Processing natural bamboo into white bamboo through photocatalyzed lignin oxidation.

Scalable and highly efficient bamboo whitening remains a great challenge. Herein, an effective bamboo whitening strategy is proposed based on photocatalyzed oxidation, which involves H2O2 infiltration and UV illumination. The as-prepared white bamboo well maintains the nature structure of natural bamboo and demonstrates high whiteness and superior mechanical properties. The absorbance value is significantly decreased to 3.5 and the transmittance is increased to 0.04 % in UV-visible wavelength range due to the removal of light-absorbing chromospheres of lignin, resulting in a high whiteness when the UV illumination time is 8 h. In addition, the white bamboo displays a high tensile strength of 30 MPa and a high flexural strength of 36 MPa due to the well-preserved lignin units (lignin preservation is about 89 %). XRD patterns and analysis show that photocatalyzed oxidation has no effect on the crystal parameters of cellulose. Compared with the traditional bamboo whitening technology, our photocatalyzed oxidation strategy demonstrates significant advantage including chemical and time conservation, high efficiency, environment friendliness, and mechanical robustness. This highly efficient and environmentally friendly photocatalyzed oxidation strategy for the fabrication of white bamboo may pave the way of bamboo-based energy-efficient structural materials for engineering application.

Comprehensive Investigation of the Temperature-Dependent Electromechanical Behaviors of Carbon Nanotube/Polymer Composites.

The performances of flexible piezoresistive sensors based on polymer nanocomposites are significantly affected by the environmental temperature; therefore, comprehensively investigating the temperature-dependent electromechanical response behaviors of conductive polymer nanocomposites is crucial for developing high-precision flexible piezoresistive sensors in a wide-temperature range. Herein, carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composites widely used for flexible piezoresistive sensors were prepared, and then the temperature-dependent electrical, mechanical, and electromechanical properties of the optimized CNT/PDMS composite in the temperature range from -150 to 150 °C were systematically investigated. At a low temperature of -150 °C, the CNT/PDMS composite becomes brittle with a compressive modulus of ∼1.2 MPa and loses its elasticity and reversible sensing capability. At a high temperature (above 90 °C), the CNT/PDMS composite softens, shows a fluid-like mechanical property, and loses its reversible sensing capability. In the temperature range from -60 to 90 °C, the CNT/PDMS composite exhibits good elasticity and reversible sensing behaviors and its modulus, resistivity, and sensing sensitivity decrease with an increasing temperature. At room temperature (30 °C), the CNT/PDMS composite exhibits better mechanical and piezoresistive stability than those at low and high temperatures. Given that environmental temperature changes have significant effects on the sensing performances of conductive polymer composites, the effect of ambient temperature changes must be considered when flexible piezoresistive sensors are designed and fabricated.

Impact mechanisms of aggregation state regulation strategies on the microwave absorption properties of flexible polyaniline.

In the field of electromagnetic (EM) wave absorption, intrinsic conductive polymers with conjugated long-chain structures, such as polyaniline (PANI) and polypyrrole (PPy), have gained widespread use due to their remarkable electrical conductivity and loss ability. However, current research in this area is limited to macroscopic descriptions of the absorption properties of these materials and the contribution of various components to the absorption effect. There has been insufficient exploration of the impact mechanisms of polymer aggregation states on the material's absorption performance and mechanism. To address this, a series of flexible PANI sponge absorbers with different molecular weights and aggregation states were prepared. By carefully controlling the crystallinity and other aggregation characteristics of PANI through the adjustment of its preparation conditions, we were able to influence its electrical conductivity and electromagnetic parameters, thereby achieving control over the material's absorption properties. The resulting PANI sponge absorbers exhibited an effective absorption bandwidth (EAB) that covered the entire X-band at a thickness of 3.2 mm. This study comprehensively explores the absorption mechanisms of conductive polymer absorbers, starting from the microstructure of PANI, and providing a more complete theoretical support for the research and promotion of polymer absorbers.

Superstrong, Lightweight, and Exceptional Environmentally Stable SiO2@GO/Bamboo Composites.

Development of lightweight structural materials from fast-growing bamboos is of great significance to building a sustainable society. However, previously developed structural bamboos by delignification combined with densification would easily fail under large external loading after exposure to water due to structure collapse, severely limiting their practical applications. Here, we demonstrate an ultrastrong and exceptional environmentally stable bamboo composite consisting of a graphene oxide (GO)/bamboo core and hierarchical SiO2 protection layer. The GO/bamboo composite exhibits ultrahigh tensile strength (641.6 MPa), superb flexural strength (428.4 MPa), and excellent toughness (17.5 MJ/m3), which are increased by about 480, 250, and 360% compared with natural bamboo, respectively. As a result, the specific tensile strength of the GO/bamboo composite is up to 513.3 MPa·cm3/g due to its low density (1.25 g/cm3), outperforming engineering structural materials such as aluminum alloys, steels, and titanium alloys. These large improvements benefit from the well-preserved bamboo scaffold and the strong hydrogen bonds between bamboo fibers and GO nanosheets. On the other hand, the SiO2@GO/bamboo composite shows superhydrophobicity due to the construction of hierarchical SiO2 layers, which endows it with outstanding water resistance. Moreover, the bamboo composite shows an ultralow coefficient of thermal expansion (≈2.3 × 10-6 K-1), indicating its excellent dimensional stability. Considering the ultrahigh mechanical performance and outstanding environmental stability, the developed lightweight SiO2@GO/bamboo composite is hopeful to be a green and sustainable structural material for practical engineering applications.

High-Performance Bamboo Steel Derived from Natural Bamboo.

It is highly desirable to develop green and renewable structural materials from biomaterials to replace synthetic materials involved from civil engineering to aerospace industries. Herein, we put forward a facile but effective top-down strategy to convert natural bamboo into bamboo steel. The fabrication process of bamboo steel involves the removal of lignin and hemicellulose, freeze-drying followed by epoxy infiltration, and densification combined with in situ solidification. The prepared bamboo steel is a super-strong composite material with a high specific tensile strength (302 MPa g-1 cm3), which is higher than that (227 MPa g-1 cm3) of conventional high specific strength steel. The bamboo steel demonstrates a high tensile strength of 407.6 MPa, a record flexural strength of 513.8 MPa, and a high toughness of 14.08 MJ/m3, which is improved by 360, 290, and 380% over those of natural bamboo, respectively. Particularly, the mechanical properties of the bamboo steel are the highest among the biofiber-reinforced polymer composites reported previously. The well-preserved bamboo scaffolds assure the integrity of bamboo fibers, while the densification under high pressure results in a high-fiber volume fraction with an improved hydrogen bonding among the adjacent bamboo fibers, and the epoxy resin impregnated enhances the stress transfer because of its chemical crosslinking with cellulose molecules. These endow the bamboo steel with superior mechanical performance. Furthermore, the bamboo steel demonstrates an excellent thermal insulating capability with a low thermal conductivity (about 0.29 W/mK). In addition, the bamboo steel shows a low coefficient of thermal expansion (about 6.3 × 10-6 K-1) and a very high-dimensional stability to moisture attack. The strategy of fabricating high-performance bamboo steel with green and abundant natural bamboo as raw materials is highly attractive for the sustainable development of structural engineering materials.

High-Performance Fiber-Film Hybrid-Structured Wearable Strain Sensor from a Highly Robust and Conductive Carbonized Bamboo Aerogel.

Bamboo, one of the most abundant biomaterials, has been used as a building material since ancient times; however, its application in functional materials has been rarely explored. Herein, a highly robust and conductive carbonized bamboo aerogel (CBA) is obtained from the natural bamboo through a simple three-step process of pulp oxidization, freeze-drying, and carbonization. The CBA obtained shows not only a low density of 0.02 g/cm3 but also a high conductivity of 6.42 S/m and remarkable elasticity with a maximum recoverable compressive strain of 60% due to its unique three-dimensional (3D) network randomly stacked with the hybrid structure of carbonized bamboo fibers and films. After encapsulation with silicone resin, the CBA/silicone composite prepared exhibits excellent flexibility and stretchability with a low Young's modulus (0.09 MPa) and a large failure strain (275%). Importantly, the CBA/silicone composite also offers remarkable strain-sensing performance with a maximum gauge factor of 30.6, a short responsive time of 50 ms, and a stable response to cyclic loading over 1000 cycles, which is comparable to those of the piezoresistive composites based on expensive nanomaterials. Moreover, the CBA/silicone composite demonstrates the capability as a wearable strain sensor for human motion recognition comprising finger bending, breathing, and throat movement. Considering the green and sustainable nature of bamboo as a raw material, combined with the excellent piezoresistive performance, low production cost, and simple preparation process, the flexible strain sensors with CBA/silicone composite as a sensing element are promising in wearable electronic devices, personalized healthcare, and artificial intelligence systems.

Unveiling the Mechanisms for the Plant Volatile Organic Compound Linalool To Control Gray Mold on Strawberry Fruits.

Fungal infections significantly alter the emissions of volatile organic compounds (VOCs) by plants, but the mechanisms for VOCs affecting fungal infections of plants remain largely unknown. Here, we found that infection by Botrytis cinerea upregulated linalool production by strawberries and fumigation with linalool was able to inhibit the infection of fruits by the fungus. Linalool treatment downregulated the expression of rate-limiting enzymes in the ergosterol biosynthesis pathway, and this reduced the ergosterol content in the fungi cell membrane and impaired membrane integrity. Linalool treatment also caused damage to mitochondrial membranes by collapsing mitochondrial membrane potential and also downregulated genes involved in adenosine triphosphate (ATP) production, resulting in a significant decrease in the ATP content. Linalool treatment increased the levels of reactive oxygen species (ROS), in response to which the treated fungal cells produced more of the ROS scavenger pyruvate. RNA-Seq and proteomic analysis data showed that linalool treatment slowed the rates of transcription and translation.

Systematically quantitative proteomics and metabolite profiles offer insight into fruit ripening behavior in Fragaria × ananassa.

Profound metabolic and proteomic changes involved in the primary and the secondary metabolism are required for the ripeness of fleshy fruit such as strawberries (Fragaria × ananassa). Here we present the quantitative proteomic profiling in parallel with metabolic and transcriptional profiling at five developmental stages of strawberry fruit ripening, and correlations between changes in representative metabolites and the abundance of related proteins were analyzed. Hierarchical clustering analysis of the quantitative proteomic profiling identified 143 proteins in strawberry fruit across five developmental stages. Meanwhile, both protein abundance and gene expression spanned a wide range of roles, such as the primary and the secondary metabolism, defense system, and response to stress stimuli. The decreased abundance of proteins contributed to the carbohydrate metabolism and the up-regulated expression of secondary biosynthetic proteins was found to be positively correlated with the accumulation of primary and secondary metabolites during strawberry development. Moreover, with the same annotations and high homology, the gene function of key genes involved in primary and secondary metabolism (FaTPI, FaPAL, FaMDH and FaME) was confirmed in Nicotiana via the transient expression assay, which provides further evidence for the role of those genes in metabolism of strawberry fruit. The results of the present study may serve as an important resource for the functional analysis of the proteome and offer new perspectives on regulation of fruit quality.

Role of Wood Fibers in Tuning Dynamic Rheology, Non-Isothermal Crystallization, and Microcellular Structure of Polypropylene Foams.

Microcellular polypropylene (PP)/wood fiber composite foams were fabricated via batch foaming assisted by supercritical CO2 (scCO2). Effects of wood fibers on rheology, crystallization, and foaming behaviors of PP were comprehensively investigated. The obtained results showed that the incorporation of wood fibers increased the complex viscosity and the storage modulus of the PP matrix. Jeziorny's model for non-isothermal crystallization kinetics indicated that wood fibers did not change the crystal growth. However, the crystallization rate of the PP matrix was decreased to a certain extent with increasing wood fiber loadings. The wood fiber exerts a noticeable role in improving the cell density and reducing the cell size, despite decreasing the expansion ratio. Interestingly, a "small-sized cells to large-sized cells" gradient cell structure was found around the wood fibers, implying cell nucleation was induced at the interface between wood fiber and PP matrix. When wood fiber loadings were specifically increased, a desirable microcellular structure was obtained. However, further increasing the wood fiber loadings deteriorated the cell structure. Moreover, the crystallinity of the composite foams initially decreased and then slightly increased with increasing wood fiber loadings, while the crystal size decreased.

Preparation of Desirable Porous Cell Structure Polylactide/Wood Flour Composite Foams Assisted by Chain Extender.

Polylactide (PLA)/wood flour composite foam were prepared through a batch foaming process. The effect of the chain extender on the crystallization behavior and dynamic rheological properties of the PLA/wood flour composites were investigated as well as the crystal structure and cell morphology of the composite foams. The incorporation of the chain extender enhanced the complex viscosity and storage modulus of PLA/wood flour composites, indicating the improved melt elasticity. The chain extender also led to a decreased crystallization rate and final crystallinity of PLA/wood flour composites. With an increasing chain extender content, a finer and more uniform cell structure was formed, and the expansion ratio of PLA/wood flour composite foams was much higher than without the chain extender. Compared to the unfoamed composites, the crystallinity of the foamed PLA/wood flour composites was improved and the crystal was loosely packed. However, the new crystalline form was not evident.

Styrene-Assisted Maleic Anhydride Grafted Poly(lactic acid) as an Effective Compatibilizer for Wood Flour/Poly(lactic acid) Bio-Composites.

This study aimed to evaluate the effect of styrene-assisted maleic anhydride-grafted poly(lactic acid) (PLA-g-St/MAH) on the interfacial properties of wood flour/poly(lactic acid) (PLA) bio-composites. PLA-g-St/MAH was synthesized by free-radical melt grafting using styrene as a comonomer and dicumyl peroxide as an initiator. The structure of PLA-g-St/MAH was characterized by Fourier transform infrared spectroscopy. Wood flour/PLA composites were prepared by compression molding using PLA-g-St/MAH as a compatibilizer. The effects of PLA-g-St/MAH on the rheological and mechanical properties, as well as on the fractured surface morphology of the composites were investigated. Results indicated that storage modulus, complex viscosity, equilibrium torque, and shear heat were significantly increased. The mechanical properties of the wood flour/PLA composites were also significantly increased after the addition of PLA-g-St/MAH. The maximum values were achieved at the loading rate of 3 wt % because of the improved interfacial adhesion between the wood flour and the PLA matrix.