Showing papers on "Composite number published in 2004"

Big returns from small fibers: A review of polymer/carbon nanotube composites

Abstract: This paper reviews recent studies conducted on carbon nanotube/polymer composites. Carbon nanotubes are promising new materials for blending with polymers with potential to obtain low-weight nanocomposites of extraordinary mechanical, electrical, thermal and multifunctional properties. The size scale, aspect ratio and properties of nanotubes provide advantages in a variety of applications, including electrostatically dissipative materials; advanced materials with combined stiffness, strength and impact for aerospace or sporting goods; composite mirrors; automotive parts that require electrostatic painting and automotive components with enhanced mechanical properties. The various processing methods for producing these nanocomposites are discussed, in particular melt mixing, solution processing and in-situ polymerization. Some key results are summarized, relating to the mechanical, electrical, thermal, optical and surface properties. Finally, the challenges for the future are discussed in terms of processing, characterization, nanotube availability, nanotube tailoring, and the mechanisms governing the behavior of these remarkable nanoscale composites. Polym. Compos. 25:630–645, 2004. © 2004 Society of Plastics Engineers.

All-Cellulose Composite

Abstract: An all-cellulose composite, in which both the fibers and the matrix are cellulose, was prepared by distinguishing the solubility of the matrix cellulose into the solvent from that of the fibers through pretreatment. The structure, mechanical, and thermal properties of this composite were investigated using an X-ray diffraction, a scanning electron microscope, a tensile test, and dynamic viscoelastic and thermomechanical analyses. The tensile strength of uniaxially reinforced all-cellulose composite was 480 MPa at 25 °C, and the dynamic storage modulus was as high as 20 GPa at 300 °C. These were comparable or even higher than those of conventional glass-fiber-reinforced composites. In addition, a linear thermal expansion coefficient was about 10-7 K-1. This all-cellulose composite shows substantial advantages, that is, it is composed of sustainable resources, there is less interface between the fiber and the matrix, it possesses excellent mechanical and thermal performance during use, and it is biodegradab...

High Performance Nanotube‐Reinforced Plastics: Understanding the Mechanism of Strength Increase

Abstract: Polymer–multiwalled carbon nanotube composite films were fabricated using two types of polymer matrices, namely poly(vinyl alcohol), (PVA) and chlorinated polypropylene. In the first case, the PVA was observed to form a crystalline coating around the nanotubes, maximising interfacial stress transfer. In the second case the interface was engineered by covalently attaching chlorinated polypropylene chains to the nanotubes, again resulting in large stress transfer. Increases in Young's modulus, tensile strength, and toughness of × 3.7, × 4.3, and × 1.7, respectively were observed for the PVA-based materials at less than 1 wt.-% nanotubes. Similarily for the polypropylene-based composites, increases in Young's modulus, tensile strength and toughness of × 3.1, × 3.9, and × 4.4, respectively, were observed at equivalent nanotube loading levels. In addition, a model to describe composite strength was derived. This model shows that the tensile strength increases in proportion to the thickness of the interface region. This suggests that composite strength can be optimized by maximising the thickness of the crystalline coating or the thickness of the interfacial volume partially occupied by functional groups.

Mechanical properties of continuous natural fibre-reinforced polymer composites

Abstract: The mechanical behaviour high density polyethylene (HDPE) reinforced with continuous henequen fibres (Agave fourcroydes) was studied. Fibre-matrix adhesion was promoted by fibre surface modifications using an alkaline treatment and a matrix preimpregnation together with a silane coupling agent. The use of the silane coupling agent to promote a chemical interaction, improved the degree of fibre-matrix adhesion. However, it was found that the resulting strength and stiffness of the composite depended on the amount of silane deposited on the fibre. A maximum value for the tensile strength was obtained for a certain silane concentration but when using higher concentrations, the tensile strength did not increase. Using the silane concentration that resulted in higher tensile strength values, the flexural and shear properties were also studied. The elastic modulus of the composite did not improve with the fibre surface modification. The elastic modulus, in the longitudinal fibre direction obtained from the tensile and flexural measurements was compared with values calculated using the rule of mixtures. It was observed that the increase in stiffness from the use of henequen fibres was approximately 80% of the calculated values. The increase in the mechanical properties ranged between 3 and 43%, for the longitudinal tensile and flexural properties, whereas in the transverse direction to the fibre, the increase was greater than 50% with respect to the properties of the composite made with untreated fibre composite. In the case of the shear strength, the increase was of the order of 50%. From the failure surfaces it was observed that with increasing fibre-matrix interaction the failure mode changed from interfacial failure to matrix failure.

Synthesis and characterization of plasma spray formed carbon nanotube reinforced aluminum composite

Abstract: A trend has been perceived in the field of composite materials to employ carbon nanotubes as reinforcement in synthesizing composites of unique properties. In this endeavor, free standing structures of Al-based nanostructured composite with carbon nanotubes as second phase particles has been synthesized by plasma spray forming technique. Optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy has been carried out to analyze the composite structure and to verify the retention of carbon nanotubes. Besides, density and microhardness measurements have been performed to understand the effect of carbon nanotube reinforcement on the mechanical properties of the composite. The characterization affirms the presence of unmelted and chemically unreacted carbon nanotubes in the composite. Moreover, the composite experienced an increase in relative microhardness due to the presence of carbon nanotube.

Reactive Hot Pressing of ZrB2–SiC Composites

Abstract: A ZrB 2 -SiC composite was prepared from a mixture of zirconium, silicon, and B 4 C via reactive hot pressing. The three-point bending strength was 506 ± 43 MPa, and the fracture toughness was 4.0 MPa.m 1/2 . The microstructure of the composite was observed via scanning electron microscopy; the in-situ-formed ZrB 2 and SiC were found in agglomerates with a size that was in the particle-size ranges of the zirconium and silicon starting powders, respectively. A model of the microstructure formation mechanism of the composite was proposed, to explain the features of the phase distributions. It is considered that, in the reactive hot-pressing process, the B and C atoms in B 4 C will diffuse into the Zr and Si sites and form ZrB 2 and SiC in situ, respectively. Because the diffusion of Zr and Si atoms is slow, the microstructure (phase distributions) of the obtained composite shows the features of the zirconium and silicon starting powders.

One-time use composite tool formed of fibers and a biodegradable resin

Abstract: The present invention is directed to disposable composite downhole tool formed of a resin-coated fiber. The fiber is formed of a degradable polymer, such as a poly(lactide) or polyanhydride. The resin is formed of the same degradable polymer as the fiber. It chemically bonds to the fiber, thereby making a strong rigid structure once cured. The fiber may be formed into a fabric before being coated with the resin. Alternatively, the fiber is formed of a non-biodegradable material.

All-organic dielectric-percolative three-component composite materials with high electromechanical response

Abstract: By combining the high-dielectric copper phthalocyanine oligomer (PolyCuPc) and conductive polyanline (PANI) within polyurethane (PU) matrix an all-organic three-component dielectric-percolative composite with high dielectric constant is demonstrated. In this three-component composite system, the high-dielectric-constant PolyCuPc particulates enhance the dielectric constant of the PU matrix and this combined two-component dielectric matrix in turn serves as the high-dielectric-constant host for the PANI to realize percolative phenomenon and further enhance the dielectric response. As a result, an electromechanical strain of 9.3% and elastic energy density of 0.4 J/cm(3) under an electric field of 20 V/mum can be induced.

Preparation of polypropylene/carbon nanotube composite powder with a solid‐state mechanochemical pulverization process

Abstract: A solid-state mechanochemical pulverization process, that is, pan milling, was used to prepare a polypropylene (PP)/carbon nanotube (CNT) composite powder. The composite powder was then melt-mixed with a twin-roll masticator to obtain a PP/CNT composite. The morphology of the PP/CNT powder and the PP/CNT composite was investigated. The crystallization and mechanical properties of the latter were also studied. After 20 milling cycles (ca. 60 min), the average diameter of PP/3 wt % CNT composite powder particles was a few micrometers. The length of the CNTs was reduced from a few micrometers to 0.4–0.5 μm. The CNTs became straighter and more uniform in length. The effects of incorporating the CNTs into PP were as follows: (1) the crystallization rate and temperature of PP increased, (2) a strong b-plane orientation of PP was induced, and (3) the Young's modulus and yield strength of PP increased. Interfacial adhesion between PP and the CNTs was improved by the mechanical action of the solid-state pulverization process used, which favored the dispersion of the CNTs into PP. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 378–386, 2004

System and process for producing nanowire composites and electronic substrates therefrom

Abstract: The present invention relates to a system and process for producing a nanowire-material composite. A substrate (602) having nanowires (606) attached to a portion (604) of at least one surface is provided. A material is deposited over the portion to form the nanowire-material composite. The process further optionally comprises separating the nanowire-material composite from the substrate to form a freestanding nanowire-material composite. The freestanding nanowire material composite is optionally further processed into a electronic substrate. A variety of electronic substrates can be produced using the methods described herein. For example, a multi-color light-emitting diode can be produced from multiple, stacked layers of nanowire-material composites, each composite layer emitting light at a different wavelength.

Effect of Two-Stage Process on the Preparation and Characterization of Porous Carbon Composite from Rice Husk by Phosphoric Acid Activation

Abstract: Activated carbon composite prepared from rice husk using phosphoric acid activation has been studied through precarbonization of the precursor followed by chemical activation. This method can produce carbons with micro- and mesoporous structure. The ratio of chemical activating agent to precarbonized carbon was fixed at 4.2. The surface area, pore volume, and pore size distribution of carbon composite samples activated at three different temperatures (700, 800, and 900 °C) were measured using nitrogen adsorption isotherms at 77 K. The pore-opening and pore-widening effects occurred simultaneously during the process, as evidenced by scanning electron micrographs. The X-ray diffraction curve revealed the evolution of crystallites of carbon and silica during activation at higher temperature. The FTIR spectrum also provided evidence for the presence of silica in the carbon composite. The proper choice of the preparation conditions had an influence on the micropore and mesopore volumes of the activated carbon ...

A strong magnetoelectric voltage gain effect in magnetostrictive-piezoelectric composite

Abstract: A magnetoelectric laminate composite consisting of magnetostrictive Terfenol-D (Tb1–xDyxFe2–y) and piezoelectric Pb(Zr,Ti)O3 layers has an extremely high voltage gain effect of ≈300 at its resonant state, offering potential for high-voltage miniature transformer applications.