In light of promising research showing the by-products of wine production could help make plastics greener, The Central App takes a look at what scientists have found, and what is happening here.

Wine production doesn’t use every part of the fruit. It leaves behind a pile of skins, stems, and seeds called grape marc – but research has found we may be able to use those left-overs, one use is to help produce more durable plastics.

The process of plastic manufacture would be greener, scientists say, and the resulting plastic would be stable for longer, with a greater potential for recycling.

Central Otago is a key wine-producing area, so could our wine industry potentially support production of greener plastics? What is being done with grape marc here?

We eat antioxidant-rich foods to prevent cell damage, antioxidants from grapes could be good for plastics.

Grapes are full of polyphenols – these chemical compounds often act as antioxidants, preventing chemical reactions which cause molecules to lose electrons, and materials to degrade.

In the human body, these chemical reactions can damage cells, and antioxidants we ingest through the food we eat or supplements we take, help to delay the damaging reactions from occurring. 

These same reactions can cause plastics to become brittle when they’re exposed to light and air for a long time.  Most plastics slow down these reactions by using stabilisers that contain antioxidant compounds.

Researcher at the University of Clermont Auvergne in France, Audrey Diouf-Lewis and her colleagues, successfully used a polyphenol cocktail extracted from Pinot grape marc as a natural antioxidant to stabilise plastics and make them last longer.

First, they placed the raw grape marc from Pinot noir grapes into a microwave for 20 minutes, then freeze-dried the resulting liquid into a light brown powder full of polyphenols. Next, they incorporated the powder into the molecular matrix of melted polypropylene, a plastic that is widely used for the manufacture of packaging and reusable containers.

The research team pressed the treated plastic into a sheet. They tested it by subjecting it to air and ultraviolet (UV) light in an “accelerated ageing chamber”, and then a dark oven set to 80°C, then 90°C.

In the ageing chamber, plastic without stabiliser began to crack after 25 hours. 

Plastic treated with the grape marc stabiliser lasted twice as long before it began to get brittle. 

In the 80°C oven, untreated plastic lasted 7 hours before its molecules started to oxidise, while the treated plastic lasted 94 hours. Oxidation happened faster at higher temperatures.

“It’s not yet as good as the commercial stabilisers currently in use,” says Diouf-Lewis. 

“But it is a green stabiliser, so if you add more it’s not dangerous like if you add more from a petrol source.”

Massey University published a study in 2020, looking at the many different ways grape marc could be repurposed in Aotearoa New Zealand, with their research concentrated on the Marlborough region.

The report noted an estimated 70,000 tonnes of grape marc was produced in the Marlborough wine-producing region per annum, and indicated this was predicted to increase as the industry continues to grow.

They further noted that disposal or re-purposing of grape marc had become problematic for Marlborough.

The report further states ‘re-purposing grape marc presents revenue opportunities. Not doing so carries liabilities.’

The scope of the research conducted by the team at Massey University was focused on the wide variety of ways to repurpose grape marc, and the wide-ranging environmental and financial benefits. 

NZ Extracts is one company currently using wine industry waste to extract antioxidants and polyphenolic compounds, and they are marketing these compounds, not for use in plastic manufacture, but for health supplements. (Continue reading below).

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Another processing route currently being scaled-up in Marlborough is the drying and pelletising of grape marc by Pacific Rim Environmental Services (Preece(c), 2018). The advantage is that dried marc can be stored almost indefinitely. During processing, some of the dried product (or other dry biomass) can be combusted to provide the heat for drying, thus avoiding the use of fossil fuels, while at the same time reducing the dry matter tonnage needing to be repurposed. Dried grape marc can be spread to land, or sold as animal feed or bedding material, or sold as pellet burner fuel. 

The report noted that industry here should be evolving to extract value from grape marc in multiple ways.

General manager of Central Otago Wine Glenn Shuitmann says the common usage for grape marc is in composting and reapplication to vineyard soils.

Dr Kirstin Wright worked as a research scientist at Lincoln University and is now owner of Three Miners vineyard in Earnscleugh.

“In the past our viticulturist has taken our grape marc and he has turned it into compost. 

“We got our grape marc back last year for the first time so that we could make some compost, mixed with wood chips and leaves to put on our vines.”

The Massey study concluded the simplest activity for raw grape marc is indeed direct land-spreading, which needs to be done immediately after pressing. The need to immediately land-spread raw grape marc to avoid anaerobic degradation can be offset by composting, as is being done at Three Miners vineyard. 

However, the Massey University findings also indicate that for growing wine regions, the sheer amount of grape marc being produced can become problematic, as has already happened in Marlborough.

Journal reference: Journal of Applied Polymer Science, DOI: 10.1002/app.46607

Massey University's full research report to the Marlborough District Council can be found here.

Images Unsplash