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To enhance the reinforcement effects of regenerated cellulose nanofibers (RC-NF) in poly(ε-caprolactone) (PCL), we synthesized RC-NF-3-aminopropyltriethoxysilane (APS), the surface-modified RC-NF by APS. The RC-NF were fabricated by the saponification of electrospun cellulose-acetate nanofibers. The surface modification by APS was confirmed by the X-ray photoelectron spectroscopy (XPS). To enhance the mechanical property of PCL, the RC-NF and the RC-NF-APS were separately compounded into PCL by compression molding. It was found that, when the fiber concentration of RC-NF-APS was 17 wt %, the Young's modulus at room temperature increased from 698.0 to 744.7 MPa, whereas the storage modulus at 55 C almost increased from 180 to 220 MPa. The micrographs of the fracture surface of the composites revealed that the surface modification prevented the pull-out of RC-NF from PCL. It was concluded that the mechanical properties of the composites were enhanced due to the improvement of the compatibility between RC-NF and PCL by the surface modification with APS.

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Poly(ε‐caprolactone) (PCL) is one of the ecofriendly biodegradable polymers with excellent moldability but with rather low mechanical properties especially for the industrial and biomedical use. In this research, to overcome the problem, the two types of cellulose nanofibers, the cellulose acetate nanofibers (CA‐NF) and the cellulose nanofibers (C‐NF), were composited into PCL for the enhancement of the mechanical properties of PCL. CA‐NF were prepared by electrospinning and converted into C‐NF afterward by deacetylation. It was found that the Young's modulus of the CA‐NF/PCL composite at the fiber concentration of 35 wt% significantly increased by ~3 times as compared with that of neat PCL, whereas C‐NF/PCL of the same fiber concentration also increased by ~4.5 times. It was also found that the Young's moduli of CA‐NF/PCL nearly reached the theoretical values calculated by the equation suggested by Tsai, but that the Young's moduli of C‐NF/PCL could not reach the theoretical values. It indicates that CA‐NF possessed better compatibility with PCL than C‐NF, agreeing well with the fracture‐surface analyses of the two composites by the scanning electron microscopy.

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