Multifunctional flame-retarded and hydrophobic cotton fabrics modified with a cyclic phosphorus/polysiloxane copolymer

A novel cyclic-shaped copolymer containing silicon and phosphorus, poly (tetramethylcyclosiloxyl spirocyclic pentaerythritol diphosphonate) (PCTSi) was successfully synthesized and characterized by Fourier transform infrared spectra (FT-IR), 1H and 13C nuclear magnetic resonance (1H NMR and 13C NMR) for the preparation of flame retardant and hydrophobic cotton fabrics. The surface morphology of treated cotton fabrics was characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The thermal degradation and combustion properties of cotton fabrics before and after treatment were investigated by thermogravimetric (TG) analysis, limiting oxygen index (LOI) test, vertical burning test and cone calorimetry test. After treated with PCTSi, the LOI value of coton fabrics increased to 29.5%, which was significantly higher than untreated cotton fabrics and the LOI value remained at above of 26.0% after 20 washing times. In the vertical burning test, the PCTSi treated cotton fabrics showed no afterflame and afterglow with a minimum char length of 8.5 cm. Thermogravimetric analysis coupled with Fourier transform infrared analysis (TG-FTIR) results indicated that flame-retardant cotton fabrics released nonflammable gases and less flammable gases than the untreated cotton fabrics. X-ray diffraction analysis demonstrated that the crystal structures of the PCTSi-treated cotton were almost unaffected. According to the results of TG-FTIR, SEM, EDS, and analyses of char residues, the cyclic-shaped copolymer can significantly improve flame retardant performance of cotton fabric by promoting the generation of char layer and the release of noncombustible volatiles. The treated cotton fabrics showed excellent hydrophobic properties, which reached a contact angle (CA) of 150° compared with cotton fabrics without treatment. In addition, 119.18° of CA and 26.0% of LOI value can be maintained after 20 washing times.