Optimizing foamability and foam stability of aqueous cellulose nanofibril foams through the sequential addition of cationic and anionic surfactants, Advanced Coating Symposium (TAPPICON26)

Cellulose nanofibrils (CNFs) have gained attention as a foam stabilizing agent in the preparation of wood fiber-based foams. In these systems, an ionic surfactant, such as sodium dodecyl sulfate (SDS), is commonly used as the foaming agent. This work shows how the sequential addition of the cationic surfactant, cetyltrimethylammonium bromide (CTAB) followed by the anionic SDS can lead to an improvement in the foamability and foam stability of the CNF-based foams. It is shown that the addition of CTAB up to the maximum adsorption amount on CNFs, imparts partial hydrophobicity to CNFs, which in turn allows the CNFs to anchor more effectively at the air-water interface during the foaming process. From zeta potential measurements, it was found that 0.154 mmol CTAB/g of CNFs was the maximum concentration of CTAB required to achieve the partial hydrophobicity of CNFs and to minimize the level of free CTAB in the solution phase that would form mixed micelles with the SDS added in the second step. It was found that the foamability and foam stability obtained with the sequential addition of CTAB then SDS passed through a maximum at a CTAB concentration of 0.154 mmol CTAB/g CNFs and foamability was 10% higher compared to foams generated by addition of SDS alone. In contrast, a lower formability (223.6 + 10.0)% and foam stability was observed when SDS was added first, followed by 0.154 mmol CTAB/g CNFs. These findings help optimize the surfactants-assisted foam forming process of lignocellulosic materials.

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