The extensional viscosity properties of long-chain branched fluorothermoplastics and correlations to molecular structure

Autor: Klaus Hintzer, Harald Kaspar
Rok vydání: 2011
Předmět:
Zdroj: Rheologica Acta. 50:577-599
ISSN: 1435-1528
0035-4511
DOI: 10.1007/s00397-011-0584-8
Popis: The uniaxial extensional rheology behaviour of tailor-made long-chain branched TFE39/HFP11/ VDF50 terpolymers, LCB-THVs, is investigated at 265°C using the extensional viscosity fixture (TA Instruments). Within the window of applied extension rates (0.03 s − 1 ≤ e ∙ ≤ 30 s − 1) the model polymer fluids show weak to marked strain-hardening behaviour depending on their level of branching. A straightforward data filtering and evaluation procedure capable to extrapolate for quasi steady-state conditions from the similarity of the data sets is presented. Flexible approximation functions for the nominal transient elongational viscosity curves $\eta _{\text{E}}^{+} (t,\varepsilon^{\bullet})$ and for quasi steady-state elongational viscosity curves $\eta_E^{\text{\ddag}} (\varepsilon^{\bullet})$ are proposed. In the latter case, there are three adjustable parameters employed which have the physical meaning of: the elongational stress response time τ controlling the location of the maximum in the $\eta_E^{\ddag} (\varepsilon^{\bullet})$ function, the polydispersity ξ of a unimodal LCB population, and its effective amount. An approximation function is also proposed for bimodal LCB distributions, which applies very well for the LDPE IUPAC A standard resin. Empirically, τ is found to depend on the size dimension of branching λ, derived from molecular characterization, by the relationship τ∼λ 3.3.
Databáze: OpenAIRE
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