BARRIER FILM | MATERIALS
Research to understand the fundamentals behaviour of barrier materials continues to offer fresh insights – and generate new materials. Lou Reade reports
Blocking progress: latest advances in barrier materials
Gas barrier is a key material property, involving a complex interaction of chemistry and physics – which may explain why there is still plenty of fundamental research going on in this area. Researchers at North Carolina State University in the US, for instance, have studied the morpholo- gies of layer-by-layer (LBL) assemblies – comprising clay particles and polyelectrolytes. The clay particles were montmorillonite (MMT), while the two polyelec- trolytes were PEI and sulphonated PET (called PETi). Layer by layer deposition, which is mainly done by alternating immersion of substrates in oppositely charged solutions, can lead to multilayer films with a thickness down to only a few nanometres (nm). The samples, prepared with these types of
coatings on polystyrene, showed low permeability against gases like oxygen. Testing using techniques such as transmission electron microscopy and X-ray diffractometry showed an increased level of intercalation and orientation of LBL assemblies, below a certain range of MMT concentration in deionised water. Above this concentration, the LBL assemblies’ gas barrier improvement levelled out. Comparing the LBL assemblies formed from the two polyelectrolytes, the ones with PEI showed
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better orientation and regularity levels – which may be due to PEI making more significant interactions with the surfaces of the clay platelets than PETi. Also, sandwiching the LBL coating between two
layers of polymeric films could protect this high barrier coating from developing defects, which might otherwise occur by external abrasive stresses, said the researchers.
Grease resistance Closer to market, Nova Chemical has developed a family of HDPE films with high grease resistance – making them suitable for a range of food packag- ing applications. As part of the process, the company also devised a semi-quantitative method to measure the level of grease or oil permeation. “It is now possible to develop cost-effective and
recyclable PE film packaging structures with good grease barrier performance by using certain single site catalysed PE resin architectures,” said the company’s Dan Falla, in an Antec presentation. Grease-resistant plastic packaging usually uses high spec resins such as EVOH, but these make recycling more difficult. Nova began a study to assess the effectiveness of its PE resins for grease
May 2018 | FILM & SHEET EXTRUSION 21
Main image: Nova’s grease-resistant HDPE films could make them suitable for a range of food packaging applications
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