Biowaste could be repurposed in optical devices

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An international group of researchers has explored the feasibility of using lignocellulose as a replacement for non-renewable materials like sand and plastics in the manufacture of optical devices.

The consumption of non-renewable raw materials for construction, digital devices, and other goods is a major environmental problem. Researchers from Aalto University, the University of Turku, the Research Institute of Sweden, and the University of British Columbia, have proposed in an Advanced Materials study that a promising solution may be found in renewable biomass. Specifically, the researchers examined how lignocellulose could be used for optical applications, potentially replacing commonly used materials like sand.

“We wanted to map out as comprehensively as possible how lignocellulose could replace the unrenewable resources found in widely used technology, like smart devices or solar cells,” said Professor Jaana Vapaavuori, a materials scientist at Aalto University in Finland.

Lignocellulose refers to plant biomass, such as that used for the production of biofuels. It encompasses carbohydrate polymers (cellulose and hemicellulose) and an aromatic polymer (lignin) and is found in almost every plant on Earth. When broken down and reassembled, lignocellulose can be transformed into totally new, usable materials with different properties.

In their extensive review of the field, the researchers assessed the various manufacturing processes and characteristics needed for optical applications, such as transparency, reflectiveness, UV-filtering, haze, reflectance, and structural colour (colour produced by structures on the micro- or nanoscale, such as in butterfly wings). Advanced materials built from sustainable resources like biowaste demonstrate enormous promise in optoelectronics due to their potentially lower cost, while meeting or even exceeding current demands in performance.

“Through combining properties of lignocellulose, we could create light-reactive surfaces for windows or materials that react to certain chemicals or steam. We could even make UV protectors that soak up radiation, acting like a sunblock on surfaces,” said Vapaavuori.

Professor Kati Miettunen, materials engineer at Finland’s University of Turku, explained: “We can actually add functionalities to lignocellulose and customise it more easily than glass. For instance, if we could replace the glass in solar cells with lignocellulose, we could improve light absorption and achieve better operating efficiency.”

As forests – also a critical carbon sink – are already straining under high demand for biomass, the researchers suggest that good use could be made of biowaste instead; more than a billion tonnes of biomass waste is created by agriculture and industry each year. Vapaavuori said: “There is massive untapped potential in the leftovers of lignocellulose from other industries.”

There is considerable R&D interest in turning biowaste into bio-based materials with desirable properties. At Aalto University, scientists have developed light fibres and light-reactive fabrics from this resource.

The study authors argue that the shift from the lab to scaling-up and commercialisation could be achieved through two pathways. Either new uses for biowaste could be created through government interventions, or R&D efforts bring about such “cool demos and breakthroughs” that it stimulates demand for renewable alternatives to conventional products.

“We believe that we need both political direction and solid research,” Vapaavuori continued.

A major obstacle standing in the path of development and commercialisation of lignocellulose-based products has been manufacturing cost. Since the early 2000s, there was considerable interest in nanocellulose, but it is only now that the energy consumption and cost of production have dropped enough to make industrial use possible. Another ongoing challenge lies in a fundamental ingredient of processing: water.

“Cellulose loves water. To use it in optical applications, we need to find a way make it stable in humid conditions,” Vapaavuori said.

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