SURFACE ACTIVITY OF A THIOURETHANE-GROUP OLIGOMERIC MODIFIER (TGF-8) IN SODIUM LIQUID GLASS AND ITS IMPLICATION FOR WETTING OF PAPER SUBSTRATES

The surface activity of the thiourethane-group oligomer TGF-8, synthesized from thiourea, glycerol and formaldehyde, was studied in undiluted sodium liquid glass (silicate modulus 2.8, ρ = 1.38 g/cm³) by the stalagmometric method at 20 °C. Increasing the TGF-8 content from 0 to 10 wt% lowered the surface tension from 67 to 48 mN/m (by 28.4 %). The Gibbs equation applied to the 2–8 wt% range gave an apparent surface excess Γ ≈ 4.0·10⁻⁶ mol/m² and an area per adsorbed molecule A ≈ 0.41 nm². Above 8 wt% the surface tension changed only within about 1 mN/m, which indicates apparent saturation of the liquid–air interface. At this content the surface tension of the adhesive approaches the surface free energy reported for recycled paperboard, which favours wetting of the substrate.