Ji-hong Zhang

Super toughened immiscible polycarbonate/poly(L-lactide) blend achieved by simultaneous addition of compatibilizer and carbon nanotubes

Polycarbonate/poly(L-lactide) (PC/PLLA) blend exhibits great potential application in several fields, including package, toy, electronic element and automobile. However, the poor mechanical properties of the immiscible PC/PLLA blend restrict its application. In this work, a compatibilizer maleic anhydride grafted ethylene–octene copolymer (EOR-g-MAH) and functionalized carbon nanotubes (F-CNTs) were introduced into the immiscible PC/PLLA blend by simple melt-compounding processing. Mechanical property measurements showed that even at low environmental temperature (0 °C), the blend composites exhibited excellent fracture toughness, e.g. 40.9 ± 2.1 kJ m−2 at F-CNT content of 2 wt%. To better understand the toughening mechanism, the morphologies of the blend composites and the dispersion of F-CNTs and the rheological properties were systematically investigated. The results showed that with the combined effects of EOR-g-MAH and F-CNTs, the decreased PLLA particles were achieved. Most of F-CNTs selectively located in the PC matrix and some F-CNTs entered into PLLA particles. Specifically, at relatively high content (>2 wt%), F-CNTs formed percolated network structure. Then, the toughening mechanism was proposed on the basis of the morphology evolution, the formation of F-CNT network structure and the impact-fractured surface morphologies. This work demonstrated that even for the immiscible polymer blend, the super toughened blend composites could be achieved by the combined effects of compatibilizer and carbon nanotubes, and therefore it provides an alternative strategy for largely improving the fracture toughness of immiscible polymer blends.

Largely improved fracture toughness of an immiscible poly(L-lactide)/ethylene-co-vinyl acetate blend achieved by adding carbon nanotubes

In this work, different contents of CNTs were introduced into an immiscible poly(L-lactide)/ethylene-co-vinyl acetate (PLLA/EVA) blend that exhibited a sea-island structure to further demonstrate the toughening probability of CNTs on the immiscible polymer blends. The fracture toughness was evaluated through impact measurements. The impact-fractured surface morphologies as well as the morphological changes of the blend induced by adding CNTs were characterized using scanning electron microscope. Furthermore, rheological properties and glass transition behaviors of samples were comparatively investigated to better understand the toughening mechanisms. The results demonstrated that although the presence of CNTs resulted in the formation of EVA particles with irregular shape and simultaneously increased diameters and matrix ligament thickness, which were usually thought to be unfavorable for the improvement of fracture toughness according to the Wus toughening mechanism, the blend composites still exhibited largely enhanced fracture toughness compared with the binary blend, and the impact strength increased gradually with increasing content of CNTs. The plastic deformation ability of PLLA matrix during the fracture process was greatly enhanced, especially when CNTs formed the physical network structure. Further results demonstrated that the glass transition behavior of EVA particles was greatly influenced by CNTs. Then, the toughening mechanism was proposed on the basis of the morphological changes of EVA particles, the formation of CNT physical network structure and the glass transition behavior of EVA. The other mechanical properties were also measured and analyzed. This work further demonstrated the toughening effect of CNTs on the immiscible polymer blends, and the methodology can be widely adopted in industry application.

Crystallization of poly( l -lactide) in the miscible poly( l -lactide)/poly(vinyl acetate) blend induced by carbon nanotubes

In this work, carbon nanotubes (CNTs) were introduced into miscible poly(l-lactide)/poly(vinyl acetate) (PLLA/PVAc) blend and the crystallization behaviors of PLLA with the presence of PVAc and CNTs are systematically discussed. The dispersion state of CNTs was characterized using scanning electron microscope, and the crystallization behaviors of PLLA in different conditions including melt crystallization and cold crystallization were comparatively investigated using polarized optical microscope, differential scanning calorimetry and wide angle X-ray diffraction. The results showed that the crystallization of PLLA was greatly restricted by PVAc. CNTs exhibit apparent nucleation effect, promoting the occurrence of both melt crystallization and cold crystallization. However, the nucleation effect of CNTs in the ternary composites is weakened as compared with that in the binary PLLA/CNTs composites. It was suggested that the relatively higher interfacial affinity between PVAc and CNTs, which possibly resulted in more PVAc molecule rather than PLLA molecule around the surface of CNTs, was the main reason for the reduced nucleation efficiency.