Sodium dodecyl sulphate (SDS) residue analysis of foam-formed cellulose-based products

Surfactant residues in foam forming are related to the circulation of surfactant in the foaming process, but they may also affect the properties of the foam-formed product. In this work, residues of an anionic surfactant, sodium dodecyl sulphate (SDS), in foam-formed products were studied. Two different methods were applied for the determination of SDS: ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy) and solvent extraction spectrophotometry. The dry matter content of the sample before the drying step has a significant effect on the SDS residue. Another factor that has a significant effect on the SDS residues is the amount of precipitated dodecyl sulphate (DS). It was found that SDS does not degrade in the drying phase and will remain in the salt form in the final product. SDS residue decreased when the temperature of the fibre suspension was increased. Theoretical values for SDS residues were estimated from the original surfactant concentration and the amount of water remaining in the product before the drying phase. When all the surfactant was in soluble form, measured SDS residues were close to the theoretical values, which indicates that SDS was not permanently adsorbed onto softwood cellulose fibres.