Electrospun polyamide (PA) 66 nanofiber bundles with high conductivity, improved strength, and robust flexibility were successfully manufactured through simply adsorbing multiwall carbon nanotubes (MWNTs) on the surface of electrospun PA66 nanofibers. The highest electrical conductivity (0.2 S/cm) and tensile strength (103.3 MPa) were achieved for the bundles immersed in the suspension with 0.05 wt % MWNTs, indicating the formation of conductive network from adsorbed MWNTs on the surface of PA66 nanofibers. The decrease of porosity for the bundles immersed in the MWNT dispersion and the formation of hydrogen bond between PA66 nanofibers and MWNTs suggest a superb interfacial interaction, which is responsible for the excellent mechanical properties of the nanocomposite bundles. Furthermore, the resistance fluctuation under bending is less than 3.6%, indicating a high flexibility of the nanocomposite bundles. The resistance of the nanocomposite bundle had a better linear dependence on the temperature applied between 30 and 150 °C. More importantly, such highest working temperature of 150 °C far exceeded that of other polymer-based temperature sensors previously reported. This suggests that such prepared MWNTs-adsorbed electrospun PA66 nanofiber bundles have great potentials in high temperature detectors.

In this study, pre-shear and ultrahigh molecular weight polyethylene (UHMWPE) were introduced to suppress the skin–core structure of injection-molded high density polyethylene (HDPE) parts. The structural characteristics of the injection-molded parts were systematically elucidated through scanning electron microscopy (SEM), two-dimensional wide-angle X-ray diffraction (2D-WAXD) and two-dimensional small-angle X-ray scattering (2D-SAXS). The results showed that oriented lamellae were formed in the core region upon pre-shear, and the orientation level of oriented lamellae in core region was further enhanced with increasing concentration of UHMWPE. More interestingly, a much narrowed orientation gap between the shear region and core region was obtained if the UHMWPE concentration was increased to 5 wt%. Moreover, crystallinity, long period, and lamellar thickness also increased with increasing UHMWPE concentration upon pre-shear. Naturally, the tensile strength of the blend parts was promoted due to the narrowed orientation gap between the shear region and core region along with an enhanced orientation level and increased crystallinity, long period, and lamellar thickness.

A novel highly porous 3-D poly(ɛ-caprolactone) (PCL) scaffold with micro-channels was fabricated by injection molding and diluent acetic acids leaching technologies. In this study, the chitosan fiber was employed to form the microchannel in PCL matrix. The morphology, porosity and mechanical properties of the scaffolds were studied and calculated. It was found that the larger the content of chitosan fiber is, the higher the porosity would be, due to the volumetric expansion of chitosan fiber in PCL matrix during it being leached. In addition, the less the content of chitosan fiber is, the higher the compressive modulus would be.

The strain-sensing behaviors of carbon black (CB)/polypropylene (PP) and carbon nanotubes (CNTs)/PP conductive composites prepared by the vacuum-assisted hot compression were studied and compared. When ten extension-retraction cycles were applied, it was found for CB/PP, the value of the maximum responsivity (ΔR/R0, ΔR—the instantaneous variation of the resistance during the test, R0—the original resistance) decreased gradually with increasing the cycle number, but it began to rise from the seventh cycle. The value of the min ΔR/R0 increased during the whole test. While for CNTs/PP, both the values of the max and min ΔR/R0 decreased rapidly. It is suggested that the different behaviors mainly depend on the distinction in the dimension of the conductive fillers and the preparation technique.

A numerical simulation for the isothermal flow-induced crystallization (FIC) of polymer melt in a simple shear flow is presented. The model is based on a two-phase suspension model established for crystallization and has the advantage of taking into account the polymer melt rheological behavior through the first normal stress difference calculation. A FENE dumbbell model and a rigid dumbbell model are used to describe the amorphous phase and the semi-crystalline phase, respectively. Crystallization is described as a spherulitical nucleation and growth process. The results show that the short-term shear has a large effect on the crystallization dynamics of polymer.Graphical abstractThe evolution of flow-induced crystallinity for shear rate 2 s−1 at different characteristic locations. One can notice that near the location y = 0.1, the polymer undergoes a weak shearing and crystallizes slowly; from the location y = 0.1 to 0.9, the flow-induced crystallinity increases gradually.Highlights► The model is based on a two-phase suspension model established for crystallization. ► A FENE dumbbell model is used to describe the amorphous phase. ► A rigid dumbbell model is used to describe the semi-crystalline phase. ► The crystallinity is calculated through the evaluation of first normal stress difference.

Ultra-thin LLDPE parts were prepared by microinjection molding. Mechanical properties and microstructure of samples before and after annealing at different temperatures (60, 80, 100 °C) were analyzed. Tensile test indicates that toughness has been enhanced at least 7 times after being annealed in parallel with significant increase of tensile strength. Microstructure characterizations, including differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), scanning electronic microscope (SEM) and polarized Fourier transform infrared spectroscopy (FTIR) were performed to investigate the variations of microstructure and to further establish the relationship between microstructure and mechanical properties. It is suggested that the increased crystallinity and perfection of crystals upon annealing are beneficial to the reinforcement. Formation of a stronger physical cross-linking network due to the increase of connecting points is in favor of the enhanced strength as well. Moreover, the notable improvement of toughness in the annealed ultra-thin LLDPE parts is ascribed to combined effects of microvoids developed in both the annealing and deformation process. This work offers a simple approach to prepare ultra-thin LLDPE parts with excellent toughness and strength.

Carbon fiber (CF) woven fabric (52% by weight) reinforced epoxy composite and carbon nanofiber (CNF, 12% by weight) paper coated on the surface of the CF/epoxy composite were fabricated by resin transfer molding (RTM). The surface erosion characteristics of molded CF composites were investigated by sand erosion test using silica particles with a size around 150 μm as the erodent. The eroded surfaces were examined by scanning electron microscopy (SEM) and weight loss. The CNF paper was able to provide a much stronger erosion resistance compared to the CF reinforced epoxy composites, which is attributed to the high strength of CNFs and their nanoscale structure. Finite element (FE) computer simulations were used to qualitative interpret the underlying mechanisms.

Large-scale stereoscopic structured heazlewoodite (Ni3S2) microrod arrays and scale-like microsheets were successfully prepared by a facile and environmentally benign approach, in which deionized water and ethanol were used as the environmentally friendly solvent. Uniform bamboo shoot-like Ni3S2 microrods and scale-like Ni3S2 microsheets were distributed evenly at the surface of a porous three-dimensional nickel substrate. Studies found that the growth process of Ni3S2 is dependent on the reaction temperature and solution polarity. An increase in reaction temperature could achieve a rod structure while an increase in solution polarity could obtain a denser structure. Due to the large surface area and regular morphology, the stereoscopic structured Ni3S2 microrod arrays and scale-like Ni3S2 microsheets were employed as cathode materials for lithium-ion batteries, and the initial discharge capacity of Ni3S2 microrod arrays reached 592 mA h g−1.

The effects of melt structure and shear flow on the polymorphic nature of β-cylindrites were investigated by means of wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), polarized light microscopy (PLM), differential scanning calorimeter (DSC), and Scanning Electron Microscope (SEM). The temperature-resolved SAXS/WAXD experiments indicate that the NMP (near melting point) melting process (the annealing temperature between Tm “the nominal melting temperatures” and Tm0 “the equilibrium melting temperature”) erases the polymer crystalline structure of unit lattice, however, the lamellar structures of iPP can survive in this melt for long time, even annealing (partially melting) temperature above the Tm. We call this incomplete relaxed melt (include survived lamellar structures) as “ordered melt”. The observations from SAXS experiments of ordered melt suggest that between 167 and 180 °C, the long period (L) increases from 29.2 to 48.9 nm (Strobl method) and the lamellar thickness (dc) increases from 9.2 to 12.9 nm with increasing Tm∗. The long period and lamellar thickness changed slightly with increasing melting time. In order to study the effect of ordered structures in NMP melt on crystals structure after shear flow, the shear-induced specimens were prepared by extruding the near melting point (NMP) ordered melt of iPP through capillary die. It was found that, even only very low shear stress (σw = 0.020 MPa) have been applied to ordered melt, the shear-induced β-cylindrites can be observed. Length and number of the β-cylindrites decreases with increasing temperature of ordered melt (Tm∗  = 177–190 °C), and the content of β-iPP remained almost invariant when Tm∗ was set from 177 to 180 °C, however, as Tm∗ was above 180 °C, the β-iPP content obviously decreased. According to the results of shear-induced β-cylindrites from ordered melt, here we proposed the formation process of β-cylindrites, it is suggested that the survived lamellar structures may remain in the NMP ordered melt which can act as shear-precursor during the course of recooling and initiate the shear-induced crystallization. The structures (the size and density of survived lamellar structures) of ordered melt strongly influence by partially melting temperature.

In this study, poly(ε-caprolactone) (PCL)/sodium chloride (NaCl), PCL/poly(ethylene oxide) (PEO)/NaCl and PCL/PEO/NaCl/hydroxyapatite (HA) composites were injection molded and characterized. The water soluble and sacrificial polymer, PEO, and NaCl particulates in the composites were leached by deionized water to produce porous and interconnected microstructures. The effect of leaching time on porosity, and residual contents of NaCl and NaCl/HA, as well as the effect of HA addition on mechanical properties was investigated. In addition, the biocompatibility was observed via seeding human mesenchymal stem cells (hMSCs) on PCL and PCL/HA scaffolds.The results showed that the leaching time depends on the spatial distribution of sacrificial PEO phase and NaCl particulates. The addition of HA has significantly improved the elastic (E′) and loss moduli (E″) of PCL/HA scaffolds. Human MSCs were observed to have attached and proliferated on both PCL and PCL/HA scaffolds. Taken together, the molded PCL and PCL/HA scaffolds could be good candidates as tissue engineering scaffolds. Additionally, injection molding would be a potential and high throughput technology to fabricate tissue scaffolds.Highlights►PCL/NaCl, PCL/PEO/NaCl and PCL/PEO/NaCl/HA composites were injection molded. ►Leaching time depends on the distribution of PEO phase and NaCl particulates. ►The elastic and loss moduli of PCL/HA scaffolds have significantly improved. ►Human hMSCs have attached, survived and proliferated well on PCL and PCL/HA scaffolds. ►Molded PCL and PCL/HA scaffolds could be good candidates for tissue engineering.

Polyamide 66 (PA 66) nanofibers, with the mean diameter of about 140 nm, were prepared by electrospinning. Nano-hybrid shish-kebab (NHSK) structure was achieved in PA 66 nanofibers/isotactic polypropylene (iPP) composites via isothermal solution crystallization. The morphology of such NHSK was observed by scanning electron microscopy (SEM). It was found that PA 66 nanofibers act as “shish”, and iPP crystals serve as “kebabs”. Furthermore, the concentration of iPP solution remarkably affects the morphology of the NHSK, i.e., the size of iPP crystals becomes much bigger with the increasing iPP solutions' concentration. The reason for this can be explained as that the high concentration of iPP solutions contain more free chains which can participate into the process of crystallization.

Formation of β-cylindrites of isotactic polypropylene under various wall shear stress (σw), supercooled temperature of melt (Te) and crystallization temperature (Tc) has been investigated by polarized light microscopy (PLM), wide angle X-ray diffraction (WAXD), and differential scanning calorimeter (DSC). To have better control over the thermomechanical history, instead of a reciprocating screw, the samples were prepared by extruding supercooled melt through capillary die. β-cylindrites can be observed by PLM in the extruded specimen even at a lower σw (0.020 MPa), and the number of β-cylindrites nuclei increases rapidly with the lowering of Te. The nucleation density of β-cylindrites increases with the raising of wall shear stress under a given Te of 160 °C. Furthermore, at lower supercooled temperature of melt (145 °C), the radius of β-cylindrites decreases with the increasing of σw, and the number of β-cylindrites nuclei almost remain invariant. At relatively higher σw (0.090 MPa), a saturation of β-cylindrites nuclei is observed with decreasing Tc. A modified model based on above results has been proposed to explain the effect of the original structure of quiescent supercooled melt on the formation of β-cylindrites under low shear stress.

Nanohybrid shish–kebab (NHSK), induced by polyamide 66 (PA66) nanofiber, was successfully fabricated in high-density polyethylene (HDPE)/xylene solution via isothermal crystallization. The crystalline morphological features of NHSK were observed by scanning electron microscopy. In the structure of NHSK, PA66 nanofiber serves as shish and HDPE lamellae act as kebabs periodically surrounding the nanofiber. Additionally, it reveals that both HDPE solution concentration and crystallization time have significant effects on the size of HDPE kebab. That is, as the concentration and crystallization time increase, the diameter of the kebab increases. Moreover, when crystallization time further increases, the crystals decorated on PA66 nanofiber exhibit a three-dimensional growth (i.e., aggregate of crystallites) rather than a two-dimensional one (i.e., disk-like lamellae normal to the axis of nanofiber).