The research included the preparation of flame retardant coating onto the cotton fabric by sol-gel technology. As a flame retardant agent, organophosphonate (OP) in combination with the sol-gel precursor tetraethyl orthosilicate (TEOS) was selected. Samples were finished in a one-step and two-step procedure. In the one step procedure, the samples were finished with TEOS or OP. In the two-step procedure, samples were firstly treated by TEOS followed by OP. After finishing, samples were once, twice and three times washed in order to determine the washing fastness of the coating. The presence of coating was determined by scanning electron microscopy and infrared spectroscopy by Fourier transform. Functional properties were investigated by a vertical test of flammability and thermogravimetric analysis. The influence of coating on the physical and mechanical properties of fabric was determined by the measurements of fabric stiffness, air permeability, breaking strength and elongation. The results of vertical test of flammability show that OP totally stopped the fibres burning and gloving and that the presence of TEOS precursor did not significantly affect the flame retardancy of OP. The flame retardant properties of the coating deteriorated significantly after the first washing cycle. This indicates that OP was largely removed from the fibres during the washing and that the presence of TEOS did not increase the washing fastness of OP. The presence of OP increased the thermal stability of the fibres which additionally increased, if OP was used in combination with TEOS. The application of OP increased the flexibility of the fabric, but the application of TEOS increased its stiffness. The breaking force and elongation decreased after the application of OP resulting in the deterioration of the fabric breaking strength. The presence of TEOS did not significantly influence the breaking strength of the fabric.
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