In an increasingly environmentally aware market place, John Craig, marketing manager for food and beverage process instruments at Thermo Electron Corporation, looks at some of the ways you can put technology into the production line to identify potential contamination in recycled PET packaging products

We can all recall various horror stories about contaminants in food and drink products. If a consumer finds foreign matter in your product, or worse still suffers injury as a result of it, the costs in legal fees and damages could run to hundreds of thousands of pounds. But the resulting damage to your brand image and lost sales could cost you millions. Indeed, your brand could be gone in a puff!

One of the major issues with recycling PET containers, such as the multi-trip containers often found in the water coolers at gyms and offices, is that some end users have a habit of storing liquids in them other than the original contents, from waste products to fuels and lubricants.

These products will contaminate the body of the PET container and, in some cases, at levels of the ppb magnitude, can still be detected in the smell and flavour of the new contents. Worse still, they may present a hazard to health. Either can ruin a product’s reputation.

To check each container individually before reuse has either required the sophistication of laboratory-quality testing equipment or a room full of that most sensitive of detectors, the human nose.

These options carry either a high capital price tag or high overheads and, with increasing automation in production processes, there is a move to place more inspection instrumentation on-line rather than off. Where one human, using the ‘nose method’, has an output in the region of 1000 units/hr, and needs to stop for rest breaks and meals, a machine needs only to stop for planned maintenance, and can continuously sample over 7000 containers/hr.

Three of the most often found contaminant groups are aromatic hydrocarbons, aliphatic hydrocarbons and ammonia-based materials. Each of these groups is detected by a different type of test, which starts with a puff of air being blown into the container.

Three separate modules carry out an individual test and then sample the expelled air.

The major challenge in making these tests available at the production line has been the transfer of laboratory-based technologies into a production line environment without sacrificing too much of the accuracy and integrity of the tests. The processes have been simplified to the level that they will identify the presence of an unwelcome contaminant and measure whether it is present at an unacceptably high level.

Among any one group of contaminants, the individual substance cannot be identified using these tests and, because of the sourcing of recycled containers and their lack of traceability, this data is unlikely to provide any useful information.

Aromatic hydrocarbons

The detection of aromatic hydrocarbons can be done using a strobe analysis module. The SAM uses an ultra-violet light source and a set of filters to produce a light beam at a specified wavelength. This beam of light is directed into a cylinder containing the sample of air. If the air sample contains hydrocarbon atoms the UV light will excite these.

The natural reaction of the excited molecule is to disperse the extra energy they have been given by fluorescing – that is giving off light. The fluorescing hydrocarbon molecules also give off UV light but at a different wavelength from that by which they were originally excited. By measuring the wavelength of the fluoresced UV light, it is possible to determine the level of contamination present in the PET container.


Ammonia-based contaminants

The detection of ammonia-based materials is achieved using a chemiluminescence detector, a system that uses infrared light in the same way that night vision cameras do by detecting and magnifying small amounts of energy. In the chemiluminescence detector, the air sample is passed through a catalytic converter, which is heated to a temperature of 850deg C.

If there is ammonia [NH3] in the sample this process will cause nitrous oxide [NO] to be formed.

The sample then passes into a chamber where ozone [O3] is introduced.

The O3 reacts with the NO to produce excited nitrous oxide (NO2). In the same way that the excited hydrocarbons in the SAM gave off UV light to dispel the extra energy, so the excited NO2 molecules give off an infrared light that is measured by a photo-multiplier to determine the amount of contaminants present.

Aliphatic hydrocarbons and alcohols

Aliphatic hydrocarbons are, for the most part, gaseous at ambient temperatures and include compounds such as methane, butane and propane.

These and alcohols can be detected by another system that uses UV light – the water analysis module.

An air sample is passed into an ionisation chamber, where it is bombarded by light from a powerful [10.6 eV] UV lamp. Any OH or hydrocarbon molecules are excited and ionised.

The positive ion attaches itself to the molecule, leaving the negative ion – as a free electron – to be attracted to a positively charged ion detector, which then measures the current produced by the resulting electrons.

The amount of current measured relates to the quantity of contaminants found in the air sample, providing a standard by which the containers can be rejected or approved for reuse.

Consistent testing, consistent protection

One of the advantages of automating the testing processes within the production process is that a measurable and testable level of consistency can be achieved.

Bringing high-quality testing to the production line not only allows more efficient production process planning to be achieved, but also allows the user to choose the point at which testing is done.

By placing the testing stage at the appropriate point within the overall process, the user is able to optimise the security of a product.

This will reduce the likelihood of consumer claims for damages and will also go a long way to protecting the reputation of valuable brand image, the loss of which could cost millions of pounds.