MSE PhD Defense: Stephanie Lin

MSE Grad Presentation
Event Date:
Friday, May 9, 2014 - 1:00pm to 3:00pm
MRDC 4404


Dr. Meisha L. Shofner (Adviser, MSE)
Dr. Yulin Deng (CHBE)
Dr. Karl I. Jacob (MSE)
Dr. Dong Qin (MSE)
Dr. Donggang Yao (MSE)


 This research is directed toward determining the design space that is 
available for cellulose nanocrystals /poly(3-hydroxybutyrate)(CNC/PHB) 
composites. In order to develop this understanding, the 
processing-structure-properties relationships of CNC/PHB nanocomposites were 
examined at several different steps in a stepwise processing method.  The 
as-processed morphology of solvent cast (SC) and anti-solvent compression 
molded (ASCM) samples were examined using DSC, optical microscopy and 
ATR-FTIR and the effect of processing and CNC addition on the isothermal and 
nonisothermal crystallization was examined using DSC, hot stage microscopy, 
and a novel fast scanning chip calorimeter, the Flash DSC.  The results show 
that the addition of water during SC processing significantly reduced the 
rate of crystallization at both isothermal and nonisothermal conditions. 
This reduction in crystallization rate was due to  the presence of water 
suppressed the intramolecular hydrogen bonding. When CNCs were added, the 
overall crystallization kinetics were increased for isothermal 
crystallization and crystallization upon cooling occurred at higher 
temperature. These results indicated CNCs act as a nucleating agent.  Even 
though the overall kinetics of crystallization were increased with CNC 
addition, the growth rate of the spherulites was reduced with the addition 
of CNCs.
         From the variable heating experiments performed on the Flash DSC, the 
addition of CNCs suppressed the reorganization behavior of PHB upon heating. 
The isothermal crystallization experiments performed on the Flash DSC 
examined in how the RAF, MAF and crystallinity change during the initial 
stages of primary crystallization with the addition of nanofillers. Results 
from the isothermal experiments showed that during short isothermal hold 
times the RAF parallels the crystallinity whereas for long isothermal hold 
times the amount of RAF decreased significantly.  The effect of processing 
on the mechanical behavior of CNC/PHB composites was examined for one SC 
processing method and the ASCM processing method the viscoelastic nature of 
the composite was influenced by the processing method. The addition of CNCs 
increased the strain to failure of both types of  samples initially but as 
storage time increased, embrittlement caused decreases in the strain to 
failure of samples from both processing methods. However the ASCM processing 
method slowed down the embrittlement processs more due to the reduction in 
mobility of the amorphous content. The knowledge that was obtained from this 
work can be used when designing processing protocols and heat treatments for 
PHB-based nanocomposites materials to allow greater control over 
crystallization processes and mechanical properties expanding opportunities 
for materials design.