Usama F. Kandil

The overall effect of reactive rubber nanoparticles and nano clay on the mechanical properties of epoxy resin

Abstract Epoxy resin, a thermoset polymer matrix used for technical applications; exhibit some outstanding properties such as high modulus, high chemical resistance and high dimension stability. However, the high crosslink density of epoxy makes this material brittle with low impact strength and poor resistance to crack propagation, which limits their many end use applications. It is an important objective to explore new routes toward toughening of epoxy resins without affecting stiffness, strength, and glass temperature. The main objective of this work is to incorporate reactive rubber nanoparticles (RRNP) and organically modified nanoclay (Cloisite-30B) into epoxy matrix with the aim of obtaining improved material with higher toughness without compromising the other desired mechanical properties. Epoxy hybrids nanocomposites containing RRNP, Cloisite-30B and RRNP/Cloisite-30B mixture were synthesized and characterized to compare the different properties which normally result from the use of single filler and hence aiming to improve toughness/stiffness balance.

Improved Strength and Toughness of Carbon Woven Fabric Composites with Functionalized MWCNTs

This investigation examines the role of carboxyl functionalized multi-walled carbon nanotubes (COOH-MWCNTs) in the on- and off-axis flexure and the shear responses of thin carbon woven fabric composite plates. The chemically functionalized COOH-MWCNTs were used to fabricate epoxy nanocomposites and, subsequently, carbon woven fabric plates to be tested on flexure and shear. In addition to the neat epoxy, three loadings of COOH-MWCNTs were examined: 0.5 wt%, 1.0 wt% and 1.5 wt% of epoxy. While no significant statistical difference in the flexure response of the on-axis specimens was observed, significant increases in the flexure strength, modulus and toughness of the off-axis specimens were observed. The average increase in flexure strength and flexure modulus with the addition of 1.5 wt% COOH-MWCNTs improved by 28% and 19%, respectively. Finite element modeling is used to demonstrate fiber domination in on-axis flexure behavior and matrix domination in off-axis flexure behavior. Furthermore, the 1.5 wt% COOH-MWCNTs increased the toughness of carbon woven composites tested on shear by 33%. Microstructural investigation using Fourier Transform Infrared Spectroscopy (FTIR) proves the existence of chemical bonds between the COOH-MWCNTs and the epoxy matrix.

Synthesis and characterization of phenol/formaldehyde nanocomposites: Studying the effect of incorporating reactive rubber nanoparticles or Cloisite-30B nanoclay on the mechanical properties, morphology and thermal stability

Abstract In this work, phenol/formaldehyde nanocomposites were synthesized using reactive rubber nanoparticles (RRNP) and cloisite30B nanoclay with different percentages and were fully investigated. A little amount of these nanomaterials enhanced the mechanical properties of the produced composites. This enhancement is attributed to the interaction of these nanomaterials with the bakelite matrix. In bakelite/RRNP, the mechanical properties enhancement is due to the chemical connection of RRNP to the bakelite matrix while in bakelite/Cloisite30B, this enhancement is due to polar/polar interaction. It was observed that the composites exhibited an intercalated disordered structure by means of Xray diffraction (XRD) and transmission electronic microscopy. The crosslinking density of the bakelite network was greatly influenced by the presence and type of nanomaterial that was added to the resin. The thermal stability was investigated with TGA/DSC which proved that these nanocomposite are (10–20)% more thermally stable than neat Bakelite resin.

Effect of fiber loading on the mechanical and physical properties of “green” bagasse–polyester composite

Abstract The main aim of this work is to fill unsaturated polyester resin with bagasse agricultural waste, as reinforcement, to prepare green wooden–polymer composites. Bagasse fibers were treated with 5% sodium hydroxide and then with dilute sulfuric acid. Bagasse–polyester composites were prepared by addition of 5, 10 and 15% of untreated and alkali treated bagasse fibers to polyester. The crosslinking reaction was performed using methyl ethyl ketone peroxide as a catalyst and cobalt octoate as an accelerator. The prepared composites were then exposed to post-curing at elevated temperature for completely crosslinking. The flexural behavior of the prepared composites was studied. An enhancement in the mechanical properties was achieved after chemical treatment. In addition, water absorption and chemical resistance were conducted showing that the produced bagasse–polyester composite with appreciable mechanical and physical properties is a new partner and cost effective material for many advanced industrial applications in addition to their environmental friendly behavior.

Monitoring Damage Propagation in Glass Fiber Composites Using Carbon Nanofibers

In this work, we report the potential use of novel carbon nanofibers (CNFs), dispersed during fabrication of glass fiber composites to monitor damage propagation under static loading. The use of CNFs enables a transformation of the typically non-conductive glass fiber composites into new fiber composites with appreciable electrical conductivity. The percolation limit of CNFs/epoxy nanocomposites was first quantified. The electromechanical responses of glass fiber composites fabricated using CNFs/epoxy nanocomposite were examined under static tension loads. The experimental observations showed a nonlinear change of electrical conductivity of glass fiber composites incorporating CNFs versus the stress level under static load. Microstructural investigations proved the ability of CNFs to alter the polymer matrix and to produce a new polymer nanocomposite with a connected nanofiber network with improved electrical properties and different mechanical properties compared with the neat epoxy. It is concluded that incorporating CNFs during fabrication of glass fiber composites can provide an innovative means of self-sensing that will allow damage propagation to be monitored in glass fiber composites.

Monitoring Moisture Damage Propagation in GFRP Composites Using Carbon Nanoparticles

Glass fiber reinforced polymer (GFRP) composites are widely used in infrastructure applications including water structures due to their relatively high durability, high strength to weight ratio, and non-corrosiveness. Here we demonstrate the potential use of carbon nanoparticles dispersed during GFRP composite fabrication to reduce water absorption of GFRP and to enable monitoring of moisture damage propagation in GFRP composites. GFRP coupons incorporating 2.0 wt % carbon nanofibers (CNFs) and 2.0 wt % multi-wall carbon nanotubes (MWCNTs) were fabricated in order to study the effect of moisture damage on mechanical properties of GFRP. Water absorption tests were carried out by immersing the GFRP coupons in a seawater bath at two temperatures for a time period of three months. Effects of water immersion on the mechanical properties and glass transition temperature of GFRP were investigated. Furthermore, moisture damage in GFRP was monitored by measuring the electrical conductivity of the GFRP coupons. It was shown that carbon nanoparticles can provide a means of self-sensing that enables the monitoring of moisture damage in GFRP. Despite the success of the proposed technique, it might not be able to efficiently describe moisture damage propagation in GFRP beyond a specific threshold because of the relatively high electrical conductivity of seawater. Microstructural investigations using Fourier Transform Infrared (FTIR) explained the significance of seawater immersion time and temperature on the different levels of moisture damage in GFRP.

Investigation of FRP Lap Splice Using Epoxy Containing Carbon Nanotubes

AbstractIn many situations, it is necessary to splice multiple layers of fiber-reinforced polymer (FRP) composite laminates. The relatively low bond and shear strength of FRP layers usually necessitates long lap splices. In this paper, the authors demonstrate how lap splices shorter than those used in standard FRP design today can be made viable by incorporating carbon nanotubes in the epoxy resin. Experimental and numerical investigations are conducted to evaluate the significance of using multiwalled carbon nanotubes (MWCNTs) on FRP lap splice. Double lap shear joints of carbon-fiber-reinforced polymer (CFRP) were fabricated and tested with various amounts of functionalized MWCNTs (0.5, 1.0, and 1.5%). Experiments show that the shear stress-strain response of the CFRP lap splice can be engineered with the appropriate amount of MWCNTs to increase the bond strength by 50% and/or the failure strain by 300%. The numerical modeling shows that the shear-slip at the interface governs the bond strength and duct...

Controlling off-axis stiffness and stress-relaxation of carbon fiber-reinforced polymer using alumina nanoparticles

This investigation experimentally examines the effect of incorporating alumina nanoparticles on the off-axis stiffness and stress-relaxation of carbon fiber-reinforced polymer composites. Four epoxy–alumina nanoparticle nanocomposites incorporating 0.0, 1.0, 2.0, and 3.0 wt% alumina nanoparticles of the total weight of epoxy are examined. Off-axis tension stiffness and stress-relaxation tests were performed on carbon fiber-reinforced polymer coupons fabricated with alumina nanoparticles–epoxy nanocomposites. Dynamic mechanical analysis testing of neat epoxy and epoxy nanocomposites incorporating alumina nanoparticles was used to identify the stiffness and relaxation behavior of the alumina nanoparticles–epoxy nanocomposite matrix. Fourier transform infrared spectroscopy was used to observe chemical changes when alumina nanoparticles are mixed with epoxy. It is shown that using alumina nanoparticles at a concentration close to 2.0 wt%, can reduce the off-axis stiffness by ∼30% and increase the off-axis stress-relaxation of carbon fiber-reinforced polymer by ∼10%.

Use of Carbon Nanotubes to Improve Fracture Toughness of Polymer Concrete

Bridge deck overlays often require materials that are durable and easy to apply and that have a long fatigue life. In many applications, polymer concrete (PC) has been chosen not only because it meets such requirements but also because it offers additional features such as high friction. However, the service life of PC overlays is reduced, and cracking occurs because of the continuous increase in traffic loads. This paper investigates the use of multiwalled carbon nanotubes (MWCNTs) to improve the fracture toughness and fatigue service life of PC. Pristine MWCNTs (P-MWCNTs) and MWCNTs functionalized with carboxyl (COOH-MWCNTs) were used at 0.0- (neat), 0.5-, 1.0-, 1.5-, and 2.0-wt.% contents. Three-point bending tests of notched beams were carried out in which the loading rate was controlled by crack mouth opening displacement. Direct tension tests were also used to examine the effect of MWCNTs on the tensile properties of PC. The results showed that MWCNTs improved the fracture toughness of PC by up to 56% and 112% for P-MWCNTs and COOH-MWCNTs, respectively. Samples prepared with P-MWCNTs showed increased ductility; samples with COOH-MWCNTs provided increased tensile strength. Microstructural analysis with a scanning electron microscope and Fourier transform infrared spectroscopy revealed how different types of MWCNTs at different weight contents influenced the behavior of PC.

Improving shear strength of bolted joints in pultruded glass fiber reinforced polymer composites using carbon nanotubes

The structural design of the bolted fiber reinforced polymer elements is typically governed by the capacity of the joint rather than the fiber reinforced polymer member, while the joint capacity is typically governed by the shear strength of the fiber reinforced polymer. Here, the possibility of improving the shear strength of bolted joints is investigated in the unidirectional glass fiber reinforced polymer plates by incorporating the multiwalled carbon nanotubes during glass fiber reinforced polymer fabrication. Glass fiber reinforced polymer double-shear bolted lap joints were fabricated using up to 1.0 wt% multiwalled carbon nanotubes–-epoxy nanocomposites. Finite element modeling using multicontinuum theory and element deletion techniques was performed to explain the joint behavior. The experimental investigations show that incorporating multiwalled carbon nanotubes improved the shear strength, ductility, and energy absorption significantly. Microstructural analysis proves that a chemical reaction between multiwalled carbon nanotubes and epoxy improves the shear strength of the matrix.