Controls of gradient morphology and surface properties of polymer blends

The phase morphology and surface composition of ethylene-vinyl acetate (EVAc) and polypropylene (PP) blends were investigated in this work. It was found that the 70/30 PP/EVAc blend formed a gradient phase morphology in the cross section by annealing, The particle size of the EVAc dispersed phase increased gradually along the direction vertical to the sample surface from the middle to the surface with increasing annealing time and temperature. The EVAc component on the surface of the blends after annealing was detected using Fourier transform infrared spectroscopy coupled with attenuated total reflectance (ATR-FTIR) and electron spectroscopy for chemical analysis (ESCA). The oxygen consistent with the EVAc on the surface of the PP/EVAc blends (70/30) also increases with increasing time and temperature. It means that the component of the EVAc accumulates on the surface with the formation of the gradient phase morphology in the blends. No significant difference in the gradient phase morphology was found for both the thin and thick PP/EVAc blend samples at the same annealing conditions. Moreover, the EVAc copolymer was melt-grafted with acrylamide (AAm) and then blended with PP. It was also found that PP/EVAc-g-AAm formed a gradient phase structure during annealing, the same as that of a PP/EVAc blend. With the dispersed phase EVAc as a carrier, the grafted polar groups were transported onto the surface of the blend sample with formation of an EVAc gradient dispersed phase. Thus, the gradient phase structure control of blends is an effective method for the material surface modification of materials.