As Pierre has explained the properties of polymer-clay nanocomposites strongly depends on the quality of nanoclay dispersion in the polymeric matrices. The modulus of a composite, however, depends on the modulus of its ingredients. The higher modulus of clay particles increases the modulus of composite. You may find a lot of prediction models which predict the composite modulus based on the modulus and volume fraction of their ingredients. But in the case of strength, it depends on the dispersion of the particles and the interface formed between the matrix and filler. In poor dispersion and lack of good interface, the particles/agglomerates/clusters may act as voids which decrease the strength. In nanoparticles, usually an optimum filler loading is usually observed which after that the strength declines.

The mechanical properties also depend on the nanoclay dispersion, i.e. agglomerated, intercalated, or exfoliated nanoclay morphology. In either case, the modulus of modified epoxy will increase compared to the neat epoxy. However, in particular agglomerated clay may under tension loading cause localized stress concentrations leading to reduced strength of modified epoxy.

As Pierre has explained the properties of polymer-clay nanocomposites strongly depends on the quality of nanoclay dispersion in the polymeric matrices. The modulus of a composite, however, depends on the modulus of its ingredients. The higher modulus of clay particles increases the modulus of composite. You may find a lot of prediction models which predict the composite modulus based on the modulus and volume fraction of their ingredients. But in the case of strength, it depends on the dispersion of the particles and the interface formed between the matrix and filler. In poor dispersion and lack of good interface, the particles/agglomerates/clusters may act as voids which decrease the strength. In nanoparticles, usually an optimum filler loading is usually observed which after that the strength declines.

On addition, nanoclay may also affect the curring density of your epoxy resin. Did you observe any variation of tg?

thanks every one.

@brent neal : am using ultrasonication by probe method and TEM shows dispersion is going means its exploited. thing is that after seeing my result strength is decreasing. i was thinking my procedure is not correct. there is any problem if i go with this result menas strength decreasing???

Dispersion of clay is very Important parameter to determine the final properties of the the nanocomposite

Check the dispersion of the clay. Agglomeration may caused the decrease in strength, but not in modulus.

So, think about the quality of interface. What kind of clay have you used? Is that a modified one (i.e organoclay). If so, what is the nature of organic part? Is the organic part compatible with your resin?

By the way, Have you collected XRD patterns to verify the intercalation/exfoliation?

One factor which has been mentioned in all responses is dispersion of clay. It is true that dispersion is critical factor and is most difficult part in nano-clay dispersion but we also need to consider that what is promoting dispersion? Clays do no easily disperse in organic polymers this is reason we do modifications by using organic compounds to make it organophilic. I assume there are two critical factors, dispersion and dispersion facilitating regions or parts such as epoxy itself or other groups such as hydroxyls etc. if clay itself is well dispersed through epoxy interactions then epoxy curing efficiency is being affected therwise if clay is not well dispersed then there are crystalline regions due to clay agglomeration and those lead to lower flextural properties. Confirm your results with XRD to see crystalinity and also use TGA to see thermal behaviour then combine all to get clear picture. Dispersion of clay is always a challenge use longer sonication times it may be helpful.

Dear Pramod Marru

I consider that a set of parameters related with the process of mixing and the interface between materials are the main causes of diverse mechanical properties of the composites obtained. I suggest that your research must be reviewed carefully to give useful results to the research community.

Thank u all for u r valuable suggestions

Hi

See this article:

Strength as others have said depends on defects...places where stress can concentrate and/or a crack can initiate. There are so many ways for strength to be reduced when you mix resin and clay. Its true that dispersion affects it. But I would initially look at interfacial stress transfer. The interface between nanoparticle and resin has to be cohesive or this would represent a place for a crack to start. Perhaps do a SEM of a crack surface, if its high enough resolution image you can see if the interface is pulling away from the clay particles during loading. The other thing we saw under the TEM is if the clay particles formed stacks, the first crack was between two clay particles. That is the waxy layer between two clay particles is not very strong, this initiates a crack, and then this can propogate through the resin.

Quality of nanoclay dispersion and interface between epoxy and nanoclay are keys to improve the strength. One of our articles as attached may help you. In our study, epoxy nanocomposites were prepared by different mixing devices that can generate different shear forces, such as a mechanical stirrer, a microfluidizer, and a homogenizer. We want to intersatnd the effect of dispesion of nanoclay in epoxy on it performance. The results indicate that the modulus increases almost linearly with the clay loading and also is improved with the quality of dispersion, although the latter plays a less important role. On the other hand, only good dispersion can improve the strength, while poor dispersion results in loss of strength.