726 3.6 Fourier Transform Infrared Spectroscopy - FTIR The FTIR spectra of natural and organo clays are shown in Figure 11 and they were used to evaluate possible changes in clay bonds due to the presence of the CTAB surfactant. FTIR spectra show absorption bands around 3700 cm−1 that could be attributed to the stretching vibration of the Al(Mg)-OH group, while the H-O-H-stretching vibrations can be observed at approximately 3330 cm−1, and the coordinated and zeolitic water, at 3440 cm−1 [Montano ET AL., 2017]. The vibration band at 1640 cm−1 is attributed to coordinated and absorbed water; Si-O-Si characteristic peaks can be observed around 1030, 1110, 915 and 470 cm−1 [Madejová, 2003]. There are shoulders around 790-759 cm−1, probably due to Si-O stretching in clays. The bands around 690 cm−1, 530 cm−1 and 425 cm−1 would correspond to Al(Mg)-OH, Si-O-S and SiO-Al bonds [Zamudio ET AL., 2011]. There are strong absorption peaks in the organo clays FTIR spectra around 2920 cm-1 and 2850 cm-1, attributed to the CH2 stretching vibration [Middea ET AL., 2017]. The band around 1490 cm-1 can be assigned to the asymmetric angular deformation of the (CH3)4N+ groups [Middea ET AL., 2017], indicating the organic cation of the CTAB structure. The results show that CTAB molecules were intercalated into the interlayer space of clays. Figure 11 - FTIR spectra of samples. (a) Natural Bofe and Chocolate clays; (b) Organo Bofe and Chocolate clays. 4. CONCLUSIONS This study evaluated the performance of two processes, casting and extrusion, for producing poly(lactic acid) (PLA) biocomposites using ecologically correct materials, specifically fine montmorillonite particles from mineral beneficiation, for food packaging applications. The results showed that both processes successfully produced plastics with enhanced performance, although with distinct visual, structural, thermal and morphological characteristics. Casting produced thinner films, while extrusion yielded thicker sheets. The organophilization of two Brazilian bentonites (Bofe and Chocolate clays) using cetyl trimethylammonium bromide (CTAB) was effective, as confirmed by increased basal spacing, presence of CH₂/(CH₃)₄N⁺ group bands in FTIR spectra, and decomposition events of CTAB in TGA/DTA analysis. The organophilization process modified the properties of the smectites, enabling the production of biocomposites with improved characteristics. The results demonstrate the potential of using fine montmorillonite particles from mineral beneficiation to develop sustainable packaging materials, promoting resource recovery and reducing environmental impact. ACKNOWLEDGEMENTS The authors acknowledge the support of Brazilian Agricultural Research Corporation (EMBRAPA), Mineral Technology Center (CETEM), Program of Metallurgical and Materials Engineering, COPPE/UFRJ, CNPq, CAPES, and FAPERJ.
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