Foam Processing of Fibers As a Sustainable Alternative to Wet-Laying: Fiber Web Properties and Cause–Effect Relations

Abstract

Wet-laying is a mature technology that is applied in large scale for the manufacture of nonwovens, including paper products. However, it usually uses large volumes of water and is energy-intensive. Here we used foam-laying to substantially diminish the volume of water consumed in the formation of fiber networks (5-fold reduction) and to reduce the water content of the nonwovens produced before drying, achieving a reduced energy demand. The prospects of foam-laying were evaluated by comparing foam-laid and wet-laid webs of two types of wood fibers: stiff (lignin-containing) or flexible (lignin-free). Also, the effect of foaming agent type (anionic, cationic, nonionic, and amphoteric) was elucidated. Reference webs were produced by conventional wet-laying, with or without surfactants. Foam-laying was effective in producing a more uniform areal mass distribution (better formation) after wet-pressing. This effect was more evident for the webs synthesized with the flexible fibers. Unlike the layered network structures that were obtained by wet-laying, foam-laid webs exhibited a more felted network, with fibers positioned in the out-of-plane direction. As a result, higher air permeability, web porosity, and light scattering coefficients were measured for the foam-laid webs. The enhanced porosity (lower density) was related to the effect of bubbles during foam-laying and the reduction in surface tension of the foamed-fiber dispersion. The resistance to delamination of low-density webs obtained by foam-laying in the out-of-plane direction was preserved. However, the reduction in tensile strength and modulus of foam-laid webs were determined, owing to the reduced density of the formed structures. Notably, the type of foaming agent used played a minor role as far as the resultant properties of the webs, making the process flexible in terms of the selection of environmentally friendly alternatives. Overall, we compared the physico-mechanical properties of fiber networks formed by web-and foam-laying, depending on fiber type and foaming agent, yielding a property space that is useful in the design of lightweight structures (nonwovens, including paper). The prospects of water and energy savings by foam-laying are the major benefits in the sustainable use of fibers for the assembly of porous materials, such as lightweight nonwoven and paper products.

How Cellulose Nanofibrils Affect Bulk, Surface, and Foam Properties of Anionic Surfactant Solutions

“…Aqueous foams are important in numerous applications − for which often a precise control of the foam generation and stability is required. − Typical destabilizing processes are drainage, coalescence, and coarsening, − all of which may occur simultaneously . Drainage can be slowed down by increasing the viscosity of the continuous phase; in turn, it improves the foam’s resistance against coalescence.…”

Surface Activity and Foaming Capacity of Aggregates Formed between an Anionic Surfactant and Non-Cellulosics Leached from Wood Fibers

“…The unique properties of foams fulfill a wide range of purposes in nature and industry, for example, for the protection of embryo, the dispersion of fibers in nonwoven manufacture, − the assembly of functional materials via templating, the delivery of drugs, and the formulation of household and food products . In such applications, it is of critical importance to understand foam generation and stabilization.…”

Overview on Foam Forming Cellulose Materials for Cushioning Packaging Applications

“…This is caused by the presence of hydrophobic regions on the cellulose fibers surface (e.g., lignin) [ 96 , 97 ]. The type of foaming agent may affect the tensile strength by changing the strength of inter-fiber bonds or the network structure [ 98 ]. For laboratory Kraft sheets with density of 200 kg/m 3 , Al-Qararah [ 42 ] found a slight reduction in tensile strength at high SDS surfactant concentration comparing with water-formed structure in similar conditions.…”