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.

Graphene has been publicized as the game changing material of this millennium. To this day, scalable production leading to exceptional material properties has been difficult to attain. Most methods require harsh chemicals, which result in destroying the graphene surface. A method was developed, exploiting high speed elongational flow in a novel designed batch mixer; creating a distribution of pristine few to many layer graphene flakes. The method focuses on exfoliating in a molten polyamide 66 (PA66) matrix, creating a graphene reinforced polymer matrix composite (G-PMC). The process revealed that high speed elongational flow was able to create few layer graphene. Graphite exfoliation was found driven in part by diffusion, leading to intercalation of PA66 in graphite. The intercalated structure lead to increases in the hydrogen bonding domain, creating anisotropic crystal domains. The thermal stability of the G-PMC was found to be dependent to the degree of exfoliation, PA66 crystal structure and composite morphology. The aim of this research is to characterize uniquely produced graphene containing polymer matrix composites using a newly created elongational flow field. Using elongational flow, graphite will be directly exfoliated into graphene within a molten polymer.

Fiber-reinforced polymer matrix composites offer lightweight, high mechanical performance but have required much effort to achieve good fiber–matrix adhesion and uniform distribution, and generally suffer from low impact resistance. In this work, a uniform, high shear melt-processing method was used to prepare carbon fiber (CF) reinforced polyetheretherketone (PEEK), carbon nanofiber (CNF) reinforced PEEK, and multi-scale CF and CNF reinforced PEEK composites. Scanning electron microscopy images show good fiber distribution and fiber–matrix interaction, as well as surface crystallization of PEEK from the fiber surfaces. Tensile modulus and strength increase most significantly with the addition of CF but with a loss in ductility. The multi-scale composite of CF–CNF-PEEK displays the stiffening effect from the CF and retains more ductility due to the CNF. Further, the CF–CNF-PEEK composite displays the highest impact energy absorption. This study shows that good mixing of CFs and CNFs is achievable in PEEK using a uniform, high shear processing method that can easily produce intricate shapes and provides a stiff, high impact energy absorption multi-scale carbon fiber-reinforced composite.