Effects of an inorganic ammonium salt treatment on the flame-retardant performance of lyocell fibers

Abstract

Lyocell fibers are produced by dissolving cellulose in a N-methylmorpholine-N-oxide/ water solution. The resulting cellulose/N-methylmorpholine-N-oxide/water mixture is extruded through an orifice, drawn into an air gap, and then precipitated in a coagulation bath [1]. In contrast with rayon fibers, lyocell fibers have higher tenacity, a higher modulus, lower shrinkage when dried, and lower reductions of tenacity and the modulus when wet. Moreover, lyocell fibers are round and have molecular chains that are highly oriented along the fiber axis, and it is easy to control their fineness [2].However, lyocell fibers are often subjected to high temperatures, which can cause degradation of the fibers. When lyocell fibers are heated, they undergo a series of interrelated physical and chemical changes, including physical changes in weight, strength, color, and crystallinity. In addition, heat treatment can cause the material to move through different transitional phases and expand or contract, melt and recrystallize or undergo major structural changes [3].Thermal decomposition of the lyocell fibers leads to many kind of formations, such as solid residue, high-boiling point volatiles, and gaseous products. These kinds of products are formed through two competitive pathways. The first pathway involves many transformations, such as dehydration, rearrangement, carbonyl groups formation, the evolution of carbon monoxide and carbon dioxide, and the carbonaceous residue formation [4]. These phenomena take place rapidly in the presence of a variety of organic and inorganic catalysts, particularly Lewis acids, which catalyze the dehydration reactions. The second pathway competes with the first pathway and produces many oxygenated compounds and involves the thermal scission of glycosidic bonds between the glucopyranose units of cellulose [5]. These oxygenated compounds account for the majority of the weight loss of the solid residue. Therefore, it is important to control the reaction pathways during the initial pyrolysis stage to generate flame-retardant materials. Thus, flame-retardant enhanced lyocell fibers should be investigated for industrial applications. Recently, various treatment processes have been used to improve the flame-retardant properties of lyocell fibers. Because catalysts accelerate pyrolysis reactions, it is important to study the effects of catalysts on the pyrolysis of lyocell fibers. An effective catalyst should [6,7] decrease the pyrolysis temperature, increase the amounts of water and carbon dioxide produced during the reaction, and increase the amount of char formed.Therefore, it is important to control the reaction pathways during the initial stage of pyrolysis when generating flame-retardant materials. In this study, the effects of two different inorganic ammonium salts, (NH 4 ) 2 SO 4 and NH 4 Cl, on the flame-retardant properties of lyocell fibers were studied. Combining these salts could have a synergistic effect on the pyrolysis of lyocell fibers, including the induction of a slow pathway that invo...

Enhancing the flame retardancy of lyocell fabric finished with an efficient, halogen-free flame retardant

“…The main decomposition step of the control sample occurred at 280-380 C, either under air or nitrogen atmosphere, involving the degradation of cellulose molecular chains and the generation of fatty coke. 6 The weight loss was 71.18% and 77.65% under air and nitrogen atmospheres, and the maximum weight loss rates were reached at 323 C and 338 C, respectively. The residual char of the fabric was further decomposed above 380 C in which some of the aliphatic coal coke was converted to aromatic coal coke.…”

“… 5 Blend spinning refers to mixing a suitable flame retardant with a spinning solution, then the resulting spinning solution is introduced into a coagulation bath through the spinneret, and then the flame retardant fiber is prepared by drawing. 6 Delholm et al mixed organically modified montmorillonite nanoparticles into a cotton cellulose/NMMO solution to significantly increase the char residue of the resulting regenerated cellulose during the combustion process. Specifically, when the clay additive was 15%, the residual char increased to 30%.…”

Structure and properties of flame‐retardant Lyocell fibers prepared by blending method

“…Bai and Kim et al used inorganic salts as flame retardants to study the influence of several different inorganic salts on the flame retardancy of Lyocell fiber and found that the amount of carbon residue of the fiber increased with a higher content of flame retardant. [ 14–16 ] The presence of carbon residue inhibits the diffusion of combustion gases into the pyrolysis zone and therefore protects the material surface from the influence of heat and air. Hall et al prepared flame‐retardant Lyocell fibers by using N‐methylol dimethylphosphonopropionamide (Pyrovatex CP) as a flame retardant.…”

Synthesis of Novel Arginine-Based Flame Retardant and Its Application in Lyocell Fabric

“…For the issue of environmental protection, wet-spun cellulose fibers derived from green solvent were first studied in the early1980s [1]. Lyocell fibers are fabricated by first dissolving cellulose in N-methylmorpholine-N-oxide/aqueous solution to form an even spinning solution, then it was extruded through a spinneret, and immersed into a coagulation bath to form lyocell fibers by drawing [2]. Compared with the traditional viscose process, the production of lyocell fibers is a simple and resource-saving method for the production of regenerated cellulose fibers [3].…”