Nonisothermal differential scanning calorimetry data for neat polypropylene and polypropylene with variously treated cellulose fillers has been used to solve for the Avrami exponent, n. Results show neat polypropylene to have an Avrami exponent value very close to the theoretically expected value of 4.0. The addition of untreated cellulose fiber to polypropylene, which has been shown to produce a transcrystalline region, results in an exponent value of 2.7-2.9 for the initiation stage, followed by a value of 3.9 for the bulk stage. Treatment of the cellulose with alkyl ketene dimer, alkenyl succinic anhydride, or stearic acid results in intermediate exponent values from 2.7 to 3.9. These results verify the effectiveness of surface treatments in reducing the natural nucleating ability of cellulose. Sample mixing and filler content were also shown to play a role in the crystallization process.