Researchers develop solar panel recycling solution

Researchers from Deakin University’s Institute for Frontier Materials have found a way to extract silicon from discarded solar panels and repurpose it into nano-silicon for batteries, potentially eliminating the biggest barrier to photovoltaic cell recycling.

Material scientists Mokhlesur Rahman and Ying Chen, who lead the investigation, said silicon recovery is to key to repurposing discarded solar cells and will prevent the high-value waste from going to landfill.

“Although silicon semiconductors make up a relatively small part of solar panel cells, the material’s value is extremely high. Scientists have been looking for ways to repurpose the silicon for some time, and we believe this to be the missing piece of the puzzle,” Dr Rahman said.

According to the researchers, the average service life of a solar panel is between 15 to 25 years, with modelling suggesting that without silicon recycling there will be 1.5 million tonnes of solar panel waste in landfill by 2050.

“Silicon cells are the most important component of a solar panel, transferring the sun’s energy into electrons.  They’re also a high-value material being a chemical element and far too precious to end up as waste, which is why this finding is significant,” Prof Chen said.

“We can’t claim solar panels to be recyclable, in a circular economy sense, until scientists find a way to harvest and repurpose their most valuable components.”

According to Dr Rahman, repurposed silicon can be used to make high-energy anodes, the transporters that move electrons around inside a battery.

“Surprisingly, the recovered silicon seems to work the same way as commercial silicon does,” Dr Rahman said.

“Our preliminary investigation validates the concept of disassembling silicon-based photovoltaic panels, and repurposing the existing silicon into nano-silicon for the battery industry, creating huge potential as an alternative source for the sector.”

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Fashioning cotton gin

Researchers at Deakin University are transforming cotton gin trash into a bioplastic film and creating reuse potential for the global problem of textile waste.   

The fashion industry is one of the largest industrial polluters in the world, with the United Nations Environment Authority estimating that globally, the equivalent of one garbage truck of textiles is burned or sent to landfill each second.

Additionally, War on Waste calculations suggest 6000 kilograms of clothing is sent to landfill every 10 minutes. The ABC program attributes the scale of the problem largely to fast fashion.

The United Nations Environment Authority makes similar arguments, suggesting in a 2018 statement that recycling itself cannot fully address throwaway fashion culture. According to the authority, the number of times an individual garment is worn has declined by 36 per cent in the last 15 years.

Existing within the linear economy of make, use, dispose – throwaway fashion largely conforms to wider patterns of consumption. Dr Maryam Naebe of Deakin University’s Institute for Frontier Materials (IFM) is attempting to address this by studying ways to repurpose the textiles present in throwaway clothes.

Deakin’s IFM was established to develop scientific solutions to some of the major challenges facing waste generation. The institute attempts to do this via scientific and engineering innovation in material design and performance. The aim, according to Maryam, is to develop new materials and structures that are both affordable and possess low social cost.

The focus of Maryam’s research is sustainable approaches to value adding in natural fibres and textiles. Her most recent work centres around a common waste by-product of the textile industry, cotton gin.

Under Maryam’s lead, a team of scientists from IFM, including PhD candidate Abu Naser Md Ahsanul Haque and Associate Research Fellow Dr Rechana Remadevi, have developed a method of turning cotton gin trash into a biopolymer.   

Cotton gin trash refers to cotton waste left over from the ginning process, which involves separating cotton from seeds. The resulting waste stream is a mix of seeds, stems, short fibres and other by-products.

As a senior researcher in fibre science and technology, Maryam noticed the huge reuse potential of cotton gin waste.

“About 29 million tonnes of cotton lint is produced each year, but up to a third of that ends up as cotton gin trash, where it’s then sent to landfill or burnt,” Maryam says.

“After group brainstorming, we realised cotton waste represented a major environmental problem, which created significant losses in material value.”

Maryam and her team’s method for transforming cotton gin trash involves dissolving the waste in environmentally-friendly chemicals. The dissolved biomass then becomes an organic polymer, which can be re-cast into a useable bioplastic film.

Maryam says as a bioplastic, the organic polymer could be used in any throwaway application where synthetic plastics or films are already in use such as packaging, bale wrap and waterproofing supplies.

“Compared to synthetic plastics, our bioplastic is made without the need for toxic chemicals, which makes it safer and cheaper to produce at a mass scale,” Maryam says.

According to Maryam, the repurposed polymer can also be used as a fertiliser.

“The product also has the added bonus of contributing to a circular economy, as it can be placed in the soil to assist the regrowth of its original form,” Maryam says.

“The material is fabricated from a natural biodegradable cellulosic source and is therefore capable of being decomposed by bacteria or other living organisms.”

Maryam says in addition to presenting a sustainable solution to the problem of synthetic plastic, the process could also offer cotton farmers an additional source of income by generating a resale market for cotton waste.

While Maryam and her team feel positive about the scale up potential of their research, she says they are still in the beginning stages.

“Cotton gin trash is challenging to work with. A lot of waste streams are quite homogeneous, containing only one or two different materials,” Maryam says.

“Cotton gin waste however is heterogeneous, and consists of a lot of varied and unwanted material.”

Challenging waste stream aside, the process has already been successfully applied to create a membrane-like wastewater filter. Maryam says the filter has been used to remove dyes from textile manufacturing in wastewater, highlighting the circular aspect of the process.

According to Maryam, current testing shows the bioplastic filter has the same efficiency as charcoal, the current standard for the dye filtration process.

Despite working on the process for only 18 months, Maryam says researchers are now testing the method on other organic waste and fibre material.

She says testing has already produced demonstrated results with lemongrass and hemp, with good progress shown for barley straw and wheat straw.

Given exhibited results, Maryam says the process would not be difficult to up-sell or commercialise. She says however, as with most research, that up scaling requires funding and support, both from industry and government.

“Research projects often get stuck in the infancy stage because they do not get the funding support required,” Maryam says.   

“I would really like to see support for this kind of work, not just for my project, but all research that explores sustainable solutions for waste. If given the support to commercialise, work like this could create real change.”

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Researchers develop concrete solution for recycled glass

Deakin School of Engineering researchers have found ground waste glass can be used as a substitute for sand when making polymer concrete – a material commonly used in industrial flooring.

Senior engineering lecturer Dr Riyadh Al-Ameri said the addition of glass resulted in a stronger product that was less costly to produce.

“This research provides the evidence the construction industry needs to see the potential of glass as a substitute for sand when making polymer concrete and, potentially, concrete,” Dr Al-Ameri said.

“Concrete is a major construction material and sand is one of its primary components, so finding an alternative to sand makes good economic sense.”

Polymer concrete uses polymers, typically resins, to replace lime-type cements as a binder.

According to Dr Al-Ameri, this produces a high strength, water-resistant material suited to industrial flooring and infrastructure drainage, particularly in areas subject to heavy traffic such as service stations, forklift operating areas and airports.

“We have found that substituting sand with ground recycled glass makes the polymer concrete stronger and is a sustainable use of one of the major types of recyclables in the domestic waste stream,” Dr Al-Ameri said.

“Any changes that reduce the cost of production will lead to significant gains across the industry, potentially on a global scale.”

Deakin Engineering student Dikshit Modgil worked with Melbourne-based Orca Civil Products as part of his masters research into the suitability of recyclable glass in polymer concrete production.

Orca Civil Products Director Alan Travers said the research partnership had produced results that would be useful in taking the concept further to commercialisation.

“The specific type of waste glass used in this project was unsuitable for recycling back into glass and the amount that is stockpiling is becoming a community problem,” Mr Travers said.

“The concept has even more appeal to us because of predicted shortages of natural, mined sands in the medium term.”

Dr Al-Ameri said the next stage of Deakin’s research would look at substitutes for the aggregate in polymer concrete, optimising the substitution rate, assessing durability, and the commercialisation of the new product.

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Deakin researchers could recycle jeans into joints

Advanced textile recycling methods could see denim jeans transformed into artificial cartilage for joint reconstruction.

Deakin University researchers Dr Nolene Byrne and PhD candidate Beini Zeng have discovered how to dissolve denim and turn them into an aerogel that can be used for cartilage biosculpting, water filtration and used as a separator in advanced battery technology.

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Dr Byrne said the denim recycling technique would also help contribute to the fight against textile waste.

“Textile waste is a global challenge with significant environmental implications, and we’ve been working for more than four years to address this problem with a viable textile recycling solution,” she said.

“With population growth and the development of third world countries combined with today’s rapid fashion cycles, textile waste is always increasing, leading to millions of tonnes of clothes and other textiles being burnt or dumped in landfill.”

Dr Byrne said Deakin’s Institute for Frontier Materials team used an “upcycling” approach to get around cost-effectiveness issues.

“One of the main drawbacks of textile recycling efforts is that any advanced technique requires the use of chemicals, which can then make the procedure less cost-effective,” she said.

“We use environmentally-friendly chemicals, and by upcycling our approach to create a more advanced material we can address the limitations affecting other less cost-effective methods.

“We are now entering pilot-scale trials and look to be at commercial scale within 3 to 5 years with industry support.”

Dr Nolene Byrne (left) and PhD candidate Beini Zeng (right)

She said the process worked because denim was made from cotton, a natural polymer comprised of cellulose.

“Cellulose is a versatile renewable material, so we can use liquid solvents on waste denim to allow it to be dissolved and regenerated into an aerogel, or a variety of different forms,” she said.

“Aerogels are a class of advanced materials with very low density, sometimes referred to as ‘frozen smoke’ or ‘solid smoke’, and because of this low density they make excellent materials for bioscaffolding, absorption or filtration.

“When we reformed the cellulose, we got something we didn’t expect – an aerogel with a unique porous structure and nanoscopic tunnels running through the sample.”

Dr Byrne said she believed the sticky nature of the denim cellulose solution was likely responsible for the unique aerogel structure that resulted, something ideally suited for use as synthetic cartilage.

“That’s exactly what cartilage looks like – you can’t 3D print that material – and now we can shape and tune the aerogel to manipulate the size and distribution of the tunnels to make the ideal shape,” she said.

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