Effect of MgO whiskers on thermal behavior and mechanical properties of injection molded poly(L‐lactide)

Poly(L‐lactide) (PLLA) composites containing various content of MgO whiskers (MgO‐Ws) and surface grafted MgO whiskers (g‐MgO‐Ws) were prepared by injection molding technique. The g‐MgO‐Ws showed better dispersion in the matrix and improved interface compatibility with the matrix compared with the MgO‐Ws, which was confirmed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results of differential scanning calorimeter (DSC) and polarized optical microscopy (POM) of the MgO‐Ws/PLLA and g‐MgO‐Ws/PLLA composites revealed that the crystallization rate and crystallinity of PLLA were improved by the introduction of MgO‐Ws and g‐MgO‐Ws, but the thermogravimetric measurements showed that the thermal stability of the PLLA matrix decreased by the addition of the whiskers. The tensile, flexural, and impact properties of the resulting composites were systematically studied, and the g‐MgO‐Ws/PLLA composite exhibited remarkably higher tensile strength, modulus, and toughness than those of the pure PLLA and MgO‐Ws/PLLA composite. The highest tensile strength of 62.9 ± 3.2 MPa, tensile modulus of 1,222.3 ± 25.2 MPa, and fracture energy of 459.1 ± 24.3 J/m² were obtained for the g‐MgO‐Ws/PLLA composite with 2.5% whiskers content, which were 30.8%, 13.7%, and 105.5% higher than those of PLLA matrix, respectively. Loading the whiskers with appropriate content can also improve the flexural and impact properties of the PLLA matrix. The highest impact strength, flexural modulus, and flexural strength were obtained for the g‐MgO‐Ws/PLLA composite with 1% whiskers content. POLYM. COMPOS., 39:E1807–E1820, 2018. © 2018 Society of Plastics Engineers