Transport of liquids in barrier plastics

Journal of Membrane Science, 3 (1978) 309-336 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The

309

Netherlands

TRANSPORT OF LIQUIDS IN BARRIER PLASTICS

DAVID S. WEINBERG Owens-Illinois, Inc., P 0. Box 1035, Toledo,

Ohio 43666

(U.S.A.)

Summary The transport of 1,1,24richloroethane, 1,1,2-trichloroethylene, and l,l,l-trichloroethane in the high nitrile polymer Barex @ 210 has been characterized as a function of temperature, polymer moisture content, polymer morphology, film thickness, and composition of liquid mixtures. The characterization studies were conducted using a novel liquid sorption procedure and a new variable temperature liquid permeation instrument. Although the liquids are structurally similar, they exhibit remarkably different transport behavior. 1,1,2Trichloroethane is a strong penetrant, 1,1,24richloroethylene is a weak penetrant, and l,l,l-trichloroethane is nearly a non-penetrant for Barex@ 210. The results obtained in this study are useful in evaluating transport mechanisms and provide guidance in designing procedures for evaluating barrier plastics as packaging materials for liquid products.

Introduction Well publicized efforts are underway to develop satisfactory plastic containers for liquid products such as carbonated beverages, liquor, medicinal and health products, personal products, and household chemicals [ 11. Recently attention has been focused on “barrier polymers” such as the high nitrile polymers, certain polyesters, and poly(viny1 chloride), since these polymers exhibit improved resistance to the transmission of gases, vapors, and liquids [ 2, 3, 41. However, the interaction of barrier polymers and liquids limits the use of these materials in many applications. We report here the results of a study of the transport behavior of three commercially important chlorinated hydrocarbons, 1,1,2-trichloroethane, 1,1,2-trichloroethylene and l,l,l-trichloroethane in the commercially important high nitrile barrier polymer Barex@ 210 using a novel liquid sorption procedure and a new liquid permeation instrument [ 53. A preliminary account of this work was presented before the Organic Coatings and Plastics Division of the American Chemical Society in New Orleans in March, 1977 [6]. Experimental 1. Ma teriuls

A. Barex@ 210 films. Barex @ 210 1 mil extruded and blown film (oriented

310

1.25 X 1.25) was obtained from Vistron Corp. and extruded 4.7 mil (oriented 1.0 X 1.4), 7.5 mil (oriented 1.0 X 1.1) and 38.8 mil (oriented 1.0 X 1.1) film was obtained from Vinyl Plastics, Inc. Chemical and spectroscopic analyses revealed only minor compositional differences between the films. Barex@ 210 film oriented 2.0 X 2.0 and 3.0 X 3.0 was produced using a Long Extensional Tester in the simultaneous stretch mode at 4 in/set and 105” C, with air quenching. “Dry film” (moisture content < 0.05%) was dried in vacua at room temperature for at least two weeks, “moist film” (moisture content = 0.6%) was obtained by exposing the film to laboratory air, and “wet film” (moisture content = 2.92%) was obtained by saturating the film with water at room temperature. Annealed film was obtained by heating the extruded film at 100” C (20” C above Ts) for 1 h in an oven, and cooling with the door closed. B. Liquids The liquids were the highest quality commercially available and all were at least 98% pure by gEgchromatographic (g.c.) analysis. Some of the chlorinated hydrocarbons were dried over activated Linde type 3A molecular sieves, some were used as received, and some were saturated with water. 2. Liquid sorption procedure A. Liquid sorption cells. Glass liquid sorption cells consisted of three sections made from 55/50 glass joints and tubes. The bottom section was an 8” long, l-7/8” diameter tube, closed at one end and containing a male joint at the other; the middle section consisted of a wide bore condenser with a female joint on the bottom and a male joint on the top; the top was a cap made from a female joint. Exit tubes were located on the cap and top of the condenser for evacuation or purging of the cell. B. Kinetic runs. A set of 25 1” X 6” film samples with identical areas were prepared from strips using a steel rule die and Diamat Die Cutter; the strips were cut from a roll in the extrusion direction to minimize thickness variations. The average thickness of each film was determined from its weight, area, and density. The films were placed between filter paper strips and attached to metal identification plates with stiff wires, which extended the length of the cell; the films were placed in the cell and the cell placed in a constant temperature bath. Thermometers were calibrated against a platinum resistance thermometer and the constant temperature baths were maintained to + 0.1” C. Hot liquid was added when the cell reached thermal equilibrium. Films were removed periodically with the aid of the wires, dried for 45 sec., dissolved in vials containing 5 ml aliquots of NJV-dimethylformamide (DMF) diluent and internal standards, and the sorbed penetrant (sorption concentration 0.01% to 110% of film weight) was determined using gas chromatography. A PerkinElmer 900 gas chromatograph was used with a 6’ X l/8” 10% Carbowax 20 M on 80/100 mesh chrom W (A/W) column and operated isothermally at 100” C in the flame ionization mode; a Columbia Scientific Industries Supergrator 1 was used for data acquisition. Calibration standards were analyzed regularly

311

to correct for any drift in response factor ratios. The run was continued until the films were saturated; the composition of liquid mixtures did not change significantly during the run because only small quantities of liquid were sorbed. Control studies indicated that free liquid was completely removed from the surface of the film by the drying procedure, with only a minimal loss of sorbed liquid. Also, studies employing pure liquids gave the same results whether the runs were conducted gravimetrically or by the g.c. procedure. The data were plotted as M,/M, vs dt/Z or t/Z, or 100 M,/W vs dt/l or t/Z and the sorption rates were characterized using the sorption half-times per mil of film thickness, tM. 3. Liquid permeation procedure A. Liquid permeation instrument design and construction. The liquid permeation instrument employed permeation cells which operated at atmospheric pressure. Liquid was placed on top of a polymer film separating two halves of the cell. It diffused through the film and evaporated into the lower half of the cell, where aliquots of vapor were periodically taken and analyzed using gas chromatography. Two non-magnetic stainless steel permeation cells were located in an explosion-proof Gruenberg oven. The lower half of each cell was well stirred by portable stainless steel fan stirrers, to insure that the permeated vapor was uniformly distributed throughout the cell. The fan stirrers were driven by circular magnets located under each cell, and these in turn were rotated by stirring motors located outside of the oven, through a mechanical linkage. The top half of each cell had inlet and outlet ports which were connected by Teflon tubing to valves located on top of the oven through which the liquid sample was introduced. The top of the cell also had a wide diameter bolt with a Teflon O-ring which could be taken off at the end of a run to remove the liquid. The bottom of the cell contained ports for sampling the permeated vapor, for purging the cell, and for introducing calibration standards. There was also a recessed ridge for holding a circular film support, which was a ring with a fine 40 X 40 mesh screen soldered to a stiff 10 X 10 mesh screen. Both the top and bottom of the cells had grooves for Teflon O-rings; the grooves were located in concentric positions, with the bottom O-ring groove having the larger diameter, to insure leakproof seals. The two halves of the cell were connected using three bolts. Temperature was maintained at 30 -300” C using a Love Temperature Controller; temperature fluctuation was less than 0.1” C in the 30-110” C range. A Carle microvolume gas chromatography sampling valve located within the oven was connected by l/8” stainless steel tubing, Swagelok fittings, and Whitey valves to the sampling port of each permeation cell, to a Welch vacuum pump, and to the gas chromatograph. A second Carle valve was located outside of the oven for sampling reference gas standards. A manometer was used to measure the pressure of the reference gas introduced into the sampling

312

valve coil and a McLeod gauge was used to detect system leaks. Samples taken by the Carle valves were analyzed on a Varian Associates Series 1700 gas chromatograph equipped with dual 5’ X l/8” Carbowax 20 M SO/l00 Varaport 30 chromatography columns and flame ionization detectors. The signal generated was amplified and fed to an Infotronics CRS 208 inte grator with Victor P-10 printer and a Hewlett Packard Electronik 194 Re corder. The peak areas of the eluted components were printed out and the amomit of permeated sample was calculated from the peak areas using a calibration equation corrected for instrument drift and sample consumed during the analyses. Calibration. A metal foil was substituted for the polymer film during the calibration of the cell, and the oven was heated to the temperature to be used in the kinetic run. A known quantity of liquid sample (0.5 ~2 to 20 ~1) was injected into the cell through a Teflon-faced silicone rubber septum and the stirrer started. The liquid evaporated and was uniformly distributed throughout the cell. Aliquots of vapor were taken and analyzed in the same manner as during a kinetic run (refer to the next section). The procedure eliminated the necessity of determining the permeation cell volume (about 300 cc) or sampling valve coil volume and minimized problems associated with the adsorption of the permeated vapor on the walls of the cell. A ratio of calibration sample peak area and reference peak area was used to minimize errors resulting from a drift in the instrument response factors. The reference standard was 10% methane in helium and the amount introduced into the Carle valve located outside of the oven was a function of room temperature and atmospheric pressure. The following expression relates the amount of calibration sample in the cell to the measured peak area, and is independent of fluctuations in room temperature, atmospheric pressure, or instrument response factors: Ms=m- PPS +b TP,

(1)

The fraction of sample in the permeation cell consumed during each analysis was determined by purging the cell with the reference standard, conducting 25 consecutive analyses (the cell was pressure equalized after each set of analyses without significant loss of sample), and analyzing the data using the following equation:

mJ?I _ k ’ (l-na--

l wo

TP, A plot of In [p(P,),/TP,] vs. n-l gave a straight line with slope ln(l-fl. value off was found to be 0.0136.

The

B. Kinetic runs. A circular film punched out with a die was placed on the recessed screen support in a cavity in the lower half of the permeation cell;

313

the edge of the film was tightly clamped to the cell by the Teflon O-ring when the cell was bolted together. The stirrer was started, the oven heated, and the top and bottom of the cell gently purged with inert gas. When the cell reached the desired temperature, purging was stopped, and hot liquid was added to the top of the film through a valve located on top of the oven. When ahquots of permeated vapor were taken, the Carle valve and tubing up to the permeation cell were evacuated, the vacuum pump closed out of the system, the cell sampling port opened to fill the sampling valve with an aliquot of permeated vapor, the cell sampling port closed, and the aliquot in the sampling valve injected into the gas chromatograph. The pressure in the cell dropped to 0.9864 of atmospheric pressure (i.e. 0.0136 of the cell contents were “consumed”) and was reconstituted to atmospheric pressure with negligible sample loss by exposure to inert gas or oven air. The permeated vapor was purged from the cell when its partial pressure reached 10% of its saturated vapor pressure, to minimize problems of back diffusion and sample condensation. Control studies indicated that after purging, the desorption of adsorbed vapor from the cell walls was minimal. The total amount of liquid which permeated into the cell between purgings is given by the following easily derived expression: ws=("s)n+f

n-l kz 1 wsh

I

(3)

The data are plotted as W, vs. t; the initial appearance of permeated vapor in the cell is designated the “appearance time,” L,, and the slope of the curve in the stationary state, divided by the film area and multiplied by the film thickness, is the transmission coefficient, JZ. C. Performance. The permeation of liquids through glassy polymers is dependent on a number of variables and therefore comparison of the results obtained in this study with published results is of limited significance. However, in a control study, it was found that the permeability coefficient for the transport of ethyl acetate through Phillips Petroleum Co. high density polyethylene (11.8 mils thick) at 74” F was P = 4.5 g-mil/lOO in2-day, while Salame [ 71 reported P = 4.50 g-mil/lOO in2-day at 73” F. Although the precise agreement of the results is fortuitous, it does indicate that the liquid permeation instrument described here and traditional instruments are capable of yielding comparable data. Results and discussion Polymer/liquids/tempemture Dry Barex@ 210 film (1 mil nominal thickness) rapidly sorbs l,l,Btrichloroethane, slowly sorbs 1,1,2trichloroethylene, and is almost inert to l,l,l-trichloroethane at 80.4” C. The first liquid is sorbed to a high equilibrium

314

concentration and the second to a moderate concentration. The results are summarized in Table 1 and selected sorption curves are plotted in Figs.1 and 2. The sorption curves for 1,1,2trichloroethane and 1,1,2-trichloroethylene are linear functions of d/t/l for M, < 0.6 M,:

MJM,

= Cd/t/i

(4)

The curves thus have a strong Fickian character [ 81, as expected, since the temperature of the sorption runs is the same as the Tg of the polymer [9]. However, in order to characterize sorption rates, the sorption half-time per mil of film thickness, t%, is used in place of a diffusion coefficient in view of the heterogeneous nature of the graft copolymer and the extensive swelling TABLE

1

Transport of liquids in extruded and blown Barex @ 210 film at 80.4” C (nominal thickness = 1 mil) Sorptiona

1,1,2-Trichloroethane 1,1,2-Trichloroethylene l,l,l-Trichloroethane

Permeationb

tlh (min)

100 M-/W

L,

4.85 3870 40,000c

110 38.2 < 0.5

17 4800 20,000c

(min)

aFilm thicknesses for 1,1,2trichloroethane, 1,1,2trichloroethylene, and were 1 = 2.26 x lo-“, 2.29 x 10m3, and 2.28 x lOma, respectively. bFilm trichloroethane, 1,1,2trichloroethylene, and l,l,l-trichloroethane were 2.41 X lo-‘, 2.41 x lo-” cm, respectively. cElapsed time of sorption or

n x 1O’O (g/cm-set) 18.2 0.00584 N.D. l,l,l-trichloroethane thicknesses for 1,1,2I= 2.29 x 10e3, permeation run.

80.4% Q8-

‘0

2

4

6

8

IO

12

14

16

18

20

Jiil . tc3 hLc’n) Fig.1. Sorption of 1,1,2-trichloroethane by extruded and blown Barex@ 210 film content < 0.05%; nominal thickness = 1 mil). Refer to Table 1.

(moisture

315

804°C

Jvl. Id3 (cm’ !A?) Fig.2. Sorption of 1,1,2-trichloroethylene by extruded and blown Barex@ 210 film (moisture content < 0.05%, nominal thickness = 1 mil). Refer to Table 1.

which occurs. The t, values are calculated 2.54 X 1O-3 tlh =

(

* 1

1

t

using eqn. (5):

SF

(5)

The calculation is most meaningful when the film thickness does not deviate greatly from the value I = 2.54 X 10V3 cm, since thick films exhibit anomalous sorption behavior (vide infra). The permeation of 1,1,2&ichloroethane through dry Barex@ 210 film (1 mil nominal thickness) is much faster than that of 1,1,2-trichloroethylene, which in turn is much faster than that of l,l,l-trichloroethane at 80.4” C, as indicated in Table 1 and Figs. 3 and 4. The transmission coefficient, Jl, for 40

I

I

I

I

I

I

I

I

I 8Q4”C

32

Purge

M(mg) 2[

l’i

,:

I I I I 1 50 80 70 80 90 IO0 Urnin) Fig.3. permeation of 1,1,2-trichloroethane through extruded and blown Barex@ 210 film (moisture content < 0.05%, nominal thickness = 1 mil). Refer to Table 1. ‘0

I IO

1 20

I 30

I 40

316 20

I

I

I

I

I

I

I

I

I 80.4T

16 12Mtmg) 84-

‘0

20

40

60

80

100 t (mid

120

140

160

I80

200

. IO-*

Fig.4. Permeation of 1,1,2-trichloroethylene through extruded and blown Barex@ 210 film (moisture content < 0.05%, nominal thickness = 1 mil). Refer to Table 1.

1,1,2trichloroethane is remarkably small in view of the substantial quantity of liquid present in the film in the permeation steady state (100 M/W = N-90, i.e., 80-90 grams of liquid per 100 grams of polymer). For 1,1,2trichloroethane the ratio of the permeation appearance time La, to the sorption halftime, t$j, is 4-5 for films of similar thickness. This ratio is in the expected range, i.e., for ideal Fickian diffusion, La/t: = 3.4 and for pure Case II tmi~ art 181, La/t: = 4.0. However, the ratio for 1,1,2+ichloroethylene is E La/t?4 = 1.25; this small value suggests that some 1,1,2-trichloroethylene rapidly permeates through the film before extensive swelling occurs. This result was also obtained for 1,1,2-trichloroethane at low temperature and 1,1,2trichloroethane/l,l,2-trichloroethylene mixtures at higher temperature and will be discussed further below. Significant quantities of l,l,l-trichloroethane did not permeate through Barex@ 210 film during the course of the permeation run alluded to in Table 1. The substantial difference in the transport behavior of the three liquids in Barex@ 210 is attributed to differences in their polarity as reflected by their solubility parameters [lo] (S = 8.57, 9.28, and 10.18 for l,l,l-trichloroethane, 1,1,2-trichloroethylene, and l,l,Btrichloroethane, respectively, compared to S = 11.8 estimated for Barex@ 210). Presumably, the nitrile groups in Ba.rex@ 210 impart solvent resistance to the polymer by the formation of transient “nitrile-nitrile crosslinks”; disruption of the crosslinks by interaction with penetrants of increasing polarity permits rapid swelling of the softer segments present in the polymer. Dry Barex@ 210 film (1 mil nominal thickness) sorbs 1,1,2trichloroethane more slowly at 60.0” C than at 80.4” C, but the value of 100 AL/W remains unchanged. The results are shown in Table 2 and the sorption curve is plotted in Fig.5. The sorption curve has strong Case II (polymer relaxation controlled)

317

TABLE

2

Sorption of 1,1,2trichloroethane (nominal thickness = 1 mil)

by dry, extruded and blown Barex@ 210 film

T(“C)

1 x lo3 (cm)

tH (min)

80.4 60.0 50.2 44.5 40.4 29.6

2.26 2.69 2.62 2.67 2.63 2.25

4.85 15.5 70.7 130 607 7500

t/1 .

Kf6(cm’ set)

Fig.5. Sorption of 1,1,2+ichloroethane by extruded and blown Barex@ 210 film (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 2.

character [ 81, since the sorption is a linear function of t/Z for Mt/i% < 0.6 : M,/M, = k t/l

(6)

Consequently, h,+ is calculated from tlz using eqn. (7), subject to the same restriction mentioned for eqn. (5) : 2.54 X 1O-3

ts = (

1

1

t

z

(7)

Presumably k provides a measure of the rate of movement of the liquid boundary through the film and this behavior is typical for glassy polymers below Tg. On the other hand, Barex@ 210 film (nominal thickness = 1 mil) sorbs 1,1,2&ichloroethylene too slowly at 60” C to reach equilibrium in an acceptable period of time. After 26 days, 100 M&V = 4, with no decrease in the sorption rate detectable. Further study of the behavior of 1,1,2trichloroethylene was confined to mixtures of this component and 1,1,2trichloroethane.

318

Barex@ 210 film (nominal thickness = 1 mil) does not sorb detectable quantities of l,l,l-trichloroethane at 60” C, and the behavior of this liquid was not considered further. Two permeation runs using 1,1,2-trichloroethane were conducted at 60” C. In the first study, a permeation run which had been initiated at 80.9” C was subsequently cooled to 60.5” C, as shown in Table 3 and Fig.6. In a second study, TABLE

3

Permeation of 1,1,2trichloroethane (nominal thickness = 1 mil)

through dry, extruded and blown Barex@ 210 film

T(“C)

IX lO”(cm)

L, (min)

Jl X lOLo (g/cm set)

80.ga

2.29 2.29 2.29

21

60.5’ 40.9”

18.3 11.7 7.2

60.86 40.9b

2.32 2.32

50 -55

40.4=

2.34

< 22

3.02

50.2d 45.9d 40.4d 35.4d 30.5d

2.29 2.29 2.29

90

3.43 2.97 2.42 1.91 1.70

2.29 2.29

6.87 3.01

aRun initiated at 80.9” C and subsequently cooled. bRun initiated at 60.8” C and subsequently cooled. CRun initiated at 40.4” C. dRun initiated at 50.2” C and subsequently cooled.

40

80.9

,> CI

TEMP. (“Cl 60.5

cc

40.9

Fig.6. Permeation of 1,1,2-trichloroethane through extruded and blown Barex@ 210 film (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 3.

319

the run was initiated at 60.8” C, as shown in Table 3 and Fig.7. Apparently the first JZvalue measured is high, due to morphological and/or chemical changes induced in the film at 80.4” C, and the second value is taken as correct. The technique of initiating a permeation run at a high temperature and subsequently, reducing the temperature will be discussed further below. The ratio La/t6 = 3.4-3.8, compared to a theoretical value of 4 for Case II transport for films of identical history and thickness. TEMP. PC) 60.8

40

32-

40.9

.> II

Purge

24M (mg) 16 -

8-,

,.‘I

i

ii /

‘0

2

4

6

f

h

“~~WW~~‘;r68 8’18 2030 t (mid .l6’

Fig.7. Permeation of 1,1,2_trichloroethane through extruded and blown Barex@ 210 (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 3.

film

Below 60” C, the sorption behavior of 1,1,2trichloroethane greatly increases in complexity, although 100 Mm/W = 110 at each temperature. The initial sorption rate increases until the sorption curve becomes a linear function of t/Z, as indicated in Table 2 and Fig.5 The following empirical equation describes the behavior for M,/M, < 0.6: M,/M,

= k {t/Z- [tL/Z] [1-exp(-t/T)]

)

(8)

The value of k is estimated from the slope of the straight line portion of the curve, tL/Z from the extrapolated intersection of this line with the abscissa, and 7 /I from the slope of a curve plotted by rearranging eqn. (8) and using the previously calculated k and tL/Z values. Refinement of the calculation is not necessary, since the exponential term rapidly approaches 0 above Mt/Moo = 0.2 and there is always scatter in the experimental data. Parameters obtained from runs at various temperatures are shown in Table 4. The value of ts is calculated from tlz using eqn. (9) again subject to the limitation that Zshould not vary greatly from 2.54 X 10S3 cm: tq$ =

2.54 X lo-” z

)t;

+tJ1-

2*54;

lo-“)

(9)

320

TABLE

4

Sorption run parametersa T(“C)

k X lOa (cmlsec)

60.0 50.2 40.4 29.6

142 37 4.4 0.32

tL/l x 10T6 (seclcm) ~____ 0.0141 0.31 2.2 24

____~ 7/Z x 10T6 (se&m) 0 0.17 3.3 18.9

aRefer to eqn. (8) in the text.

The equation assumes that tL varies little with film thickness, and this in fact appears to be true (vide infra). The apparent activation energy for the sorption process yielding the linear portion of the sorption curve may be estimated from a plot of In k vs. l/r; a straight line is obtained and AE = 40.8 kcal/mol. This high value is typical for non-Fickian sorption behavior [ 111. The anomalous sorption behavior may be a result of stress-accelerated sorption; i.e., as the outer layer of film swells, it exerts a stress on the unswollen inner core, thereby accelerating sorption until a quasi-equilibrium state is reached. Alte~d,t&,a contribution from a skin effect, which becomes more pronounced as the temperature is reduced, may be important. The permeation behavior of 1,1,2-trichloroethane is also extremely complex below 60” C. Two permeation runs were initiated at 80.9” C and 60.8” C, respectively, and each was subsequently cooled to 40.9” C; a third run was initiated at 40.4” C and the results are summarized in Table 3 and plotted in Figs.6, 7 and 8. The 80.9” C run yields an anomalously high transmission coefficient

16 12 M (mg)

0-

tImin) 16’ Fig.8. Permeation of 1,1,2-trichloroethane through extruded and blown Barex@ 210 film (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 3.

321

at 40.9” C, presumably for the same reason it gave a high value at 60.5” C. On the other hand, the run initiated at 60.5” C gives essentially the same JZ value upon cooling to 40.9” C as the run initiated at 40.4” C. However, the L, value is unexpectedly small for the 40” C run; in fact it is substantially smaller than the value obtained at 50” C. The result is quite reproducible and suggests, along with the shape of the permeation curve, that a limited quantity of liquid rapidly permeates through the glassy structure before the bulk of the liquid breaks through [ 121. In an earlier permeation study, the permeation run was started at 50.2” C and after the stationary state was reached the temperature was reduced to 40.4” C and 30.5” C, and then increased to 35.4” C, 45.9” C, and 50.2” C. The results are summarized in Table 3. The entire run lasted two weeks and the final Jl value is only 1 O-l 5% lower than the initial value, suggesting that only minor changes occur in the film morphology at these temperatures. A plot of In k vs. l/T is linear, and yields an apparent activation energy of AE = 7.2 kcal/ mol. Presumably the value is so much lower than the analogous value measured in the sorption runs because the stationary state permeation rates are little affected by temperature as a consequence of the high degree of film platicization. Polymer moisture content Moist Barex@ 210 film (moisture content = 0.6%, nominal thickness = 1 mil), sorbs 1,1,2trichloroethane at nearly the same rate at 60.0” C, and at somewhat faster rates at lower temperatures, than the dry film, as indicated in Table 5. The value of 100 J&/W = 110 at all temperatures. The apparent activation energy is AE = 39.9 kcal/mol, which is only slightly smaller than for the dry film. Thus, variable moisture levels in the 0.05 to 0.6% range have limited influence on sorption behavior. Wet Barex@ 210 film (moisture content = 2.92%, nominal thickness = 1 mil) sorbs 1,1,2trichloroethane at nearly the same rate as the dry film at 58.6” C, but at a much faster rate than the dry film at 29.6” C, as indicated in Table 5. The value of 100 M&W = 110-l 20 at each temperature, with considerable scatter in the data. A crude activation energy calculated using only two data TABLE

5

Effect of moisture content of extruded and blown Barex@ 210 film on the sorption of 1,1,2+richloroethane (nominal thickness = 1 mil) Moisture content (%) 0.05 0.6 2.92

t,

(min)

80.4” C

59.3 f 0.7” c

50.3 f O.l”C

40.0 f 0.5” c

29.6” C

4.85

15.5 18.7 17.5

70.7 54.2

607 597

7500 5420 58.6

322

points is AE = 5.5 kcal/mol. The substantial increase in rate at the lower temperature must be due to film plasticization [ 131; moisture is less effective in increasing sorption rates at elevated temperature since the polymer chains are already quite mobile. Polymer morphology Dry, annealed Barex@ 210 film (nominal thickness = 1.4 mil) sorbs 1,1,2trichloroethane at a rate (per unit of film thickness) only a little slower than that of the dry extruded and blown film at 60” C, but at a dramatically reduced rate at 30” C. The results are depicted in Table 6. The value of 100 M,/W is the same as that of the unannealed film at each temperature. The activation energy, AE = 55.1 kcsl/mol, is about as high as is generally observed for anomalous transport [ 111. Presumably the reduction in free volume during annealing leads to a considerable reduction in the mobility of the polymer chains and hence to the sorption rate at low temperature, but is relatively ineffective in decreasing sorption rates at elevated temperatures. TABLE

6

Effect of polymer morphology on the sorption of 1,1,2-trichloroethane Polymer morphology

tS (min) 59.0 + 0.1” c

50.1 f O.l”C

40.2 f. 0.2” C

by Barex@ 210 film

29.6” C

Annealeda 40.3 446 4110 250,000 Blownb 15.5 70.7 607 7500 Oriented 2 x 2c 28.2 Oriented 3 x 3d 17.6 _ ONominal film thickness = 1.4 mil. bNominal film thickness = 1 mil. =Nominal film thickness = 9 mil. dNominal film thickness = 4 mil.

Dry Barex@ 210 film (oriented 2.0 X 2.0, nominal thickness = 9 mils and oriented 3.0 X 3.0, nominal thickness = 4 mils) sorbs 1,1,2&chloroethane at about the same initial rate as a corresponding unoriented film at 60” C, as shown in Table 6 and Fig.9. However, near the end of the sorption for the 2.0 X 2.0 oriented film and as Mt/M- approaches 0.75 for the 3.0 X 3.0 oriented film, shrinkage occurs and the sorption rate slows enormously. This is probably due primarily to the thickening of the film which takes place. The results obtained from a permeation run conducted at 50” C and subsequently cooled to 40” C and 30” C are shown in Table 7. The La value is smaller than that observed for a corresponding unoriented film, while the Jl value is about one-half as large. The activation energy for permeation is estimated to be 7.3 kcal/mol.

323

l

Onented 30

X 30,

Nomlnal Thtckness = 39mil

0 Ownted 20 X 20,

‘0

I

2

3

4 t/1 . IO*

Fig.9. Sorption of 1,1,24richloroethane < 0.05%). Refer to Table 6.

Nommal Thckness = 89 mil

5

(cm’ set)

6

7

8

9

IO

by oriented Barex@ 210 film (moisture content

Film thickness Dry Barex@ 210 film (nominal thickness = 4.7 or 7.5 mils) sorbs 1,1,2trichloroethane in a manner analogous to that previously reported for the 1 mil extruded and blown film. The results for the 80”, 60”, and 40” C sorption runs are shown in Table 8. The 100 M,/W values equal 104 and 107 for the 4.7 and 7.5 mil films, respectively, independent of the temperature of the run. The sorption curves show considerably more curvature than observed for the thin films and, although morphological differences may play a role, this result is probably due primarily to anomalous thickness effects [ 141. The sorption rates are also faster than anticipated from the previous results, obtained from 1 mil film, as indicated by the low ts values shown in Table 8; the values were estimated by the procedures described previously for the 1 mil film. No attempt was made to determine precisely the value of tL, in view of the nonlinearity of the curves, but it appears that the values are quite similar to the values observed for the 1 mil film. This provides additional evidence for the notion that the lag time is due to a surface layer effect. The results obtained from permeation runs conducted on the films are detailed in Table 9. Each run was initiated at 50” C and cooled to 40” C and then 30” C. The La values probably should not be compared to the values obtained with the 1 mil film, since no attempt was made to conduct the runs under comparable circumstances. However, the difference in the films should be minimized when the permeation steady state is reached, due to the high level of plasticization of the film. The increase in the Jl value is striking and suggests that most of the resistance to permeation must reside in the surface layer, as in the case for the thick oriented film discussed above, probably as a result of the highly nonlinear concentration gradient. The JZvalues are not strongly influenced by temperature, and AE = 11.1 and 12.2 kcal/mol for the 4.7 and

2.29 11.2

3

Blown Oriented 3

x

1 X lo3 (cm)

Polymer morphology

90 400-450

3.43 9.42

N.D. N.D.

L, (min)

La (min) (g/cm-see)

40.4” c

50.2” C n x 1O’O

Effect of polymer morphology on the permeation of 1,1,2-trichloroethane

TABLE 7

2.42 6.97

(g/cm-set)

Jl x 1O’O

N.D. N.D.

La (min)

30.5” c

through Barex@ 210 film

1.70 4.32

(g/cm-set)

Jl X lOlo

325

TABLE

8

Effect of film thickness on the sorption of 1,1,2trichloroethane Film thickness 1 X 10” (cm)

2.66 12.2 18.7

f ? f

0.03a 0.5 0.1

by Barex@ 210 film

tH (min) b 80.3 f 0.1” c

60.1” C

40.2 f 0.2” C

4.35 1.41 1.07

15.5 16. 20.5

608 % 392 % 315

aFilm thickness for 80” C run was 2.26 x lo-” cm. bt, values are not included since the sorption curves exhibit considerable curvature; however, a crude extrapolation indicates the values are approximately the same as observed previously for the 1 mil films.

7.5 mil films, respectively. It is not clear why these apparent activation energies are higher than the values obtained for the extruded and blown or oriented films. Liquid mixtures The solubility of binary mixtures of 1,1,2&chloroethane and l,l,Ztrichloroethylene in Barex@ 210 film is described in Table 10 and Fig.lO. The results are essentially identical at 80.4” C and 60.0” C. The results from the sorption runs are depicted in Table 11 and Figs.11 and and 12. The sorption behavior is complex and, in view of the complexity, the sorption curves are plotted as M,/M, vs. t/Z. Consequently, the ts values were calculated using eqn. (4) since the film thicknesses do not deviate excessively from 1 mil. Barex@ 210 sorbs both components simultaneously, with 1,1,2trichloroethylene (the weaker penetrant) lagging a little behind 1,1,2-trichloroethane (the stronger penetrant). The ratio of the amount of l,l,Ztrichloroethane to 1,1,2&ichloroethylene dissolved in the polymer gradually decreases during the course of a kinetic run until at equilibrium the ratio dissolved in the polymer divided by the ratio in the feed equals 1.25 f 0.1. The activity of each component in a binary mixture is reduced by the presence of the other component; consequently the rate of sorption of 1,1,2-trichloroethane is slower in the mixture than in the pure state. As the 1,1,2-trichloroethane enters the polymer, it plasticizes it and thus the 1,1,2-trichloroethylene in the mixture enters the polymer faster than it does in the pure state. The net result is that as the concentration of the stronger penetrant in the original mixture increases, the rate of sorption of each component increases. The effect is smaller at 80.4” C than at 60.0” C, presumably as a result of the enhanced mobility of the polymer chains. However, at each temperature, In ts decreases nearly linearly with an increase in VTA, as shown in Fig.13, indicating that addition of small quantities of the strong penetrant to the weak penetrant leads to an excessive increase in the overall sorption rate when plasticization of the polymer is important in the sorption process.

2.29 11.65 18.7

Film thickness 1 X lo3 (cm)

2.42 10.5 11.0

L, (min) N.D. N.D. N.D.

Jl X lOlo (g/cm-set)

3.43 18.5 21.6

L, (min)

90 750-800 1550-1600

JZ X 10” (g/cm-set)

40.4” c

through Barex@ 210 film

50.2” c

Effect of film thickness on the permeation of 1,1,2-trichloroethane

TABLE 9

Jl X 10” (g/cm-set) 1.70 5.94 6.24

L, (min) N.D N.D. N.D.

30.5” c

321

TABLE

10

Solubility of 1,1,2-trichloroethane/l,l,2-trichloroethylene blown Barex@ 210 film ~__ “TA

“TE

@TE

@TA

QP

mixtures in extruded and

(@TA/@TE)

+ tVTAIVTE)

Temperature = 80.4” C; moisture content < 0.05% 1.0 0.8 0.6 0.5 0.4 0.2 0.0

0.0 0.2 0.4 0.5 0.6 0.8 1.0

0.468 0.371 0.268 0.230 0.181 0.0863

0.0747 0.157 0.178 0.209 0.253 0.231

0.531 0.554 0.576 0.592 0.609 0.661 0.769

1.24 1.14 1.29 1.29 1.36

Temperature = 60.0” C; moisture content = 0.6% 1.0 0.8 0.6 0.5 0.4 0.2 0.0

l.O-

0.0 0.2 0.4 0.5 0.6 0.8 1.0

0.468 0.369 0.270 0.218 0.185 N.D. N.D.

I

0.0731 0.139 0.181 0.204 N.D. N.D.

I

0.531 0.558 0.590 0.600 0.610 N.D. N.D.

I

1.26 1.29 1.26 1.35 N.D. N.D.

I

So.4OC 0.8 -

Fig.lO. Solubility of mixtures of 1,1,2trichloroethane (TA) and 1,1,2trichloroethylene (TE) in extruded and blown Barex@‘IlO film (P). (Moisture content < 0.05%; nominal thickness = 1 mil). @, volume fraction in the polymer phase; YTA, volume fraction of TA in the liquid phase. Refer to Table 10.

328

TABLE

11

Sorption of 1,1,2-trichloroethane/l,l,2trichloroethylene blown Barex@ 210 film (nominal thickness = 1 mil) ?A

VTE

I X

lo3 (cm)

tH (min) TA

Temperature 1.0 0.8 0.6 0.5 0.4 0.2 0.0 Temperature 1.0 0.8 0.6 0.5 0.4 0.2 0.0

= 80.4’ C, moisture 0.0 0.2 0.4 0.5 0.6 0.8 1.0

2.26 2.25 2.38 2.34 2.34 2.38 2.13

= 60.0” C, moisture 0.0 0.2 0.4 0.5 0.6 0.8 1.0

content

2.69 2.72 2.54 2.29 2.29 2.19 2.29

TE

< 0.05% 4.85 18.4 52.0 92.2 180 1070

content

mixtures by extruded and

17.4 55.0 123 223 1180 3870

= 0.6% 15.5 54.2 289 752 2900 N.D. N.D.

60.7 334 957 3100 N.D. N.D.

The permeation behavior of the binary mixtures is depicted in Table 12 and Figs.14-17. It is significant that in each run the appearance time of each component is the same, although the 1,1,2kichloroethane enters the polymer preferentially. The La/t; ratios decrease as the concentration of 1,1,2-trichloroethylene in the liquid increases, and this, together with the result for the La values, provides additional evidence that some of the liquid rapidly penetrates through the film before extensive swelling occurs. Little fractionation of the liquid mixture occurs and (JTA/JTE)+( VA/VTE) is close to 1. As indicated in Fig.18, In La is a decreasing linear function of vTA and as indicated in Fig.19, In JZ for both 1,1,2-trichloroethane and 1,1,2-trichloroethylene are strongly increasing, somewhat linear functions of vTA. Thus, in addition to substantially increasing the sorption rates, addition of small quantities of 1,1,2-trichloroethane to 1,1,2-trichloroethylene even more substantially increases permeation rates, presumably as a consequence of the critical role of film plasticization in the permeation process.

329

60TA 40TE 80 4oc 0 /

8OTA 20TE 804%

TA

0

40-

.

4

I

20

TE

I

I

I

40

60

80

WI-‘SEX)

40TA

‘0

40

80

20TA

60TE

120

I60 t/l * lo*

0

100

200

80TE

300

400

500

bAec)

Fig.ll. Sorption of mixtures of 1,1,2-trichloroethane (TA) and 1,1,2&ichloroethylene (TE) by extruded and blown Barex@ 210 film (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 11.

Conclusion The transport of 1,1,24richloroethane in Barex@ 210 occurs with greater facility than that of 1,1,2-trichloroethylene or l,l,l-trichloroethane, presumably as a consequence of its higher polarity. The transport mechanisms are a sensitive function of temperature. At 80” C, the sorption of 1,1,24richloroethane and 1,1,24richloroethylene has strong Fickian character, although the sorption of 1,1,24rich!oroethylene is complicated by the penetration

330

60TA 40TE 600°C

80TA

20TE

TE

‘0

IO

20

30

40

0

t/1 .

40TA

20

40

80

100

d6(cm’ SIX)

20TA

60TE

t/l

60

80TE

. ici6 (cm’ st3c)

Fig.12. Sorption of mixtures of 1,1,24richloroethane (TA) and 1,1,24richloroethylene (TE) by extruded and blown Barex@ 210 film (moisture content = 0.6%; nominal thickness = 1 mil). Refer to Table 11.

of significant quantities of liquid through the film before extensive swelling occurs. At 6O”C, the sorption of 1,1,2+ichloroethane follows polymerrelaxation-controlled kinetics, while the sorption of 1,1,2Mchloroethylene and l,l,l-trichloroethane occurs too slowly to be monitored. Below 60” C, the sorption of l,l,%trichloroethane is extremely complex; a lag-time is observed, as a result of stress-accelerated sorption or a skin effect. At 40” C, some of the liquid rapidly penetrates through the frozen glassy residue before extensive swelling occurs.

331

uTA

Fig.13. Plot of In tH vs. vTA for sorption of 1,1,2trichloroethane and 1,1,2trichloroethylene from binary mixtures by extruded and blown Barex @ 210 film (moisture content < 0.06% or 0.6%; nominal thickness = 1 mil). Refer to Table 11. TABLE

12

Permeation of 1,1,2-trichloroethane/l,l,2trichloroethylene mixtures through extruded and blown Barex@ 210 film (moisture content < 0.0596, nominal thickness = 1 mil) YTA

‘TE

I x lo5 (cm)

TA 1.0 0.8 0.6 0.5 0.4 0.2 0.0

0.0 0.2 0.4 0.5 0.6 0.8 1.0

2.32 2.20 2.41 2.34 2.38 2.36 2.41

JZ x lOlo (g/cm-set)

L, (min)

14 38 136 207 430 1604

TE

38 135 207 430 1504 4800

TA 18.2 4.89 0.929 0.462 0.194 0.018

TE

1.25 0.582 0.435 0.284 0.059 0.00584

The rate of sorption is strongly dependent on polymer morphology and moisture content at 30” C, but is virtually independent of both of these at 60” C, presumably as a result of the enhanced mobility of the polymer chains at the higher temperature. Film thickness has an anomalous effect on both sorption and permeation rates; the sorption curves for thick films (4-8 mils) exhibit substantially more curvature than the corresponding curves for thin films (1 mil), and both the sorption and permeation rates for the thick film are faster than anticipated from the results from the thin film. This result is apparently due to skin effects. Temperature has a critical effect on sorption

332 25

I

Purge

I

I

80.4%

2015Mhg) IO5-

OO

I

2 3 4 t (mid . l6* Fig.14. Permeation of an 80 : 20 mixture of 1,1,2trichloroethane (TA) and 1,1,2trichloroethylene (TE) through extruded and blown Barex @ 210 film (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 12. 20 16 Purge

I2 Mhg) 84 ,‘0 t (mid * i6* Fig.15. Permeation of a 60 : 40 mixture of 1,1,2trichloroethane (TA) and 1,1,2trichloroethylene (TE) through extruded and blown Barex@ 210 film (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 12.

rates, with activation energies falling in the range of 40-55 kcal/mol while it has a limited effect on stationary state permeation rates with AE = 7-12 kcal/ mol; presumably the latter result is a consequence of the high degree of film plasticization. The sorption and permeation behavior of liquid mixtures is exceedingly complex. 1,1,2Trichloroethane rapidly penetrates-Barex@ 210, plasticizes it, and in the process carries 1,1,2trichloroethylene into the film with it. The ratio of 1,1,2trichloroethane to 1,1,2&ichloroethylene dissolved in the poly-

333

16-

12M (mg)

Purge

8-

Fig.16. Permeation of a 40 : 60 mixture of 1,1,2trichloroethane (TA) and 1,1,2trichloroethylene (TE) through extruded and blown Barex @ 210 film (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 12.

20

30

40 t (mid . Iti

50

60

70

80

Fig.17. Permeation of a 20 : 80 mixture of 1,1,2+ichloroethane (TA) and 1,1,2trichloroethylene (TE) through extruded and blown Barex @J210 film (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 12.

mer film at equilibrium is somewhat greater than it is in the feed, but essentially no fractionation occurs in a permeation experiment; thus the normally slowly permeating 1,1,2trichloroethylene permeates much faste; through the film than the normally rapidly permeating 1,1,24richloroethane, when the concentration of the former in the feed is greater than that of the latter.

InL, 42-

OO

I

I

I

a

0.2

0.4

0.6

0.8

UTA

Frg.18. Plot of In L, vs.vTA for permeation of binary mixtures of 1,1,2trichloroethane and 1,1,24richloroethylene through extruded and blown Barex@ 210 film (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 12.

I

-20

I

I

I

-

0

L 0.2

1 0.4

1 0.6

I 0.8

1.0

9A

Fig.19. Plot of In Jl vs. vTA for permeation of binary mixtures of l,l,P-trichloroethane and 1,1,24richloroethylene through extruded and blown Barex@ 210 film (moisture content < 0.05%; nominal thickness = 1 mil). Refer to Table 12.

Acknowledgment The author wishes to thank Ms. B.J. Koltay for conducting many of the sorption runs, Mrs. M.B. Henderson for conducting some of the permeation runs, and Owens-Illinois, Inc. for permission to publish this paper.

335

List of symbols b

7

J

Jl k k’ 1

L

La ii MS

WIl

Mt

WC.

lOOM/W ; p: t tz t, tL

T W'o Ws +TE @TE @P 7 P VTA VTE

intercept, eqn. (1) constant, eqn. (4) fraction of sample in cell consumed in each analysis, eqn. (2) flux ( g/cm2-see) transmission coefficient (g/cm-see) constant, eqns. (6) and (8) constant, eqn. (2) initial film thickness (cm) lag time (min) appearance time, i.e., time required for detectable quantity of penetrant to permeate through membrane (min) slope, eqn. (1) mass of permeated penetrant (g) amount of calibration sample in cell (g), eqn. (1) amount of sample measured by nth analysis, eqn. (3) mass of sorbed liquid at time t (g) mass of sorbed liquid at equilibrium (g) grams liquid sorbed per 100 grams polymer number of analyses, eqn. (2) calibration sample peak area, eqns. (1) and (2) reference peak area, eqns. (1) and (2) time (min) actual sorption half-time (min) sorption half-time per mil of film thickness (min) constant, eqn. (10) temperature (” C or “A, as noted) amount of sample originally in cell, eqn. (2) total amount of vapor which had permeated into cell since previous purging, eqn. (3) volume fraction of 1,1,2-trichloroethane volume fraction of 1,1,2-trichloroethylene dissolved in polymer volume fraction polymer constant, eqn. (8) pressure (atm), eqns. (1) and (2) volume fraction 1,1,2-trichloroethane in binary mixtures with 1,1,2&ichloroethylene volume fraction 1,1,2trichloroethylene in binary mixtures with 1,1,2trichloroethane.

336

References

10 11 12 13 14

M.S. Thompson, Package Development, 1 (1971) 26. Modern Plastics, 50 (1973) 62. Package Engineering, 21 (1976) 38. Chemical Week, August 25, 1976, p.25. J.D. Idol and K.E. Blower, in P.F. Bruins (Ed.), Packaging with Plastics, Gordon and Breach Science Publishers, New York, 1971, p.151. D.S. Weinberg, Org. Coat. and Plast. Preprints, 37 (1) (1974) 325, 337. M. SaIame, SPE Transactions, 1 (1961) 153. H.B. Hopfenberg and H.L. Frisch, Polym. Let., 7 (1969) 405. H. Fujita, in J. Crank and G.S. Park (Eds.), Diffusion in Polymers, Academic Press, New York, 1968, Chpt. 3. C.M. Hansen, J. Paint. Techn., 39 (1967) 104. H.B. Hopfenberg and V. Stannett, in R.N. Haward (Ed.), Physics of Glassy Polymers, J. Wiley and Sons, New York, 1973, Chpt. 9. See, for example, P. Meares, J. Polym. Sci., XXVII (1958) 405. F.A. Long and L.J. Thompson, J. Polym. Sci., XIV (1954) 312. G.S. Park, J. Polym. Sci., XI (1953) 97.