Slide1 : Development of leak-proof, inert and physically
resistant migration cells at high temperature and the validation
of overall migration values obtained Keun-Taik Lee*, Kwang-Ho Lee1 and Seung-Inn Hong2
Department of Food Sci., Kangnung National University, Kangnung, Korea,
1 Korea Food and Drug Administration, Seoul, Korea,
2 Graduate School of Biotechnology, Korea University, Seoul, Korea
Slide2 : Background The use of a microwave oven as well as a conventional oven for cookery is now
widespread. Reheating ready-prepared foods packaged in plastics resulted in
temperatures up to 121℃ and microwave susceptors in contact with foods frequently
reached above 200℃ (Castle et al., 1990). Consequently, more studies are required to
determine the safety of the packaging materials exposed to high temperatures above
100℃. In this regard, the standardization of the testing condition and the development
of the migration cells for simulating the real heating conditions have been attempted in
such experiments. Up till now, the use of vegetable oil as a fatty food simulant was not
satisfactory due to its instability at high temperatures and the analytical difficulty.
Compared to this, Tenax is rather advantageous, however it still lacks the relevant
experimental data and is limited for applications of all the types of film materials
depending on the contained additives. In consideration of these facts, it would be
efficient and useful if volatile solvents could be employed for the test simulating high
temperature conditions exceeding 100℃. Migration cells shall be of such design, for
example having freedom from leakage and minimum area of the test specimen not in
contact with the food simulant (CEN, 2002a; FDA, 2002). Various migration cells in
different designs have been developed and are being used in the field (ASTM, 2002;
Begley and Hollifield, 1991; CEN, 2002a; Goydan, 1990; Snyder and Breder, 1985).
However, those cells have still some restrictions for single- and double-sided contact
uses and in aspects of chemical and physical inertness and resistance at high
temperatures above 100℃ without cell distortion including gasket and leakage even
when using a volatile solvent, and moreover availability of repeated use.
Slide3 : Objectives The primary objective of this study was to develop migration cells fulfilling the above mentioned requirements. Furthermore, this study has examined the effectiveness of single- and double-sided migration cells for use at high temperatures above 100℃ and validated the overall migration values obtained with the cells. After all, the use of volatile solvents for migration testing at high temperatures would provide many advantages in aspects of shorter testing time,
easier lab work and probably more accuracy of results etc. Materials 1) Migration cells : Single- and double-sided migration cells were developed as shown in Fig. 1 and 2. These consisted of a stainless-steel body, cap and clamp, and Teflon gasket.
2) The reference films : (1) a copolymer film of linear low density polyethylene (LLDPE)/polyethylene(PE) modified with ethylene methacrylate (EMA) (46㎛/88㎛ thickness) and supplied by the Veterinary and Food Administration, Denmark and (2) Nylon (23㎛) and polyethylene (94㎛) films supplied by CSL, UK.
3) Data-logger : NVQF/1Tc, TMI Orion, France
4) Scale : A table top scale(2.5D, CAS Co., Korea) possessing at an accuracy of 0.5g.
5) CPP film (80㎛) for the test at 121℃
Slide4 :
2. Validation of OMVs compared with the reference values
The migration tests were carried out in two separate institutes, Kangnung University (A) and
Korea Environment and Merchandise Testing Institute (B).
(1) OMVs measurement with single-sided contact cell
A reference film of LLDPE/PE+EMA (0.8dm2) was prepared according to the procedure
described in CEN (2002a,d) and set into the test cell before adding 80mL iso-octane, in which
LLDPE layer contacted with the solvent. Cell assembly was kept at 40℃ in an incubator for 2h.
(2) OMVs measurement with double-sided contact cell
An immersion testing method (CEN, 2002a,c) was used for measuring the OMVs from
reference films of nylon into 95% ethanol and PE into 3% acetic acid. The testing condition was
40℃ for 10days, respectively.
3. Temperature changes during the testing time in the migration cell
By using a data-logger, temperature changes in the cell during heating in a drying oven set at
121℃ were recorded. The food simulants including n-heptane and olive oil and the migration
cell assembly were preheated. Methods
The appropriateness of these cells for migration testing was examined by measuring the overall migration values (OMVs) and the actual temperature change in the cell during the test time using a data-logger. OMVs were measured according to the CEN methods (CEN, 2002 a,b,c,d). OMVs obtained with developed cells were compared with the values of certified reference films.
1. Leak test
To assure the leak of testing solvent from the migration cell, the cells were heated at 60, 100, 120, 130 or up to 150℃ for 1h each after having added n-heptane or 95% ethanol. The weight difference of cells before and after test was measured.
Slide5 : Results and Discussions
1. Leak test for the developed migration cells
Single- and double-sided migration cells were found to be leak proof within 0.5g accuracy when analyzing the weight differences before and after holding the cell at 60, 100, 120, 130 and 150℃ for 1h, respectively, after having added the n-heptane and 95% ethanol into the cells (data not shown). As the accuracy of the scale used in this experiment was 0.5g, it can be concluded that the evaporation of the simulating solvent from the migration cell was maintained below 0.5g during the testing time. Even if evaporation has occurred, the analysis data for OMV would not be
substantially affected by this because OMV is based on the non-volatile residue.
2. Comparison of the OMVs obtained with single-sided migration cell
Table 1 shows the results for the comparison of the values obtained with the reference OMVs and the values obtained from the two different labs (A, B) using a developed single-sided migration cell.
The OMVs obtained with iso-octane at 40℃ for 2h for the reference film of LLDPE/EMA-PE copolymer with a certified value of 15.1±1.0mg/dm2 by using a developed single-sided cell were 14.5±0.4 (A) and 16.0±0.4mg/dm2 (B), respectively. The OMVs obtained with the developed single-
sided migration cell were revealed to produce the comparable data with those of reference film.
Slide6 : 3. Comparison of the OMVs obtained with double-sided migration cell
Table 2 shows the results for the comparison of the values obtained with the reference OMVs and those obtained from the two different labs (A, B) using a developed double-sided migration cell.
The OMVs obtained with 95% ethanol at 40℃ for 10days for the reference film of nylon film with a certified value of 2.6±1.0mg/dm2, while the measured values by using the developed double-sided cell were 3.2±0.6 (A) and 3.6±1.0mg/dm2 (B), respectively. This result indicates that the measured value with a developed double-sided migration cell was comparable with the reference value. For the PE film, the reference value when testing with 3% acetic acid at 40℃ for 10days was 49.4±6.5mg/dm2, the OMVs obtained with a developed double-sided migration cell were 51.6±0.4 and 53.4±0.9mg/dm2, respectively. The OMVs for the reference films of nylon and PE by using a
developed double-sided cell did not differ significantly. 4. Temperature changes in the migration cells
The temperature change in the cell can be affected by various factors, such as cell structure or wall thickness and solvent type etc.. Several difficulties have been reported in obtaining consistent and comparable results with the test conditions for simulating exposures at temperatures of use in excess of 121℃. The main source of inconsistency appears to be due to variation in the time required to achieve the test temperature with oil and other fatty food simulants (CEN, 2002a).
After pouring the preheated simulant into a preheated single-sided cell, the cell was maintained at 121℃ for 2h in a drying oven and the temperature in the cell was recorded as shown in Fig. 3 and
4. The temperature in the cell reached the set temperature after almost 1.5h.
Slide7 : 5. OMVs depending on testing time and temperature
The effect of pre-heating, real migration testing time and testing temperature slope on the OMV was examined. Table 4 shows that the OMVs after contact with CPP film (80㎛) in 95% ethanol for 2 and 4h were 2.1 and 2.6mg/dm2, respectively. The values for olive oil were 19.8 and 21.6mg/dm2, respectively. These results implicate that the prolongation of testing time from 2 to 4h has not
substantially increased the OMVs.
Slide8 : Conclusions
Migration cells sustainable under high pressure and at temperatures above 100℃, which are available in the shapes of either single- or double-sided contact were developed. The results obtained with the overall migration tests implicate that the developed cells could be successfully used for migration tests with volatile solvents not only at temperatures below the boiling point but even at high temperatures up to 150℃. The use of a solvent could eventually facilitate the migration test by substituting the current simulants being used at high temperatures when comparable
migration data should be provided.
Slide9 : References
1. ASTM (2002). Standard practice for construction of test cell for liquid extraction of flexible
barrier materials. F-34-02, West Conshohocken, PA 1928-2959, USA.
2. Begley, T.H. and Hollifield, H. (1991). Application of a poly(tetrafluoroethylene) single-sided migration cell for measuring migration through microwave susceptor films. ACS Symposium Series No. 473, Food and Packaging Interactions II, Risch, S.H. and
Hotchkiss, J.H. (eds.), Ch. 5, pp. 53-66.
3. Castle, L. et al. (1990). Migration testing of plastics and microwave-active materials for high-temperature food-use applications. Food Additives and Contaminants 7(6):779-796.
4. CEN (2002a). Materials and articles in contact with foodstuffs-Plastics. Part 1: Guide to the selection of condition and test methods for overall migration. EN 1186-1: 2002, European
Committee for Standardization.
5. CEN (2002b). Methods of test for materials and articles in contact with foodstuffs. Part 2: Test methods for overall migration into olive oil by total immersion. EN 1186-2, European
Committee for Standardization.
6. CEN (2002c). Methods of test for materials and articles in contact with foodstuffs. Part 3: Test methods for overall migration into aqueous food simulants by total immersion. EN 1186-3,
European Committee for Standardization.
Slide10 : 7. CEN (2002d). Methods of test for materials and articles in contact with foodstuffs. Part 5. Test
method for overall migration from plastics into aqueous food simulants by cell. EN 1186-
5, European Committee for Standardization.
8. FDA (2002). Guidance for Industry : Preparation of food contact notifications and
food additive petitions for food contact substances : Chemistry Recommendations.
Center for Food Safety and Applied Nutrition.
9. Goydan, R. et al. (1990). High-temperature migration of antioxidants from polyolefins. Food
Additives and Contaminants 7(3):323-337
10. Snyder, R.C. et al. (1985). New FDA migration cell used to study migration of styrene from
polystyrene into various solvents. J. Assoc. Off. Anal. Chem. 68(4):770-775.
Slide11 : Table 1. Overall migration from LLDPE/PE-EMA film into iso-octane food
simulants by single-sided testing a Means with the same superscripts are not significantly different (p <0.05).
* Mean values±standard deviation from triplicate determinations.
1) Kangnung University 2) Korea Merchandise Testing and Research Institute.
Slide12 : a, A Means with the same superscripts are not significantly different (p <0.05).
* Mean values±standard deviation from triplicate determinations.
1) Kangnung University 2) Korea Merchandise Testing and Research Institute Table 2. Overall migrations from PA and PE films into food simulants by
double-sided testing
Slide13 : Fig. 1. Single-sided migration cell
Slide14 : Fig. 2. Double-sided migration cell
Slide15 : Fig. 3. Temperature change in the migration cell filled with olive oil and heated at 121℃ for 2h.
Slide16 : Fig. 4. Temperature change in the migration cell filled with n-heptane and heated
at 121℃ for 2h.
Slide17 : Table 3. Overall migration values from CPP fim (80㎛) into 95% ethanol and
olive oil depending on exposure time at 121℃ ab Means with the same superscripts are not significantly different (p <0.05).
Each value is the mean of triplicate determinations.