Effects of Emulsifier and Lubricant Formulation on Basalt Fiber Sizing Emulsions and Fiber Performance

Basalt fibers are prone to friction-induced damage during drawing and processing, while sizing emulsion properties significantly affect coating uniformity and fiber protection. This study aimed to optimize basalt fiber sizing formulations by evaluating the effects of emulsifier and lubricant combinations on emulsion characteristics and fiber performance. An industrial sizing formulation was selected as the reference, and three nonionic emulsifiers, namely poly(ethylene glycol) dibasic acid diester (DAPE), poly(ethylene oxide)-poly(propylene oxide) block copolymer (L44) and sorbitan monolaurate (S20) with two lubricants including polyoxyethylene esters of saturated (M) and unsaturated fatty acids (N) were investigated using independent L9(33) orthogonal experiments. A total of 27 formulations were prepared and evaluated based on solids content, viscosity, particle size, centrifugal stability, and surface tension. Six optimized formulations were further validated through fiber drawing tests. The results showed that sizing performance was controlled by the synergistic effects of emulsifier type, dosage, and lubricant ratio. Compared with the original sizing, the optimized formulations increased single-filament tensile strength by 4.46–20.82% and yarn breaking strength by 10.87–34.78%, with RA-1 (1.8% DAPE, 1.0% M, 1.6% N) exhibiting the best performance. After acid exposure, the optimized formulations maintained higher absolute yarn breaking strength than O-2, although relative strength retention varied only slightly among formulations. In contrast, alkaline exposure caused substantial strength loss, with retention rates of 50.94–53.70% and no significant differences among formulations.