Mechanically strong, hydrostable, and biodegradable all-biobased transparent wood films with UV-blocking performance

Advanced wood-inorganic composites: preparation, properties and perspectives

In recent years, the widespread use of wood products has been observed in many fields. Wooden products have excellent green and environmentally friendly characteristics, but their performance often cannot meet people's needs. Many researchers have conducted in-depth research on wood-based composite materials and their modification methods in order to improve the performance of wood. This article provides a selective review of the types, modification methods, and properties of inorganic modifiers. The preparation methods are mainly divided into immersion methods, sol-gel methods, and hydrothermal synthesis. The flame retardancy, mechanical properties, hydrophobicity, and mold resistance of modified wood have been effectively improved. In addition, modified wood also has photoresponsive properties, electrical conductivity, and thermal conductivity. Finally, the challenges and perspectives on advanced wood-inorganic composites have been proposed for guiding future studies.

Ultraviolet-Shielded Transparent Wood with Improved Interface for Insulating Windows

Recently, transparent wood (TW) has been considered for many energy-efficient building products, such as windows and decorations. However, the existing TW still faces issues with size and thickness, as well as problems with functional fillers affecting the optical and mechanical properties of TW, which limits its wide application in the window products. In this study, a wood composite material (WCM) with good optical, mechanical, and thermal insulation and UV-shielding properties was prepared by using delignified wood (DW), methyl methacrylate (MMA), and 4-vinylphenylboric acid (VPBA). Compared with NaClO2 delignification, peracetic acid (PAA) preserves hemicellulose and a more stable pore structure, which facilitates the filling of polymers into the DW template, resulting in the preparation of more extensive and thicker TW. VPBA, as a functional raw material for UV shielding, on the one hand, improves the interfacial compatibility of the TW, thus improving the optical properties (transmittance of about 90%, haze of about 55%) and mechanical properties (64.5 MPa). On the other hand, WCM was found to effectively block UV-C, UV-B (about 100%), and UV-A (about 90%) radiation while maintaining sufficient visible light transmittance. In addition, as an insulating window, WCM has low thermal conductivity and can maintain a high temperature for a long time after the loss of solar radiation, which is an ideal thermal insulation material and is expected to become a potential substitute for conventional glass.

A composite film of oxidized levan crosslinked with gelatin: strong hydrophobic and mechanical properties and effective preservation of fresh Mozzarella cheese

The fructosan levan was synthesized in vitro using a recombinant levansucrase. The levan was oxidized with sodium periodate to prepare oxidized levan (OLevan) with three oxidation degrees. OLevan, gelatin (Gel), and gallic acid (GA) were used to prepare the composite films by the method of plate pouring. The analytical results of FT-IR and XPS indicated that OLevan and gelatin were covalently crosslinked through a Schiff base reaction. The crosslinked films had better properties compared to the non-crosslinked films, especially the Gel/GA/50%OLevan film. The film had the lowest swelling degree (44.4 %), while that of Gel/GA/Levan film was 352.6 %. Gel/GA/50%OLevan film also had the highest tensile strength (25.48 MPa), while that of Gel/GA film was 9.48 MPa. Also, Gel/GA/50%OLevan film was used as a packaging material of Mozzarella cheese. The film effectively slowed down changes in the texture and color of the cheese. On the first day, the coliform in the control and PE groups had already exceeded the maximum acceptable limit of cheese (2.0 Log CFU/g). However, that of Gel/GA/50%OLevan group reached the limit on the fifth day. The results show that the new film prepared by crosslinking and composite of natural edible materials has good potential as a safe food packaging material.

A Highly CO2-Sensitive Wood-Based Smart Tag for Strawberry Freshness Monitoring

Smart tags are used for monitoring the freshness of foods. However, they often lack significant color changes, and their accuracy needs to be improved. In this study, a poplar veneer with a natural pore structure was selected as a matrix to prepare a smart tag with high pH sensitivity for tracking the freshness of strawberries. The delignified veneer was modified using 2,3-epoxypropyltrimethylammonium chloride (EPTAC) to be given positive charges to adsorb bromothymol blue (BTB) through electrostatic interactions. The adsorption capacity of the veneer reached 7.0 mg/g at 50 °C for 4 h, and the veneer showed an obvious blue color. The smart tags exhibited distinct color changes at different pHs and showed quick color changes in response to acetic acid. As the freshness of strawberries decreased, the color of the smart tags changed from blue to yellow-green, which indicated that the accuracy was high. In this study, an effective method was fabricated to prepare a highly sensitive tag, promoting popular application to ensure food quality.

Effect of Wood Species on Lignin-Retaining High-Transmittance Transparent Wood Biocomposites

This study explores lignin-retaining transparent wood biocomposite production through a lignin-modification process coupled with epoxy resin. The wood's biopolymer structure, which includes cellulose, hemicellulose, and lignin, is reinforced with the resin through impregnation. This impregnation process involves filling the voids and pores within the wood structure with resin. Once the resin cures, it forms a strong bond with the wood fibers, effectively reinforcing the biopolymer matrix and enhancing the mechanical properties of the resulting biocomposite material. This synergy between the natural biopolymer structure of wood and the synthetic resin impregnation is crucial for achieving the desired optical transparency and mechanical performance in transparent wood. Investigating three distinct wood species allows a comprehensive understanding of the relationship between natural and transparent wood biocomposite properties. The findings unveil promising results, such as remarkable light transmittance (up to 95%) for Aspen transparent wood. Moreover, transparent wood sourced from White Spruce demonstrates excellent stiffness (E = 2450 MPa), surpassing the resin's Young's modulus. Also, the resin impregnation enhanced the thermal stability of natural wood. Conversely, transparent wood originating from Larch showcases superior impact resistance. These results reveal a clear correlation between wood characteristics such as density, anatomy, and mechanical properties, and the resulting properties of the transparent wood.

A facile method to fabricate sustainable bamboo ethanol lignin/carboxymethylcellulose films with efficient anti-ultraviolet and insulation properties

Given the environmental concerns related to the non-degradability of conventional petroleum-based polymer films, the synthesis of biodegradable films utilizing natural polymers derived from biomass has emerged as a promising alternative, garnering significant attention in recent research endeavors. This research introduced an environmentally friendly and efficient method, utilizing extract liquid from the green ethanol pulping process as the solvent to completely dissolve carboxymethylcellulose into the film-forming liquid, and employing the solution pouring technique to successfully fabricate bamboo ethanol lignin/carboxymethylcellulose films (LCF). The findings revealed that the lignin content significantly influenced the LCF, endowing them with tunable mechanical properties, effective UV-blocking, and thermal insulation capabilities. With a lignin addition of 3.75 %, LCF-3.75 exhibited enhanced mechanical properties, characterized by a tensile strength of 19.4 MPa, along with superior UV-blocking efficiency, blocking 100 % of UVB and 99.81 % of UVA rays. Furthermore, relative to LCF-0, LCF-3.75 had been shown to possess enhanced hydrophobicity and thermal stability, culminating in the development of the composite films that showcased exceptional thermal insulation properties and biodegradability. The films not only harbored extensive application prospects as an anti-ultraviolet and heat-insulating glass films but also represented a potential avenue for the efficient utilization of lignin, thereby contributing to sustainable development.

Preparation of multifunctional and mechanically-reliable smart wood infiltrated with cellulose nanocrystal-reinforced polyvinyl alcohol nanocomposite

Multifunctional transparent woods have recently attracted a great interest as efficient products for many applications, such as smart window and smart packaging. Herein, a transparent wood with several desirable properties, including flame-retardant activity, ultraviolet shielding, superhydrophobicity, good roughness, durability and photostability was developed. The current photoluminescent wood showed a remarkable capacity to keep releasing light in the dark for extended durations. Multifunctional transparent wood was prepared by infiltrating a delignified wooden bulk with a combination of polyvinyl alcohol (PVA), ammonium polyphosphate (APP), cellulose nanocrystals, and rare-earth strontium aluminate nanoparticles (RSAN). Cellulose nanocrystals were prepared from microcrystalline cellulose, and used as reinforcement nanofiller to enhance the mechanical strength of the polyvinyl alcohol matrix and a dispersant agent to avoid agglomeration of RSAN. RSAN displayed diameters of 8-16 nm, while cellulose nanocrystals displayed lengths of 75-150 nm and diameters of 5-10 nm. According to photoluminescence spectra and the colorimetric space coordinates reported by the CIE Lab parameters, the transparent wood changed color to bright green when exposed to UV irradiation. For the produced phosphorescent wood surfaces, an absorption band was detected at 365 nm to generate an emission band at 519 nm.

Transparent and Efficient Wood-Based Triboelectric Nanogenerators for Energy Harvesting and Self-Powered Sensing

Wood possesses several advantageous qualities including innocuity, low cost, aesthetic appeal, and excellent biocompatibility, and its naturally abundant functional groups and diverse structural forms facilitate functionalization modification. As the most sustainable bio-based material, the combination of wood with triboelectric nanogenerators (TENGs) stands poised to significantly advance the cause of green sustainable production while mitigating the escalating challenges of energy consumption. However, the inherent weak polarizability of natural wood limits its development for TENGs. Herein, we present the pioneering development of a flexible transparent wood-based triboelectric nanogenerator (TW-TENG) combining excellent triboelectrical properties, optical properties, and wood aesthetics through sodium chlorite delignification and epoxy resin impregnation. Thanks to the strong electron-donating groups in the epoxy resin, the TW-TENG obtained an open-circuit voltage of up to ~127 V, marking a remarkable 530% enhancement compared to the original wood. Furthermore, durability and stability were substantiated through 10,000 working cycles. In addition, the introduction of epoxy resin and lignin removal endowed the TW-TENG with excellent optical characteristics, with optical transmittance of up to 88.8%, while preserving the unique texture and aesthetics of the wood completely. Finally, we show the application prospects of TW-TENGs in the fields of self-power supply, motion sensing, and smart home through the demonstration of a TW-TENG in the charging and discharging of capacitors and the output of electrical signals in different scenarios.

Construction and mechanism analysis of flame-retardant, energy-storage and transparent bio-based composites based on natural cellulose template

With the proposal of sustainable development strategy, bio-based energy storage transparent wood (TW) has shown broad application value in green buildings, cold chain transportation, and optoelectronic device fields. However, its application in most fields is limited due to its own flammability. In this study, epoxy resin, triethyl phosphate (TEP) and polyethylene glycol (PEG) were introduced into delignified balsa wood template by vacuum pressure impregnation, and bio-based TW/PEG/TEP integrating flame retardant, high strength and phase-change energy-storage performance was prepared. TW/PEG composites have no leakage during phase change process and their transparency is up to 95 %. Compared with TW/PEG, the shielding effect of char layer and the inhibition effect in condensed and gas phase significantly decrease the total heat release of TW/PEG/TEP. TW/PEG/TEP biocomposites still maintained a high enthalpy of phase change and a low peak melting temperature, which was conducive to its application around the area of low temperature phase change energy storage. In addition, the tensile strength of TW/PEG/TEP was nearly 4 times higher than that of DW, and its toughness was obviously enhanced. TW/PEG/TEP biocomposites conformed to the current concept of energy-saving and green development. It has the potential to replace traditional petrochemical-based materials and shows excellent application prospects in emerging fields.