Thermal Stability of Shish-Induced Shish-Kebab Precursor Structure from High Molecular Weight Polyethylene Chains
In-situ rheo-SAXS (small-angle X-ray scattering) and rheo-WAXD (wide-angle X-ray diffraction) techniques were used to investigate repeated melting and re-formation of the flow-induced shish-kebab precursor structure in a once-sheared polyethylene (PE) bimodal blend at the confined quiescent state. The blend consisted of a noncrystallizing low molecular weight PE matrix (LMWPE, {bar M}{sub w} = 53 000 g/mol, polydispersity = 2.2) and a small amount (2 wt %) of crystallizing high molecular weight PE (HMWPE, {bar M}{sub w} = 1 500 000 g/mol, polydispersity = 1.1) under the chosen experimental temperature. After a step shear (shear rate = 125 s{sup -1}, shear duration = 20 s, temperature = 126.5 C), combined SAXS and WAXD results confirmed that the shish-kebab structure was developed mainly from HMWPE chains, following a diffusion-controlled-like process. Although shish formed first followed by microkebabs and then macrokebabs, shish and microkebabs were melted simultaneously as an integrated entity after the macrokebab melting. Upon cooling, the shish-kebab structure could re-form rather quickly from unrelaxed stretched chain segments, but the corresponding fraction decreased with the increase in temperature. Results indicated that the shish-kebab re-formation is directly related to the relaxation behavior of stretched chain segments confined in a topologically deformed entanglement network. Under the chosen experimental conditions, the deformed HMWPE entanglement network could withstand temperature until 154 C for 3 min before totally relaxed into the isotropic state.
- Research Organization:
- Brookhaven National Laboratory (BNL) National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- AC02-98CH10886
- OSTI ID:
- 914341
- Report Number(s):
- BNL--78909-2007-JA
- Journal Information:
- Macromolecules, Journal Name: Macromolecules Journal Issue: 6 Vol. 39
- Country of Publication:
- United States
- Language:
- English
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