Barrier properties for bottle use
UK company Versaperm supplies gas permeability measurement equipment, as well as its own testing service for customers.
“We’re seeing more companies enquiring about carbon dioxide and oxygen permeability testing for polyethylene terephthalate [PET]; initially with flat sheets, which are easier to test, and then moving to bottles,” said technical director Chris Roberts. This interest is typically from the businesses designing the coatings.
‘Water vapour barrier’
“Some drinks ‘like’ oxygen, but need the carbonation, in which case you could retain the carbon dioxide, but allow oxygen ingress,” Roberts explained. “We’ve drawn an analogy with MAP where, for example, with red meat, you’d want high oxygen levels, but you don’t want the product to dry out, so you need a good water vapour barrier.”
New options for coating PET could come thanks to research happening in other industries. “There’s a lot of work being done on materials with selective permeability, for example in areas such as semi-permeable barriers for fuel cells,” he said.
Roberts added: “When it comes to the testing, it is interesting that more people are asking how low our measurements can go.” But he would not speculate as to what materials nano or otherwise were being used in these new-generation barriers.
‘More cost effective’
Other options for PET include using the inherent barrier in the polymer itself, particularly for carbonation levels. “But if you want any sort of light-weight bottle, it might be more cost-effective to coat the inside,” he said. “Wines and beers tend to be more challenging than fizzy soft drinks, partly because the chemistry will often vary and because they are more oxygen-sensitive.”
Both ethylene vinyl alcohol (EVOH) and polyvinylidene chloride offer high levels of gas barrier. Globally, demand for both materials continues to increase, but concerns include cost and recyclability. Versaperm estimates that to achieve the very highest levels of gas barrier with EVOH, the volume of the barrier component would have to be up to 10% that of the PET in the bottle.
Plasma-applied barrier coatings have been available for over 15 years. German company KHS is still having success with its Plasmax internal coating system based on silicon oxide. Highlighting the organoleptic benefits of better oxygen barriers, it has rebranded the material as FreshSafe PET. Last year, Turkish company Doganay Gida took up the technology on bottles of its Limonata drink, advertising it as CAMPET (‘cam’ is Turkish for ‘glass’).