Effect of ionizing radiation on the physicochemical and mechanical properties of commercial monolayer flexible plastics packaging materials

ARTICLE IN PRESS Radiation Physics and Chemistry 68 (2003) 865–872 Effect of ionizing radiation on physicochemical and mechanical properties of commercial multilayer coextruded flexible plastics packaging materials Antonios E. Goulasa,*, Kyriakos A. Riganakosb, Michael G. Kontominasb b a Department of Materials Science and Technology, University of Ioannina, Ioannina GR-45110, Greece Laboratory of Food Chemistry and Technology, Department of Chemistry, University of Ioannina, Ioannina GR-45110, Greece Received 4 July 2002; accepted 5 March 2003 Abstract The effect of gamma radiation (doses: 5, 10 and 30 kGy) on mechanical properties, gas and water vapour permeability and overall migration values into distilled water, 3% aqueous acetic acid and iso-octane was studied for a series of commercial multilayer flexible packaging materials based on coextruded polypropylene (PP), ethylene vinyl alcohol (EVOH), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polyamide (PA) and Ionomer. The results showed that radiation doses of 5 and 10 kGy induced no statistically significant differences (p > 0:05) in all polymer properties examined. A dose of 30 kGy induced differences (po0:05) in the mechanical properties of PA/LDPE, LDPE/EVOH/LDPE and LDPE/PA/Ionomer films. In addition, the same dose induced differences (po0:05) in the overall migration from Ionomer/EVOH/LDPE and LDPE/PA/Ionomer films into 3% acetic acid and iso-octane and in the overall migration from PP/EVOH/LDPE-LLDPE into iso-octane. Differences recorded, are discussed in relation to food irradiation applications of respective packaging materials. r 2003 Elsevier Ltd. All rights reserved. Keywords: Multilayer packaging materials; Physicochemical properties; Gamma radiation 1. Introduction Multilayer coextruded flexible packaging materials are a significant development of modern packaging technology. Their use finds ever-increasing applications in food, pharmaceutical, medicinal, cosmetics and electronics packaging because such materials combine a number of desirable properties (barrier to gases and water vapour, mechanical strength, machinability and relatively low cost) that no single material possesses (Osborn and Jenkins, 1992; Robertson, 1993; Twede and Goddard, 1998; Defosse, 1999). There are large number of possible combinations of single materials in a coextrudate. Most coextruded *Corresponding author. Tel.: +326510-97390; fax: +3265 10-98795. E-mail address: aegoulas@cc.uoi.gr (A.E. Goulas). multilayer structures are based on polyolefins [polyethylene (PE) and polypropylene (PP)]. Polyolefins have a low cost, are versatile and easy to process. Low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) are valued for their toughness and sealability properties. When oxygen, aroma, or flavour protection is necessary, high barrier materials such as ethylene vinyl alcohol (EVOH), polyvinylidene chloride (PVDC) or aluminium applied through vacuum coating processes are used (Osborn and Jenkins, 1992; Robertson, 1993; Twede and Goddard, 1998). The number of layers in a multilayer structure range from 3 to 13 but most commercial multilayer packaging materials include 3, 5 and 7 layer structures (Twede and Goddard, 1998; Defosse, 1999; Toensmeier, 2000). Special adhesives (generally polyesters, copolymers of ethylene, polyurethanes or acrylics) known as ‘‘tie’’ layers are used to ‘‘glue’’ individual layers into a single 0969-806X/03/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0969-806X(03)00298-6 ARTICLE IN PRESS 866 A.E. Goulas et al. / Radiation Physics and Chemistry 68 (2003) 865–872 structure to avoid delamination (Osborn and Jenkins, 1992; Twede and Goddard, 1998). Typical coextruded structures used in food packaging include: LLDPE/tie/EVOH/tie/LDPE used for wine and fruit juices, polyamide/ethylene-vinyl acetate (PA/EVA) used for frozen foods, PA/Ionomer and PA/LDPE used for processed meat, fish and cheese, PP/EVOH/PP and high-density polyethylene HDPE/EVOH/HDPE used for ketchup, sauces, salad dressing and juices (Twede and Goddard, 1998). In the pharmaceutical industry approximately 50% of solid pharmaceutical products (tablets, capsules or powders) are now packaged in flexible materials (Brody and Marsch, 1997). Over 90% of these packages are in the form of blister packages, using a flat multilayer web (i.e. polyvinyl chloride (PVC)/PVDC/PE) to seal the package. Other flexible multilayer structures used in cosmetics and healthcare products packaging include: LDPE/EVOH/LDPE and LDPE-LLDPE/EVOH/ LDPE-LLDPE (Defosse, 1999; Brody and Marcsh, 1997). Ionizing radiation (gamma rays or electron beams) is being used today for pasteurization or sterilization of prepackaged food, or sterilization of pharmaceutical and medicinal products as well as respective packaging materials. Gamma rays are highly penetrating and permit the treatment of bulky items (Bly, 1994; Lagunas-Solar, 1995; Diehl, 1995; Burg and Shalaby, 1996). Food irradiation as a method of food preservation has been explored and documented during the past 45 years. Numerous studies have been conducted on effects of ionizing radiation on food constituents (Lagunas-Solar, 1995; Diehl, 1995; Burg and Shalaby, 1996; Merritt, 1972; Nawar, 1983; Thayer, 1994; Lee et al., 1996). Ionizing radiation effects on polymers have also been widely investigated. They consist mainly of free radicals production. These free radicals can in turn lead to degradation and or crosslinking phenomena (release of gases, discoloration, changes in mechanical properties and gas permeability, degradation and leaching of polymer additives into solvents, etc.) whose extent depends on many factors, such as the chemical structure and morphology of the polymer, specific additives used to compound the plastic, the sample’s thickness, the absorbed irradiation dose and dose rate, the irradiation atmosphere, etc. (Brody and Marsh, 1997; Dole, 1972/ 73; Killoran, 1972; Buchalla et al., 1993a, b, 1999; Goldman et al., 1996; Deschenes et al., 1995; Goulas et al., 1995, 1996, 1998, 2002; Riganakos et al., 1999). In contrast, there is little information on the effect of ionizing radiation on properties of multilayer packaging films. Such information is significant because in the case of food irradiation the packaging material is being radiated along with the contained foodstuff (to avoid microbial recontamination) and (1) possible radiolysis products may contaminate the foodstuff and (2) possible deterioration in properties of the packaging material may cause loss of food quality. In previous work, we have studied the overall migration from commercial multilayer food packaging films into three solvents (official EU food simulants) (Goulas, 2001) as well as the effect of 5, 10 and 30 kGy doses of gamma radiation on the physicochemical and mechanical properties of commercial monolayer packaging materials (Goulas et al., 2002). The present article describes the effects of gamma irradiation on physicochemical and mechanical properties of a series of commercial 3- and 5-layer coextruded packaging films. Test methods include: (1) overall migration into food simulating solvents, (2) permeability to oxygen, carbon dioxide and water vapour, (3) mechanical properties (tensile strength, per cent elongation at break and Young’s modulus). 2. Experimental 2.1. Materials and methods 2.1.1. Materials Five multilayer (3–5 layer) commercial coextruded packaging films supplied by various industrial companies are listed in Table 1. Analytical grade acetic acid and iso-octane were supplied by Merck (Darmstadt, Germany). Water used was double distilled. The distilled water and 3% aqueous acetic acid were used as aqueous and acidic food simulants, respectively, according to EU Directive 97/48/EEC (EEC, 1997). Iso-octane was used as alternative fatty food simulant (EEC, 1997). 2.1.2. Irradiation The multilayer films were irradiated with a 240 kCi (60Co) source at 5, 10 and 30 kGy. Irradiation was carried out in the presence of air at room temperature in the ELVIONY S.A. plant (Mandra Attikis, Greece). Irradiation doses were measured using Harwell Perspex Polymethylmethacrylate (PMMA) type Red 4034 FW dosimeters. The average dose rate was 0.7 kGy/h for all irradiated samples. 2.1.3. Mechanical properties tests Tensile tests were carried out on film strips 250 mm
15 mm (PP/EVOH/LDPE-LLDPE) and 100 mm
15 mm (LDPE/PA/Ionomer, LDPE/EVOH/ LDPE, Ionomer/EVOH/LDPE and PA/LDPE) according to ASTM D 882-90 (ASTM, 1990) with an INSTRON Testing Machine model 4411 (Instron Ltd., UK). Mechanical properties were determined using a crosshead speed of 12.5 mm/min (PP/EVOH/LDPELLDPE) and 500 mm/min (LDPE/PA/Ionomer, ARTICLE IN PRESS A.E. Goulas et al. / Radiation Physics and Chemistry 68 (2003) 865–872 867 Table 1 Multilayer coextruded packaging materialsa used in the irradiation experiments Material No Material food contacting layer - Application Total thickness (mm) Thickness of individual layers (mm) 1 2 3 4 5 PP/tieb/EVOH/tie/LDPE (70%)-LLDPE (30%) LDPE/tie/EVOH/tie/LDPE Ionomerc/tie/EVOH/tie/LDPE PA/tie/LDPE LDPE/tie/PA/tie/Ionomer High barrier High barrier High barrier Barrier Barrier 45 55 75 80 135 15/3–4/7/3–4/15 20/3–4/7/3–4/20 20/3–4/7/3–4/40 20/3–4/55 80/3–4/15/3–4/35 a All packaging materials are food grade. Tie: Adhesive material consisting of anhydride modified ethylene vinyl acetate copolymer. c Ionomers are produced by high-pressure free-radical catalyzed polymerization of ethylene with an unsaturated organic carboxylic acid, partially neutralized with a metal ion. b LDPE/EVOH/LDPE, Ionomer/EVOH/LDPE and PA/ LDPE) and grip distance of 125 mm (PP/EVOH/LDPELLDPE) and 50 mm (LDPE/PA/Ionomer, LDPE/ EVOH/LDPE, Ionomer/EVOH/LDPE and PA/LDPE) according to ASTM D 882-90. 2.1.4. Gas permeability measurements Permeability values to oxygen, water vapour and carbon dioxide were determined using the MOCON OX-TRAN MH 2/20, PERMATRAN-W 3/31 and PERMATRAN-C200 permeability testers, respectively (Mocon Controls, USA). Permeability to oxygen and carbon dioxide tests were performed at a relative humidity (RH) of 6071% and 0%, respectively, and at a temperature of 2371 C while permeability to water vapour tests were performed at a RH of 100% and at a temperature of 2371 C. 2.1.5. Overall migration experiments Rectangular strips of each film sample (surface area 200 cm2) were placed in two-side contact (total contact surface area 400 cm2) with 200 ml of food simulant (distilled water, 3% aqueous acetic acid, iso-octane) in glass beakers. Two-side contact represents a worst case scenario as compared to one-side contact. Beakers were covered by parafilm so as to avoid evaporation of simulant during contact period and kept in a thermostatically controlled chamber at 4070.5 C for 10 days. For iso-octane the temperature/time of plastic/simulant contact was 2070.5 C for 2 days (EEC, 1997). The film samples were subsequently removed from the beakers and the simulant was placed in a 250 ml preweighed round bottom flask and evaporated in a rotary evaporator with distilled water in the heating bath. The round bottom flask containing the residue of evaporation was kept in a thermostatically controlled chamber at 10571.0 C for 1 h followed by 1 h in a desiccator and then weighed. An analytical balance (SARTORIUS BP221S) capable of weighing to 0.1 mg was used. The overall migration was calculated in mg/dm2 of film surface area taking into account the exposed surface area of the test sample. Blank samples were run simultaneously and corrected migration values were calculated for each simulant. For each plastics sample three determinations were performed, and final overall migration values are reported as the mean of the three determinations. 3. Results and discussion 3.1. Mechanical properties measurements Mechanical properties data of non-irradiated (control) and irradiated coextruded materials are given in Table 2. There were no statistically significant differences (p > 0:05) in mechanical properties of nonirradiated and samples irradiated at 5 and 10 kGy. Irradiation at 30 kGy resulted in a decrease in tensile strength of the LDPE/EVOH/LDPE, PA/LDPE and LDPE/PA/Ionomer films by 21.9%, 38.0%, and 10.5%, respectively. The same dose resulted in a decrease of per cent elongation at break of the LDPE/EVOH/LDPE and PA/LDPE films by 48.1% and 42.4%, respectively. These differences are statistically significant (po0:05). In contrast, Young’s modulus of all examined multilayer films showed no statistically significant change after irradiation at doses up to 30 kGy. Overall, the mechanical properties of irradiated up to 30 kGy multilayer films were not largely different from those of the nonirradiated films. Such a deterioration of mechanical properties can be attributed to radiation induced degradation of the polymers. Degradation is expressed as formation of free radicals, production of low molecular weight volatile or non-volatile radiolysis products, production of hydrogen and subsequent increase of unsaturated bonds, polymer chain scission, molecular weight decrease, etc. (Dole, 1972/73; Buchalla et al., 1993a; Brody and Marsh, 1997). Polymer degradation increases in the ARTICLE IN PRESS 868 A.E. Goulas et al. / Radiation Physics and Chemistry 68 (2003) 865–872 Table 2 Mechanical properties of multilayer films (mean of five determinations) Sample Absorbed dose (kGy) Tensile strength (MPa) Percent elongation at break Young’s modulus (MPa) PP/EVOH/LDPE-LLDPE 0 5 10 30 0 5 10 30 0 5 10 30 0 5 10 30 0 5 10 30 LDPE/EVOH/LDPE Ionomer/EVOH/LDPE PA/LDPE LDPE/PA/Ionomer 13.2a 11.4a 14.3a 11.8a 18.2a 17.0a 18.5a 14.2b 23.7a 23.3a 22.8a 22.9a 24.3a 25.1a 24.7a 15.0b 64.7a 60.3a 61.1a 57.9b 48.8a 52.3a 50.6a 46.0a 343a 296a 298a 178b 370a 391a 388a 364a 524a 580a 515a 302b 709a 698a 692a 686a 1541a 1486a 1496a 1478a 446a 443a 441a 420a 433a 414a 403a 426a 249a 253a 254a 266a 477a 454a 469a 446a Values within a column followed by different letters are significantly different (po0:05). presence of air because oxygen is extremely reactive with the free radicals produced by irradiation, as was the case in the present work (Goldman et al., 1996; Gillen et al., 1993). Little information exists in the literature on effects of irradiation on mechanical properties of multilayered packaging materials. Killoran (1972) investigated the effect of gamma radiation (60–67 kGy) on the mechanical properties of 5 multilayer laminates. The laminates consisted of polyethylene terepthalate (PET) as outer layer, aluminium foil as middle layer and either of PEpolyisobutylene blend, HDPE, PET, polyiminocaproyl, polycarbonate as inner (food contacting) layers. In general no significant differences were observed in tensile, burst and seal strength of irradiated samples. The tear resistance of the PE-polyisobutylene blend and polyiminocaproyl showed marked reductions without significant changes in other mechanical properties. Keay (1968) who examined effects of gamma radiation (absorbed doses 10, 20, 30, 50, 80 and 160 kGy) on polyester/medium density polyethylene (MDPE) and PP/MDPE laminates observed no significant differences in mechanical properties (brittleness, delamination). Fengmei et al. (2000) studied effects of gamma radiation doses (5, 10 and 25 kGy) on mechanical properties of Nylon/polyvinylidene chloride/polyethylene and observed that there was no significant difference in tensile strength and per cent elongation at break after irradiation at a dose of 5 kGy; while irradiation doses of 10 and 25 kGy slightly lowered the above mechanical proper- ties. Differences observed among various findings may be related to chemical structure of individual layers, thickness of samples, irradiation dose rate as well environmental parameters (temperature, relative humidity, etc). 3.2. Gas permeability measurements Table 3 presents oxygen, carbon dioxide and water vapour permeability values of five control and irradiated (30 kGy) multilayer packaging materials. As shown in Table 3 there were no statistically significant differences (p > 0:05) in permeability values between all irradiated and control samples. Another observation is the very low permeability values (oxygen and carbon dioxide) of multilayer structures containing ethylene-vinyl alcohol (EVOH) copolymer layer (0.3–0.7 and 1.0–2.5 cm3 m2 day1 atm1 for oxygen and carbon dioxide permeability, respectively). These copolymers are highly crystalline in nature and their properties are highly dependent on the relative concentration of the comonomers. Their barrier properties increase with increasing vinyl alcohol content (Brody and Marsh, 1997; Lagaron et al., 2001). The diffusion coefficient for gases into crystalline polymers Dc is significantly lower than that in amorphous polymers Da and is dependent on degree of crystallinity x (Seymour and Carraher, 1984): Dc ¼ Da ð1  xÞ: ARTICLE IN PRESS A.E. Goulas et al. / Radiation Physics and Chemistry 68 (2003) 865–872 869 Table 3 Permeability valuesa of multilayer films (mean of three determinations) Dose (kGy) PP/EVOH/LDPE-LLDPE LDPE/EVOH/LDPE Ionomer/EVOH/LDPE PA/LDPE LDPE/PA/Ionomer Oxygen permeability (cm3 m2 day1 atm1) Carbon dioxide permeability (cm3 m2 day1 atm1) Water vapour permeability (g m2 day1) 0 30 0 30 0 30 0.7 0.3 0.3 51.9 12.1 0.6 0.3 0.4 51.9 12.3 2.5 1.2 1.4 191 60.6 2.3 1.0 1.7 191 61.0 2.2 1.4 1.5 1.7 0.5 2.4 1.5 2.0 1.2 0.6 a There were no statistically significant differences (p > 0:05) between permeability values of control and irradiated at 30 kGy samples. Riganakos et al. (1999) studied the effect of high dose electron beam radiation (100 kGy) on the oxygen, carbon dioxide and water vapour permeability of PET//PE/EVOH/PE (// laminated, / coextruded) multilayer structure and observed no significant differences in permeability values. Deschenes et al. (1995) studied the effect of gamma and electron beam radiation (0–25 kGy) on oxygen, carbon dioxide and water vapour permeability of a Nylon/polyvinylidene chloride/EVA copolymer film and reported that the permeability to water vapour and to carbon dioxide was not significantly affected by the irradiation doses investigated. However, oxygen permeability increased with absorbed dose. KimKang and Gilbert (1991) reported that gamma radiation doses of 27–32 kGy induced no change in water vapour permeability of PE//polyvinylidene chloride//Glycol modified polyethylene terephtalate (PETG) but significantly reduced its oxygen permeability. 3.3. Overall migration into aqueous simulants Overall migration values for control and irradiated multilayer packaging materials into aqueous food simulants (distilled water and 3% aqueous acetic acid) are given in Tables 4 and 5. For distilled water there were no statistically significant differences (p > 0:05) in overall migration between irradiated and control samples. For 3% acetic acid, the lower absorbed doses of 5 and 10 kGy induced no significant differences. The higher absorbed dose of 30 kGy resulted in an 11.9% and 22.0% decrease in overall migration from the Ionomer/EVOH/LDPE and LDPE/PA/Ionomer films, respectively. Overall migration from all multilayer materials into distilled water was 0.5–2.0 mg/dm2, well below the current European Union upper limit of 10 mg/dm2 for food approved plastics packaging materials (EEC, 1990). The same was observed for migration values from PA/LDPE, PP/EVOH/LDPE-LLDPE and LDPE/ EVOH/LDPE films into 3% acetic acid (1.0–2.3 mg/ dm2). Table 4 Overall migration valuesa (mg/dm2) into distilled water from multilayer filmsb (mean of three determinations) Dose (kGy) 0 5 10 30 PP/EVOH/LDPE-LLDPE LDPE/EVOH/LDPE Ionomer/EVOH/LDPE PA/LDPE LDPE/PA/Ionomer 0.6 0.9 1.3 1.1 1.7 0.5 0.8 1.5 1.2 1.8 0.7 0.7 1.4 1.3 2.0 0.6 0.8 1.4 1.2 2.0 a There were no statistically significant differences between overall migration values of control and irradiated (5, 10, 30 kGy) samples. b Test conditions: 10 days at 40 C. Table 5 Overall migration values (mg/dm2) into 3% acetic acid from multilayer films (mean of three determinations Dose (kGy) PP/EVOH/LDPE-LLDPE LDPE/EVOH/LDPE Ionomer/EVOH/LDPE PA/LDPE LDPE/PA/Ionomer 0 5 a 1.3 1.0a 10.9a 1.9a 16.4a 10 a 1.3 0.8a 10.6a 1.9a 15.0a 30 a 1.4 0.9a 10.7a 1.7a 15.7a 1.2a 0.8a 9.6b 2.3a 12.8b Values within an horizontal line followed by different letters are significantly different (po0:05). Test conditions: 10 days at 40 C. In contrast overall migration from Ionomer/EVOH/ LDPE and LDPE/PA/Ionomer materials into 3% acetic acid (10.9 and 16.4 mg/dm2, respectively) was higher than the above overall migration limit. The high migration values of these 2 multilayer materials can be attributed to Ionomer film properties, whose structure consists of crystalline, amorphous and a third ionic phase composed of metal ions and carboxylate ions. Methacrylic acid (MAA) is incorporated into the backbone of Ionomer chains in significant amounts (7–30%) ARTICLE IN PRESS 870 A.E. Goulas et al. / Radiation Physics and Chemistry 68 (2003) 865–872 in commercial products (Brody and Marsh, 1997). Ionomer reacts strongly with acetic acid because of its relatively high chemical affinity (acid content and metal ions) (Goulas et al., 2002). This statement is supported by the fact that after 10 days of polymer/simulant contact a number of distinct spots were formed on the Ionomer surface (irradiated and non-irradiated films). A similar effect was not observed in any of the other film samples. Killoran (1972) studied effects of gamma radiation doses (60–67 kGy) on migration values of polyethylene– polyisobutylene blend into water and acetic acid and reported no significant differences in migration values between irradiated and control samples. Buchalla et al. (1993b) in a review article, reported that 60 kGy of gamma radiation caused no significant change in the extractability of 10 laminates, six of which having PE as inner layer and the rest four having PVC, PA-11, polyester and polycarbonate as the inner layer, respectively. Kim-Kang and Gilbert (1991) reported that absorbed radiation doses of 27–32 kGy resulted in a decrease in the extractables from a PE//PVDC//PETG multilayer structure into water. 3.4. Overall migration into iso-octane Overall migration values from control and irradiated multilayer packaging materials into iso-octane are presented in Table 6. The results indicate that the lower absorbed radiation doses (5 and 10 kGy) caused no statistically significant differences (p > 0:05) in overall migration into isooctane. At 30 kGy there was an increase (26.7%) in overall migration from PP/EVOH/LDPE-LLDPE and a decrease (20.7 and 16.4%) from Ionomer/EVOH/LDPE and LDPE/PA/Ionomer films, respectively. Migration values into iso-octane are significantly higher (1.7 times for PA/LDPE to 2.5 times for LDPE/EVOH/LDPE) than corresponding migration values into 3% aqueous acetic acid and also significantly higher (2.2 times for Ionomer/EVOH/LDPE to 5.0 times for PP/EVOH/LDPE-LLDPE) than corresponding Table 6 Overall migration values (mg/dm2) into iso-octane from multilayer films (mean of three determinations) Dose (kGy) PP/EVOH/LDPE-LLDPE LDPE/EVOH/LDPE Ionomer/EVOH/LDPE PA/LDPE LDPE/PA/Ionomer 0 5 a 3.0 2.5a 2.9a 3.2a 5.5a 10 a 2.8 2.8a 3.0a 3.1a 5.3a 30 a 3.1 2.6a 2.7a 3.4a 5.4a 3.8b 2.7a 2.3b 3.8a 4.6b Values within an horizontal line followed by different letters are significantly different (po0:05). Test conditions: 2 days at 20 C. migration values into distilled water. This can be explained by the capability of iso-octane to penetrate into the plastic packaging materials, causing swelling of the polymer and thus change in its structure. The consequence is an increase in the diffusivity of the potential migrants and a subsequent increase in the rate of migration (Goulas, 2001). The partition coefficient (k) between the polymer and liquid phase is expressed as the concentration in the polymer (cp ) at equilibrium divided by the concentration in the liquid at equilibrium (cL ) (Goulas, 2001): k ¼ cp =cL : For aqueous simulants, k is much higher than one and migration is substantially lower than that in organic solvents (k value close to one) (Goulas, 2001). In contrast, for structures contained ionomer film a significant decrease in migration values was observed into iso-octane as compared to 3% aqueous acetic acid (3.0 times for LDPE/PA/Ionomer and 3.8 times for Ionomer/EVOH/LDPE). The results in Table 6 show that the overall migration values from all samples are lower than the upper migration limit set by the European Union (EEC, 1990). There is very little information in the literature on effects of radiation on migration from multilayer packaging materials into fatty food simulants. KimKang and Gilbert (1991) reported that absorbed radiation doses of 27–32 kGy caused no change in extractables from PE//PVDC//PETG into n-heptane. Killoran (1972) found a high increase in migration from a polyethylene–polyisobutylene blend into n-heptane after gamma irradiation with 60 kGy. 4. Conclusions The results showed that radiation doses of 5 and 10 kGy induced no statistically significant differences (p > 0:05) in mechanical properties, permeability and overall migration of multilayer films. In contrast, the dose of 30 kGy induced a decrease (po0:05) in the mechanical properties of PA/LDPE, LDPE/EVOH/ LDPE and LDPE/PA/Ionomer. Also, irradiation induced a decrease (po0:05) in the overall migration from Ionomer/EVOH/LDPE and LDPE/PA/Ionomer into 3% acetic acid and iso-octane and an increase in the overall migration from PP/EVOH/LDPE-LLDPE into iso-octane. The overall migration values from all multilayer films into distilled water, 3% acetic acid and iso-octane were significantly lower than the upper limit for migration (10 mg/dm2) set by the EU with the exception of films containing an ionomer layer in contact with 3% acetic acid. ARTICLE IN PRESS A.E. Goulas et al. / Radiation Physics and Chemistry 68 (2003) 865–872 In most food irradiation applications the dose does not exceed 10 kGy (cold pasteurization) while in others (medical, pharmaceutical applications) the dose may reach as high as 20–25 kGy (cold sterilization). In both cases and given present results on mechanical, permeability and overall migration properties which correspond to a worst case scenario (two-side contact) one may state that properties of all tested multilayer films remain practically unaffected, complying with EU food packaging regulations. One, however, should stress the fact that overall migration values, lower than the upper limit set by the EU do not in any case guarantee that specific migration values are in compliance with EU packaging regulations. Additives such as monomers, residual solvents, plasticizers, etc., may migrate into the food contacting phase in amounts that exceed either set or proposed upper limits of specific migration (Kontominas et al., 1985; Lox et al., 1992; EEC, 1994; Goulas et al., 1995, 1998, 2000; Goulas and Kontominas, 1996; Devlieghere et al., 1998). Furthermore, irradiation may lead to the production of numerous radiolysis products, most of which, are volatile causing deterioration of packaging material’s sensory properties (i.e. off odour) (Buchalla et al., 1993a, b, 1999; Deschenes et al., 1995; Burg and Shalaby, 1996; Riganakos et al., 1999). Such volatile products are obviously not included in overall migration values since migration testing involves an evaporation step during which all volatiles are lost to the environment. These products need to be identified by appropriate techniques, e.g. purge-and trap technique (Riganakos et al., 1999). Therefore, present results should be discussed as part of the above overall perspective. Of course, due to the fact that specific effects of irradiation on plastics packaging materials are in direct correlation with plastic’s structure, additives, production methods, irradiation conditions, etc. the above results are only indicative and could not be generalized for all multilayer films. 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