Inside banknotes: paper vs polymer

Nowadays, banknotes have a basic role in market, transaction, and commodity economies, as well as many other areas of our society; despite the conversion to electronic currency and documents, banknote will continue to hold an important role in the future [1, 2]. Therefore, to still maintain the competitiveness of banknotes is necessary a continuous technological development to satisfy the always increasing requests of improving their properties such as strength, water resistance, washing resistance, durability, printability, ink fastness, etc. [3]. To address the aforementioned challenges, researchers must seek solutions in an integrated, multidisciplinary way. Up to now, the appearance of the banknotes differs from country to country, from region to region, expressing proudness of historical heritage or illustrating national symbols etc. and the design of banknote is always characterized by complexity to avoid unsanctioned duplication. Interestingly, composition and individual components of typical banknotes are almost identical throughout the world and banknote production stages are highly similar as well. Actually, banknotes are not made of paper banknotes in the usual sense – wood pulp paper would not be durable enough, and would absorb water too easily; instead, cotton paper is used, sometimes mixed with other textiles in small amounts (such as, linters). In a way, paper banknotes could be considered to be “natural polymer” banknotes, since cotton consists of about 90% cellulose [4]. Banknote paper can be classified as a durable cloth able to resist accidental washing, resistant to fading and folding multiple times; however, to increase the durability of banknotes, since 1988 many countries (e.g. Australia, UK, etc.) switched to “synthetic” polymer substrate (e.g. bi-axially oriented polypropylene) [5]. Many studies proved the economic effectiveness of synthetic polymer substrate; with printing cost reduced by about 20%, plastic banknotes show higher peel strength, may yield greater durability and ensure increased lifetime in intensive use during their circulation [6]; however, some problems in the synthetic polymer technology limit its diffusion, such as the high costs of new banknote production lines and the negative environmental impact of the plastic banknote production waste [4] In this presentation we will show a comparison between paper and plastic banknotes, using as reference 5 € and 5 £, respectively, in terms of chemical, physical but also morphological and mechanical characterisation. The interplay between the chemical and the mechanical physical properties has also been investigated. Our goal is to provide a set of reference data, regarding the mechanical properties, resistance, and durability, referred to the plastic banknote, that could be reached also by the ”environmental friendly” paper banknote by the development of suitable technologies and approaches.