CRYSTALLINITY IN THE POLYPROPYLENE CELLULOSE SYSTEM .2. CRYSTALLIZATION KINETICS

Nonisothermal differential scanning calorimetry data for neat polyprop ylene and polypropylene with variously treated cellulose fillers has b een used to solve for the Avrami exponent, n. Results show neat polypr opylene to have an Avrami exponent value very close to the theoretical ly expected value of 4.0. The addition of untreated cellulose fiber to polypropylene, which has been shown to produce a transcrystalline reg ion, 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 cellu lose with alkyl ketene dimer, alkenyl succinic anhydride, or stearic a cid results in intermediate exponent values from 2.7 to 3.9. These res ults verify the effectiveness of surface treatments in reducing the na tural nucleating ability of cellulose. Sample mixing and filler conten t were also shown to play a role in the crystallization process. (C) 1 994 John Wiley & Sons, Inc.