Structural optimisation of a multifunctional water- and oil-repellent, antibacterial, and flame-retardant sol–gel coating on cellulose fibres

This research aimed to optimise the structure of the multifunctional water- and oil-repellent, antibacterial, and flame-retardant hybrid polysilsesquioxane coating to increase its washing fastness to cotton fibres. In the pre-treatment process, pre-prepared Stöber silica particles were applied to the fibres by a pad-dry-cure process followed by the in situ generation of a tetraethyl orthosilicate (TEOS)-based particle-containing polysiloxane layer. A three-component equimolar sol mixture (MC), which included 1H,1H,2H,2H-perfluorooctyltriethoxysilane (SiF), 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (SiQ) and P,P-diphenyl-N-(3-(trimethoxysilyl)propyl) phosphinic amide (SiP) in combination with two different concentrations of TEOS (T and 3T) or organocyclotetrasiloxane 2,4,6,8-tetrakis(2-(diethoxy(methyl)silyl)ethyl)-2,4,6,8-tetramethyl-cyclotetrasiloxane (T₄) as crosslinkers, was applied to the pre-treated cotton fibres by a pad-dry-cure process. The functional properties of the coated samples before and after repeated washing were investigated by the water θ(W) and n-hexadecane θ(C16) static contact angle as well as water sliding (roll-off) (α) angle measurements, antibacterial tests, thermogravimetric analyses and burning behaviour studies. The results showed that the inclusion of T₄ into the MC sol increased the washing fastness of the coating to a significantly greater extent than the inclusion of T, and the washing fastness even further it increased if silica particles were deposited on the fibres in the pre-treatment process. The structural optimisation of the coating also led to the improvement of the functional properties of the coating, which exhibited the “Lotus effect” [θ(W) = 161° and α = 4°] and simultaneously demonstrated high antibacterial activity (the R values for Escherichia coli and Staphylococcus aureus were 81.6 and 100%, respectively), enhanced thermo-oxidative stability and “glow” retardancy. The only weakness of the optimised coating is the impairment of its oleophobicity.