Yam, Kit L. (ed.). The Wiley encyclopedia of packaging technology

Подождите немного. Документ загружается.

24. See http://www.thecoca-colacompany.com/presscenter/

presskit_contour_bottle_time_line.html.

25. 15 U.S.C. y 1127.

26. See In re Clarke, 17 U.S.P.Q. 2d 1238 (T.T.A.B. 1990).

27. See, Qualitex Co. v. Jacobson Products Co., Inc. 514 U.S. 159,

1303 (1995).

28. J. T. McCarthy, McCarthy on Trademarks and Unfair Com-

petition Fourth Edition Vol. 2, Thomson West, 2008, 11-1 to

11-210, 12-1 to 12-212.

29. Grace & Co. v. Union Carbide Corp., 581 F.Supp. 148

(S.D.N.Y. 1984).

30. In re Serv-A-Portion, Inc., 1 U.S.P.Q.2d 1915 (T.T.A.B. 1986).

31. In re Polytop, 167 U.S.P.Q 383 (T.T.A.B. 1970).

32. 15 U.S.C. yy 1058, 1059.

33. 17 U.S.C. y 102; A. R. Miller and M. H. Davis, Intellectual

Property: Patents, Trademarks, and Copyright, 3rd edition,

West Group, St. Paul, MN 2000, pp. 288–290; P. Goldstein and

R. A.Reese, Copyright, Patent Trademark and Related State

Doctrines: Cases and Materials on the Law of Intellectual

Property, 6th edition, Foundation Press, New York, 1999,

pp. 661–664.

34. Kieselstein-Cord v. Accessories By Pearl, Inc., 208 U.S.P.Q. 1

(2d Cir. 1980).

35. General information on copyrights is available at http://

www.copyright.gov/. See also Copyright Basics at http://

www.copyright.gov/circs/circ1.html.

36. Oscar Mayer Foods Corp. v. Sara Lee Corp., 15 U.S.P.Q.2d

1204 (W.D. Wisc. 1990).

37. Del Monte Fresh Produce Co. v. Dole Food Co., 59 U.S.P.Q. 2d

(S.D. Fla. 2001).

38. See uspto.gov.

39. See, for example., Crown Packaging Technology, Inc. v. Rexam

Beverage Can Co., 05-608MPT (D. Del. Jan. 22, 2008).

40. The USPTO assignment database can be accessed at http://

assignments.uspto.gov/assignments/?db=pat.

41. The USPTO classiﬁcation index can be accessed at http://

www.uspto.gov/go/classiﬁcation/uspcindex/indextouspc.htm

42. See for example, R. C. Farber, Landis on Mechanics of Patent

Claim Drafting, 3rd edition, Practicing Law Institute, New

York, 1990.

43. See, for example, North American Container Inc. v. Plastipak

Packaging Inc., 415 F3d 1335 (Fed. Cir. 2005).

PERMEATION OF AROMAS AND SOLVENTS

THROUGH POLYMERIC PACKAGING

MATERIALS

DONGHWA CHUNG

Department of Marine Food

Science and Technology,

Kangnung-Wonju National

University, Gangneung,

Gangwong,

Republic of Korea

Mass transport in food and pharmaceutical package sys-

tems encompasses a number of phenomena referred to as

either permeation, adsorption,ormigration. Permeation

includes the transfer of molecules from the product to the

external environment through the package, or from the

storage environment through the package to the product.

Adsorption involves the takeup of molecules contained by

the product into, but not through, the package, while

migration is the passage of molecules originally contained

by the package itself into the product. These mass transfer

processes also provide the basis of further physiochemical

activities within the package system. Such activities may

induce physiochemical changes in the product, as well as

physical damage of the package, or both (1). In a package/

product system, the mass-transfer processes between

product, package, and storage environment as well as

the physiochemical activities associated with them are

referred to as product/package interactions (2) (see Phar-

maceutical packaging; Packaging, food).

The permeation of water vapor and gases, such as oxygen

and carbon dioxide, has been extensively investigated for

food and pharmaceutical package systems due to its sig-

niﬁcant effects on product shelf life. In the last decade, the

overall concern on the mass transport in package systems

has shifted a little more toward the transfer of volatile

organic compounds of low molecular mass, such as aromas

and solvents, due both to shelf-life reasons and to an

incresing interest in safe and healthy food packaging .

Aromas or ﬂavors are one of the key attributes affecting

the consumer acceptance of a packaged food. Their permea-

tion through the package as well as their adsorption on the

package, called ﬂavor scalping, causes the loss of original

sensorial characteristics of the product during storage,

resulting in the reduction of product shelf life. Solvents,

such as toluene, ethyl acetate, hexane, and abietic acid, are

often contained in package materials, printing inks, or

adhesive systems. Their migration into the packaged pro-

duct not only changes the original sensorial properties of the

product but also in some cases causes the generation of off-

ﬂavors that negatively alterate the consumer perception. In

addition, the migrating solvents raise signiﬁcant concerns

about the toxicological safety of the product. Obviously, all

these concerns are related to the product/package interac-

tions. In this chapter, the permeation, rather than sorption

or migration, of aromas and solvents has been discussed

because the theory and experimental data on permeation

can be expanded to understant the other processes.

The permeation process occurs in ﬁve consecutive

steps, as schematically illustrated in Figure 1: (1) mass

transfer from the bulk of phase 1 to the adjacent surface

of package ﬁlm, (2) sorption from the adjacent surface into

package ﬁlm, (3) molecular diffusion, (4) desorption from

package ﬁlm into the adjacent surface in contact with

phase 2, and (5) mass transfer from the adjacent surface to

the bulk of phase 2.

Since the molecular diffusion within package ﬁlm is the

rate-limiting step of the whole process, the rate of permea-

tion can be described by Fick’s law of diffusion. Under

steady-state conditions, the ﬂux (J) of permeant through

the ﬁlm is given by the following Fick’s ﬁrst law:

J ¼D

ð1Þ

938 PERMEATION OF AROMAS AND SOLVENTS THROUGH POLYMERIC PACKAGING MATERIALS

where D is the diffusion coefﬁcient of permenat in the ﬁlm,

c is the concentration of permeant in the ﬁlm, and x is the

distance in the ﬁlm. Integration of equation (1) yields the

following expression of J:

J ¼

Dc ð2Þ

where l(=x

x

) is the thickness of the ﬁlm and

Dc(=c

c

) is the difference in permeant concentration

between the two surfaces of the ﬁlm. Experimental deter-

mination of these surface concentrations is very difﬁcult.

Therefore, the surface concentration is necessary to be

converted to the partial pressure (p) in bulk phase, which

is easily measurable, using Henry’s law of solubility:

c ¼ Sp ð3Þ

where S is the solubility coefﬁcient of permeant in the

ﬁlm. By substituting equation (3), equation (2) is rewrit-

ten as

J ¼

Dp ð4Þ

where Dp(=p

p

) is the drop of partial pressure across

the ﬁlm. The product of D and S is often called perme-

ability P, which is the most widely used coefﬁcient for

expressing the rate of packaging permeation:

P ¼ DS ð5Þ

Another coefﬁcient that has been frequently used is

permeance R, which has a physical meaning similar to

that of mass transfer coefﬁcient:

R ¼

ð6Þ

Substitution of equation (5) into equation (4) gives the

following well-known packaging permeation equation:

J ¼

Dp ð7Þ

The gas ﬂux J is often called the permeant transmission

rate; and in the case of water vapor, the water-vapor

transmission rate (WVTR) is commonly used.

The above equations are applicable only for situations

where D is independent of permeant concentration and S

follows Henry’s law. However, when the permeation pro-

cess involves highly interactive organic permeants such as

aroma, ﬂavor, or solvent molecules, the diffusion process is

more complex than the diffusion of simple gases, and the

diffusion coefﬁcient may vary as a function of permeant

concentration and time (3–6). Where D varies with time,

the diffusion is often called non-Fickian. Mears (7) pro-

posed the following expressions for cases where the diffu-

sion coefﬁcient is concentration-dependent:

D ¼ D

1 þacðÞ ð8Þ

D ¼ D

exp bcðÞ ð9Þ

Equation (9) is more suitable in cases where the diffusion

coefﬁcient is strongly concentration-dependent. Here D is

the differential diffusion coefﬁcient, D

is the limiting

diffusion coefﬁcient, and a and b are constants.

The variables affecting permeation and diffusion pro-

cesses in a package can be grouped as follows:

1. Compositional variables:

a. Chemical composition of the polymer and

permeant

b. Morphology of the polymer

c. Permeant characterstics

d. Concentration of the permeant

e. Presence of copermeant

2. Environmental and geometric factors

a. Temperature

b. Relative humidity

c. Packaging geometry

While an in-depth treatment of each of the above factors is

beyond the scope of this article, selected examples are

discussed to illustrate their role in the transport of organic

permeants in barrier polymers. For a more in-depth

treatment, the reader is referred to the references listed

in the Bibliography and references cited therein.

CHEMICAL COMPOSITION OF THE PACKAGING

MATERIAL

The relationship between permeant transfer characteris-

tics and the basic molecular structure and chemical

composition of a polymer is rather complex, and a number

of factors contribute to the permeation and diffusion

processes; the most important are as follows:

. Cohesive-energy density, which produces strong in-

termolecular bonds, van der Waals or hydrogen

Package film

J J

Phase 1 Phase 2

Sorption

Desorption

Diffusion

Surface

mass transfer

Surface

mass transfe

Figure 1. Schematic diagram of gas or vapor permeation

through a package ﬁlm.

PERMEATION OF AROMAS AND SOLVENTS THROUGH POLYMERIC PACKAGING MATERIALS 939

bonds, and regular, periodic arrangement of such

bonding groups.

. The glass-transition temperature (T

) of the polymer,

above which free vibrational motion and rotational

motion of polymer chains occur, so that different

chain conformations can be assumed.

With respect to the glass-transition temperature of

barrier polymer structures, DeLassus (8) reported that

glassy polymers have very low diffusion coefﬁcients for

ﬂavor, aroma, and solvent molecules at low concentra-

tions. Typically, these values are too low to measure by

standard analytical procedures. The diffusion coefﬁcient

determines the dynamics of the permeation process and

thus the time to reach steady state, which accounts for

glassy polymers exhibiting high-barrier characteristics to

organic permeants. Polyoleﬁns, being well above their

glass-transition temperature, are non-glassy polymers

and have high diffusion coefﬁcients for organic permeants,

and steady-state permeation is established quickly in such

structures.

Polymer-free volume is also a function of structural

regularity, orientation, and cohesive-energy density. The

aforementioned structure–property relationships all con-

tribute to a decrease in solubility and diffusivity and thus

permeability.

Salame (2) has proposed a relationship between poly-

mer molecular structure and permeability based on an

empirical constant (p), or ‘‘Permachor’’ constant, which,

when substituted into the Permachor equation, predicts

the gas permeability of polymer structures. The correla-

tion parameter or the ‘‘Permachor’’ constant is based on

the cohesive-energy density and free volume of the poly-

mer, two major properties of the polymer. Agreement

between the Permachor constant and ﬁlm permeability

has been shown to be quite good for oxygen, CO

, and

nitrogen, but not for water vapor and organic vapors.

The equation for relating gas permeability to the

Permachor constant is as follows:

P ¼ A expðspÞð10Þ

where A and s are constants for any given gas at tem-

perature T and p is the Permachor constant of the

polymer.

POLYMER MORPHOLOGY

Solid-state polymer chains can be found in a random

arrangement to yield an amorphous structure or a highly

ordered crystalline phase. Most polymers used in packa-

ging are semicrystalline or amorphous materials (see

Polymer properties).

Morphology refers to the physical state by which

amorphous and semicrystalline regions coexist and relate

to each other in a polymer, and it depends not only on its

stereochemistry but also on whether the polymer has been

oriented, on the conditions of temperature, strain rate,

and cooling temperature, and on the melt cooling rate.

Fundamental properties that are associated with poly-

mer morphology and will therefore inﬂuence the perme-

ability and diffusivity characteristics of the polymer

include:

. Structural regularity or chain symmetry, which can

readily lead to a three-dimensional order or crystal-

linity. This is determined by the type of monomer(s)

and the conditions of the polymerization reaction.

. Chain alignment or orientation, which allows later-

ally bonding groups to approach each other to the

distance of the best interaction, enhancing the ten-

dency to form crystalline materials.

Morphology is thus important in determining the bar-

rier properties of semicrystalline polymers. This is illu-

strated by the results of permeation studies carried out on

biaxially oriented polyethylene terephthalate (PET) ﬁlms

of varying thermomechanical history (9).

Film samples were biaxially stretched at a strain of

350%/s, based on the initial dimensions of 4 in. 4 in.,

which corresponded to an orientation rate of 14 in./s

biaxially.

The degree of orientation was 400% based on the initial

dimensions. The orientation temperature was 901C,

1001C, and 1151C, respectively.

Table 1 summarizes the results of permeation studies

carried out with ethyl acetate in PET ﬁlm biaxially

oriented at 901C and 1151C, respectively, and serves to

illustrate the effect of thermomechanical history (stretch-

ing-temperature values) on the relative barrier properties

of PET, for the permeation of ethyl acetate. The percent

crystallinity of PET ﬁlm oriented at 901C was 22%, while

the percent crystallinity of the ﬁlm sample oriented at

Table 1. Permeability of Ethyl Acetate through PET Film Biaxially Oriented at 901C and 1151C

Orientation

Temperature (1C) Vapor Activity (a

) Run Temperature (1C) Permeability

, P 10

Lag Diffusion

Coefﬁcient

, D 10

90 0.59 30 2.6 1.8

0.43 37 4.8 2.9

0.21 54 15.4 11.0

115 0.59 30 0.014

—

0.21 54 3.6 5.3

Permeability units are (kg m) (m

2

s

1

Pa

1

Diffusion coefﬁcient units are cm

s

1

No permeation after 550 h. Value of P reported represents an upper bound.

940 PERMEATION OF AROMAS AND SOLVENTS THROUGH POLYMERIC PACKAGING MATERIALS

1151C was 31%. As shown, ethyl acetate permeability

values decreased by approximately four times by increas-

ing the ﬁlm orientation temperature from 901Cto1151C.

PERMEANT CHARACTERISTICS

The most important characteristics of the permeant af-

fecting its transfer in and through a ﬁlm include:

. Carbon chain length or boiling point

. Functional groups and polarity

With respect to the carbon chain length, different

studies have been carried out to evaluate the inﬂuence

of this characteristic on permeation phenomenon, parti-

cularly inﬂuencing the aforementioned second step of this

process, that is, sorption. In particular, homologous series

of hydrocarbons, esters, aldehydes, alcohols, and benzo-

ates in the vapor phase were taken into consideration (10,

11). The obtained results showed that, in compounds

below 10 carbon atoms, both the solubility and the perme-

ability coefﬁcients (S and P, respectively) of the volatiles

increased two- to ﬁve-fold with each additional methylene

group, depending on the types of packaging ﬁlms. Ob-

viously, diffusivity (D) decreased due to the steric hin-

drance. On the contrary, for molecules with 11 or more

carbon atoms, the increments were less or negative, as in

the case of aldehydes. Different experiments on the per-

meation of alkyl esters (C

–C

), methyl ketones (C

–C

aldehydes (C

–C

), and sulfur compounds through differ-

ent plastic ﬁlms (PP, PE, PVDC, EVOH) led to similar

results (12–16). Sorption into plastic ﬁlms can take place

also in the case of longer molecules as, for instance, fatty

acids. A speciﬁc study (17) showed that these kinds

of compounds with 16–18 carbon atoms moved through

the LDPE ﬁlm, with the ﬁnal result of delaminating the

composite (multilayer) ﬂexible packaging ﬁlm. Finally,

carbon chain length and boiling point are strictly linked

each other. For instance, within sorbates, there is a

proportional relationship between boiling point and solu-

bility. Moreover, a further relationship exists between the

logarithm of the solubility coefﬁcient and the boiling point

of linear esters, alkanes, and ketones (e.g., hexyl butyrate,

n-decane, or 3-octanone) through PVDC polymers (12–16).

The effect of functional groups on the transfer proper-

ties of aroma compounds through a ﬁlm is much larger

than the boiling point in the liquid phase rather than in

the vapor phase, due to close interactions between mole-

cules (10). Hydrocarbons and oxygenated terpenes, for

example, did not over PP nor LDPE by permeation when

put in aqueous model solutions (11). The polarity of the

solutes can be effectively considered as the most impor-

tant controlling factor to explain the tendency to permea-

tion. Researchers pointed out that carvone (C

O) and

limonene (C

O), even if similar terpenes, show differ-

ent sorption and diffusion properties. In general, permea-

tion of limonene (less polar than carvone), through plastic

ﬁlms, takes place quickly, because of lesser cohesive forces

(11). In another study on the permeation of citrus oil

compounds through polyoleﬁns, it was found that terpenes

carbon length) exhibited the highest afﬁnity for the

polymers, followed by sesquiterpenes (C

) (18). In addi-

tion, the permeation of esters and aldehydes was more

intense than alcohols due to polarity. Within aldehydes,

those saturated showed a greater permeation compared

to the unsaturated ones. For orange juice aromas, the

following ranking was established in terms of afﬁnity

to LDPE: hydrocarbonsWchetonesWestersWaldehydesW

alcohols (15, 16, 19). The same ranking can be extended

to apple juice aromas associated with LDPE, LLDPE,

PET, PA, and PP ﬁlms (20). Another important factor

inﬂuencing the permeation of ﬂavor components into

plastic ﬁlms (in particular concerning the sorption step)

is the pH of the system, which can modify the polarity of

the permeant. The sorption of 2-hexanal into PE was

found to be increased by a factor of 40 between pH 3.0

and pH 5.0 (21). Analogously, sorption of alcohols into

LDPE was increased by lowering the pH up to 3.0 (19).

Finally, sorption of limonene into LDPE at 221C was

higher at pH 5.2 than at pH 2.6 (1.3 times more; results

signiﬁcant at 95% level) (22).

CONCENTRATION DEPENDENCE OF THE TRANSPORT

PROCESS

Permeance of limonene vapor through (1) oriented poly-

propylene, (2) saran-coated oriented polypropylene, (3)

two-sided acrylic (heat-seal)-coated biaxially oriented

polypropylene, and (4) one-side saran-coated, one-side

acrylic-coated polypropylene ﬁlm samples, as a function

of permeant concentration, is presented graphically in

Figure 2, where permeance (R) is plotted as a function of

permeant concentration (23). The observed concentration

dependency of the permeance values may be attributed to

the permeant/polymer interaction, resulting in conﬁgura-

tional changes and alteration of polymer-chain conforma-

tional mobility. Zobel (24) reported similar ﬁndings for the

transport of the permeant benzyl acetate through coex-

truded oriented polypropylene and saran-coated oriented

polypropylene, at various permeant concentrations.

PRESENCE OF COPERMEANT

As shown above, organic vapors are capable of exhibiting

concentration-dependent mass transport processes.

Therefore, the type and/or mixture of organic vapors

permeating will determine the magnitude of sorption

and permeation, as well as the effect of a copermeant on

permeant permeability. The synergistic effect of a coper-

meant is illustrated by the results of permeation studies

carried out on a biaxially oriented polypropylene ﬁlm. The

degree of ﬁlm orientation was 430% (machine direction)

and 800% (cross-machine direction), based on the initial

dimensions. Binary mixtures of ethyl acetate and limo-

nene of varying concentration were evaluated as the

organic permeants (25).

Results of permeation studies for selected ethyl acetate/

limonene binary vapor mixtures are presented in

Figures 3 and 4, respectively. As shown in Figure 3 (ethyl

PERMEATION OF AROMAS AND SOLVENTS THROUGH POLYMERIC PACKAGING MATERIALS 941

acetate a

= 0.10 and limonene a

= 0.18), limonene vapor

had a signiﬁcant effect on the transport properties of the

copermeant. A 500% increase in the permeability constant

of ethyl acetate was obtained, when compared to ethyl

acetate vapor permeability alone, at similar test condi-

tions. However, at this concentration level, ethyl acetate

did not appear to inﬂuence the permeation of the limonene

vapor. The transmission-rate proﬁle curve for limonene

vapor in the binary mixture is superimposed in Figure 3,

to provide a complete description of the transmission

characteristics of the mixed-vapor system.

For the ethyl acetate (a

= 0.1)/limonene (a

= 0.29) bin-

ary mixture, a permeation rate 40 times greater than the

transmission rate of pure ethyl acetate vapor, of an equiva-

lent concentration, was obtained. This is illustrated in

Figure 4, where the transmission–proﬁle plot of the binary

mixture is presented, and compared to the transmission-

rate proﬁle curve for ethyl acetate vapor alone. Again, at

this concentration level, ethyl acetate did not appear to

affect the permeation characteristics of limonene vapor.

For studies carried out with the binary mixture of ethyl

acetate a

= 0.48 and limonene a

= 0.18, the individual

components of the mixture were found to have a signiﬁ-

cant effect on the permeation rates of the copermeant.

Since the permeability is drastically affected in the

sorbate/polymer systems studied, the diffusion coefﬁcient

and/or the solubility coefﬁcient must also vary in the

presence of a copermeant to account for the observed

increases in the transmission rates for the components

of ethyl acetate/limonene binary mixtures. By direct mea-

surement of the equilibrium solubility, Nielsen and Giacin

Figure 3. Comparison of the transmission proﬁle of the binary

mixture, ethyl acetate (a

= 0.1)/limonene (a

= 0.18), with the

transmission proﬁle of ethyl acetate (a

= 0.12) through oriented

polypropylene.

Figure 2. The effect of limonene-vapor concentration on log R for

oriented polypropylene and coated oriented polypropylene struc-

tures (221711C).

Figure 4. Comparison of the transmission proﬁle of the binary

mixture, ethyl acetate (a

= 0.1)/limonene (a

= 0.29), with the

transmission proﬁle of ethyl acetate (a

= 0.12).

942 PERMEATION OF AROMAS AND SOLVENTS THROUGH POLYMERIC PACKAGING MATERIALS

(26) found that the solubility coefﬁcient values were

independent of sorbate vapor activity, over the range of

activity levels studied, and were not affected by the

presence of a copermeant.

For the ethylacetate (a

= 0.10)/limonene (a

= 0.21) bin-

ary mixture, Hensley (25) reported a permeation rate of

ethyl acetate 40 times greater than the transmission rate

for pure ethyl acetate vapor of an equivalent concentra-

tion, while sorption studies showed the solubility coefﬁ-

cient of ethyl acetate to be constant and did not deviate

from Henry’s law in the presence of a copermeant. A

possible explanation for the dramatic increase in the

permeability coefﬁcients for ethyl acetate in the presence

of limonene as a copermeant lies with the high coper-

meant dependence of the diffusion coefﬁcient.

For ethyl acetate/limonene binary mixtures, limonene

as a copermeant appears to have little or no effect on the

solubility of ethyl acetate in oriented polypropylene ﬁlm,

while signiﬁcantly changing the inherent mobility of ethyl

acetate within the polymer bulk phase. This accounts for

the observed increase in the transmission rates for ethyl

acetate through the OPP (oriented polypropylene) ﬁlm in

the presence of limonene.

While not fully understood, the proposed copermeant

dependence of the diffusion coefﬁcient may be due in part

to copermeant-induced relaxation effects occurring within

the polymer matrix. The absorption of organic vapors can

result in polymer swelling and thus change the conforma-

tion of the polymer chains. These conformational changes

are controlled by the retardation times of polymer chains.

If these times are long, stresses may be set up that relax

slowly. Thus, the absorption and diffusion of organic

vapors can be accompanied by concentration as well as

time-dependent processes within the polymer bulk phase,

which are slower than the micro-Brownian motion of

polymer chain segments that promote diffusion (7).

There is precedence in the literature in support of such

long-time-period relaxation effects occurring in polymer

ﬁlms above their glass-transition temperature (27, 28).

Thus, there may be copermeant-induced relaxation effects

occurring during the diffusion of ethyl acetate/limonene

binary mixtures in the oriented polypropylene ﬁlm inves-

tigated. Such relaxation processes, which occur over a

longer time scale than diffusion, may be related to a

structural reordering of the free-volume elements in the

polymer, thus providing additional sites of appropriate

size and frequency of formation, which promote diffusion

and account for the observed increase in the permeation

rate of ethyl acetate in the presence of limonene as a

copermeant.

EFFECT OF RELATIVE HUMIDITY

The permeation of acetone vapor through amorphous

polyamide (nylon 6I/6 T) under dry conditions and in the

presence of a humid environment serves to illustrate the

effect of water activity or moisture content on the barrier

properties of hydrophilic polymer ﬁlms. Studies were

conducted at 601C, 751C, 851C, and 951C, at a constant

permeant partial pressure value of 92 mm Hg (0.29 g/L).

Water activity (a

) of the permeant steam was maintained

at 0.7 (70% RH), when measured at 231C. Different ﬁlm

samples were used for dry- and humid-condition experi-

ments. For an experiment, each run was maintained for a

period of 8–14 days after attaining steady state, to ensure

that the system was at equilibrium (29).

The respective permeability values are summarized in

Table 2. As shown, sorption of water vapor resulted in an

increase in permeability, as compared to dry conditions,

with an increase of approximately 1.5 times being

observed.

A further illustration of the effect of water activity on

the barrier properties of polymer ﬁlms is presented in

Figure 5, where the total quantity of ethyl acetate per-

meated is plotted as a function of time, for the permeation

of ethyl acetate through SiOx PET and EVAL-F ﬁlms (30).

The test conditions were as follows: temperature 221C,

190 ppm (wt/v) concentration of ethyl acetate vapor, at

56% and 87% RH, respectively. Fluctuation of relative

humidity was 72%, and ﬂuctuation of organic vapor

concentration was 75%.

For time, W500 h of continuous testing, there was no

measurable permeation at 56% RH. The results indicate

that both test ﬁlms were excellent ethyl acetate vapor

barriers at 56% RH and ambient temperature. However,

Table 2. Summary of Permeability Values of Acetone

through Nylon 6I/6 T

Temperature (1C)

P 10

(Dry

Condition)

P 10

(Humidiﬁed

Conditions)

60 3.7 4.9

75 6.5 11.2

85 9.8 17.6

95 11.8 —

Permeability units are expressed in (kg m) (m

2

s

1

Pa

1

Figure 5. Transmission-rate proﬁle curves of ethyl acetate vapor

through SiO

PET and EVAL-F ﬁlms at 221C, 190 ppm (wt/v), and

56% and 87% RH.

PERMEATION OF AROMAS AND SOLVENTS THROUGH POLYMERIC PACKAGING MATERIALS 943

as shown, at 87% RH the EVAL-F ﬁlm had a signiﬁcant

increase in the permeation rate of ethyl acetate vapor,

while the SiO

PET ﬁlm still showed no measurable

increase in the rate of permeation. Table 3 summarizes

the permeance values. Also presented in Table 3 are

upper-limit-value estimations for ﬁlm permeance.

Liu et al. (31) studied the effect of both water activity

and permeant vapor concentration on the permeation of

toluene vapor through a saran (PVDC)-coated OPP ﬁlm.

Studies were conducted at 22711C. Since the ﬁlm inves-

tigated in the present study is a multilayer structure,

permeance values are presented to describe the barrier

properties of the total structure.

The permeability parameters determined are summar-

ized in Table 4.

A comparison of the permeance values for toluene,

determined as a function of toluene vapor concentration

and water activity, showed that the permeance values are

highly dependent on both water-activity levels and to-

luene-vapor concentration. The ﬁndings suggested that

the sorption of water vapor and/or toluene vapor leads to

relaxation in the molecular structure of the saran barrier

coating, resulting in a high concentration dependency of

the permeance values. Toluene appears to be much more

effective than water vapor in promoting relaxation of the

saran coatings, since at the highest toluene-vapor concen-

tration level studied (81 ppm), the permeance rate is

independent of water-activity or sorbed-water levels.

However, at the lower permeant concentration levels

studied, the effect of sorbed water is quite signiﬁcant,

making this polymer structure very vulnerable to the

permeation of low concentrations of toluene in the pre-

sence of sorbed water.

The results of this study also serve to illustrate the

complex interrelationship of the barrier characteristics of

the polymer ﬁlm, permeant vapor activity, and sorbed-

water concentration.

EFFECT OF TEMPERATURE ON PERMEATION

PARAMETERS

Permeability, diffusion, and solubility coefﬁcients follow a

van’t Hoff–Arrhenius relationship as given in equations

(11–13):

P ¼ P

exp

E



ð11Þ

D ¼ D

exp

E



ð12Þ

S ¼ S

exp



ð13Þ

where E

= activation energy for permeation

= activation energy for diffusion

= molar enthalpy of sorption

, D

, S

= constants

= universal gas constant

T = absolute temperature

Lin (32) determined the permeability of ethyl acetate

and toluene for the following commodity ﬁlms: (a) oriented

polypropylene, (b) high-density polyethylene, (c) glassine,

(d) saran-coated oriented polypropylene, (e) acrylic-coated

oriented polypropylene, and (f) metallized polyethylene

terephthalate/OPP laminate.

Permeation studies were carried out at three tempera-

tures to allow evaluation of the activation energies.

For each temperature, three vapor activity levels were

Table 3. The Effect of Relative Humidity on the

Permeation of Ethyl Acetate Vapor through SiO

PET

and EVAL-F Films

Relative Humidity (%) Sample Permeance

R 10

56 SiO

PET o1.1

EVAL-F o2.2

87 SiO

PET o2.2

EVAL-F 840740

Permeance units are expressed in kg m

2

s

1

Pa

1

Table 4. The Effect of Water Activity on the Permeation of Toluene Vapor through a Two-Side-PVDC Coated OPP Film

Toluene-Vapor

Concentration

(ppm) (Mass/

Volume)

Toluene-Vapor

Pressure (Pa) Water Activity (a

)

Transmission

Rate

a,b

(J) Permeance

a,c

(R) Lag Time (h)

40 1203.8 0.50 0.73 10

13

6.0 10

17

94.0

0.86 0.72 10

10

6.0 10

14

55.0

60 1778.2 0 0.4 10

11

2.2 10

15

82.0

0.50 0.32 10

10

1.8 10

14

38.0

0.86 1.6 10

10

9 10

14

29.0

81 2407.6 0 1.1 10

7

1.6 10

11

2.1

0.50 1.1 10

9

4.6 10

11

2.2

0.86 1.2 10

7

5.0 10

11

1.9

Average of replicate runs, with a 2s conﬁdence limit within 710%.

Transmission rate units are expressed in kg m

2

s

1

Permeance units are expressed in kg m

2

s

1

Pa

1

944 PERMEATION OF AROMAS AND SOLVENTS THROUGH POLYMERIC PACKAGING MATERIALS

evaluated. Since several ﬁlms investigated are multilayer

or barrier-coated structures, permeance values are pre-

sented to describe the barrier properties of the total

structure (see also Barrier polymers).

Permeance values determined at ethyl acetate vapor

activity levels of a

= 0.095, 0.21, and 0.41 for the respec-

tive barrier structures are summarized in Tables 5–9. For

the metallized polyethylene terephthalate/OPP laminate,

no measurable rate of diffusion was detected, following

continuous testing for 44 h at 701C and a vapor activity of

a = 0.41.

Determined permeance values for toluene activity le-

vels of a

= 0.067, 0.22, and 0.44 for the respective barrier

structures are summarized in Tables 10–14. There was

no measurable rate of diffusion for the polyethylene

Table 5. Permeance of Ethyl Acetate through Oriented

Polypropylene (OPP) as a Function of Vapor Activity and

Temperature

Vapor Activity

Temperature (1C) Permeance

R 10

0.095 30 0.6

40 1.7

50 4.4

0.21 30 0.7

40 1.9

50 4.4

0.41 30 0.9

40 2.1

50 4.8

The results reported are the average of duplicate analyses.

Vapor-activity values were deter mined at ambient temperature (241C).

Permeance units are expressed in kg m

2

s

1

Pa

1

Table 6. Permeance of Ethyl Acetate through

High-Density Polyethylene (HDPE) as a Function of

Vapor Activity and Temperature

Vapor Activity

Temperature (1C) Permeance

R 10

0.095 30 1.0

40 1.7

50 2.7

0.21 30 2.4

40 2.8

50 3.4

0.41 30 2.9

40 3.8

50 4.8

The results reported are the average of duplicate analyses.

Vapor-activity values were deter mined at ambient temperature (241C).

Permeance units are expressed in kg m

2

s

1

Pa

1

Table 7. Permeance of Ethyl Acetate through Glassine as

a Function of Vapor Activity and Temperature

Vapor Activity

Temperature (1C) Permeance

R 10

0.095 23 1.1

30 2.0

40 4.2

0.21 23 2.3

30 2.9

40 5.2

The results reported are the average of duplicate analyses.

Vapor-activity values were deter mined at ambient temperature (241C).

Permeance units are expressed in kg m

2

s

1

Pa

1

Table 8. Permeance of Ethyl Acetate through

Saran-Coated OPP as a Function of Vapor Activity

and Temperature

Vapor Activity

Temperature (1C) Permeance

R 10

0.095 40 1.0

50 5.0

60 15.1

0.21 40 1.6

50 5.2

60 14.9

0.41 40 2.8

50 7.7

60 26.5

The results reported are the average of duplicate analyses.

Vapor-activity values were determined at ambient temperature (241C).

Permeance units are expressed in kg m

2

s

1

Pa

1

Table 9. Permeance of Ethyl Acetate through

Acrylic-Coated OPP as a Function of Vapor Activity

and Temperature

Vapor Activity

Temperature (1C) Permeance

R 10

0.095 50 0.25

60 1.0

70 2.6

0.21 50 0.3

60 1.2

70 3.6

0.41 50 0.3

60 1.2

70 3.3

The results reported are the average of duplicate analyses.

Vapor-activity values were determined at ambient temperature (241C).

Permeance units are expressed in kg m

2

s

1

Pa

1

Table 10. Permeance of Toluene through OPP as a

Function of Vapor Activity and Temperature

Vapor Activity

Temperature (1C) Permeance

R 10

0.067 30 0.5

40 1.15

50 1.8

0.22 30 0.75

40 1.4

50 2.7

0.44 30 1.4

40 2.0

50 3.1

The results reported are the average of duplicate analyses.

Vapor-activity values were determined at ambient temperature (241C).

Permeance units are expressed in kg m

2

s

1

Pa

1

PERMEATION OF AROMAS AND SOLVENTS THROUGH POLYMERIC PACKAGING MATERIALS 945

terephthalate/OPP laminate structure following continu-

ous testing for 44 h at 701C and a vapor activity of 0.44.

From equation (11) the temperature dependency of the

transport process associated with the respective barrier

membranes, over the temperature range studied, was

found to follow the Arrhenius relationship. From the

slopes of the Arrhenius plots, the activation energy for

the permeation process (E

) was determined for the

respective ﬁlm samples, as a function of vapor activity.

The determined activation energy values for both ethyl

acetate and toluene are summarized in Tables 15, 16,

respectively.

NUMERICAL CONSISTENCY OF PERMEATION DATA

In addition to determining the permeability values of

organic permeants, it is also important to determine the

diffusion coefﬁcients and to evaluate the consistency of the

experimental data obtained. The numerical consistency of

Table 11. Permeance of Toluene through HDPE as a

Function of Vapor Activity and Temperature

Vapor Activity

Temperature (1C) Permeance

R 10

0.067 30 2.1

40 3.4

50 5.6

0.22 30 4.0

40 5.5

50 8.0

0.44 30 7.7

40 8.6

50 9.2

The results reported are the average of duplicate analyses.

Vapor-activity values were deter mined at ambient temperature (241C).

Permeance units are expressed in kg m

2

s

1

Pa

1

Table 12. Permeance of Toluene through Glassine as a

Function of Vapor Activity and Temperature

Vapor Activity

Temperature (1C) Permeance

R 10

0.067 30 2.8

40 8.9

50 5.1

0.22 30 3.5

40 5.3

50 6.6

0.44 30 4.1

40 5.5

50 6.8

The results reported are the average of duplicate analyses.

Vapor-activity values were deter mined at ambient temperature (241C).

Permeance units are expressed in kg m

2

s

1

Pa

1

Table 13. Permeance of Toluene through Saran-Coated

Oriented Polyethylene (Saran OPP) as a Function of

Vapor Activity and Temperature

Vapor Activity

Temperature (1C) Permeance

R 10

0.067 40 1.0

50 5.8

60 21.9

0.22 40 2.5

50 9.7

60 25.0

0.44 40 3.1

50 12.8

60 28.9

The results reported are the average of duplicate analyses.

Vapor-activity values were deter mined at ambient temperature (241C).

Permeance units are expressed in kg m

2

s

1

Pa

1

Table 14. Permeance of Toluene through Acrylic-Coated

Polypropylene as a Function of Vapor Activity and

Temperature

Vapor Activity

Temperature (1C) Permeance

R 10

0.067 50 ND

60 ND

70 ND

0.22 50 ND

60 ND

70 ND

0.44 50 1.4

60 2.0

70 3.1

The results reported are the average of duplicate analyses.

Vapor-activity values were determined at ambient temperature (241C).

Permeance units are expressed in kg m

2

s

1

Pa

1

Without detectable response after 44-h test.

Table 15. Activation-Energy Values for the Permeation of

Ethyl Acetate through Polymer Membranes

(kcal mol

1

)

Polymer Membranes a

= 0.095 a

= 0.21 a

= 0.41

OPP 17.7 14.6 14.5

HDPE 9.3 4.4 4.9

Glassine 14.6 9.6 N/A

(a)

Saran OPP 24.9 23.0 24.5

Acrylic OPP 25.9 27.9 25.0

N/A, data not available.

Table 16. Activation Energy Values for the Permeation of

Toluene through Polymer Membranes

(kcal mol

1

)

Polymer Membranes a

= 0.067 a

= 0.22 a

= 0.44

OPP 12.63 12.53 7.79

HDPE 9.45 6.90 1.90

Glassine 5.78 6.21 5.02

Saran OPP 34.00 34.10 35.41

Acrylic OPP N/A

N/A

30.25

N/A, data not available.

946 PERMEATION OF AROMAS AND SOLVENTS THROUGH POLYMERIC PACKAGING MATERIALS

the permeation data will affect the values of both the

diffusion coefﬁcient and the permeability and would in-

dicate any variations of the system parameters, such as

temperature, or permeant concentration changes during

the course of the permeation experiment. Gavara and

Hernandez (33) have described a simple procedure for

determining the diffusion coefﬁcient and for performing a

consistency analysis on a set of experimental permeation

data from a continuous-ﬂow permeation study. This pro-

cedure was applied to the continuous-ﬂow permeation

data obtained, to provide a better understanding of the

mechanism of the diffusion and sorption processes asso-

ciated with the permeation process. The consistency test

for continuous-ﬂow permeation experimental data has

been described in detail by Gavara and Hernandez (33)

and is summarized brieﬂy below.

The value of the permeation rate at any time J

, during

the unsteady-state portion of the permeation experiment

varies from zero, at time equal to zero, up to the transmis-

sion rate value (J

) reached at the steady state. This is

described by the following expression (34):

1=2

‘

4Dt



1=2

n¼1;3;5

exp

n

‘

4Dt



ð14Þ

Equation (14) is simpliﬁed to the following form:

g ¼

1=2



ðXÞ

1=2

expðXÞð15Þ

where g is equal to the transmission rate ratio J

and

X = ‘

/4Dt. In equation (14), D is assumed to be indepen-

dent of permeant concentration and time. For each value

of g, a value of X can be calculated, and from a plot of 1/X

versus t, the diffusion coefﬁcient (D) can be determined.

The authors further described two dimensionless con-

stants, k

and k

;

1=4

3=4

1=4

3=4

¼ 0:4405 ð16Þ

1=4

1=2

1=4

1=2

¼ 0:6681 ð17Þ

where X

1/4

, X

1/2

, and X

3/4

denote the numerical values of X

when the permeation experiment has reached values of

0.25, 0.5 and 0.75, respectively, for g, the transmission rate

ratio.

The numerical values of the constants k

and k

given in Equations (16) and (17), together with the linear

relationship of 1/X versus t, will provide values of the

diffusion coefﬁcient and a criteria to evaluate the consis-

tency of the experimental data.

The results of a series of permeation studies carried out

with limonene vapor are presented graphically in Figures

6, 7, where the transmission rate is plotted as a function

of time, and serves to illustrate the applicability of the

consistency test to permeation data obtained for polyethy-

lene and polypropylene (35). The values of k

and k

calculated from the experimental data and the associated

diffusion coefﬁcients, D

1/4

, D

1/2

, and D

3/4

, obtained by

substitution into the expressions

1=4

‘

1=4

ð18Þ

1=2

‘

1=2

ð19Þ

3=4

‘

3=4

ð20Þ

Figure 6. Transmission-rate proﬁle and consistency test for the

permeation of limonene (a

= 0.4) through high-density polyethy-

lene at 501C.

Figure 7. Transmission-rate proﬁle and consistency test for the

permeation of limonene (a

= 0.2) through oriented polypropylene.

PERMEATION OF AROMAS AND SOLVENTS THROUGH POLYMERIC PACKAGING MATERIALS 947