d
d
W. J. FRISSELL Bakelite Co., Division of Union Carbide a n d Carbon Corp., Bound Brook, A'. J.
HE plasticizers used with poly(viny1 chloride) and poly(vinyl chloride-acetate) resins may be lost from the compound in several ways. They may be leached out by contact with oil or soapy water, rubbed off by contact with clothing, as in upholstery, or vaporized during processing or service. Test methods for measuring these losses have been developed and the mechanism of loss has been studied (1, 2 ) . I n volatile loss, the basic significance of vapor pressure has been established ( 1 ) . However, the relationship between vapor pressure and volatile losses during actual processing or service has not been considered previously. This can best be approached by developing suitable processing and service tests, which are described in this article. It assesses their usefulness, as well as that of the widely used activated carbon test. SAMPLE PREPARATION
ACTIVATED CARBON T E S T
I n thi8 widely used test, samples of &mil film are sandwiched between layers of activated carbon in a 1-pint paint can. This system is heated in an oven for 24 hours a t '70" C., and the weight loss of the samples is determined. The test method is ASTRI 1203-521'. The conditions of this test are very different from t'iioae fourid in service or in an oven test where the sample is usually hung iri circulating air. The intended function of the activated carbon is to absorb plasticizer vapors as they leave the sample, thus preventing saturation of the surrounding atmosphere. Certainly, a large acceleration in rate of loss is achieved. The rapid loss arid ease of operation are the chief advantages of this test. I n an effort to check its validity, activated carbon data a t a plasticizer concentration of 50 parts per hundred of resin are plotted against vapor pressure extrapolated t o 70" C. in Figure 1.
As a preliminary to this work, materials for the activated carbon test and room aging test were prepared by blending all ingredients, fluxing on a 2-roll mill a t 170" C., and calendering into 4-mil film a t 160-170" C. Batches for use in the milling volatility test were blended before testing The following general formulation may be used t o describe all of the compounds tested: Resin (copolymer of 95% vinyl chloride and 5y0vinyl acetate) Dibasic lead phosphite Dibasic lead stearate Plasticizer
100 parts 2 parts 1 to 2 parts 40 t o 70 parts
Table I presents a list of the plasticizers tested, together with their respective trade-mark, chemical composition, and supplier. VAPOR P R E S S U R E T E S T
The high vacuum method described by Quackenbos ( 2 ) was employed for vapor pressure measurements. By this method, weight loss per unit time is measured as plasticizer escapes through small hole in a glass sphere containing the liquid. Vapor pressure then can be calcnlated from this measured rate of escape. Since vapor pressure is considered here as the fundamental measure of plasticizer volatility, the other test results are compared with it. An effort was made to correlate vapor pressures with the rated teniperature of a given plasticizer in wire insulation compounds. [The rated temperature as considered is actually the rated temperature of a compound containing the individual plasticizer. For example, di-(2-ethylhexyl) phthalate is suitable for use in BO" C. building wire insulation. Thus it may be considered to have a rated temperature of 60" C.] The temperature at a vapor pressure of 0.05 micron of mercury was found t o check well with the rated temperature for several plasticizers. A list of these temperatures and the vapor pressures a t 0.05 and 5.0 microns of mercury are given in Table I1 for all the plasticizers tested. (The 5.0 micron of mercury figure was used to permit the drawing of vapor pressure curves.) Actual testing of wire compounds by the Underwriters' Laboratories, is done a t 102'70 of the rated temperature (on the Kelvin scale) for a period of 60 days. For example, a wire insulation rated for use a t 60' C. would have a test temperature of 67' C.
0
004
008
012
016
VGDOR PRESSURE GT
020 024 70 DEG C IMICSONS)
028
032
Figure 71
The correlation between vapor pressure and activated cai bon test data is only fair. There are several plasticizers which fit11 way out of line and they are all higher in the activated carbon test than would be expected from their vapor pressures. These plasticizers are the mixed phthalate, 426, and the two glycol dioctoates, 3 G 0 and 4GO. The relatively poor correlation of the activated carbon test presents a serious problem in the range from 2 to 6% loss--the range where most of the general-purpose monomeric plasticizers fall. Despite its shortcomings, the activated carbon test has received wide acceptance in the industry. It is probably satisfactory as a rough screening test, but certainly small differences in losses in this test should not be considered important. MILEIKG T E S T
This is a method of determining volatile loss during actual processing of a plasticized vinyl compound. A 500-gram batch ia milled, a t a steam outlet temperature of 170" C., for 60 minutes 1096
June 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY Table I.
PIastiLizei Ilrsignation 10-10
unp unp unp
Drip
Daw V-2 L)Utr?K 20
10-1’ 2GB 3G0 400
Supplier Caibidc & Carbon Clie~nicalsGo. Ohio-Apex Dow Shell Oil Earrett Carhide & Carbon C1iainic;al~Co.
Plasticizer Raw Matcrials Lis1
426 77-G 810 812 8N8
Flexol Flexol Flexol Flexol Flexol
A-26 CC-55 DHP DOP HRE OGB P-26 TOF TWS H-4003 H-500 HB-40 H-150 H-290 H-600 KP-90 DCP DO5 5-71 BN-1 G-62 DOZ DNP DNA 5-140 S-141
Flexol A-26 Flexol CC-55 Flexol CC-55 l.’lexol D O P (Laboratory sample) (Laboratory sample) (Laboratory sample) Flexol TOE’ Flexol T O F Halowax 4003 Harflex 500
sv-c TCP
Chemical Coinposition Diisodecyl phthalate Dibutyl phthalate Diisodecyl cresyl phosphate Di-(a-ethylhexyl) phenyl phosphate Di-n-octyl phthalate a-Methylstyrene polymer Aromatic hydrocarbon Diisooctyl phthalate Diethylene glycol dibenzoate Triethylene glycol di-(2-etliylh?xontr) Polyethylene glycol di-(2-etliylhexoate) Mixed alcohol phthalate Dipropylene glycol dibcnsoate Higher alcohol phthalate Higher alcohol phthalate 2,2’-(2-Ethylhexamido) diethyl di(2-ethvlhexoatei Di:(2-etkylhexyl) ’adipate Di-(a-ethylhexyl) hexahydrophthalate Di-n-hexyl phthalate Di-(Z-ethylhexyl) phthalate Aromatic hydrocarbon Octylene glycol dibenzoate Di-(a-ethylhexyl) pimelate Tri-(Z-ethylhexyl) phosphate Tetrabutyl thiodisuccinate Chlorinated paraffin Not revealed Hydrogenated terphenyls n-Octyl-n-decyl phthalate n-Octyl-n-decyl adipate Pentaerythritol tetracaproate Not revealed Dicapryl phthalate Di-(Z-ethylhexyl) sebacate Not revealed Alkylated aromatic hydrocarbon Not revealed Di-(2-ethylhexyl) aselate Dinonyl phthalate Dinonvl adiwate Cresyidiphenyl phosphate Z-(Ethylhexyl) diphenyl phosphate Aromatic hydrocarbon Tricresyl phosphate
“lade-Ma1 k l’lexol 10-10 1:lexol 10-10 (Laboi atory sample) (Laboratory sample) (Laboratory sample) Dow 276 resin V-2 Dutrex 20 Elastex 10-P Elastex 10-1’ Flexol 3 G 0 3’lexol 4 Q 0 426 774 810 812 8N8
HB-40 -~~
Ohio-Apex Rohm & Haas P a n American Rohm & Haas Emery Pittsburgh Coke Alonsanto Socony Vacniim Ohio-Apex
Hercoflex 150 Hercoflex 290 Hercoflex 600 KP-90 Monoplex D C P Monoplex DOS Monoplex 9-71 Panaflex BN-I Paraplex G-62 Plastolein 9058 PX-109 PX-209 Sitnticizer 140 Santicizer 141 Sovaloid C Kronitex 4.4
Tahle 11. Temperatures a t Vapor Pressures of 0.05 and 5.0 Microns Hg Temp., ’ C., at Vapor Pressure of Plastirisera G-62 H-4003 H-600 TWS 10-10 8N8 DOS Didecyl cresyl phosphate Di-n-octyl phthalate H-150 810 TCP 812 DOZ S-71 4G0 DNP 10-P H-290 H-500 S-140 2GB DOP OGB 77-G DCP 426 9-141 Dow V-2 P-26 DNA KP-90 Dutrex 20 Di-(Z-ethylhexyl) phenyl phosphate (experimental) cc-55 A-26 TOF 3G0 DHP HRE
sv-C
DBP HB-40 BN-1 For plasticizer designations, see Table I.
0.05 micron Hg Over 150 Over 150 108 93 92 85 84 83 82 80 79 78 77 76 75 73 72 72 72 70 70 69 68 67 66 66 65 65 65 63 61 61 61 60 59 58 57 57 54 47 85 29 25 25
5 0 microns Hg Over 150 Over 150 160 142 141 147 131 138 132 138 130 136 127 125 125 123 123 121 128 124 119 122 120 114 110 121 114 111 116 113 110 107 128 105
109 105 110
111 120 89 77 75 71 73
1097 on an 8 X 16 inch 2-roll mill. A sheet thickness of 0.010 inch is normally used. Samples are taken a t intcrvalc? of 5 minut,es, then specific gravity i s m e a s u r e d arid p l o t t e d against time. The theoretical specific gravity is calculated a t the original plasticizer concentration and some slightly lower c o n c e n t r a t i o n . From these figures and the experimentally determined rate of specific gravity change, a rate of plasticizer loss is calculated. By taking the total exposed surface area of sheet and bank into consideration, this rate is then expressed in grams per square meter per minute. -2 sample calculation and t,he method used are given as follows:
1. Specific gravity is calculated from t h e g r a v i t i e s provided by the suppliers of the individual raw materials, for two plasticizer concentrations, 50 and 45 parts. From these a change in gravity per part of plasticizer is calculated. 2. C h a n g e i n s p e c i f i c gravity per minute is taken from the specific gravity us. time plot. 3. Dividing (2) by (1) gives the loss of plasticizer in part,s per minut>e. 4. The result of (3) is divided by the exposed surface area and converted from a parts to a weight basis. The result is then expressed in grams per square meter per minute. Example with 810:
0’000127 . - 0.0577 parts/min 0.0022 0.0577 parts/min. 500 g. - 0.80 g./sq. m./min. X-0.235 sq. m. 154 parts The specific gravity us. time curves are reasonably good straight lines showing that the rate of loss is constant throughout the test. The calculated rates of loss per unit area and per cent loss per hour (based on batch weight) for 10 different plasticizers are as fOllOn.8:
Plasticizer (50 Parts) G-62 H-150 810 DOP S-141 4G0 TOF DHP CC-55 A-26
Plasticizer Loss in Mill Test a t 170” C. Rate g . / s g . m.jmin. Loss/houra. % 0.1 0.5 0.8 1.0 1.0 1.2 1.2 1.3 1.6 1.8
0.3
1.4
2.3 2.8 2.8 3.4 3.4 3.7 4.5 5.1
a For per cent loss per hour a batch weight of 600 grams and a n posed area of 0.236 sq, m. were assnmed.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
2098
Vol. 48, No. 6
i,esnlting figure can bo cxpressed as the pcr cent loss for thc pariicular plast,icizer and mpcriit,iire involved. (h,li~.iil~.t,ioii~ liave hcen niacin lor t,wo ili r ~ r i i t ,4-niiI-filni rwlcndering opr.ril,~ i o r i s - ~ - i i ~ i r i ~Re IK, ~ n, b i i r ) - - i n i l l - ~ ~ a I e nlinc d e ~ on small c;c:itIct dt!v~lopnienL oqiiipinent arid I~ntitJury-rriill-t:aicridcr product>ion hie. Certain simplifying assumptions have been made, as follows:
Loss during Banburying is negligible. Since, on both mill and calender, the exposed area oE the bank is very small compared t o the exposed area 011 i,he ro11s, the bank area id negiected. All calender rolls are a t the same temperature. The milling operation is a continuous process. This results in an average loss figure, with the true loss fluctuating perhaps 60 to 707, above and below this point. Sheet temperature is the same as roll temperature. In addition to these assumptions, the effect of refeeding trim is riot considered. Calculated losses for a 50 part A-26/100 part resin compound, with the processing conditions used, are:
VAPOR PRESSURE l m m HQ.)
Figure 2
The effects of three variables-plasticizer concentration, mill temperature, and sheet thickness-were investigated using conipounds plasticized wit'h -4-26. The results are shown in two forms, rate of loss per unit area and total per cent lost in 60 minutes: Mill Temp., C. 170 170 170 1.60 170 1SO
Batch Size, G. 432
170
1230
170
462 492 462 462 462 462
Sheet Thickness, Inch 0.012 0.012
n.012 n.012 n.012 0.012
o.oia n.inn
9-26
Concn., Parts 40
50 Go 50 50 50 50
50
Rate of Loss, G./Sq. X/hlin.
Loss in GO min.,
1.6 1.8 1 .o 1.2 1.8 2.8
5.3 5.4 5.4 3.8 5.4 8.7 5.4
1.8 1.9
% '
2.2
Within the concentration range tested (-20 to GO parts), there was little change in rate of loss. The use of a thicker sheet (0.100 inch us. 0.012 inch) and a correspondingly larger batch had no effect on the rate of loss per unit area. The effect of raising temperature is to increase the rate of loss. The logarithm of rate of loss is directly proportional to temperature within the range tested (160' to 180" C.). I n Figure 2, the results of mill tests on various plasticizers are plotted against vapor pressure of the plasticizers. Since the data discussed above on A-26 are included, the temperature range represented by the graph is 160" t o 180" C. -4good straight, line is obtained down to a vapor pressure of 0.05 mm. of mercury. An equation has been derived for the straight line portion and may be expressed as: Milling rate of loss in g./sq. m./min. = 0.47 2.92 X vapor pressure (mm. Hg)
+
A similar correlation curve may be plotted for mill test us. activated carbon test and this has been done in Figure 3. Thc data are somewhat more scattered. The equation of the line is : Milling rate of loss = 0.19 X (per cent Iosa in activated carbon test) This equation is limited to the test temperatures concerned, 70" C. for the activated carbon test and 170" C. for the mill test. These equations can be used to estimate rate of loss during milling if vapor pressure or activated carbon test data are available. APPLICATION TO CALENDERING
The data on milling losses can be used to calculate estimated losses during calendering of film or sheeting. Rate of loss in grams/square meter/minute is multiplied by the actual exposed area on the mill or calender. This rate of loss in grams/minute is t,hen divided hy the throughput rate in grams/minute. The
Development
Production
Process equipment AMill, inches Calender, inches
8 X 16 8 X 10
Assumed process conditions Mill sheet width, inches Calender sheet width, inches Calender speed ft./min. Banbury batch'siee, lb. Mill temperature, C. Calender temperature, C. Mill sheet thickness, inch Calender sheet thickness, inch
12 8 170 170
37.5 120
0.004
n.004
n ,0027
o.omi
12'/a 12'/r
0.100
22
24
x fin
x
66
54 66
170 170 0.150
T'olatile losses. calculated Calender, of compound Mill, % of compound Total, % of compound
r0
Specific gravity change Calculated Actual
0,002
...
Losses on the production calender and the development calender are about t,he same. However, mill losses or1 the clevelopment mill are somewhat higher due to the very slow calendering rate. An actunl run m.as made on the development equipment t o check the calculated losses. The change in specific gravity writs close t o that cnlculated. However, this is probably more coincidental than meaningful since the specific gravity test has a precision of 10.0014 which is large enough to completely OkJ~CxlrC the reported gravity change of 0.002. The losses shown in the table, up t o two thirds of l%, actually represent a loss of about 2% of the plasticizer. This loss, though small, can have an effect on compound properties. A-26 has been employed to illustrate the usefulness of milling volatility data. It is one of the more volatile plasticizers used in vinyl compouricts. 1,ossesfor DOP m-oiild be about 6076 of those shown for A-26. As part of the milling volattility testing, data on actual us. c d culated specific gravity of the coinpourid were uccumulated. The specific gravity data talcen during a mill test can be extrapolated to zero milling time. This was done for 19 compounds and compared with the values calculated from the specific gravit,ies of the raw materials. A consistent increase in gravity varying from 0.014 to 0.022 and averaging 0.0176 was found. This average iricrease is equal to a contraction in volume of 1.7%. This volume contract,ion is taken as evidence that a plasticized vinyl compoiind is not an ideal solution. Apparently, the molecules of the monomeric plasticizers fill the interstices of the vinyl polymer molecules. ROO11 AGING
In order to investigate actual volatile losses on room temperatiur aging, n series of &mil films were weighed anti t,heIi siispentletl
June 1956
1099
INDUSTRIAL AND ENGINEERING CHEMISTRY
10 feet above the floor in a laboratory. The weight change data after 2 l / 2 years on this series are as follows: yo Weight Change ~Room
aging, 21/; yr. -18.4 2.8 2.2 2.2 0.2 0.2 0.1 4- 0 . 2 0.3 0.6 1.2 1.3
Plasticizer DBP 3G0 TW8 4G0 TOF CC-55 A-26 DHP 2GB 8K8 DOP DO5
-
+ + + + +
Activated ' carbon 2 4 hr. at 76' C. -27.0 -10.7 1.2 7.8 7.5 8.6 -10.6 -10.8 4.1 1.5 - 3.6 3.3
-
Vapor Pressure a t 23O C., Microns Hg 0.027 0,001 0.000006 0,0002 0,001 0.00067 0.00073 0.0014 0.00026 0.00008 0,00026 0.000013
Only one plasticizer shows a high loss in this test and that is dibutyl phthalate. 3 G 0 , 4G0, and TWS show small but significant losses. All of the other plasticizers show no significant changes. The comparison between these data and conventional tests is brought out in table above, Room aging data a t 50 parts of plasticizer are compared with activated carbon test data a t the same concentration and with vapor pressure a t 23" C. One fact stands out. Dibutyl phthalate is highest in loss in both room aging and activated carbon tests and also highest in vapor pressure. Aside from this there seems to be little connection between room aging and the other tests. It is possible that longer room aging, 5 or 10 years, may show a better correlation with vapor pressure and activated carbon tests. I n table below are shown results on four plasticizer extenders in mixtures with DOP for room aging of 3 months. The data are compared with vapor pressure a t 23" C. Here the room aging loss shows some relationship to vapor pressure: Plasticizer Mixtures Plasticizer
DOP, parts
Parts
Room Aging, % Wt. Change, 3 Months
Vapor Pressure a t 23' C., Microns Hg
. .
42.0 45.4 48.7
-5.3 -8.4
-1.2
0.0:s
0.003 0.001
T o sum up, the room aging tests have shown that loss under ambient room conditions is related to vapor pressure in cases where the vapor pressure is high. However, none of the commonly used vinyl plasticizers, even one as high in vapor pressure as A-26, show significant losses after aging for 2'/2 years. I t is apparent that volatile loss a t room temperature is of little importance except where highly volatile extenders or plasticizers are concerned, or where room temperature is unusually high, as might be the case where draperies are suspended over a radiator. PRACTICAL SIGNIFICANCE O F R E S U L T S
The choice of a suitable plasticizer for any given application, with respect to volatility, is dependent on three factors. The first is the temperature a t which the final product is to be used. This is frequently, but not always, room temperature. If it is room temperature, then practically the full range of commercially available vinyl plasticizers may be safely employed. Only surh highly volatile materials as dibutyl phthalate and some of the hydrocarbon type extenders should be avoided. For temperatures much above room temperature, the equation developed by Quackenbos from oven test data a t 98' C. may be employed ( 1 ) . Life (hours t o lose
lo'%)
1 2.5
I
LT 70 DEG.'C.
VS. MILLING RATE OF LOSS AT 170 DEO. C.
I
1.5
I .o
0.5
0 0
4 6 8 10 I2 ACTIVATED CARBON VOLATILITY -PER CENT LOSS 2 4
-
14
HOURS
Figure 3
loss of up t o 2y0 of the plasticizer. This loss does not have a major effect on compound properties, hut should certainly be considered in formulation development. Perhaps the more important phase of loss during processing is the economic one. I n the example cited, with A-26, the loss would amount to about, $30 for a 24-hour run of 10,000 lb. of film. A third aspect of plasticizer volatility in processing is the problem of fumes. Using the same example, the plasticizer is lost a t a rate of 2.5 pounds per hour. This means that approximately 3.9 cubic feet of pure plasticizer vapor ( a t 170" C . ) must be removed from the processing area each hour. Since the volatile loss during processing is the more important factor, it is essential to be able t o evaluate it properly. Methods of calculating losses were developed in the section on the milling test. The loss that can be tolerated is dependent on the three factors just discussed: change in properties, economic loss, and fume removal. I n room temperature service, no more volatile plasticizer than A-26 should be seriously considered. I n the discussion, the factor of chemical stability of plasticizers a t high temperatures is not considered. Recent offerings in the way of new plasticiEers and their acceptance in the industry show that the subject of voltaility is receiving closer scrutiny than ever before. Phthalates of longer chain alcohols than the commonly used octanols are gaining wide acceptance. They are usually mixed higher alcohol phthalates, such as Flexol 810. These are being used in materials where service temperatures are well above room temperature or processing is especially severe. On the other hand, mixed lower alcohol phthalates, such as Flexol426, are finding use in applications where the service temperature is not much above room temperature and processing conditions are not too severe. These materials are still somewhat below A-26 in vapor pressure. They should be fully satisfactory in thick sections such a8 floor tile, extruded welding, or injection molded toys. ACKNO W LEDGiMENT
0.080 i~~~~~ pressure (mm. H~ at servire temp,)
This same equation is also suitable for rough estimates a t 23" C. The second factor is the set of Drocessine: conditions used in making the material. Since volatile loss is a function of both temperature and exposed area, the calendering and subsequent embossing of 4-mil film is one of the most severe cases. Calendering alone, of a compound plasticized with A-26, can result in the
ACTIVATED CARBON VOLATILITY
2.0
_-___.
=
I
The author wishes to express his appreciation to his colleagues a t Development Laboratories of Bakelite Co. for their aid in the collection of data and the preparation of t h i a article. LITERATURE CITED
(1) Quackenbos, 15. M., IND.ENC.CHEM.46, 1335-44 (1954). Schula, 13, F., I b i d . , 46, 1344-9 (2) Reed, M. C., Klemm, H.F., (1 954).
RECEIVED for review
. J U ~ J 6. J
19~5.
ACCEPTIXJ February 29. I Q56.
