The effect of cellulose nanocrystals (CNCs) on the microstructure of amorphous polyetherimide (PEI)-based nanocomposite fibers and its correlation with the mechanical properties

Abstract

Polyetherimide (PEI) and PEI/cellulose nanocrystal (CNC) fibers are dry-jet wet-spun in a draw ratio (DR) range of 2.8–7. The effect of CNC concentration (0–5 wt% with respect to polymer) on the mechanical and structural properties is also studied. At a DR of 7, control PEI fibers exhibit 466 MPa and 8.1 GPa of tensile strength and modulus, while those of PEI/CNC3 fibers are 409 MPa and 9.2 GPa, respectively, which are among the best properties reported so far for PEI-based materials. The tensile strengths of CNC-containing fibers are inferior to that of the control fiber. On the contrary, the PEI/CNC nanocomposite fibers show improved tensile moduli. Although the improvement in tensile moduli of polymer fibers by incorporating nanofillers is well-known phenomenon, the structural analysis reveals interesting orientation behavior of CNCs and PEI chains. The CNCs are readily aligned along the fiber axis due to their fibrillar morphology, and show a high degree of orientation in the as-spun fibers (fCNC, as-spun = 0.63), which can be further aligned upon drawing (fCNC, drawn = 0.75), whereas the PEI chains exhibit a low degree of orientation even at the maximum extent of drawing (fPEI, composite drawn = 0.10). This is even lower than that in the control fiber (fPEI, control drawn = 0.22), suggesting that the CNCs disturb PEI alignment despite of strong hydrogen bond between them.