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Transparent bamboo offers challenge to silica glass

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Researchers at Central South University of Forestry and Technology in China have developed a transparent material derived from bamboo that is flame-retardant, smoke-suppressing, and superhydrophobic.

Researchers have developed a novel flame-retardant, smoke-suppressing, and superhydrophobic transparent bamboo, poised as a promising substitute for silica glass
Researchers have developed a novel flame-retardant, smoke-suppressing, and superhydrophobic transparent bamboo, poised as a promising substitute for silica glass - AdobeStock

Developed by Professors Yiqiang Wu and Caichao Wan and their team, the material features a three-layered flame-retardant barrier, effectively reducing heat release, slowing flame spread, and restraining the emission of combustible volatiles, toxic smoke, and carbon monoxide (CO). Their findings are detailed in Research.

Silica glass has seen increased adoption as an essential building material over the past 50 years and its versatility is reflected in global glass production, which reached approximately 130 million tons in 2020. 

In a statement, Professor C. Wan, corresponding author of the paper, said: "Despite its numerous advantages such as high transparency and the availability of raw materials, traditional silica glass still grapples with challenges including brittleness, high density, and substantial CO2 emissions and greenhouse gases during the manufacturing process."

Properties of transparent wood products include high transparency, excellent mechanical strength, and superior thermal insulation.

Limitations associated with the utilisation of transparent wood include global wood scarcity, particularly in China; the use of polymers that make it susceptible to fire; and the need to further enhance the functional properties of transparent wood beyond its basic optical and mechanical attributes.

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“Bamboo, often referred to as ‘the second forest’, boasts a fast growth and regeneration rate, allowing it to reach maturity and be utilised as a building material within four-to-seven years of growth,” said Professor Wan. “With an output four times higher than wood per acre, bamboo is recognised for its exceptional efficiency.”

“In terms of chemical composition, bamboo shares similarities with wood, mainly consisting of lignin, cellulose, and hemicellulose. Furthermore, the internal hierarchical structure of bamboo closely resembles that of wood, featuring high porosity and permeability because of neatly arranged vertical channels. This characteristic suggests the potential use of bamboo in the production of transparent composite materials,” said Y. Yang, PhD student in Professor Wan’s lab and lead author.

The team’s solution is to impregnate an inorganic liquid sodium silicate (Na2O·nSiO2) into the delignified bamboo structure using a facile and efficient vacuum-impregnation technique. A hydrophobic treatment is then applied to the intermediate product. 

“Through this strategy, we can build a three-layered flame-retardant barrier comprising a top silane layer, an intermediate layer of SiO2 formed through hydrolysis–condensation of Na2SiO3 on the surface, and an inner layer of Na2SiO3” said Professor Wan. “This strategy achieves a long ignition time of 116s, low total heat release of 0.7MJ/m2, low total smoke production of 0.063m2, and low peak CO concentration of 0.008kg/kg.” 

The bending and tensile moduli of the transparent bamboo are as high as 7.6 ± 1.3 and 6.7 ± 1.1GPa, respectively.

In addition, when used as a substrate for perovskite solar cells, the transparent bamboo shows the potential to act as a light management layer due to its high light transmittance of 71.6 per cent and fog value of 96.7 per cent, leading to a marked enhancement of 15.29 per cent in power conversion efficiency.

Transparent bamboo