In line with the worldwide goal of increasing environmental sustainability, the use of paper-based materials as partial or total replacement for plastic based products is an ambitious achievement, which becomes possible if the formability of paperboard is maximized. Formability, indeed, is the property enabling to make complex shapes out of paperboard sheets and it is directly correlated to paper extensibility. By subjecting the moist paper web to a compaction process, through a compaction unit located in the drying section of a paper machine, the extensibility of the paperboard, and therefore it is extensibilty, can be enhanced. Understanding the macro and micro mechanisms governing this compaction process would allow the full control of the final product and, consequently its optimization by increasing the stretch potential while maintaining sufficient strength and bending stiffness.
The most appropriate methodology for tackling the complexity of the interaction between final material properties and industrial process has been identified in a strategical multiscale approach. Process and material simulations are combined so that, within the structure of a macroscale continuum model simulating the full industrial process, the segment of paperboard experiencing the compression mechanisms in the nip region is being represented at the microscale detail. In this way, it is possible, after the governing mechanisms acting at the nip level have been quantified, to extract information about the structural changes occurring in the network, particularly in relation to the local deformations and damage experiences by the single fibers and the bonds. In fact, during the compaction process, each fiber experiences large deformation, finite strains and may be damaged locally. At the same time, the already formed bonds between the fibers can be either partly broken or delaminate completely allowing fibers to slide and reconnect during subsequent drying. Clarifying these mechanisms, also through parameteric studies where the physical properties of the fibers and the bonds are varied, would provide the lacking fundamental insights into the micromechanical performance of fiber-based materials in applications involving high compressive strains and subsequent loading.