Experimental determination of concentration dependence of nitrogen diffusivity in polypropylene

This study determines the diffusivity of nitrogen as a function of its concentration in polypropylene at 170, 180, and 190°C in the range, 0.99–6.75 MPa. Isothermal pressure decay experiments are utilized to obtain the uptake of nitrogen by polypropylene with time. These data when used with a detailed mass transfer model, and the principles of variational calculus allow the determination of the nitrogen diffusivity. It is found to be a peak function with values in the range of 3.88 × 10−9 to 12.94 × 10−9 m2 s−1. Suitable correlations are found to represent the diffusivity in terms of pressure and nitrogen concentration at the three temperatures. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011