Showing papers on "Epoxy published in 2004"

Microcapsule induced toughening in a self-healing polymer composite

Abstract: Microencapsulated dicyclopentadiene (DCPD) healing agent and Grubbs' Ru catalyst are incorporated into an epoxy matrix to produce a polymer composite capable of self-healing. The fracture toughness and healing efficiency of this composite are measured using a tapered double-cantilever beam (TDCB) specimen. Both the virgin and healed fracture toughness depend strongly on the size and concentration of microcapsules added to the epoxy. Fracture of the neat epoxy is brittle, exhibiting a mirror fracture surface. Addition of DCPD-filled urea-formaldehyde (UF) microcapsules yields up to 127% increase in fracture toughness and induces a change in the fracture plane morphology to hackle markings. The fracture toughness of epoxy with embedded microcapsules is much greater than epoxy samples with similar concentrations of silica microspheres or solid UF polymer particles. The increased toughening associated with fluid-filled microcapsules is attributed to increased hackle markings as well as subsurface microcracking not observed for solid particle fillers. Overall the embedded microcapsules provide two independent effects: the increase in virgin fracture toughness from general toughening and the ability to self-heal the virgin fracture event.

Reinforcing Epoxy Polymer Composites Through Covalent Integration of Functionalized Nanotubes

Abstract: Strong interfacial bonding and homogenous dispersion have been found to be necessary conditions to take full advantage of the extraordinary properties of nanotubes for reinforcement of composites. We have developed a fully integrated nanotube composite material through the use of functionalized single-walled carbon nanotubes (SWNTs). The functionalization was performed via the reaction of terminal diamines with alkylcarboxyl groups attached to the SWNTs in the course of a dicarboxylic acid acyl peroxide treatment. Nanotube-reinforced epoxy polymer composites were prepared by dissolving the functionalized SWNTs in organic solvent followed by mixing with epoxy resin and curing agent. In this hybrid material system, nanotubes are covalently integrated into the epoxy matrix and become part of the crosslinked structure rather than just a separate component. Results demonstrated dramatic enhancement in the mechanical properties of an epoxy polymer material, for example, 30–70 % increase in ultimate strength and modulus with the addition of only small quantities (1–4 wt.-%) of functionalized SWNTs. The nanotube-reinforced epoxy composites also exhibited an increased strain to failure, which suggests higher toughness.

Thermal decomposition, combustion and flame-retardancy of epoxy resins—a review of the recent literature

Abstract: An overview of the recent literature on combustion and flame-retardancy of epoxy resins is presented. A brief overview of the structures of cured epoxy resins is also presented as a background for better understanding of the thermal decomposition and combustion phenomena. The literature sources were mostly taken from the publications of 1995 and later; however, for basic descriptions of the structural and thermal decomposition principles, older publications are also cited. New developments in flame-retardant additives, epoxy monomers and curing agents are described. It is shown that the main attention in recent years has been focused on phosphorus-containing epoxy monomers and epoxy resins. Silicon-containing or nitrogen-containing products and inorganic additives remain of great interest as supplementary materials to phosphorus flame-retardants. Copyright © 2004 Society of Chemical Industry

Glass transition and relaxation behavior of epoxy nanocomposites

Abstract: With advances in nanoscience and nanotechnology, there is increasing interest in polymer nanocomposites, both in scientific research and for engineering applications. Because of the small size of nanoparticles, the polymer–filler interface property becomes a dominant factor in determining the macroscopic material properties of the nanocomposites. The glass-transition behaviors of several epoxy nanocomposites have been investigated with modulated differential scanning calorimetry. The effect of the filler size, filler loading, and dispersion conditions of the nanofillers on the glass-transition temperature (Tg) have been studied. In comparison with their counterparts with micrometer-sized fillers, the nanocomposites show a Tg depression. For the determination of the reason for the Tg depression, the thermomechanical and dielectric relaxation processes of the silica nanocomposites have been investigated with dynamic mechanical analysis and dielectric analysis. The Tg depression is related to the enhanced polymer dynamics due to the extra free volume at the resin–filler interface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3849–3858, 2004

Investigation of the dispersion process of SWNTs/SC-15 epoxy resin nanocomposites

Abstract: Due to their exceptional mechanical and functional properties, carbon nanotubes are considered by many researchers as one of the most promising reinforcement for the next generation of high-performance nanocomposites. Currently, nanotube dispersion is the most critical issue for developing high-performance carbon nanotube-reinforced composites. In this research, considerable improvements of the nanotube dispersion in single-walled carbon nanotube (SWNT)/SC-15 epoxy resin nanocomposites were obtained through the use of tip sonication and the addition of acetone. Using different dispersion formulations and processing parameters, several nanocomposites samples containing 0.5 wt.% nanotubes were fabricated. Significant improvements in the mechanical properties of the resulting nanocomposites were illustrated by a 50.8% increase in the storage modulus. The significant improvements of nanotube dispersion and mechanical performance were attributed to the combined use of tip sonication and acetone as dispersion aids during sample processing.

Nanomechanical Characterization of Single-Walled Carbon Nanotube Reinforced Epoxy Composites

Abstract: Nanomechanical properties of single-walled carbon nanotube (SWNT) reinforced epoxy composites with varying weight percentage (0, 1, 3, and 5 wt%) of nanotubes were measured by nanoindentation and nanoscratch techniques. Hardness and elastic modulus were measured using a nanoindenter. Scratch resistance and scratch damage were studied using the AFM tip sliding against the SWNT reinforced sample surfaces. Nanoindentation/nanoscratch deformation and fracture behaviour was studied by in situ imaging of the indentation impressions/scratch tracks. Viscoelastic properties of the nanocomposites were measured using nanoindentation dynamic mechanical analysis tests. The reinforcing mechanisms are discussed with reference to the nanotube dispersion, interfacial bonding, and load transfer in the SWNT reinforced polymer composites.

Thermal and mechanical properties of tetrafunctional epoxy resin toughened with epoxidized soybean oil

Abstract: A potential epoxy resin, i.e. epoxidized soybean oil (ESO), was synthesized to toughen the tetrafunctional epoxy resins. The ESO was blended with the epoxy resins to obtain the modified network having ESO content from 0 to 20 wt.%. The neat epoxy resins and modified networks were characterized by the thermal and mechanical properties. As a result, thermal stability and glass transition temperature of the blends were slightly decreased with increasing the ESO content. This might be caused by the reduction of cross-linking density of the epoxy network, which could be attributed to the incomplete curing reaction in the blend systems. The critical stress intensity factor and flexural strength were increased up to 10 wt.% ESO content. This could be interpreted in terms of the addition of larger ESO molecule weight into the epoxy resins, resulting in increasing the flexible properties of the epoxy resins, or the final toughness of the blend systems.

A Review of Current Flame Retardant Systems for Epoxy Resins

Abstract: The review covers materials currently available or which appear to be in serious development, with emphasis on electrical laminates and encapsulation, and brief coverage of other applications. The dominant technology for FR-4 printed wiring boards uses tetrabromobisphenol-A reacted into the epoxy resin. Nonhalogen systems include additives such as alumina trihydrate, alumina trihydrate plus red phosphorus, and aromatic phosphates. Reactives include a dihydrooxaphosphaphenanthrene oxide and various adducts thereof, and hydroxyl-terminated oligomeric phosphorus-containing esters. A further approach is the modification of the epoxy resin by placement of aromatic groups between the glycidyloxyphenyl groups, and/or by use of a triazine-modified novolac as crosslinker. Flame retardant epoxy coatings continue to make use of ammonium polyphosphate plus char-forming additives.

Epoxy Nanocomposites Based on the Synthetic α-Zirconium Phosphate Layer Structure

Abstract: The morphology and mechanical properties of epoxy nanocomposites based on synthetic α-zirconium phosphate (α-ZrP) layer structure have been investigated. The interlayer surfaces of α-ZrP can be easily modified because of its high surface ion exchange capacity characteristics. The α-ZrP structure is layered claylike and possesses aspect ratios of at least 100. The state of exfoliation has been confirmed using direct transmission electron microscopy observation at various locations of the sample. With an addition of only 1.9 vol % α-ZrP, the tensile modulus of the α-ZrP-reinforced epoxy nanocomposite is increased by 50%, and the yield strength improved by 10%. However, the ductility of the matrix (elongation at break) is drastically reduced after the α-ZrP reinforcement. The fundamental structure−property relationship of α-ZrP-based epoxy nanocomposite is discussed.

Unidirectional hemp and flax EP‐ and PP‐composites: Influence of defined fiber treatments

Abstract: In some technical areas, mainly in the automotive industry, glass fiber reinforced polymers are intended to be replaced by natural fiber reinforced polymer systems. Therefore, higher requirements will be imposed to the physical fiber properties, fiber-matrix adhesion, and the quality assurance. To improve the properties of epoxy resins (EP) and polypropylene (PP) composites, flax and hemp fibers were modified by mercerization and MAH-PP coupling agent was used for preparing the PP composites. The effects of different mercerization parameters such as concentration of alkali (NaOH), temperature, and duration time along with tensile stress applied to the fibers on the structure and properties of hemp fibers were studied and judged via the cellulose I-II lattice conversion. It was observed that the mechanical properties of the fibers can be controlled in a broad range by using appropriate mercerization parameters. Unidirectional EP composites were manufactured by the filament winding technique; at the PP matrix material, a combination with a film-stacking technique was used. The influence of mercerization parameters on the properties of EP composites was studied with hemp yarn as an example. Different macromechanical effects are shown at hemp- and flax-PP model composites with mercerized, MAH-PP-treated, or MAH-PP-treated mercerized yarns. The composites' properties were verified by tensile and flexural tests.

Chemistry and Mechanical Properties of Epoxy-Based Thermosets Reinforced by Reactive and Nonreactive SBMX Block Copolymers

Abstract: Polystyrene-block-polybutadiene-block-poly[(methyl methacrylate)-stat-(methacrylic acid)] (SB(MA)) block copolymers incorporating acid-reactive functionalities in the last block have been synthesized and studied as modifiers for epoxy thermosets based on the diglycidyl ether of bisphenol A (DGEBA). Different techniques including differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM) have been used to demonstrate the effectiveness of the reaction-induced modification compared to that with the nonreactive or slowly reacting polystyrene-block-polybutadiene-block-poly[(methyl methacrylate)-stat-(tert-butyl methacrylate)] SB(MT) triblock copolymer. Morphological characteristics revealed by TEM indicate that SB(MT) and SB(MA) are both miscible with the epoxy prepolymer. The kinetics of grafting, network formation, and possibly phase separation were quantified from FT-IR, DSC, and cloud point investigations of DGEBA/DDS (4,4‘-diaminodi...

Migration of bisphenol A from can coatings--effects of damage, storage conditions and heating

Abstract: Bisphenol A (BPA) is an important monomer used in the manufacture of epoxy resins for internal food can linings. Experiments were conducted to investigate the effects of different storage conditions and can damage on the migration of BPA to foods. These experiments were conducted in a systematic fashion by filling empty epoxyphenolic coated cans with four foods: soup, minced beef, evaporated milk and carrots and a food simulant (10% ethanol). Filled cans of each food type or simulant were then sealed and processed using appropriate conditions, before storage at three different temperatures: 5°C, 20°C and 40°C. For each of the storage regimes, 50% of the cans were dented to establish if this would lead to increased BPA migration. Cans were removed from these stocks at intervals of 1, 3 and 9 months storage at 5°C and 20°C or 10 days, 1 and 3 months at 40°C. Some initial problems of heterogeneity between samples was overcome by determining the amount of BPA in food as well as in the can lining. It was found...

Enhancement of the wear resistance of epoxy: short carbon fibre, graphite, PTFE and nano-TiO2

Abstract: Enhancements of the wear resistance of epoxy using various fillers, e.g. short carbon fibre (CF), graphite, polytetrafluoroethylene (PTFE) and nano-TiO 2 , have been systematically investigated in the present study. Wear properties were carried out on a block-on-ring apparatus. The best wear resistant composition was achieved by a combination of nano-TiO 2 with conventional fillers; as an example, epoxy+15 vol% graphite+5 vol% nano-TiO 2 +15 vol% short-CF exhibits a specific wear rate of 3.2×10 −7 mm 3 /Nm, which is about 100 times lower when compared to the neat epoxy. Worn surfaces were investigated using a scanning electron microscope and an atomic force microscope, from which it is assumed that a mechanism of nanoscale rolling governs this positive effect of the nanoparticles. The main concept of this paper is to strength the importance of integrating various functional fillers in the design of wear resistant polymer composites.