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'.,:’.': 4.51"“ I llllllllllllllllllllllllllllllllllllllllllll 300909 6524 This is to certify that the thesis entitled 7%? 55‘7ch /’ 0F Momm ABM/6' (47/0/15 04/ 727/; $fi7f/EK (flfl/flf 7Z‘I/57/(5 0F jurfyc C" Sagan/”760 Fdékfr/ra/yg’ 7/4 // presented by (wt/6' €5.65wa has been accepted towards fulfillment of the requirements for K f5 . degree in WfIflG/A/Cr’ (2% L Mam. Major profeJL or Date f/g? ’ 9/ 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution - ‘c. ‘___._— ‘- Q-‘- opdsdo- w—h- fi -' " LIBRARY Michigan State 1 University x .l — PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. DATE DUE DATE DUE ‘ DATE DUE '3" 1'. iii; P .1. IP‘QIE ‘ i! i _ n) «I: m; ‘2 _ rgavarcl'afi 1m ll It: 1:296 4 MSU Is An Affirmative Action/Equal Opportunity Institution czblmmma-ot TEE EFFECT OF NEUTRALIZING CATIONS ON THE BARRIER CHARACTERISTICS OF A SURFACE SULFONATED POLXSTYRENE FILM BY Lone Esbensen A THESIS Submitted to Michigan State university in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE School of Packaging 1991 ABSTRACT THE EFFECT OF NEUTRALIZING CATIONS ON THE BARRIER CHARACTERISTICS OF A SURFACE SULFONATED POLYSTYRENE FILM BY Lone Esbensen The effect of the following cations; Has; 14?, Na‘, K*, Mg", Ca++ and Ba“, on the barrier properties of a surface sulfonated polystyrene film was investigated. The polystyrene film (4 mil) was sulfonated to a level of approximately 0.8 pg S/cm’, with a depth of sulfonation of approximately 50 A, Based on ESCA, it was estimated that the film contained 1 SO; group per 2% monomer repeat units. Permeability of limonene vapor (a-0.6) through both a control and the ammonium stabilized sulfonated polystyrene film exhibited anomalous behavior, which was attributed to the solubility of limonene in the polymer. The permeability of oxygen and water vapor through the respective cation stabilized sulfonated polystyrene films showed no correlation between the cation valance, atomic radii, or atomic number, and the diffusion coefficient and permeance. At the level of surface sulfonation of the test fill, the barrier properties were found to be equivalent to an unmodified polystyrene film. ACIMOILEDGMENTS I most gratefully thank the following people : Dr. Jack Giacin, for his guidance, support and expertise while serving as my main advisor Dr. Ruben Bernandez, for his advise and technical expertise while serving on the guidance committee Dr. Lawrence Drzal, for serving on the guidance committee Dr. Heidi Hoojat, for her assistance and patience The Center for Food and Pharmaceutical Packaging Research, for project funding iii TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES INTRODUCTION LITERATURE REVIEW Sulfonation Process SO3 Chemistry Sulfonating Agents Sulfonation in Dilute Solution Reaction of Polyethylene Films with SO, Photoreaction of Polyenesulfonic Acids Effect of Sulfonation upon Mechanical Properties Effect of Sulfonation upon Barrier Properties Polystyrene Characteristics Mechanical Behavior of Polystyrene Solubility of Polystyrene Crazing and Stress Cracking in Polystyrene Permeation Theory Diffusion in Amorphous Polystyrene MATERIALS AND muons ' Film Samples iv Page vii ix 11 12 12 13 15 15 18 20 21 25 32 32 Page Sulfonation Process 33 Surface Analysis 33 Ion Exchange 35 Organic Vapor Permeability 37 Solubility Experiments 43 Oxygen Permeance 44 Water Vapor Permeance 48 Tensile Properties 49 RESULTS AND DISCUSSION 50 Sulfonation Process 50 Surface Analysis 51 Ion Exchange 57 Organic Vapor Permeability and Solubility Experiments 62 Oxygen Permeance 66 Statistical Analysis 68 Water Vapor Permeance 74 Tensile Properties 78 SUMMARY AND CONCLUSIONS 80 APPENDICES Appendix A 83 Standard Calibration 83 Limonene Permeation 86 Appendix B 88 Computer Program for Oxygen Diffusion Coefficient and Permeance 88 Page Statistical Analysis 90 Appendix C 92 Water Vapor Transmission Rate Data 92 Appendix D 94 Surface Analysis 94 BIBLIOGRAPHY 9 5 vi LIST OF TABLES Table Page 1. Sulfuric Acid and SO, as Sulfonating Agents 7 2. Mechanical-Property Guide for Polystyrene 17 3. Solubility of Polystyrene in Various Solvents 19 4. Diffusivity Data for Various Penetrants in Polystyrene (T < T9) 27 S. Permeabilities for Various Penetrants in Polystyrene in Zone I 29 6. Atomic Concentration Determined by the ESCA Technique 51 7. Cation Concentrations as Determined by ICPAES 58 8. Level of Cation Exchange Achieved Expressed as a Percentage 60 9. The Influence of the Neutralizing Cation on Oxygen Barrier Properties of a 4 mil Surface Sulfonated Polystyrene Structure 67 10. The Influence of the Neutralizing Cation on Water Vapor Barrier Properties of a 4 mil Surface Sulfonated Polystyrene Structure 75 11. Effect of Neutralizing Cation upon Tensile Properties 78 vii Table A1. Limonene Calibration Curve Data 81. ANOVA for Oxygen Diffusion Coefficient and Permeability (1.5 mil PS vs. the Various Sulfonated 4 mil PS Structures) 32. ANOVA for Oxygen Diffusion Coefficient and Permeability (Ammonium Stabilized Sulfonated PS vs. the Various Neutralizing Cations) C1. Water Vapor Transmission Rate Data Obtained for the Various Film Structures at 37°C and 85 % R.H. Based on Replicate Determinations D1. Surface Tension of an unmodified PS and the Various Surface Sulfonated PS Films viii Page 84 90 91 92 94 LIST OF FIGURES Figure 1. Possible Canonical Forms of Sulfur Trioxide 2. Trimeric Form of Sulfur Trioxide 3. Polymeric Form of Sulfur Trioxide 4. Resonance Configurations Resulting from Reaction of Benzene with Sulfur Trioxide 5. Temperature-Concentration Diagram for Penetrant- Polymer Diffusion 6. Schematic of Permeation Test Apparatus 7. Ox-Tran 100 Oxygen Permeability Tester - Flow Diagram 8 . ESCA Spectra of -C-SO,'NH.+ Film Structure 9. A Narrow Detailed Scan of the Nitrogen Peak Obtained from ESCA Survey 10. Schematic of Sulfonated Polystyrene Surface Structure Based on ESCA Survey 11. Photographic Illustration of Limonene- Surface Sulfonated Polystyrene Interaction 12. Oxygen Diffusion Coefficient as a Function of Neutralizing Cation Radii 13. Oxygen Permeance as a Function of Neutralizing Cation Radii ix Page 26 40 46 52 55 56 65 70 71 Figure 14. 15. 16. 17. A1. A2. A3. C1. Oxygen Diffusion Coefficient as a Function of Atomic Number Corresponding to Neutralizing Cation Oxygen Permeance as a Function of Atomic Number Corresponding to Neutralizing Cation Water vapor Permeance as a Function of Neutralizing Cation Radii Water Vapor Permeance as a Function of Atomic Number Corresponding to Neutralizing Cation Limonene Standard Calibration Curve Replicate Determination of Limonene Permeation through Ammonium Stabilized Surface Sulfonated PS Replicate Determination of Limonene Permeation through 1.5 mil PS and 4 mil Sulfonated PS Weight Gain as a Function of Elapsed Time for Ammonium Stabilized Surface Sulfonated PS Page 72 73 76 85 86 93 INTRODUCTION In recent years, much attention has been focused on chemical modification of the surface of polymers, and the effect of such a treatment on the polymers barrier properties. For example, surface fluorination during blow-molding can impart excellent organic vapor barrier properties to polyolefins. Here, the surface layer is chemically modified and is inert to the attack of most organic compounds (Hehta and Bush, 1988). Polyethylene can also be readily sulfonated by treatment with gaseous 80,, with fuming sulfuric acid, or with SO, in chlorinated hydrocarbons to provide useful industrial materials (Ihata, 1988a). Recently walles (1989) described the effect of surface sulfonation on the barrier properties of a high density polyethylene (HDPE) article and showed that sulfonation, followed by air purging and neutralization with NH, gas, resulted in an excellent organic vapor barrier, at a surface concentration of between 75-200 pg SO3/cmz surface area. Further, the sulfonation process was readily adapted to both post-mold (Welles, 1973, 1971) and in-mold sulfonation (walles, USP applied). Sulfonation thus offers a new approach to chemically induce specific barrier properties in polymers, independent of their chemical composition and molecular structure through surface modification. Kinetic studies showed that sulfonation was a diffusion controlled process, with reactive gases penetrating the polymer surface up to depths of a micron or more. Thus, modification of the surface as well as the surface region is possible. In SO3 gas sulfonation, the $03 gas is able to penetrate below the surface resulting in up to two-thirds of the sulfonic acid groups, C-SO,i-i, not being neutralizable by aqueous NaOH, while NH, gas can diffuse, react and neutralize all acid groups (Walles, 1989). The oxygen barrier properties of sulfonated polyethylene (PE) were found to be strongly dependent upon the nature of the counterion, N‘. For example, Walles (1989) reported that Na+ as the counterion was 6 times as effective as was an' in providing a barrier to oxygen diffusion. Lithium ion (Li‘) was 12 times better than Nut} all at a surface concentration of about 70 pg SO3/cm2 surface area, which for a 25 pm film equals about 1 t bulk sulfur. Data on the permeation of water vapor, oxygen, and low molecular weight organic penetrants through a sulfonated polystyrene (PS) film have not been presented. This study, therefore, focuses specifically on determining the barrier properties of a sulfonated polystyrene, and the relationship of the films transport characteristics to the nature of the neutralizing cation. The primary objectives of the proposed study include: 1) Characterization of the sulfonated polystyrene film to provide an understanding of the spatial and depth distribution of the sulfur groups. 2) Determination of the transmission rates of oxygen and water vapor through sulfonated polystyrene film as a function of the neutralizing cation, to include: Nflfl) Li*, Na‘, K‘, Ca**, Mg++ and Ba*+, under similar conditions of test. . 3) Determination of the effect of the nature of the neutralizing cation on the mechanical properties of the surface modified polystyrene. LITERATURE REVIEI W 80, CHEMISTRY : The chemistry of sulfur trioxide (80,) is complicated, as it exists in both the monomeric and several polymeric forms. The SO, molecule is planar, triangular, and symmetrical, and is a resonance hybrid in which the oxygen atoms are equivalent. The exact distribution of electrons between sulfur and oxygen is uncertain. Figure 1 (Gilbert, 1965) represents possible canonical forms. Figure 1. Possible Canonical Forms of Sulfur Trioxide (Gilbert, 1965) When undergoing chemical reactions sulfur trioxide exhibits a marked tendency toward increasing the number of electrons in the outer shell from eight to ten, or even to twelve, indicating a strongly electron-deficient sulfur atom. At the same time, the oxygen atoms are electron-rich. The 803 molecule may thus be described as a "Lewis acid on one side (i.e. the sulfur), and a Lewis base on the other (oxygen)", in other words; it is amphoteric (Gilbert, 1965). These characteristics account for the ease with which sulfur trioxide polymerizes, and its activity as a sulfonating agent, with the acidic sulfur atom attacking electron-rich (basic) systems, and the basic oxygen atoms accepting acidic protons. Sulfur trioxide vapor is monomeric, as are solutions of SO3 in $0,, CCl,, SOIClz, and other solvents. Whereas in more concentrated solutions, there is an increasing quantity of the trimeric form, as represented in Figure 2 (Gilbert, 1965). Figure 2. Trimeric Form of Sulfur Trioxide (Gilbert, 1965) The freshly distilled liquid will revert to solid polymers of various possible chain lengths and degrees of cross- linking if exposed to moisture. The polymeric form of SO3 may be represented as illustrated by Figure 3 (Gilbert, 1965). Figure 3. Polymeric Form of Sulfur Trioxide (Gilbert, 1965) SULFONATING AGENTS : 8A comparison of sulfuric acid and sulfur trioxide as sulfonating agents is presented in Table 1. Table 1. Sulfuric Acid and SO, as Sulfonating Agents (Gilbert, 1965). FACTOR COMPARED 1980, SO, reaction rate slow instantaneous I heat input requires heat for strongly exother- completion mic throughout extent of partial complete reaction side reactions minor sometimes extensive viscosity of re- low sometimes high action mixture boiling point 290-317'C 44.5'C solubility in halogenated very low misable solvents The reported disadvantages of SO,, namely it's high heat of reaction with consequent decomposition or side reactions, and high viscosity, can most often be overcome by choice of reaction conditions, or the use of a solvent. REACTION MECHANISM OF SULFONATION : The sulfonation of many aromatic compounds involves the following steps; (Morrison and Boyd, 1983) 211,80, 3:! H,O‘* + 1180; 4- so, (1) so, + C41. =2 m-n-so; slow (2) easy-1140; + use; a c.1-1,so,- 4- 11,50, fast (3) CJQSO,’ + H,O* =2 Cfi,SO,H + 3,0 equilibrium far (4) to the left The sulfonation of polystyrene (PS) will follow the above pattern, as the repeating unit of PS contains a phenyl-group (mono-substituted benzene). In step (2) the electrophilic reagent, 80,, is attached to the benzene ring to form the intermediate carbocation. In step (3) a hydrogen ion is lost to form the resonance- stabilized substitution product, as represented in Figure 4. As shown, the anion of benzene sulfonic acid, being a strong acid, is highly dissociated (step 4). o. . $094 a S:{)——a \\ /2 ——9R * H O 0 II: benzene R 50- ' W. . / 3 sulfonic send Figure 4. Resonance Configurations Resulting from Reaction of Benzene with Sulfur Trioxide (Moore and Barton, 1978) Sulfur trioxide is thus a powerful electrophile, capable of reacting with the aromatic s electron system to form a neutral, but dipolar intermediate. Transfer of a proton from the ring to the SO; group provides re-aromatization of the ring, and forms benzene sulfonic acid (Moore and Barton, 1978). SULFONATION IN DILUTE SOLUTION : Sulfonation is a method of preparing new polymers through chemical modification of existing ones. To establish the mechanism, kinetics, and steric aspects of the process, 10 sulfonation of dilute solutions of polynorbornene (PN) in CCl, was carried out using SO,-triethyl phosphate complexes of various stoichiometries dissolved in dichloroethane (DCE) or trifluoro-trichloroethane (TTE) (Planche et al., 1988). The use of unassociated SO, was shown to lead to extensive degradation. Therefore, SO,-triethyl phosphate (TEP) was used to allow for easy control of the reagent strength by regulating the SO,/TEP ratio. A SO,/TEP ratio of 1/1 was utilized for the sulfonating solution. The reation was allowed to progress for 15 to 300 minutes, whereafter it was stopped by addition of methanol. The acid polymer was neutralized by adding a concentrated solution of NaOH in methanol. The reaction mechanism appeared to be one of electrophilic substitution on the double bond, yielding high sulfonation ratios (ca. 85 t). The unstrained cyclopentane ring in the PN structure remained untouched, acting as a screen between two successive double bonds which may be considered independent and of equal reactivity, whatever their environment. Kinetic studies revealed the initial reaction to be of first order in both reactants (SO, and PN). At room temperature the reaction quickly became diffusion-controlled due to precipitation of the partially sulfonated polymer. The initial rate was almost independent of the isomeric structure (cis or trans) of PN. Furthermore, the molecular weight and solution viscosities had no 11 influence on reaction rate and final sulfonation ratio. The absence of an effect of molecular weight may be due to similar chain flexibility of the polymers, resulting in similar glass transition temperatures. Moreover, a large part of the reaction is carried out in heterogeneous medium, where the role of diffusion is predominant, mainly depending on the particle size and porosity. The final sulfonation ratio obtained was strongly dependent upon the concentration of SO, and seemed to be controlled by the conditions of diffusion inside the precipitated solid (Planche et al., 1988). REACTION OF POLYETHYLENE FILMS WITH 80,: Surface sulfonation of polyethylene (PE) with gaseous SO, was reported by Ihata (1988a) to lead to the formation of sulfonic acids with highly conjugated CsC unsaturated bonds. HDPE was sulfonated with gaseous SO, and with SO, in ethylene dichloride, whereafter it was neutralized with aqueous NaOH. The sulfonated PE films were characterized by spectrophotometric analyses including infrared, resonance Raman, and UV-VIS spectroscopy. The reaction of PE film with SO, was suggested to be initiated by the abstraction of a hydrogen atom by SO, to give a PE radical, which could either react with SO, to give a sulfonic acid group, or eliminate a hydrogen atom to form an unsaturated bond. The 12 spectrophotometric analyses indicated an increase in the latter reaction as the sulfonation reaction proceeded (Ihata, 1988a). PHOTOREACTION OF POLYENESULFONIC ACIDS : Ihata (1988b) reported conjugated polyenesulfonic acids to be sensitive to UV and visible light. The photoreaction induced desulfonation by cleavage of C-S bonds to eliminate sulfonic acid groups. EFFECT OF SULFONATION UPON MECHANICAL PROPERTIES : The exposure of linear PE to a sulfuric acid atmosphere was reported by Balta Calleja (1984) to substantially improve the mechanical properties of the thin sulfonated surface of the polymer. The surface microhardness of polyethylene increased with sulfonation time, yielding hardness values which were in the vicinity of some metals. Furthermore, Fonseca et al. (1985) reported an increase in suface conductivity, as well as the critical surface tension of linear PE exposed to fuming sulfuric acid at room temperature. This improvement of surface properties was attributed by the authors to the insertion of polar 80, groups at the polyethylene surface. 13 EFFECT OF SULFONATION UPON BARRIER PROPERTIES : Walles (1989) has reported the treatment of the inside of HDPE automotiVe gas tanks with about 20 % SO, in air, followed by air purging and neutralization with NH, gas, to result in an excellent gasoline barrier, at a surface concentration of about 75-200 pg SO,/cm’. This barrier layer was found to have -C-SO,‘NH,” groups to a depth of 20-25 pm. The barrier characteristics obtained by applying the sulfonation process were, however, found to be strongly dependent upon the nature of the counterion. For example, the NH,“ ion may be replaced by various metal ions from water solution via ion exchange. Best barrier results were obtained with Li, Na, Cu, Mg, Sr, V, Mn, Co, and Ni. Na+ was shown to be 6 times as effective to create a barrier to O2 diffusion, as was Nfiflu Idf was 12 times better than NH4*, all at a surface concentration of about 70 pg SO,/cm’, of a 25 pm thick polyethylene gas tank. Highly reflective metal layers with a metallic-type total barrier were also obtained when using copper and silver as counterions. This ultra thin, very regular, super barrier metallic layer was created applying two different methods. The first being combining sulfonation with reductive metallization. Here a barrier layer was created containing polymer molecules and free metal atoms. The second method was a very light sulfonation to which tin ions were bonded, 14 followed by a spray of water-based silver-ammonia complex freshly mixed with a reducing agent. The tin catalysed deposition of silver resulting in a very dense metallic layer. For very demanding applications the sulfo- metallization may be repeated (walles, 1989). 15 P2lxstxrene_£barasterietics The polymer polystyrene (PS) is a high molecular weight thermoplastic with the repeating unit; (-CI-i,-CHC,H,-)x. Polystyrene is crystal-clear, hard, rigid, and free of odor and taste. Moldings, extrusions, and films of very low unit cost, resulting from ease of fabrication, thermal stability, low specific gravity, and low cost, are obtainable. Furthermore PS materials are useful as low-cost insulating materials due to excellent thermal and electrical properties. Commercial polystyrenes are normally rather pure polymers. PS containing a negligible amount of monomer and other solvents are useful in the packaging of food. A wide variety of speciality polystyrenes are also available. While these polymers are essentially pure PS, their molecular structures and/or additives are so adjusted as to make them customized to special applications (Kirk- Othmer, 1969). MECHANICAL BEHAVIOR OF POLYSTYRENE : Tensile testing of polystyrene may be conducted in accordance with ASTM D882-83 (1987) "Test Methods for Tensile Properties of Thin Plastic Sheeting". The stress- strain data, namely being; tensile strength and elongation 16 at yield and rupture, and modulus, are usually reported for room-temperature measurements. The determined strength of a material is dependent upon the following variables : (1) the rate of extension; With increasing rate of extension, the tensile strength and modulus increase, whereas the elongation at break tends to decrease. (2) the temperature; Increased temperature lowers the strength of PS, whereas elongation and modulus are only slightly affected. (3) polymer orientation; Tensile strengths as high as 18,000 psi have been reported for PS films and fibers. PS tensile strengths below 2,000 psi have been obtained in the direction perpendicular to the flow. Thus, the orientation of the polymer in a fabricated specimen can significantly alter the stress-strain data, as compared with the data obtained on an isotropic specimen (i.e. compression molded). Impact strength may be determined using a notched impact test or various dart-drop tests. Polystyrene is a brittle polymer under normal-use conditions exhibiting very low impact strength (Kirk-Othmer, 1969). Typical mechanical property values of polystyrene are summarized in Table 2. 17 Table 2. Mechanical-Property Guide for Polystyrene (Plastics Technol.) PROPERTY PS specific gravity 1.05 tensile yield, psi 6,100 I elongation, rupture, % 1.8 modulus, psi 460,000 impact strength, notched 0.4 Izod, ft-lb/in dart-drop impact strength very low relative ease of excellent fabrication 18 SOLUBILITY OF POLYSTYRENE The solubility of a nonpolar polymer, such as polystyrene, is determined largely, but not entirely, by the absolute value of the difference between the solubility parameter of the polymer, and that of the solvent. It has been observed that with nonpolar solvents, the difference beween the solubility parameters must be less than 0.9. Whereas, with many polar solvents the solubility parameter difference may be larger, and still a certain degree of solubility is achieved. The swelling of slightly cross-linked polystyrene in a variety of solvents increases in general, as the difference in solubility parameter value decreases. As polystyrene is a high molecular weight glassy polymer, it does not dissolve easily in low-molecular-weight solvents (Ueberreiter, 1968). The gross solubility of polystyrene in solvents of differing solubility parameter is given in Table 3. 19 Table 3. Solubility of Polystyrene in Various Solvents (Suh, 1967) POLYMER SOLUBILITY g POLYSTYRENE/ PARAMETER 100 g SOLVENT (cal /cm’) * (GROSS SOLUBILITY) polystyrene 9.1 SOLVENT n-heptane 7.45 0.016 ethyl acetate 9.03 >90 benzene 9.15 >90 acetone 9.81 0.30 ethyl alcohol 12.80 0.00 20 CRAZING AND STRESS CRACKING IN POLYSTYRENE : Internal crazes in polystyrene may start at flaws, or in regions where polymer chains are aligned normal to the applied stress, and ultimately stop instead of becoming catastrophic cracks as they encounter other regions with polymer chains aligned parallel to the stress (Maxwell, 1949). At a given strain level, the crazes will grow slowly with time. However, if the strain level is increased, new crazes will appear and start to grow. The application of nonsolvents/solvents for polystyrene will markedly interfere with the crazing process. Nonsolvents can significantly lower the critical stress and the critical crack elongation needed to cause crazing (Raetz, 1970). Whereas good solvents can lead to immediate catastrophic failure when applied to a mildly stressed polystyrene. The critical stress value increases as the difference between the solubility parameters of the polymer and solvent is increased. Also influencing the critical stress value are surface tension, and molecular size and shape of the solvent. The rate of craze formation may be at least partially diffusion-controlled. Thus, the molecular size of the stress-cracking reagent can affect craze initiation and growth (Hopfenberg, a). 21. W Permeability may be defined as the transmission of gases or vapors through a resisting material which has no macroscopic pores (Paine, 1983). The transport of a gas or vapor through polymeric films commonly utilized for packaging purposes typically involves the activated diffusion process. This process consists of three steps; (1) absorption of the permeating species, with gas or vapor dissolving into the polymer matrix at the high penetrant concentration surface; (2) diffusion through the polymer wall along a concentration gradient; and (3) desorption from the surface at the lower concentration (Stannett and Yasuda, 1965). The diffusion flux (F) of a permeant in a polymer can be defined as the amount passing through a surface of unit area normal to the direction of flow during unit time, independent of the aggregation of polymer. That is: F - Q / At (5) Where Q is the total amount of permeant passing through area A during time t. Fick's first law of diffusion expresses the existing proportionality of the transfer of a diffusant through a unit area to the negative gradient of 22 concentration at any point in the polymer (Crank and Park, 1968). Given by: F - - o (dC/dx) x (5) Where D is the diffusion coefficient with units of (length)2 time“, x is the length in the direction of diffusion, and C is the concentration of the permeant in the polymer. As the diffusion proceeds, Fick's second law of diffusion describes the non-steady state (Crank, 1975). dC/dt I d/dx ( D * dC/dx ) (7) Solutions of Equation (7) depend upon the initial and boundary conditions, as well as on whether or not D can be considered a function of penetrant concentration, and/or time. Equation (5) can be integrated, assuming D is independent of permeant concentration, to give: F'D(Ci’¢i)/L (8) Where C, and C, are the steady state concentration at the two surfaces of the film, and L is the film thickness. 23 For experimental and predictive purposes, the concentration of the permeant at the polymer surface may conveniently be related to the concentration of permeant in the surrounding gas phase. For gases and vapors, the permeant concentration is proportional to the partial pressure of the permeant, through the ideal gas law equation (Henry's Law). The concentration of the permeant in the polymer, C, can thus be expressed in terms of the solubility (Sp) and the partial pressure, as: C ' (SP) (AP) (9) Where the solubility is a function of temperature, and may be a function of the partial pressure or the concentration. Assuming Henry’s Law is applicable, it follows: c a 8 (AP) (10) Where 8 is the Henry's Law solubility coefficient, which is independent of Ap and C (Crank, 1975). Substitution in Equation (8) yields: F ' 0*5 (P1 " P2) / L (11) Where p1 and p, are the permeant pressures at the two 24 surfaces of the film, and the product D*S defines the permeability coefficient (P) (Barrer, 1939), by the relationship; nits-p (12) When both D and S are independent of penetrant concentration, P is a constant at any given temperature. However, where considerable interaction between the polymer and the permeant occurs, P is no longer constant but will vary with C and Ap (Zobel, 1982; Hernandez et al., 1986 and references cited therein). For the specific case, where the diffusion coefficient is time-dependent, the transmission process will be anomalous, and is said to be non-Fickian (Fujita, 1961; Meares, 1965; Crank and Park, 1968). 25 213W: Various regions of penetrant transport in high polymers exist, which may be illustrated by a temperature-penetrant concentration (or penetrant activity) diagram (Alfrey, 1965 and Hopfenberg, b). The diagram delineates the proposed regions of diffusional transport in terms of the two controllable variables; namely temperature and penetrant concentration, as represented by Figure 5. The feature distinguishing the three proposed diffusion regions is the ratio of the characteristic time of diffusion and some characteristic time for the molecular rearrangement and relaxation process in the polymer-solvent system. Zone I; here the combination of low solvent activity and a temperature below the glass transition temperature (Tg) results in a polymer matrix essentially unaffected by the presence of the penetrant during the entire diffusion process. The lack of interaction between the polymer and penetrant is due to the frozen state of the polymer under these conditions. Above T9 the penetrant molecules must migrate through a discontinuous network of microvoids which is constantly being altered by the random oscillations of chain segments. This Fickian-type migration is described by Equation (6). The diffusion process can however be assumed to be concentration-independent and can be related to the 26 temperature only by an Arrhenius-type expression; D - Do exp (-E/RT) (13) where for a given polymer, the pre-exponential factor, Do, and the activation energy for diffusion, E, are functions only of the molecular properties of the penetrant. Table 4 summarizes the diffusion of relatively small inert molecules in polystyrene in zone I. \ Zone ll \ / \ Zone lll / é Combined \ (F/i/c’kian diffusio% E. diffusion — relaxation \ \ § \ E; \ \ /// Zone I \ / (Fickian diffusion) C//////// 7: Temperature Figure 5. Temperature-Concentration Diagram for Penetrant- Polymer Diffusion (Alfrey, 1965) 27, Table 4. Diffusivity Data for Various Penetrants in Polystyrene (T < Tg) Pene- Temp, D x 10‘, Do, a, Refe- trant Celsius cm2/ sec cm’l sec kcal/g-m rence water 25 0.035 Cutler, 1953 25 0.21 Thomas, 1945 35 0.022 Deeg, 1944 oxygen 25 0.11 0.125 8.3 Stan- nett, carbon 25 0.058 0.128 8.7 1968 dioxide n- 30 1.85 x 5.6 Hopfen- pentane 10‘ berg 40 2.5 x 10‘ 45 2.9 x 10‘ 50 3.35 x 10‘ 28 The inconsistencies between these diffusivity data may be due to difference in the structural characteristics of the polystyrene samples. Furthermore, contributing to the nonreproducibility of this type of measurement is the possibility of the presence of voids and/or cracks allowing for convective transport, thus complicating the transport process (Schulz, 1956). However, the data show that the diffusion rate decreases with increasing penetrant molecular size. Another expression for mass transport through polymer films is in terms of permeability, which is the product of the diffusion coefficient and the penetrant solubility. Available permeability data for polystyrene in zone I are presented in Table 5. Table 5. Permeabilities for Various Penetrants in Polystyrene in Zone I PENETRANT TEMPERATURE PERMEABILITY REFERANCE Celcius x 10’ cc*cm/ cm¥*s*cmHg oxygen 22 0.174 Davis, 1946 23 0.174 Brown, 1959 23 0.18 DOW 25 0.21 Major, 1962 water 20 100 Muller, 1942 25 83.5 Aiken, 1945 32 84.0 38 83.0 25 97 Korvezee, 50 107 1947 25 79.5 Thomas, 1945 25 104 25 107 35 107 Cutler, 1953 35 108 Simril, 1950 benzene 35 1060 Simril, 1950 30 The data presented are quite consistent considering that permeability measurements are relatively sensitive to imperfections in the film structure, such as cracks and pinholes, which may very likely occur in the thin films employed for permeation studies. The permeability observed for benzene is relatively large, possibly due to swelling of the polymer, and thus more indicative of steady-state transport in zone II (Simril, 1950). Zone II; here the characteristic relaxation time of configurational change of polymer chains and the characteristic diffusion time are quite similar. Thus, the diffusion and the molecular relaxation processes are coupled phenomena, and cannot be regarded as individual and independent of each other. Under such conditions there is no certain relationship between penetrant concentration and the molecular spacing and orientation of polymer chains. Thus, the classical theory of diffusional transport is not applicable in zone II. Studies at moderate penetrant activities will yield anomalous sorption and permeation curves. The methylene chloride-polystyrene sorption curves of Park (1953) at 25°C exhibit a distinct sigmoid character and a pronounced thickness effect, both distinctive features of non-Fickian diffusion phenomena. Experiments at somewhat higher penetrant activities will yield case two transport, solvent crazing, and swelling fracture. 31. Zone III; a temperature above the glass-transition temperature of the polymer leads to high mobility of polymer segmental units and to a characteristic relaxation time, which is small compared to the characteristic diffusion time. The polymer molecules are assumed to instantaneously reach an equilibrium configuration consistent with the penetrant concentration at any point in the polymer, and the diffusion coefficient becomes purely concentration- dependent. The penetrants can thus interact with the polymer and change the state of same. The diffusion process can therefore be defined by Equation (7). The amount of available diffusivity data is rather limited, as it is very difficult to perform sorption and permeation experiments at temperatures above the glass transition of polystyrene (Boyer, 1970). 32 MATERIALS AND METHODS mm In this study, a surface sulfonated polystyrene film provided the base polymer structure. The film characteristics were varied by incorporating a series of neutralizing cations into the base structure. Films : A 4 mil polystyrene (PS) film, surface sulfonated to a level of 0.8 pg sulfur/cm2 surface area which is represented as: -C-SO;, provided the base structure. The film structures with the respective neutralizing cations incorporated are represented as follows: a. -C-SO,‘NH,*, Cation; ammonium b. -C-SO{Li*, Cation; lithium c. -C-SOflNa*, Cation; sodium d. -C-SO,‘X*, Cation; potassium e. -C-SO,‘Mg**, Cation; magnesium f. -C-SO,Ca**, Cation; calcium g. -C-SO,'Ba‘”, Cation; barium 33 W The surface sulfonation process was performed on a solid phase sulfonator at Coalition Technologies, Ltd. (Birmingham, MI). The polystyrene film was exposed to 2 % SO, in air for less than 0.1 sec. W A surface analysis of the -C-SO,‘NH,+ film structure by x-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy for Chemical Analysis (ESCA), was conducted on a Perkin-Elmer PHI 5400 system at the Composite Materials and Structures Center, M.S.U. The test specimen is irradiated with monoenergetic x-ray resulting in photoionization of atoms in the surface region, followed by emission of electrons. The photons can penetrate the solid sample to a depth of 1-10 pm, whereas the emitted electrons can escape only tens of Angstroms of solid. Therefore, the electrons detected originate within the tens of Angstroms of the top surface region and are thus representative of this region only. 34 An evaluation of the surface tension of both an unmodified and the various surface sulfonated polystyrene films was performed by Accu Dyne Test (Diversified Enterprises, East Wallingford, VT 05742). The wetability of the films was estimated utilizing water/glycerol solutions of differing surface tensions. The results are presented in Appendix D, Table D1. 35 IQD.EX£DAD§§ MATERIALS: 2) 3) Salts; Lithium Chloride, GR, obtained from EM Science, (Cherry Hill, N.J.). Sodium Chloride, Analytical Reagent, obtained from Mallinckrodt, Inc. (Paris, KY). Potassium Chloride, A.C.S. Grade, obtained from Columbus Chemical Industries, Inc. (Columbus, WN). Magnesium Chloride 6-Hydrate, Baker Analyzed Reagent, obtained from J.T. Baker Inc. (Phillipsburg, N.J.). Calcium Chloride Dihydrate, Baker Analyzed Reagent, obtained from J.T. Baker Inc. (Phillipsburg, N.J.). Barium Chloride Dihydrate, GR, obtained from EM Science, (Cherry Hill, N.J.). Acid; Hydrochloric Acid, 36.5-38.0 2, Baker Instra Analyzed Reagent for Trace Metal Analysis, obtained from J.T. Baker Inc. (Phillipsburg, N.J.). Water; Double-deionized water obtained from The Department of Food Science, (Michigan State University, East Lansing). 36 PROCEDURE: The C--SO,'NH,+ structure film was immersed in 5 % solutions of the above mentioned salts for 1 hour to allow for cation exchange to take place. The films were then removed from the salt solutions and washed with double-deionized water to remove excessive salt solution from the surface of the film. Confirmation of the cation exchange reaction was carried out as follows; 50 cm2 samples of the above mentioned film structures were immersed in 100 ml of 5 % HCl for 1 hour, thus resulting in a proton exchange, leaving the former neutralizing cations in solution, and the film structure as -C-SO;H*. The solutions containing the respective neutralizing cations, and a sample of the 5 % HCl as reference were then submitted to The Animal Health Diagnostic Laboratory, Analytical Toxicology Section, Veterinary Clinical Center, (M.S.U.), for cation analysis. The cation analysis was performed on a Thermo Jarrell Ash Polyscan 61E, whose method of operation is based on Inductively Coupled Plasma Atomic Emission Spectroscopy. 37 MW MATERIALS: 1) Permeant 2) The permeant, limonene was used as the organic vapor. The selection is based on the ease of analysis and the known contribution of this compound to the aroma profile of food products. (R)-(+)-limonene, 97%, was obtained from Aldrich Chemical Co., Inc. (Milwaukee, WI). Carrier Gas High purity dry grade nitrogen gas produced by AGA Inc. (Cleveland, OR) was employed throughout the experiment, as the carrier gas of the permeant. PROCEDURE: 1) Permeability Measurements The permeation test system, based on the quasi-isostatic method, was assembled and tested as part of this study. A schematic diagram of the permeation test apparatus is represented by Figure 6. It allows the collection of permeation data as a function of temperature and vapor concentration. The permeability cell, constructed of aluminum, is composed of two cell chambers and a hollow center ring. The right and 38 left cell chambers both have a volume of 50 cmP, which is also the approximate volume of the center cavity. In operation, the test films, two to each permeation cell, are placed so as to effectively isolate the right and left cell chambers. Hermetic isolation of the chambers from each other, and from the atmosphere is achieved by the compression of overlapping Viton o-rings on the film specimens. Viton is a fluorocarbon elastomer resistant to attack and swelling by most organic vapors. The cell chambers and the center ring are equipped with an inlet and outlet valve and sampling port. A constant concentration of permeant vapor is produced by bubbling nitrogen gas through the liquid permeant contained in a gas washing bottle. To obtain a lower vapor concentration, the permeant vapor stream is mixed with a stream of pure carrier gas (nitrogen). Flow meters were used to provide a continuous indication of the maintenance of a constant flow rate. Gas flows were regulated with NU PRO needle valves, Type B-25G. When performing permeation runs, the films to be tested are mounted in the permeability cell and the cell assembled. A constant, low partial pressure of permeant vapor is then flowed through the center cell chamber at a flow rate of approximately 10 ml/min. This allows the permeability of two film specimens to be determined concurrently, under 39 identical conditions, at a selected temperature and vapor concentration (Baner et al., 1986). 40 E- Waste . p. III E l l R | - R Waste . II : y 4 PC I" i . : N a R i N I ‘ I .C::: : ‘Vb .,,‘ : T L - N J _+ E """"""" E = Environmental Oven R = Rotameter Vg = Organic Vapor T = Nitrogen Tank Pc = Permeability Cell N = Needle Valve Figure 6. Schematic of Permeation Test Apparatus 41 2) Operation In the quasi-isostatic procedure, the increase in penetrant concentration in the lower concentration cell chambers is monitored by utilizing gas chromatography with flame ionization detection for analysis. At predetermined time intervals, a specific volume of headspace gas is removed from the right and left cell chambers with a gas-tight syringe and injected directly into the gas chromatograph. Throughout the run a constant pressure in the high concentration cell chamber is maintained by continually flowing the vapor stream through and discharging it at atmospheric pressure. In the low concentration cell chambers a constant, total pressure is maintained by replacing the volume of headspace gas removed for analysis with an equal volume of nitrogen. The quantity of vapor permeated over time is then monitored until a steady-state rate of diffusion is reached. The film specimens were stored at ambient conditions for a period of at least two weeks prior to being tested. 3) Gas Chromatographic Analysis Analysis of permeant concentration was carried out by a gas chromatographic procedure. A Hewlett-Packard Model 5890 gas chromatograph equipped with flame ionization detection interfaced to a Hewlett-Packard Model 3392A integrator was 42 employed for quantification. The gas chromatographic conditions were as follows; Column: 60 meter; 0.25 mm I.D.; Fused silica capillary; Polar bonded stationary phase; Supelcowax 10 (Supelco Inc., Bellefonte, PA) Carrier Gas: Helium at 32.6 ml/min; Temperature: Injection temperature -- 80°C; Detector temperature -- 250°C; Oven temperature -- 150°C; Temperature program rate -- 4°C/min; Retention time of limonene: 10.21 min; A.standard curve of detector response vs. absolute quantity injected was constructed from standard solutions of known concentration. Standard solutions were prepared by dissolution of known quantities of limonene in dichloromethane. 43 W MATERIALS: Solvents; (R)-(+)-limonene, 97%, obtained from Aldrich Chemical Company, Inc. (Milwaukee, WI) Ethyl acetate, 99.5+% A.C.S. Spectrophotometric Grade, obtained from Aldrich Chemical Co., Inc. (Milwaukee, WI) c. Acetone, ChromAR, HPLC, obtained from Mallinckrodt, Inc. (Paris, KY) d. 1-Propanol (Normal), Certified, Obtained from Fisher Scientific (Fair Lawn, N.J.) PROCEDURE: 1 in2 samples of both the unmodified PS and the -C-SO,'NH,* film structure were exposed to saturated vapor of the above mentioned solvents to enable observance of the degree of their solubility in the polymer. Saturated vapors were generated from the liquid solvents contained in glass jars stored at ambient conditions.The samples were weighed initially and then visually examined over a period of 4 days, and finally weighed again. 44 Qxxssn_Permeanse MATERIALS: 1) Permeant Oxygen supplied in the form of compressed air (02 partial pressure equals 0.21 atm), obtained from AGA Gas, Inc. (Cleveland, OH) 2) Carrier Gas Nitrogen dry grade gas containing 1% hydrogen, supplied by AGA Speciality 8 Medical Gases Division (Maumee, 0H) PROCEDURE: 1) Permeance Measurements The permeance of oxygen through the film samples (exposing the unmodified polystyrene surface to air) was determined in accordance with ASTM STD D 3985-81 ”Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using A Coulometric Sensor” (1981). The studies were carried out on an Ox-Tran 100 Permeability Tester (Modern Controls, Inc., Elk River, MN), whose operation is based on the isostatic method. As the transmission rate of oxygen through PS is rather high, precautions were taken to protect the sensor. This was achieved by utilizing a masked sample, thus reducing the exposed area by a factor 10. Furthermore the permeant was 45 supplied in the form of air, thus reducing the partial pressure of oxygen by a factor 4.8. 2) Operation During a permeation run on the Ox-Tran 100 the test specimen is clamped into a cell having a 100 cm2 diffusion area or when modified a 10 cm2 diffusion area. A silicone lubricant was applied to the cell rim to assure a tight seal. Initially both cell sides are purged with oxygen free carrier gas (nitrogen containing 1% hydrogen). When a stable zero reading has been established on the recorder, oxygen is introduced into the upper half of the diffusion cell. The nitrogen is continually flowed through the lower cell. A flow diagram of the apparatus is illustrated by Figure 7. As oxygen diffuses through the barrier, it is entrained by the nitrogen and carried to the detector. The detector current rise is recorded on a strip chart. The recorder value levels off when the oxygen transmission rate is at a steady state transmission rate. The detector current measured is directly related to oxygen transmission rate. 46 PACKAGE TEST FITTINGS /" '- \ UPPER llnrrussn CELL CELL ..”;:?.,3,. .. , L . LOWER /.....' ..... ...o,.. CELL I N2 BUBBLER 0:35:33 xvczu FLOW COULO- CONTROL METRIC osrecron AREA FLOW METER 02 #:1833652 ADJUSTMENT O cmmm + - oxvoeu Figure 7. Ox-Tran 100 Oxygen Permeability Tester - Flow Diagram (Soroka and Castelletti, 1979) 47. 3) Calibration Standard Reference Material 1470 (polyester) obtained from The National Bureau of Standards (Washington, D.C.) was employed to calibrate the instrument. The Certificate (Barnes, 1982) lists the oxygen permeance for the standard material to be; 0.352 pmol/m’irs or 69.1 cc/m’irday. This standard permeance value divided by the detector current in mV, obtained when testing the standard PET, thus defines the convertion factor to be applied when converting from mV output to permeance for various test specimens. 48 EAL£I_¥ARQI_2§IIBADQ§ MATERIALS: Desiccant; Drierite, Anhydrous CaSO, supplied by W .A. Hammond Drierite Co., Xenia, OH. PROCEDURE: Determination of water vapor transmission rate through the test specimens (exposing the unmodified polystyrene surface to the water vapor) was carried out in accordance with ASTM STD E 96 ”Water vapor Transmission of Materials” (1980). Replicate samples of all film structures were sealed to the open mouth of a test dish with a diameter of 0.082 m, the exposed film surface area thus being 0.0053 m2. After recording the initial weights, the dishs were placed in an environmental chamber set at 37.8°C and 85% R.H. Periodic weighings on a Mettler H80 Balance (Mettler Instrument Corp., Hightstown, N.J.) then allowed the determination of the rate of water vapor transmission through the test specimens. 49. W MATERIALS : Test specimens; length;7 in, width;1 in, thickness;0.004 in cross-sectional area;0.004 in2 PROCEDURE : Determination of the tensile properties of replicate samples of all film structures was carried out in accordance with ASTM STD D 882-83 ”Tensile Properties of Thin Plastic Sheeting". The tensile testing was performed on an Instron 4201 (Canton, MA), whose operation is based on the static weighing method. A force (lbs) versus extension (in) recording was obtained for each sample. Instron Operating Settings were as follows; Gage length: 5 in Crosshead speed: 0.5 in/min Load range: 25% of full scale load a 50 lbs Extension, full scale: 1 in 50 RESULTS AND DISCUSSION W Based on information obtained from Coalition Technologies, Ltd. (Birmingham, MI 48009) the sulfonation process resulted in a polystyrene film modified to; 0.8 pg S/cmF,*with the depth of sulfonation being 50.A, The above values for the extent of sulfonation and the depth of sulfonation are average values typical for the process employed for the sulfonation of the polystyrene film evaluated in the present study. 51 Surfase_Analxsis X-ray Photoelectron Spectroscopy (XPS or ESCA) analysis confirmed the presence of ammonium-stabilized sulfonate groups on the polymer surface (see Figure 8). The measured atomic concentrations of sulfur, oxygen, nitrogen and carbon (hydrogen is not detectable) are listed in Table 6 Table 6. Atomic Concentration Determined by the ESCA Technique ._____Element Concentratien_ill___ 0 1s 17.90 N 18 5.63 c 1s 72.15 8 2p 4.32 52 1O : : : = i : : : : i : : . . : : : 7 Sulfonated Polystyrene <0 1 s I 8 on I ‘3 ‘ S l- E 3‘: I 0 .. L u": U321 .. 13 2 -~O 2 g or II 21" I m m 'l’ meMWM . l ‘——t—l : 4‘ 900 Figure 8 . ESCA 800.700r600'500'400'300'2001100' o BINDING ENERGY (8V) Spectra of -C--SO,'NH,+ Film Structure 53 Based on the proposed composition of the surface layer, the expected relationships between the elements are as follows: 1 S : 3 O, and 1 S : 1 N. Assuming the polymer surface is free of sulfur contamination (non-bonded sulfur), the true atomic concentration of sulfur equals the measured value of 4.32 %. The expected atomic concentration of nitrogen is thus exceeded by 30.3 %. A closer examination of the nitrogen peak (see Figure 9.) reveals the presence of two peaks, with one peak accommodating for 73.42 % of the total peak area. This percentage of the determined total nitrogen atomic concentration equals 4.13 %, suggesting a 96 % level of neutralization with ammonium. The expected oxygen atomic concentration is exceeded by 38.1 %. Assuming the excess nitrogen and oxygen derive from contamination on the surface, the actual atomic concentration of carbon is equal to 78.40 %. The relationship between carbon and sulfur is then as follows: 18 C : 1 S. Each repeating unit of polystyrene contains 8 carbons, thus based on a stoichiometric relationship, 1 sulfonate group is present for 2% repeating unit of PS. This is illustrated in Figure 10. The dimensions are derived from the length of a carbon- carbon single bond being equivalent to 1.54 A.(Jastrzebski, 1976). In addition to the stoichiometric relationship, the size relationship between the molecular volume of the repeat styrene unit and the sulfonate group could provide further 54, insight into the spatial distribution of the sulfonate groups. Such an approach would allow consideration of steric hindrance to both substitution, and carbon bond rotation. 55 N(Ell E 464 463 ' 4oz ' 4o1 ' 4oo ' 399 ' 398 BINDING ENERGY (0V) Figure 9. A Narrow Detailed Scan of the Nitrogen Peak Obtained from ESCA Survey .—L 0) >0 l l To .|. o ('3 s» l o l o ____|_ o l O- O O .Z (I) I O 4s+ col Figure 10. Schematic of Sulfonated Polystyrene Surface Structure Based on ESCA Survey. 57 IQD_EXQhAnQB The bonding between SO,‘ and NH,* on the polystyrene film surface is ionic in nature. Ionic compounds dissociate completely in an aqueous solution (Thorup, 1986). When immersing the --C-SO,‘NH,+ structure in 5 % salt solutions the iflg‘ ions will therefore dissociate into solution, whereas the 80; ions will remain on the polymer surface, covalently bonded to the carbon backbone. The positively charged cations in solution are electrostatically attracted to the negatively charged sulfonate groups, and since the concentration of the cation from the respective salt solution is in great excess, the probability of exchanging the ammonium ions is high. In order to determine achieved levels of ion exchange, 100 :ml solutions of the respective cations exchanged from 50 cm? film samples in 5 % HCl were analyzed by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICPAES). The results from the ICPAES analysis are presented in Table 7., where [c] denotes the concentration of the respective exchanged cations in solution, and [q] denotes the concentration of the cations in question in the aqueous blank solution. 58 Table 7. Cation Concentrations as Determined by ICPAES Cation Concentration; Concentration in blank; [e] [6.] DRILLED!) DMZ!) lithium .014 .013 sodium .290 .106 potassium .586 .210 magnesium .0289 .006 calcium .335 .057 barium .398 .000 The cation concentration to be expected can be estimated based on an assumed sulfur surface concentration of 0.8 pg S/cm’, as follows: 59. Monovalent cations: 1 mole S - 1 mole SO; - 1 mole Li‘, Na+ or K+ S : Molecular weight - 32.0 g/mole Moles Na“ - 8x10” g S/cm2 x 50 cm2 / 32.0 g/mole - 2.5x10‘ moles Na+ : Molecular Weight - 23.0 g/mole g Na*/100 ml - 2.5x10‘ moles x 23.0 g/mole - 2.875x10" g/100 ml - 2.875x10'7 g/ml - 0.288 ppm Na+ Divalent cations: The calculation follows the same principle except; 1 mole S - 1 mole SO; - 0.5 mole Mg“, Ca++ or BaH The estimated cation concentrations [c.l , the actual measured concentrations ([c]-[c,]) and the derived percentage level of ion exchange are presented in Table 8. 60 Table 8. Level of Cation Exchange Achieved Expressed as a Percentage Cation Estimated Conc.; Measured Conc.; % Ion Exchange [9.] ([c} - [all 11521—2131.). mfg/v) mug/v) [cJ lithium .173* .001 0.6 sodium .288 .184 64 potassium .489 .376 77 magnesium .152 .0229 15 calcium .251 .278 111 barium .858 .398 46 *sample size - 100 cm? The low values obtained for the estimated percent ion exchange for Li+ and Mig++ are not fully understood. However, a diffusional resistance does not appear to be the cause, as high levels of exchange were observed for both monovalent and divalent cations of larger atomic radii. While not fully understood, the apparent low level of Li+ and MigH exchange may be the result of experimental error in preparation of the aqueous solutions for analysis, or during the ICPAES analysis itself. Both of which could result in significantly lower values of ion concentration than theoretical. In 61 future studies, an alternate analytical procedure such as ESCA is recommended to quantify the surface concentration of neutralizing cation, and thus confirm the percent ion exchange values obtained by the spectroscopic method. Alternatively, the apparent low levels of ion exchange effected by Li+ and Mg**'may be the result of the lack of dissociation of the ammonium sulfonate groups at the pH of the aqueous LiCl and MgCl, solutions employed, or the relative electronegativity of the respective cations. However, since the ion exchange of Li+ and Mg**ihas been previously reported by Walles (1989) for surface sulfonated polymers, these effects seem unlikely to account for the low exchange values obtained in the present study. 62. MW The repeatability of permeation results obtained when exposing both unmodified and surface sulfonated polystyrene film to limonene vapor was not acceptable, as illustrated by Figures A2 and A3 in Appendix A. Due to the anomalous results obtained for limonene vapor permeability, these studies were discontinued. However, in order to provide an explanation of the abnormal diffusional behavior observed, solubility experiments were initiated: The aggressiveness of limonene and ethyl acetate vapors toward unmodified polystyrene and surface sulfonated polystyrene was found to be significant. For example after less than 15 min. exposure to limonene and ethyl acetate vapor (a-1), swelling, stress cracking and initial stages of dissolution were observed. After 1 hour the samples were totally dissolved. After 1 hour exposure to acetone vapor the unmodified Ps sample weight is increased by 22 % and the surface sulfonated PS by 23 8, whereas propanol vapor has no evident influence on polystyrene. After 4 days exposure to propanol vapor the sample weight is increased by 2 % and 0.7 %, respectively. The high solubility of organic vapors in polystyrene is 63, furthermore confirmed when comparing the solubility parameters presented in Table 3. The difference in polystyrene and ethyl acetate solubility parameters is only 0.07, thus resulting in a significant solubility of polystyrene in ethyl acetate. A similar relationship between polystyrene and limonene accounts for the non-Fickian diffusional behavior observed for the organic vapor permeability experiments. In this case the relatively high penetrant activity employed resulted in a type two transport phemonena (Boyer, 1970). The polystyrene-limonene interaction furthermore resulted in solvent induced crazing, which was enhanced by increasing temperature. After exposure of the surface sulfonated PS to limonene vapor at a vapor activity of 0.6 at 25°C for 9 days, a certain degree of solvent induced crazing was evident by the formation of a regular pattern of white one directional lines in the material. After exposure at identical conditions for a period of 6 days, followed by exposure at 60°C and a corresponding higher vapor activity for 1 day, extensive solvent induced crazing was observed. A regular pattern of white perpendicular lines was etched into the surface of the material (see Figure 11.). The same formation of perpendicular lines without etching onto the surface was observed for unmodified polystyrene. The data from both the permeation and solubility experiments 64 indicates the poor barrier properties of unmodified and surface sulfonated polystyrene toward organic penetrants. Furthermore if clarity is a critical factor caution is suggestable when utilizing a surface sulfonated polystyrene at elevated temperatures for packaging of products containing aggressive organic compounds. 65 Figure 11. Photographic Illustration of Limonene- Surface Sulfonated Polystyrene Interaction 66 QX!S§U.E§IR§AD£! The oxygen diffusion coefficient, D0,, and permeance, P0,, for the various film structures were determined by utilizing a computer program for calculating these parameters, as presented in Appendix B. The data necessary for running the computer program is in the form of time (sec) versus voltage output (mV), which is obtained by performing permeation runs on the Ox-Tran 100 Permeability Tester. Table 9. presents average values for DO, and P0,, based on replicate determinations at 23°C and 50 % R.H., as a function of neutralizing cation. Table 9. also lists cation atomic radii, and the atomic number for the respective neutralizing cations. 67 Table 9. The Influence of the Neutralizing Cation on Oxygen Barrier Properties of a 4 mil Surface Sulfonated Polystyrene Structure Cation Ion Radii Atomic Diffusion Coef Permeance 1W ammonium 7 8.3 i 1.0 1110 r 10 lithium 76 3 7.4 1 1.0 1260 i 70 sodium 102 11 8.0 1 0.4 1160 t 30 potassium 138 19 8.1 i 0.2 1190 i 110 magnesium 72 12 7.756 t 0.004 1200 t 60 calcium 100 20 7.50 i 0.06 1240 t 110 barium 135 56 7.7 1 0.2 1170 t 10 Figures 12. and 13. plot oxygen diffusion coefficient and oxygen permeance, respectively, versus neutralizing cation atomic radii. Whereas Figures 14. and 15. plot the same parameters versus atomic number of the respective cations. As shown, there is no correlation between neutralizing cation radii or atomic number and oxygen diffusion coefficient and oxygen permeance. Thus, at the level of surface sulfonation, the neutralizing cation has little or no influence upon the oxygen barrier properties of the test films. Values from the literature for the oxygen diffusion 68 coefficient (D0,) and oxygen permeability (Pp0,) through polystyrene obtained at 23°C and 25°C, respectively, are listed in Tables 4. and 5., and are summarized below; DO, - 11 x 104 cmzlsec PpO, - 4,650 cc(STP)*mil/m2*day*atm Experimental values obtained for an unmodified 1.5 mil PS film under similar test conditions are stated below; DO, - 2.4 :l: 0.2 x 10" cm’lsec PpO, - 4,680 :l: 150 cc(STP)*mil/m’*day*atm The range of values obtained for the various surface sulfonated 4 mil PS films are as follows; DO, - 6.4 - 9.3 x 10" cm’lsec ppo, - 4,400 - 5,400 cc(STP)*mil/m2*day*atm STATISTICAL ANALYSIS : A statistical analysis of the obtained data for oxygen barrier characteristics was carried out. The statistical test applied was; Analysis of Variance I or ANOVA (Steel and Torrie, 1980). In order to determine whether a statistically significant difference exists between oxygen barrier property values for an unmodified and a surface modified PS, oxygen diffusion 69 coefficient and permeability data for the unmodified polystyrene (1.5 mil) were compared with the various cation stabilized surface sulfonated polystyrene structures (4 mil). The ANOVA data are presented in Appendix B, Table B1. A statistically significant difference was found to exist for the oxygen diffusion coefficient data, with a confidence level of; 90 % for NHfi) 95 % for Li*, 99 t for Na+ and 99.5 % for K‘, Mg“, CaH and Ba“. The difference in oxygen diffusion coefficient values may however derive from a difference in thermo-mechanical history between the test and control films. No statistically significant difference was found to exist for the oxygen permeability data. Furthermore, the same parameters for the surface sulfonated PS, neutralized with the various cations, were compared to the ammonium stabilized structure, as presented in Table 82. No statistically significant difference was found to exist for neither oxygen diffusion coefficient nor oxygen permeability values, except for the oxygen permeability value obtained for the barium stabilized structure. Thus, the polymer surface modification achieved at the level of sulfonation has no evident effect on the oxygen barrier properties of polystyrene. This is not surprising when considering the limited depth of sulfonation. 70 10 95- g E T 0) 8: :I \ _ N : _ 1 El : :1. 3 : “I" 7E O : 1- .— 2“ E .l- 8 a:— 5 :- +- N 3+ "' U’t; a O @4- 24 02 m: IllllIllllIllllIlllJIllllIllllIllIll 7O 80 90 100 110 120 130 140 Ion Radii (pm) Figure 12. Oxygen Diffusion Coefficient as a Function of Neutralizing Cation Radii 71 1400 I "F I ‘l' «1300?— - E : g _ 5. : T o _ '° : «£1200:- J_ \ Z I E EAL J g : 331100; J S‘ I O _ 0- : 1000:-+ 1 + “ cv'+ 4» 02+ a a: 82 8’2 IllllIlLllIllllIJlllIllllIlllJIlllll 7O 80 90 100 110 120 130 140 Ion Radii (pm) Figure 13. Oxygen Permeance as a Function of Neutralizing Cation Radii 72 10 E or 9:— - E O ._ 1' I = I \ 83' "a : I 3, E .1. m I— I 7': CD : '- : . : dL (V E O 6': O : E 5— + + «+4: 3 2; t1 «IO-Ia e .1225 :0 In IlllllllllIlllllllllIlllllllllIlllllllllIllllllllJIlllllllll 0 1 O 20 30 4O 50 60 Atomic Number Figure 14. Oxygen Diffusion Coefficient as a Function of Atomic Number Corresponding to Neutralizing Cation 73 1400__ E _ ‘l' .— T A 1300 — - E5 2 iii 2 - s : F a h- ‘U 2 0|. 1200:." ..l- E} _ 5: : , I F- I a L”. : - 3 1100; I .a : J. C) _ 0- I 1000:- + + + + + I‘m” +Nm N40 .IZIZHE 13¢) In IlllllllllIlllllllllIlllllllllIlllllllllIlllllllllIllllllllL O 10 20 30 4O 50 60 Atomic Number Figure 15. Oxygen Permeance as a Function of Atomic Number Corresponding to Neutralizing Cation 74. EQI£I_!§RQI_E§IDEIDQ§ The data in form of weight gain as a function of elapsed time, obtained for the various film structures, are presented in Appendix C, Table C1. As a typical example of the linear relationship exhibited by the respective film structures, Figure C2. presents a plot of weight gain (g Inc) as a function of elapsed time (hrs) for the ammonium stabilized surface sulfonated polystyrene. The slope of the curve thus equaling the water vapor transmission rate. Water vapor transmission rate may be converted to permeance by taking into account the exposed surface area and water vapor pressure difference at the conditions of test. Average values of water vapor permeance through the various film structures, based on replicate determinations at 37.8‘C and 85 % R.H., are presented in Table 10. 75 Table 10. The Influence of the Neutralizing Cation on Water Vapor Barrier Properties of a 4 mil Surface Sulfonated Polystyrene structure Cation Ion Radii Atomic Permeance ML mm: (mm ammonium 7 514 i 6 lithium 76 3 517 i 1 sodium 102 11 507 i 4 potassium 138 19 531 t 3 magnesium 72 12 513 t 0 calcium 100 20 536 t 4 barium 135 56 532 i 1 Figures 16. and 17. plot water vapor permeance as a function of neutralizing cation atomic radii, and atomic number of the corresponding cation, respectively. At this level of sulfonation no influence of neutralizing cation atomic radii or atomic number upon water vapor barrier properties is evidenced. 76 540__ “F 5 i- I] A 530— E : fl _ m _ >. I a I 13 520': on I E I I :2 s— 0 1 ‘ «51°- F I: I 0- : 500:- ; ++ + + U! “a N :2 82 8‘5: llllllllllllllllllllllllllllllllllll 70 80 90 100 110 120 130 140 Ion Radii (pm) Figure 16. water vapor Permeance as a Function of Neutralizing Cation Radii 77 540 E- -r .. 530 :— EE 2 fl — ‘9 : > .— ‘V L'. "3 520 : T cu _ g : I g : O I _ IN 510 ;- F a : .Jb : ‘— t;:: a!” +°k °E 4225 :0 m JunnlanInllnllhnlnllldllnullnllullnnlhnlnllu 0 10' 20 30 4O 50 60 Atomic Number Figure 17. Water vapor Permeance as a Function of Atomic Number Corresponding to Neutralizing Cation 78. W Average values of tensile strength and modulus of elasticity for the various film structures, based on replicate determinations, are presented in Table 11. Table 11. Effect of Neutralizing Cation upon Tensile Properties Cation Mean Standard Mean Standard Tensile Deviation Modulus of Deviation Strength (psi) Elasticity (psi) (1381) x105 (psi) NH." 11,205 166 3.40 2,200 Li+ 9,938 742 3.23 0 Na+ 11,056 90 3.42 10,600 K+ 10,279 147 3.11 3,600 Mg" 10,624 37 3.20 1,400 Ca“ 11,168 152 3.23 16,300 Ba++ 11,301 47 3.42 1,000 79 The tensile properties exhibit no evident correlation with the valance of the neutralizing cation, nor with the atomic ion radii, or atomic number of the cation. 80 BUIHARY AND CONCLUSIONB The effect of a series of neutralizing cations on the barrier properties of a surface sulfonated polystyrene film was investigated. The cations evaluated included : Nfifly Li*, Na*, K+, Mg**, Ca++ and Ba*+. The respective structures were obtained by an ion exchange procedure from the ammonium stabilized sulfonated polystyrene film. The estimated values for the extent of sulfonation, and the depth of sulfonation of the polystyrene film (4 mil) were as follows: 0.8 pg S/cm2 and 50 A, respectively. The presence of ammonium-stabilized sulfonate groups on the sample I surface was confirmed by an ESCA survey. The determined atomic concentrations of sulfur, oxygen, nitrogen and carbon indicated a 96 8 level of neutralization with ammonium, and a surface concentration of 1 sulfonate group per 2% monomer repeat unit on the polymer surface. Permeability of limonene vapor, at a vapor activity of 0.6 and 25°C, through the ammonium-stabilized surface sulfonated polystyrene exhibited anomalous behavior, which was attributed to the solubility of limonene in the polymer. Similar results were obtained for a non-sulfonated polystyrene film serving as a control. The high level of solubility of limonene in polystyrene is supported by 81 numerical values of the solubility parameters of limonene and polystyrene. The polystyrene-limonene interaction furthermore resulted in solvent induced crazing, which was enhanced by increasing temperature. An etching of white perpendicular lines into the material was observed after exposure to limonene vapor (a-0.6) for a period of 6 days at 25°C, followed by exposure at 60°C for an additional day. Exchange of the neutralizing cation ammonium with the following cations: Li‘, Na‘, K‘, ug“, Ca++ and BaH had no effect on the barrier characteristics of the surface sulfonated polystyrene film for the penetrants, oxygen and water vapor, at the level of sulfonation present in the test structures. There was no correlation between the valance, atomic radii, or atomic number of the respective neutralizing cations and the oxygen diffusion coefficient, oxygen permeance, and water vapor permeance of the test film structures. Further, the barrier characteristics for oxygen and water vapor were found to be equivalent to an unmodified polystyrene film. The tensile properties exhibited no evident correlation with the valance of the neutralizing cation, nor with the atomic radii, or atomic number of the cation. At the level of sulfonation the only significant difference as compared to an unmodified polystyrene is an increase in surface polarity, which can be attributed to insertion of 82 polar sulfonate groups at the polystyrene surface, thus enhancing the wetability of the polymer. APPENDICES 83. Appendix A Standard Calibration A calibration curve for limonene was generated based on the following concentrations of limonene in solvent; 8.4, 16.8, 42, 168 and 210 ppm (w/v). A 1.0 pl sample was injected directly into the gas chromatograph and the area response recorded. Limonene concentration was plotted versus area response. The slope equals the calibration factor in (ppm/A.U.) which may be converted into (g/A.U.) by considering the quantity of sample injected. Table A1. and Figure A1. show the calibration data and the standard calibration curve for limonene, respectively. Limonene standard calibration factor - 5.300 x 10'” (g/A.U.) 84 Table A1. Limonene Calibration Curve Data Area unit Area Unit Area Unit My) First 111;]. 59.9mm.— 8.4 15541 15232 15387 16.8 31761 29844 30803 42 82862 78201 80532 168 307270 313990 310630 210 398110 402070 400090 85 200 4— OAverage values ; - of replicates \ .— 5 _. S 150 - Q .— .E ‘ a _ g _ a is 1CK)_- ‘0 o u— 0 — C r- 2 so — o .— .§ r A .— 0 P- l 1 l 1 1 1 L 1 l 1 0.0 1 .0 2.0 3.0 4.0 5.0 Area Response .1O5(A.U.) Figure A1. Limonene Standard Calibration Curve 86 Limonene Permeation 0.20 : 04 mil Sulf. PS/NH4+ .. " + i _ e4 mil Sulf. PS/NH4 E 0.15 — E — O. 1— Q — .5 ‘5 010 _ w . a — C o _ o _ g .— 0 0.05 -— e c _ o .5. " A — P- 0.00 — l 1 1111,] 1 11 1 l 11 1.11 1 1 11 l 1 0 50 100 150 200 Time(hrs) Figure A2. Replicate Determination of Limonene Permeation through Ammonium Stabilized Surface Sulfonated PS (Performed at 25°C and a Vapor Activity of 0.6) 87 ' O 1.5 mil unmodified PS & F“ e 4 mil Sulf. PS/NHI — re 0) I I Limonene Concentration .10' 9 (w/v) I 1 JllIlILlllILlll 0 50 100 150 Elapsed Time (hrs) Figure A3. Replicate Determination of Limonene Permeation through 1.5 mil PS and 4 mil Sulfonated PS (Performed at 25’C and a Vapor Activity of 0.6) 10 30 32 33 35 36 37 38 39 40 50 60 7O 80 90 100 110 120 160 170 180 190 200 205 210 220 230 240 250 260 270 280 290 88 Appendix B Computer Program for Oxygen Diffusion Coefficient and Permeance REM THIS PROGRAM CALCULATES THE DIFFUSION COEFFICIENT FROM PERMEABILITY REM CONTINUOUS FLOW EXPERIMENTS. REM PROGRAM WRITTEN BY RUBEN J. HERNANDEZ. JAN/1988. MODIFIED BY L. ESBENSEN ' REM ON 12-9-91 DIM F(50), T(50), X(50), DF(50) REM THE UNITS OF TIME USED WILL DETERMINE THE UNITS IN THE DIFF. COEFF. REM REM PRINT "ENTER THE RUN IDENTIFICATION NUMBER" REM INPUT SUN PRINT "ENTER THE TEMPERATURE AT STEADY STATE" INPUT W PRINT "ENTER THE NUMBER OF DATA POINTS" INPUT D PRINT "ENTER THE FLOW F AND TIME T STARTING FROM ZERO" FOR I=1 To D PRINT "ENTER F" INPUT F(I) PRINT "ENTER T" INPUT T(I) NEXT I PRINT "ENTER YOUR GUESS FOR x" INPUT GUESS PRINT "ENTER INFINITE VALUE FOR F" INPUT FI FOR I=1 TO D DF(I)=F(I)/FI A=.443l3*F(I)/FI x-GUESS FOR J=1 To 7 B=SQR(X) C=EXP(-X) L=1/B H=(.5*L-B)*C E=(B*C)-A =x-(E/H) 300 310 320 330 380 390 400 410 420 430 440 445 450 460 470 480 490 500 510 520 530 540 550 560 562 563 564 570 600 610 620 630 635 636 637 638 639 640 642 645 646 647 648 650 655 659 89 NEXT J X(I)=X GUESS=X NEXT I REM LINEAR REGRESSION ST=O SX=0 SXT=O STSQ=O SXSQ=O FOR I=1 TO 0 X(I)=1!/X(I) ST=ST+T(I) SX=SX+X(I) SXT=SXT +(X(I)*T(I)) SXSQ=SXSQ+(X(I)*X(I)) STSQ=STSQ+(T(I)*T(I)) NEXT I SLOPE=(ST*SX-D*SXT)/(ST*ST-D*STSQ) DUM1=(D*SXT)-(SX*ST) DUM2=(D*STSQ)-(ST*ST) DUM3=(D*SXSQ)-(SX*SX) DUM4=SQR(DUM2*DUM3) R=DUM1/DUM4 LPRINT "RUN NUMBER: " SUN PRINT LPRINT "TIME (SEC) ", "FLOW", "X", "FLOW PERCENT" FOR I=1 TO D LPRINT T(I),F(I),X(I),DF(I) NEXT I PRINT PRINT DIFF= ((.0101602)*SLOPE/4 LPRINT "DIFFUSION COEFF IN cm2/sec. =" DIFF LPRINT LPRINT "PERMEANCE IN cm3(STP)/m2.day.atm ="FI*69.1*10/(4.775*.21) PRINT LPRINT REM LPRINT "THE CORRELATION COEFF. =" R LPRINT LPRINT "TEMPERATURE IN C =" W LPRINT REM THE VALUE OF THE DIFFUSION COEFFICIENT IS FOR TIME IN SECONDS REM THE THICKNESS IS L=1-/16E-03 cm (4.0 mil) END 90 Statistical Analysis Table Bl. ANOVA for Oxygen Diffusion Coefficient and Permeability (1.5 mil PS vs. the Various Sulfonated 4 mil PS Structures) Comparing: Observed F Required F DQL___Jhuh, 191_____§i_____131_ 0.51. PS/Nflf’ 9.46 8.29 8.53 18.51 98.50 198.5 PS/Li+ 23.81 1.55 PS/Na+ 155.5 0.10 PS/K+ 324.0 0.030 PS/Mg++ 576.0 0.24 PS/Ca++ 520.0 0.39 PS/Ba“ 281.0 -0.056 91 Table 32. ANOVA for Oxygen Diffusion Coefficient and Permeability (Ammonium Stabilized Sulfonated PS vs. the various Neutralizing Cations) Comparing: Observed F Required F 01—21:? 101__§_t__15: 0.51 NI!,*/Li+ 0.13 4.52 8.52 18.51 98.50 198.5 NH,‘*/Na* 0. 012 2 . 55 NH,*/K* -0. 0099 0. 53 NHf/Mg‘” 0 . 090 2 . 19 NI-If/Ca‘” 1.02 1.39 MIR/Ba” 0.065 19.33 Appendix C Water vapor Transmission Rate Data Table 1C. water Vapor Transmission Rate Data Obtained for The Various Film Structures at 37.8°C and 85 % R.M. Based on Replicate Determinations "34+ L14- Na” X4» “9“» ca++ 38'” Time Wt. of (g) - - - - (hrs) gain 190 19.0 .1192 .1197 .1183 .1247 .1188 .1256 .1249 24.0 .1482 .1491 .1470 .1548 .1478 .1559 .1551 46.0 .2863 .2889 .2832 .2980 .2863 .3004 .2986 67.0 .4199 .4232 .4153 .4359 .4197 .4390 .4360 72.0 .4484 .4511 .4430 .4657 .4486 .4693 .4663 91.0 .5664 .5699 .5600 .5886 .5675 .5933 .5889 115.3 .7181 .7220 .7085 .7443 .7179 .7501 .7448 145.3 .9052 .9108 .8926 .9377 .9044 .9447 .9395 163.0 1.017 1.023 1.003 1.053 1.015 1.061 1.053 93 "0 _ e4 mil Sulf. PS/NH'; .0 m l .0 a: 1 Weight Gain (9) o '1. l .0 a: l (LCD- I .1 1 1 1 I 1 1 1 1 I. 1 1 1 1 I 1 o 50 1 00 1 50 Elapsed Time (hrs) Figure C1. weight Gain as a Function of Elapsed Time for Ammonium Stabilized Surface Sulfonated PS 94 Appendix D Surface Analysis Table D1. Surface Tension of an Unmodified PS and the Various Surface Sulfonated PS Films _£iln_fi§IRQSNI£; .8urfasa_Tsnaien_id¥nsaLEnL_ polystyrene 32 (Skeist, 1977) non-sulfonated PS < 36 ammonium-sulf. PS I 56 lithium-sulf. PS 56 sodium-sulf. PS 56 potassium-sulf. PS 56 magnesium-sulf. PS 56 calcium-sulf. PS 56 barium-sulf. PS 56 BIBLIOGRAPHY 95 BIBLIOGRAPHY Aiken,W.H., Doty,P.M., and Mark,H. Modern Packaging, 45:137 (1945) Alfrey,T. Chemical Engineering News, 43:64 (1965) ASTM D 3985-81 “Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using A Coulometric Sensor” Annual Book of ASTM Standards, Part 35, ASTM Headquarters, 1916 Race St., Philadelphia, PA (1981) ASTM 0 882-83 "Tensile Properties of Thin Plastic Sheeting" Selected ASTM Standards on Packaging, Second Edition, ASTM Headquarters, 1916 Race St., Philadelphia, PA (1987) ASTM B 96-80 "Water vapor Transmission of Materials" Selected ASTM Standards on Packaging, Second Edition, ASTM Headquarters, 1916 Race St., Philadelphia, PA (1987) Balta Calleja,F.J., Fonseca,C., Perena,J.M., and Fatou,J.G. ”Surface Hardening of Polyethylene through Sulphuric Acid Exposure" Journal of Materials Science Letters, 3 :509-511, Chapman and Hall Ltd. (1984) Baner,A.L., Hernandez,R.J., Jayaraman,K., and Giacin,J.R. ”Organic vapors Through Barrier Membranes” Symposium on Current Technologies in Flexible Packaging. ASTM ST? 912 (1986) Barnes,J.D. “National Bureau of Standards Certificate. Standard Reference Material 1470. Polyester Plastic Film for Gas Transmission” National Bureau of Standards, Washington, D.C. (1982) Barrer,R.M., "Permeation, Diffusion and Solubility of Gases in Organic Polymer“ Trans. Faraday Soc. 35:628 (1939) Boyer,R.F. "Physical Properties-Diffusion” Encyclopedia of Polymer Science and Technology, Volume 13, Interscience Publishers, John Wiley 8 Sons (1970) Brown,W.E., and Sauber,W.J. Mbdern Plastics, 36:107 (1959) 96 Crank,J., The Mathematics of Diffusion, 2nd Edition. Oxford, England, Clarendon Press (1975) Crank,J., and Park,G.S. Diffusion in Polymers, New York, Academic Press (1968) Cutler,J.A., and McLaren,A.D. Tappi, 36:423 (1953) Davis,D.W. Paper Trade Journal, 123:33 (1946) Deeg,G., and Frosch,C.J. Modern Plastics, 22:155 (1944) Dow Chemical Company, unpublished data Feldman,L.C., and Mayer,J.W. ”Fundamentals of Surface and Thin Film Analysis” Chapter 9 'x-Ray Photoelectron Spectroscopy (XPS), North Holland Publishers (1986) Fonseca,C., Perena,J.M., Fatou,J.G., and Bello,A. "Sulphuric Acid Etching of Polyethylene Surfaces” Journal of Materials Science, 20:3283-3288, Chapman and Hall Ltd. (1935) Fujita,H. "Diffusion in Polymer -Diluent Systems" Hochpolym. Forsch., 3:1 (1961) Gilbert,E.E. Sulfonation and Related Reactions, Interscience ‘ Publishers (1965) Hernandez,R.J., Giacin,J.R., and Baner,A.L. ”The Evaluation of the Aroma Barrier Properties of Polymer Films" Journal of PLastic Film and Sheeting, 2:187 (1986) Hopfenberg,H.8., and Frisch,H.L. Polymer Letters, in press. Hopfenberg,H.B., Holley,R.H., and Stannett,v. Polymer Engineering Science, in press. Hopfenberg,H.B., Holley,R.H., and Stannett,v. private communication Ihata,J. "Formation and Reaction of Polyenesulfonic Acid. 1. Reaction of Polyethylene Film with 803” Journal of Polymer Science: Part A: Polymer Chemistry, 26:167- 176, John Wiley 4 Sons, Inc. (1988) Ihata,J. ”Formation and Reaction of Polyenesulfonic Acid. II. Photoreaction of Polyenesulfonic Acids" Journal of Polymer Science: Part A: Polymer Chemistry, 26:177- 185, John Wiley 8 Sons, Inc. (1988) 97 Jastrzebski,z.D. ”The Nature and Properties of Engineering Materials", Second Edition, John Wiley 8 Sons, Inc. (1975) Kirk-Othmer, Encyclopedia of Chemical Technology, Second Edition, V01 19, Interscience Publishers, John Wiley 5 Sons (1969) Korvezee,A.E., and Mbl,E.A.J. Journal of Polymer Science, 2:371 (1947) Major,C.J., and Xammermeyer,x. MOdern Plastics, 39:135 (1962) Maxwell,B., and Rahm,L.F. Industrial Engineering Chemistry, 41:1990 (1949) Meares,P. ”Transient Permeation of Organic Vapors Through Polymer Membranes" Journal of Applied Polymer Science, 9:917 (1965) Mehta,R.K., and Bush,D.M. 'Fluorinated HDPE Protects Flavors" Packaging, August:100 (1988) Moore,J.A., and Barton,T.J. Organic Chemistry, An Overview, Holt-Saunders International Editions (1978) Morrison, and Boyd, Organic Chemistry, Fourth Edition, Allyn and Bacon (1983) Muller,P.H. KOllOid 2., 1003355 (1942) Paine,F.A., and Paine,H.Y., A Handbook of Food Packaging, London, Leonard Hill (1983) Park,G.S. Journal of Polymer Science, 11:97 (1953) Planche,J.P., Revillon,A., and Guyot,A. ”Chemical Modification of Polynorbornene. I. Sulfonation in Dilute Solution" Journal of Polymer Science: Part A: Polymer Chemistry, 26:429-444, John Wiley 5 Sons, Inc. (1988) Plastics Technology, 12:10,32 (1966), and 13:13,38 (1967) Raetz,R.W. Encyclopedia of Polymer Science and Technology, 4:294-307 (1970) Schulz,G.V., and Gerrens,H. z.Phys.Chem.(Frankfurt), 7:182 (1956) 98 Simril,v.L., and Hershberger,A. Modern Plastics, 27:97 (1950) Skeist,I.(ed.), Handbook of Adhesives, Second Edition, Litton Educational Publishing, Inc. (1977) Soroka,W., and Castelletti,L.T. ”Effect of Mocon Oxtran 100 Operating Variables on Polyester Film Oxygen Transmission Rate” Report No. ENG. R-79-32. Department of Engineering, Packaging Design and Development Section, Ontario Research Foundation, Canada (1979) Stannett,v.T., in Crank,J., and Park,G.S., eds., Diffusion in Polymers, Academic Press, New York (1968) Stannett,v., and Yasuda,H. "The Measurement of Gas and Vapor Permeation and Diffusion in Polymer" Testing of Polymers, velume 1, Chap. 13, John Wiley 8 Sons, Inc. (1955) Steel,R.G.D., and Torrie,J.H., Principles and Procedures of Statistics, a Biometrical Approach, Second Edition, McGraw-Hill (1980) Suh,K.W., and Clarke,D.H. Journal of Polymer Science (A-1), 51:571 (1957) Thomas,A.M., and Gent,W.L., Proc.Phys.Soc.(London), 57:324 (1945) Thorup,N. 'Elementer Fysisk Kemi" 2. Udgave, Polyteknisk Forlag (1986) Ueberreiter,K., in Crank,J., and Park,G.S., eds., Diffusion in Polymers, Academic Press, Inc., New York (1968) Walles,W.E. "Barrier Properties Added to Plastics via Sulfonation and Reductive Metallization' ACS Dallas, April (1959) Walles,W.E. Resinous Enclosure Members Rendered Impermeable by Sulfonation, USP 3,740,258 (1973) Walles,W.E. Resinous Enclosure Members Rendered Impermeable by Sulfonation and Neutralization, USP 3,613,957 (1971) Walles,W.E. In Mbld Sulfonation System, USP applied Zobel,M.G.R. "Measurement of Odour Permeability of Polypropylene Packaging Films at Low Odourant Levels" Polymer Testing, 33:133 (1982) N STRTE UNIV. L Q IBRRRIES IIIIIII II IIIIIIIIIIIII 51211 ICHIG III” 31 293009096