Changing the Structural and Mechanical Anisotropy of Foam-Formed Cellulose Materials by Affecting Bubble–Fiber Interaction with Surfactant

Abstract

Cellulose fiber materials suitable for filtering, insulation, protective, and hygiene applications can be formed using aqueous foam as a carrier phase. The subtle fiber–bubble interaction provides a tool which can be utilized to alter both structural and mechanical material properties. Earlier model surface studies have only indicated clear surface-bubble adhesion when both the surface hydrophobicity and surface tension of the solution are high enough. In this work, we first show that for silica model surfaces these basic mechanisms are similar for both nonionic polyethylene glycol sorbitan monolaurate (Tween 20) and anionic sodium dodecyl sulfate (SDS) surfactants. In the second step, thick nonwoven materials were foam formed from hydrophilic or hydrophobic viscose fibers using small amounts of cellulose microfibers (CMFs) to form a bonding agent. There was a clear variation in structure and strength properties between the samples made using different fibers and surfactants. The partial alignment and layering of fibers in the wet foam led to anisotropy in the mechanical properties of the formed samples. Using SDS, the fiber alignment was very strong for hydrophilic fibers but was reduced for hydrophobic fibers because of stronger coupling to bubbles during structure forming, impacting the microscale fiber network. For nonionic Tween 20, in addition to surfactant adsorption on the fibers, the ethoxylated surfactant headgroups are suggested to form bridges between CMFs and other fibers, restricting fiber movements during formation. For hydrophilic fibers, this showed up as a lower in-plane compression modulus but higher transverse strength for Tween 20 compared with SDS surfactant. For hydrophobic fibers, the sensitivity of the mechanical properties on surfactant type was even stronger.

Energy Absorption and Resilience in Quasi-Static Loading of Foam-Formed Cellulose Fibre Materials

“…In our study, fibre orientation was not quantified. However, Ketola et al (2022) showed that structures made with SDS had higher structural orientation in the xdirection, whereas with Tween 20, the samples had a higher z-directional strength. Consequently, if similar structural orientation was also realised with wood fibres, z-oriented micro-structures formed with Tween might have collapsed more in compression, causing their poorer recovery.…”

“…Instead, the buckling of a long fibre segment activates stress build-up in several shorter ones so that the material carries a monotonically increasing load without significant densification. The above buckling theory has been found to explain not only the stress-strain behaviour (Ketoja et al 2019(Ketoja et al , 2022Pöhler et al 2020;Ketola et al 2022) but also the measured acoustic emission during compression (Mäkinen et al 2020).…”

Cellulose Fibers-Based Porous Lightweight Foams for Noise Insulation

“…The concluding remarks within the work of Xu et al [ 37 ] suggests that thin layers of sustainable natural materials such as CF can be used to significantly improve the capability of traditional porous media to absorb noise. CF-based materials suitable for filtering, insulation, protective, and hygiene applications can be formed/obtained using aqueous foam as a carrier phase [ 38 , 39 , 40 , 41 , 42 ]. The subtle fiber−bubble interaction provides a very useful tool that can be utilized to alter both structural and mechanical material properties.…”

“…The subtle fiber−bubble interaction provides a very useful tool that can be utilized to alter both structural and mechanical material properties. Indeed, the results within the study by Ketola et al [ 38 ] revealed that there was a clear variation in structure and strength properties between the samples made using different fibers and surfactants. Following the previous idea, the work [ 43 ] presents and discusses mechanisms that underlie the formation process, and thus, influence physical properties of formed fiber networks.…”

Applications of Xylan Derivatives to Improve the Functional Properties of Cellulose Foams for Noise Insulation

“…Regarding the subtle fiber–bubble interactions, the research [ 41 ] demonstrates that these interactions provide a suitable tool that can be used to alter both structural and mechanical material properties of foam-formed cellulose-based materials. A large ensemble of studies was developed within the area of soundproofing, being mainly focused on materials or composites suitable for applications in noise insulation practice [ 42 , 43 , 44 , 45 , 46 ].…”