Visualizing heat flow in bamboo

A new understanding of how variations in thermal conductivity are linked to the bamboo’s elegant structure.

Scanning thermal microscopy is a powerful tool for investigating biological materials and structures like bamboo and its cell walls. Alongside nanoscale topographical information, the technique reveals local variations in the thermal conductivity of this elegant natural material.

In a new study, scientists used the technique to map heat flows across bamboo cell walls to understand better how variations in thermal conductivity are linked to the bamboo’s elegant structure.

The building sectors are responsible for 36% of global final energy utilization and almost 40% of total direct and indirect CO2 emissions. Energy demand from buildings and buildings construction continues to rise, driven by improved access to energy in developing countries, greater ownership and use of energy-consuming devices, and rapid growth in global buildings floor area, at nearly 3% per year.

Renewable, plant-based materials, for example, bamboo, have immense potential for sustainable and energy-effective buildings. Their utilization would significantly decrease emanations compared with traditional materials, moderating the human effect on climate change. This methodology would likewise help keep carbon out of the atmosphere by diverting timber away from being burnt as fuel.

During the study, scientists scanned cross-sections of bamboo vascular tissues. These tissues transport fluid and nutrients within the plant. The subsequent pictures uncovered an unpredictable fiber structure with alternating layers of thick and thin cell walls.

Peaks of thermal conductivity inside the bamboo structure coincide with the thicker walls, where chains of cellulose – the basic structural component of plant cell walls– are laid down almost parallel to the plant stem. These thicker layers also give bamboo its strength and stiffness. Interestingly, the thinner cell walls have lower thermal conductivity because of cellulose chains being nearly at a correct point to the plant stem.

Darshil Shah, a researcher at Cambridge University’s Department of Architecture, said, “Nature is an amazing architect. Bamboo is structured in a really clever way. It grows by one millimeter every ninety seconds, making it one of the fastest-growing plant materials. Through the images we collected, we can see that it does this by generating a naturally cross-laminated fiber structure.”

“People may worry about the fire safety of bamboo buildings. To address this properly, we have to understand the thermal properties of the building material. Through our work, we can see that heat travels along the structure-supporting thick cell wall fibers in bamboo, so if exposed to the heat of a fire, the bamboo might soften more quickly in the direction of those fibers. This helps us work out how to reinforce the building appropriately.”

“At present, products such as laminated bamboo are most commonly used as flooring materials due to their hardness and durability. However, their stiffness and strength are comparable to engineered wood products, making them suitable for structural uses as well. Cross-laminated timber is a popular choice of timber construction material. It’s made by gluing together layers of sawn timber, each at a right angle to the layer below.”

“Seeing this as a natural structure in bamboo fibers is an inspiration for the development of better building products.”

Scientists are further planning to observe the impact of heat flow in the bamboo when its surface is burned and forms char. The use of scanning thermal microscopy to visualize the intricate make-up of plants could also be useful in other areas of research, such as understanding how microstructural changes in crop stems may cause them to fall over in the fields resulting in lost harvests.

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