Coordination between yttrium ions and amide groups of polyamide 6 and the crystalline behavior of polyamide 6/yttrium composites

Different amounts of yttrium ions were introduced into polyamide 6 (PA6) matrix by solution casting process. Structure, morphology and properties of the obtained PA6/Y3+ composite films were investigated by using FT-IR spectroscopy, Raman spectroscopy, scanning electron microscope (SEM), polarized optical microscope (POM) and differential scanning calorimeter (DSC) methods. Yttrium ions show strong coordination ability and their complexation with amide groups of PA6 can be reflected by the appearance of new bands in the amide A and amide I regions in FT-IR and Raman spectra. Furthermore, the FT-IR and Raman spectra of the PA6/Y3+ composite show that the resultant chain conformations of the amide groups in the composite films are twisted from the ideal trans conformation. The DSC results reveal that Y3+ ions cause a significant reduction of the melting point of PA6. In addition, the existence of Y3+ prevents the crystallization of molten PA6/Y3+ composite films during the cooling process. Moreover, the PA6/Y3+ composite can convert into γ phase PA6 or α phase PA6 when different solvents are used to remove Y3+ ions and induce crystallization of PA6.