Recycling PET for food contact applications

HOME ARCHIV 2003 22.09.2003 Recycling PET for food contact applications
 

DG PETCORE Frank Koelewijn: "I am concerned with the haste with which legislators in candidate countries scramble to impose laws just to meet EU requirements. They risk making costly mistakes. Instead, they should request fast moving consumer goods manufacturers to come up with a sound business plan for the collection of recyclable household waste such, that it meets local economic, social and cultural needs. It is so much easier to do things right in the first place, instead of having to repair a dysfunctional collection system."

When it comes to the bottle-to-bottle application, we see quite a different story as global demand increased by 30%. The reason behind the increase in demand for bottle-grade material is both the fact that advanced technologies allow post consumer containers to be recovered to a food grade and the commitment of some companies in the bottling industry to “close the recycling loop”. Under these circumstances, bottle-to-bottle recycling has a bright future ahead.

Not all recovered PET is suitable for bottle blowing though. RPET aimed at re-integrating the beverages container production process needs to go through specific recovery procedures. In order to both secure the organoleptic properties of the product that will be packaged in a container manufactured with recovered material and to ensure full safety, the recovery process aimed at food contact applications must thoroughly eliminate impurities from the recovered material. Throughout the years several processes have been developed to do just that.

However, before recovered material can be used in food-contact applications, the process and the material recovered from a given process must be audited. Once all tests have proven that the recovered material, because it reaches purity grades close to and indistinguishable from those of the virgin resin, is suitable for food contact, the process needs to be formally recognised by an official authority.

In the USA, it is the Food and Drug Administration (FDA) that grants food contact approval for recovered material. When it comes to Europe, although the EU is currently in the process of harmonising legislation, a global EU-wide system is not in place yet.

To set the bases for harmonisation on food contact approval, the European Commission's Joint Research Centre (JRC) launched, in 1999, a 3- years project focussed on recyclability of PET and paper and board (the “Fair” project). The aim was to propose practical recommendations, based on extensive testing to detect quality and safety-in use of recycled PET for food packaging, in order to generate appropriate legislation on recycled materials including economic test procedures for the evaluation and safety of recycled material for food  packaging applications.

For the time being, national authorities are responsible for monitoring the quality of the recycled material. The principle of “mutual recognition” whereby a Member State decides to recognise a process approved by another Member State, is applicable but not mandatory.

Food-approved recovery techniques

Those techniques that rely on depolymerization, the breaking-up of the polymer molecules, produce, after purification, PET raw materials (ethylene glycol, terephthalic acid, dimethyl terephthalate, bishydroxyethylterephthalate - depending on the process) that are ready to be used for PET resin production. Many depolymerization processes have received US FDA “non objection” letters approving the material as food-compliant.

When it comes to mechanical recycling, the output is the clean flake (or pellet if the flake is further extruded), in other words, the shredded post consumer bottle. In this case, it is evident that the recovered raw material needs to be thoroughly cleansed before being used to produce beverage bottles.

What are the steps involved in mechanically recovering PET and how does food-approved mechanical recycling differ from the “classical” fibre-grade recovery process?

The “classical” technique involves sorting of collected bottles to take out any non-PET containers, grinding of bottles into flakes, flake washing and removal of labels and caps and finally flake drying. The end product, PET flakes or pellets (sometimes the end application requires that flakes be melted and extruded) are fully suitable for the manufacture of fibres or jars for soaps or household detergents.

The food-compliant techniques, so-called “superclean” processes, in addition to the “classical” PET recovery steps, include a further deep cleansing process that takes care of volatile contaminants while at the same time increases the intrinsic viscosity (IV) of the flake to a bottle grade. Generally speaking, these processes involve procedures such as high temperature washing, high temperature treatments under vacuum or nitrogen and filtration.

The “deep cleansing” processes differ from one method to another. For example the procedure may involve the use of a “chemical stripper” that removes the surface of the flake and all impurities sticking to it. In this case the process is a mix of mechanical and chemical recovery.

The process may also simply involve thermal and mechanical process stages without the need for chemical treatment. In this case the material undergoes continuous crystallisation and is upgraded by solid-state polycondensation in a batch reactor under vacuum or nitrogen and at high temperature) to the viscosity level of standard bottle-grade pellets. Any volatile contaminants are eliminated during this solidstate polycondensation (SSP) process.

Potential demand for recovered food-grade PET such that other techniques are undoubtedly being developed as we speak. However, the crucial point for European PET recycling remains that a EU-wide food contact approval needs to be set into place.