Covalent Conjugates of Graphene Nanoparticles and Polymer Chains and Composite Materials Formed Therefrom

#The present invention relates to high efficiency mixing methods to transform a polymer composite containing well-crystallized graphite particles into nano-dispersed single or multi-layer graphene particles having various commercial applications.

#Polymer compositions are being increasingly used in a wide range of areas that have traditionally employed the use of other materials such as metals. Polymers possess a number of desirable physical properties, are lightweight, and inexpensive. In addition, many polymer materials may be formed into a number of various shapes and forms and exhibit significant flexibility in the forms that they assume, and may be used as coatings, dispersions, extrusion and molding resins, pastes, powders, and the like.

#The various applications for which it would be desirable to use polymer compositions require materials with electrical conductivity. However, a significant number of polymeric materials fail to be intrinsically electrically or thermally conductive enough for many of these applications.

#FIG. 1 is a flowchart illustrating various steps that an in situ exfoliation method of fabricating a graphene-reinforced polymer matrix composite may implement.

#FIG. 2 is a graph illustrating the log shear stress versus the log shear strain rate collected for a polymer at three different constant temperatures.

#FIGS. 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, and 3i (collectively “FIG. 3”) illustrate the morphology analysis of 2% graphite exfoliated in polysulfone at mixing times of 3 minutes shown in 20 μm scale and 1K× magnification (FIG. 3a), in 1 μm scale and 10K× magnification (FIG. 3d), and in 1 μm scale and 50K× magnification (FIG. 3g); 30 minutes in 10 μm scale and 1K× magnification (FIG. 3b), in 1 μm scale and 10K× magnification (FIG. 3e), in 1 μm scale and 50K× magnification (FIG. 3h); and 90 minutes in 10 μm scale and 1K× magnification (FIG. 3c), in 1 μm scale and 10K× magnification (FIG. 30, in 1 μm scale and 50K× magnification (FIG. 3i), according to an in situ exfoliation method of the present disclosure.

#This disclosure provides a high-efficiency mixing method to transform a polymer composite that contains well-crystallized graphite particles into nano-dispersed single or multi-layer graphene particles. The method involves in situ exfoliation of the graphite layers by compounding in a batch mixer or extruder that impart repetitive, high shear strain rates. In both processes, longer mixing times provide enhanced exfoliation of the graphite into graphene nanoparticles within the polymer matrix composite (PMC). In addition, additives may be used to promote sufficient graphene/polymer bonding, thereby yielding a low-density graphene-reinforced polymer matrix composite (G-PMC). The method is low cost to produce a G-PMC that offers numerous property advantages, including increased specific stiffness and strength, enhanced electrical/thermal conductivity, and retention of optical transparency.

#The terms “graphene” or “graphene nanoparticles” refer to the name given to a single layer of carbon atoms densely packed into a benzene-ring structure. Graphene, when used alone, may refer to single-layer graphene, few-layer graphene, multi-layer graphene, graphene flakes, and/or graphene platelets, in a pure and uncontaminated form.

#Graphite, the starting material from which graphene is formed, is composed of a layered planar structure in which the carbon atoms in each layer are arranged in a hexagonal lattice. The planar layers are defined as having an “a” and a “b” axis, with a “c” axis normal to the plane defined by the “a” and “b” axes. The graphene particles produced by the inventive methods have an aspect ratio defined by the “a” or “b” axis distance divided by the “c” axis distance. Aspect ratio values for the inventive nanoparticles exceed 25:1 and typically range between 50:1 and 1000:1.