Chemical Science International Journal

Aims: To establish how a guanidinium polyacrylate (GPA) modifier obtained from waste guanidine thiocyanate controls the charge state, colloidal stability, rheology and service properties of poly(vinyl alcohol) (PVA)–colloidal silica composite adhesives.

Study Design: Experimental study combined with colloid-chemical modelling (electrokinetics, ionic strength, DLVO and Stern–Langmuir analysis).

Place and Duration of Study: Department of Chemical Technology, Bukhara State Technical University, Uzbekistan, from 5 March 2024 to 15 September 2026.

Methodology: Composites were prepared with a basic formulation of 40 g GPA, 100 g of polymer matrix, 15 g of 30 % colloidal silica sol and 5 g of 37 % formalin; the GPA content was varied from 0 to 60 g and the sol content from 5 to 25 g. ζ-potential, hydrodynamic particle size, storage stability, rheological parameters, contact angles, work of adhesion, lap-shear adhesion strength, mechanical properties, water resistance and antibacterial activity were measured.

Results: Increasing the GPA content shifted the ζ-potential from −28.6 to +16.8 mV, with charge reversal between 30 and 40 g and a maximum particle size (128.5 nm) at 30 g. Stoichiometric neutralisation of the silica surface charge would require only 0.01–0.07 g GPA, whereas the practical formulations (20–60 g) have an ionic strength of 0.17–0.50 mol/kg and a Debye length below 1 nm; the DLVO barrier vanishes above about 100 mM, so stability is provided mainly by adsorbed PVA and hydration forces. At 15 g of sol, the composite had η = 950 mPa·s, n = 0.68, particle size 89.6 nm and a storage life of 120 days. Adhesion strength was 6.8, 5.2, 6.1 and 6.4 MPa on metal, wood, glass and ceramics (44.4–61.9 % above the unmodified reference), water uptake after 24 h was 1.8 % (7.6 % for the reference), and the inhibition zone of 18.4 mm retained 91.8 % after washing.

Conclusion: The GPA content and the silica-to-modifier ratio are the key variables that link the charge state of the dispersion with adhesion, water resistance and washing-resistant antibacterial activity; the basic formulation (40 g GPA and 15 g of 30 % sol per 100 g of matrix) provides the best compromise between these opposing requirements.