As converters and brand owners race to develop 100% PE film mono-webs or laminations for the How2Recycle® Store Drop-Off program, it has become clear that this approach will not work for all flexible packaging structures over the short term. There is a reason the majority of stand-up pouches and many other flexible pouch formats utilize thin gauge PET films as the print web and/or barrier web in a multi-material lamination. PET film is low cost, easy-to-print, easy-to-metallize, high clarity, high barrier and high stiffness. Although many companies are working to develop PE-based alternatives to PET film with MDO-PE and BOPE films, these are still some way from being both economically viable and meeting all the performance requirements currently offered by PET films.
The Secret Life of PET
This means that many flexible pouches will remain in mixed material formats containing PET film for some time. So, if this means these pouches can not become part of the How2Recycle® program, what role can PET films play in the Circular Economy? They are a great way to incorporate recycled content into packaging materials, thus making flexible PET films part of the demand-side of the Circular Economy equation.
A large infrastructure already exists to produce PET chips from post-consumer recycled sources, primarily PET bottles. According to APR1, there were approximately 5.9 billion pounds of PET bottles sold in the US in 2017. 29.2%, or 1.7 billion pounds, were collected through recycling programs while 1.6 billion pounds were re-processed into recycled PET chip, or r-PET. Reclaim & recycle rates are even higher in some other parts of the world: over 50% in the EU2 and over 80% in Japan3.
2 Paths to Recycling: Physics or Chemistry
The lowest cost approach to incorporating bottle grade r-PET resin into PET film is by chopping it into flake and then blending it with film grade PET resin prior to extrusion, a process known as mechanical recycling. This presents some challenges. First of all, bottle grade resin has a higher intrinsic viscosity (molecular weight), which affects its processability on a biaxially oriented film line. Second, it tends to have a whitish tinge, compared to the clear look of film grade PET resin. Finally, the bottle grade r-PET resin has gone through an entire additional melting and processing history, so it is more likely to contain gels than virgin resin. Therefore, when PET film manufacturers are using mechanically recycled PET resin, they can not go much above 30% content by weight before this resin starts to negatively impact the mechanical and visual properties of the film.
The only way to achieve a higher PCR content in PET film without harming film properties is to use chemically recycled r-PET resin. This means that after the r-PET is processed through a sorting facility, the PET chain is chemically broken apart to re-constitute its basic monomer components. Typically, it undergoes glycolysis by adding monoethylene glycol (MEG) to the PCR-PET in a chemical reactor, producing bis (2-hydroxyethyl) terephthalate (BHET). This compound can then undergo hydrolysis by adding water to produce MEG and PTA, the original building blocks of PET resin4. These monomers can then be re-polymerized to make essentially “new” resin, which is virtually indistinguishable from virgin PET film grade resin. In this manner, PCR contents of up to 90% are possible in PET packaging film.
Several major PET film suppliers have developed PCR-PET films based on chips that have been mechanically or chemically recycled. Film suppliers using mechanically recycled r-PET resin offer films with 30% PCR content, while those using chemically recycled r-PET resin offer films with 70% to 90% PCR content.
Finally, a High Barrier Film for the Circular Economy
Metallized PET films are well known to offer some of the highest oxygen and moisture barrier performance properties of any material available to flexible packaging, including foil. Since PCR-PET films give similar performance to virgin PET films, they can be metallized and converted using traditional techniques. Celplast and its partners have done so, and through Celplast’s own state-of-the-art lab it has confirmed the barrier & metal adhesion of metallized PCR-PET films are similar to what can be achieved using a traditional PET film.
Importantly, since the metallizing process adds less than 0.1% by weight to the total metallized film structure, the aluminum layer has no impact on the overall PCR content percentage of the metallized PET film. Celplast will soon be offering its certified high barrier FOILMET® and DURAMET® metallized PET films, and certified high bond SUPERMET® and ULTRAMET® metallized PET films in PCR versions, available in the 30% to 90% PCR content range.
President, Celplast Metallized Products Limited