Abstract
Exposing polymers to high-pressure and supercritical CO2 is a useful approach in polymer processing. Consequently, the mechanisms of polymer–polymer interaction under such conditions are worthy of further investigation. Two-dimensional correlation analysis and two-dimensional disrelation mapping were applied to datasets of polycaprolactone –poly(lactic acid) blend with or without high-pressure CO2 obtained using in situ attenuated total reflection Fourier transform spectroscopic imaging. The relatively weak dipole–dipole intermolecular interactions between polymer molecules were visualized through the disrelation maps for the first time. Because of the specially designed polymer interface, the interactions between the same type of polymer molecules and different types of polymer molecules were differentiated. Under exposure to high-pressure CO2, all three types of interactions: interaction between polycaprolactone molecules and poly(lactic acid) molecules, interaction between polycaprolactone molecules and interaction between poly(lactic acid) molecules become weaker than those in the polymer interface without high-pressure CO2. The resulting increase in the Flory interaction parameter is the main cause of phase separation in the PCL–PLA blend under high-pressure CO2. The findings from this study will be of benefit for polymer processing with high-pressure and supercritical CO2.
Highlights
Because of its low toxicity, flammability, and cost, highpressure and supercritical CO2 is becoming more popular in many industrially relevant processes so as to make them ‘‘greener’’.1 In contrast with organic solvents, it does not contaminate the final product as it is trivially removed by reducing the pressure
The focus of this research is the interfacial region between the PCL bulk area and PLA bulk area. This is because intermolecular dipole–dipole interactions (C1⁄4OÁÁÁC1⁄4O) between PCL molecules and PLA molecules can only occur in this region
A specially designed PCL– PLA interface was prepared in order to distinguish the intermolecular dipole–dipole interaction (C1⁄4OÁÁÁC1⁄4O) between PCL molecules and PLA molecules from that interaction between the same type of polymer molecules
Summary
Because of its low toxicity, flammability, and cost, highpressure and supercritical CO2 is becoming more popular in many industrially relevant processes so as to make them ‘‘greener’’.1 In contrast with organic solvents, it does not contaminate the final product as it is trivially removed by reducing the pressure. In order to fully realize the potential of polymer processing with high-pressure and supercritical CO2, the mechanisms of polymer–polymer interactions require further investigation.[5] To be more specific, the non-covalent bonds between molecular chains prevent the interaction between additives and functional groups of polymers and inhibit the access of these additives into the space between polymer molecules. As a result, it has an adverse effect on the penetration of polymer additives which can modify the polymer properties. ATR FT-IR spectroscopic imaging with 2D correlation analysis and 2D disrelation mapping was used to investigate the interaction occurring in the PCL–PLA interfaces before and under exposure to highpressure CO2
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