Better look on application of your composite to define the targeted requirements. Most probably, starting with low renforcing ratio is better, lower than 5% wt.
At present time enough time-cost experimental determination of the optimal content of filler is dominating in materials science. As an alternative, the methods of composite micro- and macromechanics are seemed a very attractive because they allow us to calculate and predict the optimal composition.
1- The cooking: which means that the researcher doesn't now what is going on inside the material. Thus, he/she try to mix the material with different percents and test the property that he/she interested in. This way is accepted when the researcher deals with new phenomena, such as what was happen in the superconductivity field in the earlier stages, otherwise this kind of work is not a scientific research.
2- The systematic work: in this way the researcher analyzes his system and specifies the required performance for the material. Then he/she finds the key properties required to get that performance based on his/her knowledge of the performance-property relationship. Then he/she decides the suitable type and amount of material to be added in order to get the required property base on his/her knowledge of the structure-property relationship. This kind of work is, as you see, based on deep knowledge of the system.
I would like to offer different perspective of polymer nanocomposites. Please kindly have a look at this high filler content polymer nanocomposites review. The answer may depend on the fabrication method as well.
Article Polymer Nanocomposites Having a High Filler Content: Synthes...