Foreign bodies entering the food processing chain and passing undetected through to consumers is a major concern for the food industry and something which is monitored and reported on by organisations such as Food Standards Agency. Examples of foreign bodies include metal, wood, ceramic, glass, rubbers and plastics and, due to the varying nature of these, often different detection techniques are necessary to target each. One of the most difficult categories to detect is rubbers and plastics due mainly to their comparative low density (similar to many foods) and non-conductive/non-magnetic nature. Polymers are used extensively throughout food production lines and hence being able to detect foreign body fragments of them is an important consideration. This is the basis of the key role to be played by detectable polymer compound.

Early revisions of ‘detectable’ polymers relied purely on visual detection to prevent foreign body contamination. Polymer products were (and commonly still are) coloured blue to render them easier to detect on a food line due to the lack of naturally occurring blue in food products. Further enhancements lead to the introduction of modified polymers, detectable by conventional metal detection systems. This remains probably the most common format of detectable polymer.

Moving on from metal detection systems, X-ray detectors are becoming increasingly popular in the food industry. Compared to metal detection systems, they have the advantage that they primarily rely upon density differences to food products and hence are able to detect a range of additional foreign bodies such as glass, ceramic, bone etc. With the growth in popularity of X-ray, it is important to consider the suitability of this technique for detection of polymer foreign bodies and, in doing so, the importance of dual detectable polymer compound.

X-ray detection is different to metal detection and principally relies upon a differential in density between food product and foreign body generating a detectable difference in absorption. The greater the difference in density between foreign body material and food product, the greater the detection sensitivity. Due to the low density of most polymers, this differential is typically not sufficient to allow reliable and repeatable detection of standard polymer foreign bodies.

It is common to simply assume a metal detectable polymer will also show good X-ray detectability.  Indeed, ‘standard’ metal detectable polymers will show an increased level of X-ray detectability over unfilled polymers due to the increased density caused by the additive.  However, this is by no means optimised and good design of dual detectable polymer compound requires a special focus.

The X-ray image below highlights how the use of dual detectable polymer compound is shown to create a foreign body which is detectable by an X-ray machine (right and middle), whereas a traditional metal detectable foreign body of identical thickness is not detectable (left).

Radical Materials, through the Scopic brand, develop and manufacture polymer compounds and masterbatches with specific focus on the detection technique being employed and can therefore supply solutions which are optimised for individual detection systems or dual detectable polymer compound.  Using in-house detection systems from leading manufacturers such as Minebea Intec, levels of detection can be shown and reported using closely replicated fragment sizes and food products and optimisations made as necessary.