Use of biopolymers

When it comes to developing sustainable packaging materials, so-called biopolymers are also being considered as an alternative. The term “biopolymers” comprises two classes of materials: firstly those polymers which are manufactured from renewable raw materials, such as PLA or PHA. These polymers are biodegradable. The second class of materials includes those polymers which can be manufactured entirely or partially from renewable resources, but which are not biodegradable, examples being PET or PE.

Based on current knowledge, thermoplastic PLA is the most practical alternative for producing thermoformed packs made of biopolymers from renewable resources. Due to its low barrier properties and impact resistance, the applications for thermoformed packs made of this material are limited however. It is often used in the fresh fruit and vegetable sectors. If one is going to evaluate biopolymers overall, it is important to consider not just the economic aspects such as price and availability, but also the recyclability of these materials at the end of their life cycle. In the absence of sufficient consumer education about these materials, as well as the lack of integrated disposal systems, it is not yet practical to completely separate these materials into their constituent parts. This could lead to situations where biodegradable polymers are fed into the recycling stream for conventional plastics instead of industrial composting facilities.

Materials made of PP or APET

Another approach is the development of packs, which consist of just one material, i.e. so-called mono materials. These can then simply be fed back into the particular closed-loop system. From today's perspective, prime candidates for this solution are PP (polypropylene) and APET (amorphous polyethylene terephthalate).

When using mono materials for packing food products, it is important to take into account the change in barrier properties compared with composite materials, which may have been used previously, as well as the effects of this on the packed product. It should also be noted that a reduction in the functional layers, such as the sealing layer, can also alter the parameter window of the materials. This means the running parameters on the machine have to be adjusted.

The volume of packaging material can also be reduced by the use of thinner thermoformable films. Materials can be used, which have comparable barrier properties despite their reduced thickness, and these provide the same product protection as thicker materials. By using a suitable pack design, the same rigidity and pack functionality as with thicker materials can be achieved. These design features include the use of stabilising ribs on the side walls of the pack, as well as modifying the shape in the corners and on the pack base.

Another aspect is the forming process used during thermoforming packaging. By using alternative forming methods, the material flow in the forming die can be optimised, which means that again thinner materials can be used without compromising product protection. Examples of this are so-called plug assist forming or explosive forming. In the case of explosive forming, better forming can be achieved by rapid pressure build-up in the forming die, since the film material is distributed more quickly and evenly than with a standard forming system. By combining explosive forming with plug assist, this positive effect can be amplified even more, enabling up to 20 percent thinner films to be used while maintaining the same forming quality.