Over the last 20 years polymers have revolutionised a series of industries spanning from aerospace to everyday consumer products. Compared with other materials like steel, aluminium and timber, polymers are easier to process, lower in cost, show higher durability and their mechanical-surface properties can be easily adjusted according to the application. Many plastics are processed with a range of ‘ingredients’ such as the use of tallow in plastics.
Banknotes is a typical example of how polymers have become a problem-solving material. Traditional banknotes which are based on special and expensive paper suffer from poor tear properties and they have limited life. On the other hand, banknotes made of fully recyclable polymers have been proven as excellent alternativesto the traditional ones and are currently being used in many countries around the world including the UK. Polymer banknotes yield excellent tear and mechanical properties, which make them last much longer with immediate impact on the environment (reduced waste, recyclable) and on the cost of production-replacement. On top of this, polymer banknotes allow the addition of more security features not available in the paper ones.
The main components of the new banknotes are the polymer (mainly long hydrocarbon chains), the security features and a series of additives such as color pigments and lubricants. Lubricants are vital because they promote flow, and help in the production process and very importantly decrease the frictional forces between the banknotes. There are different types of lubricants (stearic acids, esters, wax etc.) depending on the application and on the compatibility between the polymer and additives. Stearic acids, a blend of fatty acids which is sourced from animal fat (tallow), are used as lubricants in the British and other banknotes. Their low cost (food waste by-product), high compatibility and excellent low friction properties make them ideal additives for banknote applications.
Why tallow in plastics?
This process of using fatty acids derived from animal fats has become headline news as different groups have protested against the use of animal products in the production of the new £5 note. It should be noted that these lubricants are used in extremely low quantities in many other applications such as plastic bags (slip agents). There are alternative options such as non-animal fats and hydrocarbon waxes, but these might increase the cost of production, reduce efficiency, affect recyclability and finally negatively affect the environment.