農 業 施 設31巻2号 2000. 9. 79～86

Original

Gas Permeability Characteristics of Plastic Films for Packaging of Fresh Produce

Rokhani HASBULLAH*, Gardjito**, Atjeng M. SYARIEF** and Takayoshi AKINAGA*

*Department of Bioproduction, Faculty of Agriculture, University of the Ryukyus. 1 Senbaru, Nishihara, Okinawa, 903-0213 **Department of Agricultural Engineering, Bogor Agricultural University, Bogor, 16002, Indonesia

Summary

A steady state concentration increase method was developed for the simultaneous measurement of the gas

permeability coefficient of plastic films to oxygen, carbon dioxide, and nitrogen. Several polypropylene and polyethylene plastic films with a thickness of 15 μm were used in this experiment. The permeability coefficients of the plastic films to carbon dioxide, oxygen, and nitrogen were measured at 8, 14, 20, and 26℃. The results show that temperature has a significant effect on the permeability coefficients of all the gases tested (O2, CO2, N2). The

gas permeability coefficients increase with increasing temperature. The temperature effect on gas permeability coefficients could be expressed by an Arrhenius equation with the coefficient of determination (R2) values ranging between 0.904 and 0.999. The ratio of permeabilities of CO2 to O2 at 25℃ are 2.0 and 4.0 for the polypropylene and

polyethylene films, respectively

Keywords: gas permeability, polypropylene, polyethylene, modified atmosphere packaging

1. Introduction

The design of film plastic packages for modified Mannapperuma et al., 1989; Zagory et al., 1989). atmosphere packaging (MAP) of produce requires the Respiration rate of produce and gas permeability of knowledge of the gas permeability of the films. Many plastic film changes by different amounts in response researchers have reported on changes in gas concentra- to temperature changes (Exama et al., 1993). tion from the packaging of produce in plastic films The availability of gas permeability data of plastic (Henig and Gilbert, 1975; Deily and Rizvi, 1981; film at several temperatures will help the researcher to Mannapperuma and Singh, 1987). Current attempts of design the packaging for the shelf storage of fresh understanding and modeling the dynamic process of a produce. Likewise, it will help to make any mathematical modified atmosphere (MA) in a plastic film packaging model more accurate. The objective of this study was are hampered by the lack of data in some cases. The to develop a mathematical model for the gas permeability effect of temperature fluctuation must be considered in coefficient of some film plastics as a function of designing MAP systems. All MAP models have assumed temperature. the package would be maintained at optimal storage 2. Theory temperature of the produce (Deily and Rizvi, 1981; Mannapperuma and Singh, 1987; Chinnan, 1989; The methods available for testing gas permeability

Received on November 4, 1999 are classified as pressure increase, volume increase, Correspondence of author: [email protected] and concentration increase depending on the principle

-5- 80 Rokhani HASBULLAH, Gardjito, Atjeng M. SYARIEF, Takayoshi AKJNAGA involved. The pressure and volume increase principles where P is the gas permeability coefficient of the film are the basis of the ASTM D-1434 standard method, (ml.mm/m2.d.atm.), Q is the gas flow rate (ml/hr), b while a steady state concentration increase principle is is the thickness of the film (mm), X is the gas the basis of the ASTM D-3985 standard method (Brown, concentration (%), A is the surface area of the film 1992). This method is applicable only to oxygen due to (m2), and subscripts 1, 2, and 3 denote the Oz, CO2 and the limitation of the detection technique. Na gases, respectively (Figure 2). The apparatus for the steady state concentration The equations above use a double subscript notation increase method consists of a permeability cell with for the gas concentrations in the gas streams. The first two chambers separated by the test film. One chamber subscript denotes the permeated gas while the second is flushed with pure oxygen while the other with gas denotes the carrier gas. mixture consisting of 98% nitrogen and 2% hydrogen The temperature effect on film permeability can (Brown, 1992). The concentration of oxygen perme- be expressed as an Arrhenius type relationship as in ated into the nitrogen stream is measured using a the following equation. coulometric sensor once steady conditions are reached. P=Poexp(-E/RT) (4) Gilbert and Pegaz (1969) introduced a test cell with three chambers which used two samples of the same where P is the gas permeability coefficient (ml.mm/ film. Mannapperuma and Singh (1990) have developed m2.d.atm), PO is the preexponential factor (ml.mm/ this method with automatic gas sampling using a gas m2.d.atm), E is the activation energy of permeation chromatograph so it requires less labor compared to (J/mol), R is the gas constant (8.314 J/mol-K), and T is existing methods. The principle of this method, when the temperature (K). two chambers separated by a permeable film are swept 3. Materials and Methods by two streams of pure gases for a sufficiently long time a steady state results where each gas stream will The polymeric polypropylene and polyethylene contain a trace of the other gas. The magnitude of this (stretch-wrap) films, both had a 15-pm thickness, used trace fraction depends only on the permeation rate of in this research were purchased from PT Altindo the trace component and the flow rate of the sweeping Mulia Jakarta, Indonesia. gas. This principle can be implemented to simultane- The instrumentation for the gas permeability ously measure the permeability of films to oxygen, measurement is schematically shown in Figure 1. This carbon dioxide, and nitrogen. instrumentation consists of the permeability cell with The mass balance of each permeated gas in each three chambers (Figure 2) in conjunction with an HP stream was used to evaluate the film permeabilities. 6890 gas chromatograph, gas cylinders, pressure The oxygen and carbon dioxide permeabilities were regulators, toggle valves and needle valves. The determined by writing the mass balances for these two operation of this setup was automated using solenoid gases in the nitrogen stream, while the nitrogen valves and a gas manifold. The common port of the permeability could be obtained by similar mass balances gas manifold was connected to the ten port valves of for nitrogen in the oxygen or carbon dioxide streams as the gas chromatograph. An IBM PC computer with a in the following equation (Mannapperuma and Singh, PI0-12 card and ERB-24 board (Metrabyte, 1989) 1990). controlled the operation of the solenoid valves. Two circular samples of film, approximately 90 P1=Q3bX13/A(X11+X12-2X13) (1) mm in diameter, were placed so as to separate the three chambers of the cell. Inside diameter of the cell P2=Q3bX23/A(X21+X22-2X23) (2) was 75 mm, therefore the surface permeability was

P3=Q1bX31/A(X33-X31) (3) 0.0044 m2. The cell was clamped tightly together and a high vacuum grease was used to avoid any leaks. The

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Permeability cell

Solenoid valves

Pressure stabilizer

-■- Toggle valve

-○-Needle valve

Gas chromatograph

Figure 1. Schematic diagram of gas permeability measurement system.

Gas Composition Clamping bolt

Figure 2. Permeability cell and the double subscript notation.

cell was placed inside the incubator and the inlet and 26℃).

outlet gas lines were connected. Steady streams of the Determination of the gas permeability coefficient three pure gases of oxygen, carbon dioxide, and requires a highly accurate instrument to simultane- nitrogen were allowed to flow through the three ously analyze the gas composition of oxygen, carbon chambers of the cell. The appropriate gas flow rates dioxide, and nitrogen. In this experiment an HP 6890 were set by adjusting the needle valves to about 120 gas chromatograph(GC) with thermal conductivity ml/hr. The soap bubble flow meter was used to detector(TCD) was used to separate these gases. Two

measure the gas flow rate. The gas stream could be different types of columns connected to the ten port

sampled after steady state conditions are reached 6-8 valve of the GC were used. It allows the automatic hours after the gas stream flows through the three injection of a gas sample without using a gas syringe. A

section of the cell. Three replicate gas samples in the molecular sieve 5A column and a porapak Q column of outlet gas stream were analyzed at 30-minute intervals. 1.8mlength were used. The operating conditions of

The gas permeability of the packaging film was the GC were a 200℃ detector temperature, 70℃ measured at four different temperatures (8, 14, 20, and injector temperature, and 50℃ column temperature.

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The gas carrier was helium with a column flow rate of The gas permeability coefficients were deter- 15 ml/minute, reference flow rate of 25 ml/minute and mined using Equations 1 to 3 with the same data. gas sample of 0.5ml. The gas chromatograph was Figure 3 shows the gas permeability coefficient of the calibrated with a gas mixture of 1% O2+1% CO2+1 polypropylene and polyethylene films at several N2+helium balance. different temperatures. These figures illustrate the strong influence of 4. Results and Discussion temperature on the permeability of all three gases. The

Tables 1 and 2 contain the experimental results of gas permeability coefficient increased with increasing the gas concentrations during the experiments using temperature. the polypropylene and polyethylene film plastics. The gas permeability coefficients are also presented

Table 1. Steady-state gas concentrations during gas permeability measurements of polypropylene film.

Table 2. Steady-state gas concentrations during gas permeability measurements of polyethylene film.

-8- Gas Permeability Characteristics of Plastic Films for Packaging of Fresh Produce 83 in the form of an Arrhenius plot in Figure 4. The other films from the literature for comparison. Arrhenius equation parameters such as the preexpo- The permeability ratio is represented by the nential constant and activation energy of permeation of carbon dioxide to oxygen permeability ratio. This ratio the films are shown in Table 3. value is one of the important parameters in the design The accuracy of fit of the gas permeability of polymeric packages for fresh produce, besides the coefficient curve for O2, CO2 and Nz was proven by the recommended modified atmosphere and respiration higher coefficient of determination (R2). The R2 values rate of the given commodity (Mannapperuma and Singh, for these films were between 0.904 and 0.999. These 1990). It determines the relative proportions of carbon results indicated the goodness of fit of the Arrhenius dioxide and oxygen in the package (Zagory, 1992) and equation to the observed permeability data. determines the possible combination of oxygen and Table 4 shows the values of the gas permeability carbon dioxide concentrations inside the package. Films coefficient, activation energy, and permeability ratio of with high ratio values will allow CO2 to escape relatively the plastic films used in this experiment as well as easily from the package, resulting a low CO2 concentra-

(a) polypropylene film (b) polyethylene film

Figure 3. The gas permeability coefficient of polypropylene and polyethylene films at several different temperatures.

(a) polypropylene film (b) polyethylene film

Figure 4. Arrhenius plot of gas permeability coefficient of polypropylene and polyethylene films.

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Table 3. Preexponential factor and permeability activation energy of the polypropylene and polyethylene films.

Table 4. Gas permeabilities, activation energy and permeability ratio for several packaging films.

a) from Mannapperuma and Singh(1989) b) from Geeson et al.(1985) at 21ｰC c) recalculated from Hasbullah(1992) d) recalculated from Exama et al.(1993)

tion in the package. On the other hand, films with 5. Conclusion lower ratio values will allow greater CO2 buildup in the package. The permeability ratios of the polypropylene The principle of the steady state concentration and polyethylene films in this experiment at 25℃ are 2.0 increase method could be implemented for simultane- and 4.0, respectively. For polypropylene, the ratio of ous measurement of permeability of packaging films to permeability obtained in this experiment is lower than oxygen, carbon dioxide, and nitrogen gases. The gas the values found by Geeson et al.(1985). Various factors permeability coefficients of the polypropylene and affect the measurement of permeability coefficient, polyethylene films increased with increasing tempera- including the test conditions, film characteristics and ture. The temperature effect on film permeability could the test methods. For polyethylene, the ratio permeabil- be expressed as Arrhenius equation with R2 values ity is close to the values of polyethylene-low density ranging from O.904 to O.999. The ratio of the film found by Mannapperuma and Singh(1989) using permeability coefficient of CO2 to O2 at 25℃'are 2.0 the same method. and 4.0 for the polypropylene and polyethylene films,

-10- Gas Permeability Characteristics of Plastic Films for Packaging of Fresh Produce 85 respectively. Fresh fruit and vegetable storage requires to measure gas permeability, Package Engineer- specific permeability properties of the film packaging. ing, 14(1): 66-69. 7. Hasbullah, R.(1992): Modified atmospheric packag- The permeability data of the film tested in this study ing of fruits and vegetables research instrumentation. could be advantageously used with fresh fruits and Training report in Department of Agricultural vegetables to provide desirable storage conditions. Engineering University of California Davis, CA. 8. Henig, Y. S. and Gilbert, S. G.(1975) : Computer Acknowledgments analysis of the variables affecting respiration and quality of produce packaged in polymeric films, J. The authors wish to express special thanks to Food Sci., 40: 1033-1035. Prof. R. P. Singh and Dr. J. D. Mannapperuma for their 9. Mannapperuma, J. D, and Singh, R. P.(1990): assistance in setting-up the apparatus used in this Modeling of gas exchange in polymeric packages research. Appreciation is extended to the Inter of fresh fruits and vegetables, Paper for ASAE Winter Meeting, Chicago, December 1990. University Center for Food and Nutrition (IUC-FN), 10. Mannapperuma, J. D., Zagory, D., Singh, R. P. and Bogor Agricultural University for invaluable assistance. Kader, A. A.(1989): Design of polymeric packages for modified atmosphere storage of fresh produce. References Presented at the Fifth International Controlled Atmosphere Research Conference, Wenatchee, 1. Brown (1992): Plastics in food packaging: proper- WA, USA, June 14-16,1989. ties, design, and fabrication. Marcel Dekker, Inc. 11. Mannapperuma, J. D. and Singh, R. P.(1987): A New York. computer-aided model for gas exchange in fruits 2. Chinnan, M. S.(1989): Modelling gaseous environ- and vegetables in polymeric packages, ASAE ment and physicochemical changes of fresh fruits Paper No. 87-6526. Chicago, USA. and vegetables in modified atmospheric storage. 12. Metrabyte Corporation (1989): Data acquisition In: Quality factors of fruits and vegetables (Jen, J. and control, Vol.21, 1989. Metrabyte Corporation, J. ed.). American Chemical Society, Washington 440 Myles Standish Boulevard, Taunton, MA D. C., p. 189-210. 02780. 3. Deyly, R. F. and Rizvi, S. S. H.(1981): Optimization 13. Zagory, D.(1992): Extended shelf life packages of parameters for the packaging of fresh peaches for produce: new technology, new opportunities. in polymeric films. J. Food Process Eng., 5: 23-41. Presented at the 9th Annual Foodplas Conference; 4. Exama, A., Arul, J., Lencki, R. W., Lee, L. Z. and Plastics Institute of America, Orlando, FL, March Toupin, C.(1993): Suitability of plastic films for 3-5, 1992. modified atmosphere packaging of fruits and 14. Zagory, D., Mannapperuma, J. D., Kader, A. A., vegetables. J. Food Science, 58(6): 1365-1370. Singh, R. P.(1989): Use of a computer model in 5. Geeson, J. D., Browne, K. M., Maddison, K., the design of modified atmosphere packages for Stepherd, J. and Guaraldi, F.,(1985): Modified fresh fruits and vegetables. Fifth Int. Controlled atmosphere packaging to extend the shelf life of Atmosphere Res. Conference, Wanatchee, WA, tomatoes, J. Food Technology, 20: 339-349. June 14-16. 6. Gilbert, S. G. and Pegaz, D.(1969): Find new ways

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生鮮農産 物包装 用 プ ラスチ ックフイル ムのガ ス透過特性

ロハ ニ ハ ス ブ ラ*・ ガ ジ ト**・ アチ ェ ン M. シ ャ リフ**・ 秋 永 孝 義*

*琉 球 人 学農 学 部 生物 生産 学 科, 〒903 -0213 沖縄 県 西 原 町 **ボゴ ール農 業 大 学 農業 工 学 科, ボ ゴ ール 16002, イ ン ドネシ ア

要 旨

厚 さ15μmの ポ リプ ロ ピ レ ン とポ リエ チ レ ン フ ィル ム を 用 い て, プ ラス チ ック フ ィル ムのO2, CO2, N2の 透 過 係 数 を 定常濃 度 増 加 法 で 同 時 に測 定 し た。8, 14, 20と26℃で フ ラ スチ ッ ク フ ィル ムのO2, CO2, N2の透 過 係 数 を測 定 した 。 測 定 結 果 か ら, 供 試 した 全 て の ガ ス (O2, CO2, N2) で 透 過 係 数 が温 度 に影 響 を 受 け る こ と が わ か っ た。 ガ ス透 過 係 数 に 対 す る温 度 の 影 響 は ア レニ ウ ス式 で 表 す こ とが で き, そ の 決 定 係 数 (R2) は0.904～0.999で あ っ た。O2に 対 す る CO2の透 過 率比はポリ プ ロ ピ レ ン で2.0, ポ リエ チ レ ンで4.0で あ っ た 。

キ ー ワ ー ド: ガ ス 透 過 係 数, ポ リプ ロ ピ レ ン, ポ リエ チ レ ン, MA包 装

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