Blending glassy polymers with liquid rubber diluents is a commonly employed toughening strategy, as in HIPS (high-impact polystyrene). These rubber particles are successful in achieving toughness due to their capacity to cavitate and initiate crazes.
In rubber toughening, there is a critical particle size below which few improvements in toughness are observed. This is because the stress field surrounding a given particle does not penetrate sufficiently into the matrix polymer to initiate a craze.
However, there is often a reported upper limit on particle size, above which larger pools or rubber diluent act as supercritical flaws to initiate craze fracture. I am trying to rationalize why this may be, especially as stress concentration is independent of particle size.
Stress concentration is dependent of particle size, at microfillers it causes cracks or crazes, at nanofillers no cracks are observed since the cracks in the matrix sorround the filler particles and not break them. therefore nanofillers are much safer to use. For this reason agglomeration of nanoparticles may also cause cracks
When working on EPDM and Gutta Percha rubber compatibilization of plastics, one factor found to increase fracture failure was the voids present between the different molecular structured' particles (seen under SEM). These voids were reduced by addition of adhesion promoters between the two macromolecule's types and decreasing particle sizes.
Dear all, large particles have low specific surface area compared to smaller ones, this means less contact and thus adhesion with coarse particles, with less ability to transmit stress, where the interface will be subjected to high shearing and fracture. My Regards
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering
- Powders