Ind. Eng. Chem. Res. 1987, 26, 1668-1670
1668
Migration of BHT from Impact Polystyrene to Foods and Food-Simulating Liquids Arthur D. Schwope,* Derek E. Till, Daniel J. Ehntholt, Kenneth R. Sidman, and Richard H. Whelan Arthur D. Little, Inc., Acorn Park, Cambridge, Massachusetts 02140
Patricia S. Schwartz Food and Drug Administration, Washington, D.C. 20204
Robert C. Reid Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
T h e migration of the additive BHT (3,5-di-tert-butyl-4-hydroxytoluene) from impact polystyrene (IPS)to foods and food-simulating liquids (FSL) was measured by using radiolabeled BHT. With foods a t 4 and 21 "C, very low BHT losses were found for times comparable to typical shelf lives. For aqueous FSL a t an accelerated temperature of 49 O C , migration levels were also small and for water and 8% aqueous ethanol were linear in the square root of time. Acetic acid (3%) yielded the lowest migration rate of all FSL tested, and a partitioning equilibrium of BHT between the IPS and acid was possible. Oils as FSL extracted significantly more BHT, but comparison of the present results with those in the literature indicated large differences between investigators. Styrene monomer migrations from crystal polystyrene to foods and food-simulating liquids (FSL) have recently been reported (Till et al., 1982a). In this present paper, the results of that work have been extended to include the migration of the antioxidant BHT (3,5-di-tert-butyl-4hydroxytoluene) from impact polystyrene (IPS) sheets. IPS consists of a polystyrene matrix with dispersed, discrete rubber domains. Its principal food packaging uses are in the forms of tubs for margarine, deli foods, yogurt, and the like. Additives such as antioxidants, mineral oils, and lubricants are typical constituents added to food-grade IPS. It is of value to compare the migration behavior of the two polystyrene systems since the additive BHT is a significantly larger and more complex molecule than styrene monomer, but the presence of rubber and mineral oil in the IPS should reduce the glass transition temperature and provide a polymer matrix which is less crystalline and more permeable to migrants. The IPS used was Fosta Tuf-Flex 730, produced by American Hoechst. The polymer had a weight average molecular weight of about 200 000, a number average molecular weight of 70000, and Tgof 95 "C. The rubber content was in the range 4-10% and was distributed in spherical particles with an average diameter of 5 pm. Two additives were incorporated in the commercial polymer: a proprietary antioxidant (not BHT) at a level of about 400 ppm and about 1.6 wt 70 mineral oil. The IPS was melt blended with radiolabeled 14C-BHT in a Brabender Plasticorder at 160 "C. Typical BHT concentrations were about 1200 ppm, but some plaques were prepared with other levels to investigate the effect of initial BHT concentrations. In a few instances, additional mineral oil was added to ascertain its effect on migration. Each blend was hot pressed at 170-180 "C to form 0.38-0.51-mm-thickplaques. BHT levels in the final specimens were determined by heptane extraction and HPLC fractionation. The BHT fraction from the column accounted for more than 99.4% of the radioactivity.
* Author t o whom correspondence should be addressed.
The experimental equipment and procedures employed in the extraction experiments were described in Till et al. (1982a). Tests were made with five FSL (water, 8% and 50% aqueous ethanol, corn oil, and 3% acetic acid). nHeptane, an often used FSL, could not be employed as it degraded the IPS. All FSL tests were carried out at 49 "C. Seven foods were studied at 4 "C: sour cream, yogurt, cottage cheese, beef liver, vanilla pudding, gelatin, and margarine. The last two were also included in the styrene-polystyrene study (Till et al., 1982a). A t 21 "C, migration to mayonnaise, nonfat dry milk powder, and apple jelly was also investigated; mayonnaise was also used in the referenced stryene work.
Results Migration to sour cream, yogurt, cottage cheese, vanilla pudding, and gelatin at 4 "C was less than 1kg/dm2 in the 14-day tests with initial BHT levels of over 1200 ppm-a value significantly above that normally employed for antioxidants in IPS. For typical ratios of food mass to package area for these foods, BHT concentrations in the foods were less than 10 ppb-a level close to the detectable limit. Assuming that the migrating species was BHT, less than 0.01% was extracted. The low gelatin result is in agreement with earlier findings that essentially no styrene monomer migrated into this food. Beef liver (or, perhaps, the blood) contained 14C representative of a migration of about 3-4 pg/dm2 after 7 days, and essentially the same quantity was found in margarine after 42 days. For the styrene-polystyrene study, about 5 pg/dm2 of styrene monomer was lost in 90 days to margarine. Thus, even for relatively high loadings of the migrants and over extended shelf-life periods, only a few micrograms/squared decimeters of either additive migrated at 4 "C. For the 21 "C food experiments, essentially no BHT migrated to either apple jelly or to dry skim milk powder in 45 days. The low value found for the milk powder is surprising, as other tests with BHT as a migrant in highand low-density polyethylene have shown that this food was an excellent sink for BHT (Till et al., 1982b, 1986). For mayonnaise at 21 "C, in a 44-day test, only 1.1pg/dm2
08~8-5885/81/2626-~668$01.50/0 0 1987 American Chemical Society
Ind. Eng. Chem. Res., Vol. 26, No. 8, 1987 1669 A WATER 10
-
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8 % ETHANOL
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Figure 1. Migration of BHT to aqueous food-simulating liquids a t 49 "C.
was extracted. In a companion test, sometime during the experiment, the mayonnaise emulsion broke and, upon opening the test cell, the IPS was found to be in contact with a continuous oil layer. In this test, 16 pg/dm2 was removed. Thus, in some ways, this experiment was similar to those using corn oil where, as noted below, comparable BHT losses were observed. A t 21 "C,in a 100-day test, 25 pg/dm2 of styrene monomer migrated to mayonnaise. Summarizing the food tests, there were extremely low migration levels of BHT from IPS at 4 and 21 "C except in the case of the mayonnaise which separated to mimic a liquid oil. In essentially all cases, the migration was well below that noted for styrene monomer from polystyrene and very much less than found for BHT migrating from polyolefiis into comparable foods. As discussed below, the effective diffusion coefficients of BHT in IPS are quite low, and in addition, it appears that partitioning greatly favors the polymer phase, probably because of the presence of the mineral oil and rubber domains. However, as the quantity of the mineral oil was varied from 1.6 to over 5 wt %, no differences in the migration results were seen; perhaps the level was above the threshold value. For the food-simulating liquids (FSL), consider first the 49 "C data for water, 8% aqueous ethanol, and 3% acetic acid. The migration was divided by the initial BHT concentration, and this normalized migration is plotted (as ng/(dm2.ppm)) in Figure 1. For water and 8% ethanol, the migration appears to correlate well with the square root of time-at least up to 35 days, the maximum test period. By use of a simple Fickian diffusion model (Till et al., 1982a), an effective diffusion coefficient for BHT in IPS is found to be about 3 X cm2/s at 49 "C. This value is 2 orders of magnitude below the 3 X cmz/s value for the diffusion coefficient reported for styrene monomer in crystal polystyrene at 40 "C with the same FSL. The BHT migration results to 3% acetic acid are also shown in Figure 1. They are comparable to the water test values for short times but are less at long times as though partitioning were playing a role. Till et al. (1986) discuss the mechanism of BHT migration to aqueous FSL and suggest that the process is complex with partitioning in competition with BHT decomposition in the aqueous phase. This hypothesis explains why water and dilute ethanol solutions show no sign of partitioning with the BHT-IPS system or in similar BHT-polyolefin cases. With acidic aqueous solutions, Gandek (1986) has shown that the rate of BHT decomposition is reduced and partitioning is, therefore, more evident. A few tests using IPS packed in activated carbon at 49 "C led to BHT losses similar to those shown in Figure 1;
200
400 SOUARE ROOT
600
of
TIME,
800 (recondr)'/z
1000
li 3
Figure 2. Migration of BHT to corn oil and 50% aqueous ethanol a t 49 "C. Table I. Ten-Day Migration of BHT from IPS to Oils initial BHT T , BHT migration, oil "C concn ng/(dmz.ppm) ref corn 49 1000 42 this work sunflower 45 2000 7 Uhde and Woggin, 1971 sunflower 40 620" 100 Pfab and Mucke, 1977 coconut 45 5000 20 Bergner and Berg, 1972 The IPS contained 6.5% of an unspecified plasticizer.
thus, it is concluded that the rate-determining step for migration to the aqueous FSL is diffusion within the IPS and that neither water nor dilute alcohol penetrate the IPS nor modify the polymer structure. Migration levels for corn oil and 50% aqueous ethanol were somewhat greater than for the FSL described above, and the 49 "C data are shown in Figure 2. Fickian behavior is not found with either FSL. This is in contrast to the styrene monomer migration from polystyrene where the migration to these FSL correlated well with the square root of time. Over the range of concentrations studied (1.6-5 wt %), no effect of the mineral oil content in the IPS was found on the migration to 50% aqueous ethanol or corn oil. Other tests indicated that the migration was proportional to the initial BHT loading, so the normalized migratim of Figures 1and 2 is an appropriate way to correlate the results.
Discussion and Conclusions For migration tests using oils, the results from the present study have been compared to those of other investigators in Table I. The scatter in the results is disturbing. In addition, Klahn and Figge (1980) studied the system tricaprylin-IPS-BHT and reported a RHT diffucm2/s at 40 "C corresponding sion coefficient of 6.1 X to a migration of over 800 ng/(dm2.ppm) for a 10-day test. Unfortunately, in most studies, the polymers were not well characterized; thus, it is difficult to ascertain whether or not the variations noted are due to the polymer itself, to additives, or to some difference in the test procedures. The FSL, at 49 "C, were more aggressive than the foods we tested at 4 and 21 "C. For foods, BHT migration from IPS occurred at very low levels; in most cases, for typical shelf-life times, less than 2 kg/dmz and often less than 1
I n d . Eng. Chem, Res. 1987,26, 1670-1672
1670
pg/dm2 migrated. Such levels approached the BHT detection limits. Registry No. B H T , 128-37-0;IPS, 108815-92-5;ethanol, 6417-5; acetic acid, 64-19-7; water, 7732-18-5. Literature Cited
Pfab, von W.; Mucke, G. Dtsch. Lebensm.-Rundsch. 1977, 73, 1. Till, D. E.; Ehntholt, D. J.; Reid, R. C.; Schwartz, P. S.; Schwope, A. D.; Sidman, K. R.: Whelan. R. H. Ind. Eng. - Chem. Fundam. 1982a, 21, 161. Till, D. E.; Ehntholt, D. J.; Reid, R. C.; Schwartz, P. S.; Schwope, A. D.: Sidman, K. R.: Whelan, R. H. Ind. Eng. Chem. Prod. Res. Dev. i982b, 21, 106. Till, D. E.; Schwope, A. D.; Ehntholt, D. J.; Sidman, K. R.; Whelan, R. H.; Schwartz, P. S.; Reid, R. C. Food Chem. Toxicol. 1986, in press. Uhde, W. J.; Woggin, H. Dtsch. Lebensm.-Rundsch. 1971,67, 257. I
Bergner, K. G.; Berg, H. Dtsch. Lebensm.-Rundsch. 1972,68,282. Gandek, T. Ph.D. Thesis, Massachusetts Institute of Technology, Cambridge, 1986. Klahn, J.; Figge, K., "Application of a Mathematical Model on the Migration of Low Molecular Components out of Polystyrene into Fat", Third International Symposium on Migration, Hamburg, Oct 22-24, 1980.
Received f o r review October 27, 1986 Accepted May 7, 1987
Viscosity-Temperature Correlation for Glycerol-Water Solutions Yen-Ming C h e n and A r n e J. Pearlstein* Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, Arizona 85721
A four-parameter correlation of the temperature dependence of the viscosity of aqueous glycerol solutions is presented. For large temperature ranges, the errors associated with our correlation are 1-2 orders of magnitude less than those obtained with the exponential and Arrhenius fits and are considerably smaller than the errors due to using the form suggested by Litovitz (1952) for hydrogen-bonded liquids. For pure glycerol, our correlation is slightly better than the five-parameter fit of Stengel et al. (1982). Empirical relationships between fluid viscosity and temperature are required in a number of fluid mechanical situations, including convective stability problems (Palm, 1960; Stengel et al,, 1982; Busse and Frick, 1985) and multiplicity calculations for parallel shear flows in channels (Davis et al., 1983), as well as in numerous heat-transfer applications (Siebers et al., 1985; Carey and Mollendorf, 1980). In addition, the rates of diffusion-controlled chemical reactions depend linearly on temperature and inversely on solvent viscosity, through the Debye equation (Calvert and Pitts, 1966). Also, most methods for estimating self-diffusion and binary diffusion coefficients employ the viscosity of the fluid or solvent (Reid et al., 1977). Thus, it is important to be able to accurately correlate the temperature dependence of the viscosity of pure liquids and liquid solutions. A number of equations have been proposed for the correlation of viscosity-temperature data. Among these are the Arrhenius form p ( T ) = BebIT(Andrade, 1934),the exponential form p ( T ) = Ce-fT (Reynolds, 1886),the Litovitz form
p ( T ) = AeaIRT3
(1)
(Litovitz, 1952), and more complicated expressions (0'Donne11 and Zakarian, 1984). Glycerol and its aqueous solutions are important in many of the fluid mechanical (Stengel et al., 1982; Chen and Thangam, 1985),heat-transfer (Seki et ai., 1978), and chemical kinetics (Hasinoff, 1977) applications. Several correlations for glycerol (Litovitz, 1952; Stengel et al., 19821, as well as one for glycerol-water solutions (Litovitz, 1952), have been developed. Litovitz (1952) proposed a remarkably accurate twoparameter fit (eq 1) for the viscosity of glycerol-water solutions of fixed composition as a function of temperature. The basic idea is that there is an inverse square relation
between temperature and activation energy for the intermolecular hydrogen-bonding interactions in highly associated liquids. In (l), R is the universal gas constant, T is the absolute temperature, and A and a depend on composition. Equation 1 is much better than the exponential correlations used by Stengel et al. (1982) for pure glycerol and Chen and Thangam (1985) for aqueous glycerol solutions. For pure glycerol, Stengel et al. (1982) also proposed a five-parameter empirical fit for the kinematic viscosity (cm2/s)
+
v ( T ) = exp[4.5490 - 0.123092' 9.1129 X 10-4T24.7562 X 10?l"3 + 1.3296 X 10-8T4] (2)
in the range -16.5 OC IT I90 "C, where T is the temperature in "C,and the coefficient of the T 3term is corin Stengel et al. [Note that rected from -4.7562 X glycerol melts at 18.6 "C, but there is a nonequilibrium supercooled glassy liquid state which can persist to -50 "C (Stengel et al., 1982).] Four-Parameter Correlation In the present work, we propose a four-parameter correlation p ( T ) = DeE/T3+FT+GIT
(3)
for aqueous glycerol solutions, in which T is again the absolute temperature. The present correlation, based on the Litovitz, Arrhenius, and exponential forms, is superior to each of these at all of the compositions considered and for pure glycerol gives results which are slightly better than the five-parameter correlation of Stengel et al. (1982). We note that the Litovitz, Arrhenius, and exponential forms are special cases of (3), which is therefore, necessarily more accurate than any of them. In what follows, we compare (3) to the Litovitz, Arrhenius, and exponential correlations for various glycer-
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