Properties of lightweight fibrous structures made by a novel foam forming technique

Abstract

We describe a novel method for the production of lightweight fibrous structures of densities as low as 8.8 kg.m −3. The method is based on the use of liquid foam as a carrier medium for dispersed Kraft fibres. Different to the process of foam forming, where the quick removal of the foam results in the formation of thin fibrous sheets, our samples are allowed to slowly drain and dry until all foam has disappeared. This procedure results in bulk samples whose height (up to 25 mm) and density are controlled by initial fibre concentration and liquid fraction of the foam. Above a minimum density, the compression modulus of elasticity of the samples increases linearly with density. Furthermore, we show compressive strength of the structures being controlled via the initial liquid fraction of the foam, making this an important process parameter for the fabrication of such structures.

Compression Strength Mechanisms of Low-Density Fibrous Materials

“…The obtained values varied in the range of 3 to 8 kg/m 3 . Looking at their data (Figures 7 and 8 of Burke et al [3]), our theoretical model (Equation (8)) appears also to describe their stress–strain behavior reasonably well at 15 kg/m 3 . The same holds at high strains for the case studied by Alimadadi and Uesaka ([1], Figure 11a; see also Figure 15 of Alimadadi et al [19]) at as low a material density as 5 kg/m 3 .…”

“…General fibrous materials exhibit rigidity percolation, a critical density at which the structure acquires stiffness [3,14]. The threshold density is affected by, e.g., the nature of the fiber-to-fiber contacts, fiber orientation, and fiber bending stiffness.…”

“…Below this density, Young’s and shear moduli are both considered to be zero. For low-density 3D wood–fiber networks, Burke et al [3] recently found the critical density to vary linearly with respect to the initial liquid fraction of foam used to form the structure. The obtained values varied in the range of 3 to 8 kg/m 3 .…”

“…Foam forming is a new technology which enables the production of ultra-light fiber networks with a density as low as 5 kg/m 3 [1]. The strength behavior for very low densities has been analyzed in several papers [1,2,3]. However, the intermediate density range of 20 kg/m 3 to 100 kg/m 3 , perhaps the most relevant for practical applications, has been rather poorly understood.…”

Dewatering of foam-laid and water-laid structures and the formed web properties

“…Foam forming offers possibilities for cost saving and environmental impact reduction through better energy and water efficiency (Smith and Punton 1975;Lehmonen et al 2013) and higher dryness levels after the forming section (Smith et al 1974;Wiggins 1973;Torvinen et al 2015). Perhaps even more importantly, foam forming enables widening of the product portfolio with highly porous structures (Madani et al 2014;Jahangiri et al 2014;Alimadadi and Uesaka 2016;Pöhler et al 2016;Li et al 2017;Burke et al 2019) and non-woven sheets composed of long fibers (Koponen et al 2016a, b).…”