Date of Award

12-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Packaging Science

Advisor

Thomas, Ron L

Committee Member

Batt , Heather P

Committee Member

Whiteside , Scott W

Abstract

CH 1 ABSTRACT
The objective of this study was to investigate the effects of various solvents on the crystallinity and thermal expansion stability of PLA film. Three different PLA films were produced by the solvent casting technique; PLA in chloroform (PLA-C), PLA in methylene chloride (PLA-M), and PLA in methylene chloride: acetonitrile = 50: 50 (PLA-MA). The PLA-MA had higher % crystallinity, 46.15, than the PLA-C, 24.03, and the PLA-M, 14.25. With this increase in crystallinity, the PLA-MA had improved thermal expansion stability as shown by very low accumulated dimensional changes at 20-100 ¡C. Wide angle x-ray diffraction identified multiple crystalline structures for the PLA-MA. Film barrier properties were also measured. PLA-MA had the lowest oxygen permeability. However, there was no significant difference in water vapor permeability among the three PLA films. The mechanical property tests revealed that the PLA-C and PLA-M were ductile while the PLA-MA was brittle in behavior. The PLA-MA was very hazy as compared to the PLA-C and PLA-M. This work has shown that the PLA-MA had increased % crystallinity and, more importantly it had improved thermal expansion stability which can be very beneficial for the flexible packaging industry.
CH 2 ABSTRACT
The objective of this research was to determine the optimum solvent mixture to improve flexibility while maintaining the thermal stability of PLA solvent-cast films. PLA films were produced from mixed solvent solutions of (M: methylene chloride) and (A: acetonitrile) using the solvent-casting technique. The ratio of solvents used were 70% methylene chloride with 30% acetonitrile (73MA), 60% methylene chloride with 40% acetonitrile (64MA) and 50% methylene chloride with 50% acetonitrile (55MA). The single solvent solution was 100% methylene chloride (100M). Differential Scanning Calorimetry (DSC) showed films with increased amounts of acetonitrile had higher amounts of % crystallinity due to the full formation of crystals during the casting process and no enthalpy of crystallization. Thermomechanical Analysis (TMA) revealed the addition of acetonitrile increases the thermal stability of the PLA films. Stress strain curves showed that high crystalline films were brittle while less crystalline films were ductile. Both Wide Angle X-ray Diffraction (WAXD) and Transmission Electron Microscopy (TEM) showed 55MA and 64MA had the highest % crystallinity, more developed crystal structure and more pronounced lattice images. Film 73MA was the only film that exhibited both flexibility and good thermal stability. The 30% concentration of acetonitrile developed crystals that stopped growing due to solvent evaporation, but upon heating in TMA, the crystals began to grow fully thus improving thermal stability. This work shows that PLA film produced by solvent casting from solvent mixture compared to a traditional single solvent will have better thermal and mechanical performance.
CH 3 ABSTRACT
The objective of this study was to investigate the effects of various solvents on the crystallinity and thermal expansion stability of PLA film. Four different PLA films were produced by the solvent casting technique; PLA in chloroform (100C), 70% chloroform: 30% acetonitrile (73CA), 60% chloroform: 40% acetonitrile (64CA) and 50:50 chloroform acetonitrile (55CA). 55CA had the highest % crystallinity at 26.1%. 73CA showed the least amount of % crystallinity. With this increase in crystallinity, 64CA had improved thermal expansion stability with no accumulated dimensional changes. 73CA with low % crystallinity showed improvements as well. Wide angle x-ray diffraction identified multiple crystalline structures for all films with acetonitrile. The mechanical property tests revealed that 100C and 73CA were ductile while 55CA and 64CA were brittle. More haze was seen in the more crystalline 55CA and 64CA compared to 73CA and single solvent 100C. 73CA had increased thermal expansion stability with the addition of acetonitrile to increase crystallinity, yet behaved like an amorphous film with improved flexibility.

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