Electrical properties of polypropylene-based composites controlled by multilayered distribution of conductive particles

The Electrical Conductivity and Mechanical Properties of Monolayer and Multilayer Nanofibre Membranes from Different Fillers: Calculated Based on Parallel Circuit

Advanced research on improving the performance of conductive polymer composites is essential to exploring their potential in various applications. Thus, in this study, the electrical conductivity of multilayer nanofibre membranes composed of polyvinyl alcohol (PVA) with different electroconductive fillers content including zinc oxide (ZnO), multiwalled carbon nanotubes (MWNTs), and Ferro ferric oxide (Fe₃O₄), were produced via electrospinning. The tensile property and electrical conductivity of monolayer membranes were explored. The results showed that PVA with 2 wt.% MWNTs nanofibre membrane has the best conductivity (1.0 × 10^-5 S/cm) and tensile strength (29.36 MPa) compared with other fillers. Meanwhile, the combination of multilayer membrane ZnO/Fe₃O₄/Fe₃O₄/MWNTs/ZnO showed the highest conductivity (1.39 × 10^-5 S/cm). The parallel circuit and calculation of parallel resistance were attempted to demonstrate the conductive mechanism of multilayer membranes, which can predict the conductivity of other multilayer films. The production of multilayer composites that enhance electrical conductivity and improve conductive predictions was successfully explored.

"Toolbox" for the Processing of Functional Polymer Composites

The processing methods of functional polymer composites (FPCs) are systematically summarized in “Toolbox”. The relationship of processing method-structure-property is discussed and the selection and combination of tools in processing among different FPCs are analyzed. A promising prospect is provided regarding the design principle for high performance FPCs for further investigation.

ABSTRACT

Functional polymer composites (FPCs) have attracted increasing attention in recent decades due to their great potential in delivering a wide range of functionalities. These functionalities are largely determined by functional fillers and their network morphology in polymer matrix. In recent years, a large number of studies on morphology control and interfacial modification have been reported, where numerous preparation methods and exciting performance of FPCs have been reported. Despite the fact that these FPCs have many similarities because they are all consisting of functional inorganic fillers and polymer matrices, review on the overall progress of FPCs is still missing, and especially the overall processing strategy for these composites is urgently needed. Herein, a “Toolbox” for the processing of FPCs is proposed to summarize and analyze the overall processing strategies and corresponding morphology evolution for FPCs. From this perspective, the morphological control methods already utilized for various FPCs are systematically reviewed, so that guidelines or even predictions on the processing strategies of various FPCs as well as multi-functional polymer composites could be given. This review should be able to provide interesting insights for the field of FPCs and boost future intelligent design of various FPCs. [Image: see text]

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40820-021-00774-5.

Preparation and properties of silicone rubber materials with foam/solid alternating multilayered structures

In this paper, silicone rubber materials with foam/solid alternating multilayered structures were successfully constructed by combining the two methods of multilayered hot-pressing and supercritical carbon dioxide (SCCO2) foaming. The cellular morphology and mechanical properties of the foam/solid alternating multilayered silicone rubber materials were systematically studied. The results show that the growth of the cell was restrained by the solid layer, resulting in a decrease in the cell size. In addition, the introduction of the solid layer effectively improved the mechanical properties of the microcellular silicone rubber foam. The tensile strength and compressive strength of the foam/solid alternating multilayered silicone rubber materials reached 5.39 and 1.08 MPa, which are 46.1% and 237.5% of the pure silicone rubber foam, respectively. Finite element analysis (FEA) was applied and the results indicate that the strength and proportion of the solid layer played important roles in the tensile strength of the foam/solid alternating multilayered silicone rubber materials. Moreover, the small cellular structures in silicone rubber foam can provided a high supporting counterforce during compression, meaning that the microcellular structure of silicone rubber foam improved the compressive property compared to that for the large cellular structure of silicone rubber foam.

Nacre-Inspired Polymeric Materials with Body Heat-Responsive Shape-Memory Effect, High Optical Transparence, and Balanced Mechanical Properties

In this work, inspired by the hierarchical architecture of nacre, we have fabricated poly(propylene carbonate) (PPC)/thermoplastic polyurethane (TPU) alternating multilayer films via layer-multiplying coextrusion. Based on the glass transition at around 37 °C of PPC, the multilayer films exhibited an outstanding body heat-responsive shape-memory effect (SME) with high shape fixation and recovery ratios (96.1 and 93.6%), much better than the conventional cocontinuous blend with the same compositions. It was revealed that the high phase continuity and abundantly two-dimensional interfaces both capable of promoting stress transferring and load distribution maximally contributed to the SME. Furthermore, the multilayer films showed a superior recovery stress storage capacity and the force generated by shape recovery allowed automatic expansion of the spiral in 37 °C water and efficient lifting of a load 880 times its weight. Different from the opacity of the blend, a high optical transparence was observed in the multilayers because of the parallel assembly of transparent PPC and TPU enabling light to directly pass through the films. Besides, the nacre-like films had layer debonding and layer stepwise breaking during stretching, resulting in a 90% increase in tensile strength, a 70% increase in elongation at break, and onefold improvement in yield stress, compared with those of the blend. Our approach paves a new way for developing bioinspired structural materials with excellent optical, mechanical, and shape-memory properties, which can be extended to different amorphous polymers and elastomers. Also, the materials presented herein have great potential in applications of biomedical devices and soft robotics.

The Effect of MWCNTs Filler on the Absorbing Properties of OPEFB/PLA Composites Using Microstrip Line at Microwave Frequency

Oil palm empty fruit bunch (OPEFB) fiber/polylactic acid (PLA)-based composites filled with 6–22 wt.% multi-walled carbon nanotubes (MWCNTs) were prepared using a melt blend method. The composites were analyzed using X-ray diffraction (XRD), Fourier transforms infrared (FTIR), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) of the MWCNTs. The composites were characterized for complex permittivity using the coaxial probe at 8–12 GHz range and the transmission/reflection coefficients were measured through micro strip line. The dielectric permittivity measurements carried out at X-band frequency revealed that 22 wt.% MWCNTs nanocomposite display higher dielectric constant (ε′) and dielectric loss (ε″) values of 4.23 and 0.65, respectively. A maximum absorption loss of 15.2 dB was obtained for the 22 wt.% nanocomposites at 11.75 GHz. This result suggests that PLA/OPEFB/MWCNTs composites are a promising cheap and lightweight material for the effective microwave absorption in the X-band frequency range.

Designing a Polymer-Based Hybrid with Simultaneously Improved Mechanical and Damping Properties via a Multilayer Structure Construction: Structure Evolution and a Damping Mechanism

Though hindered phenol/polymer-based hybrid damping materials, with an excellent loss factor, attract more and more attention, the significantly decreased mechanical property and the narrow damping temperature range limit the application of such promising materials. To solve the problems, a polyurethane (hindered phenol)/polyvinyl acetate multilayer system with varied layer numbers was prepared in this study. The multilayer microstructures were first verified through the scanning electron microscopy. A subsequent molecular dynamics simulation revealed the promoted diffusion of polyurethane (hindered phenol) and polyvinyl acetate layers, the compact chain packing of the polyurethane (hindered phenol) layer, the extended chain packing of the polyvinyl acetate layer, the intermolecular hydrogen bonds among the three components and the enhanced interface interactions between the two layers in a quantitative manner. Further the mechanical and dynamic mechanical analysis detected the successful preparation of the multilayer hybrids with simultaneously improved mechanical and damping properties. Then, by a combination of molecular dynamics simulation and experiment, the relationship between the structure evolution and the properties of the multilayer hybrids was established, which was expected to have some guiding significance for industrial production.

A self-assembled, nacre-mimetic, nano-laminar structure as a superior charge dissipation coating on insulators for HVDC gas-insulated systems

Nacre is well-known for its unique properties due to its "bricks-and-mortar" structure. We employed this biological paradigm to fabricate nano-laminar coatings with controlled arrangement of montmorillonite (MMT) nanoclay sheets and polyvinyl alcohol (PVA) polymer binders by a self-assembly process. The abundant inorganic/organic interfaces were demonstrated to play critical roles in enhancing charge dissipation laterally on the insulator surface, so that the surface charge accumulation is suppressed under dc stress. Moreover, the stacking barriers help to protect insulator surfaces from hot electron bombardment, inhibiting further electron avalanche. In this manner, the flashover strength of the insulator is improved by 18%. This strategy is practical and scalable, allowing for industrial applications.

Flame Retardant Polypropylene Composites with Low Densities

Polypropylene (PP) is currently widely used in areas requiring lightweight materials because of its low density. Due to the intrinsic flammability, the application of PP is restricted in many conditions. Aluminum trihydroxide (ATH) is reported as a practical flame retardant for PP, but the addition of ATH often diminishes the lightweight advantage of PP. Therefore, in this work, glass bubbles (GB) and octacedylamine-modified zirconium phosphate (mZrP) are introduced into the PP/ATH composite in order to lower the material density and simultaneously maintain/enhance the flame retardancy. A series of PP composites have been prepared to explore the formulation which can endow the composite with balanced flame retardancy, good mechanical properties, and low density. The morphology, thermal stability, flame retardancy, and mechanical properties of the composites were characterized. The results indicated the addition of GB could reduce the density, but decreased the flame retardancy of PP composites at the same time. To overcome this defect, ATH and mZrP with synergetic effect of flame retardancy were added into the composite. The dosage of each additive was optimized for achieving a balance of flame retardancy, good mechanical properties, and density. With 47 wt % ATH, 10 wt % GB, and 3 wt % mZrP, the peak heat release rate (pHRR) and total smoke production (TSP) of the composite PP-4 were reduced by 91% and 78%, respectively. At the same time, increased impact strength was achieved compared with neat PP and the composite with ATH only. Maintaining the flame retardancy and mechanical properties, the density of composite PP-4 (1.27 g·cm-3) is lower than that with ATH only (PP-1, 1.46 g·cm-3). Through this research, we hope to provide an efficient approach to designing flame retardant polypropylene (PP) composites with low density.

Nanolayer coextrusion: An efficient and environmentally friendly micro/nanofiber fabrication technique

Researchers have developed many types of nanoscale materials with different properties. Among them, nanofibers have recently attracted increasing interest and attention due to their functional versatility and potential applications in diverse industries, including tapes, filtration, energy generation, and biomedical technologies. Nanolayer coextrusion, a novel polymer melt fiber processing technology, has gradually received attention due to its environmental friendliness, efficiency, simplicity and ability to be mass-produced. Compared with conventional techniques, nanolayer coextruded non-woven nanofibrous mats offer advantages such as a tunable fiber diameter, high porosity, high surface area to volume ratio, and the potential to manufacture composite nanofibers with different components to achieve desired structures and properties. Dozens of thermoplastic polymers have been coextruded for various applications, and the variety of polymers has gradually continued to increase. This review presents an overview of the nanolayer coextrusion technique and its promising advantages and potential applications. We discuss nanolayer coextrusion theory and the parameters (polymer and processing) that significantly affect the fiber morphology and properties. We focus on varied applications of nanolayer coextruded fibers in different fields and conclude by describing the future potential of this novel technology.

Effects of zinc acetate and cucurbit[6]uril on PP composites: crystallization behavior, foaming performance and mechanical properties

In this study, polypropylene (PP) foams were prepared with 1.0 wt% of cucurbit[6]uril (Q[6]), zinc acetate (Zn(Ac)2), Zn@Q[6] (a supramolecular compound synthesized from Q[6] and Zn(Ac)2), or a mixture of Zn(Ac)2 and Q[6] (weight ratio of 1:1) through injection molding in the presence of a chemical blowing agent, azodicarbonamide. The effect of the additions on the crystallization behavior and foaming performance of PP and the mechanical characterizations of the foaming samples were determined. The results showed that the additions can change the crystallization type from homogeneous to heterogeneous, increase the crystallization rate and shrink the size but increase the density of spherulites. Among the additions, Q[6] most significantly altered the crystallization properties. Scanning electron microscopy (SEM) images revealed that the PP foaming performance can be improved by Zn(Ac)2 addition at a lower temperature (175°C); however, further increasing the temperature had an undesirable effect. Q[6] exhibited the optimum foaming improvement effect on PP in a wide temperature range (175–195°C). Adding nanoparticles also enhanced the tensile properties, flexural strength and impact strength of foaming PP at low temperatures. However, with increasing temperature, the poor cell structure demonstrated undesirable effects in terms of tensile strength, flexural strength and impact strength.

Facile Fabrication of Electrically Conductive Low-Density Polyethylene/Carbon Fiber Tubes for Novel Smart Materials via Multiaxial Orientation

Electromechanical sensors are indispensable components in functional devices and robotics application. However, the fabrication of the sensors still maintains a challenging issue that high percolation threshold and easy failure of conductive network are derived from uniaxial orientation of conductive fillers in practical melt processing. Herein, we reported a facile fabrication method to prepare a multiaxial low-density polyethylene (LDPE)/carbon fibers (CFs) tube with bidirectional controllable electrical conductivity and sensitive strain-responsive performance via rotation extrusion technology. The multidimensional helical flow is confirmed in the reverse rotation extrusion, and the CFs readily respond to the flow field leading to a multiaxial orientation in the LDPE matrix. In contrast to uniaxial LDPE/CF composites, which perform a "head to head" conjunction, multiaxial-orientated CF networks exhibit a unique multilayer structure in which the CFs with distinct orientation direction intersect in the interface, endowing the LDPE/CF composites with a low percolation threshold (15 wt %) to those of the uniaxial ones (∼35 wt %). The angles between two axes play a vital role in determining the density of the conductive networks in the interface, which is predominant in tuning the bending-responsive behaviors with a gauge factor range from 12.5 to 56.3 and the corresponding linear respond region from ∼15 to ∼1%. Such a superior performance of conductive LDPE/CF tube confirms that the design of multiaxial orientation paves a novel way to facile fabrication of advanced cost-effective CF-based smart materials, shedding light on promising applications such as smart materials and intelligent engineering monitoring.

Structural design of polyurethane/poly(butylene succinate)/polycaprolactone compounds via a multilayer-assembled strategy: achieving tunable triple-shape memory performances

Novel strategy for structural design of multicomponent systems via layer-multiplying co-extrusion: achieving tunable triple-shape memory performances of polyurethane/poly(butylene succinate)/polycaprolactone compounds.

Strategy for Fabricating Multiple-Shape-Memory Polymeric Materials via the Multilayer Assembly of Co-Continuous Blends

Shape-memory polymeric materials containing alternating layers of thermoplastic polyurethane (TPU) and co-continuous poly(butylene succinate) (PBS)/polycaprolactone (PCL) blends (denoted SLBs) were fabricated through layer-multiplying coextrusion. Because there were two well-separated phase transitions caused by the melt of PCL and PBS, both the dual- and triple-shape-memory effects were discussed. Compared with the blending specimen with the same components, the TPU/SLB multilayer system with a multicontinuous structure and a plenty of layer interfaces was demonstrated to have higher shape fixity and recovery ability. When the number of layers reached 128, both the shape fixity and recovery ratios were beyond 95 and 85% in dual- and triple-shape-memory processes, respectively, which were difficult to be achieved through conventional melt-processing methods. On the basis of the classic viscoelastic theory, the parallel-assembled TPU and SLB layers capable of maintaining the same strain along the deforming direction were regarded to possess the maximum ability to fix temporary shapes and trigger them to recover back to original ones through the interfacial shearing effect. Accordingly, the present approach provided an efficient strategy for fabricating outstanding multiple-shape-memory polymers, which may exhibit a promising application in the fields of biomedical devices, sensors and actuators, and so forth.

Polypropylene/basalt thick film composites: structural, mechanical and dielectric properties

In this work, polypropylene/volcanic basalt rock (PP/VBR) thick film composites with different VBR powder mass ratio varying from 0.5 wt.% to 20.0 wt.% were prepared by using the hot press technique. The effects of VBR powder doping on mechanical, structural and dielectric properties of PP were investigated by stress-strain measurements, Fourier transform infrared analysis, thermal gravimetric analysis, scanning electron microscopy and dielectric spectroscopy methods. The highest tensile strength, percentage strain and energy at break were achieved for 0.5 wt.% VBR powder doped PP composite. According to the stress-percentage strain curves of the samples, it was observed that 0.5 wt.% VBR powder doping increases the mechanical performance of PP polymer. In addition, regardless of the doping concentration level of basalt powder, the real part of complex dielectric function (ε′) of all PP composites display approximately frequency independent behavior between 100 Hz and 1 MHz. On the other hand, 0.5 wt.% VBR powder doped PP composite has also the lowest dielectric constant at the vicinity of 2.7 between 100 Hz and 1 MHz. The composite also has considerably low dielectric loss which has a crucial importance for technological applications. For these reasons, PP/0.5 wt.% VBR composite with the highest tensile strength can be considered as a suitable candidate for microelectronic devices. Furthermore, the alternative current conductivity mechanism was determined as nearly constant loss due to approximately constant dielectric loss between 10 Hz and 1 MHz.

Polypropylene/poly(methyl methacrylate)/graphene composites with high electrical resistivity anisotropy via sequential biaxial stretching

The morphological transformation of PP/PMMA/graphene nanocomposites during biaxial stretching leads to anisotropic electrical conductivity.

Tunable Shape Memory Performances via Multilayer Assembly of Thermoplastic Polyurethane and Polycaprolactone

Shape memory materials containing alternating layers of thermoplastic polyurethane (TPU) and polycaprolactone (PCL) were fabricated through layer-multiplying extrusion. As a type of special co-continuous morphology, the multilayer structure had stable and well-defined continuous layer spaces and could be controlled by changing the number of layers. Compared with conventional polymer blends, the multilayer-assembled system with the same compositions had higher shape-fixing and -recovery ratios that could be further improved by increasing the number of layers. By analyzing from a viscoelastic model, the deformation energy preserved in elastic TPU layers would be balanced by adjacent PCL layers through interfacial shearing effect so that each component in the multilayer structure was capable of endowing the maximum contribution to both of the shape-fixing and -recovery stages. Besides, the influence of the hardness of TPU layers and the morphology of PCL layers were respectively concerned as well. Results revealed that choosing low-hardness TPU or replacing neat PCL layers by TPU/PCL blend with co-continuous morphology were beneficial to achieving outstanding shape memory performances.

Poly(propylene)-grafted thermally reduced graphene oxide and its compatibilization effect on poly(propylene)–graphene nanocomposites

We synthesized PP-graft-thermally reduced graphene oxide (PP-g-TRGO2, PP-g-TRGO4 and PP-g-TRGO6) as a compatibilizer, to obtain high performance PP/graphene nanoplatelets nanocomposites.

Dielectric hysteresis behaviors of polyvinylidene fluoride-based multilayer dielectrics controlled by confined distribution of conductive particles

PVDF-based multilayer dielectrics were fabricated through layer-multiplying extrusion and the dielectric hysteresis behaviors were successfully tailored by confined distribution of conductive particles.