Effect of softening duration on physical, mechanical and microstructural properties of flattened densified Bambusa bambos

The half-split Bambusa bambos culms were flattened after subjecting them to different steaming durations in the range of 20–40 min. The flattened bamboos from bottom, middle and top sections were further subjected to the densification process using a hot press. Various physical and mechanical properties of the flattened and densified bamboo (FDB) were evaluated and compared with control. Analytical techniques such as scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) were applied to study the microstructure and chemical changes due to flattening and densification. The results showed that softening duration had significant effect on all the properties of the FDB. The flattened sheets prepared from the bottom, middle and top portions of bamboo showed different properties. The density of the FDB was observed to increase significantly compared to untreated bamboo. The significant density improvements lead to relatively uniform distribution of the vascular bundles through the radial direction of the culm wall. Although the water absorption of the FDB boards was significantly reduced compared to control, no improvement was observed in the dimensional stability after water submersion for 24 h. With the increase in softening duration, various mechanical properties such as flexural strength, flexural stiffness and tensile strength parallel to fibre direction of FDB were improved significantly. The SEM observations showed that the microstructure of parenchyma and vessel elements changed significantly while fibre microstructure was undisturbed. FTIR analysis showed that hemicellulose content was slightly reduced while other chemical constituents of bamboo were not much affected. The crystallinity of the bamboo was found to be increased after flattening and densification leading to improvement in strength properties. These findings may be of practical importance for efficient utilization of bamboo in production of value-added FDB composites.