PEF as a multilayer barrier technology: a sustainable way to enable long shelf life in PET bottles

Avantium is already producing FDCA and PEF at a smaller scale from its pilot plant in the Netherlands and is using this material to accelerate the market introduction of various high-value applications, including those in packaging. Made from renewable resources, compatible with existing recycling equipment and with outstanding barrier properties (approximately 10 times better O2 and 20 times better CO2 barriers with respect to PET /1/, PEF is full of potential promise: not as a replacement for PET, but as a side-by-side complementary technology, enabling a full polyester solution for applications where both the performance and sustainability of the incumbent is not sufficient.
 

PEF, a performance material

Avantium currently offers a 100% plantbased, PEF grade for development in application areas such as rigid and flexible packaging, injection molded articles, films and fibers. This resin offers outstanding barrier performance, coupled with balanced thermomechanical and processability properties. Avantium’s PEF is compatible with PET recycling assets, can be identified and sorted using near infrared technology and can also be recycled as a separate stream. When PEF is processed as part of the PET recycling stream, even 100% PEF bottles will have no negative impact on haze, color and other properties of the resulting rPET products at market penetration levels of at least up to 2% PEF into the rPET /2/.

Barrier requirements in rigid packaging

PET’s success as the material of choice for beverage packaging is due to its ideal combination of performance, design freedom, ease of processing and excellent recyclability. Despite the relatively good natural barrier of PET to O2 and CO2 ingress, limitations are quickly reached when it comes to particularly sensitive food and drink products, where the required product shelf life cannot be guaranteed by monomaterial PET packaging alone.

Emerging markets, urbanization and e-commerce are all driving forces behind the transition towards a more circular economy and therefore the increase in demand for sustainable packaging solutions such as smaller serving sizes and longer shelf life. In smaller volume bottles, the surface-to-volume ratio is higher than in larger containers, so gases are exchanged with the exterior at a higher rate. Reducing the weight of packaging has also become an important part of the sustainable design toolbox, although this may often prove to be counterproductive as reduced wall thickness without any extra barrier results in a reduced shelf life, and may lead to higher rates of food and drink spoilage and waste.

Technologies for improved barrier in PET bottles

A variety of approaches can be used to improve the barrier of PET packaging. Inorganic plasma coatings are technically effective, but offer limited flexibility in bottle design. Moreover, plasma coatings require very high initial capital investments to implement, as additional in-line coating systems must be purchased and installed at the blowing and/or filling plant. This is not a financially, or logistically, suitable option if increased barrier is required only seasonally, for certain niches of a product range or simply if the high CAPEX costs and increased complexity cannot be offset by production volumes and margins.

Multilayer bottles are a valid alternative, and consist of a layer of a different, higher barrier material co-injected with PET at the preform stage, which during SBM forms a thin film sandwiched inbetween PET in the bottle wall. Multilayer technology offers the advantage of being more flexible, since the thickness of the barrier layer can be tuned to match seasonal and geographical demand (for instance in a product intended only for export), or to satisfy the individual requirements of different products produced on the same production line. When it comes to selecting a barrier material for a multilayer bottle, polyamides such as MXD6 typically offer a passive barrier to O2 and CO2 and are widely used in bottles for CSD, carbonated waters and, to a lesser extent, for products that have a higher oxygen sensitivity. Additionally, the polyamide/ PET interface can delaminate. Although this can help during recycling, where it increases the efficiency of separation, it poses severe issues during the functional life of the bottle.

Emerging technologies such as poly(glycolic acid) (PGA) have been in development for a number of years, but have not yet found full implementation in the market.

To gain extra protection for oxygensensitive products, active barrier materials (aka ‘oxygen scavengers’) are also commonly used in PET. Instead of slowing the ingress of oxygen into the package like passive barriers, scavengers react with oxygen in the bottle walls, consuming it before it reaches the interior of the package. After their complete exhaustion the OTR of the packaging increases back to that of virgin PET.

''Co-injection processing of Avantium PEF on Husky’s latest multilayer technology is straightforward, and similar to the processing technology of PET. Several combinations were injected mid-layer centered or biased towards center, including different percentages of PEF, in open and closed dome structures. The material posed no limitation for optimal processing, therefore we were able to deliver best-inclass material distribution, positioning and consistency expected of Husky coinjection platforms. The ease of processing of Avantium’s PEF material on Husky’s HPP5 Multi-Layer Systems creates an exciting new opportunity for the optimization of package performance and achieving the greatest benefits from this promising barrier material.”

Lee Riddle Team Leader, Packaging Development Center, Husky

A common issue for incumbent barrier materials like polyamides is their poor recyclability, which can hinder fully circular bottle-to-bottle recycling. Only a small amount of multilayer containers with no more than 5% of polyamide is tolerated in the PET recycling stream, which also relies on the complete removal of the incompatible materials via air elutriation and/or caustic wash before the rPET is further processed. If residual polyamides stay in the PET stream during recycling, it results in a yellow and hazy blend with PET, which was recently reported by Avantium /2/. The demand for a barrier material with vastly improved compatibility with PET is high, in order to support the recycling process and produce more and better quality rPET.

Advantages of PEF as barrier material in multilayer PET containers

Avantium’s PEF offers several advantages when compared to incumbent barrier materials, and positions itself as a valid alternative due to its unique properties:

• Good passive barrier for both O2 and CO2
• Excellent surface compatibility with PET, resulting in a low tendency towards delamination
• Far more compatible with PET than polyamides in general and in particular during the recycling process. In the case of non-complete barrier layer removal during the sorting step, the remaining PEF will not deteriorate the quality of the resulting rPET resin.