Paper Number
EF10 

Session
Emulsions, Foams and Interfacial Rheology

Title
Impact of rheological properties on the foaming behavior of linear and branched polylactide

Presentation Date and Time
October 8, 2014 (Wednesday) 11:40

Track / Room
Track 6 / Washington C

Authors (Click on name to view author profile)

1. Najafi, Naqi (Ecole Polytechnique de Montreal, Mechanical Engineering)
2. Heuzey, Marie-Claude (École Polytechnique de Montréal, Chemical Engineering)
3. Carreau, Pierre J. (École Polytechnique de Montréal, Chemical Engineering)
4. Therriault, Daniel (Ecole Polytechnique de Montreal, Mechanical Engineering)
5. Park, Chul B. (University of Toronto, Mechanical and Industrial Engineering)

Author and Affiliation Lines (in printed abstract book)
Naqi Najafi¹, Marie-Claude Heuzey¹, Pierre J. Carreau¹, Daniel Therriault², and Chul B. Park^3
1Chemical Engineering, École Polytechnique de Montréal, Montréal, Canada; ²Mechanical Engineering, Ecole Polytechnique de Montreal, Montreal, Canada; ³Mechanical and Industrial Engineering, University of Toronto, Toronto, Canada

Speaker / Presenter 
Najafi, Naqi

Text of Abstract
In this work, a chain extender (CE), Joncryl © ADR, was added to a polylactide (PLA) at two concentrations, 0.4 and 0.7 wt%, using two different strategies. The rheological properties and foamability of the neat PLA and PLA containing the CE were studied. The steady and transient rheological properties of the neat PLA and CE-treated PLAs revealed that the introduction of the CE profoundly affected the melt viscosity and elasticity. The linear viscoelastic properties of CE-enriched PLAs suggested that a long chain branching (LCB) structure was formed from the reaction with the CE. LCB-PLAs exhibited an increased viscosity, more shear sensitivity, upturning at high viscosity in Cole-Cole plots, and longer relaxation time in comparison with the linear PLA. The LCB structure was also found to affect the transient shear stress growth and elongational flow behavior. A prominent overshoot was found in the transient shear response of the LCB-PLAs due to an increase of the entanglement density. The LCB-PLAs also exhibited a pronounced strain hardening, whereas no strain hardening was observed for the linear PLA. Batch foaming of the linear and LCB-PLAs was also examined at foaming temperatures of 130, 140, and 155 ?C. In addition to the improvement of the cell integrity, the increased melt strength and elasticity, resulting from LCB, increased the void fraction by more than two times and the cell density by more than two orders of magnitude.