4.4.1. PACKAGING SPECIFICATIONS



Step A) Specify the package geometry

Pre-defined geometry:

Select one of the 5 pre-defined forms (rectangular, cylindrical, spherical, spherical segment, truncated cone) and enter the package dimensions. Accept the values and pass to the next window.

Surface to volume ratio (S/V):

If the exact geometry of the package is not accessible, it can be defined with a surface-to-volume ratio. Enter the surface area of the package in contact with the food, the internal volume of the package (equal to the food volume) and the thickness of the packaging material. The mass of packaged food (density of 1), the ratio S/V and the dimensionless value are computed and displayed. If S/V is smaller than the ratio S/V for a sphere of identical surface (optimal ratio) an error message is given. Accept the values and pass to the next window.



Step B) Specify the number of layers (up to 10) and the package properties of each layer:



1) Set the thickness of each layer

2) Set the density of each layer

3) Input the initial concentration of the diffusing substance in each layer

4) Input the partition coefficients

For each layer of the packaging you need to fix the value of the partition coefficient. The partition coefficient K is the ratio at the thermodynamic equilibrium of the migrant concentration in the material to the migrant concentration in the food [K = Cmat / Cfood] or to the migrant concentration in the next layer.

5) Input (or estimate) the diffusion coefficients:

For each layer of the packaging you need to fix the value of the diffusion coefficient. The program offers 4 different ways to enter this value:

-         Known:
If the diffusion coefficient of the diffusing substance in a layer is known, you can enter it directly into the program.



- Arrhenius:

If the factors of the Arrhenius equation for the diffusion coefficient are known, extrapolate D from the Arrhenius equation. Enter the values for the activation energy (Ea), the pre-exponential factor (A).



- Piringer:

Many different models have been developed to estimate the diffusion coefficient from simple parameters. Approximation of D can be done with the ‘Piringer model’. This model has been developed by Dr. O. Piringer and co-workers [Baner, A.L., Franz, F. and Piringer, O., Deutsche Lebensmittelrundschau, 90 (1994), 137.; ibid. 90 (1994) 181. Piringer, O., Food Additives and Contaminants, 11 (1994) 221.]. It is an empirical model, which estimates the D from its molecular weight (MW), a constant (Ap) and the diffusion temperature (T). The model is suitable for compounds with MW < 1000 Da. It is also a worst case model: the approximated D is generally larger than the real, measured value. The program SML uses the lastest version of the Piringer model with refined Ap constant. It was published in a draft CEN-report: Materials and articles in contact with foodstuffs - Plastics: Estimation of migration by generally recognized diffusion models in support of EU Directive 90/128/EEC (Migration modelling), CEN/TC194/SC1/WG4 N106, version 1, August 2001.

The constant Ap is polymer specific. Simply select the type of polymer your layer is made of. Enter the molecular weight (MW) of the diffusing substance. The extrapolated data of D is displayed on the right side of the window for the displayed temperature of migration. Accept the values and pass to the following window.



EU-positive lists:



List of starting substances and additives regulated in the European Directive 2002/72/EC

The program SML includes a list of chemical substances used in the fabrication of polymeric materials intended to enter into contact with foodstuffs. This list covers the starting substances regulated in the EU legislation on plastics.

To enter the list, select the option, find a compound in the EU-list by clicking on the 'EU-list' button. The information on each individual substance is depicted as a data card.



The card contains the following fields:

Substance name
Reference number
CAS registry number
Molecular weight (MW) of the substance (if specified)
Remarks (e.g. other specific limitation as Qm value or migration limit if SML value is fixed in the legislation).

Chemical structure (if available)

The data are ordered by MW: to display another data card, drag the position-bar underneath the chemical structure (using the mouse pointer + mouse left key) or click on the arrows. It is possible to search a particular compound in the list with the reference number, the CAS registry number or with the molecular weight. Click on the icon with the 'hand point', then select the type of filter (Reference, CAS, MW) and proceed. Clicking on the 'OK' button of the data card enters the MW of the selected substance in the "Piringer model". The diffusion coefficient of this particular compound is approximated. If the MW of the selected compound is not specified (e.g. natural, polymeric substance with large MW distribution), the value 0 g/mol is taken as input. Adjust the MW to the desired value before continuing the simulation.

Press on the 'print' button to print the data card of an individual compound.

Proprietary list:



list of substances that can be freely customized by the user.

The program SML enables the insertion of any new chemical substance used in the fabrication of polymeric materials intended to enter into contact with foodstuffs.

To enter the list, select the option and find a compound in the Proprietary-list by clicking on the 'Proprietary list' button. The information on each individual substance is depicted as a data card. Three substances are entered in the list by default (Butadiene, N-Methylolacrylamide and Vinylidene chloride). Simply click on the button 'Add new substance' to add your own substances in the list. If available, the picture of the chemical structure can be inserted in the list as *.jpeg format. Once the substance is added the properties are saved as ASCII file in the file 'customized synoptic.txt'. The corresponding pictures (if available) are stored in the subdiretory 'customized synoptic pictures'. The properties of a substance that has already been entered in the list can be modified at any time by clicking on the button 'Modify substance'.



The card contains the following fields:

Substance name
CAS registry number
Molecular weight (MW) of the substance (if specified)
Remarks (e.g. other specific limitation as Qm value or migration limit if SML value is fixed in the legislation).

Chemical structure (if available)

The data are ordered by MW as for the EU-list: to display another data card, drag the position-bar underneath the chemical structure (using the mouse pointer + mouse left key) or click on the arrows. It is possible to search a particular compound in the list with the CAS registry number or with the molecular weight. Click on the icon with the 'hand point', then select the type of filter (CAS, MW) and proceed. Clicking on the 'OK' button of the data card enters the MW of the selected substance in the "Piringer model". The diffusion coefficient of this particular compound is approximated. If the MW of the selected compound is not specified (e.g. natural, polymeric substance with large MW distribution), the value 0 g/mol is taken as input! Adjust the MW to the desired value before continuing the simulation.

Press on the 'print' button to print the data card of an individual compound.

- Customized kinetics equation:



Abitlity to enter customized kinetics equation for temperature dependent coefficients.

6) Specify the diffusing properties of the simulant (optional)

You can simulate the diffusion of a substance present in the food or food simulant into the material. Check the box Ds and enter the requested values (diffusion coefficient of simulant in each layer, initial concentration and solubility of the stimulant in the packaging).