Polymer-based nanocomposites
Dr. Jun Ma
School of Advanced Manufacturing & Mechanical Engineering University of South Australia
Conventional composites: dispersion particles ~1 µm in diameter.
Nanocomposites: dispersion particles 1–100 nm in diameter
-Fracture toughness:
Resistance to propagation of a sufficiently sharp crack [1].
Importance of toughening: Introduction
Liquid rubber – toughened epoxy
Cavitation & matrix shear yielding
-90-nm rubber – toughened epoxy
3-nm rubber – toughened epoxy New toughener: 3 nm rubber particle
Crack tip under polarizer: neat
epoxy and its nanocomposite Tensile-fractured part under polarizer: neat epoxy and its nanocomposite
New toughening method
New toughener: 55 nm rubber particle
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Fracture surface of neat epoxy
Optical micrograph of a thin section of fractured
nanocomposite 5%: with polarizer and without polarizer
New toughener: 55 nm rubber particle
Crack tip of neat epoxy: without loading and with 80% critical load
propagated crack tip of epoxy/rubber nanocomposite 5 wt-% without loading
Conclusions for rubber-toughened epoxy
1. 90-nm and micron-sized rubber particles toughen epoxy with loss of stiffness and strength; similar toughening effect was observed on 3-nm rubber nanoparticles which however show no reduction of stiffness; of all the tougheners, 5 wt% 55-nm rubber particles obtained best toughening effect without loss of stiffness and strength.
2. These particles show different toughening mechanisms. Liquid rubber: cavitation followed by matrix shear yielding. 3-nm rubber particles: plasticisation.
New toughener: 25 nm silica particle
Crack tip of nanocomposite 20 wt-%: without polarizer and with polarizer
New toughener: 25 nm silica particle
propagated crack tip of nanocomposite 20 wt-%, under 80% critical loading, 10 μm away from crack tip
New toughener: 25 nm silica particle
propagated crack tip of nanocomposite 20 wt-%, under 80% critical loading, 50 μm away from crack tip
propagated crack tip of nanocomposite 20 wt-%, under 80% critical loading, 200 μm away from crack tip
New toughener: 25 nm silica particle
propagated crack tip of nanocomposite 20 wt-%, under 80% critical loading, 500 μm away from crack tip
propagated crack tip of nanocomposite 20 wt-%, under 80% critical loading, 800 μm away from crack tip
New toughener: 25 nm silica particle
propagated crack tip of nanocomposite 20 wt-%, under 80% critical loading, 1000 μm away from crack tip
1. 25-nm silica particles are able to toughen and stiffen brittle epoxy simultaneously.
2. No particle interface debonding was observed, different to conventional epoxy/silica composite. The toughening
mechanism was attributed to the formation and development of nanovoids and a thin dilatation zone.
Conclusions for nanoparticle-toughened epoxy
1. Nanoparticle size. Superior toughening effect is probably achieved when the particle size is in the range of 10 – 90 nm.
2. Nanoparticle strength. The tensile strength of nanocomposites depends on the nanoparticle strength.
3. Nanoparticle hardness. Not critical, but appropriate hardness promote matrix deformation for superior toughening effect.
4. Nanoparticle interface. Not critical as micron-sized particles, but strong nanoparticle interface is recommended for the fine particle dispersion.
Interface-tuned epoxy/clay nanocomposites
-Exfoliation degree:
-Conclusion for Interface-tuned epoxy/clay nanocomposites