Scientists develop ‘super slippery’ packaging for ketchup

The days of struggling to squeeze every last drop out of the tomato ketchup onto your chips could soon be over… thanks to the carnivorous pitcher plant.

Scientists have come up with an ingenious technique to dramatically cut waste inspired by the insect eating flower.

The ‘super slippery’ industrial packaging combines a cheap plastic with natural oils like cottonseed that is added to the interior surface – so sticky foods slide out with ease.

And this will save tons of perfectly good food being wasted every year.

The high-tech invention actually finds its roots in the pitcher plant that entices insects to the edge of a deep cavity filled with nectar and digestive enzymes.

The leaves that form the plant’s eponymous shape have a slippery ring, created by a secreted liquid, around the periphery of the cavity.

When the insects move onto this slippery ring, they slide into the belly of the plants.

Lead author Ranit Mukherjee, a doctoral student in engineering at Virginia Tech , said: "This slippery periphery on the pitcher plant actually inspired our product."

The pitcher plant’s innovation – which engineers are now copying with great success – is the combination of a lubricant with some type of surface roughness that can lock that lubricant into place very stably with surface tension.

Explained co author Professor Jonathan Boreyko: "We are taking that same concept, but the roughness we are using is just a common attribute of everyday plastics, which means maximal practicality."

In addition to minimising food waste, Prof Boreyko cited other benefits to the improved design, including consumer safety and comfort.

He explained: "We are not adding any mystery nanoparticles to the surfaces of these plastics that could make people uncomfortable.

"We use natural oils like cottonseed oil, so there are no health concerns whatsoever. There’s no fancy recipe required."

Food left behind in packaging is not simply a nuisance. It also contributes to the millions of pounds of perfectly edible food that Americans throw out every year.

Even small amounts of sticky condiments, dairy products, beverages and meat that remain trapped in packaging mount up over time – just for a single household.

The study published in Scientific Reports demonstrates how vegetable oils can flow freely out of commonly used plastic sachets despite the surface tension.

And the method can also be applied to inexpensive and readily available plastics such as polyethylene and polypropylene, the team say.

These hydrocarbon-based polymers make up 55 percent of the total demand for plastics in the world today.

So potential applications for the research stretch far beyond just ketchup packets. They are also among the easiest plastics to recycle.

Mr Mukherjee said: "Previous SLIPS, or slippery liquid-infused porous surfaces, have been made using silicon or fluorine-based polymers, which are very expensive.

"But we can make our SLIPS out of these hydrocarbon-based polymers, which are widely applicable to everyday packaged products."

SLIPS are porous surfaces or absorbent polymers that were only created seven years ago by a team at Harvard University.

They can hold a chemically compatible oil within their surfaces through ‘wicking’ that pulls moisture via a process known as capillary action.

These surfaces are not only very slippery but also self-cleaning, self-healing and more durable than traditional alternatives.

In order for SLIPS to hold these oils the surfaces must have some sort of nano- or micro-roughness, which keeps them in place by way of surface tension. This can be achieved by applying a coating or an absorbent polymer.

But current SLIPS that use silicone- and fluorine-based absorbent polymers aren’t attractive for industrial applications due to their high cost. Adding roughness to surfaces can likewise be an expensive and complicated process.

Prof Boreyko said: "We had two big breakthroughs. Not only are we using these hydrocarbon-based polymers that are cheap and in high demand, but we don’t have to add any surface roughness, either.

"We actually found oils that are naturally compatible with the plastics, so these oils are wicking into the plastic itself, not into a roughness we have to apply."

While the method has obvious implications for industrial food and product packaging, it could also find widespread use in the pharmaceutical industry.

The oil-infused plastic surfaces are naturally anti-fouling, meaning they resist bacterial adhesion and growth.

The team has been awarded a provisional patent for future marketing of their sachets.

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