An atomic-force microscopy technique reveals new insights into what holds paper together. The results, reported in the journal Scientific Reports, could potentially be used to help improve the strength of packaging paper and reduce the material and energy inputs into the paper production process.
Paper is a versatile material that has been used for centuries, mainly for the exchange of information or for protecting and storing goods. Although the importance of paper for information exchange might decrease with the advent of tablets and e-books, its role as a natural and degradable packaging material is likely to increase. Various types of bonds, as well as microcompression and capillary bridges are all thought to contribute to the bonding between pulp fibres, but it has remained uncertain which mechanisms are dominant.
Christian Teichert and colleagues used atomic-force microscopy to probe the mechanical properties of bonds between individual pulp fibres at the nanoscale and to analyse the breaking force between two bonded paper fibres. They show that a single fibre-fibre bond is loaded with a calibrated cantilever statically and dynamically until the bond breaks. The authors reveal that tiny fibres called fibrils, or fibril bundles, which act as bridging elements between the fibres, play a crucial role in bonding. This mechanical interlocking system boosts the bond energy by a factor of two for highly refined pulp.