High-performance bamboo-/wood-based structural or building materials have attracted more and more attention as a kind of renewable carbon cycle materials. However, biomass materials are prone to mildew, poor surface hydrophobicity and bad dimensional stability when used outdoors, which seriously restricts their applications. In this work, nano-Fe3O4/bamboo bundles/phenolic resin oriented recombination ternary composite boards are successfully fabricated by directional recombination and hot-pressing of nano-Fe3O4 decorated bamboo bundles. Through the combination of iron/alkali liquid step-by-step impregnation and nanocrystalline in-situ crystallization, nano-Fe3O4 particles are pre-modified on bamboo bundle surface with characteristics of directional arrangement along the fiber direction. The obtained samples which are named as T1, T2 and T3 with increasing nano-Fe3O4 loading content, exhibit enhanced hydrophobicity along with varied physico-mechanical properties. Among them, T2 possesses the best compressive properties, dimensional stability, and mildew resistance, being attributed to the role from nano-Fe3O4 in bridging and enhancing the interactions between bamboo bundles and phenolic resin through ion-dipole interaction between iron atoms and electron-rich oxygen atoms. Furthermore, on the basis of maintaining the unique pore-line staggered structural characteristics of bamboo, the construction of micro continuous equivalent circuit network of the ternary composites is realized, endowing their efficient electromagnetic dissipation capacity. Our work provides systematic experimental and theoretical support for the application of high-performance outdoor recombinant bamboo board in specific scenes.

Nano-Fe3O4/bamboo bundles/phenolic resin oriented recombination ternary composite with enhanced multiple functions

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

The aim of this study was to investigate the effects of the heat treatment time and initial moisture content of bamboo on the corresponding chemical composition, crystallinity, and mechanical properties after saturated steam heat treatment at 180 °C. The mechanism of saturated steam heat treatment of bamboo was revealed on the micro-level, providing a theoretical basis for the regulation of bamboo properties and the optimization of heat treatment process parameters. XRD patterns of the treated bamboo slices were basically the same. With the increase in the initial moisture content of bamboo, the crystallinity of bamboo increased first and then decreased after treatment. Due to the saturated steam heat treatment, the content of cellulose and lignin in bamboo slices increased while the content of hemicellulose decreased, but the content of cellulose in bamboo with a 40% initial moisture content increased first and then decreased. The shear strength of treated bamboo changed little within 10 min after saturated steam heat treatment, and then decreased rapidly. During the first 20 min with saturated steam heat treatment, the compressive strength, flexural strength, and flexural modulus of elasticity of the treated bamboo increased, and then decreased.

Effect of Saturated Steam Heat Treatment on Physical and Chemical Properties of Bamboo

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

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

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

As an important ecological, industrial and cultural biomass resource, bamboo has become a sunrise forestry industry in China. Magnetic bamboo-based composites not only have important engineering application value, but also have great potential in new technology fields such as electronics, optics, energy and so on. In this paper, we combine the traditional bamboo recombination technology with in-situ coprecipitation to fabricate magnetic reconstituted bamboo board. By doing this, it is convenient to improve the loading capacity of magnetic nanomaterials in composites from 2D surface loading to 3D body loading. SEM, EDS mapping, VSM, FT-IR and AFM are introduced to investigate the synthesized magnetic reconstituted bamboo board along with its corresponding magnetized bamboo bundle units to verify their successful synthesis and related properties. Furthermore, compared with the common bamboo board reconstituted with heat-treated bamboo bundles, Fe3O4 loaded reconstituted bamboo board possesses excellent magnetism and mildew resistance. Especially, no infection is observed on the surface of the magnetic reconstituted bamboo board after incubation for as long as 31 days.

Fabrication of a novel magnetic reconstituted bamboo with mildew resistance properties

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

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

With the aim of utilizing reconstituted bamboo as a carbon cycle-oriented material, the improvement of physical and mechanical properties has been actively studied to solve using problems. The saturated steam heat treatment process has been widely used in worldwide. With the development and exploration of this technology, two-step saturated steam heat treatment process appears in some practical production, that is, after a period of saturated steam heat treatment at a lower temperature, the bamboo bundles are taken out and seasoned for a period of time, and then put back into the heat tank again, and heated at a higher temperature for another period of time. During the two-step saturated steam heat treatment, the physical and mechanical properties of bamboo changed. However, the mechanism of two-step saturated steam heat treatment has not been thoroughly discussed. For purpose that this paper all discuss and find out the mechanism of two-step saturated steam heat treatment on the change of physical and mechanical properties of reconstituted bamboo. In this work, the one and two-step saturated steam heat treatments were carried out according to the actual production parameters, and the physical and mechanical properties of the reconstituted bamboo board made of treated bamboo bundles were analyzed, including the color change, the thickness swelling (TS), modulus of elasticity (MOE), modulus of rupture (MOR) and shear strength. The results indicate that two-step saturated steam heat treatment is better than one-step. Based on the detailed study of the chemical composition, crystallinity and micro-morphological characteristics of the heated bamboo bundles, it is further revealed that during two-step saturated steam heat treatment, oxygen air is added to the reaction system between the two heat treatment processes to further catalyze the oxidation of hemicellulose and enhance the crystallinity of cellulose, so as to improve the properties of the final products. Our work has optimized the saturated steam heat treatment process which is widely used in industry, pointing out a new idea in the experimental and theoretical basis for the development of recombinant bamboo manufacturing industry. 

Xinwu Wu

Papers

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

Effect of Saturated Steam Heat Treatment on Physical and Chemical Properties of Bamboo

Fabrication of a novel magnetic reconstituted bamboo with mildew resistance properties

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

Study on the Effect of Two-Step Saturated Steam Heat Treatment Process on the Properties of Reconstituted Bamboo