Identification of Plastic Films

Samples

PE-HD/PA6 and PE-LD/PA6 composite films

Conditions

Measuring cell: DSC30

Pan: Aluminum standard 40 µl, lid pierced

Sample preparation: A disk is punched out of the film and placed flat in the standard aluminum pan.

DSC measurement: Heating from 30 °C to 290 °C at 10 K/min

Atmosphere: Nitrogen, 50 cm3 /min

Interpretation

The upper curve is obtained from a composite of PE-HD (PolyEthylene of High Density) and PA6 (polyamide 6) that is normally used for the packaging of finished products (cooking bags). PE-HD melts at approximately 125 °C, PA6 at 220 °C.

In the bottom curve the PE melting peak is 15 °C lower. This film is also a PA/PE composite, but uses PE-LD (PolyEthylene of Low Density) which melts at 110 °C. The film is a common packaging material for sausages and cheese.

Another suitable film, made of polypropylene and polyester ( PET), which is also usable in microwave ovens, could easily be distinguished from the present film since the melting ‘point’ (DSC peak temperature) of PET is 256 °C (with a glass transition at 69 °C) and that of polypropylene 165 °C.

Evaluation

Interpretation

This three-layer composite has a gas-impermeable layer of EVAL (polyEthylene/ VinylALcohol copolymer) between the PE-LD and the PA6. The melting point of EVAL is approximately 180 °C. With increasing ethylene content (32% to 44%), the melting point decreases. The content varies depending on the requirements. However, increasing barrier capability is accompanied by poorer processability. There is also a melting peak of an adhesive at 98 °C.

Such films are used in the food sector for cheese and semi-finished products with high barrier requirements towards oxygen (evacuated packages or those with a protective atmosphere).

Evaluation

Component                           Adhesive                  PE-LD             EVAL             PA6

Peak temperature, °C         97.7                           113.5                181.6             221.0

Conclusion

The identification of plastic materials is essential for the examination of competitive products as well as for the quality control of finished goods. DSC can not only identify the major components of polymers, but can also detect minor components such as adhesives, if these have a melting behavior which differs from that of the polymers.

_{Identification of Plastic Films | Thermal Analysis Application No. HB 1007 | Application published in METTLER TOLEDO TA Application Handbook Food}