'Belt and braces' barrier extends shelf-life on plastics

RPC Superfos in Denmark has already won a WorldStar for its range of four polypropylene barrier packs with a two-tier ethylene vinyl alcohol (EVOH) oxygen barrier, which it created for Bornholms. The distribution of the layers can be tailored to suit different packs. But product design manager Torben Noer says additional technologies such as oxygen scavengers could, in future, provide even longer shelf-life.

“We’re​ trying​ out a​ scavenger​,” he said, pointing to the period of up to two weeks immediately after autoclaving when EVOH barrier is not effective. “That’s a long time for the product to go without a barrier.”​

Risky ​

As Noer pointed out, the tried and tested route of relying on in-mould labels alone to provide barrier protection can be risky. “There may be gaps in the label coverage,”​ he said. “You might see a change in colour in the product over time as oxidation sets in.”​

Going beyond three years in plastics could be problematic, Superfos admitted. “What’s not really been done so far is to use active labels or indicators to improve shelf-life still further,” ​said Noer. “But, of course, that would add cost to the pack.”​

When it comes to calculating shelf-life requirements, there seem to be few short cuts, according to the firm. “You can come up with all sorts of estimates on barrier,​” he said. “They will give you an idea, but are unlikely to be very accurate.​” Laboratory measurements of oxygen transmission rates on a material may yield very low values, for example. “But the only way of really finding out is to carry out a real-time test,”​ he said.

Greatest impact ​

An oxygen cabinet will speed up any potential process of oxidation. “But in real life, it’s often the combination of oxygen and ultraviolet light over time that has the greatest impact, and that can’t be accelerated,”​ Noer stated.