With the rapid growth of China’s economy and people’s high-level pursuit of life, eco-friendly materials are gradually used in home decoration, furniture and construction industries. Compared to wood, bamboo has its own advantages such as large strength, good toughness, and great abrasion resistance when it is applied as a material to structural engineering or home decor. However, bamboo also has several limitations, for example, a small diameter, a longitudinal difference in diameter, thin and hollow walls, and a disposition to corrosion and cracking. Therefore, there is an urgent need to develop a new efficient and high-value utilization technology of bamboo. “Bamboo flattening” is a kind of high-efficiency utilization technology adopted to construct flattened bamboo boards from bamboo tubes or pre-softened arc-shaped bamboo sheets. Prior to flattening, pretreatments are requested, including softening, outer layer removal, and inner layer removal. For the bamboo tubes, penetrating grooves are requested to be created which are supposed to be widened during the saturated steam heat treatment and are conducive for the tubes to enter into the flattening machine. Moreover, tapered, rectangular or “V”-shaped protrusions nails with uniform dispersions, or diamond-shaped line grooves with a width, depth and spacing of 1.5–2.0 mm, 2.0–4.0 mm and 5.0–8.0 mm are always created to release the generated internal stress during the flattening processes. For the arc-shaped bamboo slices, a non-notched flattening method is introduced with a machine equipped with the unfolding rolling component, the flattening component, and the reverse roller component. There are no grooves, nails or guide lines on the inside surface of the obtained bamboo board. It is worth mentioning that all boards obtained should be treated by cooling, shaping and drying. Bamboo flattening technology can increase the utilization rate of bamboo resource from the original 30–55 %, reduce the amount of adhesive by 30 %, and increase the added value by more than 20 %. Herein, the achievements in bamboo flattening technology based on published papers and patents are described, along with their underlying physicochemical mechanisms.

Bamboo flattening technique: a literature and patent review

Bamboo is now widely used in construction, papermaking, textile, furniture and other fields because of its renewable, fast-growing, high-strength, high-yield and easy processing. However, compared with wood, bamboo and bamboo products are more vulnerable to damage by fungi and pests. An effective and eco-friendly method is urgently needed to improve their physical and chemical properties, decay resistance and anti-mildew properties, and hydrophobic properties. Here, bamboo was heated with methyl silicone oil. The effect of different temperatures (140 °C–200 °C) and different times (2 h–6 h) on the properties of bamboo was studied systematically, including chemical composition, physical and mechanical properties, surface wettability, decay resistance and anti-mildew property. No starch granules were observed inside the parenchymal cell lumen of bamboo specimen heat treated at 200 °C for 6 h. And with the increase of heat treatment temperature and time, the content of cellulose and hemicellulose decreases gradually while relative content of lignin increases due to its better thermal stability. Accordingly, the surface wettability decreases due to the changes of the surface functional groups and micro-morphologies. Under the condition of oil heat treatment at 160 °C for 2 h, the compressive strength parallel to grain of bamboo samples reach the maximum of 109.52 MPa. With further increase of heating temperature, the corresponding compressive strength decreases. The resulted bending strength and MOE both display similar changing trend. However, the optimal parameter is at 180 °C for 2 h, with the highest bending strength and MOE values of 142.42 MPa and 12,373.00 MPa, respectively. Finally, the decay resistance and anti-mildew property are dramatically enhanced with increased heat treatment temperature and time. All the corresponding changing mechanisms are investigated in depth and in detail. Our results provide comprehensive process parameters and micro-mechanism for the performance of oil heat treatment of bamboo, which can be used to guide the actual production.

/pdf/the-effect-of-oil-heat-treatment-on-biological-mechanical-4emeh9lyk6.pdf

The effect of oil heat treatment on biological, mechanical and physical properties of bamboo

Bamboo fiber has attracted a lot of interest due to its high specific strength and renewability. Unidirectional long bamboo fiber reinforcing is essential to fully realize its strength. The reinforcing efficiency can also be affected by the physical and chemical structure of bamboo fibers. Therefore, this study reviews the cell wall structure of the bamboo fiber. The alternately arranged structure with thin and thick layers contributes substantially to the mechanical strength of the bamboo fiber. In addition, this study evaluates the mechanical properties, water absorption, and flame retardancy of polymeric and cementitious composites reinforced with long bamboo fibers. Thermoset polymer-based bamboo fiber composites typically show higher mechanical strength than thermoplastic-based fiber composites. Chemical treatment and flame retardant can significantly enhance the hydrophobicity and flame retardancy of fiber composites, respectively. Because of its superior interface performance, the short bamboo fiber has a greater reinforcing effect in cement mortar than in concrete. This study can serve as a reference for further investigations on bamboo fiber/bundle reinforced composites and promote their applications. 

Structural and mechanical properties of bamboo fiber bundle and fiber/bundle reinforced composites: A review

Bamboo heat treatments and their effects on bamboo properties

Tunable nano-effect of Cu clusters derived from MOF-on-MOF hybrids for electromagnetic wave absorption

https://www.techscience.com/jrm/v9n5/41556/pdf

Fabrication of Crack-Free Flattened Bamboo and Its Macro-/MicroMorphological and Mechanical Properties

Bamboo is a biomass material, which is a great substitute for wood with the potential to reduce the demand for woody materials. However, there is still a huge challenge to obtain crack-free bamboo boards with an ideal width due to the hollow cylinder and large curvature of bamboo culms. Herein, a method is demonstrated that can flatten bamboo culms by high-pressure saturated steam (180 °C/6 min) under a compression force of 8–10 MPa by two rollers. The macro- and micro-mechanical properties of the flattened bamboo board were also characterized in this paper. Results indicated that the saturated steam had no significant effect on the microstructure of the bamboo, whereas it decreased its hygroscopicity due to the degradation of the hemicellulose. The mechanical properties of the cell walls bamboo samples treated by softening and flattening were elevated compared with those of the untreated ones. During the flattening process, the parenchymal cells became compact. The elastic modulus of bamboo fibers increased from 16.14 to 18.75 GPa, while the hardness increased from 0.58 to 0.77 GPa. The improved mechanical properties of cell walls and increased density had a positive effect on the modulus of elasticity of the bamboo board.

A new approach for fabricating crack-free, flattened bamboo board and the study of its macro-/micro-properties

Bamboo flattening, a novel and efficient bamboo processing and utilization technology, can effectively flatten bamboo culms into crack-free board. The technology enables the efficient and value-added utilization of bamboo in the manufacture of furniture and engineered composites. In this study, we compared the effects of three types of flattening technologies on the macro-mechanical, macro-physical, micro-morphology, and micro-mechanical properties of untreated, softened a flattened bamboo samples. As expected, the hemicellulose and cellulose concentrations of the saturated steam treated sample (18.05% and 38.9%, respectively) were less than those the untreated sample (21.3% and 40.1%, respectively). Moreover, scanning electron microscopy (SEM) analysis showed that the notched flattening technology (NFT) inserted indents and grooves on the bamboo surface. However, the “non-notched flattening technology (NNFT)” only compressed the bamboo tissue. The flattening process increased the equilibrium moisture content and density of bamboo. The enhanced density, lignin content, and cellulose crystallinity index enhanced the bamboo cell wall properties. The non-notched-flattened bamboo board exhibited a higher cell wall modulus of elasticity and hardness (20.1 and 0.89 GPa, respectively) than the untreated bamboo samples (13.7 and 0.49 GPa, respectively). The enhanced bamboo cell wall mechanical properties of the non-notched-flattened bamboo board. Finally, we explored the practical applications, economic benefits, and limitations of the current “Non-notched bamboo flattening technology”. 

Bamboo flattening technology ebables efficient and value-added utilization of bamboo in the manufacture of furniture and engineered composites

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.

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

Bamboo scrimber is a new type of bamboo-based panel that is prone to be affected by biological and service environments under outdoor conditions. In this paper, the physical and mechanical performance and the microchemical and surface properties of untreated and hot-oil-treated bamboo scrimber were analyzed to illustrate the processing mechanism of scrimber. Methyl silicone oil treatment was carried out at 120, 140, and 160 °C for 2, 4, and 6 h. The density, mechanical properties, air-dried moisture content, surface morphology, chemical structure, swelling properties, color, and contact angle of the bamboo scrimber were analyzed to evaluate the treatment effectiveness. Observation of the environmental-scanning electron microscope indicated that the glue layer of the bamboo scrimber was not significantly damaged after hot oil treatment. At low temperatures, the mechanical properties did not change significantly. Infrared-spectrum analysis showed a significant decrease in mechanical properties at higher temperatures and longer treatment time for the degradation of hemicellulose. The contact angle test and swelling properties test showed that the hot oil treatment improved the dimensional stability and reduced the wettability on the surface of the bamboo scrimber. The above analysis results show that the treatment at 140 °C for 2 h is most effective.

https://www.mdpi.com/1420-3049/25/19/4488/pdf

Tiancheng Yuan

Papers

Fabrication of Crack-Free Flattened Bamboo and Its Macro-/MicroMorphological and Mechanical Properties

A new approach for fabricating crack-free, flattened bamboo board and the study of its macro-/micro-properties

Bamboo flattening technology ebables efficient and value-added utilization of bamboo in the manufacture of furniture and engineered composites

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

Effects of One-Step Hot Oil Treatment on the Physical, Mechanical, and Surface Properties of Bamboo Scrimber.