Shooting star PET – Charting New Horizons

19/10/05 Its rise was almost unprecedented: In 1998, no more than 1.7 million litres of non-alcoholic beverages reached consumers in PET bottles. Five years later, in 2003, the public really developed a taste for plastic. Just under six billion litres, i.e. some 42 percent of the soft drinks filled in Germany, were bottled in this modern plastic packaging. Since then, the plastic material has again increased its market share to more than 50 percent. Growth in this packaging material is clearly a force to be reckoned with.

PET was indubitably the past decade’s shooting star in the packaging market. One segment after another gave in to its charms. With carbonated drinks already under its belt, PET is now moving into dairy; and inroads have also been made into juices. Even in beer markets with a strong glass-bottle tradition, such as Germany, the tide is beginning to turn. Discounters in particular are heavily plugging PET containers, now that even professional tasters are on their side.

For many years, it was suspected that plastics altered the flavour of beer. But now blind studies have revealed that PET containers are as neutral to the taste as the traditional types of packaging, such as glass bottles and cans made of tin plate or aluminium. If anyone, then only so-called “sensory evaluators” or tasters are capable of distinguishing the subtlest nuances and sniffing out the PET container. The man on the street is unable to taste the difference between the various packaging materials.

The development of PET packaging has reached the fine-tuning stage. And the improvement starts with raw materials production, which in the past was geared to the main sales driver, the textile industry. In the end effect, two thirds of the 35 million tonnes of material produced in the world every year are consumed by this industry. Of the remaining twelve million tonnes or so, the packaging industry and the beverage bottling sector, in particular, takes the lion’s share. For this reason, it is clear more attention needs to be given to precisely these production processes. At interpack 2005, to be staged in Dusseldorf from 21 to 27 April, there will be great interest in technological solutions relating to the packaging material PET and how such plastic containers are filled.

In the past, pellets were used for manufacturing preforms. Preforms are a preliminary stage in bottle production, which occurs at the bottler’s.

Now, one manufacturer is planning to use molten plastic directly in turning out preforms, thus not only eliminating the pellets stage but also saving costs. The process is still at the development stage and the main stumbling block is preventing the plastic from being damaged during polymerisation.

Another focus is the rapid increase in the number of cavities in the preform system. For cost reasons, the number of nozzles on these machines should be as high as possible. The trend is towards having 144-cavity plants. Currently, however, models with 72 moulds dominate and numerous smaller models are also still in operation. Rising energy costs make this area of development particularly fertile ground for reducing costs.

Bottlers are particularly interested in PET’s properties as a packaging material. The polymer has a number of outstanding mechanical and optical features. Only its poor performance as a barrier against oxygen (O2) and carbon dioxide (CO2) stands on the cons list. In drinks bottling, however, these same properties play a vital role and are much sought-after by both consumers and bottlers. Some applications suffer particularly from the lack of barrier properties:

§ Due to the relatively large surface area, bottles with a small volume are particularly affected. For content volumes of less than 0.6 litres, the carbon dioxide content decreases particularly rapidly.

§ The flavour intensity of products sensitive to oxygen such as juice, dairy products or tea diminishes within a relatively short period of time. Beer and wine suffer from the same problem.

Even though there are already a number of solutions to boost the barrier properties of PET available, so far none of them has really gained acceptance. Often, they fall short of the mark because of high costs, barrier performance or compromised recyclability.

New technologies, such as coating with silicon oxide generated from gaseous siloxanes through plasma treatment, are expected to increase barrier properties substantially. Developments in additives for plastics have not yet made it out of the labs.

By contrast, Plasma Impulse Chemical Vapour Deposition or PICVD has already been approved by America’s Food and Drug Administration (FDA). PICVD is a process that applies extremely thin coats of silicon dioxide (SiO2), which is said to achieve unprecedented barrier properties.

Several layers can be applied in a single process at low temperature. The material has good adhesion and is considered inexpensive compared to other barrier solutions.

From Australia, there is a new oxygen scavenging resin, which was used as a coating for the first time in Europe in 2004. The improved surface layer offers additional protection against delamination, benefiting both the appearance and the quality of the contents. However, as a shield against oxygen, it is only effective to a certain degree, making it unsuitable for carbonated drinks.

A French company offers barriers based on hydrogenated carbon that is suitable even for high-output bottle production. The barrier offers effective protection against oxygen and preserves the fizz in carbonated beverages. A layer of the material is applied to the container’s internal wall.

Lids are the area of development to which a Swiss company has turned its hand. In low-neck containers, an aluminium foil inserted between the neck ring and the bottle’s neck serves as a seal. A handy pull tab makes removing the foil a cinch. At the neck of the bottle, a non-drip spout provides the answer to easy pouring. The manufacturer is already planning numerous variants, promising significantly reduced material input for all concerned.

The world’s largest manufacturer of PET for packaging purposes has looked into the material’s optical properties. By altering the product specifications of one polymer, the cloudiness usually found in wall thickness over four millimetres is prevented. Now, the manufacturer claims, walls of up to eight millimetres are crystal clear.

The effects of UV radiation on PET packaging is another unknown quantity that has remained elusive until now. This complex factor has not yet been sufficiently – and hence conclusively – investigated. What has been established is that ultraviolet light and its components trigger complicated reactions in drinks. The results are unfavourable changes in brand-specific characteristics, such as colour, nutritional value and above all flavour.

Studies have shown, for example, that citric acid and trace elements tend to become unstable under the influence of ultraviolet light. Future research will focus on the absorption of wavelengths between 370 and 390 nm. Additives that block wavelengths up to 370 nm are already available. Severe product damage, however, occurs at wavelengths further up the spectrum. An American chemical company has responded to the challenge by creating an additive, now on offer, for the light rays above 370 nm.

In the meantime, developers in bottling technology have set their sights clearly on cost reduction. One manufacturer from Germany has accordingly succeeded in reducing by a third the space required for a complete bottling and packaging line for plastic containers. The still-water bottling plant is capable of a throughput of more than 25,000 half-litre bottles. At the same time, 24,000 bottles holding 1.5 litres of water are filled and then shrink-wrapped or packed on trays.