Changing the structural and mechanical anisotropy of foam-formed cellulose materials by affecting bubble-fiber interaction with surfactant

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

Versatile templates from cellulose nanofibrils for photosynthetic microbial biofuel production

Versatile templates were fabricated using plant-derived nanomaterials, TEMPO-oxidized cellulose nanofibrils (TEMPO CNF) for the efficient and sustainable production of biofuels from cyanobacteria and green algae. We used three different approaches to immobilize the model filamentous cyanobacteria or green algae to the TEMPO CNF matrix. These approaches involved the fabrication of: (A) a pure TEMPO CNF hydrogel; (B) a Ca2+-stabilized TEMPO CNF hydrogel; and (C) a solid TEMPO CNF film, which was crosslinked with polyvinyl alcohol (PVA). The different immobilization approaches resulted in matrices with enhanced water stability performance. In all cases, the photosynthetic activity and H2 photoproduction capacity of cyanobacteria and algae entrapped in TEMPO CNF were comparable to a conventional alginate-based matrix. Green algae entrapped in Ca2+-stabilized TEMPO CNF hydrogels showed even greater rates of H2 production than control alginate-entrapped algae under the more challenging submerged cultivation condition. Importantly, cyanobacterial filaments entrapped within dried TEMPO CNF films showed full recovery once rewetted, and they continued efficient H2 production. The immobilization mechanism was passive entrapment, which was directly evidenced using surface sensitive quartz crystal microbalance with dissipation monitoring (QCM-D). The results obtained demonstrate a high compatibility between CNF and photosynthetic microbes. This opens new possibilities for developing a novel technology platform based on CNF templates with tailored pore-size and controllable surface charges that target sustainable chemical production by oxygenic photosynthetic microorganisms.<br /