Paper Number
PO28
Session
Poster Session
Title
Nonlinear shear rheology of isotactic polypropylene melts
Presentation Date and Time
October 23, 2019 (Wednesday) 6:30
Track / Room
Poster Session / Ballroom C on 4th floor
Authors
- Parisi, Daniele (Foundation for Research and Technology Hellas, Institute of Electronic Structure & Laser)
- Seo, Jiho (Penn State University, Materials Science and Engineering)
- Han, Aijie (Pennsylvania State University, Materials Science and Engineering)
- Colby, Ralph (Pennsylvania State University, Materials Science and Engineering)
Author and Affiliation Lines
Daniele Parisi, Jiho Seo, Aijie Han, and Ralph Colby
Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802
Speaker / Presenter
Parisi, Daniele
Text of Abstract
Strong flow fields are inevitable components of polymer processing. When semicrystalline polymers are involved, such conditions might induce conformational changes and ordering. This phenomenon is known as Flow Induced Crystallization (FIC). These flow-induced modifications in the polymer crystallinity and crystalline morphology strongly affect the mechanical properties of the final product, attracting broad interest. In this experimental work, we investigate the nonlinear rheological response under shear flow of a set of seven isotactic polypropylene (iPP) melts with different molecular characteristics (158 kg/mol < Mw < 627 kg/mol and varying molar mass distribution). Experiments were all performed at 170 °C, slightly above the melting temperature. By combining different rheological techniques such as dynamic oscillatory shear, start-up shear experiments with a cone partitioned plate (CPP) and capillary rheometry, we have obtained flow curves that cover many decades in shear rate. The well resolved shear thinning region, nearly unaffected by flow instability, allowed us to detect the effect of FIC on the mechanical response, along the line of a previous experimental work on the same samples. Results are then compared with flow curves obtained with parallel plates combined with polarized optics using a transparent bottom plate and a reflecting top plate. The visual observation of the sheared systems allows a direct detection of the crystalline structures induced by the flow and at the same time, how this phenomenon depends on edge fracture (which is significantly present in plate-plate geometry) and on the molecular structure of the strictly linear iPPs.