Screening Ionic Liquids for Dissolving a Melamine Formaldehyde Resin Prepolymer to Fabricate Flame-Retardant Fibers

The melamine fiber has been widely used because of its excellent flame retardancy. We tried to fabricate melamine fibers using ionic liquids (ILs) as solvents, melamine formaldehyde resin prepolymer (pre-MF) as flame-retardant material, and cellulose as the supporter. The best ILs for dissolving water-insoluble pre-MF were screened by COSMO-RS, in view of the richness of ILs and the complexity of pre-MF. The logarithmic activity coefficients (ln gamma) of three models were calculated to evaluate the dissolution ability of pre-MF in 432 ILs. According to the results of ln gamma and excess enthalpies, anions play a leading role in the dissolution process of pre-MF in ILs, while cations have little effect on it. The solubility experiments of pre-MF in 8 ILs were determined, which are consistent with the trend of ln gamma predicted. It is important that the ILs composed of OAc-, Dec(-), HCOO-, DEP-, DBP-, DMP-, Ben(-), Cl-, and Br- and different cations studied in this work have good dissolution ability for pre-MF. Besides, MF/cellulose composite flame-retardant fibers were prepared finally using EmimDEP as the solvent and cellulose as the supporter with good mechanical properties and flame retardancy: the breaking strength and limiting oxygen index are 2.24 cN/dtex and 31%, respectively.