Flame Retardancy and Thermal Behavior of Wool Fabric Treated with a Phosphorus-Containing Polycarboxylic Acid

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.

Polyimide/wool blended woven fabrics for comfortable fire protective clothing

“…The first stage is observed from 30 to 150°C, with the evaporation of small amount of moisture and ammonia. In the second stage between 200 and 600°C, the elevated temperature made the wool fiber break off, that is, the cleavage of the side amide, the disulfide bonds and carboxyl groups, leading to the main volatiles of NH 3 , SO 2 and CO 2 16,24,31 . By contrast, PI fabrics show only one stage during the combustion process (from 500 to 650°C).…”

“…In the second stage between 200 and 600 C, the elevated temperature made the wool fiber break off, that is, the cleavage of the side amide, the disulfide bonds and carboxyl groups, leading to the main volatiles of NH 3 , SO 2 and CO 2 . 16,24,31 By contrast, PI fabrics show only one stage during the combustion process (from 500 to 650 C). Except for the disappeared peak at SO 2 , strong peak signals have been detected for the other five kinds of volatiles, attributing to the cracking of the imide rings in the PI chains.…”

“…In this stage, higher temperature leads to the breakage of the hydrogen bond in the peptide helical structure, as well as the disulfide bonds, releasing several volatile gases, such as hydrogen sulfides and sulfur dioxide species. 16,24 Compared with a gentle and steady decrease of the weight to 11.3% of the sample in argon condition, there is another rapid weight loss for the sample in the air condition, with the T max at nearly 520 C, and the final residue at 800 C is 5.2%. It is also declared that the wool char was further oxidized in the air condition.…”

“…Therefore, wool is often blended with other fibers to improve their comfort properties 14,15 . In addition, natural high nitrogen and water content endows wool with low flammability 16 . Wool blends have been studied as a flame‐retardant candidate for years 17,18 .…”

“…14,15 In addition, natural high nitrogen and water content endows wool with low flammability. 16 Wool blends have been studied as a flameretardant candidate for years. 17,18 For example, Morgan and Galaska 19 tested the flammability of several kinds of wool blended fabrics, including wool/cotton, wool/linen, and wool/nylon, demonstrating that fabric type had great effects on the combustion results.…”