Microstructure and mechanical properties of carboxylated carbon nanotubes/poly(L-lactic acid) composite

Poly(L-lactic acid) (PLLA)/MWNTs composites were prepared by mixing solubilized PLLA with solutions of MWNTs treated by four kind of acids. Fourier transform infrared (FT-IR) spectra revealed that carboxyl groups were grafted to the surface of MWNTs. The water solubility showed that the MWNTs treated by HNO₃/H₂O₂ and HNO₃/H ₂SO₄ could suspend in the air at room temperature for more than 100 days. Thermogravimetric analysis (TGA) showed that MWNTs treated by HNO₃/H₂O₂ and HNO₃/H ₂SO₄ obtained relatively high COOH content. Mechanical properties of composites showed that the Young's modulus of the carboxylated MWNTs/PLLA composites increased compared to the pure PLLA. Scanning electron microscopy (SEM) images of fracture morphology confirmed that the dispersion of carboxylated MWNTs was more homogeneous than the pristine MWNTs in polymer matrix. MWNTs treated by HNO₃/H₂O₂ could get more COOH group and less damage.