Savvas G. Hatzikiriakos

Department of Chemical and Biological Engineering, The University of British Columbia, Vancouver, BC, Canada

Rheology and Processing of Poly(lactides) and its enantiomeric diblock copolymers

Abstract

 

Rheology and Processing of Poly(lactides) and its enantiomeric diblock copolymers

Savvas G. Hatzikiriakos

Department of Chemical and Biological Engineering

The University of British Columbia, Vancouver, BC, Canada

A series of controlled microstructure poly(lactide) (PLA) samples were synthesized using a novel chiral dinuclear indium catalyst capable of living polymerization of lactide. PLAs with different

The wall slip and processability as can be assessed by their melt fracture behaviour of several polylactides (PLAs) have been investigated. PLAs with molecular weights greater than a certain value were found to slip, with the slip velocity to increase with decrease of molecular weight. The onset of melt fracture for the high molecular weight PLAs was found to occur at around 0.2 to 0.3MPa, depending on the geometrical characteristics of the dies, and independent of temperature. Addition of 0.5wt% of a polycaprolactone (PCL) into the PLA that exhibits melt fracture was found to be effective in eliminating and delaying the onset of melt fracture to higher shear rates.

L- to D- monomer ratios were investigated. The melt rheological study includes determination of zero shear viscosity and its relationship with the molecular weight, the relaxation spectrum and its relation with molecular weight characteristics, as well as plateau modulus and other important rheological parameters that are helpful in predicting the linear viscoelasticity of PLA. Emphasis is placed on the uniaxial melt behavior of these polymers where in spite of their linear macrostructure, PLAs exhibit strain hardening effects. In addition, different compositions of nearly monodispersed diblock copolymers of DL-lactide (PDLLA) or D-lactide (PDLA) and L-lactide (PLLA) were synthesized. The effects of molecular weight and block length ratio on the rheological behavior of DL and L-lactide diblock copolymers in the disordered state were investigated. We found that the time-temperature (t-T) superposition principle is applicable to the diblock copolymers PLLA-b-PDLLA. However, the t-T superposition failed at low temperatures close to the temperature of crystallization. In contrast, diblock copolymers PLLA-b-PDLA formed stereocomplex crystallites of high melting point (slightly above 200 °C) that causes a viscosity enhancement. The failure of t-T superposition was found due to existing of micro homo or stereocomplex crystallites.

Savvas G. Hatzikiriakos

received his Diploma in Chemical Engineering from the Aristotle University of Thessaloniki (AUTh), Greece, in 1984, before obtaining his M.Sc.E. from the University of Toronto (Canada) in 1988 and then his PhD in Chemical Engineering from McGill University in 1991 (Canada). Since 1991 he has been a Professor in the Department of Chemical Engineering at the University of British Columbia, Vancouver, Canada, where he is the Director of the Polymer Rheology and Processing and Surface Science laboratory. He is the author of over 170 refereed papers and over 250 presentations in Conferences on Polymer Processing, Rheology, and Surface Science.



Date: 11/5/2015
Time:12:00 (coffee & cookies will be served at 00:00)
Place:FORTH Seminar Room 1