Levich Institute Seminar Announcement, 08/30/2005
Steinman Hall, Room #312
(Chemical Engineering Conference Room)
Professor Gad Marom
The Hebrew University of Jerusalem
Casali Institute of Applied Chemistry
"In-situ Synchrotron WAXD and SAXS Studies of Orientated Cystallization under Shear Flow Conditions in Discontinuous Fiber Reinforced Polypropylene Composites"
Flow conditions in polymer melts that contain acicular fillers such as short fibers and whiskers produce two main effects on the molten matrix and filler, respectively. The first is to promote chain disentanglement and create longer sequences of aligned chain segments; the second is to orientate the acicular filler parallel to the flow lines. In their turns, both the aligned chain molecules and fibers generate orientated crystalline morphology by two separate mechanisms. In the first, the aligned molecular arrays can act as nuclei for folded-chain crystallization, growing perpendicular to the flow direction and resulting in 'shish-kebab' morphology, in which the 'shish' consists of extended chains aligned parallel to the flow direction, and the 'kebabs' are made of transversely grown lamellae. In the second, the fibers, with a relatively high nucleus concentration at their surfaces, generate cylindrical transcrystallinity of preferential orientation with respect to the fiber direction.
This paper addresses the combined effect of flow conditions and fiber surface nucleation on matrix crystallization in systems of aramid or polyethylene fiber reinforced polypropylene.. It exemplifies the use of advanced characterization techniques based on synchrotron WAXS and SAXS, including microbeam and in-situ procedures, to analyze the crystallographic structure and crystalline morphology of the matrix. The in-situ experiments study the kinetics and orientation effects of shear flow induced crystallization while the microbeam experiments generate structural information as a function of the distance from the fiber surface.
BRIEF ACADEMIC/EMPLOYMENT HISTORY
Research and development projects, as well as theoretical studies in composite materials and hybrids, polymers and biomedical composites, encompassing: microstructure-property relation; morphology of bulk crystallinity and transcrystallinity; fracture mechanisms and failure modes; mechanical and physical property testing ∓ evaluation; calorimetric, thermal, thermomechanical and thermophysical properties; biomedical composites for soft tissue prostheses; carbon nanotube based composites