Compatibilizing Biodegradable Poly(lactic acid)/polybutylene adipate-co-terephthalate Blends via Reactive Graphene Oxide for Screw-Based 3D Printing.

Vinyl-functionalized graphene oxide (VGO) was used as a reactive compatibilizer to prepare poly(lactic acid)/polybutylene adipate-co-terephthalate (PLA/PBAT) blends. The linear rheological and scanning electron microscopy results confirmed that the VGO nanosheets were quite efficient in compatibilizing PLA/PBAT blends. The size of the PBAT dispersed phase was remarkably decreased in the presence of VGO nanosheets. Moreover, the VGO nanosheets exhibited strong nucleating effects on the crystallization process of PLA. The crystallinity of PLA component in the compatibilized blend with various VGO nanosheets was higher than 40%, upon the cooling rate of 20 °C/min. The prepared PLA/PBAT pellets were applied to 3D printing, using a self-developed screw-based 3D printer. The results showed that all the prepared PLA/PBAT blend pellets can be 3D printed successfully. The notched Izod impact test results showed that, in the presence of VGO, an increase of at least 142% in impact strength was achieved for PLA/PBAT blend. This could be attributed to the compatibilizing effect of the VGO nanosheets. Thus, this work provides a novel way to prepare tough PLA-based materials for 3D printing.

Non-Isothermal Crystallization Kinetics of Polyether-Ether-Ketone Nanocomposites and Analysis of the Mechanical and Electrical Conductivity Performance.

High-performance polyether-ether-ketone (PEEK) is highly desirable for a plethora of engineering applications. The incorporation of conductive carbon nanotubes (CNTs) into PEEK can impart electrical conductivity to the otherwise non-conductive matrix, which can further expand the application realm for PEEK composites. However, a number of physical properties, which are central to the functionalities of the composite, are affected by the complex interplay of the crystallinity and presence of the nanofillers, such as CNTs. It is therefore of paramount importance to conduct an in-depth investigation to identify the process that optimizes the mechanical and electrical performance. In this work, PEEK/CNTs composites with different carbon nanotubes (CNTs) content ranging from 0.5 to 10.0 wt% are prepared by a parallel twin-screw extruder. The effects of CNTs content and annealing treatment on the crystallization behavior, mechanical properties and electrical conductivity of the PEEK/CNTs composites are investigated in detail. A non-isothermal crystallization kinetics test reveals a substantial loss in the composites' crystallinity with the increased CNTs content. On the other hand, mechanical tests show that with 5.0 wt% CNTs content, the tensile strength reaches a maximum at 118.2 MPa, which amounts to a rise of 30.3% compared with the neat PEEK sample after annealing treatment. However, additional annealing treatment decreases the electrical conductivity as well as EMI shielding performance. Such a decrease is mainly attributed to the relatively small crystal size of PEEK, which excludes the conductive fillers to the boundaries and disrupts the otherwise conductive networks.

Ultrahigh and Tunable Electromagnetic Interference Shielding Performance of PVDF Composite Induced by Nano-Micro Cellular Structure.

Lightweight and efficient electromagnetic interference (EMI) shielding materials play a vital role in protecting high-precision electronic devices and human health. Porous PVDF/CNTs/urchin-like Ni composites with different cell sizes from nanoscale to microscale were fabricated through one-step supercritical carbon dioxide (CO2) foaming. The electrical conductivity and electromagnetic interference (EMI) shielding performance of the composites with different cell sizes were examined in detail. The results indicated that the nanoscale cell structure diminishes the EMI shielding performance of the composite, whereas the microscale cell structure with an appropriate size is beneficial for improving the EMI shielding performance. A maximum EMI shielding effectiveness (SE) of 43.4 dB was achieved by the composite foams which is about twice that of the solid composite. Furthermore, as the supercritical CO2 foaming process reduces the density of the composite by 25-50%, the EMI SSE (specific shielding effectiveness)/t(thickness) of the composite reaches 402 dB/(g/cm2), which is the highest value of polymer foam obtained to the best of the authors' knowledge. Finally, compression tests were performed to show that the composites still maintained excellent mechanical properties after the supercritical CO2 foaming process.

Preparation of high-expansion open-cell polylactic acid foam with superior oil-water separation performance.

Environmentally friendly and non-toxic polylactic acid (PLA) foam has shown great application prospects in heat preservation, adsorption and other fields. However, it is still challenging to prepare high-expansion PLA foam. Herein, a cooling batch foaming process under supercritical CO2 (sc-CO2), based on pre-melted non-crystalline state, was proposed to prepare PLA foams with high expansion ratio. The CO2 dissolved in the polymer melt will lower the crystallization temperature of PLA. Due to the lack of crystallization, the foaming temperature of PLA can be reduced, which increases the CO2 saturation and helps foam. When foaming is triggered before crystallization, ultrahigh expansion foam can be produced. Based on pre-melting treatment, the maximum expansion ratio of PLA has reached 59.7-fold. At the same time, an open-pore structure is produced by this method, which can selectively absorb oil from water. In addition, the adsorption capacity of CCl4 reaches 15 g/g, and there is no significant attenuation in 20 adsorption-desorption cycles. This work provides a green, solvent-free method to prepare biodegradable oil-adsorbing foam.

Highly stretchable and self-foaming polyurethane composite skeleton with thermally tunable microwave absorption properties.

Stretchable and lightweight polymer composite material possessing tunable microwave absorption (MA) properties under thermal radiations remain a significant challenge. Here, we proposed a facile strategy to fabricate stretchable, magnetic composite skeletons by incorporating the tadpole-like CNTs@Fe3O4nanoparticles into self-foaming polyurethane (PU) matrix and the electromagnetic responsive of CNTs@Fe3O4/PU composite foams with different CNTs contents under heating-cooling cycle in a temperature range of 253 -333 K were carefully investigated. Enhanced complex permittivity and shifting peak frequency were observed at elevated temperatures. For instance, the 70-CNTs@Fe3O4/PU sample with 15 wt% loading content at 333 K exhibits excellent MA properties including a minimum reflection loss (RLm) of -66.9 dB and ultrabroad effective frequency bandwidth (RL ≤ -20 dB) of 9.98 GHz at the thickness of 1.58-3.37 mm. Meanwhile, great recoverability in terms of RL-fprofile was achieved in the process of thermal cooling back to 253 K. Such adjustable MA property was attributed to the well-matched impedance and dramatic attenuation ability, benefiting from the temperature-dependant electrical conductivity, abundant interfacial polarization and interior microcellular structures. Besides, the rising temperature increased the sample elongation and electrical conductivity with a slight sacrifice of maximum tensile strength. This stretchable PU skeleton with a unique assembly of CNTs and Fe3O4nanoparticles are expected to be promising candidates as smart absorbers for application in the harsh environments.

Thermal-Recoverable Tough Hydrogels Enhanced by Porphyrin Decorated Graphene Oxide.

Artificial tissue materials usually suffer properties and structure loss over time. As a usual strategy, a new substitution is required to replace the worn one to maintain the functions. Although several approaches have been developed to restore the mechanical properties of hydrogels, they require direct heating or touching, which cannot be processed within the body. In this manuscript, a photothermal method was developed to restore the mechanical properties of the tough hydrogels by using near infrared (NIR) laser irradiation. By adding the porphyrin decorated graphene oxide (PGO) as the nanoreinforcer and photothermal agent into carrageenan/polyacrylamide double network hydrogels (PDN), the compressive strength of the PDN was greatly improved by 104%. Under a short time of NIR laser irradiation, the PGO effectively converts light energy to thermal energy to heat the PDN hydrogels. The damaged carrageenan network was rebuilt, and a 90% compressive strength recovery was achieved. The PGO not only significantly improves the mechanical performance of PDN, but also restores the compressive property of PDN via a photothermal method. These tough hydrogels with superior photothermal recovery may work as promising substitutes for load-bearing tissues.

Nanoshaping of glass forming metallic liquids by stretching: evading lithography.

Lithography-free nanomanufacturing by elongation and fracture of glass forming metallic liquid is presented. The viscous metallic liquid confined in a cavity is laterally downsized to nanoscale by stretching. The extent of size-reduction can be controlled by tuning the active volume of liquid and the viscous and capillary stresses. Very high aspect-ratio metal nanostructures can be fabricated without using lithography or expensive molds. A systematic study is performed using glass forming Pt-Cu-Ni-P alloy to understand the effects of viscosity, surface tension, pulling velocity, and cavity size on the evolution of cylindrical liquid column under tension. The results are quantitatively described using a phenomenological model based on lubrication theory and surface tension induced breakup of liquid filaments. A new manufacturing approach based on variable pulling velocity and/or spinning of metallic liquid is proposed for fabrication of complex geometries.