Interfacial crystallization of isotactic polypropylene molded against the copper surface with various surface roughnesses prepared by an electrochemical process

The influence of surface topography of copper (Cu) sheet on the heterogeneo us nucleation of isotactic polypropylene (iPP) at the iPP/Cu interface had been investigated mainly using polarized optical microscope with hot stage. Various textures of Cu surfaces prepared by sandpaper polishing and electr ochemical anodizing had been made and they were utilized to induce interfac ial nucleation of iPP upon supercooling. This process enables us to change the topological feature of the copper surface without changing their chemic al compositions. The pretreated surfaces were quantitatively characterized by a surface texture instrument in terms of RMS roughness (R-a). Copper sur face with higher surface roughness induced more nuclei of iPP and led to a thicker transcrystalline layer in the interfacial region upon supercooling over the temperature range 128 degreesC < T-c < 134 degreesC. Based on the theory of heterogeneous nucleation, it was found that the induction time co rrelates well with the nucleation rate in determining the interfacial free energy difference function Delta sigma of iPP The ratio of Delta sigma at t he interface to that in the bulk matrix (Delta sigma (TCL)/Delta sigma (bul k)) for the polished surface (R-a = 0.09 mum) is 2.89, implying the transcr ystallization growth is unfavorable from a thermodynamic point of view. The ratio of Delta sigma (TCL)/Delta sigma (bulk) becomes smaller as the curre nt density for anodizing increases, indicating the transcrystallization gro wth is getting favorable. Moreover, induction times and nucleation rates we re also measured to characterize quantitatively the nucleating ability of v arious Cu surfaces. (C) 2001 Kluwer Academic Publishers.