Yamin Pan

Wide distribution of shish-kebab structure and tensile property of micro-injection-molded isotactic polypropylene microparts: a comparative study with injection-molded macroparts

In this paper, injection-molded isotactic polypropylene (iPP) microparts and macroparts were respectively fabricated by the molds with different thickness under the same processing conditions. Comparative study on microstructure and mechanical property was carried out by means of scanning electron microscopy (SEM), two-dimensional wide-angle X-ray diffraction (2D-WAXD), two-dimensional small-angle X-ray scattering (2D-SAXS), differential scanning calorimetry (DSC) and tensile test. SEM images reveal that the two parts show distinctly different hierarchical structure. An obvious ‘skin–core’ structure is present for the macroparts, while a wide distribution of shish-kebab structure develops in both shear and core layer for microparts, exhibiting a specific ‘core-free’ morphology. 2D-WAXD, 2D-SAXS and DSC results show that microparts have higher orientation degree and crystallinity as compared to macroparts, which are responsible for the remarkably high tensile strength and modulus. Our work provides a good example for better understanding processing structure–property relationship of iPP through tuning their internal microstructure.

Conductivity and phase morphology of carbon black-filled immiscible polymer blends under creep: an experimental and theoretical study.

Blends of carbon black (CB)-filled co-continuous immiscible polystyrene/poly(methyl-methacrylate) (PS/PMMA) with a PS/PMMA ratio of 50/50 and CB selectively located in the PS phase have been prepared by melt blending. The simultaneous evolution of conductivity and phase morphology of blend composites was investigated under shear and in the quiescent state at 200 °C. It was found that shear deformation had a significant influence on the conductivity of the unfilled PS/PMMA blend and its composites, which was attributed to the change of phase morphology during shear. After the shear stress of 10 kPa, the conductivity of PS/PMMA blends filled with 2 vol% of CB decreased by about two orders of magnitude and the phase morphology transformed from a fine co-continuous structure into a highly elongated lamellar structure. The deformation of phase morphology and the decrease of conductivity were weakened upon decreasing the shear stress or increasing the CB concentration. During subsequent recovery, pronounced phase structure coarsening was observed in the mixture and the conductivity increased as well. A simple model describing the behavior of conductivity under shear deformation was derived and utilized for the description of the experimental data. For the first time, the Burgers model was used to describe the conductivity, and the viscoelastic and viscoplastic parameters were deduced by fitting the conductivity under shear. The results obtained in this study provide a deeper insight into the evolution of phase structure in the conductive polymer blend composite induced by shear deformation.

Reversal phenomena of molten immiscible polymer blends during creep-recovery in shear

In this work, the creep-recovery behavior of immiscible poly (styrene)/poly (methyl methacrylate) blends and their pure components in the molten state were systematically investigated. A stationary plateau in the recoverable compliance of pure components is observed. Unexpectedly, for immiscible polymer blends, the recoverable compliances show different phenomena. For blends with a fine co-continuous morphology, the recoverable compliances exhibit a one-reversal phenomenon, whereas a two-reversal phenomenon is found in the blends with a sea-island morphology. Moreover, these reversal behaviors become less pronounced with decreasing temperature, increasing creep stress, increasing annealing time, or incorporation of nanoparticles. Three competitive effects, i.e., the recovery of oriented polymer matrix, the interfacial tension which drives the deformed droplets to their equilibrium shape, and the phase coarsening process, are used here to explain the different behaviors.

Suppression of the hierarchical structure of water-assisted injection moulded iPP in the presence of a β-nucleating agent and lamellar branching of a β-crystal

The thickness of oriented zones in water-assisted injection moulded β-iPP parts increased with the increasing of β-nucleating agent (β-NA) content. More interestingly, the high β-NA content suppressed the hierarchical structure effectively, which is consistent with the almost invariable crystallinity and orientation. Meanwhile, an unexpected lamellar branching of the β-crystal was observed.

Preparation and Characterization of a Bipolar Membrane Modified by Copper Phthalocyanine 16-Carboxylic Acid and Acetyl Ferrocene

A bipolar membrane (BPM) of carboxymethyl cellulose (CMC) and chitosan (CS) with superior performance was prepared based on the macromolecules containing metal elements. A carboxymethyl cellulose cation layer was modified by copper phthalocyanine 16-carboxylic acid (CuPc(COOH)16) to improve its ion exchange capacity as well as cation transfer rate and promote water splitting at the intermediate layer. Chitosan was crosslinked with acetyl ferrocene to prepare the anion layer. A casting method was used to prepare the BPM which showed excellent physical and chemical properties after modification. To improve the compatibility of the anion-exchange layer and cation-exchange layer, polyethylene glycol (PEG) was blended with both the CMC and CS. Scanning electron microscopy (SEM) images illustrated a structure that consisted of an anion layer and a cation layer that were closely combined with each other. The swelling results implied a proper hydrophilic performance and good shape stability in an alkali solution ([OH−]≤10 mol·L−1) of the BPM. After modification, the BPM with the metal elements exhibited good thermal stability, as shown by the thermogravimetry (TG) results. Compared with the BPM that was unmodified, both the AC impedance and the working voltage were decreased sharply. Furthermore, the modified BPM exhibited higher ion penetrability which is beneficial for its wide application.