Talc as nucleating agent of polypropylene: morphology induced by lamellar particles addition and interface mineral-matrix modelization

The efficiency of talc used as nucleating agent (0.5% by weight) in polypropylene (PP) was determined taking into account the particle size d(50), particle morphology and BET specific surface areas. These findings were compared to a mineral with similar properties, pyrophyllite. Talc samples with the finest particle sizes induce a significant increase in the starting crystallization temperature of PP and irrespective of the particle size d(50), pyrophyllite was found to be less efficient than talc. X-Ray results show that PP oriented crystallization due to talc or pyrophyllite addition, corresponds to an epitaxial growth whereby the mineral c*-axis is merged with the PP b*-axis. Microscopic observations revealed that in the presence of talc, nuclei density of PP increased strongly. In addition, a large number of nuclei was observed to appear everywhere on the talc surface. A PP-talc interface model is proposed by matching the (001) talc plane and the (010) PP plane. In this model, 3% of PP cell accommodation on talc is necessary with a 15degrees angle between PP chains elongation and the crystallographic directions of talc. Hexagonal rings on talc surface are believed to represent hydrogen bonds with PP methyl groupings. This fine structure relation between talc and PP is discussed, and is used to characterize the differences observed between the efficiency of talc and that of pyrophyllite. (C) 2002 Kluwer Academic Publishers.