Preparation and properties of flame-retardant viscose fabrics modified with phosphated polyethyleneimine

Objective As one of the most important regenerated cellulose materials, viscose fibers are easily flammable and it has potential threat to human lives and properties. Researches show that viscose textiles can obtain flame retardancy by flame-retardant additives and finishing. Compared with flame-retardant additives, textile finishing is easy to operate. 1,2,3,4-Butane tetracarboxylic acid (BTCA), as a common cross-linker, has been widely applied to prepare functional cellulose textiles. However, its highly acidic condition may cause big strength loss of viscose fabrics. It is necessary to find an efficient way to reduce strength loss of flame-retardant viscose fabrics cross-linked with BTCA.Method A multi-amino phosphated polyethyleneimine (BPEI-DP) was synthesized through simple Atherton-Todd reaction and applied to prepare flame-retardant viscose fabric crosslinking with BTCA. The design of BPEI-DP can decrease the acidic condition of BTCA and flame-retardant viscose fabric with low strength loss was achieved. Also, the BTCA crosslinking can improved the washing durability of flame-retardant viscose fabric. The flame retardancy, heat release, thermal stability, washing durability and mechanical properties were investigated.Results The limiting oxygen index (LOI) value of the viscose fabric was found to increase to 28.9% after finishing with BPEI-DP and BTCA, and the treated fabric presented self-extinguishing behavior with no afterflame/aftergrow appearance and damage length of 9.9 cm in the vertical burning test (Fig. 2 and Tab. 1). The viscose fiber becomes rougher after flame-retardant finishing and some additional characteristic absorption peaks were appeared on the treated viscose fabric (Fig. 3 and Fig. 4), which indicates that flame retardancy was successfully deposited onto the viscose fibers. BPEI-DP/BTCA flame-retardant system showed significantly improvement in the carbon-forming ability of viscose fabric. The appearance of flame-retardant fiber was well maintained after combustion (Fig. 6). 40.0% and 14.8% of char residues were maintained at 800 oC under N2and air atmosphere, respectively(Fig. 7 and Tab. 2). From cone calorimetry test (CCT), it is found that the with maximum heat release rate(pHRR) was reduced by 34% from 284 kW/m2 to 189 kW/m2 (Fig. 8 and Tab. 3). The washing resistance of BPEI-DP/BTCA treated viscose fabric was comparable to that of Pyrovatex CP. LOI value has slight reduction along with the increase of washing cycles. After 20 standard washing cycles, LOI value decreased from 28.9% to 24.9%, which is much higher than control viscose fabric (Fig. 9). This flame-retardant finishing system effectively maintained the strength of flame retardant viscose fabric. The breaking forces in the warp and weft direction reduced from (406±18) N to (284±13) N and (254±6) N to (168±11) N, respectively. Compared with control viscose fabric, the strength retention rate could reach about 70% and the whiteness has a significant reduction from (77.6±0.3)% to (30.1±0.5)% after flame-retardant finishing (Tab. 4).Conclusion This study provides ideas for the design and preparation of flame-retardant cellulose fabric with low strength loss. BPEI-DP can not only render viscose fabric with good flame retardancy through improving the char-forming capacity, but also reduce the strength loss of viscose fabric crosslinking with BTCA by decreasing its acidic condition. However, the washing durability of BPEI-DP/BTCA treated viscose fabric is unsatisfactory and this finishing system has bad effect on the whiteness of viscose fabric. Therefore, more efficient and friendly flame-retardant system need to be developed to improve the washing durability and inherent properties of flame-retardant fabric. © 2023 China Textile Engineering Society. All rights reserved.