than 0.02'37, of water. The diisocyanate employed was Sacconate 80 (Allied Chemical Corp.), an 80:20 mixture of 2.4- and 2,6-toluene diisocyanate (acidity 0.003%). 4,4'-Methylenebis (o-chloraniline) (E. I . du Pont de Nemouri 8 i Co., Inc.) and T-12 dibutyltin dilaurate (M. 8i T. Chemicals. Inc.) were used as received. Processing. ONE-SHOTMETHOD. A premix of polyols and M O C A was heated to 90 ' C. to dissolve the M O C A and then cooled to 80 'C. The catalyst was added! and the mixture degassed under a vacuum of 5 mm. of mercury. Nacconate 80 was introduced all at once and the resulting mixture stirred a t high speed for 30 seconds. The system was rapidly vented with dry nitrogen. The mixture was poured into a cavity mold preheated to 150 ' C., then allowed to gel for 15 minutes a t 130' C. under pressure. After demolding, the specimen was cured at 130' C. for 4 to 8 hours. Pot life was 0.5 to 6 minutes. PREPOLYMER METHOD. ' l h e Actol poly01 was gradually added to excess T D I and the mixture heated 3 hours a t 80' C . The resulting prepolymer was converted to an elastomer b!. the technique described for the one-shot procedure, except that the prepolymer and the curing agent were mixed a t 110' C . and no vacuum was used. Pot life was approximately 1 to 2 minutes. Testing. ,411 specimens \\ere allowed to age 10 days at 24' C. and 507, RH prior to testing. The following test methods were used : .4S7'.\1 .\.frthod
Specific gra\ ity Hardness, shorr Tensile strength Elongation at break Tensile modulus Tear strength Torsional modulus (for 7 i by Clash-Berg method) Abrasion resistancr Compression load Compression set Elastic recoverv
D D D D D D
297-551' 1484-59 412-51T 412-51T 412-51T 624-54, Die C
D 1043-51
D D D A
1044-56 575-46, Method A 395-55, Method B '/,-inch thick X '/8-inch wide strip was placed under a 13-kg. load for 4 minutes; recovery from strain was measured us. time after load was released (6)
,
I
.-
E
A B O
5000 r
I I
.+
6000r
ln
0
v,
A C Shore Hardness ,O
A B D
c E
70 51 60 33 34
D v,
z
E
Y 0 Figure 2.
100
200 300 400 ELONGATION, O/!
E
1000-
500 0
Tensile stress-elongation curves
Figure 3. Results and Discussion
'The composition of the elastoplastics studied is given in 'Table I ; mechanical properties are shown in Table I1 and Figure 2. The data in 'Table I1 clearly illustrate the feasibility of formulating products with a wide range of excellent elastoplastic characteristics a t a high level of tensile strength. 'This wide formulation latitude is characteristic of urethanes in general. The stress-strain curves for these materials (Figure 2) show a transition from products with elastic characteristics ( E and C) having no yield point to the product with a well defined yield point ( A ) typical of plastics (3>8). As expected, this transition correlates with hardness and the other mechanical properties of these materials. Thus, the softer, more elastic products (C and E ) also exhibit, for example. lower moduli, higher elongation, lower compression load, and lower tear strength than the harder products. Surprisingly, however, tensile strength does not clearly reflect thrse differences i n mechanical behavior. The dry heat-aging behavior of the five formulations studied is shown in Figure 3. As can be seeii, here the correlation with hardness no longer holds. Instead, the data indicate a striking difference in the behavior of the two types of polymers studied. \$'hereas products '4, B, and c' obtained by the oneshot technique exhibit relatively good resistance to heat aging as indicated by the gradual slope of the corresponding tensilrtemperature curves, products D and E , prepared by the prepolymer route? exhibit a rather rapid loss of tensile strength in the early stages of aging. Since the possibility existed that this unexpected result was caused by the differences in composition of these polymers, a prepolymer-type product ( F ) of the same composition as A was also evaluated. The results (Figurr 4) support previous findings. While the tensile strength and hardness of A and F are essentially identical, the heat resistancc of the product obtained by the onc-shot process is superior to that of the prepolymer-based one. The t\vo polymers also show different glass transition temperatures. These findings indicate that the t\vo processes give rise to structural differences, probably differences in the distribution of building blocks along the polymer chains. Data illustrating the behavior of product 4 on immersion into different liquid media are shown in Table 111. As can be seen. resistance to ivater: aqueous acid and alkali, oil, and ali-
Table II.
20
1 6 8 12 HOURS AT 15OOC.
4
24
Effect of heat aging on tensile strength
Mechanical Properties of Cured Polypropylene Glycol-TDI Elastoplastics Process _ _ ~ One-Shot Prepolymer__ _ _ Formulation ~ ~ _ A B C D E ~
I
-
Cure l i m e , Hours at 730" C. - _ _ 4 4 4 4 1.18 1.17 116 1.17 1.14 70 51 33 60 34 8
Specific gravity Hardness, shore 11 Tensile strength. psi. 5000 Elongation, $6 190 'Tensile modulus (lOO~e), p.s.i. 3600 Tear strenqth, p i . 720 Abrasion &stance, wheel C-18, 1000-g. load, mg./1000 cycles 260 Compression load, 20% deflection, p.s.1. 4550 Compression set (20% deflection), c /e 48
5500 260
4300 380
5200 270
4900 490
2600 620
1200 440
3000 720
410
278
250
200
224
1880
1100
2800
850
24
23
27
28
960
5000
I w
\F Tensile Strength
1 v,
0 Figure 4.
4
Hardness
Shcfe D
0 HOURS AT
12 16 150°C.
20
Effect of heat aging on tensile strength One-shot vs. prepolymer system
VOL. 3
NO. 2
JUNE 1964
131
_
Table 111.
Resistance of Elastoplastic A to Hydrocarbons, Water, and Aqueous Agents
Immersion time: 168 hours.
Original hardnesr: 70D.
Immersion Medium
Ttmp. ! C.
Hardness, Shore D after Immersion
Water Water Water 10% HzSOi 10% NaOH ASTM oil 1 ASTM oil 3 Octane
25 50 70 25 25 25 25 25
67 42 39 62 64 70 68 68
Table IV.
Hardness, shore Tensile strength, p.s.i.
Table V.
Comparison of Polypropylene Glycol-TDI Polymers with Commercial Urethane Elastoplastics Polyprojylene PolytetraGlycolmethylene PolyesterTDI, Glycol- T D I MDI Formula A TYP (Prepolymer) (Prepolymer) ( One-Shot) Specific gravity 1.15 1.20 1.19 Hardness, shore D 70 69 70
Tensile strength, p.s.i. 6000 4000 5000 Cost to consumer per pound of cured product, 6 1.12” 0.96“ 0.50 Includes vendors’ prepolymer price plus cost of curing agent. Prices prevailing August 1963.
Variation of Tensile Strength with Hardness for Three Urethane Systems Polyester-MDI” 88-91 A 83-85
D ... 6500-7500
50-55’ 5000-6000
6000-7000
55-60’ 4000-4500
66-69’ 3500-4500
Polvtetramethvleneb Glvcol- T D I
Hardness, shore Tensile strength, p.s.i.
A 85 D ,.. 4500
92
...
5000
..
70 6000
Polypropylene Glycol- T D I
Hardness, shore Tensile strength, p.s.i. 0
See ( 9 ) .
b
A 70A D ... 3000
... 33 4300
See (7).
phatic hydrocarbons is very good, as indicated by relatively slight changes in hardness. At higher temperatures, water immersion tends to soften the polymer. Resistance to water, in general, can be improved by formulation adjustments-for example, by replacing butanediol with a triol such as trimethylolpropane. In Tables I V and V, the properties of elastoplastics derived from polypropylene glycol and T D I are compared with similar products based on polytetramethylene glycol-TDI and polyester-MDI. As can be seen (Table IV), the polyester-MDI undergoes a significant decrease in tensile strength as hardness is increased. The two TDI-based systems, on the other hand, show an increase in tensile strength a t increasing hardness. Thus, a t a hardness level of 70 D, the polypropylene glycolT D I system occupies an intermediate position as regards tensile strength (Table V). The impact resistance of the two T D I based systems was also measured and found to be very good, the polytetramethylene glycol-derived product being somewhat better in this respect than product A . O n the other hand, the considerable economic advantage of the one-shot polypropylene glycol-TDI system is obvious. Conclusions
Low-cost polypropylene glycol-TDI elastoplastics of high strength and very good mechanical, chemical, and heat-aging characteristics are feasible. While only selected systems have been discussed, a wide range of products of different characteristics can be obtained by suitable formulation changes. This is particularly facilitated in the one-shot system.
132
... 70 5000
I&EC P R O D U C T RESEARCH A N D D E V E L O P M E N T
Elastoplastics of the type described should find applications where a combination of hardness, strength, impact resistance, and abrasion resistance is needed-for example, in impellers, propellers, tooling fixtures, industrial rolls, bearings, bushings, air hammers, wear plates. solid tires, and valve seats. Use in gears, for example. for business machines, should also be feasible in view of the known self-lubricating, low-noise performance of urethane elastoplastics in this application. literature Cited
(1) Axelrood, S. L., Hamilton, C. W., Frisch, K. C., Znd. Eng. Chem. 53, 889 (1961). (2) Bylsma, H. R., Pitchforth, L. L., Jr., Division of Rubber Chemistry, ACS, Fall Meeting, Oct. 18, 1962. (3) Carswell, T. S., h’ason, H. K., Mod. Plastics 21, 121 (1944). (4) Damusis, A , , McClellan, J. M., Wissman, H. G., Hamilton, C. W., Frisch, K. C . , IND.ENG.CHEM.PROD.RES. DEVELOP. 1, 269 (1962). (5) Davies, 0. L., “Design and Analysis of Industrial Experiments,” 2nd ed., Hafner Publishing Co., New York, 1956. (6) Houwink, R., “Elastomers and Plastomers,” Vol. 111, p. 32. Elsevier, New York, 1948. (7) Nadler, M. L., Rubber World 144, 78 (1961). (8) Xielsen, L. E., “Mechanical Properties of Polymers,” p. 101, Reinhold, New York, 1962. (9) Pigott, K. A , , Cote, R. J., Ellegast, K., Frye, B. F., Mueller, E., Archer, T V . , Allan, K. R., Saunders, J. H., Rubber Aqe 90, 629 (1962). (10) Saunders, J. H., Rubber Chem. Technol. 83, No. 5, 1259 (1960). (11) Smith, T , L., Magnusson, A. B., J . Polymer Sci. 12, 391 (1960).
RECEIVED for review February 12, 1964 ACCEPTEDApril 15, 1964
20th Annual Technical Conference, Society of Plastics Engineers, Inc., Atlantic City, N. J., January 1964.
