Friday is here, and the weekly 'A Taste of Science for the Weekend' column is back — issue #56.
This time: endothermic pyrolysis, lignin, and the connection to concrete, biodegradable plastic, and sunscreen.
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In the video you can see the remarkable resilience of a natural coconut shell.
A copper ball heated to 1,000 degrees Celsius, placed directly on the shell, causes it almost no damage — in stark contrast to what happens when the ball touches the inner part of the nut.
How does this happen?
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Lignin is a natural polymer — it is built from a chain of molecules bonded together.
It is extremely common in plant shells and husks, and coconut shell contains a particularly high amount of it — around 50%.
Lignin's unique chemical structure gives it a number of especially useful properties.
It is mechanically strong and resistant to degradation, impermeable to water, antibacterial, energy-rich, and absorbs UV radiation.
In the paper production process, lignin is separated from cellulose in order to yield the flexible paper we know, and the resulting lignin residue is an extraordinarily useful material.
Lignin can be found in concrete as a reinforcing agent, as a fuel substitute, in biodegradable plastics, in cardboard packaging, in cosmetic products, in sunscreen as a UV filter — and the list goes on.
These applications exploit the diverse properties of lignin together with its wide natural availability.
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When the copper ball touches the coconut shell, endothermic pyrolysis takes place.
Pyrolysis is the thermal decomposition of a material in the absence of oxygen.
Endothermic pyrolysis is a process that absorbs energy from its surroundings, as opposed to an exothermic process, which releases energy into its surroundings.
The scorching ball causes the lignin in the coconut shell to convert into charcoal; in doing so, the process absorbs a large amount of energy rather than transferring it inward into the nut, and the charcoal in turn acts as a highly effective thermal insulator.
There are additional factors behind the coconut's resilience — among them an exceptionally complex structure that slows heat propagation and prevents crack formation, as well as a high water content that undergoes evaporation while absorbing energy.
Shabbat Shalom ☺️
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