Intralaminar Reinforcement for Biomimetic Toughening of Bismaleimide Composites Using Nanostructured Materials

Abstract

Many conventional composite materials are composed of multiple layers of continuous fiber reinforced resin produced by lamination of b-staged prepreg and subsequent cure. These materials exhibit very high strength and stiffness in the plane, dominated by the properties of the fibers. The Achilles heel of such composites is the interlaminar strength, which is dependent on the strength of the unreinforced resin, often leading to failure by delamination under load. Current methods for increasing the interlaminar shear strength of composites consist of inserting translaminar reinforcement fibers through the entire thickness of a laminated composite, such as z-pin technology developed by Foster-Miller [1]. While effective, this technique adds several processing steps, including ultrasonic insertion of the z-pins into the laminate, subsequently causing a significant cost increase to laminated composites. Described in this paper is a process utilizing single-walled carbon nanotubes (SWNTs) and vapor grown carbon nanofibers as reinforcing elements promoting interlaminar shear strength and toughness in carbon fiber/bismaleimide (BMI) resin composites. The resulting composites mimic the natural reinforcing mechanism utilized in insect cuticles. Three different methods of increasing the affinity of these carbon nanofillers for the BMI matrix were explored. The mechanical properties of these composites were assessed using end notch flexure testing. The results indicated that including nanofiller at the laminae interface could increase the interlaminar shear strength of carbon fiber/BMI composites by up to 58%. SEM micrographs revealed that the nanofiller successfully bridged the laminae of the composite, thus biomimicking the insect cuticle. Composite fabrication techniques developed on this program would have a wide variety of applications in space and aerospace structures including leading and trailing edges of aircraft wings.

Improving the Dispersion and Integration of Single-Walled Carbon Nanotubes in Epoxy Composites through Functionalization

“…The use of functionalized nanotubes for epoxy composite fabrication was reported by Tiano et al 16 The sidewall surfaces of the nanotubes were functionalized via free-radical polymerization of poly(methyl methacrylate). With the 1 wt % load of functionalized nanotubes in the epoxy, an improvement in mechanical properties by an 11% increase in stress and a 21% increase in modulus over those of the unfilled epoxy was demonstrated, which is different from the observed sharp decrease of these parameters when using pristine nanotubes.…”

“…A number of recent research efforts have used nanotubes for polymer composites' reinforcement. − Some strategies have been proposed to overcome the various barriers for accomplishing dispersion including the use of ultrasonication, high shear mixing, the aid of surfactants, the use of chemical modification through functionalization, wrapping the tubes with polymer chains, and combinations of these. However, to date, very limited success for nanotube-reinforced epoxy composites has been achieved, mainly because of poor dispersion.…”

Chemical Derivatisation of Multiwalled Carbon Nanotubes Using Diazonium Salts

“…[5,10,11] Physisorption onto carbon was recently reviewed by Zen et al [12] For example CNTs can be modified by wrapping polymers around them [13] or by adsorbing molecules containing porphyrin rings onto the surface. [14] Whilst CNTs have been covalently derivatised in the past, this has mainly been restricted to functionalising the surface of the CNTs using organic chemical reaction pathways with small organic molecules or functional groups with the specific aim of improving the properties of CNTs such as solubilising them in a particular media, [14][15][16][17] improving their mechanical properties such as strength or binding ability when formed in composite materials such as CNT-epoxy resins [18,19] or polymers. [20] Where covalent attachment of modifying molecules to the CNT surface has been achieved to impart an improved electroanalytical response, this has been carried out by electrochemical oxidation/reduction of the modifier and subsequent chemisorption.…”

Coarse Molecular-Dynamics Analysis of Structural Transitions in Solid Materials

“…Surface functionalization is the process by which various chemical functional groups are attached to the nanotube sidewalls and/or endcaps using either covalent or non-covalent bonding. This process was first proposed for nanotubes by Tiano et al [21]. By specifically choosing functional groups based upon the composite matrix material, a dramatic increase in the interfacial bonding in the composite can be achieved.…”