Preparation and properties of the flame-retardant viscose fibers based on the intumescent dithiocarboxyphosphate microcapsules

Bisneopentyl glycol dithiocarboxyphosphate (2,2-oxybis [5,5-dimethyl-1,3,2-dioxaphosphorinane] 2,2-disulphide, DDPS) was usually utilized as a commercial flame retardant of viscose fibers, while confronting the low flame-retardant efficiency and inferior interfacial interaction with viscose fibers matrix. To solve the above problems, the sulfonated melamine formaldehyde resins were uniformly coated onto the core surface of DDPS particles by in-situ polymerization, resulting in the generation of an intumescent microcapsule DDPS (MDDPS). The structure and composition of MDDPS were characterized by EDS, TEM, SEM and FTIR, respectively. Then, MDDPS was incorporated into viscose fiber spinning solution to prepare the flame retardant MDDPS/viscose fiber via the wet spinning. The results found that MDDPS/viscose fiber maintains the mechanical properties of DDPS/viscose fiber, due to the significant interfacial interaction. What's more, compared to viscose fibers, the reductions of heat release rate, total heat release, peak smoke production rate and peak CO production rate of MDDPS-5/viscose fibers reach up to 63.9%, 75.3%, 57.7% and 55.9%, respectively. The analysis of char residues for MDDPS/viscose fiber reveals the formation of intumescent chars onto fiber surface to restrain heat and mass transfer. In conclusion, this study provided a significant method for flame-retardant viscose fiber preparation with intumescent pyrophosphate microcapsule coating.