Session D40 - Poster Session I.
POSTER session, Monday afternoon, March 12
Exhibit Hall, Washington State Convention Center
The morphology development on the melting of ultrahigh molecular weight polyethylenes (UHMWPE), formed from melt crystallization at high different pressures, was studied by ultra small-angle X-ray scattering (USAXS)and DSC. The heating rate used was 5C/min. At 41M psi, UHMWPEs show dominant chain-extended lamellae (CEL) at Mw 4MM, 5MM and 6MM. At 30M psi, UHMWPEs show dominant chain-folding lamellae (CFL) at Mw 4MM, 5MM and 6MM. At 35M psi, UHMWPEs show both CEL and CFL at Mw 5MM and 6MM and a dominant CFL at Mw 4MM. With dominant CFL, USAXS shows a measurable long spacing, which increases with temperature. With dominant CEL, USAXS shows an immeasurable long spacing and relatively strong ultra-small angle scattering intensity. The integrated scattering intensity shows an exponential increase with temperature. The thickest CEL and CFL melt at the end of the DSC endotherm, where the USAXS (corrected for melt scattering) shows a diffuse profile only. This CEL or CFL thickness was estimated using an approach based on the single lamella structure factor. The results show a largest thickness about 100nm for CEL and about 50nm for CFL.
Acknowledgement: This work was supported by a NSF grant (DMR 9732653).