. February 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY SUMMARY
Cation exchange resins of pure hydrocarbon structure, such as sulfonated styrene-divinylbenzene polymers, are resistant to attack by chlorine of any concentration, the only result of contact being to bleach the sulfonated polymer. Cation exchangers of sulfonated phenol-formaldehyde or carbonaceous types require varying amounts of chlorine to cause disintegration. The result of such attack is the formation of water-soluble, colored breakdown products which causes colored effluent after stand periods.
d
315
A probable mechanism for the attack of chlorine on sulfonated phenol-formaldehyde resins is offered. LITERATURE CITED
(1) Datta and Bhoumik, J. Am. Chem. SOC., 43, 314 (1921). (2) Datta and Mitter, Ibid., 41,2028 (1919). RECEIV~D November 8, 1948. Presented before the Division of Water, Sewage, and Sanitation Chemistry a t the 114th Meeting of the A\IERICAN CHEMICAL SOCIETY, St. Louis, Mo.
Plasticizing Crystalline Polymers C . B. HAVENS T h e Dow Chemical C o m p a n y , Midland, Mich. Methods used for the evaluation of plasticizers in vinylidene chloride copolymers are presented. Equations are derived which express plastics properties as a function of plasticizer concentration. For each plasticizer three oonstants--jl(,, ICrn, and &-are determined. These constants express plasticizer effectiveness in reducing melt viscosity, modulus or stiffness, and flex temperature, respectively. The effect of copolymer composition upon plasticizer compatibility and effectiveness is shown. Impact, tensile strength, and elongation data are presented.
L
4
INEAR crystalline polymers are becoming increasingly important, particularly in the textile field. Notable among these are vinyl chloride, vinylidene chloride, ethylene, and amide-type polymers and copolymers. Because some of the properties of such polymers may be appreciably modified by the addition of plasticizers, their plasticization is of considerable technological interest. The development of adequate plasticizers requires a n understanding of the mechanism of plasticizer action. Furthermore, rapid and reliable means of evaluation are desired. Crystalline polymers differ from amorphous polymers, among other things, in that high tensile strengths are developed at relatively low molecular weights. The amorphous polymers derive their strength largely from the intermingling of the long polymer chains and the relatively weak van der Waals forces between them, Linear crystalline polymers derive their strength largely from relatively strong secondary valence bonds between polymer chains. This results in more or less ordered areas or crystallites. The secondary valence bonds in crystalline polymers are somewhat analogous to cross linking in rubber, and may be considered as intermediate between the weak van der Waals forces operative in amorphous polymers and the primary valence cross links in cross-linked polymers. I n this paper, methods of plasticizer evaluation are presented and discussed. Such properties as melt viscosity, stiffness, and crystallization are considered and experimental data on vinylidene chloride-vinyl chloride copolymers are presented. The term Saran B is used here to indicate a copolymer of 8570 vinylidene chloride and 15y0 vinyl chloride. TEST METHODS
In investigating large numbers of compounds as plasticizers, i t is desirable to have a rapid, reliable means of evaluating plasticizer effectiveness at normal use temperatures (0 'to 100' C.), a t low temperatures (-20" to -50" C.), and a t the fabricating temperatures (140" to 200" C.). The vinylidenc chloride-
vinyl chloride copolymers investigated appear to be Newtonian fluids at 180" C. Viscosity at 180' C. was determined by means of a parallel plate plastometer. Young's modulus us. temperature data from -30" to 150' C. were obtained, using the apparatus of Moll and LeFevre ( 3 ) . Specimen size was approximately 2 X 0.25 X 0.020 inch. Impact, tensile strength; and elongation data were obtained using conventional type equipment and small scale test specimens rather than -4.S.T.M. test specimens. MELT VISCOSITY
I n the fabrication of vinylidene chloride-vinyl chloride copolymers, the melt viscosity is an important consideration, The logarithm of the melt viscosity varies linearly with plasticizer concentration. This may be expressed mathematically as: log &V/ = log N o
- K,B
(1)
where N j is melt viscosity, in poises, of the plasticized polymer; N O is melt viscosity, in poises, of the unplasticized polymer; K , is a constant denoting plasticizer effectiveness in reducing melt viscosity; and B is per cent plasticizer. For a given copolymer composition, K, is independent of polymer molecular weight. K, varies somewhat with copolymer composition. With rare exceptions, the equation is valid over the range of 0 to 16% plasticizer, and usually over the range of 0 to 30% plasticizer. Typical data are given in Table I.
OF SARANB us. PLASTICIZER TABLE I. PROPERTIES CONCENTRATION
Viscosity,
a
b
Modulus .Young's
Lb./Sq. Inch X 10-4 at 40' C. 10.0 8.8 6.4 6.3 4.1 16 3.0 Ku = 0.070. K m = 0.033. Kt = 2.06. Tempcrature a t modulus of 25 X 104 lb./sq. inch.
1-Chloronaphthalene" 0 2 4 8 12
Poises at 180' C. 33,000 25,000 17,500 8,400 4,900 2,500
Flex Temperature, C.b 15 10 5 0 - 8 17
-
The equation has also been found t o hold for plasticizer mixtures: log Nf = log No
- (KviBi + KesBz . . .)
(2)
wherein subscripts 1, 2, etc., indicate the first and second component, etc. Typical examples of calculated observed values for multicomponent compositions are given in Table 11.
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
316
TABLE11. MELT VISCOSITY
MULTICObIPONEPiT COMPOSITIONS
No I
2
Plasticizing Componrnts
i:C
D
OF
%
Kt
2.5
0.073\
2.6
0.131
Melt Viscosity, Poises Obseired
Calcd
E
70
Errol
6,700
7,300
8.3
5,600
5,800 30,500
3.5
..,
3
B
SARAN
...
Thus, from a single melt viscosity determination, it is possible to derive a constant which denotes plasticizer effectiveness in a given copolymer. STIFFNESS
In formulating compositions for various applications such as bristles, fabrics, or moldings, stiffness is an important consideration. The logarithm of the Young's modulus at 40" C. varies linearly with plasticizer concentration, which may be expressed mathematically as: log M f = log M o
- KmB
(3)
where M f is the Young's modulus, pounds per square inch of the plasticized polymer at 40" C., M O is the Young's modulus, pounds per square inch, of the unplasticized polymer at 40" C., K , is a constant denoting plasticizer effectiveness in decreasing modulus or stiffness a t 40" C., and B is per cent plasticizer The equation appears to be valid over the range of 0 to 16% plasticizer for the copolymers investigated. Typical data are given in Table I. This equation is similar to the melt viscosity equation and mag be expanded in a similar manner t o handle plasticizer mixtures: log M / = log Mo
- (KmiBi
+ KmzB2 . . .)
(4)
wherein the subscripts refer to the first component, second component. etc.
Vol. 42, No. 2
copolymer with regard to effectiveness in reducing melt viscosity, stiffness, and flex temperature. Given the constants for the individual plasticizers, it is possible by means of Equations 1 to 6, inclusive, to calculate melt viscosity, stiffness, and flex temperature for any concentration (at least up to 16%) of a single plasticizer or mixture of plasticizers in Saran B. Numerous Saran B compositions containing from one to five components have been studied, and, with rare exceptions, no appreciable deviations from the calculated values have occurred. Constants for a number of plasticizers are given in Table 111. These constants may be used to calculate the percentage required of a given plasticizer or mixture of plasticizers to produce a desired combination of p r o p e r t i e s . F o r example, if a composition P i s desired which has a giben flex temperature and is as st ff a8 possible k! 150 a t 40 a C , the best plastiI cizers are those which 140 have the highest ratio of KtIK,. From Table 1 130 1 111,it is seen that Aroclor 20 40 60 80 100 PERCENT POLYMER IN 1254has the highest ratio DIBUTYL P H T H A L A T E SOLUTION of Kt/Kn. The poorest Figure l. Clear Point us. plasticizer for this purPer Cent Polymer in Dibutyl pose would be tricresyl Phthalate Solution phosphate, for which K J Kn 4.1 as compared with a value of 24 for Aroclor 1254. If a composition is required which has a given melt viscosity and is as stiff as possible, the plasticizer with the highest ratio of K,/K, is indicated. From Table I11 it is seen that butyl stearate, with a ratio of 8.3, is the best choice. The plasticizer having the highest ratio of Kt/K, will give the lowest flex temperature for a given melt viscosity. 1-Chloronaphthalenehas a ratio of 29.4 as compared with 11.8 for Aroclor 1254. In a similar manner, it is possihle to derive formu-
FLEX TEMPERATURE @'UNPLASTICIZED POLYMER M O N O M E R CHARGE 85% VeCIz 15% VCI
The flex temperature is defined as the temperature a t a Young's modulus of 25 X lo* pounds per square inch. The flex temperature varies linearly with plasticizer concentration according to the following equation:
Tf = To - KtB
I
'
I
I
(5)
wheie T j is flex temperature, C., of the plasticized polymer, To is flex temperature, 'C., of the unplasticized polymer; Kt is a constant denoting plasticizer effectiveness in reducing fleu temperature; and B is per cent plasticizer. This equation appears to be valid over the range of 0 to 16y0 plasticizer for most copolymers, and up to 25 to 307, for some copolymers, Typical data are given in Table I. The flex temperature equation has been found t o hold for plasticizer mixtures, and hence:
T' = To
- (KuBL+ Kt& . . .)
An examination of Equations 1 t o 6 shows that from a single plasticized composition it is possible t o obtain three constants, K,, K,, and K t , which characterize plasticizer behavior in a given
c
1
wherein the numerical subscripts refer to the first component, second component, etc. For certain copolymers, the flex temperature corresponds ver) closely to the temperature a t a n impact of 3 inch-pounds. The flex temperature determination requires only a very small fraction of the time and material required to determine the temperature a t a n impact of 3 inch-pounds. USE O F PLASTICIZER CONSTANTS
L,
-;I
(6)
,1
; I
CRYSTALLINE GLASSY SOLID
I I I
L
-
TRANS I.ITION J. I REGION I
1
0
CRYSTALLINE
TRANSITION
PHOUS AMOR-
PLASTIC
-REGION
FLUID
40 80 120 TEMPERATURE O C
160
Figure 2. Resistance to Deformation us. Temperature for Saran Copolymers
2 0
I N D U S T R IA L A.N D E N G I N E E R I N G C H E M I S T R Y
February 1950
317
3.5 I
2 B g 3.0 f
z 2.5
A
E
20
Y
3 5
1.5
c
3
;I0 W
P8 6
I2
16
PERCENT PLASTICIZER
I 0
24
Copolymer prepared from monomer charge of 85% vinylidene chloride and 15% vinyl chloride
lations wherein melt viscosity, flex temperature, and st,iffness are all specified.
CONSTANTS FOR SARAN R TABLE 111. PLASTICIZER Kv 0.186 0.177 0.166 0.136 0.123 0.096 0.070 0.051
Km 0.024 0.029 0.020 0.035 0.035 0.042 0.033 0.025
Kt K v / K m K t / K m 2.5 7.8 10.4 3.0 5.9 10.4 1.8 9.0 8.3 2.1 3.9 6.0 2.2 3.5 6.3 1.7 2.3 4.1 2.06 2.1 6.3 0.6 2.0 24.0
I
K/Kv 13.4 17.0 10.8 15.4 17.9 17.7 29.4 11.8
TEMPERATURE COEFFICIENT OF SOLVENT POWER
Doolittle (1) has shown that for nitrocellulose the linear high molecular weight ester-type plasticizers tend to have negative temperature coefficients of solvent power, whereas low molecular weight and cyclic compounds tend to have positive temperature coefficients. Phase equilibrium studies upon solutions of a vinylidene chloride-vinyl chloride copolymer in butyl stearate indicate a maximum in the solvent power of butyl stearate at 150" t o 160' C. At 50% polymer concentration, a clear homogeneous solution formed in this temperature range. Phase separation was found to occur upon either raising or lowering the temperature. Doolittle (1) has observed a similar effect with acetone solutions of a vinyl chloride-vinyl acetate copolymer. He found t h a t the solvent power of the acetone increases as the temperature is raised above 50' C. to a maximum at 70" to 90' C., and that at 134' C. the acetone is a nonsolvent. The results of phase equilibrium studies upon solutions of polyvinylidene chloride in dibutyl phthalate are shown in Figure 1, and indicate a positive temperature coefficient in the region of 140" to 175" C. The mixture was heated t o form a clear solution and then cooled until slightly cloudy. The temperature was then raised until the solution just cleared up. This temperature was taken as the clear point.
I
24
2 x 0.25 x 0.020 inch thick were molded in a hot press a t 180' C. The specimens were placed in a controlled temperature bath and Young's modulus was determined by bending. Melt viscosity was determined by means of a parallel plate plastometer. The curve of melt viscosity us. temperature was determined experimentally for both plasticized and unplasticized specimens and was found t o have the slope shown over the range of 170' t o 200" C. The poorly compatible plasticizer, butyl stearate, is more effective in the molten region and less effective in the plastic or crystalline region than is the more compatible plasticizer, 1-chloronaphthalene (see Table IV). EFFECT UPON HARDNESS. Rockwell indentation hardness was found t o decrease linearly with increasing plasticizer concentration for plasticizers exhibiting good compatibility. Dibutyl phthalate gave a linear relationship up to 24% plasticizer, as shown in Figure 3. Butyl sirearate caused a considerable decrease in hardness up to 8 to 10% plasticizer, but increasing concentrations produced no further effect. This may be a result of plasticizer exudation. EFFECTUPON IMPACT STRENGTH.Notched impact strength at 25" C . was found t o increase with increasing plasticizer concentration for 1-chloronaphthalene and dibutyl phthalate, but not for butyl stearate, as shown in Figure 4. 1-Chloronaphthalene gave the greatest increase in impacl strength, the increase continuing through 24% plasticizer. With increasing concentrations of dibutyl phthalate, the notched impact increased
I
PLASTICIZER EFFECTIVENESS FROM -40'
I
6 I!? ia PERCENT PLASTICIZER
Figure 4. Notched Impact Strength us. Plasticizer Concentration
Figure 3. Rockwell Indentation Hardness us. Plasticizer Concentration
Plasticizer Triethylene glycol dicaprylate Tri-2-ethyl hexyl phosphate Butyl stearate Dioctyl phthalate Dibutyl phthalate Tricresyl phosphate 1-Chloronaphthalene Aroolor 1254
0.5
TO 200' C.
A plot of "resistance to deformation" us. temperature over the range of -40" to 200' C. is shown in Figure 2. Specimens
I
.
6
I
I
12 18 PERCENT PLASTICIZER
Figure 5. Ultimate Elongation Plasticizer Concentration
24
US.
INDUSTRIAL AND ENGINEERING CHEMISTRY
318
I
6
Figure 6.
I
I
I
I2 18 PERCENT PLASTICIZER
24
Tensile Strength us. Plasticizer Concentration
to a maximum a t about 12rc plasticizri and then dropped of1 gradually. EFFECT GPOX ULTIMATE ELOSGATION. The ultimatc elongation n ab found to increase with increasing plasticizer concentration for I-chloronaphthalene arid dibutyl phthalate, but not foi butyl stearate, as shown in Figure 5 . 1-Chloronaphthalene gave the greatest increase in ultimate elongation, the increase continuing through 24% plasticizer. Increasing the concentration of dibutyl phthalate produced a regular increase in elongation to a maximum of 627, elongation a t 1870plasticizer, followed by a rapid decrease in elongatioii with a fuithei incIeasc in plastioizcr concentration.
,-
0 oLCHLORONAPHTHALENE A
DIETHYL MALONATE
IO
20
30
40
Vol. 42, No. 2
of refraction of amorphous polyvinylidene chloride is in the order of 1.60 as compared with 1.64 for the crystalline polymer. The addition of a plasticizer having an index of refraction above 1.60 tends to improve clarity, because the difference in index of refraction between the plasticized amorphous polymci, and the crystallites decreases with increasing plasticizer concentration. A plast,icizer having an index of refraction belov 1.60 tends to have the opposite effect. The addition of a plasticizer in excess of its compatibility result,s in the formation oi' a dispersed plasticizer phase saturated &,h respect to the polymw. If there is a difference in index of reiract,ion between the amorphous polymer-rich phase and t'he plasticizer-rich phasc, haziness is t o be expected. The results of experiments on a copolymer prepared from ii monomer mixt,ure of 85y0 vinylidene chloride and 15% vinyl chloride are shown in Figure 7. Light transmittance measurcnients give a rough indication of haziness. 1-Chloronaphthalencl, refractive index 1.633, gives increasing clarit'y up to a conceiitration of 30 to 35y0. A further increase in plasticizer concentration results in haziness. Diethyl malonate, refractive ind 1.114, causes a gradual decrcasc in clarity up to about 15' plasticizer. Clarity decreases rapidly with a further increasc, i n plasticizer concentration, indicating the presence of a (lispcrsed plasticizer-rich phase. EFFECTOF PLASTICIZER VISCOSITYUPON NODULUS. hsburning equivalent compatibility for a series of plasticizers, tlic: change in modulus with a change in plasticizer might be assume:l to be due a t least in part to differences in plasticizer viscosity. The aryl phosphate plasticizers, perhaps, more or less approach this ideal, for all appear to shox good compat'ibility. A plot of the logarithm of the modulus a t 20" C. us. the logarithm of tho plasticizer viscosity a t 60" C. gives a linear plot over a viscosity mnge of 8.3 to 4800 centipoises, as shown in Figure 8. Tho highest viscosity plasticizer, Dow P-12, lowers the modulus only from 18 X lo4 to 16 X l o 4 pounds per square inch, although present in 15y0 concentration. The lo\Test viscosity plasticizer. triphenyl phosphate (TPP), gives a modulus of 4.8 X l o 4pounds per square inch a t 15% concentration. Although the dat,a are not conclusive, the conclusion is furlher substantiated by the fact that in an investigation of a large number of plast,icizers, all those having a high viscosity a t room temperature were found to yield much stiffer compositions than plasticizers having a viscosity of 50 centipoises or less a t room temperature. Jones (2) has clone considerable work along this line and has found that, in general, plasticizer effectiveness decreases with increasing plasticizer viscosity. CRYST.4LLlNTTY @ S . COPOLl'AIER COMI~OSITlOIi. When a melted crystalline compound or a solution of a crystalline compound is alloived to cool, a constant-temperature region occurs in a plot of temperature us. time. This occurs a t the frcezing point or crystallizing temperature, arid is due t o the heat of crystallization. The extent of deviation from a normal cooling curve is somewhat indicative of thc heat of crystallization.
PERCENT PLASTICIZER
Figure 7. Light Transmittance vs. Plasticizer Concentration
EFFECTC P O N TENSILE STEENCrTH. Tensile strength was found to decrease with increasing plasticizer coiicentration in a more or less regular manner, as shovn in Figure 6. 1-Chloronaphthalene gave a smooth curve up to 247, plasticizer. Dibutyl phthalate gave a smooth curve up to 1870 plasticizer. With a further increase in plasticizer concentration, tensile strength drops off very rapidly, indicating the presence of a dispersed plasticizer phase. EFFECTUPON CLARITY. Crystalline saran copolymers tend t o be slightly hazy, owing to the difference in index of refraction hetween the amorphous polymer and the crystallites. The index
F
9104 I
Figure 8.
l
i
i
j
10 IO2 lo3 PLASTICIZER VISCOSITY cps. AT 60'C
Plasticizer Viscosity us. Polymer Modulus
! io4
February 1950
319
INDUSTRIAL AND ENGINEERING CHEMISTRY c
TABLE IV. PLASTICIZER EFFECTIVENESS
Plasticizer Triethylene glycol dicaurvlate C
PlastiDensity, cizer Melt G./Cc. Viscosity, Viscositya, Viscosity at Cp. a t Poises a t 20° C., 180° C. 180' C. a t 180" C. Cp. 0.8366
1.031
390
0.748 0.785 1.140 0.821 1.452 0.514 1,888
480 020 1,250 1,700 3,900 4,600 8,800
Poor Very poord Fair Good * Good Exwllentl Excellent
0.8017 0.747 0.8020 0.9133 1,0458 1-Chloronaphthalene 1.068 Aroclor 1254 1.3813 Unplasticized polymer 1.w 28,500 . . a For polymer containing 10% by weight of plasticizer indicated. b Plasticizer exudation detected by wiping molded sheet with cinaret paper. c Plasticizer SC. d Sweats out a t above 5% plasticizer. e Sweats out a t above 14% plasticizer. / Sweats out a t above 17% plasticizer. I Unable t o obtain a reliable value, a n estimated value of 1.6 wa8 used.
.. .
*
W
Exudation Ratinnb
1 0 . 5 Very poor 13.8 10.0 81.1 20.0 120.0 4.3 25,500
5 50 P
. .. .
.
a I
E2
40
iI
30
s 20 (r
w
N
10 v)
4
a 20
40
60
80
100
PERCENT VINYLCHLORIDE (MONOMER C H A R G E )
F i g u r e 10. Plasticizer Compatibility V S . Copolymer Composition
Fifty per cent solutions of saran copolymers in dibutyl phthalate were made up in 18 X 150 mm. Pyrex test tubes and allowed to cool with stirring, The temperature was found t o decrease rapidly at first, and then suddenly level off a t some definite value for each copolymer. Rapid precipitation of the polymer took place. This period of polymer crystallization was followed by a period of normal cooling, as shown in Figure 9. A 507" solution of polyvinylidene chloride was found to have a freezing point of 151.5' C. and showed evidence of considerable heat of crystallization. A 50% solution of a copolymer prepared from a monomer charge containing 25% vinyl chloride and 75% vinylidene chloride has a freezing point of 70" c., with only a very slight evidence of heat of crystallization. The weakening in intermolecular forces produced by the addition of a copolymerieing agent would be expected t o result in increased plasticizer I I I I I I compatibility. 20 40 60 80 100 EFFECTOF COPOLYMERCOMPOSITIONUPON PLASTICIZER PERCENT V I N Y L CHLORIDE (MONOMER CHARGE) COMPATIBILITY.Specimens were plasticized and sheets 0.030 inch thick were compression-molded a t 180" C. Toughness Figure 11. Plasticizer Effectiveness us. Copolymer Composition was evaluated by making a cut in the sheet and tearing it in two by hand. The minimum plasticizer concentration producing a, cheesy tear was recorded as the plasticizer compatibility. Both steaiate was unusual in that it showed a maximum in the vinyl dibutyl phthalate and 1-chloronaphthalene showed increasing chloride charge composition ws. plasticizer compatibility curve compatibility with increasing vinyl chloride charge. Butyl a t approximately 30% vinyl chloride charge. Results are shown graphically in Figure 10. EFFECT OF COPOLYMEIL COMPOSITIONUPON PLASTICIZER EFFECTIVENESS. With incieasing vinyl chloride content, the e POLY~NYLIDENEC H L ~ R I D E crystallinity of the copolymer appears to decrease and, in general, 0 5% VINYL CHLORIDE (MONOMER CHARGE A b % V I N Y L CHLOOR\DE (MONOMER CHARGE) plasticizer compatibility increases. -4plot of per cent reduction D 2 5 % V I N Y L CHLORIDE (MONOMER CHAROE) I I I in modulus with the addition of l0YG plasticizer us. copolymer composition indicates increasing effectiveness in reducing modulus with increasing vinyl chloride content in the copolymer, as shown in Figure 1 1 . With a monomer charge of 85% vinyl W K chloride and 15y, vinylidene chloride, an 81% reduction in I3 modulus takes place as compared a i t h a 4770 reduction in 2 140 a W modulus for polyvinylidene chloride Most plasticizers are only about 75% as effective in reducing the melt viscoqity of EIcopolymers with a monomer charge of 30% vinyl chloride a$ compared with copolymers prepared fiom a monomei charge containing 15% vinyl chloride. 100
I
LITERATURE CITED
I 2
F i g u r e 9.
I 4 TIME- MINUTES
T
I
(1) Doolittle, A. K., IND. ENG.CHEM.,38, 535 (1946). (2) Jones, H., Trans. Inst. Rubber Ind.,21, 298 (1946). (3) Moll and LeFevre, IND.ENG.CHEM., 40, 2172 (1948).
6
Thermal Evidence of Polymer Crystallinity
RECEIVED ,July 8, 1948. Presented before the Division of Paint, Varnish, and Plastics Chemistry, Symposium on Plasticizers, a t the 114th Meeting of the AMERICAN CHEMICAL S O C I E T Y , Washington. D C.
