Characterization of raw and thermochemically-treated mesocarp fibers of Oenocarpus bataua, an Amazon palm

Background: Patauá ( Oenocarpus bataua Mart.) is a palm tree belonging to the botanical family Arecaceae that occurs throughout the Amazon. Like açaí, an edible pulp is extracted from its fruits, remaining a fiber-rich waste. Revealing the potential of such raw or thermochemically modified fibers for producing bioproducts is a novelty in the literature. Therefore, this work aimed to characterize patauá fibers in natural and alkali-treated conditions to support future bioproduct applications. Alkaline treatments were performed under mechanical stirring combining two NaOH levels (5 and 10%) and two temperatures (80 and 100°C). Morphological characterization was performed by light microscopy and scanning electron microscopy (SEM). The contents of the structural and non-structural chemical components were determined, and chemical groups were evaluated by Fourier-transform infrared spectroscopy (FTIR). The physical characterization included moisture content, apparent density, and water absorption tests. Results: The macerate revealed short fibers with typical elongated morphology, mean cell wall thickness (4.10 µm) greater than the mean lumen width (3.01 µm), and mean length of 445 µm. The alkaline treatments partially individualized the fibers from bundles, cleaned extractives from the surface, and unblocked superficial pits by removing silica-rich structures. They substantially removed non-cellulosic components, but FTIR showed condensed lignin exposed on the fiber surface. Density and water uptake increased concerning natural fibers. Patauá’s short length and susceptibility to modification through thermochemical treatments that concentrated cellulose up to 50% indicated great potential for developing composites and nanofibers. Regardless of the NaOH content, 100°C was more efficient in concentrating cellulose. Conclusion: Patauá fibers have unique natural characteristics. They occur as flatted fiber bundles, have silicon-rich structures obstructing their superficial pits, and comprise more lignin than cellulose.