It is very common when the nanofillers don't have very good interaction with polymer matrix.
Without good interaction, the weak van der walls force is enough to bond the fillers to polymer.This weak bonds can transfer the stress between fillers and polymer, therefore show a higher modulus at small strains.
However, when go to high strains, you will find the materials are more brittle, with a low elongation at break. And you will see a low strength.
As Lukas said, without good interaction, the homogeneity of material is low and easy to have crack to break.
Why tensile strength decrease upon addition nanofiller eh elastic tensile modulus increase ? Anyone help please
Since homogenity of a material is decreased and thus places for crack nucleation introduced by this process?
It is very common when the nanofillers don't have very good interaction with polymer matrix.
Without good interaction, the weak van der walls force is enough to bond the fillers to polymer.This weak bonds can transfer the stress between fillers and polymer, therefore show a higher modulus at small strains.
However, when go to high strains, you will find the materials are more brittle, with a low elongation at break. And you will see a low strength.
As Lukas said, without good interaction, the homogeneity of material is low and easy to have crack to break.
Thanks for your comment.
But graphit well known as attract some polymer on its surface and increase crystallinity. Why could not interact good with polymer
Are you using graphite, graphene, or graphene oxide?
Adding of them can give more nuclei to raise crystallinity. But only graphene oxide has strong interaction with polar polymer. ( Hydrogen bonds)
What is about graphite. Does it have a good interaction with filler
Graphite is a common material with thousands layers of graphene, so it is not a nanofiller.
Usually graphite oxide may have good interaction but graphite itself not.
So for polar polymer, such as PMMA, PLA, polyurethane, graphene oxide with good dispersion will have the best interaction.
Thanks.
Why graphite increase tmcrystallinity if there is no interaction ?
Graphite can behave as nuclei for hete-crystallization.
Actually many nanofillers have similar effect on crystalline, so it is not really relevant to interaction.
I guess you are doing polyethylene, since PE is pretty unpolar, it is difficult to have good interaction with fillers.
C.W Macokso has a new paper for graphene in PE and he found the dispersion is poor.
There are two possible answers to this question is: 1) because the small particles reduce the mobility of the matrix, which might even develop an interphase around the filler, of a stiffer polymer. This has been widely experienced with very small particle and is one of the main drawback of these fillers (this induces a low impact resistance). You might also 2) end up with a similar problem with bigger particles (higher modulus, lower strain at break) because of the stress reinforcement around the filler. Usually the best tradeoff is with about 1µm particles. This is true with almost all polymers including the "tough" PET and the "weak" rubbers.
You should actually look at the product of the specific surface by the thickness of the interphase. Smaller particles with larger interphase will end up with brittle materials (not tough). You can make an estimation of the fraction of the volume of the polymer that is altered by the presence of the filler. This is a typical size effect (although not wanted !)
more details please , still not clear
I means that tensile modulus increase but tensile strength decrease for same sample , Why ?>
It is very interesting to know parameters of your experience? Concentration of particles, polymer type? It is important to know repeatability of the phenomenon, his statistics and a method of definition of the module and strengh
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