Abstract
The compound 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) is an eco-friendly water treatment agent possessing flame-retardant phosphorus element and multi-carboxylic acid groups in its molecular structure. In the present work, PBTCA is employed as a finishing agent to improve the flame retardancy of the wool fabrics by the pad-dry-cure technique. The treated wool (10.2% weight gain) by 100 g/L of PBTCA showed an increased flame retardancy with a limiting oxygen index value (LOI) of 44% with a minimum char length of 40 mm. Importantly, the treated wool can self-extinguish after 30 washing cycles. The PBTCA-treated wool exhibited better stability with obviously increased char residue of 39.7% and 28.7% at 600 °C, while only 25.9% and 13.2% were measured for the control wool in nitrogen and air atmosphere, respectively. In addition, the high thermal stability of the treated wool with astonishing char-forming ability is confirmed by the SEM images of the wool after the isothermal heating treatment at different temperatures. Finally, a two-stage flame-retarding mechanism of enhanced crosslinking and char formability of PBTCA-treated wool is proposed and analyzed by infrared spectroscopy (TG-FTIR) and thermal (DSC and TGA) results of the pyrolytic volatiles of the treated wool.
Highlights
As one of the most essential natural protein fibers, wool is widely used in apparel, interior textiles, and industrial applications due to its superior aesthetic qualities along with excellent breathability, warmth, elasticity, and especially, the inherent low flammability
The high amount of nitrogen, sulfur, and moisture contents are responsible for the intrinsic flame retardancy with a limiting oxygen index (LOI) of ≈25% [1,2]
Even after 30 washing cycles, the treated wool fabrics still can sustain and self-extinguish in the burning process, showing a char length of 205 mm and LOI of 25.6. These findings indicated that the PBTCA-treated wool possessed good resistance to the laundry
Summary
As one of the most essential natural protein fibers, wool is widely used in apparel, interior textiles, and industrial applications due to its superior aesthetic qualities along with excellent breathability, warmth, elasticity, and especially, the inherent low flammability. The halogen-based compounds including chloroand bromo- derivatives had been investigated and coated to develop high efficiency and durable wool [2]. From the 1970s, the mordanting treatment of wool using zirconium/titanium complexes and their modified compounds has been investigated extensively [9,10]. Based on these findings, the famous “Zirpro” process was developed for making a flame-retardant wool with excellent washing durability. The effluents produced during the process have been criticized for the heavy metal pollution [11,12], and the treated wool turned yellow and lost its flame resistance if exposed to light or washed in alkaline solution [13]. Into the flame-retardant mechanism and physical properties of the wool, the treated wool fabrics are examined using the thermo-analytical method, isothermal heat treatment, and infrared analysis
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