Researchers have developed an innovative method for designing and manufacturing three-dimensional moulded bamboo, achieving complex structural transformations through a combination of partial delignification, uneven drying, and compression moulding. This breakthrough technique allows for precise control over bamboo’s transverse deformation, enabling it to be moulded into various shapes such as 90°, 180°, 270°, 360° curves, and polygonal forms including triangles, squares, pentagons, and hexagons.
The research details a process beginning with partial delignification, which modifies the bamboo’s cell wall structure to increase cell wall gaps and reduce inter-wall bindings, facilitating transverse cell deformation under drying stresses. A key factor is uneven drying, where a temperature difference of 50°C is applied on opposite sides of the bamboo, directing moisture migration and creating drying stresses that cause the bamboo to deform in a controlled manner. For example, a bamboo segment of 5 cm height and 8 cm diameter was flattened after 600 minutes under such conditions. An analytical model divided the bamboo into multiple regions along the thickness and width to quantify moisture and internal stress distributions, revealing shifts from tension to compression in different regions as drying progressed. Larger temperature differentials shortened the time required for shaping.
Following drying, compression moulding at the fibre saturation point (around 30% moisture content) consolidates the bamboo while preserving its natural heterogeneous cellular structure. The resulting product benefits from tightly packed cellulose fibres and an increased density of hydrogen bonds, which enhance bonding strength between fibres and improve mechanical properties. Scanning electron microscopy confirmed the integrity of bamboo cellular structures throughout processing.
Mechanical testing showed significant enhancement in the moulded bamboo’s strength and resilience compared to natural bamboo. Tensile strength increased from 193.7 MPa to 875.4 MPa, bending strength from 173.6 MPa to 375.3 MPa, compression strength from 73.7 MPa to 102.7 MPa, and impact resistance from 988.1 to 2033.3 J/m. Density ranged between 1209 to 1315 kg/m³. Compared with traditional engineering materials such as carbon fibre reinforced plastics, metals, ceramics, and polymers, moulded bamboo displays comparable specific stiffness and strength but at a considerably lower cost, offering a lightweight and economically viable alternative.
Moisture resistance and dimensional stability, crucial factors for construction materials, were tested under high humidity conditions. Coated moulded bamboo displayed minimal rebound and maintained stability in water immersion tests over 24 hours. The treatment process, particularly lignin removal, reduces cell wall expansion ability but strengthens dimensional stability due to the loss of hemicellulose and enhanced hydrogen bonding.
At a molecular level, spectroscopic analyses revealed a reduction in lignin and hemicellulose content and an increase in crystallinity and hydrogen bond density within cellulose fibres following treatment. The interplay between cellulose fibres and bound water molecules contributes substantially to the mechanical performance of moulded bamboo, as water acts as an adhesive through hydrogen bonding.
Environmental impact assessments using life cycle analysis report that producing 1 kg of moulded bamboo emits 5.24 kg of CO2 equivalent and 0.0256 kg of SO2 equivalent emissions, figures which are lower compared to many conventional building materials. The analysis covers the entire lifecycle from raw material acquisition to end-of-life disposal, showing reduced fossil resource consumption, ecotoxicity, eutrophication, acidification, and water usage. These factors highlight the potential of moulded bamboo as a sustainable material option that could contribute to carbon neutrality goals.
Economic viability was also considered by constructing lightweight rigid beams, demonstrating that moulded bamboo offers superior cost-effectiveness compared to traditional materials like stone, wood, cast iron, and steel. The researchers further suggest that the processing method for thinner bamboo requires less pretreatment and drying time, supporting scalability for industrial production.
The Nature publication reports these findings, underscoring the material's potential applications in lightweight construction and engineering where strength, toughness, sustainability, and cost are critical factors.
Source: Noah Wire Services