Pulp fiber networks of high density – why are properties so good?

Pulp fibers offer significant advantages compared to fossil-based plastics in terms of eco-friendly characteristics. However, the mechanical properties of paper are generally insufficient for many load-bearing applications where plastic sheets are used. Paper properties are most often controlled by interfiber adhesion. At higher densities, deformation mechanisms appear to change, and an unexpected improvement in properties is observed. High-density fiber networks show a non-linear dependence of modulus and strength on density. Data are presented for bleached kraft pulp, hemicellulose-rich bleached pulp, and unbleached kraft pulp. Short aspen fiber (1 mm length) sheets in terms of mechanical properties were compared to long spruce fiber (2.5 mm length) sheets in dense paper structures (fiber aspect ratio of 84 vs 44). The effects of density, fiber type, and dimension are discussed. Additionally, the effects of fiber strength and interfiber bonding are analyzed. The potential of high-density fiber networks is discussed, as well as the implications for processing fiber network materials.