I've recently been reading some literature and found that in thermoplastics and thermosets that the addition of nanofiller often increases the modulus in both tension and compression.What causes this increase in both directions?
The module of elasticity of nano particles is very big (about 1000 GPA), and the module of elasticity of polymers from 1,5 to 4 GPA. And by "the rule of mix" the module increases at an additive of nanoparticles, here it is only necessary to add them much. To add microspheres or short fibers more simply and the cheapest way.
There are two questions here - (1) why stiffness in tension and compression may be slightly different in polymers - this has to do with the complex macromolecular nature of polymeric networks which cannot be treated on atomistic level.
The other question (2) is how nanoparticles may effect the stiffness of such networks. In thermosets, the rule-of mixtures referred to in a previous answer does indeed apply. However, in some semicrystalline thermoplastics with nanofillers, the increase in stiffness is much higher than can be accounted for by just rule of mixtures; this is due to the nanoparticles causing an increase in levels of crystallinity (e.g. nanoclays in PP or PA).
in some semicrystalline thermoplastics with nanofillers, the increase in stiffness is much higher" - - You can prove it? I didn't see any publication with such results yet. These are groundless assumptions of theorists. There are no facts.
Dear Jamel Alexander,
Properties that are related with the behaviour of atoms and electrons are called intrinsic or fundamental properties. It can be made plausible that the elastic constants of metals primarily depend on the interatomic forces and the lattice distances. Hence, for metals these constants can be taken as intrinsic properties only slightly depending on e.g. composition.
The opposite holds for polymers: the Young's modulus is an extrinsic property dependent on structure and mixture/blending composition. As stated above the rule of mixtures often applies for the relation between e.g. the Young's modulus and the volume fraction of reinforcing particles. For thermoplastic semicrystalline polymers, the presence of reinforcing particles may yield changes in the amount of the crystalline part of the polymer concerned with effects on the Young's modulus. Further, for thermoplastic polymers the presence of (nano)particles may affect binding forces between the polymerized chains and hence show an effect on the value of the Young's modulus. The same reasoning may apply to thermosets, as is indicated in one of the answers above. The forgoing implies that for polymers the relation between structural parameters and elastic constants whether in tension or in compression deserves separate case studies.
An elementary introduction to these issues is provided by
Materials Science in Design and Engineering; see attached link
http://www.delftacademicpress.nl/m017.php
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