Supercritical CO2 intercalation of polycaprolactone in layered silicates

Supercritical carbon dioxide (scCO2) intercalation of polycaprolactone (PCL) in layered silicates (clay) is studied. Wide angle X-ray diffraction patterns find that PCL is slightly intercalated in unmodified montmorillonite clay (NaMMT) but considerably intercalated in organic-modified montmorillonite clay (OMMT). The interlayer spacing in OMMT increases considerably from 1.94 nm in OMMT to 3.58 nm in the OMMT/PCL 10/90 sample. PCL8 having molecular weight of 80,000 is harder to intercalate into OMMT than PCL1 having molecular weight of 10,000. Higher scCO2 pressures at a temperature allow larger intercalations of PCL in OMMT to exhibit larger interlayer spacings in OMMT. The interlayer spacings in OMMT, however, are not clearly found to relate with the CO2 temperature at a given pressure. TGA data show that OMMT enhances the thermal stability of PCL1, with a higher content of OMMT giving a higher amount of PCL1 residue. DSC data find that the PCL1-intercalated OMMT expedites the melt-crystallization rate of PCL1 from the melt but suppresses the crystallinity of PCL1. Study of Avrami's rate constants k and exponent n finds that the PCL1-intercalated OMMT enhances the isothermal crystallization rate of PCL1 and that the crystal growth dimension is 3 for pure PCL1 but decreases with increasing OMMT content in the blends. Modulus data find that the PCL1-intercalated OMMT is an effective reinforcement for PCL8.

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