Toddy palm fruit have an apparent density below 0.8 g/cm³ and offer an interesting lightweight construction potential in polylactide (PLA) composites reinforced with 37 mass-% fibres. Single fibre bundles show similar mechanical properties compared with coir: tensile strength of 240 MPa, Young´s modulus of 3.8 GPa and an elongation at break of 31%. However, density and diameter (~ 50 µm) of fruit fibre bundles are significantly lower. The compression moulded composites have a density of 0.9 g/cm³ and achieved an unnotched Charpy impact strength of 12 kJ/m², a tensile strength of 25 MPa, Young's modulus of 1.9 GPa and an elongation at break of 9%. Due to the high porosity of the composites and the different stress-strain behaviour of fibre and matrix the fibre-reinforcement potential could not be fully used. Maximum stress of the composite was reached at the elongation at break of the PLA-matrix (~2%) while the fibre achieved its maximum stress at an elongation of ~31%. After reaching the maximum stress of the composite, the fibres were pulled out from the matrix with low energy absorption, resulting in a decrease in stress and a limited reinforcement potential. Additionally, the study investigates whether an insect attack by the Asian fruit fly on the mesocarp has a significant influence on the mechanical fibre characteristics. The results have shown that only the rough surface of the fibre bundles is smoothed by insect infestation. The mechanical properties were not significantly affected. For this reason insect-infested fruits of the toddy palm, which are no longer suitable for food production, can be used for the production of sustainable composite materials.

No abstract

Thailand has a huge variability of bast fiber plants, some of which have been little researched regarding their applicability in composites. Bast fiber(bundle)s from different species were investigated and incorporated into a polylactide (PLA) matrix by injection molding. Hemp and kenaf were used as well-studied fibers, while roselle, Fryxell and paper mulberry are less extensively characterized. Tensile strength, tensile modulus and interfacial shear strength (IFSS) of single fiber(bundle)s were highest for hemp, followed by kenaf, roselle, Fryxell and paper mulberry. Despite the lower tensile strength and IFSS of paper mulberry, the highest tensile strength was achieved for the paper mulberry/PLA composite followed by hemp/PLA. Scanning electron microscope (SEM) analyses showed that the single cells in paper mulberry fiber bundles, in contrast to the other fiber types investigated, were only partially bonded to each other, which explains the lower strength of the fiber bundles. The higher aspect ratio of fiber(bundle)s of paper mulberry in the PLA composite can explain the good composite characteristics. Apart from hemp, paper mulberry shows the best reinforcing effect in the PLA matrix and offers interesting potential for composite applications. Compared to neat PLA, the tensile strength could be increased by 24% and the tensile modulus by 54%.

Cellulose nanofiber (CNF) was successfully isolated from kenaf bark by microfluidization at 20,000 psi for 40 passes. The combination of hydrothermal process and xylanase treatment prior to CNF isolation led to effective cellulose purification. The fiber used for enzymatic pretreatment for CNF isolation had an 85.9% whiteness index and 85.1% cellulose content. The crystallinity of the cellulose extracted from the kenaf bark continued to increase with successive treatments, as indicated by X-ray diffraction analysis. In addition, the enzyme-treated fiber showed increased thermal stability, as shown by thermogravimetric analysis. After CNF isolation, morphological characterization of the CNF was performed via field emission-scanning electron microscopy and transmission electron microscopy. The CNF had an average diameter that ranged from 5 to 10 nm and no undesired elemental contamination, as evidenced by energy dispersive X-ray spectroscopy. The mechano-enzymatic treatments used in this work to obtain CNF were judged to be a promising technique for the fabrication of biomedical and other high-value materials.