Three-dimensional formability of paper

In this paper factors that control the extensibility and formability of paper are reviewed and described in a systematic way. The extensibility of paper depends on three principal factors: single fibers, inter-fiber connections, and the structure of the fiber network. Extensibility of fibers can be increased by several means, but highly extensible fibers do not necessarily form paper with high extensibility. This emphasizes the role of inter-fiber connections and network structure in this property. On the other hand, an increase in extensibility is accompanied often by the reduction in tensile stiffness and tensile strength. With suitable chemicals, both the strength and extensibility of paper can be improved simultaneously. Recent advancements in the improvement of the extensibility of paper are also presented. Several approaches have been studied: mechanical modification of fibers, application of polymers to the paper, in-plane-compaction and free shrinkage during unrestrained drying. In best cases the contribution of several combined treatments was found to be additive. Elongation of paper could be improved from 4% to 30% by a combination of several methods. Such improvements in the elongation of paper imply a great potential to con-tribute to the development of novel and attractive paper-based packaging.