Study On Synthesis And Application In Cotton Fabrics Of Halogenfree Flame Retardant With Phosphorus-nitride-silicon

Cotton fabrics are widely used to home furnishings and various industrial products as well as apparel, such as protective suit, medical supplies etc, so it has become an indispensable part of our lives. Although cotton fabrics show excellent softness, breathability, and ability to absorb moisture, it is still more combustible fibers due to its LOI is just 18%, which completely limited its applications. In order to expand the application fields of cotton fabrics and to meet fire safety regulations, it is very important to develop a halogen-free and environmentally-friendly flame retardant with low smoke, low toxicity as well as high flame retardancy from the point of scientific significance and application prospects.In this paper, two halogen-free and environmentally-friendly flame retardant with multiple active groups（named PSD-Si and TCT-Si） were synthesized by using dichloro-phenyl phosphate, cyanuric chloride and（3-aminopropyl）triethoxysilane as starting materials. The molecular structures of PSD-Si and TCT-Si were well characterized by ¹H NMR, ³¹ PNMR and FTIR spectroscopies. Effects of reaction time, molar ratio of raw materials, solvent, reaction temperature and acid-blinding agent were investigated, in which the corresponding optimal reaction condition was obtained. The thermal behavior of TCT-Si were studied by thermogravimetry analysis（TGA）, indicating that they have good thermostabilities.The prepared PSD-Si and TCT-Si were applied to cotton fabrics by the dip-pad-cure process, repectively. The effects of the dosage of eatalyst and flame retardants, the type of catalysts on the flame retardancy of cotton fabrics had been studied by using the Limiting oxygen index（LOI） and vertical flammabilty test（VFT）, in which the optimal condition of the treatment process was determined. Meanwhile, the chemical reaction between flame retardants and cellulose occurs, which was proved by means of the ATR-FTIR. Furthermore, the effect of the dosage of catalyst on the thermal and combustion properties of the treated cotton fabric was investigated using thermogravimetric analysis（TGA） and microscale combustion calorimeter（MCC）.These results showed that the addition of catalyst was effective in the improvement of char yield and decreasement of heat release for the treated cotton fabrics. On the optimal condition of the flame-retardant treatment, the char yield of cotton fabrics treated with PSD-Si is 39.4% while that treated with TCT-Si is 43.4%, wherein the corresponding pHRR values were decreased by 81.8% and 85.6%, respectively. The contact angle test indicated that the cotton fabrics treated with PSD-Si is hydrophilic whereas the one treated with TCT-Si is hydrophobic. The morphology of cotton fabrics treated/untreated and before/after combustion was observed by scanning electron microscopy（SEM） and Raman spectroscopy. These results indicated that（i） flame retardants can be successfully grafted onto cotton fabrics,（ii） the structure of the treated cotton fabrics after burning still remains intact,（iii） the crystallite size of the carbon layer becomes smaller and the quality of char layer was improved when the treated cotton fabrics was burned,（iv） the addition of PSD-Si and TCT-Si can improve the thermal stability, the char formation and flame retardancy of cotton fabrics.The water resistance of the cotton fabrics treate with PSD-Si and TCT-Si were investigated when the treatment process of cotton fabrics was optimal. The laundering results indicated that the cotton fabrics treated with PSD-Si and TCT-Si have a certain water resistance, in which the LOI of the corresponding treated cotton fabrics can reach to 26.0% after 5 laundering cycles. The ATR-FTIR test showd that there still existed a certain flame retardant grafted on the surface of cotton fabrics, further indicating that the chemical reaction between flame retardants and cellulose indeed occurs. The TGA and MCC tests demonstrated that the treated cotton fabrics have a high thermal stability and a low heat release after 50 laundering cycles. The SEM and Raman tests displayed that compared with untreated fabrics, the structure of the treated cotton fabrics after burning still remains intact and the quality of char layer was improved, further demonstrating that the the addition of PSD-Si and TCT-Si can improve the water durability of cotton fabrics. Meanwhile, the flame retardancy of cotton abrics treated with TCT-Si is excellent than that treated with PSD-Si, even after 50 laundering cycles. Therefore, we can conclude that due to the more active groups that the flame retardant contains, the chemical cross-linking reactions easily occurs and further the much flame retardant can be grafted onto the surface of cotton fabric, which well improved the durability and flame retardancy of cotton fabrics.