Effect of a nucleating agent on the fracture toughness of isotactic polypropylene

A new single specimen J-integral method gives a good quantitative characterization of iPP fracture behavior. The structural and morphological characterization of the; different types of materials reveals that the effect of nucleation was significant. This effect serves as a basis for the interpretation of the mechanical behavior of materials with different morphologies. An increase in crystallinity results in a reduction in fracture toughness and an enhancement of crack growth. At constant crystallinity, an increase in spherulite size within the same type of material results in more brittleness. A significant reduction in spherulite size, by the use of a nucleating agent, also results in increased brittleness. Hence, the factor affecting the fracture toughness of the polymer is not the change in spherulite size; it is rather the change in crystallization temperature and its implications on the tie molecule concentration during the original crystallization process. The spherulite size effect may be just a reflection of the ''inside of the spherulite'' (crystallinity, lamellar thickness, amorphous layer) and not the state of the boundaries.