Step-wise multi-scale deconstruction of banana pseudo-stem (Musa acuminata) biomass and morpho-mechanical characterization of extracted long fibres for sustainable applications

Banana Pseudo-stem (BPS) is an annual renewable agricultural by-product with a potential for valorization in the production of paper, textile fibre or new bio-based materials. A gradual deconstruction process was implemented to determine BPS chemical composition and isolate sub-components that may be valorized in the formulation of bio-based polymer composites. At each step, the residues were analyzed by FTIR, X-ray diffraction and TGA-DTG. The chemical composition of the starting material (% of dry weight) was evaluated as: 13.4% total extractives, 6% pectins, 14.7% lignins, 28% hemicelluloses and 38% cellulose. The deconstruction process for BPS was efficient but led to mercerized cellulose (cellulose II) as a final residue, as assessed by the intense X-ray scattering peaks centered at 20.5 degrees and 21.5 degrees. Cellulose II formation was induced by the high concentration of the alkaline KOH solution used to dissolve hemicelluloses in holocellulose. The step-wise removal of non-cellulosic sub-components led to a more thermally stable residue. Long fibres were also obtained from BPS at a yield of 60%. These fibres display cellulose I structure and a thermal stability similar to the extracted cellulose. SEM analyses of long fibres showed transversal and lateral defects, the presence of surface hairiness and an almost cylindrical morphology. Uniaxial tensile tests were carried out at room temperature on 150 specimens randomly chosen among the less hairy fibres, with diameters ranging from 40 to 140 pm. Mechanical investigations (Young modulus: 6.3-26 GPa; nominal stress at break: 140-768 MPa; nominal strain at break: similar to 3%) reveal a significant disparity strongly influenced by fibre diameter, except for the nominal strain at break which remains fairly constant around 3%. These results are comparable to the upper range of the values reported for fibres extracted from BPS through alternative chemical routes or for fibres obtained from other annual plants such as jute and hemp.