DEVELOPMENT OF THE DISPLACED FOAM DISPERSION TECHNIQUE FOR THE - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS DEVELOPMENT OF THE DISPLACED FOAM DISPERSION TECHNIQUE FOR THE MANUFACTURE OF MULTISCALE COMPOSITES M. McCrary-Dennis, O.I. Okoli* C. Zeng High-Performance Materials Institute, FAMU – FSU College of Engineering, Tallahassee, FL, USA * Corresponding author: Okenwa I. Okoli (okoli@eng.fsu.edu) Keywords : Carbon nanotubes, dispersion, foams, multiscale composites, nanomaterials [ Error! thermal, and mechanical properties 1.0 Introduction Reference source not found. ]. Over the past five decades, the utilization of advanced composites has shown increasing promise Some of the more widely used methods for with their well documented advantages of high manufacturing conventional composite parts are wet stiffness to weight rations, corrosion resistance, and lay-up, pultrusion, resin transfer molding (RTM), functional integration. As such, the market share of and vacuum assisted resin transfer molding structural composites has continued to experience (VaRTM). Others include autoclave processing, exponential growth. Traditional fiber reinforced resin film infusion (RFI), prepreg method, filament composites (FRCs) have matured with respect to winding, and fiber placement technology [5]. their material properties. For instance, their in-plane, fiber-dominant properties make them highly Multiscale composites, especially with the use of desirable compared to metals, but their through- carbon nanotubes (CNTs), have yielded enhanced thickness or z-axis properties are matrix-dominant structural (through thickness) properties, and and, thus, have limited their use. [1-2]. increased electrical and thermal conductivities. The manufacturing of such composite structures have Researchers have worked on improving the thru- however proved difficult or cumbersome, primarily thickness properties of composites by introducing because the introduction of CNTs increases the nanomaterials to manufacture multiscale composites. viscosity of the resins. The current processes This has also allowed for multifunctionality in through which CNTs are integrated are time composite structures. consuming, can be hazardous, and often require a high technical knowledge/skill level, limiting the 2.0 Manufacture of Multiscale Composites number of qualified handlers. This in turn can hinder 2.1 Current Processes and slow, productivity. Additionally, the processes may yield undesirable results; for example, voids FRCs have found extensive use in aerospace, weaken areas of the composite; filtration impedes automotive, construction, recreational equipment the complete impregnation of CNTs within the and industrial sectors but their previously stated desired part; and non-uniform dispersion gives way limitations have prohibited them from reaching their to a variation in the material properties over the area full potential [ Error! Reference source not of the composite. This makes laminate manufacture found. ]. The incorporation of nanoparticles in through resin infusion, difficult with many polymers opens a new prototype where polymer researchers resorting to open mold techniques. matrices can be tailored to optimize specific Moreover, current techniques mostly result in the properties, just as fiber orientation is used to application of CNTs throughout the entire laminates, optimize conventional advanced composites. For rather than in selected areas. Subsequently, one of instance, nanoparticles such as carbon nanofibers the main barriers, to the widespread use of CNT (CNFs) and carbon nanotubes (CNTs) have been applied composites, is an efficient mass-producible recognized as promising nanoconstituents in manufacturing process. In this paper the novel polymer nanocomposites (PNCs). This is because CNFs and CNTs possess excellent electrical,

Development of DFD Technique for Manufacture of Multiscale Composites Displaced Foam Dispersion (DFD) technique will sample relative to the neat FRC sample [9]. The Tg address some of these issues. reduction was suggestive that the cross link density decreases due to interference of the functional groups on the CNTs during curing. As a result, the 2.1.1 Nanocomposites and Multiscale Composites presence of the functionalized CNTs disrupts the Researchers using CNFs and CNTs in the optimized epoxy resin-curing agent ratio in the manufacture of polymer nanocomposites (PNCs) curing reaction. have reported mechanical, electrical, and thermal 2.1.2 Problems Currently Existing in the property enhancements which result from the Manufacture of Multi-Scale Composites synergy of the matrix and the nanoparticles [6]. Studies have shown that chemically modifying the A major barrier to the widespread use of composites surfaces of nanoparticles helps them disperse better is the inability to efficiently mass produce them. The in polymer matrices and results in improved physical incorporation of carbon nanotubes which have been properties [7]. Thus, enhancing the PNC matrix reported to improve the mechanical, thermal, and properties should lead to property enhancements in electrical properties of resin systems [1, 2], further the FRC system and result in a composite with the complicates the problem. Two main issues need to potential to perform in a multifunctional capacity. be addressed to effectively improve the material Modifying the fiber reinforcement constituent within properties of polymers when adding carbon a FRC system by grafting [8] or electrophoretically nanotubes as filler constituents. These issues are the depositing [9] nanoparticles onto the fiber can serve interfacial bonding, and the proper dispersion of the as another way to develop multifunctional individual CNTs in the polymeric matrix. composites. Thus, multi-scale fiber reinforced Investigations focusing on the interfacial bonding composites (M-FRCs) can be manufactured by have been performed by Wagner and colleagues [8]. either modifying the resin matrix or fiber They performed pull-out tests of individual carbon reinforcement. Qiu et al. [9] studied CNT-Glass- nanotubes embedded in a polymer matrix to evaluate epoxy multiscale composites, and reported a 27% the interfacial shear strength of the nanotube increase in tensile modulus, and 16% increase in polymer system. The interfacial adhesion to the tensile strength, based on 1 wt% functionalized CNT polymer can be enhanced by chemical inclusions. In studies that have modified the fiber functionalization of the nanotube surface. Molecular reinforcement, researchers have also reported dynamics simulations by Gates et al. [11] predicted improved mechanical and thermomechanical an influence of chemical bonding between the properties [10]. Bekyarova et al. [4] studied the nanotubes and the matrix on the interfacial adhesion. effect of electrophoretically dispersing (EPD) 0.25 wt% functionalized CNTs onto carbon fiber The dispersion of the CNTs in the matrix system is preforms followed by fabrication of M-FRCs using imperative. Nano-scaled particles exhibit an the VARTM process. They observed a 27% enormous surface area being several orders of enhancement in interlaminar shear strength (ILSS). magnitude larger than the surface of conventional The mechanical property enhancements were fillers. This surface area acts as interface for stress attributed to the use of functionalized CNTs which transfer, but is also responsible for the strong enhanced their dispersion, and improved the CNT- tendency of the CNTs to form agglomerates. An polymer matrix interfacial bonding. In a study efficient exploitation of their properties in polymers investigating the dimensional stability of is therefore related to their homogeneous dispersion epoxy/CNT/glass-fiber M-FRC, other researchers in the matrix, a break-up of the agglomerates and a reported that their 1 wt% MFRC sample exhibited a good wetting with the polymer. 25% reduction in coefficient of thermal expansion (CTE) relative to their neat sample [4]. The CTE The manufacturing of M-FRCs has also been reduction was suggestive of well dispersed CNTs difficult due to the rather significant increase in resin throughout the matrix of the M-FRC. In the same viscosity once CNTs have been added. This change research they reported an 11ºC reduction in the glass in resin morphology impedes resin infusion through transition temperature (Tg) of their 1 wt% M-FRC 2