There is no way to solve CaCO3. If you solve it in an aqueous acid it is no longer CaCO3. At the most it is possible to make a suspension. For your purpose a suspension in an organic solvent seams to be appropriate. The easiest way is to buy a fine milled CaCO3 type which is already surface modified so that it can be dispersed in an organic matrix. Calciplast from Alpha is such a product (see first link below). If you want to use unmodified CaCO3 you need a mill, e.g. a ball mill, in which you put an organic solvent of your choice e.g. some weight-% oleic acid and 50 weight-% CaCO3 and start milling. At the end you will have a rather stable suspension. The second link shows the solubility of oleic acid in many different organic solvents. I guess that your polyester is polylactide (PLA). Therefore chlorinated solvents, like chloroform, or (better) dioxane or THF could be good solvents because the also solve the PLA. To improve the stability of the suspension it is advantageous to add additional a polymeric dispersant or to use a polymeric dispersant instead of oleic acid. Furthermore the oleic acid could worsen the properties of your composite. The third link shows you a brochure from BASF concerning this topic. The anionic polyacrylate type Efka PA seems to be the most appropriate and should be added in amounts of some weight-%. This should be also added if you make the dispersion with already surface modified Calciplast, because it increases the viscosity so that the CaCO3 does not immediately settle down. Furthermore Efka PA could have a positive effect on compatibility of the kenaf fiber to the polyester.

http://www.alpha-calcit.de/EN/Produkte/Calciumcarbonat.php

http://pubs.acs.org/doi/pdf/10.1021/j150501a008

www.dispersions-pigments.basf.com/portal/load/fid807190/Dispersing%20Agents.pdf

Hello dear it is difficult, but usually when is employed carbonate is used stearic acid for avoiding the interactions particle-particle between the carbonate particles.

Dear Mr. Ashifat  

As far as I know the caco3 types of additive will not contribute to the mechanical properties of the composites as compared to the reinforcement fibers. Moreover,  caco3 is normally adding to the polyester during the mixing process as a powder and you can search what exactly the benefits and the contributions of caco3 as powder to the polyester composites.