Investigation on the double melting peak of PLLA using Modulated DSC - - PowerPoint PPT Presentation

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

Investigation on the double melting peak of PLLA using Modulated DSC

• M. Coletti, C. Gracia Fernandez

TA Instruments

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

TA Instruments

• Worldwide manufacturer of equipment for Thermal

Analysis, Rheology, Microcalorimetry and ThermoPhysical analysis

• Strongly oriented to innovation,

has a brand new line of Differential Scanning Calorimeters: the Discovery DSC

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

Modulated DSC

• Typical DSC tests employ constant gradients of

temperature and/or isothermal steps

• MDSC superposes an oscillating signal

40 50 60 70 80

Modulated Temp (°C)

18 20 22 24 26 28

Time (min)

Universal V4.7B TA Instruments

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

Modulated DSC

• Sample is exposed to several heating rates and it is possible to

separate phenomena that are HR dependent (melting, glass transition) from kinetic phenomena (crystallisation)

• 0.2
• 0.1

0.0 0.1

Nonrev Heat Flow (W/g)

• 0.3
• 0.2
• 0.1

0.0 0.1 0.2

Rev Heat Flow (W/g)

• 0.3
• 0.2
• 0.1

0.0 0.1 0.2

Heat Flow (W/g)

50 100 150 200 250 300

Temperature (°C)

Exo Up Universal V4.7B TA Instruments

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

Problem: PLLA double melting peak

• Poly (L-lactic acid) is a widely studied thermoplastic biopolymer
• Has a complicated melting process
• Here we try to understand better what happens during the melting

(after cooling at 40°C/min from the melt)

(data from C. Gracia-Fernandez, S. Gomez-Barreiro, J. Lopez-Beceiro, Mater. Res. Vol. 27, No. 10, 2012)

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

Heat only MDSC

• When studying melting processes with MDSC it is

important to follow some guidelines:

§ At least four oscillations over the peak § Period should be longer than any characteristic time of the process investigated § Use Heat Only: amplitude is set so that the minimum heating rate during modulation at any time is 0°C/min

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

Period too short (60s – 2°C/min)

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

Testing conditions

• Period is prolonged to 120s (to cope with typical

crystallisation times)

• Heating rate is reduced to 1°C/min (to keep 4 oscillations)
• Amplitude is set to 0.32°C (to maintain heat only

conditions)

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

Proper Rev – NonRev separation

• Melting is all in the Rev

signal and crystallisation is in the NonRev

• Two exo peaks at around

same T of endo

• What is happening?

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

Suggested interpretation

• The two exo signals are peaked almost at the same T of

the endo

• Simultaneous melting-crystallisation phenomena (crystal

perfection)

• Requires three crystalline forms: one formed during cold

crystallisation, one during the first melting and one during the second melting

• The first form melts at a similar T as the second

(convolution method as developed by Artiaga, Lopez-Beceiro et al.)

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

Conclusions

• MDSC can be a powerful technique to study complex

phenomena, provided proper testing conditions are selected

• In general, with a long enough period of oscillation and

providing enough cycles across the event, a good separation of kynetic and heating rate dependent phenomena can be obtained

TAINSTRUMENTS.COM TAINSTRUMENTS.COM

WWW.TAINSTRUMENTS.COM MCOLETTI@TAINSTRUMENTS.COM

THANK YOU!