Cork, a natural product with many uses, is more common in labs than one might expect. Its remarkable properties make it useful in things we expose to the very hot, very cold, or very wet. Read more about this unique and truly organic material.
Physical Properties of Cork
Natural cork is an elastic, lightweight material and a good insulator that is impermeable, durable and hypoallergenic. It can compress to half its thickness & expands back to its original shape and volume. Cork is the only natural solid that does this on one axis without bulging out the other. It squeezes into small spaces to form a tight seal. Cork adapts to temperature and pressure change. It doesn’t absorb water and weighs just 0.16 grams/cc and so it floats (the original life preservers used them).(1)
have a pentagonal and sometimes hexagonal prism shape. The smallest cells measure 10-20µm so that roughly 40 million can fill a cubic centimetre. Some stoppers can have as many as 800 million cells in them. These properties make cork a good gasket material, excellent badminton shuttlecock, superb acoustic and thermal insulator in walls, floors and ceilings and durable bulletin boards(2)
Cork cells are 14 sided polyhedrons which are highly compressible and elastic. They are ideal for stoppering bottles, test tubes and flasks and popular as subflooring for sound insulation.
Cork Heat & Sound Insulation
The 40 million cells/cc make cork an excellent sound and vibration insulator. The native environment of the cork oak, Quercus suber, is grassland where periodic intense fires burn most plants to the ground. The tree evolved its thick bark to protect its underlying tissues from the heat of the fire. It burns so slowly in fact that it is used as a fire retardant.
Cork insulates from cold so effectively that it seals dewars to keep nitrogen liquid at -196C for extended periods. It burns without a flame and does not emit toxic gases during combustion and is ideal for insulated clamps that secure test tubes and flasks for heating.
Clamps lined with cork resist both heat and compression which makes them superior tools for holding glassware such as test tubes and flasks while flame heating.
Important Properties for Stoppers
The most familiar use for cork is as stoppers for wine bottles to keep air out to prevent contamination and evaporation. Its molecular structure, principally suberin & lignin, is resistant to water, alcohol, ether, chloroform, concentrated sulphuric acid, hydrochloric acid. They are washed thoroughly before shipment from our supplier & are hypoallergenic. We recommend them over rubber for use with food and drink.
When combined with glassware, they make attractive and economical containers for product display or food and beverage storage. Cork stopper and glassware combinations are available in test tubes, Erlenmeyer flasks and boiling flasks and we can even print your brand on them.
Cork stoppers readily compress for easy insertion, make good airtight seals and are reusable.
1) The Amazing Natural Properties of Cork.
2) Cork (material) – Wikipedia
3) Cork: properties, capabilities and applications. This 21 page paper covers everything from microscopy to chemistry to physical properties.
4) Cork: The Underrated Material You Need More of in Your Home