A chemist welcomes an ingenious advance in plastics technology.

It's a rare joy to come across a communication that is truly concise, with a genuinely surprising but ultimately logical result, and compellingly modest conclusions that could materially benefit our society. Anne Hiltner at Case Western Reserve University in Cleveland, Ohio, and her colleagues take two well established facts — confined polymers form single crystals, and a blend of polymers, when stretched and folded by clever processing, makes very many thin layers — and use them to make something novel: a two-polymer blend with an oxygen permeability 100 times lower than either of its components (H. Wang et al. Science 323, 757–760; 2009).

Plastics are often used in packaging as multilayer coatings. When each layer is thick, the barrier to oxygen is the sum of the properties of its components. The team found that as the layers were stretched, making them thinner, and folded back on themselves to make many layers, the plastic film became an even better oxygen barrier.

When a polymer crystallizes in a confined film it typically makes large pancake-like crystals around 10 nanometres thick and many micrometres across. Using simple mathematical models, the team showed that the improved barrier properties were due to the stretched and folded polymers forming alternating layers of such crystals. The core of each crystal is essentially impermeable to oxygen, which thus has to go across the pancake to find the edge — and at each alternate layer it faces another impermeable core: like a person having to go 1 kilometre sideways to go 1 metre forwards.

This astounding improvement is essentially free and could be incorporated into current packaging materials at little cost, reducing their environmental and energy impact. It makes a cold beer in a biodegradable plastic bottle a distinct possibility — and for me that would be a rare joy indeed!

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