NECKING MECHANISM AND ITS ELIMINATION IN UNIAXIALLY DRAWN FILMS OF POLY(ETHYLENE NAPHTHALATE) (PEN) POLYETHERIMIDE (PEI) BLENDS/

The influence of blend composition on the deformation behavior of cast amorphous PEN/PEI blends were investigated above their respected glas s transition temperatures. PEN inherently shows a sharp necking phenom enon when stretched at temperatures as high as 20 degrees C above its glass transition temperature. This was attributed to highly localized rapid alignment of naphthalene planes parallel to the surface of the f ilms. The addition of PEI was observed to reduce this necking behavior . The neck formation completely disappears when the PEI fraction excee ds 10% in the blend. X-ray studies indicate that the increase of PEI h inders the rapid alignment of naphthalene planes parallel to the surfa ce of the films. The presence of PEI chains in the blend was found to increase the overall friction between the polymer chains in the system and this was found to prevent the formation of highly localized necks . (C) 1997 John Wiley & Sons, Inc.