M ULTIFUNCTIONAL R IGID P OLYURETHANE N ANOCOMPOSITE F OAM MADE WITH G RAPHENE N ANOPLATELETS 2012 Society of Plastics Engineers Annual Technical Conference O VERVIEW Nanocomposites are the new material standard set to tackle old and new challenges in our ever changing technological needs. Polymers have been shown to be a great cost-effective matrix material for nanocomposites as adding small weight percents of nanofillers have greatly enhanced their properties and performance. The use of polymer foams as matrix materials with their microscope structure widens the potential application of polymer nanocomposites. Combining rigid polyurethane foam with a nanomaterial like graphene nanoplatelets, which have diverse properties, results in the creation of a multifunctional structured material with vastly improved performance. This research investigates the benefits and challenges of adding a nanoplatelet morphology to a water-blown rigid polyurethane foam using pour-in-place methods. D ESCRIPTION OF M ATERIALS Graphene is a single layer of graphite consisting of a planar hexagonal arrangement of π-bonded carbons Cost effective method for making graphene nanoplatelets (GnP) was developed at MSU and involves natural graphite intercalated with acid groups between graphene layers, which upon microwave heating, expands forcing the layers apart Forms platelets of high tensile modulus at 1000 GPa, electrical and thermal conductivities of 10 7 S/m and 3000 W/mK, in the through plane direction. Rigid Polyurethane Foam : 12 lb/ft 3 closed-cell, pour-in-place, molded density, water- blown polyurethane-polyisocyanurate foam from Stepan. Contains an isocyanate (polymeric MDI) and a polyol blend (polyether, surfactant, catalysts and blowing agent) E XPERIMENTAL P ROCEDURE 1.The GnP is pre-treated at 450 °C for two hours and has average lateral dimensions of 25 μm (GnP-25) or 5 μm (GnP-5). 2.GnP is added first to polyol blend then the isocyanate as needed and sonicated 3.The dispersion is checked before components are combined and stirred for 30 s and poured into a teflon-lined mold 4.Lid and a weight is added on top to control density Diandra Rollins and Lawrence T. Drzal Michigan State University, East Lansing, MI R ESULTS D ISCUSSION Small additions of GnP can greatly enhance the mechanical properties. GnP-25 achieved percolation threshold at 4 wt% where there is a change in electrical resistivity from 44.7 GΩ to 90 kΩ a decrease of over 10 6 Ω! Challenge is finding a balance between the electrical and mechanical properties as high loadings and large nanoplatelets form agglomerations which act as stress concentrators Agglomeration is most likely formed during mixing due to high viscosity of components and short mixing time C ONCLUSIONS AND F UTURE W ORK This work has successfully shown that graphene nanoplatelets can be used to improve both mechanical and electrical properties These methods and materials are low cost compared to previous research conducted Creation of a thermally conductive network means greater chance for agglomeration as scattering of phonons require better contact between platelets Functionalization of the GnP to improve dispersion and percolation will also be investigated R EFERENCES 1.Fukushima, H. “Graphite Nanoreinforcements in Polymer Nanocomposites.” Ph.D. Dissertation, Michigan State University, East Lansing, MI pp (2003). 2.Xu, X.-B., et al. Ultralight conductive carbon-nanotube polymer composite. Small, 3, 408 (2006). SPE Poster Number: G33 April 2-4, 2012, Orlando, FL USA H 2 SO 4, HNO 3 Heat Pulverize Figure 2: Reflectance optical microscopy images of isocyanate with 2 wt% GnP-25 (left) and polyol blend with 6 wt% GnP-5 (right). Figure 3: Polyurethane-Polyisocyanurate rigid 12 lb/ft 3 foam with 6 wt% GnP-5. Expansion of graphite Graphite showing graphene layers Acid-intercalated graphite Expanded graphite wormsGraphene nanoplatelets Figure 6: Compressive mechanical properties of rigid foam showing the average of four samples and the standard error. Figure 7: Electrical resistivity of rigid foam showing the average of three samples measured with two-point probe and the standard error. 200 μm Average Cell Diameter: 65 μm ± 63 μm Figure 1: Schematic of synthesis to make GnP. Figure 4: SEM image of PUR/PIR with 6 wt% GnP-5 and corresponding cell sizes taken from a count of 60 cells. Figure 5 : Field-emission SEM images of PUR/PIR with 2 wt% gnP-25 and 7 wt% GnP-5.