The kinetics of heterogeneous mutual radiation grafting

The grafting‐time curves of heterogeneous mutual radiation grafting systems are often of the same type. There is a small auto‐accelerative period after which the rate rises to a maximum and then levels off to a steady, lower rate. The grafting of styrene to wool fibers is shown to give this type of conversion curve. The reasons for this particular rate‐time behavior have not been successfully explained although a number of kinetic treatments have been presented. A kinetic treatment is presented in this paper which postulates that the radical content continues to build up during the grafting process, leading to the gradual depletion of monomer in the substrate polymer and a final diffusion‐controlled rate of grafting. This situation leads to the maximum rate type of grafting‐time curve actually found. The necessary kinetic parameters have been estimated for the two extreme portions of the grafting curve in the case of the wool‐styrene system and further approximated by trial and error. Good agreement between the calculated and experimental rates of grafting was obtained.