Special packaging plastics [German version]

Plastic Explanation
Cellulose acetate (CA) Unlike the other plastics mentioned here, this thermoplastic is produced from a natural raw material, namely cellulose.

Cellulose acetates frequently contain special plasticizers, which may give rise to problems in food packaging applications, since the plasticizers, which may be harmful to health, can migrate out of the plastic. CA is also highly transparent (crystal clear) and has good toughness and strength. Its water absorption capacity is problematic as there is an associated risk of swelling. CA films may be waterproofed by coating them with certain other plastics or waxes, so combining the positive features of the materials.

The temperature range over which CA may be used is between approx. 0 and 90°C.

CA is primarily converted into films for packaging applications.
Polyamide (PA) PA is a synthetic polymer obtained by polycondensation. Depending upon the number of carbon atoms present, this thermoplastic is divided into various grades, most of which share the same properties.

PA is used in packaging applications for producing films. Due to its resistance to very low temperatures (down to -40°C), PA is used for packaging frozen goods. The oxygen and aroma barrier properties of PA film also make it suitable for vacuum packaging. Amorphous polyamides yield crystal clear films, while partially crystalline polyamides exhibit a milky haze when uncolored.

Plasticizers are added to PA films made from certain grades of PA, so excluding them from use in foodstuffs packaging. The absorption and release of water may also have negative effects.
Polyethylene (PE) PE is a member of the polyolefin family, which are partially crystalline thermoplastics. PE is classed by density as
PE-LD, low density polyethylene, density approx. 0.92 – 0.94 g/ cm3, produced by the high pressure process, and
PE-HD, high density polyethylene, density approx. 0.94 – 0.96 g/cm3, produced by the low pressure process.

Both PE-LD and PE-HD exhibit a milky haze when uncolored (nearly crystal clear only when converted into thin films) and are insensitive to water. The temperature range over which PE may be used is approx. -50 – +60°C for PE-LD, while the upper limit for PE-HD is approx. 90°C, thanks to its higher density.

PE films are in particular characterized by good water vapor barrier properties. Their permeability to gases and aroma substances is, however, disadvantageous. Thanks to its higher density, PE-HD has better barrier properties towards oxygen, carbon dioxide, water vapor and aroma substances than does PE-LD.

PE is not only converted into films (PE films, composite films, shrink films), but is also used to produce bottles, bottle crates, drums, jerricans, boxes, bowls etc..
Polypropylene (PP) PP is a partially crystalline thermoplastic. Like polyethylene, PP is a member of the polyolefin family.

Uncolored, PP exhibits a milky haze. PP may be used at temperatures of approx. 0 to 160°C.

PP is used in packaging applications for producing films, transport boxes, packaging tapes, pots and bottles. Thanks to its high upper temperature limit, it is suitable for foodstuffs which are heated in the container in a microwave oven and for hot filling of liquids into bottles.
Polyvinyl chloride (PVC) PVC, which is a thermoplastic polymer, is primarily divided into two groups: firstly, plasticized PVC, to which certain plasticizers have been added, and, secondly, rigid or unplasticized PVC (without plasticizers). Both have the same amorphous molecular structure. Depending upon the production process and the incorporated additives, various grades of PVC are obtained with sometimes differing properties.

For example, the temperature range within which PVC may be used is determined amongst other things by the plasticizer content. Plasticizer content also has an impact upon suitability for food contact (only in the case of plasticized PVC) for foodstuffs packaging applications. Depending upon grade, PVC ranges in color from crystal clear to a milky haze. Rigid PVC is relatively impermeable to water vapor.

PVC is used in packaging applications for producing films, bottles, pots, skin and blister packages.
Polystyrene (PS) PS is an amorphous thermoplastic formed by addition polymerization. Its most valuable characteristic is its very clear and glossy surface which is used, for example, in sales packaging (blister packs).

Disadvantages of PS films are their high permeability to gases and water vapor. PS is not suitable for high temperature applications (e.g. hot filling) as vapors may be released that contain the monomer styrene, which is classed as an irritant.

PS is primarily used for blister packaging and as a base layer for composite films.