Abstract:

Objective To address the lengthy process and high energy consumption of microfiber synthetic leather made from staple fibers, this study employed spunbonded alkaline-soluble copolyester/polyamide 6 (COPET/PA6) island-in-sea filament hot-rolled nonwovens as the substrate. The alkali reduction splitting process, which directly affects the physical-mechanical properties and hand feel, was investigated. Additionally, methods to mitigate the significant anisotropy in mechanical properties were explored.

Method Using weight loss and fibrillation rate as evaluation indices, single-factor experiments were carried out to examine the influences of alkali concentration, treatment temperature and time on the fibrillation of the leather substrate. To improve its mechanical properties, the substrate was pretreated with dimethyl silicone oil, then modified with aluminum tannin and tannin extract as crosslinkers. Orthogonal experiments were designed to optimize the synergistic crosslinking modification of the two crosslinkers.

Results In the alkali reduction splitting process, the alkali concentration, treatment temperature, and time significantly influenced the splitting efficacy of the nonwoven substrate. The optimal process parameters were determined as an alkali concentration of 24 g/L, a temperature of 90 ℃, and a duration of 30 min. The splitting effect improved with increasing alkali concentration up to 24 g/L; beyond this level, damage to the substrate occurred. The splitting rate was rapid below 90 ℃ but decreased above this temperature, which also caused substrate damage. As treatment time extended, the splitting effect exhibited two distinct stages, with 30 min as the critical threshold. To address the significant anisotropy in mechanical properties between the machine and transverse directions of the island-in-sea filament microfiber synthetic leather substrate, modification treatments were conducted to enhance the mechanical performance and reduce directional disparity. Experimental results indicated that with 1.0% dimethicone addition, the differences in breaking strength and tearing strength between the two directions reached their minimum. Building on this foundation, the effects of two crosslinking agents-aluminum tannin and wattle extract-on the mechanical properties of the substrate were investigated, and the combined crosslinking modification process was optimized. The optimal formulation was determined to be 8% aluminum tannin combined with 6% wattle extract. Fourier transform infrared spectroscopy confirmed the successful occurrence of crosslinking reactions. Following the combined crosslinking modification, the moisture permeability of the substrate improved, while air permeability and softness exhibited slight reductions.

Conclusion This study successfully established an alkali reduction splitting process for COPET/PA6 island-in-sea filament microfiber synthetic leather substrates, achieving a high degree of openness while minimizing the impact on mechanical properties. Furthermore, a combined crosslinking modification using aluminum tannin and wattle extract effectively mitigated the anisotropy in mechanical properties and enhanced the overall mechanical performance of the filament-based microfiber substrate. The resulting microfiber leather substrate demonstrates potential for applications in garments and decorative materials. This research provides a viable solution to address the challenges of lengthy production processes and high energy consumption associated with conventional microfiber synthetic leather. However, although the combined crosslinking modification effectively improved mechanical properties, it led to a slight decrease in air permeability and softness. Future research should focus on exploring modification techniques to minimize these adverse effects on wear comfort.

Key words: microfiber synthetic leather, island-in-sea filament, nonwoven fabric, alkali deweighting process, mechanical property