(95ab) Co2-Induced Glass Transition Behavior of Poly(Acrylic Acid) Investigated by High-Pressure Calorimetry
AIChE Annual Meeting
2005
2005 Annual Meeting
Education
Poster Session (Student): Materials Engineering & Sciences
Monday, October 31, 2005 - 12:30pm to 4:00pm
Supercritical CO2 is an environmentally responsible solvent with tunable physical properties. A diverse array of polymerizations and polymer processing techniques has been reported using CO2. Foaming or CO2 swelling occurs when a polymer is placed in contact with supercritical CO2. CO2 swelling can either be used to extract or add materials into a polymeric substance. A high-pressure isothermal calorimetric method has been developed to observe alterations in the glass transition temperature (Tg) of poly(acrylic acid) (PAA) due to the adsorption of gaseous and supercritical CO2. PAA is a hydrophilic commodity polymer used as a thickener and a water absorbent (e.g. baby diapers). Recently, Liu and coworkers (Liu,T.,Continuous Precipitation Polymerization of Acrylic Acid in Supercritical Carbon Dioxide,2005 ) have demonstrated the ability to synthesize PAA in supercritical CO2 via continuous precipitation polymerization. Theoretical calculations of CO2-induced Tg depression, stemming from the amount of CO2 adsorbed in PAA, suggest that the morphology of PAA particles depend on experimental operating conditions during precipitation polymerization and the proximity of these conditions to Tg. The goal of this project is to evaluate (i) Tg for PAA polymerized in supercritical CO2 ,(ii) the reduction of Tg for PAA in the presence of CO2 (20.7 to 206.8 bar), (iii) and the validity of the theoretical model for Tg depression. CO2-induced Tg depression was investigated in custom designed high-pressure sample cells using a Setaram C80 calorimeter. PAA samples synthesized in supercritical CO2 (206.8 bar, 50 to 90°C) have a Tg ranging from 114 -120°C, which is analogous to PAA that is produced conventionally by solution polymerization. PAA adsorption of compressed CO2 yielded a reduction in the Tg to 100°C at 58.7 bar ± 0.6. In the presence of supercritical CO2 the Tg reduced to 80°C at 126 bar. These reductions in Tg are consistent with theoretical calculations for Tg approximation using the Chow's equation.