关键词: 棉织物, 阻燃, 层层自组装, 聚乙烯基膦酸, 多乙烯多胺

Abstract:

Objective Cotton fibers are ideal materials for clothing, furniture and bedding because of good hygroscopicity, wear comfort and biodegradabity. However, cotton fabrics are flammable and have been identified as one of the main sources of household fire. This research aims to enhance the flame retardance of cotton fabrics using a flame retardant system composed of polyvinylphosphonic acid (PVPA) and polyethylene polyamine (PEPA) to achieve environmental-friendly flame retardant cotton fabrics.

Method Vinylphosphonic acid (VPA) was used as a monomer to synthesize PVPA, and a flame retardant coating system on cotton fabrics with PVPA and PEPA was constructed via layer-by-layer assembly (LBL). The surface morphology, flame retardancy and physical properties of coated cotton fabrics were measured, and the flame-retardant mechanism of gas phase and condensed phase were explored.

Results In this study, the VPA was successfully prepared using 2,2'-azobis[2-methylpropionamidine] dihydrochloride (AIBA) as initiator, and its conversion rate reached 93.6% by means of ³¹P nuclear magnetic resonance (³¹P NMR) (Fig. 2). When the PVPA/PEPA flame-retardant system was prepared by the layer-by-layer assembly method, the flame retardant coating formed evenly on cotton fabric surfaces through the measurement of Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM) (Fig. 3 and 5). When the number of finishing layers reached 12, the weight gain of the coated cotton fabric was 38.0%, and the limiting oxygen index (LOI) of flame retardant cotton fabric reached 29.8%. The research showed that the flame of the coated cotton fabric self-extinguished and the damaged length was 31 mm during the vertical burning test. After 10 standard washing cycles, the LOI value of the coated cotton fabric was 27.1% (Tab. 1). The cone calorimetric test showed that the peak heat release (PHRR) and total heat release (THR) of coated cotton fabrics decreased by 16.8% and 19.7%, respectively, lower than that of uncoated cotton fabrics (Fig. 7). The above results indicated that the coated cotton fabric had good flame retardant property. Accordingly, the volatile components of flame retardant coated cotton during thermal degradation were studied by the combination technology of thermogravimetric analyzer and infrared spectrometer (TG-IR) (Fig. 9), and the structure of residual carbon after vertical burning test was investigated by SEM and X-ray photoelectron spectroscopy (XPS) (Figs. 10 and 11). These results indicated that the flame-retardant coating played a key role in the cohesive phase flame retardant process, when cotton fabrics were burned, forming a stable carbon insulation layer, insulating the transfer of heat and gas, and inhibiting the occurrence of combustion reactions. Besides, it was found that from the test results of electronic fabric strength machines and whiteness meters, the tensile strength and whiteness values decreased from 730.7 N and 89.2 % to 512.6 N and 74.2%, respectively, after the flame retardant coating, which suggested the flame-retardant system had a small impact on the breaking strength and whiteness of the fabric (Tab. 4). It ascribed that the alkaline PEPA reduce the acid embrittlement caused by VPA on cotton fabrics in the flame-retardant coating system.

Conclusion A flame-retardant coating was prepared by the layer-by-layer assembly method, which was applied to flame retardant coated cotton fabrics, achieving good physical properties of cotton fabrics while flame retardant finishing, and meeting the requirements of household curtains, interior decoration, and industrial textile fabrics.

Key words: cotton fabric, flame retardant, layer-by-layer assembly, polyvinylphosphonic acid, polyethylene polyamine