Tailoring the structures and properties of biodegradable poly(lactic acid)/poly(butylene adipate-co-terephthalic acid) blends via reactive graphene oxide

In conventional elastomer-toughened PLA blends, the huge sacrifice in strength and modulus due to poor compatibility is a major problem plaguing such materials. In this work, oxide-epoxy-graphene (SGO-GMA) nanoparticles that can chemically react with both components of PLA/PBAT blends are prepared to serve as compatibilizer by "thiol-ene click" reaction. It is found that SGO-GMA tends to be dispersed in the PBAT phase thermodynamically. However, the one-step process, SGO-GMA is dispersed in both PBAT and PLA phases because of the chemical reaction limiting its migration, and the crystallization rate of the PLA phase is significantly increased. In contrast, in the two-step process, SGO-GMA is anchored at the interface by the in-situ reaction between epoxy groups in GMA with PLA and PBAT. Consequently, the mechanical properties of the samples prepared using a two-step process demonstrate a significant advantage. Specifically, incorporating 1 wt% SGO-GMA into PLA/PBAT blends results in simultaneous enhancements in tensile strength, elongation at break, and impact strength by 7.9%, 40.7%, and 57.1%, respectively. The improved mechanical properties that based on the roles functionalized GO compatibilization are expected to facilitate the application of PLA in tissue engineering materials, in vivo and in vitro medical devices and other fields.

Polyurethane-grafted graphene oxide from repurposed foam mattress waste

Polyurethanes (PU) make up a large portion of commodity plastics appearing in applications including insulation, footwear, and memory foam mattresses. Unfortunately, as thermoset polymers, polyurethanes lack a clear path for recycling and repurposing, creating a sustainability issue. Herein, using dynamic depolymerization, we demonstrate a simple one-pot synthesis for preparation of an upcycled polyurethane grafted graphene material (PU-GO). Through this dynamic depolymerization using green conditions, PU-GO nanofillers with tunable PU to GO ratios were synthesized. Chemical analysis revealed that the polyurethane graphenic materials primarily contained the polycarbamate hard-segment of polyurethane while the soft polyol component was removed in washes. PU-GOs were incorporated into bulk polyurethane foam to create composites as a filler at 0.25, 0.5, 1.0, and 2.0 weight percent filler and the thermal and mechanical properties of the resulting foams were analyzed. All PU-GO fillers were shown to improve thermal insulation up to a filler content of 0.5%, with all but 2 of the fillers demonstrating improvements up to 2% of filler content. The greatest decrease in thermal conductivity was 38.5% compared to neat PU foam, observed with the composites containing 0.5% of PU10-GO1 and 1.0% of PU3-GO1. Mechanical performance was tested for each foam and showed that lower polyurethane content graphenic composites produced foams that were less susceptible to fatiguing and more durable over cyclic loading, while higher polyurethane content graphenic composites had mechanical stability similar to neat PU but initially had greater impact resistance. Taken together, these novel PU-GO fillers prepared from repurposed PU mattress show promise as a sustainable additive to improve PU performance.

Impact of graphene oxide lateral dimensions on the properties of methacrylated gelatin nanocomposite hydrogels

The size and shape of nanoparticles have a profound effect on the properties of nanocomposites. For instance, the lateral dimensions of graphene oxide (GO) platelets affect several properties, including their antibacterial and pharmacokinetic functions. However, the impact of lateral dimensions has been poorly studied in nanocomposites, and their effect on hydrogels is still unknown. The current study aims to determine the effect of GO lateral dimensions on the mechanical, rheological, thermal, and antibacterial properties of gelatin hydrogels. The hydrogels were fabricated via photopolymerization of methacrylated gelatin and GO derived from the oxidation of commercial graphene. The observations indicate that an increase in GO sheets improves the mechanical strength with an increase in compressive modulus and a low mechanical hysteresis (<10%). Furthermore, low mechanical energy is dissipated even after several deformation cycles. The nanocomposite hydrogels demonstrated bactericidal effects on two clinical strains with an extensively drug-resistant phenotype, primarily through contact. Additionally, an increment in lateral dimensions increased the bactericidal capacity of Gram-negative strains. Thus, the significant effect of the lateral dimensions of GO sheets on the properties of hydrogels is demonstrated.

Nanomaterials-patterned flexible electrodes for wearable health monitoring: a review

ABSTRACT

Electrodes fabricated on a flexible substrate are a revolutionary development in wearable health monitoring due to their lightweight, breathability, comfort, and flexibility to conform to the curvilinear body shape. Different metallic thin-film and plastic-based substrates lack comfort for long-term monitoring applications. However, the insulating nature of different polymer, fiber, and textile substrates requires the deposition of conductive materials to render interactive functionality to substrates. Besides, the high porosity and flexibility of fiber and textile substrates pose a great challenge for the homogenous deposition of active materials. Printing is an excellent process to produce a flexible conductive textile electrode for wearable health monitoring applications due to its low cost and scalability. This article critically reviews the current state of the art of different textile architectures as a substrate for the deposition of conductive nanomaterials. Furthermore, recent progress in various printing processes of nanomaterials, challenges of printing nanomaterials on textiles, and their health monitoring applications are described systematically.

Characterization of Polyamide 6/Multilayer Graphene Nanoplatelet Composite Textile Filaments Obtained Via In Situ Polymerization and Melt Spinning

Studies of the production of fiber-forming polyamide 6 (PA6)/graphene composite material and melt-spun textile fibers are scarce, but research to date reveals that achieving the high dispersion state of graphene is the main challenge to nanocomposite production. Considering the significant progress made in the industrial mass production of graphene nanoplatelets (GnPs), this study explored the feasibility of production of PA6/GnPs composite fibers using the commercially available few-layer GnPs. To this aim, the GnPs were pre-dispersed in molten ε-caprolactam at concentrations equal to 1 and 2 wt %, and incorporated into the PA6 matrix by the in situ water-catalyzed ring-opening polymerization of ε-caprolactam, which was followed by melt spinning. The results showed that the incorporated GnPs did not markedly influence the melting temperature of PA6 but affected the crystallization temperature, fiber bulk structure, crystallinity, and mechanical properties. Furthermore, GnPs increased the PA6 complex viscosity, which resulted in the need to adjust the parameters of melt spinning to enable continuous filament production. Although the incorporation of GnPs did not provide a reinforcing effect of PA6 fibers and reduced fiber tensile properties, the thermal stability of the PA6 fiber increased. The increased melt viscosity and graphene anti-dripping properties postponed melt dripping in the vertical flame spread test, which consequently prolonged burning within the samples.

SMA-Assisted Exfoliation of Graphite by Microfluidization for Efficient and Large-Scale Production of High-Quality Graphene

In this paper, the sodium salt of styrene-maleic anhydride copolymer (SMA) was used as a stabilizer in the process of graphite exfoliation to few-layer graphene using the technique of microfluidization in water. This method is simple, scalable, and cost-effective, and it produces graphene at concentrations as high as 0.522 mg mL^-1. The generated high-quality graphene consists of few-layer sheets with a uniform size of less than 1 μm. The obtained graphene was uniformly dispersed and tightly integrated into a polyamide 66 (PA66) matrix to create high-performance multifunctional polymer nanocomposites. The tensile strength and thermal conductivity of 0.3 and 0.5 wt% EG/PA66 composites were found to be ~32.6% and ~28.8% greater than the corresponding values calculated for pure PA66, respectively. This confirms that the new protocol of liquid phase exfoliation of graphite has excellent potential for use in the industrial-scale production of high-quality graphene for numerous applications.

Tuning chain extender structure to prepare high-performance thermoplastic polyurethane elastomers

In this work, a novel strategy is developed to solve the issue of mutually exclusive high mechanical robustness and thermo-stability for thermoplastic polyurethane (PU). A leaf-like and reticulate interfingering superstructure can be seen. The superstructure of polyurethanes can also be tuned by the polarity of chain extender molecular via changing the number for ferrocene redox centres, thus to further enhance the thermal stability and elasticity of PUs. As a result, by incorporating bisferrocene units into the main chain of PU, a high-performance PU elastomer can be synthesized with a highest initial degradation temperature of T_5% of 345 °C, a highest tensile strength of 42.3 MPa with an elongation over 1000%, as well as a toughness of 19.6 GJ m⁻³. These results conclusively suggest that high-performance thermoplastic polyurethane elastomers had great promise for potential application in a wide range of practical fields.

Ester-containing ferrocenyl diols are introduced as chain extenders to tune the polyurethane superstructure to optimize thermo-stability and elasticity simultaneously.