An international research group led by Jaana Vapaavuori of Aalto University in Finland has produced an extensive review of the opportunities of plant biomass, or lignocellulose, for optical applications, replacing less environmentally friendly but commonly used materials such as sand and plastics. As reported in Advanced Materials [Kaschuk et al. Adv. Mater. (2021) DOI: 10.1002/adma.202104473], the group showed how to produce solar cells and glass from biowaste as a viable substitute for unrenewable resources.
The team summarized what is needed for producing and applying plant-based optically functional materials in new smart material applications. As Vapaavuori said, “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”.
Lignocellulose, which is composed of carbohydrate polymers such as cellulose and hemicellulose, and the aromatic polymer lignin, is present in nearly every plant. When such biomass is broken down into extremely small parts and then put back together, it can be used to develop totally new biocomposite materials such as particle panels and wood/plastic composites for construction.
However, its characteristics such as transparency, reflectiveness, UV-light filtering, and structural colors mean the material can also be used in optical applications, as investigated in this study. The use of combinations of its properties could lead to the development of light-reactive surfaces for windows or materials that react to chemicals or steam, and perhaps even UV protectors that can soak up radiation, thus providing a sunblock to surfaces.
This is helped by an ability to add functionalities and customize lignocellulose, such as replacing glass in solar cells to improve their efficiency and light absorption. The strategies for isolating the key building blocks of the material are examined in the review, along with the effects of fibrillation, fibril alignment, densification, self-assembly, surface-patterning, and compositing in terms of their role in engineering optical performance.
Also highlighted is the extent of unused lignocellulose produced by industry and agriculture every year, estimated to be over a billion tons of biomass waste. The review pinpoints that to scale up such lignocellulose for commercial use would need new uses for bio-based waste from both research and government regulation to help push demand for renewable alternatives for optical applications. Although such scaling up has been seen as overly expensive, it is becoming more realistic with reductions in energy consumption and cost of production. However, another challenge, that of water use in its processing, remains problematic.
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