720 2.1.2 Organo Clay modification The surface modification of clays was performed using cetyltrimethylammonium bromide (CTAB – C₁₉H₄₂BrN, molar mass = 364.45 g mol⁻¹), a cationic surfactant with a C-16 hydrocarbon tail. Organoclays were prepared via cation exchange reaction, assuming a cation exchange capacity (CEC) of 100 meq/100 g for each clay type [Middea et al., 2018]. 20 g of each clay were dispersed in 500 mL deionized water (4 wt% solids) and ultrasonicated (1 cm probe, Branson Inc.) for 2 × 3 min cycles at 50% amplitude. The suspension was left to stand for 24 h at room temperature for complete hydration. Then, 7.289 g CTAB (≈ 1.0 × CEC) were slowly added to avoid micelle formation [Zhuang et al., 2016]. The mixture was transferred to an ultrasonic bath (Thornton INPEC Electronic) for 8 h to promote intercalation. After sonication, the suspension was mechanically stirred for 3 h to ensure homogeneous coverage of clay lamellae. The organoclay was washed with deionized water, centrifuged at 5,000 rpm for 15 min (Cientec CT-6000), and dried at 60 °C for 48 h. Figure 2 illustrates the organophilization process of montmorillonites. Figure 2 – Schematic representation of montmorillonite organophilization with CTAB (C₁₉H₄₂BrN), illustrating interlayer spacing expansion: d₁ < d₂ < d₃. 2.2 Biocomposites Preparation 2.2.1 Casting Biofilms were prepared by casting as previously described [Lima ET AL., 2019]. PLA (8 g) was dissolved in 36 mL chloroform (Vetec) for 2 h with magnetic stirring. For composites, 0.08 g organoclay was added to the PLA solution. 18 mL of each solution was poured into Petri dishes (φ 150 mm) and dried for 48 h at room conditions. 2.2.2 Extrusion Masterbatch preparation: 15 g organoclay was dispersed in 300 mL chloroform (ice bath, tipultrasound: 2 × 3 min, 50% amplitude). 15 g PLA was dissolved in 500 mL chloroform (magnetic stirring). Dispersed clay was mixed with PLA solution (tip-ultrasound: 5 min, ice bath). Solution was poured into Petri dishes, dried, cut, and oven-dried (50 °C). Nanocomposite (4 wt% organoclay): 228 g PLA + 24 g masterbatch extruded in twin-screw extruder (L/D = 25, D = 19 mm, BA Process Equipment MP19). Temperature: 170, 175, 180, 175, 180 °C. Rotation: 100 rpm. Filament pelletized, dried (60 °C, 24 h), and injection-molded (Arburg Allrounder 270S 400-100) into ASTM D638 Type I specimens. Conditions: 170210 °C, 2500 bar, mold: 30 °C, cooling: 50 s. See Figure 3 for overview. Figure 3 – Overview of biocomposite production process using bentonite fines from mineral beneficiation for eco-friendly food packaging
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