Graphene/polyethylene nanocomposites: Effect of polyethylene functionalization and blending methods

Mechanical and Viscoelastic Properties of Stacked and Grafted Graphene/Graphene Oxide-Polyethylene Nanocomposites: A Coarse-Grained Molecular Dynamics Study

High-performance natural materials with superior mechanical properties often possess a hierarchical structure across multiple length scales. Nacre, also known as the mother of pearl, is an example of such a material and exhibits remarkable strength and toughness. The layered hierarchical architecture across different length scales is responsible for the efficient toughness and energy dissipation. To develop high-performance artificial nacre-like composites, it is necessary to mimic this layered structure and understand the molecular phenomena at the interface. This study uses coarse-grained molecular dynamics simulations to investigate the structure-property relationship of stacked graphene-polyethylene (PE) nanocomposites. Uniaxial and oscillatory shear deformation simulations were conducted to explore the composites' mechanical and viscoelastic behavior. The effect of grafting on the glass-transition temperature and the mechanical and viscoelastic behavior was also examined. The two examined microstructures, the stacked and grafted GnP (graphene nanoplatelet)-PE composites, demonstrated significant enhancement in the Young's modulus and yield strength when compared to the pristine PE. The study also delves into the viscoelastic properties of polyethylene nanocomposites containing graphene and graphene oxide. The grafted composite demonstrated an increased elastic energy and improved capacity for stress transfer. Our study sheds light on the energy dissipation properties of layered nanocomposites through underlying molecular mechanisms, providing promising prospects for designing novel biomimetic polymer nanocomposites.

Review of sustainable, eco-friendly, and conductive polymer nanocomposites for electronic and thermal applications: current status and future prospects

Biodegradable polymer nanocomposites (BPNCs) are advanced materials that have gained significant attention over the past 20 years due to their advantages over conventional polymers. BPNCs are eco-friendly, cost-effective, contamination-resistant, and tailorable for specific applications. Nevertheless, their usage is limited due to their unsatisfactory physical and mechanical properties. To improve these properties, nanofillers are incorporated into natural polymer matrices, to enhance mechanical durability, biodegradability, electrical conductivity, dielectric, and thermal properties. Despite the significant advances in the development of BPNCs over the last decades, our understanding of their dielectric, thermal, and electrical conductivity is still far from complete. This review paper aims to provide comprehensive insights into the fundamental principles behind these properties, the main synthesis, and characterization methods, and their functionality and performance. Moreover, the role of nanofillers in strength, permeability, thermal stability, biodegradability, heat transport, and electrical conductivity is discussed. Additionally, the paper explores the applications, challenges, and opportunities of BPNCs for electronic devices, thermal management, and food packaging. Finally, this paper highlights the benefits of BPNCs as biodegradable and biodecomposable functional materials to replace traditional plastics. Finally, the contemporary industrial advances based on an overview of the main stakeholders and recently commercialized products are addressed.

Covalently bonded interface in polymer/boron nitride nanosheet composite toward enhanced mechanical and thermal behaviour

This experimental study aimed to enhance the mechanical and thermal properties of BN (hexagonal boron nitride) nanosheet-reinforced high-density polyethylene by functionalizing its interface. The challenges associated with this nanocomposites are its poor dispersion and weak interface. Accordingly, to improve the load transfer at the interface, BN nanosheets were chemically modified with silane functional groups ((3-aminopropyl)tri-ethoxy silane), making it possible to form covalent bonds between the maleic anhydride-grafted polyethylene and nanosheet. Consequently, three different types of nanocomposite samples were fabricated based on the covalently bonded or non-bonded interface. Two nanocomposite configurations featured a non-bonded interface between the nanofiller and PE matrix (p-BN/PE and (silane functionalized) s-BN/PE). In contrast, the third configuration had a covalently bonded interface (silane-functionalized h-BN + maleic anhydride-grafted PE, i.e., PE-g-BN). According to the zeta potential analysis, the silane-functionalized BN nanosheets were stable suspensions and uniformly dispersed in the polymer matrix. The tensile and flexure strength of the nanocomposites showed over 100% improvement due to the covalently bonded interface. The lamellae structure of PE in the bonded interface samples was responsible for achieving higher mechanical strength in the nanocomposites. Furthermore, the thermal conductivity of the nanocomposites was significantly affected by the type of interfacial bonding, BN wt%, and operating temperature.

Fabricating Well-Dispersed Poly(Vinylidene Fluoride)/Expanded Graphite Composites with High Thermal Conductivity by Melt Mixing with Maleic Anhydride Directly

Maleic anhydride (MA) is introduced to fabricate poly(vinylidene fluoride)/expanded graphite (PVDF/EG) composites via one-step melt mixing. SEM micrographs and WAXD results have demonstrated that the addition of MA helps to exfoliate and disperse the EG well in the PVDF matrix by promoting the mobility of PVDF molecular chains and enhancing the interfacial adhesion between the EG layers and the PVDF. Thus, much higher thermal conductivities are obtained for the PVDF/MA/EG composites compared to the PVDF/EG composites that are lacking MA. For instance, The PVDF/MA/EG composite prepared with a mass ratio of 93:14:7 exhibits a high thermal conductivity of up to 0.73 W/mK. It is 32.7% higher than the thermal conductivity of the PVDF/EG composite that is prepared with a mass ratio of 93:7. Moreover, the introduction of MA leads to an increased melting peak temperature and crystallinity due to an increased nucleation site provided by the uniformly dispersed EG in the PVDF matrix. This study provides an efficient preparation method for PVDF/EG composites with a high thermal conductivity.

Effect of functionalized graphene addition on mechanical and thermal properties of high density polyethylene

High density polyethylene (HDPE)/graphene nanocomposites were successfully synthesized by compounding of HDPE, as polymer matrix, with hexamethylenediamine functionalized graphene. The resulting nanocomposite was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and thermal gravimetric analysis (TGA) techniques. SEM characterization confirmed the good dispersion (homogeneous and uniform) of graphene in the polyethylene matrix. The TGA technique revealed a slight improvement in thermal resistance. Functionalized graphene improved a better thermal stability of HDPE (up to 6 °C) than non-functionalized graphene (up to 2 °C). Mechanical tensile and torsion tests showed that HDPE/functionalized graphene nanocomposites exhibit high tensile strength and low torsional strength compared to HDPE/non-functionalized graphene nanocomposites. Compared to pure HDPE, the Young’s modulus increased by 80% and 30%, whereas, the torsion modulus increased by about 34% and 44% for the HDPE/functionalized and HDPE/non-functionalized graphene, respectively. Regardless of this increase, it can be seen that the torsion modulus of HDPE/non-functionalized graphene is much higher than that of HDPE/functionalized graphene.

A Comparative Analysis of Chemical, Plasma and In Situ Modification of Graphene Nanoplateletes for Improved Performance of Fused Filament Fabricated Thermoplastic Polyurethane Composites Parts

The limited number of materials and mechanical weakness of fused deposition modeling (FDM) parts are deficiencies of FDM technology. The preparation of polymer composites parts with suitable filler is a promising method to improve the properties of the 3D printed parts. However, the agglomerate of filler makes its difficult disperse in the matrix. In this work, graphene nanoplatelets (GnPs) were surface modified with chemical, low-temperature plasma and in situ methods, in order to apply them as fillers for thermoplastic polyurethane (TPU). Following its modification, the surface chemical composition of GnPs was analyzed. Three wt% of surface-modified GnPs were incorporated into TPU to produce FDM filaments using a melting compounding process. Their effects on rheology properties and electrical conductivity on TPU/GnPs composites, as well as the dimensional accuracy and mechanical properties of FDM parts, are compared. The images of sample facture surfaces were examined by scanning electron microscope (SEM) to determine the dispersion of GnPs. Results indicate that chemical treatment of GnPs with zwitterionic surfactant is a good candidate to significantly enhance TPU filaments, when considering the FDM parts demonstrated the highest mechanical properties and lowest dimensional accuracy.

Recent Advances in Polymer Nanocomposites for Electromagnetic Interference Shielding: A Review

The mushrooming utilization of electronic devices in the current era produces electromagnetic interference (EMI) capable of disabling commercial and military electronic appliances on a level like never before. Due to this, the development of advanced materials for effectively shielding electromagnetic radiation has now become a pressing priority for the scientific world. This paper reviews the current research status of polymer nanocomposite-based EMI shielding materials, with a special focus on those with hybrid fillers and MXenes. A discussion on the theory of EMI shielding followed by a brief account of the most popular synthesis methods of EMI shielding polymer nanocomposites is included in this review. Emphasis is given to unravelling the connection between microstructures of the composites, their physical properties, filler type, and EMI shielding efficiency (EMI SE). Along with EMI shielding efficiency and conductivity, mechanical properties reported for EMI shielding polymer nanocomposites are also reviewed. An elaborate discussion on the gap areas in various fields where EMI shielding materials have potential applications is reported, and future directions of research are proposed to overcome the existing technological obstacles.

Hydrochar as an environment-friendly additive to improve the performance of biodegradable plastics

Plastic additives affect the properties of plastics, which further determine the application range of plastics. However, most plastic additives have environmental friendliness or performance issues limiting their application. Hydrochar (HC) from waste biomass by hydrothermal carbonization has been proved to contain organic matter as function substances, like a binder, and is environment-friendly material. Currently, hydrochar as a plastic additive has not been previously reported. In this study, the HC/PBAT composites were produced by hydrochar blending with poly (butylene adipate-co-terephthalate) (PBAT) which is a biodegradable polymer. The hydrochar produced at different hydrothermal carbonization temperatures (180 °C, 210 °C, 240 °C, 270 °C, and 300 °C) and the addition of hydrochar (10 wt%, 20 wt%) were investigated. The results showed that the elastic modulus of the composites was increased by 27.4 MPa and 32.5 MPa compared with virgin PBAT while adding 10 wt% and 20 wt% hydrochar, respectively. Moreover, the stiffness of the composite was improved, and the balance of stiffness and toughness of the composites was effectively maintained when adding 10 wt% hydrochar treated at 300 °C. The elongation at break, tensile strength, and the elastic modulus of its composites were 630.8 ± 13.7%, 23.0 ± 0.4 MPa, and 100.5 ± 2.7 MPa, respectively. Furthermore, the crystallization temperature of the composites was increased after hydrochar was added into PBAT, and the maximum was 87.9 °C. It also means that hydrochar has a great nucleation effect during plastic processing. Therefore, hydrochar can be used as an environment-friendly additive to promote the performance of biodegradable plastic and promise to be applied in the field of biodegradable plastics.

Comparative Study of Graphene Nanoplatelets and Multiwall Carbon Nanotubes-Polypropylene Composite Materials for Electromagnetic Shielding

Graphene nanoplatelets (GNPs) and multiwall carbon nanotubes (CNTs)-polypropylene (PP) composite materials for electromagnetic interference (EMI) shielding applications were fabricated as 1 mm thick panels and their properties were studied. Structural and morphologic characterization indicated that the obtained composite materials are not simple physical mixtures of these components but new materials with particular properties, the filler concentration and nature affecting the nanomaterials’ structure and their conductivity. In the case of GNPs, their characteristics have a dramatic effect of their functionality, since they can lead to composites with lower conductivity and less effective EMI shielding. Regarding CNTs-PP composite panels, these were found to exhibit excellent EMI attenuation of more than 40 dB, for 10% CNTs concentration. The development of PP-based composite materials with added value and particular functionality (i.e., electrical conductivity and EMI shielding) is highly significant since PP is one of the most used polymers, the best for injection molding, and virtually infinitely recyclable.

Dependence of Electrical Conductivity on Phase Morphology for Graphene Selectively Located at the Interface of Polypropylene/Polyethylene Composites

Conductive composites of polypropylene (PP) and polyethylene (PE) filled with thermally reduced graphene oxide (TRG) were prepared using two different processing sequences. One was a one-step processing method in which the TRG was simultaneously melt blended with PE and PP, called TRG/PP/PE. The second was a two-step processing method in which the TRG and the PP were mixed first, and then the (TRG/PP) masterbatch was blended with PE, called (TRG/PP)/PE. The phase morphology and localization of the TRG in TRG/PP/PE and (TRG/PP)/PE composites with different PP/PE compositions were observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The TRG was found to be selectively dispersed in the PE phase of the TRG/PP/PE composites, resulting in a low percolation threshold near 2.0 wt%. In the (TRG/PP)/PE composites, the TRG was selectively located at the PP/PE blend interface, resulting in a percolation threshold that was lower than 1.0 wt%. With the addition of 2.0 wt% TRG, the (TRG/PP)/PE composites exhibited a wide range of electrical conductivities at PP/PE weight ratios of 10 w/90 w to 80 w/20 w. Moreover, electrical and rheological measurements of the composites revealed that the co-continuous phase structure is the most efficient candidate for the fabrication of conductive composites.

Fabrication of graphene-based porous materials: traditional and emerging approaches

The anisotropic nature of ‘graphenic’ nanosheets enables them to form stable three-dimensional porous materials. The use of these porous structures has been explored in several applications including electronics and batteries, environmental remediation, energy storage, sensors, catalysis, tissue engineering, and many more. As method of fabrication greatly influences the final pore architecture, and chemical and mechanical characteristics and performance of these porous materials, it is essential to identify and address the correlation between property and function. In this review, we report detailed analyses of the different methods of fabricating porous graphene-based structures – with a focus on graphene oxide as the base material – and relate these with the resultant morphologies, mechanical responses, and common applications of use. We discuss the feasibility of the synthesis approaches and relate the GO concentrations used in each methodology against their corresponding pore sizes to identify the areas not explored to date.

Due to their anisotropic nature, graphene nanosheets can be used to form 3-dimensional porous materials using template-free and template-directed methodologies. These fabrication strategies are found to influence the properties of the final structure.

Relationship between the Microstructure and Performance of Graphene/Polyethylene Composites Investigated by Positron Annihilation Lifetime Spectroscopy

The quantitative characterization of microstructure is most desirable for the establishment of structure-property relationships in polymer nanocomposites. In this work, the effects of graphene on the microstructure, mechanical, electrical, and thermal properties of the obtained graphene/polyethylene (PE) composites were investigated. In order to reveal the structure-performance relationship of graphene/PE composites, especially for the effects of the relative free volume fraction (fr) and interfacial interaction intensity (β), positron annihilation lifetime spectroscopy (PALS) was employed for its quantitative description. The relative free volume fraction fr gives a good explanation of the variation for surface resistivity, melting temperature, and thermal stability, and the variation of tensile strength and thermal conductivity agree well with the results of interfacial interaction intensity β. The results showed that fr and β have a significant effect on the properties of the obtained graphene/PE composites, and the effect on the properties was revealed.

Effect of the reduced graphene oxide (rGO) compaction degree and concentration on rGO-polymer composite printability and cell interactions

Graphene derivatives combined with polymers have attracted enormous attention for bone tissue engineering applications. Among others, reduced graphene oxide (rGO) is one of the preferred graphene-based fillers for the preparation of composites via melt compounding, and their further processing into 3D scaffolds, due to its established large-scale production method, thermal stability, and electrical conductivity. In this study, rGO (low bulk density 10 g L^-1) was compacted by densification using a solvent (either acetone or water) prior to melt compounding, to simplify its handling and dosing into a twin-screw extrusion system. The effects of rGO bulk density (medium and high), densification solvent, and rGO concentration (3, 10 and 15% in weight) on rGO dispersion within the composite, electrical conductivity, printability and cell-material interactions were studied. High bulk density rGO (90 g L^-1) occupied a low volume fraction within polymer composites, offering poor electrical properties but a reproducible printability up to 15 wt% rGO. On the other hand, the volume fraction within the composites of medium bulk density rGO (50 g L^-1) was higher for a given concentration, enhancing rGO particle interactions and leading to enhanced electrical conductivity, but compromising the printability window. For a given bulk density (50 g L^-1), rGO densified in water was more compacted and offered poorer dispersability within the polymer than rGO densified in acetone, and resulted in scaffolds with poor layer bonding or even lack of printability at high rGO percentages. A balance in printability and electrical properties was obtained for composites with medium bulk density achieved with rGO densified in acetone. Here, increasing rGO concentration led to more hydrophilic composites with a noticeable increase in protein adsorption. Moreover, scaffolds prepared with such composites presented antimicrobial properties even at low rGO contents (3 wt%). In addition, the viability and proliferation of human mesenchymal stromal cells (hMSCs) were maintained on scaffolds with up to 15% rGO and with enhanced osteogenic differentiation on 3% rGO scaffolds.

Self-assembly in biobased nanocomposites for multifunctionality and improved performance

Concerns of petroleum dependence and environmental pollution prompt an urgent need for new sustainable approaches in developing polymeric products. Biobased polymers provide a potential solution, and biobased nanocomposites further enhance the performance and functionality of biobased polymers. Here we summarize the unique challenges and review recent progress in this field with an emphasis on self-assembly of inorganic nanoparticles. The conventional wisdom is to fully disperse nanoparticles in the polymer matrix to optimize the performance. However, self-assembly of the nanoparticles into clusters, networks, and layered structures provides an opportunity to address performance challenges and create new functionality in biobased polymers. We introduce basic assembly principles through both blending and in situ synthesis, and identify key technologies that benefit from the nanoparticle assembly in the polymer matrix. The fundamental forces and biobased polymer conformations are discussed in detail to correlate the nanoscale interactions and morphology with the macroscale properties. Different types of nanoparticles, their assembly structures and corresponding applications are surveyed. Through this review we hope to inspire the community to consider utilizing self-assembly to elevate functionality and performance of biobased materials. Development in this area sets the foundation for a new era of designing sustainable polymers in many applications including packaging, construction chemicals, adhesives, foams, coatings, personal care products, and advanced manufacturing.

Effects of Graphene Nanoplatelets on Mechanical and Fire Performance of Flax Polypropylene Composites with Intumescent Flame Retardant

The integration of intumescent flame-retardant (IFR) additives in natural fiber-based polymer composites enhances the fire-retardant properties, but it generally has a detrimental effect on the mechanical properties, such as tensile and flexural strengths. In this work, the feasibility of graphene as a reinforcement additive and as an effective synergist for IFR-based flax-polypropylene (PP) composites was investigated. Noticeable improvements in tensile and flexural properties were achieved with the addition of graphene nanoplatelets (GNP) in the composites. Furthermore, better char-forming ability of GNP in combination with IFR was observed, suppressing HRR curves and thus, lowering the total heat release (THR). Thermogravimetric analysis (TGA) detected a reduction in the decomposition rate due to strong interfacial bonding between GNP and PP, whereas the maximum decomposition rate was observed to occur at a higher temperature. The saturation point for the IFR additive along with GNP has also been highlighted in this study. A safe and effective method of graphene encapsulation within PP using the fume-hood set-up was achieved. Finally, the effect of flame retardant on the flax–PP composite has been simulated using Fire Dynamics Simulator.

Dispersion of Graphite Nanoplates in Polypropylene by Melt Mixing: The Effects of Hydrodynamic Stresses and Residence Time

This work combines experimental and numerical (computational fluid dynamics) data to better understand the kinetics of the dispersion of graphite nanoplates in a polypropylene melt, using a mixing device that consists of a series of stacked rings with an equal outer diameter and alternating larger and smaller inner diameters, thereby creating a series of converging/diverging flows. Numerical simulation of the flow assuming both inelastic and viscoelastic responses predicted the velocity, streamlines, flow type and shear and normal stress fields for the mixer. Experimental and computed data were combined to determine the trade-off between the local degree of dispersion of the PP/GnP nanocomposite, measured as area ratio, and the absolute average value of the hydrodynamic stresses multiplied by the local cumulative residence time. A strong quasi-linear relationship between the evolution of dispersion measured experimentally and the computational data was obtained. Theory was used to interpret experimental data, and the results obtained confirmed the hypotheses previously put forward by various authors that the dispersion of solid agglomerates requires not only sufficiently high hydrodynamic stresses, but also that these act during sufficient time. Based on these considerations, it was estimated that the cohesive strength of the GnP agglomerates is in the range of 5–50 kPa.

Monomer Selection for In Situ Polymerization Infusion Manufacture of Natural-Fiber Reinforced Thermoplastic-Matrix Marine Composites

Awareness of environmental issues has led to increasing interest from composite researchers in using "greener" materials to replace synthetic fiber reinforcements and petrochemical polymer matrices. Natural fiber bio-based thermoplastic composites could be an appropriate choice with advantages including reducing environmental impacts, using renewable resources and being recyclable. The choice of polymer matrix will significantly affect the cost, manufacturing process, mechanical properties and durability of the composite system. The criteria for appropriate monomers are based on the processing temperature and viscosity, polymer mechanical properties, recyclability, etc. This review considers the selection of thermoplastic monomers suitable for in situ polymerization during resin, now monomer, infusion under flexible tooling (RIFT, now MIFT), with a primary focus on marine composite applications. Given the systems currently available, methyl methacrylate (MMA) may be the most suitable monomer, especially for marine composites. MMA has low process temperatures, a long open window for infusion, and low moisture absorption. However, end-of-life recovery may be limited to matrix depolymerization. Bio-based MMA is likely to become commercially available in a few years. Polylactide (PLA) is an alternative infusible monomer, but the relatively high processing temperature may require expensive consumable materials and could compromise natural fiber properties.

Melt Rheology and Mechanical Characteristics of Poly(Lactic Acid)/Alkylated Graphene Oxide Nanocomposites

Poly(lactic acid) (PLA) nanocomposites were synthesized by a solution blending and coagulation method using alkylated graphene oxide (AGO) as a reinforcing agent. Turbiscan confirmed that the alkylation of GO led to enhanced compatibility between the matrix and the filler. The improved dispersity of the filler resulted in superior interfacial adhesion between the PLA chains and AGO basal plane, leading to enhanced mechanical and rheological properties compared to neat PLA. The tensile strength and elongation at break, i.e., ductility, increased by 38% and 42%, respectively, at the same filler content nanocomposite (PLA/AGO 1 wt %) compared to nonfiller PLA. Rheological analysis of the nanocomposites in the molten state of the samples was performed to understand the filler network formed inside the matrix. The storage modulus increased significantly from PLA/AGO 0.5 wt % (9.6 Pa) to PLA/AGO 1.0 wt % (908 Pa). This indicates a percolation threshold between the two filler contents. A steady shear test was performed to examine the melt flow characteristics of PLA/AGO nanocomposites at 170 °C, and the viscosity was predicted using the Carreau-Yasuda model.

The Role of Reduced Graphene Oxide in the Suspension Polymerization of Styrene and Its Effect on the Morphology and Thermal Properties of the Polystyrene/rGO Nanocomposites

Reduced graphene oxide (rGO) was used to obtain Polystyrene (PS)/rGO nanocomposites via in-situ suspension polymerization. The main goal of the article was to determine how rGO influences the morphology and thermal properties of PS beads. The obtained samples were studied by means of a scanning electron microscope (SEM), and calorimetric and thermogravimetric analysis (DCS, TGA). It was proven that the addition of rGO, due to the presence of polar functional groups, causes significant changes in bead sizes and size distribution, and in their morphology (on the surface and in cross-section). The increasing amount of rGO in the polymer matrix increased the size of beads from 0.36 to 3.17 mm for pure PS and PS with 0.2 wt% rGO content, respectively. PS/rGO nanocomposites are characterized by distinctly improved thermostability, which is primarily expressed in the increase in their decomposition temperature. For a sample containing 0.3 wt% rGO, the difference is more than 12 °C in comparison to pure PS beads.

A Regenerative Polymer Blend Composed of Glycylglycine ethyl ester-substituted Polyphosphazene and Poly (lactic-co-glycolic acid)

In the pursuit of continuous improvement in the area of biomaterial design, blends of mixed-substituent polyphosphazenes and poly (lactic acid-glycolic acid) (PLGA) were prepared, and their morphology of phase distributions for the first time was studied. The degradation mechanism and osteocompatibility of the blends were also evaluated for their use as regenerative materials. Poly [(ethyl phenylalanato)25(glycine ethyl glycinato)75phosphazene](PNEPAGEG) and poly [(glycine ethyl glycinato)75(phenylphenoxy)25phosphazene](PNGEGPhPh) were blended with PLGA at various weight ratios to yield different blends, namely PNEPAGEG-PLGA 25:75, PNEPAGEG-PLGA 50:50, PNGEGPhPh-PLGA 25:75, and PNGEGPhPh-PLGA 50:50. The molecular interactions, domain sizes, and phase distributions of the blends were confirmed by atomic force microscopy (AFM) as the PNEPAGEG-PLGA and PNGEGPhPh-PLGA blends showed different domain sizes and phase distributions. Due to the extensive hydrogen bonding within the two polymer components, PNEPAGEG-PLGA exhibited small-sized domains and well-distributed morphology. While for the PNGEGPhPh-PLGA blends, the presence of phenylphenol (PhPh) caused the formation of PLGA large-sized domains as the PLGA formed a continuous phase and PNGEGPhPh constituted a dispersed phase. In addition to AFM results, scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and Fourier transform infrared spectroscopy (FTIR) results demonstrated the miscibility of the blends. The PNEPAGEG-PLGA and PNGEGPhPh-PLGA blends presented in situ 3D interconnected porous structures upon degradation in phosphate-buffered saline (PBS) media at 37°C. However, the blends showed different mechanistic pathways to the formations of the pores. The difference in the erosion patterns could be attributed to the nature of molecular attractions that exist in the blends. Furthermore, the novel blends were able to support cell growth as compared to PLGA, and accommodate cell infiltrations, which ultimately augmented surface area for better cell-material interactions.

Precontrolled Alignment of Graphite Nanoplatelets in Polymeric Composites Prevents Bacterial Attachment

Graphene coatings composed of vertical spikes are shown to mitigate bacterial attachment. Such coatings present hydrophobic edges of graphene, which penetrate the lipid bilayers causing physical disruption of bacterial cells. However, manufacturing of such surfaces on a scale required for antibacterial applications is currently not feasible. This study explores whether graphite can be used as a cheaper alternative to graphene coatings. To examine this, composites of graphite nanoplatelets (GNP) and low-density polyethylene (LDPE) are extruded in controlled conditions to obtain controlled orientation of GNP flakes within the polymer matrix. Flakes are exposed by etching the surface of GNP-LDPE nanocomposites and antibacterial activity is evaluated. GNP nanoflakes on the extruded samples interact with bacterial cell membranes, physically damaging the cells. Bactericidal activity is observed dependent on orientation and nanoflakes density. Composites with high density of GNP (≥15%) present two key advantages: i) they decrease bacterial viability by a factor of 99.9999%, which is 10 000-fold improvement on the current benchmark, and ii) prevent bacterial colonization, thus drastically reducing the numbers of dead cells on the surface. The latter is a key advantage for longer-term biomedical applications, since these surfaces will not have to be cleaned or replaced for longer periods.

Enhancement of Charge Transport in Polythiophene Semiconducting Polymer by Blending with Graphene Nanoparticles

This paper describes a study on the charge transport in a composite of liquid-exfoliated graphene nanoparticles (GNPs) and a polythiophene semiconducting polymer. While the former component is highly conducting, although it consists of isolated nanostructures, the latter offers an efficient charge transport path between the individual GNPs within the film, overall yielding enhanced charge transport properties of the resulting bi-component system. The electrical characteristics of the composite layers were investigated by means of measurements of time-of-flight photoconductivity and transconductance in field-effect transistors. In order to analyze both phenomena separately, charge density and charge mobility contributions to the conductivity were singled out. With the increasing GNP concentration, the charge mobility was found to increase, thereby reducing the time spent by the carriers on the polymer chains. In addition, for GNP loading above 0.2 % (wt.), an increase of free charge density was observed that highlights an additional key role played by doping. Variable-range hopping model of a mixed two- and three-dimensional transport is explained using temperature dependence of mobility and free charge density. The temperature variation of free charge density was related to the electron transfer from polythiophene to GNP, with an energy barrier of 24 meV.

Elaboration and Characterization of Active Films Containing Iron-Montmorillonite Nanocomposites for O2 Scavenging

Iron particles of sizes between 6 and 20 nm forming aggregates of 57 ± 17 nm were synthesized by chemical reduction of iron precursors on the surface of montmorillonite (MMT). This active MMT-Fe powder was then uniformly distributed in a linear low-density polyethylene (LLDPE) matrix by extrusion at atmospheric conditions, as confirmed by wide-angle X-ray scattering (WAXS), which also detected a partial exfoliation of the nanoclays. Thermogravimetric analysis (TGA) did not detect any significant modification of the degradation temperature between nanocomposites and active nanocomposites. 57Fe Mössbauer spectroscopy evidenced the formation of a majority of iron boride in MMT-Fe as well as in the active film containing it. The LLDPE.Fu15.MMT-Fe3.75 and LLDPE.Fu15.MMT-Fe6.25 films had oxygen-scavenging capacities of 0.031 ± 0.002 and 0.055 ± 0.009 g(O2)/g(Fe), respectively, while the neat powder had an adsorption capacity of 0.122 g(O2)/g(Fe). This result confirms that the fresh film samples were partially oxidized shortly after thermomechanical processing (60% of oxidized species according to Mössbauer spectroscopy). No significant difference in oxygen permeability was observed when MMT-Fe was added. This was related to the relatively small film surface used for measuring the permeability. The reaction-diffusion model proposed here was able to reproduce the observed data of O2 adsorption in an active nanocomposite, which validated the O2 adsorption model previously developed for dried MMT-Fe powder.

Strong Interaction with Carbon Filler of Polymers Obtained by Pyrene Functionalized Hoveyda-Grubbs 2nd Generation Catalyst

Hoveyda-Grubbs 2nd generation catalyst that has the alkylidene functionalized with pyrene (HG2_pyrene) was synthesized and characterized. This catalyst can be bound to carbonaceous filler (graphite, graphene or carbon nanotubes) by π-stacking interaction, but, since the catalytic site become poorly accessible to the incoming monomer, its activity in the ROMP (Ring Opening Metathesis Polymerization) is reduced. This is due to the fact that the above interaction also occurs with the aryl groups of NHC ligand of the ruthenium, as demonstrated by nuclear magnetic resonance and by fluorescence analysis of a solution of the catalyst with a molecule that simulated the structure of graphene. Very interesting results were obtained using HG2_pyrene as a catalyst in the ROMP of 2-norbornene and 1,5-cyclooctadiene. The activity of this catalyst was the same as that obtained with the classical commercial HG2. Obviously, the polymers obtained with catalyst HG2_pyrene have a pyrene as a chain end group. This group can give a strong π-stacking interaction with carbonaceous filler, producing a material that is able to promote the dispersion of other materials such as graphite in the polymer matrix.

Exfoliated Graphene Leads to Exceptional Mechanical Properties of Polymer Composite Films

Polymers with superior mechanical properties are desirable in many applications. In this work, polyethylene (PE) films reinforced with exfoliated thermally reduced graphene oxide (TrGO) fabricated using a roll-to-roll hot-drawing process are shown to have outstanding mechanical properties. The specific ultimate tensile strength and Young's modulus of PE/TrGO films increased monotonically with the drawing ratio and TrGO filler fraction, reaching up to 3.2 ± 0.5 and 109.3 ± 12.7 GPa, respectively, with a drawing ratio of 60× and a very low TrGO weight fraction of 1%. These values represent by far the highest reported to date for a polymer/graphene composite. Experimental characterizations indicate that as the polymer films are drawn, TrGO fillers are exfoliated, which is further confirmed by molecular dynamics (MD) simulations. Exfoliation increases the specific area of the TrGO fillers in contact with the PE matrix molecules. Molecular dynamics simulations show that the PE-TrGO interaction is stronger than the PE-PE intermolecular van der Waals interaction, which enhances load transfer from PE to TrGO and leverages the ultrahigh mechanical properties of TrGO.

Hierarchically hydrogen-bonded graphene/polymer interfaces with drastically enhanced interfacial thermal conductance

Interfacial thermal transport is a critical physical process determining the performance of many material systems with small-scale features. Recently, self-assembled monolayers and polymer brushes have been widely used to engineer material interfaces presenting unprecedented properties. Here, we demonstrate that poly(vinyl alcohol) (PVA) monolayers with hierarchically arranged hydrogen bonds drastically enhance interfacial thermal conductance by a factor of 6.22 across the interface between graphene and poly(methyl methacrylate) (PMMA). The enhancement is tunable by varying the number of grafted chains and the density of hydrogen bonds in the unique hierarchical hydrogen bond network. The extraordinary enhancement results from a synergy of hydrogen bonds and other structural and thermal factors including molecular morphology, chain orientation, interfacial vibrational coupling and heat exchange. Two types of hydrogen bonds, i.e. PVA-PMMA hydrogen bonds and PVA-PVA hydrogen bonds, are analyzed and their effects on various structural and thermal properties are systematically investigated. These results are expected to provide new physical insights for interface engineering to achieve tunable thermal management and energy efficiency in a wide variety of systems involving polymers and biomaterials.

Optimization of the cellular morphology of biaxially stretched thin polyethylene foams produced by extrusion film blowing

This work presents the production of cellular polymer films using extrusion blowing to impose biaxial stretching on the cellular structure while processing. The materials selected are linear low-density polyethylene (LLDPE) and low density polyethylene (LDPE) as the matrix, azodicarbonamide as the chemical blowing agent, and talc as the nucleating agent. The processing parameters, namely, the temperature profile, screw speed, feed rate, take-up ratio, blow-up ratio, and the matrix composition were all optimized to produce a homogeneous cellular structure with defined morphologies. The optimized films had a thickness below 300 µm, a relative density around 0.6, a cell density above 2 × 106 cells/cm3, and biaxially stretched cells with aspect ratios above 4 longitudinally and 3.8 transversally.

Breaking the Nanoparticle Loading-Dispersion Dichotomy in Polymer Nanocomposites with the Art of Croissant-Making

The intrinsic properties of nanomaterials offer promise for technological revolutions in many fields, including transportation, soft robotics, and energy. Unfortunately, the exploitation of such properties in polymer nanocomposites is extremely challenging due to the lack of viable dispersion routes when the filler content is high. We usually face a dichotomy between the degree of nanofiller loading and the degree of dispersion (and, thus, performance) because dispersion quality decreases with loading. Here, we demonstrate a potentially scalable pressing-and-folding method (P & F), inspired by the art of croissant-making, to efficiently disperse ultrahigh loadings of nanofillers in polymer matrices. A desired nanofiller dispersion can be achieved simply by selecting a sufficient number of P & F cycles. Because of the fine microstructural control enabled by P & F, mechanical reinforcements close to the theoretical maximum and independent of nanofiller loading (up to 74 vol %) were obtained. We propose a universal model for the P & F dispersion process that is parametrized on an experimentally quantifiable " D factor". The model represents a general guideline for the optimization of nanocomposites with enhanced functionalities including sensing, heat management, and energy storage.

Effect of Variation of Hard Segment Content and Graphene-Based Nanofiller Concentration on Morphological, Thermal, and Mechanical Properties of Polyurethane Nanocomposites

This study describes the development of a new class of high-performance polyurethane elastomer nanocomposites containing reduced graphene oxide (RGO) or graphene nanoplatelets (GNP). Two types of polyurethane elastomers with different contents of hard segments (HS) were used as a polymer matrix. The developed nanocomposites were characterized by thermal analysis (DSC, TG), dynamic mechanical testing (DMA), hardness testing, mechanical properties, rheology, FTIR spectroscopy, XRD, and microscopy investigation (TEM, SEM). Morphological investigation confirmed better compatibility of RGO with the polyurethane (PU) matrix compared to GNP. Both applied nanofillers influenced melting and crystallization of the PU matrix. The nonlinear viscoelastic behavior of the nanocomposites (Payne effect) was studied, and the results were compared with theoretical predictions.

High Thermal Conductivity of Flake Graphite Reinforced Polyethylene Composites Fabricated by the Powder Mixing Method and the Melt-Extruding Process

The thermal conductivity of flake graphite (FG) particulates reinforced high density polyethylene (HDPE) composites was systematically investigated under a special dispersion state of FG particles. The effects of particle size, weight filling ratio and proportion of various sizes were discussed in detail. A special composite (15 wt % 500 μm/10 wt % 200 μm/10 wt % 20 μm/5 wt % 2 μm FG + 60 wt % polyethylene (PE)) with a high thermal conductivity about 2.49 W/(m·K) was produced by combining the synergistic effect of several fillers. The component material size distribution was employed to analyze the effect of particle size. And scanning electron microscope (SEM) was adopted to observe the FG network in the composites. Thermogravimetric analysis (TGA) revealed the good thermal stability of composites. Differential scanning calorimetry (DSC) indicated that all composites own a similar melting temperature. Sample compression experiment indicated that all composites still exhibit high mechanical strength. Consequently, the easy-making flake graphite reinforced polyethylene composites with a high thermal conductivity would have a wide application in the new material field, such as a thermal interface material, a heat exchanger, voltage cable, etc.

Intercalation Polymerization Approach for Preparing Graphene/Polymer Composites

The rapid development of society has promoted increasing demand for various polymer materials. A large variety of efforts have been applied in order for graphene strengthened polymer composites to satisfy different requirements. Graphene/polymer composites synthesized by traditional strategies display some striking defects, like weak interfacial interaction and agglomeration of graphene, leading to poor improvement in performance. Furthermore, the creation of pre-prepared graphene while being necessary always involves troublesome processes. Among the various preparation strategies, an appealing approach relies on intercalation and polymerization in the interlayer of graphite and has attracted researchers' attention due to its reliable, fast and simple synthesis. In this review, we introduce an intercalation polymerization strategy to graphene/polymer composites by the intercalation of molecules/ions into graphite interlayers, as well as subsequent polymerization. The key point for regulating intercalation polymerization is tuning the structure of graphite and intercalants for better interaction. Potential applications of the resulting graphene/polymer composites, including electrical conductivity, electromagnetic absorption, mechanical properties and thermal conductivity, are also reviewed. Furthermore, the shortcomings, challenges and prospects of intercalation polymerization are discussed, which will be helpful to researchers working in related fields.