Biodegradable silica rubber core-shell nanoparticles and their stereocomplex for efficient PLA toughening

Zibiao Li, Joseph K. Muiruri, Warintorn Thitsartarn, Xing Zhang, Beng Hoon Tan, Chaobin He

Index: 10.1016/j.compscitech.2018.02.026

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Abstract

In the effort to overcome the shortcomings such as brittleness and poor mechanical stability, and increase the competitive edge of renewable poly(lactic acid) PLA over conventional petroleum-based thermoplastics, silica rubber core-shell nanoparticles for effective PLA toughening were successfully synthesized by sequential ring opening polymerization (ROP). The core-shell structure was designed with silica as inner core, P(CL-mLA) as ‘rubber’ middle layer and terminal PDLA chains (SiO2-r-PDLA), to facilitate the stereocomplex formation with PLLA matrix for enhanced interface control. The PLLA/SiO2-r-PDLA nanocomposites were fabricated through solution blending-injection molding process. Nuclear magnetic resonance (1H NMR and 13C NMR) results confirmed the presence of grafted ’rubber’ and PDLA chains from the surface of silica particle. In addition, PLLA/SiO2-r-PDLA nanocomposites showed tremendous improvement in thermal and mechanical properties using differential scanning calorimetry (DSC) and tensile testing, respectively. Besides the formation of stereocomplex in the nanocomposites, a detailed study on the melt stability of these stereocomplex nanocomposites revealed a ‘memorized’ stereocomplex behavior, i.e., having the ability to perfectly reassemble after re-crystallization from melt (melt memory effect), when rubber segment is present. Finally, structure-deformation mechanisms were studied using scanning electron microscopy (SEM) and small angle x-ray scattering (SAXS). From SAXS, crazing was clearly observed whereas SEM revealed fibrillated structures. Thus, crazing and fibrillation are the key deformation mechanisms in PLLA/SiO2-r-PDLA system. The exciting new fillers could open up new horizons for PLA advanced composites applications.