Abstract:

In this study， a natural exposure test of bumper was designed for solving the problem of a tiger stripe defect after natural exposure， and the causes of this defect were analyzed. The results indicated that the bumper showed some black and white tiger stripe defects after the natural exposure test. Compared to the black section of tiger stripe， the color difference in white section was significant， and there were many microcracks. The content of O element on the surface increased drastically， indicating a visible aging phenomenon. The rubber toughening phase in bumper material presented an unbalanced shear orientation. The orientation degree of the white segment is clearly greater than that of the black segment. This leads to the existence of large orientation internal stress in the white segment. It is easier for the bumper to fracture under the action of external environmental stress， resulting in a large number of microcracks accordingly.

Key words: polypropylene, bumper, natural exposure, tiger stripe, defect, aspect