Characterization and Comparison of Various Lewis Acid Surfactant Combined Catalyst (LASC) and Their Potential for Polylactic Acid Synthesis by Polycondensation

In Polylactic acid (PLA) production, there is a byproduct in the form of water, while Lewis acid catalysts such as Al(III), Ti(IV), and Sn(IV) which is commonly used for PLA production will be rapidly decomposed and deactivated by water. The aim for this research was to synthesize a Lewis acid water-tolerant catalyst called LASC (Lewis Acid Surfactant Combined Catalyst) by combining some Lewis metals with surfactant in the form of Sodium dodecyl sulfate (SDS) which will bind each other to become Fe(dodecyl sulfate)3 [Fe(DS)3], Al(dodecyl sulfate)3 [Al(DS)3], and Cu(dodecyl sulfate)2 [Cu(DS)2] and see their performance to the PLA production using polycondensation method. The catalyst was characterized by X-ray powder diffraction (XRD), thermal analysis (thermogravimetry analysis (TGA)), and spectroscopic analysis (FTIR). While the yield to the PLA production was analyzed gravimetrically. In the LASC spectrum, there are shifts and separations in symmetric and asymmetric modes compared to SDS spectrum which can be related to the interaction of dodecyl sulfate anions with Lewis metals cations (Fe(III), Al(III), and Cu(II). The XRD analysis shows identical position of 2θ at ± 2.4° for SDS and LASC. The interplanar spacing (dhkl) by XRD at 2θ = ± 2.4° were 3.74 nm, 3.63 nm, and 3.7 nm for SDS, Al(DS)3, and Cu(DS)2, respectively. Except for Fe(DS)3, the interplanar spacing at d001 is so small and only can be seen on the graph at 2θ = 2.32°. This LASC also show a good performance with a yield of 52%wt with ±1.2 mL of water was evaporated in the dehydration process of PLA production. The activity of this catalyst can contribute to enhancing the knowledge and applications of Lewis acid-surfactant-combined catalysts for PLA production.