MICROSTRUCTURAL CONSTRUCTION OF POLYMERS WITH IMPROVED MECHANICAL-PROPERTIES

Mechanical properties of materials are based on structure or morpholog y and on the micromechanical processes of deformation and fracture, i. e. on the ''micromechanics''. Developments mainly in electron microsco py and scanning force microscopy opened up a wide range of experiments previously impossible, including the in situ study of micromechanical processes. Direct microscopic techniques on the basis of scanning, tr ansmission, and high-voltage electron microscopy are used to study mic romechanical properties of different polymer blends of amorphous and s emicrystalline polymers. Of particular interest are polymer blends wit h improved toughness. Blends with styrene-acrylonitrile as matrix poly mer and different types of modifier particles, with their diameters ra nging between about 100 nm and 1 mu m, have been investigated. Example s of blends with a semicrystalline matrix are polypropylene (PP) blend s with different amounts of various rubber and modifier particles. New micromechanical mechanisms have been found, which can change the toug hness of some acrylonitrile-butadiene-styrene grades or improve low-te mperature toughness of PP. The examples show that detailed knowledge o f the morphology and micromechanical mechanisms helps to define criter ia of improved properties. This ''microstructural'' analysis and const ruction of polymeric systems provides a new basis Of polymer modificat ion. (C) 1998 John Wiley & Sons, Ltd.