PET in Beverage Packaging

 

PET packaging continues to show a steady growth trend. Disposable bottles for mineral water and soft drinks are making an important contribution to these high-growth rates. As a result of the high number of bottle returns, PET recycling is also booming. The EU recycling regulation, which came into force at the start of the year, now gives clear guidance here.

 

Percentage of PET in the worldwide mix for beverage packaging

 

Polyethylene terephthalate (PET) continues to show steady growth. According to information from Plastics Europe, PET consumption in Germany in 2007 was 5.4% higher than in 2006 and reached a level of 490,000 t. Worldwide consumption is about 45 million t (source: PCI). It is expected that consumption of PET worldwide will grow by about 6% p. a. over the next few years. PET will thus have reached the highest growth rate of any commodity resin as well as most engineering plastics.

 

PET manufacturers and their annual capacities (source: PCI Resin Report 2008)
 

 

Table 1 shows the ten largest PET manufacturers, along with their production capacities. As the largest textile manufacturer, China already has the largest production capacity for polyester resins in the world. Beverage packaging, however, is the primary reason for the high growth rates. With almost 25%, PET represents the largest share of all materials in the worldwide packaging mix. In Germany, just under 75% of all non-alcoholic beverages are already sold in PET bottles. Growth in Germany is clearly attributable to the growth in disposable beverage bottles. The increase in disposable packaging was slowed briefly only by introduction of the mandatory deposit in 2003. The percentage of reusable packaging for non-alcoholic beverages (glass and PET) has dropped in Germany from 51.4% at the end of 2002 to only 29.9% at the end of 2007 (source: WAFG).

 

Percentage of PET packaging for non-alcoholic beverages in Germany, 2007 total: 73.%
 

 

After a brief spike in September 2006, prices over the last three years have been relatively stable. However, because of the significant increase in the price of oil, rising costs for PET precursors can be expected. This means that a price increase in the PET markets can also be expected. Since, however, not only raw material costs but also transportation costs will increase because of the high price of oil, the weight advantage of PET bottles over glass (Fig. 4) will become increasingly important. This will likely to further replacement of glass by PET in the beverage area.

 

Price trend for PET in the time period from July 2005 to June 2008 (source: KI Kunststoff information)

 

Raw Materials, Additives and Barrier Materials

In the packaging sector, PET is hardly found any more as a pure homopolymer. Comonomers such as isophthalic acid or 1.4-cyclohexane dimethanol are added during polymerization. These comonomers slow crystallization, making it possible of faster injection molding cycles during preform production. For blow molding bottles, faster cycles are achieved through addition of infrared absorbers to PET raw materials. The preforms can then be heated faster. To achieve the low acetaldehyde values required for mineral water applications, either so-called "Aqua PET" grades with low viscosities are used, or reagents that function as acetaldehyde blockers are added. Lower viscosities result in production of less acetaldehyde during preform production. In contrast, blockers react chemically with acetaldehyde and convert the aldehyde into a poorly diffusing molecule. Anthranilamide is still the most common substance here. Both principles reduce the concentration of acetaldehyde in the bottle wall, so that migration of acetaldehyde into the mineral water is likewise reduced.

 

 

PET bottles and performs (photo: Krones AG)

 

For oxygen-sensitive beverages such as beer, fruit juices, wine and milk products, the oxygen barrier characteristics of PET alone are not sufficient. The high oxygen permeability can be reduced considerably for these beverages through use of barrier materials. A distinction is drawn here between passive and active barriers or a combination of the two. Polyamide layers placed in the center of "multi-layer" bottles are often used as passive barriers. The polyamide MXD6 with a cobalt catalyst has been employed since the 1990s as the first active barrier material (CMB Oxbar). Additional materials have appeared since then, for instance, the Aegis product from Honeywell, Heverlee, Belgium, which employs a different polyamide 6 grades as well as an iron-based system from M&G, Tortona, Italy. One problem associated with these active barriers is that the reaction with oxygen begins immediately after production of the preforms. The Polyshield family of products from Invista, Gersthofen, Germany, which is also based on MXD6 technology, is sold in two components. As a result, the trapping reaction does not begin until both components come together during production of the bottles. An additional polyester-based two-component system (ValOR A300) has been announced by Valspar, Pittsburgh, USA. Additional materials are under development or going into initial applications (e.g. Colormatrix, solO2 and HyGuard). Corresponding materials include MonoBlox from Artenius, Mendig, Diamond clear from Constar, Philadelphia, USA, and Bi-coPET from M&G. Very good barrier values are achieved when active and passive barriers are employed simultaneously. In this case, the passive barrier further prevents loss of carbon dioxide. Slight clouding of the PET bottles by the foreign polymers, however, represents a more or less unresolved issue for all technologies. The effects of barrier materials on recycling of PET bottles are still largely unclear.

 

PET bottles for oxygen-sensitive contents (photo: Fraunhofer IVV)

 

Internal coatings of silicon oxide (SIG Plasmax) or amorphous carbon (Sidel Actis) are also on the market as passive barriers. They represent alter natives to the conventional PET/PA "multi-layer" bottle. Internal coatings do not only improve the barrier characteristics with respect to oxygen, however. They can also significantly reduce migration of substances typically used in packaging applications into the bottles contents. For instance, SIG has had the SiOx internal coating evaluated by the U.S. Food and Drug Administration (FDA) with regard to its barrier action against "post-consumer" sub-stances-in PET recycling. According to this evaluation, the SiOx internal coating is so effective that so-called "super-clean" recycling processes are no longer necessary. Moreover, internal coatings affect the surface properties and can considerably improve the emptying characteristics of packaging filled with highly viscous substances such as mustard, mayonnaise or ketchup.

 

Alternative Materials

Several alternatives to PET have appeared on the market in recent years. While the discussion about polypropylene bottles for beverages has been ongoing for some time, bottles made from polylactic acid (PLA) appeared on the market quite abruptly. The driving force here: marketing arguments more than an improved material or cost reduction. The public discussion about carbon dioxide output and environmentally friendly packaging as well as renewable resources created a favorable climate for PLA bottles among consumers. The drawback of PLA bottles compared to PET bottles, however, is the considerably higher permeability. Thus, water vapor permeability is a limiting factor in PLA applications. Oxygen-sensitive contents cannot be packaged in PLA at all. The initially favorable environmental image of PLA is being blurred, however, by negative reports from PET recyclers. PLA bottles are unavoidably caught in the PET material stream. Even traces of PLA as low as 0.1% supposedly make recycled PET unsuitable for most applications, thus reducing the value of the recycled material (source: Petcore). Another alternative being mentioned is polyethylene naphthalate (PEN). In spite of the noticeably better permeation characteristics with respect to oxygen, PEN, which is considerably more inert than PET, has not yet succeeded in gaining any significant market share. The reasons here include the very high price and slight fluorescence of the material. Because of its price, PEN is suitable only as a material for reusable packaging. This limits PEN almost automatically to a niche existence. In addition, like PLA, PEN would disrupt PET recycling. In recent months, there has been an on going discussion in the USA about bisphenol A, which is used as a monomer for production of polycarbonate (PC). This has put PC applications under considerable pressure–in the food sector, primarily baby bottles and water dispensers. PET or PEN could possibly advance into these traditional PC applications as a result.

 

Recycling

According to information from the European organization Petcore, 944,000 t of used PET bottles were collected and recycled across Europe in 2006. This represents an increase of 18.5% over 2005. This means that in Europe about 35 to 40% of all PET bottles on the market are collected and recycled. The largest amount (slightly less than 60%) is collected in Germany, France and Italy. Recycling takes place largely within the European Union. In 2006, the percentage exported to the Far East dropped to 14%. The majority of PET bottles collected still ends up as fibers. In recent years, however, so-called "bottle to bottle" recycling has experienced significant growth and now counts as the second largest market for recycled PET. For a long time, the ambiguous legislation within Europe presented an obstacle to "bottle to bottle" recycling. On March 27, 2008, however, the long awaited EU Recycling Directive was published and went into effect 20 days after publication in all EU member states.

 

Applications for recycled PET in the USA in 2006 (source: Napcor)

 

After more than a decade of discussion, two EU recycling projects and various national activities, the use of "post-consumer" PET (as well as other plastics) in packaging with direct food contact is now regulated uniformly throughout Europe. In contrast to the otherwise usual company responsibility for compliance with regulations involving food contact, an official approval procedure has been instituted for the use of recycled material in direct contact with food. This means that operators of PET recycling equipment must apply for official approval with process data, cleaning efficiency and reference to an application. The European Food Safety Authority (EFSA) in Parma, Italy, is responsible for processing the petition. Little will change initially, however. For existing PET recycling equipment, the directive provides a set of transition regulations. An application must be submitted to EFSA within 18 months. After this, EFSA will evaluate the existing recycling equipment. However, EFSA has no specific deadlines in this regard. In the meantime, this equipment can remain in production. The directive includes a deadline of six months for evaluating new recycling processes, after which the EFSA is supposed to respond to be application. In the event of a positive decision, the recycled material produced can be used for direct food contact in all member states. Inspection of the equipment in general or the equipment to which the approval applies is the responsibility of the national authorities.

 

Developments in recycling will have a positive impact on plastic packaging, as use of recycled material will further improve the already positive image of PET packaging. Producers of virgin resin will also benefit from this, even though use of recycled materials is likely to initially lower sales margins. Given the projected growth rates for PET, new markets must also be created in recycling. "Bottle-to-bottle" recycling is an important option in this regard, and the EU Commission has addressed this with the Recycling Directive.

 

THE AUTHOR
DR. FRANK WELLE, born in 1966, is a research associate at the Fraunhofer Institute for Packaging Technology and Packaging (IVV) in Freising, Germany; frank.welle@ivv.fraunhofer.de.