United States Environmental Protection Agency Hazardous Waste Engineering Research Laboratory Cincinnati OH 45268 Research and Development EPA/600/S2-86/055 Sept. 1986 x°/EPA Project Summary Predicting the Effectiveness of Chemical-Protective Clothing: Model and Test Method Development A. S. Bhown, E. F. Philpot, D. P. Segers, G. D. Sides, and R. B. Spafford A predictive model and test method were developed for determining the chemical resistance of protective poly- meric gloves exposed to liquid organic chemicals (solvents). The prediction of permeation through protective gloves by solvents was emphasized. Several theoretical models and test methods for estimating permeation re- lated properties were identified during a literature review and were evaluated in comparison to performing direct per- meation tests. The models and test methods chosen were based on theo- ries of the solution thermodynamics of polymer/solvent systems and the diffu- sion of solvents in polymers (as op- posed to being based on empirical ap- proaches). These models and test methods were further developed to es- timate the solubility, S, and the diffu- sion coefficient, D, for a solvent in a glove polymer. Given S and D, the per- meation of a glove by a solvent can be predicted for various exposure condi- tions using analytical or numerical solu- tions to Pick's laws. The model developed for estimating solubility is based on Universal Quasi- chemical Functional-group Activity Co- efficients for Polymers (UNIFAP) the- ory, which is an extension of the Universal Quasichemical Functional- group Activity Coefficient (UNIFAC) method for predicting phase equilibria. The model recommended for estimat- ing diffusion coefficients versus con- centration is the Paul model, which is based on free-volume theory. The pre- dictive test method developed is a liquid-immersion absorption/desorp- tion method that provides estimates of S and D. The models and test method chosen were incorporated into an algorithm for evaluating protective gloves recom- mended for use with new chemicals. Fi- nally, limited confirmation of the devel- oped models and test method was performed by comparing estimated val- ues of S and D with reported experi- mental data and by using the estimated values to predict instantaneous perme- ation rates, breakthrough times, and steady-state permeation rates for com- parison with experimental permeation data. This Project Summary was devel- oped by EPA's Hazardous Waste Engi- neering Research Laboratory, Cincin- nati, OH, to announce key findings of the research project that is fully docu- mented in a separate report of the same title (see Project Report ordering infor- mation at back). Introduction Section 5 of the Toxic Substances Control Act (Public Law 94-469) requires prospective mMhufacturers of new chemicals to submit Premanufacture Notifications (PMNs), which are re- viewed by the U.S. Environmental Pro- tection Agency's Office of Toxic Sub- stances (OTS). PMN submittals often propose specific chemical-protective clothing to limit the dermal exposure of workers to toxic chemicals. Because OTS has only 90 days to complete each PMN review, and because testing by the ------- manufacturer must be kept to a mini- mum, the development of reliable mod- els for predicting the performance of protective clothing is desirable. Thus the first objective of this study was to develop predictive models for evaluat- ing the chemical resistance of protec- tive clothing exposed to liquid organic chemicals. No matter how sophisticated the models developed here or in future ef- forts, there may often be insufficient data available to allow a given model to make predictions as accurate as those requested (i.e., ±50% for permeation rate and ±20% for breakthrough time). Thus predictive test methods are also needed to allow estimates of the perme- ation of chemical-protective clothing under expected exposure conditions. The second objective of the study was to develop such methods, either by rec- ommending the use of existing test methods or by developing new ones. Task 1: Developing Predictive Models for the Permeation of Polymeric Membranes by Organic Solvents Because of the expense of conducting permeation tests, models that would al- low the prediction of permeation through polymeric materials would be useful for screening candidate protec- tive materials. The work reported here emphasized the prediction of perme- ation through unsupported, natural- rubber glove formulations because of the relative purity of these formulations (typically 93% latex) compared with oth- ers (e.g., PVC-based gloves typically contain >40% plasticizer). Also, experi- mental solubilities and diffusion coeffi- cients for various solvents in natural rubber are available. Applicable Mass Transport Theory If it is assumed that Pick's laws of dif- fusion are valid, that the diffusion coeffi- cient is independent of solvent concen- tration in the polymer, and that swelling of the polymer is negligible, then the permeation rate (J) for a solvent through a glove sample whose outer surface is in contact with the liquid sol- vent is given by •exp -mVDt/e2 where D is the solvent diffusion coeffi- cient, S is the solubility of the solvent in the polymer, and fis the sample thick- ness. Thus if the diffusion coefficient and solubility of the solvent in the poly- mer can be predicted by a model, then permeation-rate curves and other quan- tities of interest (e.g., breakthrough times, lag times, and steady-state per- meation rates) can be predicted. This simple model may also be modified to account for phenomena such as the generally observed concentration de- pendence of the diffusion coefficient. Solubility Predictions Two approaches to predicting solubil- ity were attempted: The Flory-Huggins theory (combined with the use of solu- bility parameters) and the Universal Quasichemical Functional-group Activ- ity Coefficient (UNIFAC-FV) or Universal Quasichemical Functional-group Activ- ity Coefficient for Polymers (UNIFAP) theory. Both approaches assumed that none of the polymer dissolved in the liquid phase (that is, that the solvent re- mained pure) and that the standard state for the solvent in both the liquid and the polymer phase was the pure solvent (for which the activity, a1r is unity). Thus it was only necessary to de- termine the solvent volume fraction in the polymer that yielded a^l to predict the solubility of the solvent in the poly- mer. If it is assumed that the molar volume of the solvent, VT is much less than the molar volume of the polymer, then the Flory-Huggins equation may be written as 1n a, = 1n (2) J - DS/f 1 + > 2 • cos(irm) (1) \ /[ m = 1 where x is the Flory interaction parame- ter for the polymer/solvent system and Q>1 is the solvent volume fraction. At equilibrium, ai = 1 and Equation 2 may be written as 0=1n*, + (1-*l) + x(1-*i)2 (3) It has been suggested that \ is related to Hildebrand's solubility parameters for nonpolar systems: where 6, and S2 are the solubility parameters for the solvent and poly- mer, respectively. In this work, . Hansen's so-called three-component or \ three-dimensional solubility parame- ters were used to calculate the separa- tion in solubility space, A, which was substituted for the difference (&i-82) in Equation 4 to make the theory more ap- plicable to polar systems. Three ap- proaches to the calculation of A have been reported: A = [(8g - S.J) A' = [4(85 -»d)2 + (8JJ-8J)2 (5) (6) A" = [8g - + 0.250(TP - Te>2]1/2 (7) x = (P!/RT» (8, - 82)2 (4) where the p and I superscripts refer re- spectively to the polymer, and the liquid solvent, 8d, is for dispersion forces, 8p is for polar effects, 8h is for hydrogen bonding, and T = (8J; + 82,)1'2 . Solubilities calculated for a series of solvents in natural rubber are listed in Table 1. These calculated solubilities correlate poorly with reported experi- mental solubilities. For this reason and because the UNIFAP approach to calcu- lating solubilities appeared to be more promising, attempts to use the Flory- Huggins theory and solubility parame- ters were discontinued. The UNIFAC theory is based on the use of functional-group interaction parameters calculated from experimen- tal phase-equilibrium data to determine the activities of each component in mix- tures. This work was extended to in- clude free-volume theory and thus to make it applicable to polymer/solvent systems. A software package (UNIFAP) is available to conduct calculations that enable the prediction of solvent solubil- ity in polymers. The primary input data are the solvent and polymer densities at the temperature of interest and the identity of the functional groups in the solvent and the polymer. The data in Table 2 compare solubili- ties calculated using UNIFAP theory with experimental data for a series of solvents in natural rubber and four other polymers. The typical agreement is within a factor of five or better. The data in Table 2 reveal two prob- ------- TaWe 1. Solubilities Calculated for Various Solvents in Natural Rubber8 (Based on Flory- Huggins Theory and Solubility Parameters) Literature solubilityb Calculated solubilityc-d Solvent Methanol Ethanol Isopropanol n-Butanol n-Pentanol Benzyl alcohol n-Propanol Acetone 2-Ethyl-1-butanol t-Pentanol Diethyl carbonate Methyl ethyl ketone Ethyl acetate n-Propyl acetate n-Hexane n-Heptane Tetralin Cyclohexane Cyclohexanone Toluene Tetrachloroethylene Carbon tetrachloride Trichloroethylene 10*xCexp 4.92 8.59 52.8 125 130 142 146 169 259 437 636 713 766 1270 1540 1580 3330 3380 3410 3870 4240 5370 5690 10s x C, 3.27 5.37 18.7 14.3 34.5 35.0 9.33 64.2 28.1 2.23 # 69.9 7400 28.4 8.57 5.7t 266 39.7 489 299 136 94.8 # 705 x C', 7.88 3.27 9.27 6.99 73.7 35.0 5.25 26.7 8.48 0.770 858 30.8 757 7.74 7.75 7.00 757 25.9 429 284 727 88.9 * 70s x C] 392 394 604 475 724 2630 439 * 483 92.9 # # * 363 752 T35 * 7380 # # * # * "The concentrations (solubilities) reported are in units of moles/cm3 of unswollen polymer at 298 K. b These values are calculated from the experimental volume-fraction data reported by D.R. Paul. These values are calculated using Flory-Huggins theory. The term C» means that Equation 5 was used to calculate the separation in solubility space; C\ corresponds to Equation 6; and C] corresponds to Equation 7. dThe symbol "*" means that no solubility could be calculated, because these systems are predicted to be miscible in all proportions. lems with UNIFAP. First, it yielded pre- dictions of total miscibility for a number of solvents, which experimentally showed large but finite solubilities. This prediction occurred because UNIFAP does not consider crosslinking. Second, the database of interaction parameters is limited to a relatively small set of functional groups. Thus the interaction parameters for functional groups needed to define given polymers or sol- vents may not be available. Diffusion Coefficient Predictions This work emphasized the prediction of solubility. However, C.W. Paul's model based on free-volume theory was used to estimate the concentration- dependence of the diffusion coefficients for benzene and n-heptane in natural rubber. Paul's model requires fewer ex- perimental data (that is, physical prop- erties) than other models of free volume theory. A comparison of the predicted concentration-dependence of the diffu- sion coefficient for benzene in natural rubber is shown in Figure 1. Although the values of the maximum in both curves are in good agreement, the loca- tions of the maximum relative to the solvent volume fraction are not. The ini- tial work in the application of the Paul model will continue in an attempt to eliminate the discrepancy shown. Prediction of a Permeation Rate Curve The solubility predicted for benzene in natural rubber using UNIFAP and the diffusion-coefficient curve given in Fig- ure 1 (despite its disagreement with ex- perimental data) were used to predict the permeation rate as a function of time for a 0.046-cm-thick glove (Fig- ure 2). This curve was calculated using the Crank-Nicholson implicit finite dif- ferences approach to solving Fick's sec- ond law of diffusion with a reference table for the diffusion coefficient. The agreement between the predicted curve and that derived from data reported by Weeks and McLeod should be consid- ered somewhat fortuitous but nonethe- less encouraging. Task 2: Developing Predictive Test Methods for the Permeation of Polymeric Membranes by Organic Solvents Permeation tests are often conducted to scree^ elastomeric materials that may be suitable for the formulation of chemical-protective clothing. Perme- ation tests are time-consuming and ex- pensive, and they often require the de- velopment of analytical methods for the permeant. These analytical methods usually are not universal, and thus skilled technicians may be required to conduct permeation tests. This work in- cluded the development of a simple test method that allows the prediction of the permeation of an organic solvent through a polymeric membrane. The test method, based on liquid-immersion absorption and desorption measure- ments, is simple, universal, and can be carried out by technicians with minimal training. Experimental For each experiment, a polymeric sample with known dimensions and weight was immersed in the solvent of interest at t=0. The sample was re- moved periodically from the solvent, blotted to remove excess solvent, and then weighed. The sample was reim- mersed in the solvent after each weigh- ing. This test was referred to as the liquid-immersion absorption test. After the weight of the polymeric sample reached a constant value (indi- cating equilibrium), it was removed from the solvent and blotted to remove excess solvent. The sample was then suspended from a hook on an analytical balance, and its weight was recorded as a function of time. This test was referred to as the liquid-immersion desorption experiment. Desorption experiments were conducted only for those samples that exhibited appreciable absorption. The materials tested were circular sam- ples of unsupported gloves that were 3.5 cm in diameter. The tests were con- ducted with the samples and solvents in the temperature range of 73 ± 6°F. Data Analysis The absorption (or desorption) of a solvent by a planar sample (if edge ef- fects are negligible) is given by Nit/Mo, = 1 - (8/ir2) (2m + 1)~2 (8) m=0 ------- Table 2. Polymer Natural rubber Butyl rubber Neoprene rubber Nitrite rubber Poly (vinyl chloride) Comparison of Solubilities Calculated Using the UNIFAP Model or Obtained Exper- imentally with Manufacturers' Chemical-Resistance Guidelines" Degradation Permeation Solvent W5 x Cuni 105 x Cmo ratingb ratingc Methanol Ethanol Isopropanol n-Butanol n-Pentanol Benzyl alcohol n-Propanol Acetone 2-Ethyl-1-butanol t-Butanol t-Pentanol Diethyl carbonate Methyl ethyl ketone Ethyl acetate n-Propyl acetate n-Hexane n-Heptane T&trftlln i cm GUI i Cyclohexane Cyclohexanone Toluene Tetrachloroethylene Carbon tetrachloride Trichloroethylene Acetone Cyclohexane Isopropanol Toluene Acetone Cyclohexane Isopropanol Toluene Acetone Cyclohexane Isopropanol Toluene Acetone Cyclohexane Isopropanol Toluene 26.5 42.4 81.6 93.3 103 27.5 100 185 114 81.5 96.9 202 277 477 587 «e 322 # 29.7 # * * 69.8 f — - *s * 49.5 * 4.92 8.59 52.8 (81.4)d 125 130 142 146 169 (263) 259 414 437 636 713 766 1270 1540 1580 3330 3380 (31907 3410 3870 (3480) 4240 5370 5690 (78.7) (3240) (6.8) (1920) (696) (1040) (95.5) (3410) (3130) (117) (389) (1560) (—)" (—) (—) (—) E E E E NA NA E E NA NA NA NA G G F NR NA NA NA NA NR NA NR NA NA NA NA NA G NA E NR NR NA E F NR NA G NR E,NN VG,NN E,NN G NA NA VG F, NN NA NA NA NA P,NN G,NN F,NN NA NN NA NN NA NN NN NN NN NA RR NA NA F,NN NN E NN NN RR E,RR F, NN NN NN E NN where t is the time, M, is the cumulative amount of sofvent absorbed (or de- sorbed), IVL is the cumulative amount absorbed at infinite time (that is, at long 1 times), DO is the diffusion coefficient for the solvent in the polymer, and i is the thickness of the sample. This equation assumes that the diffusion observed is Fickian, that the swelling of the polymer sample is negligible, and that the diffu- sion coefficient is independent of sol- vent concentration in the polymer. Absorption or desorption data may be fit to Equation 8 using nonlinear techniques to obtain an estimate of D0 and Mo, (the solubility, S, of the solvent in the polymer is M Jv where V is the volume of the unswollen sample). IVL is simply the maximum weight gain of the polymeric sample immersed in the sol- vent. If the quantity (M,/MJ is plotted as a function of t1/2/Ł the so-called reduced sorption curve is obtained. The initial slope of this curve (up to M^M«, = 0.6) may be used to estimate an apparent diffusion coefficient by using the follow- ing equation: D — (ir/tRH2 (Q) — \Ttf lw/1 \J/ where D is the apparent diffusion coeffi- cient and 1 is the initial slope of the re- duced sorption curve. Reduced sorption curves may be plotted for absorption or desorption data. Only one of these re- duced sorption curves is necessary to calculate D; however, both were used in this study when available. Once estimates of D and S are ob- tained as described above, the solvent permeation rate (J) as a function of time (through a glove sample covered on one side by an organic solvent) may be predicted using the equation 8 The units of the calculated equilibrium solubilities, Con/, and the experimental solubilities, Cexp, are moles/cm3. Degradation ratings are as follows: E = Excellent, G = Good, F = Fair, NR = Not Recom- mended, NA = Not Available. cPermeation ratings are as follows: E = Excellent (permeation rate <0.15 mg/m2/sec), VG - Very Good (permeation rate < 1.5 mg/m2/sec), G = Good (permeation rate < 15 mg/m2/ sec), F = Fair (permeation rate < 150 mg/m2/sec), P = Poor (permeation rate < 7500 mg/m2/ sec), ND = None Detected. The double letters refer to ratings using by ADL (4f; RR (recom- mended) means that a large amount of test data indicates excellent chemical resistance; NN (not recommended) means that a large amount of test data indicates poor chemical resis- tance; NA means rating not available (or conflicting ratings are reported by ADL). dThe values in parentheses were determined during immersion tests conducted under the current effort; the other data in this column were calculated from data reported by D. R. Paul. eThe symbol "*" in this column means that an activity of one was achieved only for a solvent volume fraction equal to one. (That is, the solvent and the polymer are predicted to be miscible in all proportions.) fDash indicates that no interaction parameters were available for the polymer/solvent pair indicated. BThe UNIFAP solubilities for solvents in poly (vinyl chloride) were based on the polymer struc- ture alone; the presence of plasticizer was not considered. hDash in parentheses indicates that weight loss was observed in the immersion tests with poly (vinyl chloride). J = (DS/O-1 + 2 • cos(irm) (10) I m = 1 •exp(-m2ir2Dt/e2)[ The steady-state permeation rate (JJ may be estimated using J«, = DS/e (11) The breakthrough time (fc) based on a given permeation rate (Jb) may be esti- mated using 4 ------- 0.75 0.65- « 0.55 I o "o 0.45 § 0.35 o o I Q 0.25 O.tS 0.05 T T Approximate Predictive Range 0.1 «Di <0.9 Predicted Using the Paul Model -0.05' 0.00 0.20 0.40 0.60 0.80 1.0O Benzene Volume Fraction, *i Figure 1. Diffusion coefficient of benzene in natural rubber as a function of volume fraction. 300 E ^i Permeation Rate, , § c \ \ — I I I — Permeation Data (Extrapolated from Weeks and McLeodt ,'"' - f J I I 3 5 10 Predicted Using Theoretical Model I I I 15 20 25 Time, min Jb = (DS/P) 1 + 2 m=1 cos(irm) (12) F/gun 2. Comparison of predicted and experimental permeation rate curves for benzene through natural rubber. •exp(-m2ir2Dtj/('2)[ Test Results Typical absorption and desorption curves are shown in Figure 3. Average solubilities and diffusion coefficients determined are given for four solvents and four polymers in Table 3. Predictions Predicted steady-state permeation rates and breakthrough times for the solvent/polymer combinations studied in this work are given in Table 4. This table also includes steady-state perme- ation rates and breakthrough times de- termined in permeation tests using the same polymeric glove samples and sol- vents. Figure 4 shows a predicted per- meation rate curve (calculated using Equation 10) and measured permeation rate curves for acetone through nitrile rubber and acetone through natural rubber. Conclusions and Recommendations Models that have been developed for predicting the permeation of organic compounds through protective glove polymers have often been based on em- pirical approaches with little emphasis on diffusion theory. The current work has demonstrated that predictive mod- els and test methods that yield diffusion coefficients and solubilities may be used to estimate permeation data such as breakthrough times (for a given defi- nition), steady-state permeation rates, and permeation rate curves. These fun- damental parameters may be estimated using the theoretical models or the sim- ple test methods described in this re- port. Only relatively simple diffusion theory and mathematical methods are required to calculate permeation data from diffusion coefficients and solubili- ties. These permeation data may then be used to estimate the protection af- forded by polymeric gloves recom- mended in PMN submittals. Most of the limited confirmation work conducted here was performed manu- ally. That is, although computers were used to model polymer solvent sys- tems, to perform curve fits of experi mental data, and to predict permeation- ------- 0 1234 S 67 8 9 10 11 12 13 14 15 16 17 18 Figure 3. Absorption and desorption curves for toluene in natural rubber. rate data, the computer programs written were not integrated into a single software package, and they were not made user friendly. Thus work under the confirmation task was tedious and time-consuming. For this reason, it was not possible to evaluate all of the exper- imental immersion and permeation data obtained, and the Paul model was used to predict diffusion coefficients for only two polymer/solvent systems. However, any continued research effort based on the work described here should begin with consolidation of the programs written into a single software package. Thus future confirmation work should largely begin to resemble the preparation and evaluation of PMN sub- mirtal and review software. Future efforts to continue the work described here should include the iden- tification and use of computerized data bases of physicochemical data that are needed to predict diffusion coefficients and solubilities (using, for example, the Paul model or the UNIFAP theory). Also, work should include addressing the lim- itations of the UNIFAP theory and the Table 3. Average Solubilities and Diffusion Coefficients Calculated from Liquid-Immersion Absorption and Desorption Test Data Glove Butyl rubber Natural rubber Neoprene rubber Nitrite rubber Solvent Acetone Cyclohexane Isopropanol Toluene Acetone Cyclohexane Isopropanol Toluene Acetone Cyclohexane Isopropanol Toluene Acetone Cyclohexaned lsopropanold Toluene Solubility, g/cm3 0.0457 ± 0.0010 2.7261 ±0.1088 0.0041 ± 0.0010 1.7690 ± 0.0372 0. 7527 ± 0.0099 2.6877 ± 0.0635 0.0489 ± 0.0079 3.2067 ±0.7524 0.4044 ± 0.0262 0.8787 ± 0.0739 0.0574 ± 0.0079 3.1388 ± 0.0974 7.8204 ±0.7236 0.0982 ± 0.0795 0.2340 ± 0.0234 1.4377 ± 0.0463 709 x Da 5.6 ± 7.4 750 ± 3.4 7.7 ± 73 380 ± 73 400 ±200 250 ± 30 42 ± 6.4 530 ± 67 250 ± 200 37 ± 6.7 7.3 ± 0.67 350 ± 38 420 ± 59 0.25 ± 0.067 0.42 ± 0.20 59 ± 5.9 709 x Dd — 330 ± 7.3 — 280 ± 720 380 ± 20 490 ± 750 — 260 ± 35 260 ± 36 54 ± 4.4 — 200 ± 33 450 ± 82 — — 200 ± 40 709 x Da 5.0 180 0.43 320 690 260 40 580 520 40 1.2 0.79 19 0.23 110 230 12 20 51 64 2.3 0.31 410 7.8 440 ±160 0.30 ± 0.080 0.72 ± 0.23 98 ± 15 109 x D'd — 280 ± 82 — 270 ± 770 450 ± 55 480 ± 150 — 290 ± 25 377 ± 50 43 ± 6.5 — 270 ± 46 480+ 61 — — 750 ± 78 aThe term Da is the apparent diffusion coefficient estimated from the initial slope of the reduced absorption curve. Dd is the apparent diffusion coefficient estimated from the initial slope of the reduced desorption curve. All data points [including (0,0)] for which MJM«, <0.6 were used in these calculations; if no data points meeting this criterion except (0,0) existed, then the calculation was based on (0,0) and the first data point above M/Mx = 0.6. bThe term De is the apparent diffusion coefficient calculated from a curve-fit of data obtained in an absorption test. Dd is the apparent diffusion coefficient calculated from a curve-fit of data obtained in a desorption test. °The symbol "—" means that the experiment indicated was not conducted. dSome of the nitrite-rubber samples immersed in these solvents continued to gain weight even after 530 hr. ------- Table '4. Comparison of Measured Breakthrough Times and Steady-State Permeation Rates with those Predicted from Immersion Test Data8 Breakthrough time,b min Glove Natural rubber Neoprene rubber Solvent Acetone Cyclohexane Isopropanol Toluene Acetone Cyclohexane Isopropanol Toluene Measured Predicted 17 ± 1.2 19 ± 7.7 > 750, < 7400 9.7+ 1.5 22 ± 2.0 >60 12 9.9 ± 5.3 4.7 ± 0.8 130 ±35 4.0 ± 0.1 8.6 ± 6.0 28 ± 3.8 on 3.2 ± 0.2 Steady-state permeation rate, ]Lg/(cm2-min) Measured 34 ± 3.5 520 ± 48 1 780 ± 27 150 ± 20 35 ± 27 640 Predicted Butyl rubber Acetone Cyclohexane Isopropanol Toluene >1100 55 ± 6.3 — 24 CO 5.5 ± 0.4 CO 4.7 ± 0.5 <0.47 440 ± 110 — 400 0.25 660 0.028 560 0.05 53 0.05 91 51 900 2.2 1200 120 49 0.10 1100 22 160 0.7 2.5 ± 68 ± 5.5 0.05 45 Nitrile rubber Acetone Cyclohexane Isopropanol Toluene 10 ± 2.0 >1400 — 52 3.2 ± 0.2 CO 00 72 ± 1.4 960 ± 26 <0.12 — 2JO 870 0.028 0.77 790 87 0.07 0.06 19 "The symbol "—" means that no permeation test was conducted with this glove/solvent combination. The symbol "°°" means that the permeation rate would always be less than that used to define the breakthrough time. bThe predicted breakthrough times are based on the minimum permeation rates that could be detected in permeation tests: 0.47 \t.g/(cm2-min) for acetone, 0.12 \Lg/(cm2-min) for Cyclohexane, and 0.11 \Lg/(cm2-min) for toluene, and 0.31 \ig/(cm2-min) for isopropanol. 1200 1000 800 600 400 200 - Permeation Data Predicted from Immersion Data 10 20 30 40 Time, min 50 60 70 80 Figure 4. Comparison of predicted and experimental permeation rate curves for acetone through nitrite rubber. modified Paul model described in this report. In addition, the consideration of other theoretical models should be en- couraged. Perhaps the major recommendation to result from the current study is that there should continue to be a strong emphasis on the development of pre- dictive algorithms that are based as much as possible on the rigorous inter- pretation of diffusion theory. This ap- proach will allow permeation rate and cumulative permeation curves to be cal- culated as desired; other permeation- related parameters (for example, break- through times) can be determined from these curves. Note that rigorous predic- tive algorithms can always be modified to yield simple correlations; however, the extension of an algorithm based on empirical correlations to the calculation of quantitative data is often difficult if not impossible. The full report was submitted in fulfill- ment of Contract No. 68-03-3113 by Southern Research Institute under the sponsorship of the U.S. Environmental Protection Agency. ------- A. S. Bhown, E. F. Philpot, D. P. Segers, G. D. Sides, and R. B. Spafford are with Southern Research Institute, Birmingham, AL 35255. Michael D. Royer is the EPA Project Officer (see below). The complete report, entitled "Predicting the Effectiveness of Chemical-Protective Clothing: Model and Test Method Development," (Order No. PB 86-209 087'/AS; Cost: $16.95, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Releases Control Branch Hazardous Waste Engineering Research Laboratory—Cincinnati U.S. Environmental Protection Agency Edison, NJ 08837-3679 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Official Business Penalty for'Private Use $300 EPA/600/S2-86/055 0000329 PS *GENCY 230 S DEARBORN STREET CHICAGO IL 60604 * U.S GOVERNMENT PRINTING OFFICE. 1986 — 646-017/47157 ------- |