Study of plasticizer diffusion in a solid rocket motoŕs bondline

Abstract

This work aims to determine the diffusion coefficient of the plasticizers dibutyl phthalate (DBP), dioctyl phthalate (DOP) and dioctyl azelate (DOZ) on the internal insulating layer of solid rocket motors. These plasticizers are originally present in the layers of rubber, liner and propellant, respectively. This species are not chemically bonded and tend to diffuse from propellant to insulating and vice versa. A computer program based on the mathematical model of Fick's second Law of diffusion was developed to perform the calculus from the concentration data obtained by gas chromatographic (GC) analyses. The samples were prepared with two different adhesive liners; one conventional (LHNA) and the other with barrier properties (LHNT). A common feature of both liners was that they were synthesized by the reaction of hydroxyl-terminated polybutadiene (HTPB) and diisocyanates. However, a bond promoter was used to increase the crosslink density of the LHNT liner and to improve its performance as barrier against the diffusion. The effects of the diffusion of the plasticizers were also investigated by hardness analyses, which were executed on samples aged at room temperature and at 80°C. The results showed an increase trend for the samples aged at room temperature and an opposite behavior for the tests carried out at 80°C.