297
polymer-matrix nanocomposites
Various kinds of conventional polymer composites have long
been made using a polymer matrix and various kinds of embedded second-phase materials. The volume fraction of the latter can
often be quite high. The use of a small quantity of nanoparticles,
nanotubes, or nanoplates—a few percent by weight—as a reinforcing second-phase material can dramatically alter the properties of
the nanocomposite for a much lower volume fraction than conventional polymer-matrix composites. Both thermoplastic and thermoset polymer-matrix systems can be used.
As discussed in Section 8.8, depending on the exact type of polymer
host and nanoscale reinforcing phase, both the strength and
modulus of elasticity values can be either increased or decreased.
When nanoparticles are used, materials such as polystyrene reinforced with silica nanoparticles, for example, show a modulus
increase. Section 8.8 also noted that in some instances the inclusion of nanoparticles can increase toughness and wear resistance.
Tendencies for nanoparticles to agglomerate, however, can cause
severe problems and must be avoided. When carbon nanotubes
(CNTs) are used, carefully formulated composites can show significant elastic modulus and strength increases. Carbon nanotubes can
be embedded in thermosets. In certain epoxies, for example, fairly
dramatic increases have been reported in compression strength (in
the 30% range), achieved via the use of only about 0.5% to 2.0%wt
of dispersed carbon nanotubes.
CNTs can be embedded in many types of widely used thermoplastics, such as polycarbonates, with the goal of increasing the compressive and impact strength, toughness, elongation to failure,
and other properties. For these positive benefits to occur, however,
uniform dispersion, alignment, and good interfacial bonding
between the polymer and CNTs must be achieved. Both nanoparticles and CNTs can affect the important glass transition temperature, Tg, of the nanocomposite. A thermoplastic polymer will soften
when heated above Tg. This value is thus extremely important when
we’re designing for applications in elevated temperature environments. The Tg value can potentially be increased when certain
nanocomposite formulations are used (see Section 8.8). Platelike
nanomaterials such as layered silicates can be used as nanofillers in
polymer-matrix composites as well. Significant strength, stiffness,
UV resistance, and other improvements can be obtained at quite
low volume fractions (e.g., 2–5%).
Polymer-matrix nanocomposites are being widely explored in
relation to many high-end sports, automotive, and aerospace
Structural and Mechanical Environments
polymer-matrix nanocomposites
Various kinds of conventional polymer composites have long
been made using a polymer matrix and various kinds of embedded second-phase materials. The volume fraction of the latter can
often be quite high. The use of a small quantity of nanoparticles,
nanotubes, or nanoplates—a few percent by weight—as a reinforcing second-phase material can dramatically alter the properties of
the nanocomposite for a much lower volume fraction than conventional polymer-matrix composites. Both thermoplastic and thermoset polymer-matrix systems can be used.
As discussed in Section 8.8, depending on the exact type of polymer
host and nanoscale reinforcing phase, both the strength and
modulus of elasticity values can be either increased or decreased.
When nanoparticles are used, materials such as polystyrene reinforced with silica nanoparticles, for example, show a modulus
increase. Section 8.8 also noted that in some instances the inclusion of nanoparticles can increase toughness and wear resistance.
Tendencies for nanoparticles to agglomerate, however, can cause
severe problems and must be avoided. When carbon nanotubes
(CNTs) are used, carefully formulated composites can show significant elastic modulus and strength increases. Carbon nanotubes can
be embedded in thermosets. In certain epoxies, for example, fairly
dramatic increases have been reported in compression strength (in
the 30% range), achieved via the use of only about 0.5% to 2.0%wt
of dispersed carbon nanotubes.
CNTs can be embedded in many types of widely used thermoplastics, such as polycarbonates, with the goal of increasing the compressive and impact strength, toughness, elongation to failure,
and other properties. For these positive benefits to occur, however,
uniform dispersion, alignment, and good interfacial bonding
between the polymer and CNTs must be achieved. Both nanoparticles and CNTs can affect the important glass transition temperature, Tg, of the nanocomposite. A thermoplastic polymer will soften
when heated above Tg. This value is thus extremely important when
we’re designing for applications in elevated temperature environments. The Tg value can potentially be increased when certain
nanocomposite formulations are used (see Section 8.8). Platelike
nanomaterials such as layered silicates can be used as nanofillers in
polymer-matrix composites as well. Significant strength, stiffness,
UV resistance, and other improvements can be obtained at quite
low volume fractions (e.g., 2–5%).
Polymer-matrix nanocomposites are being widely explored in
relation to many high-end sports, automotive, and aerospace
Structural and Mechanical Environments