Bamboo Microstructure Research Articles

An exploratory study on bamboo permeability for evaluation of treatability with chemical solutions

The rapid and uniform impregnation of resins and preservative fluids is critical to improving the quality and durability of wood-based materials. Permeability coefficients obtained in laboratory experiments aid in the development of optimal conditions for uniform resin filling on an industrial scale. However, due to the shape and orientation of pores in the bulk structure of bamboo, simplified permeability equations may not be sufficient to provide realistic resin impregnation predictions. In this study, the permeability coefficients for Dendrocalamus asper bamboo were determined using air flow measurements and Forchheimer's equation in the x, y, and z directions, and they were correlated to the bamboo microstructure, providing a detailed perspective on how to further investigate this property for real-world applications, such as pressure treatments with chemical solutions. Porosity was measured using mercury intrusion porosimetry (MIP) and water immersion methods to aid in the permeability analysis. The results showed that the longitudinal direction had 1000 to 10,000 times higher permeability coefficients than the radial and tangential directions. This finding is consistent with the alignment of transport vessels as well as the limited pore network in the transversal bamboo section. The outer region of bamboo had higher radial permeability than the middle and inner layers, despite having lower porosity. It is hypothesized that the greater number of vessels, albeit smaller, provides a more direct path for air to flow. The Darcian permeability coefficients of bamboo were found to be comparable to those reported in the literature for wood. This exploratory study provided insights into a novel approach for assessing the treatability of bamboo species.

Effect of Paraffin Impregnation Modification on Bamboo Properties and Microstructure

Phase-change energy-storage paraffin regulates the thermal management of buildings, and the material can regulate room temperature as it absorbs and discharges heat. As a porous adsorbent material, bamboo has high permeability. The aim of this study was to increase the amount of paraffin inside bamboo and the latent heat of the phase change. It was performed using vacuum pressurization (VP) and ultra-high-pressure (UHP) impregnation treatments. The effect of UHP impregnation and properties of bamboo were studied. The weight gain, paraffin loss and dimensional changes were measured and compared. The morphology of UHP-impregnated bamboo were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The main conclusions are as follows: After UHP impregnation, the highest weight gain was 42%. The loss of paraffin was low, and a high weight percentage gain was maintained. The crystallinity of cellulose decreased to 24% at 100 MPa. The latent heat of the bamboo slices was up to 25.66 J/g at 50 MPa, and the phase change temperature was close to room temperature. At 150 MPa, the hydroxyl content was reduced, and the hydrophilicity decreased. In addition, the content of substances such as hemicellulose in the amorphous zone was reduced under UHP, no new characteristic peaks appeared, and no chemical modifications occurred. The vascular bundles were compressed and dense, and the pores and cell gaps decreased. The thin-walled cells were deformed, and the original cell structure was completely destroyed. The surface of the cells was wrapped or covered with paraffin, confirming that the paraffin could impregnate the bamboo cells under UHP. Therefore, bamboo impregnated with paraffin can regulate temperature and save energy in buildings. It is resistant to biological attacks, and UHP improves the impregnation efficiency.

Thermal treatment of bamboo with flame: influence on the mechanical characteristics

The mechanical properties of bamboo are susceptible to degradation due to both physical and biological agents. Among the non-chemical treatments, we studied the influence of a short-time heat treatment, using an LPG-gas torch, on the mechanical properties of a bamboo (Phyllostachys viridiglaucescens) growing in Italy. The response was very encouraging as we found no significant reduction in either elastic modulus or tensile, compressive and bending strength.Several samples were subject to tension, compression and bending tests to compare the responses of the treated and untreated culms. The average tensile elastic modulus was slightly greater for the untreated culms. The average tensile strength of the untreated culms was only slightly greater, and the differences can be assumed to be insignificant from a structural point of view. The average value of the treated culms compressive elastic modulus was slightly greater than that of the untreated ones. The compressive strength was essentially the same. The bending mechanical behaviour was barely influenced by the thermal treatment.A microscopic investigation (optical and electron microscopy) was undertaken to investigate the possible deterioration of the bamboo microstructure due to the heat treatment. No appreciable damage was detectable in the treated material.The proposed heat treatments can be considered as a reliable and sustainable protection practice for bamboo culms.

Effect of bamboo species and pre-treatment method on physical and mechanical properties of bamboo processed by flattening-densification

In this study, Dendrocalamus asper and Phyllostachys edulis (Moso) bamboo were subjected to a two-phase process of flattening and densification using a non-confined thermo-hydro mechanical (THM) system (composed of two hot plates without lateral limit) to redesign bamboo's microstructure and improve its performance for applications in panel manufacturing. Different softening procedures using pre-treatments with water under vacuum/pressure conditions using a vacuum of −650 mmHg and a pressure of approximately 3100 mmHg (V/P) and boiling treatment for 1 h at 100 °C (B) before flattening were studied. All groups were flattened, dried at room temperature, and densified at the same processing parameters. The microstructural, physical, and bending properties of the obtained flattened-densified bamboo using these two pretreatments were examined and compared with untreated-undensified (UN) bamboo and samples flattened-densified in an equilibrium moisture content (EQ). The results of bending tests, comparing to the un-processed bamboo, revealed that the flattening process combined with densification promote an average increase in the Modulus of Rupture (MOR), (56% and 66%), Modulus of Elasticity (MOE) (48% and 78%), Limit of Proportionality (41% and 86%), and Specific Energy (126% and −12%) in the case of D. asper, and Moso respectively. However, the applied process increased the thickness swelling (SW) and water absorption (WA). This negative effect was more pronounced in the case of Moso compared to D. asper. The flattened-densified Moso using any type of applied pretreatments presented an average of 64% of WA and 35% of SW, while these values for D. asper bamboo were 28% and 19% of WA and SW respectively. In addition, boiling the bamboo in water as a pre-treatment prior to densification reduces the cracks number compared to the other pre-treatments, resulting in higher MOR, MOE, and dimensional stability.

Study of the long-term degradation behavior of bamboo scrimber under natural weathering

In this work, the degradation behavior of bamboo scrimber are investigated under natural weathering system for six years. Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and colorimeter were used to characterize the change of bamboo scrimber surface and microstructure. Natural weathering led to degradation of lignin and rapid color changes, demonstrated by decrease of 1232 cm−1, 1423 cm−1 and 1506 cm−1 absorption peaks, the reduction of C1and increase of C2, and ΔE* value notably. Lignin degradation resulted in micro-check formation in the cell walls of fibers and parenchyma cells within exposure time. In particular, parameters of weather resistance changed rapidly within the initial two years and stabilized in the following four years. It is also revealed that two natural regions with different type of climate have significantly affected the degradation behavior of bamboo scrimber.

Photodegradation and Photostability of Bamboo: Recent Advances

Bamboo and its products are widely used in indoor and outdoor fields. Photodegradation occurs easily on the surface when bamboo is exposed to ultraviolet (UV) light from solar radiation. This induces surface discoloration and degrades the physical properties of bamboo, which not only negatively affects its utility and aesthetic characteristics but also restricts its application in outdoor environments. In this work, we review the mechanism of bamboo photodegradation, in which the behavior of lignin is key. The changes in bamboo’s microstructure, surface color, and chemical composition during photodegradation are described in detail. Methods for enhancing its photostability, including the application of transparent coatings containing UV absorbers and hindered amine light stabilizer compounds on bamboo surfaces, are then systematically summarized, and potential approaches to combat the photodegradation of bamboo surfaces are discussed. On the basis of the recent advances of photodegradation and photostability of bamboo, this review provides new insights into the scientific application and protection of bamboo in the outdoor field.

Quantitative characterization of bamboo cortex structure based on X-ray microtomography

Bamboo is a natural fiber composite with layered structure. Millions of years of evolution have endowed bamboo with the most effective structure in nature. The ingenious microstructure provides bamboo with excellent mechanical properties. Bamboo culm is composed of the cortex, a middle layer, and a pith ring. The cortex refers to the area starting from the periphery of the culm wall to the vascular bundles. The present study obtained the two-dimensional (2D) microstructure of bamboo cortex cells by optical microscopy and characterized the three-dimensional (3D) structure through high-resolution X-ray microtomography (µCT). The 2D anatomical parameters of cortex cells were measured to verify the reliability of cortical cell classification in 3D models. Based on the analysis, the bamboo cortex cells were classified into four layers: epidermis layer, hypodermis layer, transitional layer, and parenchyma layer. The total volume of the reconstructed area of interest in μCT was 7.85 × 106 µm3, in which the total pore volume of bamboo cortex was 2.84 × 106 µm3, the average pore volume of bamboo cortex was about 1.54 × 103 µm3. Thus the porosity was 36.1%, and the relative density was 0.639. Studies on bamboo anatomical structure, especially three-dimensional digital characterization, will enrich the bamboo microstructure database. Besides, the three-dimensional structure of the bamboo cortex revealed in this study can provide a reference for optimizing composite material hierarchy and biomimetic design.

Thermal stability of polycrystalline nanowires

Abstract The equilibrium shape of a polycrystalline cylindrical nanowire with bamboo microstructure is determined. It is shown that for a certain ratio of grain boundary and surface energies a critical grain length exists above which the integrity of a nanowire cannot be preserved. Numerical calculations of the kinetics of nanowire shape evolution controlled by surface diffusion are performed. It is shown that the rate of thinning of unstable nanowires in the region of grain boundaries diverges as a break-up event is approached.

A numerical anatomy-based modelling of bamboo microstructure

Bamboo has attracted considerable recent interest in sustainable buildings as the fastest-growing natural material retaining mechanical properties similar to structural wood while being an effective CO2 absorber during its growth. Previous efforts to estimate bamboo material properties and their behaviour using homogenisation techniques used simplified assumptions on the geometry of the inhomogeneous microstructure, hence these methods failed to account for the different homogenised material properties in the directions lateral to the bamboo culm. This study presents a novel anatomy-based numerical bamboo microstructure analysis that accurately represents the geometrical features of the material, leading to a transversely anisotropic effective material model. We compare the resulting effective elastic properties to those obtained with state-of-the-art numerical and analytical approaches found in the literature. It is concluded that our anatomy-based representative volume element provides a better understanding of the material microstructure and its corresponding effective stiffness properties in the longitudinal and lateral directions.

Multi-scale evaluation of the effect of saturated steam on the micromechanical properties of Moso bamboo

Abstract The changes in chemical composition and micro-mechanical properties of Moso Bamboo fiber cells were evaluated by applying saturated steam heat treatment at 160, 170, and 180 °C for periods of 4, 6, and 8 min, and subsequent analysis by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopic, and nanoindentation methods. The hemicellulose and cellulose content decreased as expected, while the relative lignin content showed an upward trend. Significant changes in the bamboo micro-structure were detected by scanning electron microscope under the action of high-temperature and saturated steam. Both temperature and time were shown to affect micromechanical properties of the bamboo cell wall. In addition, higher cell wall elastic modulus and hardness were observed (a rise from 16.1 to 19.2 GPa and from 0.6 to 0.8 GPa, respectively), as compared with those of the untreated sample. Meanwhile, the creep ratio decreased after saturated steam heat treatment.

Durable superhydrophobic surface with hierarchical microstructures for efficient water collection

Owing to the aggravation of water pollution and fresh water shortage, fabrication of functional materials with super-wettability surfaces for harvesting atmospheric water has gained widespread attention in recent years. In this paper, a superhydrophobic surface with combination of good robustness and efficient water-collecting performance was successfully fabricated via structuring multilevel microstructures. This hierarchically structured surface was prepared by photoetching, acid-etching, anodizing and fluoroalkylsilane modification treatments. The resultant surfaces exhibited great water repellency with the water contact angle (CA) of 173° and a low sliding angle (SA) of 1.5°, and showed good chemical stability both in air and severe acidic-alkaline environments. Furthermore, favorable water proofing property was still maintained after cyclical abrasion of the prepared superhydrophobic surface, with micrometer sized square frustum pillars to provide mechanical durability and the secondary bamboo shoots-like microstructure to provide water repellency. Water harvesting efficiency of this robust superhydrophobic surface was 5.3 g·cm − 2 ·h −1 , higher than those of the previous reported surfaces. This facilely fabricated superhydrophobic surface is expected to collect micro droplets from fog/mist environments so as to relieve the lack of water. • Micro-pillars and secondary bamboo shoots-like structures were fabricated. • The superhydrophobic surface shows good acid and alkali resistance. • As designed multi-level structures lead to well mechanical robustness. • Efficient water harvesting was realized via fast transportation of droplets.

Research on vibration suppression of wind turbine blade with a multi-layer porous damping structure based on bamboo wall microstructure

As wind turbine blades are getting softer and thinner, the demand for their capability of vibration suppression is improving day by day. Drawing from bamboo’s quick recovery to its former position and mimicking the microstructure of bamboo wall, this paper puts forward a porous damping structure on the blade and sets up its mathematical model. The formula for its structural loss factor is deduced on the vibration theory. Then numerical simulation method is adopted to investigate its damping performance on one wind turbine blade by ABAQUS. The results indicate that the vibration damping property of the wind turbine blade with the porous damping structure is significantly increased. The porous damping structure dissipates more heat very quickly and its single material also displays advantages over composite material. This paper provides a reference for the design of highly efficient damping structures.

Laser Powder Bed Fusion Processing of Fe-Mn-Al-Ni Shape Memory Alloy—On the Effect of Elevated Platform Temperatures

In order to overcome constraints related to crack formation during additive processing (laser powder bed fusion, L-BPF) of Fe-Mn-Al-Ni, the potential of high-temperature L-PBF processing was investigated in the present study. The effect of the process parameters on crack formation, grain structure, and phase distribution in the as-built condition, as well as in the course of cyclic heat treatment was examined by microstructural analysis. Optimized processing parameters were applied to fabricate cylindrical samples featuring a crack-free and columnar grained microstructure. In the course of cyclic heat treatment, abnormal grain growth (AGG) sets in, eventually promoting the evolution of a bamboo like microstructure. Testing under tensile load revealed a well-defined stress plateau and reversible strains of up to 4%.

Based on Bionic Optimization Design and Strength Analysis of The Tie Rod of Aircraft Landing Gear

Based on the three-dimensional model of the cross-type tie rod in the landing gear of an aircraft, the mechanical analysis and solution are carried out, and the stress nephogram as well as the maximum position are obtained. Based on the analysis of bamboo microstructure, two kinds of imitated bamboo tie rod has been designed, one is the imitated bamboo without knots, the other is added knots. The three-dimensional modeling is carried out. The static analysis of finite element is carried out under the same working condition, and the stress nephogram and the position of the maximum value are obtained. The results of two kinds of simulated bamboo tie rod and cross-type tie rod are compared and analyzed. The results show that the mechanical properties of the whole simulated bamboo tie rod are superior to the cross-type tie rod.

Bamboo modification with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) catalyzed by maleic anhydride

Low-molecular-weight 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) was used to modify bamboo strips catalyzed by maleic anhydride. In this study, response surface methodology (RSM) was applied to optimize the treatment conditions for DMDHEU modification of bamboo. Three selected parameters, DMDHEU concentration, curing temperature, and curing time, were further optimized using response surface methodology via the box behnken design (BBD). The equilibrium moisture content (EMC), water absorption (WA), anti-swelling efficiency (ASE), mechanical properties, and mold resistances to (Aspergillus niger V. Tiegh, Penicillium citrinum Thom, Trichoderma viride Pers. ex Fr., and Botryodiplodia theobromae Pat.) were evaluated as the dependent variables. The results show that the dimensional stability and mold resistance of bamboo were enhanced remarkably, and the modulus of rupture (MOR) of bamboo was decreased after DMDHEU modification, while the modulus of elasticity (MOE) changed slightly, and the parallel-to-grain compressive strength (CS) was increased. Furthermore, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) were used to investigate the effect of modification on the bamboo microstructure and functional groups. In the context of SEM, TGA, and FTIR analyses, the thermal stability of bamboo modified with a medium or high concentration of DMDHEU was improved, the starch granules in the parenchyma cells of modified bamboo dissolved, and few resins were distributed in the lumens of treated bamboo.

Design of bionic-bamboo thin-walled structures for energy absorption

Bio-inspired engineering design has drawn considerable attention in the recent years for its great structural and mechanical features. This study aimed to explore the energy absorption characteristics of a novel bionic-bamboo tube (BBT) structure subjected to axial crushing. The tubes with six different cross-sectional configurations were devised with inspiration of bamboo microstructure. The effects of rib shape and rib number were analyzed by using the finite element code LS-DYNA. The numerical results indicated that the BBT structures with the rib shape of “X” and the rib number of six exhibited the best crashworthiness. To further improve the energy absorption capabilities of these BBT structures, the multiobjective optimization was employed with respect to design variables of configurational structure, such as the rib angle of the “X” shaped cross-section, center distance and rib thickness. The response surface method (RSM) and multiobjective particle swarm optimization (MOPSO) algorithm were adopted to maximize specific energy absorption (SEA) while minimizing peak crushing force (PCF). The optimization results demonstrated that compared to the baseline design, the SEA value of the optimized BBT structure was further increased by 6.84% without sacrificing in peak crushing force.

Effect of strain rate on mechanical properties of the bamboo material under quasi-static and dynamic loading condition

As a kind of fiber-reinforced bio-composite, bamboo material exhibits superior mechanical performance. In present work, quasi-static and dynamic Split Hopkinson Pressure Bar (SHPB) compression experiments at the nominal strain rate range of 500 s−1–2200 s−1 were carried out to investigate the effect of strain rate on mechanical behaviors of the bamboo material. In consideration of the effect of fiber directions on mechanical behaviors, the specimens were crushed with the loading direction parallel to the fiber longitudinal direction and perpendicular to the fiber direction, respectively. The experiments under both loading directions exhibited remarkable strain rate sensitivity. The yield stress for the specimens crushed along the fiber longitudinal direction increased from 38.59 MPa to 94.25 MPa, as the strain rate varied from 1.85 × 10−3 to 2200 s−1, while it increased from 7.18 MPa to 42.04 MPa for the specimens crushed perpendicularly to the fiber direction. Final deformation photographs and scanning electron micrographs of the bamboo microstructures clearly illustrated their damage morphologies and various failure mechanisms, including fiber buckling, fiber fractures, PCs collapse, delamination and crack propagation at different strain rates and loading directions. These results may provide a novel perspective on the mechanical behaviors of bamboo microstructure and design of new bio-inspired structural materials.

Electromigration: Void Dynamics

The detailed knowledge of the void evolution is helpful to understand and interpret traditional electromigration (EM) lifetime experiments. As void formation and subsequent evolution is highly dynamic, an in situ observation experiment was employed using an SEM allowing for void detection down to a few nanometers in diameter. For void nucleation, it has been suggested that due to the large anisotropy in modulus in Cu, incompatible grain boundaries can act as stress concentrators for both stress-induced and EM-induced voiding. In addition, during growth, the shape change and migration have been associated with the microstructure. To better understand void formation and evolution, we examined the Cu microstructure using EBSD during the experiment without interruption. We tested interconnects consisting of Cu-based damascene (M1) drift type structures, capped with SiCN. Void formation could be confirmed to be associated with features such as incompatible grain boundaries in some instances. In other cases, triple points and grain boundary/sidewall intersections were found as void nucleation sites. Void growth and migration is found strongly correlated with the driving current density. We show conditions under which void migration takes place or is suppressed. In particular, a critical current density of approximately 10 $\mbox{mA}/\mu\mbox{m}^{2}$ is observed, below which no void migration occurs. At current densities of 15 $\mbox{mA}/\mu\mbox{m}^{2}$ and above, all voids migrated at a net drift velocity proportional to the current density. Independent of migration, all voids are observed to grow at rates consistent with published data for a mixed near bamboo microstructure and interface diffusion.

On the influence of Dendrocalamus giganteus bamboo microstructure on its mechanical behavior

This paper reports the experimental results of the investigation on the microstructure of Dendrocalamus giganteus bamboo laminae and the influence on its mechanical properties. The laminae were extracted from the central culm sector and from specific wall thickness positions in order to identify the fiber volume fraction, porosity and other matrix constituents, due to the functionally gradient characteristic. Samples were prepared from each set of laminae, both for microanalysis and for mechanical testing, under proposed configurations. The microscale morphology was observed and characterized both qualitatively and quantitatively through transmitted and reflected light microscopy, scanning electron microscopy and X-ray microtomography. An original method was proposed to quantify porosity through a humidity variation test. Tension and compression tests were carried out and their results were discussed with respect to the bamboo microstructure. Additionally the modes of failure were registered and analyzed. Results show that voids constitute an expressive portion of the culm. The mechanical properties are dictated by the fiber volume fraction when the specimens were tested under tensile load and by the density variation when tested under compressive load.

Changes in Chemical Composition and Microstructure of Bamboo after Gamma Ray Irradiation

Changes in bamboo composition and microstructure following 60Co gamma (γ) ray irradiation were investigated by solid state 13C cross-polarization (CP) magic-angle spinning (MAS) spectroscopic nuclear magnetic resonance spectrometry (NMR) and a field emission scanning electron microscope (FESEM). The results indicated that irradiation doses lower than 100 KGy resulted in the degradation of hemicelluloses via scission of molecular chains, but there was also repolymerization and condensation in lignin. Irradiation doses higher than 100 KGy resulted in the degradation of cellulose, hemicelluloses, and lignin by significant oxidation reaction and partial scission of biopolymer chains to yield more small fragments with carbonyl groups.