Comprehensive Chemical, Structural, and Thermochemical Characterization of the Native Mexican Bamboo Guadua aculeata

Despite its high biomass productivity and structural potential, the physicochemical properties of the native Mexican bamboo Guadua aculeata Rupr. ex E. Fourn (G. aculeata) remain largely unexplored across its distinct anatomical regions. This study presents a comprehensive chemical, structural, morphological, and thermochemical characterization of the culm, branch, and leaf fractions of G. aculeata. Compositional analysis revealed marked macromolecular differentiation: cellulose and lignin contents increased significantly from the leaf (39.5% and 9.4%, respectively) to the structural branch (45.0% and 20.6%) and culm (46.1% and 20.1%) tissues, whereas hemicellulose was highest in the leaf (25.8% vs. 21.5–21.9% in branch and culm). The resulting cellulose-to-lignin ratio in the culm (~2.3) and branch (~2.2) reflects a balanced lignocellulosic matrix suitable for structural biocomposites and biorefinery applications. Ultimate analysis showed uniform carbon (42.8–43.7%) and hydrogen (5.3–5.4%) contents across fractions, while inductively coupled plasma optical emission spectroscopy (ICP-OES) identified the leaf as a major mineral reservoir, accumulating 7.72% silicon within a total inorganic ash content of 9.48% (compared to 4.25% silicon in the culm). Fourier-transform infrared spectroscopy (FTIR) evidenced a more intense and defined band at 1230 cm−1 (C–O stretching in syringyl and guaiacyl units) in culms and branches than in leaves, corroborating their higher degree of lignification. X-ray diffraction (XRD) confirmed the predominance of the native cellulose-I polymorph, with the crystallinity index decreasing from the culm (41.9%) to the branch (35.1%) and leaf (25.3%). Scanning electron microscopy (SEM) revealed thick-walled sclerenchyma fiber sheaths and compact parenchyma in the culm, contrasting with porous conductive tissues in the branch and a silica-rich stomatal epidermis in the leaf. Finally, thermogravimetric analysis (TGA/DTG) under inert and oxidative atmospheres demonstrated that the culm’s higher crystallinity and compact lignified microstructure were associated with superior thermal stability (~330 °C), whereas leaf tissues degraded earlier due to their higher amorphous carbohydrate and catalytic potassium (0.901%) contents, establishing a scientific baseline for the fraction-specific valorization of G. aculeata.