Structure and Performance of Cuticles Isolated from Wool Fibers Using Different Approaches

Abstract

Wool cuticles have a complex hierarchical structure and inherent resistance to general chemicals and enzymes. However, data on the structure and properties of the cuticle, which informs its processing and utilization remains scant. In this paper, we successfully isolated flaky cuticles using the ultrasonic technique from wool residues after keratin extraction with combined L-cysteine and urea (Cuticle-L + U). We then characterized and analyzed the chemical structure and thermal stability of the cuticle-L + U and compared it with the raw wool and wool cuticle isolated with the formic acid method (cuticle-FA). Our data show that the cuticle-L + U has a lower disulfide bond content compared to either raw wool or cuticle-FA. The solid-state 13C NMR spectra demonstrated that the raw wool had a higher content of α-helix structures (61.57%), while cuticle-FA (80.08%) and cuticle-L + U (52.32%) had more β-sheet or disorder structures. Differential scanning calorimetry (DSC) analysis indicated that both the cuticle-L + U and cuticle-FA have lower α-helical crystallinity compared to the raw wool, which further proved that the cuticle mainly consists of β-sheet and random coil structure. In addition, TG analysis and SDS-PAGE showed higher thermal stability and insolubility with the cuticle-L + U compared with cuticle-FA.

Keywords

• wool fibers
• cuticle isolation
• keratin
• l-cysteine
• secondary structure
• thermal stability