Influence of annealing on anisotropic crystallinestructure of HDPE cast flms

High density polyethylene (HDPE) flms were produced using cast flm extrusion process with different draw ratios, ranging from 16.9 to 148.8. Morphology, crystallinty and orientation state of crystalline andamorphous phases of the cast flms were investigated using scanning electron microscopy (SEM), differentialscanning calorimetry (DSC) and polarized Fourier transform infrared spectroscopy (FTIR) analyses, respectively.The anisotropic crystalline structures of row-nucleated lamellar morphology were observed for the flms producedwith high draw ratios. The crystalline phase axes orientation functions were found to be signifcantly dependent onthe applied draw ratios. As expected, annealing increased the crystallinity and melting point temperature (Tm) of thecast flms and on the other hand, it also enhanced the crystalline phase orientation. However, the results revealedthat annealing also promoted non-twisted lamellar structures, since it increased the fc values (c-axis orientationfunction) and decreased the fa values (a-axis orientation function) simultaneously. Additionally, it was found thatthe annealing induced enhancement in c-axis orientation function was more signifcant for the cast flms with lowerdraw ratios, therefore, it was dependent on the draw ratio. Polyolefns J 3:1-9

Keywords:

HDPE , cast flm extrusion , crystal orientation , annealing , crystallinity