Adding nanofillers to PLA/PCL blends to change their surface and interface properties can improve their phase morphology. Here the selective localization of CNTs and organoclays as the third component in the blend is studied. It is found that clay is selectively localized in the PLA phase and at the phase interface whereas CNTs are mainly found in the PCL phase and at the phase interface. With a reduced viscosity ratio of the blend matrices, the CNTs change their preferred localization from PCL to PLA. The effects of the different selective localization of clay and CNTs on the morphologies are studied. In addition, the crystallization behavior of ternary systems also shows a strong dependence on the selective localization of nanofillers. magnified image

DC and AC electrical conductivity of bionanocomposites based on the immiscible polymer blend poly(epsilon-caprolactone)/polylactide (PCL/PLA, w/w 70/30), loaded with multiwall carbon nanotubes (CNT), were studied in a wide frequency range, 10(-3) < or = f < or = 10(7) Hz from 143 to 313 K. The nanofiller concentration ranged from 0 to 4 wt % and it was shown to be selectively located in the PCL phase. The PCL crystallinity degree was not affected by the presence of CNT. The variation of the DC conductivity allowed the determination of the percolation threshold, p(c) = 0.98 wt %, and the critical exponent t = 2.2 of the scaling law. The linear dependence of log (sigma(DC)) versus p(-1/3) showed the existence of tunneling conduction among CNT not yet in physical contact. The temperature independent results indicated a conventional tunnel effect. The AC conductivity of the nanocomposites followed the predictions of the universal dynamic response and the s exponents were determined at low concentrations. Master curves are presented showing the length and temperature-time superpositions.

During the solid state foaming, the CO 2 saturated poly(lactic acid) (PLA) sample at 5 MPa and 20 °C has a high crystallinity of 23.2%, and the prepared PLA foams exhibits low foam expansion and nonuniform cell structure. This study presents an interesting effect of nanosilica addition on the cell morphology and expansion ratio of PLA foams. It was found that the presence of nanosilica increased the induced crystallinity of PLA up to 29.7% at 5 MPa. The resultant PLA/silica foams exhibited significant and concurrent increase in cell structure uniformity and cell density: the cell density increased about 5−10 times, the expansion ratio increased 1.4−2.1 times, and the crystallinity of foams increased 1.3 times, compared to pure PLA foams. Further investigation suggested that the formation of the tiny crystallite size and the well dispersed nanosilica aggregates were thought as the main reasons to explain the interesting effect of nanosilica addition on the foaming behavior of PLA.

The selective localization of carbon nanotubes (CNTs) in an immiscible polymer blend has attracted much attention. If the two component polymers could react with each other, do selectively located CNTs affect those reactions? Here, an immiscible polyester blend based on polycarbonate/poly(trimethylene terephthalate) (PC/PTT) is studied. CNTs introduced during melt mixing are selectively located in the PTT phase and on the phase interface during the middle stage of melt mixing. The interface‐located CNTs can act as additional substrate to catalyze or even participate in the transesterification themselves, homogenizing the phase morphology of the matrix blend. The degree of randomness of the composite systems is increased, accompanied by a reduced number‐average length of the copolymer sequences. magnified image

Carbon nanotube (CNT) filled poly(butylene succinate) composites (PBSCNs) were prepared by melt compounding. The oscillatory rheological properties and crystallization behavior and kinetics were then investigated. The results show that the percolation network of CNTs in the small amplitude oscillatory shear flow is temperature dependent and the values of percolation thresholds reduce gradually with an increase of temperature. Therefore, the principle of timeÀtemperature superposition is invalid on the dynamic rheological responses of those percolated PBSCNs. Besides, the presence of CNTs highly promotes the crystallization of PBS, increasing the overall crystallization rate. But the nucleation mechanism of PBS is not altered with addition of CNTs because the PBS itself is nucleated heterogeneously.

In this study, microcellular poly(lactic acid) foams with various crystallinities, cell morphologies, and densities were prepared using CO 2 as the physical blowing agent. The evolution of crystallinity developments of four types of poly(lactic acid) samples during the saturation, foaming, and annealing processes was investigated. Crystallization of about 20% was reached in poly(lactic acid) samples after CO 2 saturation, a high crystallinity of about 38.2% could be achieved for the foamed poly(lactic acid) that has the highest crystallization ability. Poly(lactic acid) samples had low elongation at break of 3.6-15.1%. After foaming, however, poly(lactic acid) foam presented a significant increase in the elongation at break up to 15.1 times compared with that of the unfoamed counterpart. On the other hand, microcellular foaming endowed poly(lactic acid) foams with a maximum increase in specific tensile strength of 53.1%. The influences of crystallinity, foam density, and cell morphology on the tensile properties of poly(lactic acid) foams were investigated.

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Ethylene-vinyl acetate copolymer (EVA)/poly(ε-caprolactone) (PCL) blend (50/50 w/w) with co-continuous morphology was prepared via melt mixing for fabricating microporous EVA membrane materials through selective solvent extraction. Shear flow and quiescent annealing techniques were employed to control co-continuous phase size in the EVA/PCL blend, and the timeand temperature-dependent relations of phase size were then evaluated theoretically. Using these techniques, microporous EVA membrane materials with various pore sizes ranging from 2 µm to more than 200 µm were obtained. In contrast to the porous EVA membrane prepared by the traditional way of solvent casting/particulate leaching, the as-obtained microporous membrane shows a higher level of interconnectivity and much narrower pore size distribution with uniform pore structure.