Study On Carbon Nanotubes Induced Microstructure And Properties Variations Of Polylactide Based Blend Composites

In recent years, nanocomposites have arisen researchers’attention due to their excellent comprehensive properties. Among them, the researches related to carbon nanotubes (CNTs) filled nanocomposites have been carried out extensively. With the advantages of large aspect ratio, high strength an modulus, excellent electrical and thermal conductivities, CNTs have been widely applied in the modifications of polymers, which greatly enhances the comprehensive properties of polymers. However, the introduction of CNTs exhibits a very limited effect on the property enhancement of the nanocomposite containing single polymer. Meanwhile, high content of CNTs is required to satisfy the enhancement of properties, which results in the high cost of nanocomposites. Therefore, the one-phase nanocomposite cannot satisfied the gradually increasing application demands, which makes it necessary for researches and developments of blend nanocomposites. The properties of the blend nanocomposite depend on not only the intrinsic characteristics of different components, but the morphology of the blend nanocomposites and the selective location of CNTs in the blend nanocompoistes.In this work, with the incorporation of CNTs, functionalized blend nanocomposites were achieved through melt-blending. Firstly, we aimed to investigate the effect of the selective location state of CNTs in the immiscible blend on the electrical conductivity of blend nanocomposites; secondly, the effect of CNTs on the morphology evolution was investigated through adjusting the processing conditions; finally, the investigation abou the effect of CNTs network structure on the shape memory behavior of blend nanocomposites were carried out through adjusting both microstructures of blend composites and the selective location of CNTs. Some result were obtained as follows:(1) PLLA grafted maleic anhydride(PLLA-g-MA) was successfully prepared through melt blending processing. Due the combined effects of the polarity and viscosity of PLLA-g-MA, CNTs selectively located at the interface between PLLA and high density polyethylene (HDPE), which leaded to the relatively low percolation threshold for the electrical conductivity (0.49 wt%). While, it could be concluded through the morphology observation that the introduction of CNTs accelerated the morphology evolution of the blend nanocomposite during the melt blend processing.(2) PLLA-g-MA/HDPE and PLLA-g-MA/HDPE/CNTs were prepared under different processing conditions, among which three different shear strengths and blending durations were chosen, respectively. Through the morphology observation and the rheological analysis, it was conclusively demonstrated that the incorporation of CNTs accelerated the morphology evolution of blend nanocomposites prepared under different shear strengths and with different blending durations. The rolf of CNTs in the morphological evolution of the blend nanocomposites could be understood as follows:on one hand, the presence of CNTs leaded to the increase of viscosity of the nanocomposite and the local shear stress increased accordingly, which accelerated the deformation and breakage of dispersed phases; on the other hand, the coalescence of dispesed phases was inhibited due to the selective location of CNTs at the interface of the blend nanocomosites, which leaded to the decrease of dispersed phase size.(3) PLLA/Thermoplastic polyurethane (TPU)/CNTs nanocomposites were prepared through a two-step method with TPU as the master batch. Microstructure characterization showed that CNTs distributed in the TPU phase. While, due to the filling effect of CNTs, the gradually increased TPU phase size was obtained as the CNTs content increased. In terms of the heat-induced shape memory behavior investigated at different temperatures, it was demonstrated that the mobility of TPU chains was greatly hindered by the network structure of CNTs, which further suppressed the shape recovery. For electric-induced shape memory behavior investigated at different temperatures, it depended on the competing effects between the hinderance effect of CNT network structure on the chain mobility of TPU and the enhanced chain mobility induced by the heat generation induced by the electricity. Further results demonstrated that increasing temperature was in favor of the shape recovery for both heat- and electric-induced shape memory behaviors of the PLLA/TPU/CNTs blend nanocomposites.