Graphene-reinforced polymer matrix composites fabricated by in situ shear exfoliation of graphite in polymer solution: processing, rheology, microstructure, and properties

Abstract

Effective methods are needed to fabricate the next generation of high-performance graphene-reinforced polymer matrix composites (G-PMCs). In this work, a versatile and fundamental process is demonstrated to produce high-quality graphene-polymethylmethacrylate (G-PMMA) composites via in situ shear exfoliation of well-crystallized graphite particles loaded in highly-viscous liquid PMMA/acetone solutions into graphene nanoflakes using a concentric-cylinder shearing device. Unlike other methods where graphene is added externally to the polymer and mixed, our technique is a single step process where as-exfoliated graphene can bond directly with the polymer with no contamination/handling. The setup also allows for the investigation of the rheology of exfoliation and dispersion, providing process understanding in the attainment of the subsequently heat injection-molded and solidified G-PMC, essential for future manufacturing scalability, optimization, and repeatability. High PMMA/acetone concentration correlates to high mixture viscosity, which at large strain rates results in very-high shear stresses, producing a large number of mechanically-exfoliated flakes, as confirmed by liquid-phase UV–visible spectral analysis. Raman spectroscopy and other imaging evince that single- and bi-layer graphene are readily achieved. Nevertheless, a limit is reached at high mixtures viscosities where the process becomes unstable as non-Newtonian fluid behavior (e.g. viscoelastic) dominates the system. Characterization of microstructure, morphology, and properties of this new class of nanostructured composites reveals interesting trends. Observations by transmission electron microscopy, scanning electron microscopy, and helium ion microscopy of the manufactured G-PMCs show uniform distributions of unadulterated, well-bonded, discontinuous, graphene nanoflakes in a PMMA matrix, which enhances stiffness and strength via a load-transfer mechanism. Elastic modulus of 5.193 GPa and hardness of 0.265 GPa are achieved through processing at 0.7 g ml−1 of acetone/PMMA for 1% wt. starting graphite loading when injected into a sample mold at 200 °C. Mechanical properties exhibit 31% and 28.6% enhancement in elastic modulus and hardness, respectively, as measured by nano-indentation.

In Situ Polymer-Solution-Processed Graphene–PDMS Nanocomposites for Application in Intracranial Pressure Sensors

“…Specifically, the tensile strength of as-synthesized Gr-PDMS reaches 0.571 MPa because of the formation of stronger chemical bonding than that produced via the conventional mixing method. The tensile strength and elastic modulus of such Gr-PDMS are increased by 54% and 36%, respectively, while that of the composite prepared by an in situ processing setup of concentric cylinders can only be increased by up to 28.6% and 31% [ 29 ]. Meanwhile, the processing time is significantly reduced to 1 h from the reported 2–6 h due to the improved effects of exfoliation.…”

“…However, the major drawbacks associated with solution mixing include aggregation of graphene nanosheets [ 27 ] and the low permissible graphene concentration (~0.01 mg/mL) [ 28 ], constraining the properties of the composite matrix. A seminal work in this area utilizes a concentric-cylinder shearing device with in situ rheology to assess the extent of exfoliation to fabricate graphene-reinforced polymers, which achieves the unadulterated adhesion of the graphene nanoflakes in the polymer matrix without massive aggregation [ 29 ], providing insightful instructions for the preparation of Gr-PDMS.…”

Enhancing Hydrogen Storage in AZ31 Alloy through Pd/G Composite

“…Carbon nanomaterials have been utilized in many ways in recent years to enhance the mechanical, electrical, thermal and barrier properties of polymers due to their excellent physical or chemical properties, and many researchers have used carbon-based materials as reinforcement materials for various types of polymers [13,14]. Even in recent hydrogen research, the high specific surface area, abundance of reaction sites, and excellent thermal conductivity of carbon-based materials make them a good choice for hydrogen storage, as they can increase electron transfer and improve the kinetics of the hydrogen cycle [15].…”

The Effect of AZ61 Content on Mechanical Strength and Surface Hardness of PA6-AZ61 Magnesium Alloy

“…Polymer matrix composites (PMC) have been employed in a variety of industries and applications, including electrical and electronic components, as well as biomedical implants, household appliances, and automobile parts [1]. Recent advancements in high performance polymer materials are gaining attention as having the potential to transform the materials used in automobiles [2].…”