Molecular Structure, Crystallinity, and Morphology of Uncompatibilized and Compatibilized Blends of Polyethylene/Nylon 12

Abstract

The present study is aimed at investigating differences in molecular structure, crystallinity, and morphology between uncompatibilized and compatibilized blends of high-density polyethylene (HDPE) and Nylon 12 by using Fourier-transform (FT) Raman spectroscopy, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Uncompatibilized and compatibilized blends of HDPE/Nylon 12 with a Nylon 12 content ranging from 10 to 90 wt.-% with an increment of 10 wt.-% were prepared. The compatibilized polymer blends were prepared by adding a small amount of maleic anhydride (MAH) and it was found that 0.5 wt.-% MAH yielded a good dispersion. SEM images show that both kind of blends have a different miscibility behavior. The uncompatibilized and compatibilized blends yield quite different X-ray diffraction patterns; the latter blends with a Nylon 12 content > 70 wt.-% show orientational effects in the X-ray pattern of the HDPE. The crystallinity of the HDPE of both blends was evaluated by the full width at half intensity of the (110) reflection of HDPE. To do that, the diffraction peaks were analyzed by a curve-fitting method. To evaluate the crystallinity from Raman spectra, the intensity ratio of the two bands at 1 129 and 1 110 cm−1 was used. Of note is that the 1 129 cm−1 band is caused by a symmetric CC stretching mode of all-trans (CH2)n groups arising only from HDPE. The Raman spectra and X-ray diffraction measurements revealed that when the Nylon 12 content reaches 70 wt.-%, the crystallinity of HDPE in the compatibilized blends becomes higher than that of HDPE in the uncompatibilized blends. This result is different from the general trend of crystallinity of HDPE in polymer blends. The difference suggests that the effect of the high viscosity of the Nylon-rich phase on the crystallinity is more significant than the effect of the impurity (MAH-grafted PE). It seems that the extension of the Nylon 12-rich phase during the extrusion process leads to orientational effects because of the increase in the interaction between MAH and HDPE. SEM images of HDPE/Nylon 12 compatibilized (top) and uncompatibilized (bottom) blends with a Nylon 12 content of 20 wt.-%.