skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Surface grafting of Kevlar fibers for improved interfacial properties of fiber-reinforced composites

Abstract

Matrix-specific chemical modification of the Kevlar fiber surfaces was carried out with the aim of enhancing adhesion, through covalent bonding, to selected thermoset matrix resins such as vinyl ester, unsaturated polyester and epoxy. A two-step grafting method, involving initial metalation followed by subsequent substitution, was used to graft vinyl and epoxy terminated groups onto Kevlar fiber surfaces. The physical changes in fiber surface were characterized by scanning-electron microscopy and surface area measurement and the chemical changes due to grafting were measured by contact angle measurement and neutron activation analysis; high concentrations of double bonds and epoxy groups were measured. The change in interfacial sear strength due to the surface grafting was measured by means of a single fiber pull out test. The results show a nearly twofold increase in the interfacial shear strength due to vinyl terminated grafts in the case of Kevlar/vinyl ester and Kevlar/polyester composites. Kevlar fibers containing the epoxy functionality on the surface had enhanced adhesion to epoxy matrix resin.

Authors:
Publication Date:
Research Org.:
Cornell Univ., Ithaca, NY (United States)
OSTI Identifier:
5470981
Alternate Identifier(s):
OSTI ID: 5470981
Resource Type:
Miscellaneous
Resource Relation:
Other Information: Thesis (Ph.D.)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ARAMIDS; SURFACE TREATMENTS; COMPOSITE MATERIALS; FABRICATION; FIBERS; ADHESION; CHEMICAL PREPARATION; MATRIX MATERIALS; PROCESSING; REINFORCED MATERIALS; SURFACES; MATERIALS; PETROCHEMICALS; PETROLEUM PRODUCTS; PLASTICS; SYNTHESIS; SYNTHETIC MATERIALS 360601* -- Other Materials-- Preparation & Manufacture

Citation Formats

Ravichandran, Vasudha. Surface grafting of Kevlar fibers for improved interfacial properties of fiber-reinforced composites. United States: N. p., 1991. Web.
Ravichandran, Vasudha. Surface grafting of Kevlar fibers for improved interfacial properties of fiber-reinforced composites. United States.
Ravichandran, Vasudha. Tue . "Surface grafting of Kevlar fibers for improved interfacial properties of fiber-reinforced composites". United States. doi:.
@article{osti_5470981,
title = {Surface grafting of Kevlar fibers for improved interfacial properties of fiber-reinforced composites},
author = {Ravichandran, Vasudha.},
abstractNote = {Matrix-specific chemical modification of the Kevlar fiber surfaces was carried out with the aim of enhancing adhesion, through covalent bonding, to selected thermoset matrix resins such as vinyl ester, unsaturated polyester and epoxy. A two-step grafting method, involving initial metalation followed by subsequent substitution, was used to graft vinyl and epoxy terminated groups onto Kevlar fiber surfaces. The physical changes in fiber surface were characterized by scanning-electron microscopy and surface area measurement and the chemical changes due to grafting were measured by contact angle measurement and neutron activation analysis; high concentrations of double bonds and epoxy groups were measured. The change in interfacial sear strength due to the surface grafting was measured by means of a single fiber pull out test. The results show a nearly twofold increase in the interfacial shear strength due to vinyl terminated grafts in the case of Kevlar/vinyl ester and Kevlar/polyester composites. Kevlar fibers containing the epoxy functionality on the surface had enhanced adhesion to epoxy matrix resin.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Jan 01 00:00:00 EST 1991},
month = {Tue Jan 01 00:00:00 EST 1991}
}

Miscellaneous:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that may hold this item.

Save / Share:
  • Based on a comprehensive experimental study on carbon fiber reinforced cement composites incorporating the Ashland's industrial grade carbon fiber reinforced cement composites incorporating the Ashland's inductrial grade carbon fibers (Carboflex), the optimum mix variables and processing techniques were decided. The types and proportions of different mix constituents, the fiber lengths and volume fractions, and the mixing and curing procedures which produce desirable fresh mix properties and superior hardened material performance were decided. A comprehensive experimental data set on the performance characteristics of carbon fiber reinforced cement was also generated. The research was performed in three phases: (1) Establishment of themore » mixing procedure and mix proportions for achieving desirable fresh mix characteristics; (2) Assessment of the trends in the effects of different mix variables on the strength of air cured specimens and further optimization of the mix proportions for achieving superior strength characteristics in addition to the desirable fresh mix workability; and (3) Optimization of the curing condition and full mechanical characterization for carbon fiber reinforced cement composites with some optimum values of fiber length and volume fraction. A comprehensive investigation was performed on the material properties and structural applications of steel fiber reinforced concrete. In studies on the application of steel fiber reinforced concrete a load bearing structural elements, the effects of steel fibers on improving the strength and ductility of concrete footings under bearing pressure, and enhancing bond between deformed bars and concrete were investigated.« less
  • The major theme of this dissertation is structure/property relationships in fiber-reinforced thermoplastic-matrix composites. Effort has been focused on the interface: interfacial crystallization and fiber/matrix adhesion. Included are investigations on interfacial nucleation and morphology, measurement of fiber/matrix adhesion, effects of interfacial adsorption and crystallization on fiber/matrix adhesion, and composites reinforced with thermotropic liquid crystal copolyester fibers. Crystallization of a copolyester and polybutylene terephthalate with glass, carbon, or aramid fibers has been studied with regard to interfacial morphology. Techniques employed included hot-stage optical microscopy and differential scanning calorimetry. Nucleation by the fibers was found to be a general phenomenon. Morphology could bemore » varied by changing the cooling rate. In order to better monitor fiber /matrix adhesion, a buckled plate test has been developed. The test measures transverse toughness as the parameter characterizing interfacial adhesion in unidirectional, continuous-fiber composites. The test is simple to perform yet has advantages over other interfacial evaluation techniques. The buckled plate test was found to be a sensitive measure of fiber/matrix adhesion. The buckled plate test has been used along with the transverse tensile test to examine how interfacial adsorption and crystallization affect fiber/matrix adhesion in polycarbonate/carbon fiber composites. Adsorption was found to be of primary importance in developing adhesion, while crystallization is a secondary effect. The toughness data have been fit successfully for annealing time and temperature dependence. The dependence of adsorption and transverse toughness on matrix molecular weight was found to be large, with higher molecular weights adsorbing more effectively.« less
  • A finite element model of an aligned fiber composite was used to quantify the effects of reinforcement phase geometry on the creep rate of a composite. The model has shown that large triaxial stresses develop within the composite inhibiting flow of the matrix material and reducing the composite creep rate. This strengthening effect is in addition to the strengthening from direct load transfer to the fibers. Composite creep resistance can be related to a normalized measure of the spacing between the fibers, regardless of their particular geometric arrangement. Creep tests were conducted on a model composite system fabricated by pressmore » bonding short nickel fibers with thin lead foils. Creep in this composite is controlled by creep of the matrix and by debonding of the fiber-matrix interface. Creep tests have been extended to a more practically significant system of an aluminum-5% magnesium alloy reinforced with randomly oriented alumina fibers. This composite exhibits an anomalously high stress exponent and activation energy in comparison to the unreinforced matrix material. The observed creep behavior can be accurately described by load transfer to a continuous-fiber network embedded in the matrix.« less
  • Two important phenomena which occur during the consolidation of graphite fiber-reinforced epoxy composites were examined. Both the elastic deformation behavior of the fiber network, and the permeability-resin volume fraction relationship in the fiber network are important parameters for any accurate resin flow model. Permeability measurements indicate that the fiber bed permeability is resin-volume fraction dependent. For a unidirectional aligned fiber bed, the measured transverse-fiber-bed permeabilities vary from 1.1 {times} 10{sup {minus}10} cm{sup 2} to 1.2 {times} 10{sup {minus}9} cm{sub 2} and the axial-fiber-bed permeabilities vary from 2.1 {times} 10{sup {minus}9} cm{sup 2} to 4.4 {times} 10{sup {minus}8} cm{sup 2} formore » a liquid-volume fraction range of 0.25 to 0.5. Only the axial-fiber-bed permeability was found to be dependent on the surface tension of the matrix fluid because the pressure drop due to wetting forces in significant compared to the externally applied pressure. The epoxy resin only partially wets the graphite-fiber surface during the impregnation process due to the non-zero resin-fiber contact angle. Cross-plied transverse- and axial-permeability measurements indicate the permeability decreases with increasing cross-ply angle.« less
  • The adhesion of carbon fibers to several high performance polymers, including a phosphorus-containing bismaleimite, a cyanate ester resin, and a pyridine-containing thermoplastic, was evaluated using the microbond single fiber pull-out test. The objective was to determine the chemical and mechanical properties of the fiber and the polymer which affect the fiber/polymer adhesion in a given composite system. Fiber/matrix adhesion is of interest since the degree of adhesion and the nature of the fiber/matrix interphase has a major influence on the mechanical properties of a composite. The surface chemical composition, topography, tensile strength, and surface energy of untreated AU-4 and commerciallymore » surface treated AS-4 carbon fibers were evaluated using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), single fiber tensile tests, and dynamic contact angle analysis. The commercial surface treatment which converted the AU-4 to the AS-4 fiber oxidized the carbon fiber surface. The surface of the AS-4 carbon fiber was further modified using air, oxygen, ammonia, and ethylene plasmas. The AS-4 fiber tow was also characterized following exposure to the aqueous poly(amic acid) solution used to disperse the matrix powder during aqueous suspension prepregging of thermoplastic matrix composites. The air and oxygen plasma treatments significantly oxidized and roughened the surface of the AS-4 carbon fibers. In addition, the air and oxygen plasma increased the polar component of the AS-4 fiber surface energy. The ammonia plasma increased the concentration of nitrogen on the fiber surface, without significantly altering the fiber topography (at a magnification of 50,000X). The atomic oxygen present in the air and oxygen plasma treatments is capable of reacting with both the edge and basal planes in the carbon fiber structure. As a result, the oxygen-containing plasmas progressively ablated the organic material in the carbon fiber surface.« less