Cellulose nanocrystals (CNC) are good candidates for the preparation of polymer nanocomposites, especially in conjunction with polymers such as polylactic acid (PLA) and polyolefins. Commercially available CNC is available as aqueous dispersions or as powder agglomerates (1-20 microns). The powders are obtained by spray drying or freeze drying of the aqueous dispersions. However, the powders do not yield good nano dispersions by melt processing with the above polymers. The quality of dispersion in polymer nanocomposites depends on the following factors: (i) the morphology of the agglomerates before processing; (ii) the strength of the agglomerates relative to the stresses available in melt processing equipment, such as extruders and mixers; and (iii) the surface energies of the matrix and the the nanoparticles, at both application and processing temperatures. Based on an analysis of these factors, a dispersion factor is proposed to indicate the dispersibility potential of nanoparticles in various matrices. We found that porous agglomerates can be produced by spray freeze drying. Such structures permit easy penetration and wetting by the polymer melt during melt processing. Moreover, a network microstructure of the spray freeze dried CNC (CNCSFD) nanoparticles is formed and controlled by using different CNC concentrations in the initial CNC/water dispersion. CNCSFD agglomerates were used to produce nanocomposites by melt processing with polypropylene (PP) and PLA. The quality of dispersions in nanocomposites obtained using CNCSFD was substantially better than that generated with either CNCSD or CNCFD. It was also possible to determine the rheological and mechanical percolation concentrations of CNC in the matrix. Experimental evidence was obtained using electron microscopy, rheology, mechanical Properties, and crystallization behavior of nanocomposites, in conjunction with both PP and PLA as matrices.