Electron spin resonance investigation of filler orientation in compression and injection molded polypropylene based composites

Summary Electron Spin Resonance (ESR) spectroscopy was applied for monitoring the orientation and distribution of filler particles in polymer composites by measuring the magnetic anisotropy of naturally occuring Mn(II) centers in CaCO₃ and in talc. The amplitude ratio of characteristic ESR bands gives the order parameter. The orientation of the particles changes as a function of composition, dependends on processing technology, the type of molding (injection vs compression molding) and has a specific spatial distribution in the cross-section of the injection molded specimen. Correlation is found between average orientation of anisotropic particles and the mechanical properties of various composites.