• Parisi, Daniele
• Rhoades, Alicyn M.
• Schaake, Richard P.
• Gohn, Anne M.
• Seo, Jiho
• Colby, Ralph H.

Abstract

<p>When a semicrystalline polymer melt is subjected to sufficient flow before crystallization, the nucleation rate is accelerated. In this study, the degree of acceleration is investigated with a commercial poly(ether ether ketone), using a rotational rheometer. With a constant shearing time (t_s = 1 s), the nucleation rate increases with the shear rate (10 s^-1 &lt; γ&amp;dot; &lt; 200 s^-1). At a constant shear rate (γ&amp;dot; = 20 s^-1), the nucleation rate increases with the shearing time (1 s &lt; t_s &lt; 15 s). For a constant strain (γ= γ&amp;dot;t_s = 300), high shear rates with short shearing times enhance the nucleation rate more than low shear rates with long shearing times. The specific work (W = σγ, where σ is the shear stress) reduces all nucleation times to a common curve. A flow-induced nucleation model is suggested based on the entropy reduction model of Flory and the isothermal nucleation model of Hoffman and Lauritzen. A key ingredient is the critical volume of the nucleus, found to be 8-10 nm³, which corresponds to 3-4 Kuhn segments for PEEK.</p>

Topics

• impedance spectroscopy
• polymer
• melt
• ketone
• crystallization
• semicrystalline