A cellulose nanocrystal-based dual response of photonic colors and fluorescence for sensitive benzene gas detection.

Benzene, as a common volatile organic compound, represents serious risk to human health and environment even at low level concentration. There is an urgent concern on visualized, sensitive and real time detection of benzene gases. Herein, by doping Fe3+ and graphene quantum dots (GQDs), a cellulose nanocrystal (CNC) chiral nematic film was designed with dual response of photonic colors and fluorescence to benzene gas. The chiral nematic CNC/Fe/GQDs film could respond to benzene gas changes by reversible motion. Moreover, chiral nematic film also displays reversible responsive to humidity changes. The resulting CNC/Fe/GQDs chiral nematic film showed excellent response performance at benzene gas concentrations of 0-250 mg/m3. The maximal reflection wavelength film red shifted from 576 to 625 nm. Furthermore, structural color of CNC/Fe/GQDs chiral nematic film change at 44 %, 54 %, 76 %, 87 %, and 99 % relative humidity. Interestingly, due to the stability of GQDs to water molecules, CNC/Fe/GQDs chiral nematic film exhibit fluorescence response to benzene gas even in high humidity (RH = 99 %) environment. Besides, we further developed a smartphone-based response network system for quantitively determinization and signal transformation. This work provides a promising routine to realize a new benzene gas response regime and promotes the development of real-time benzene gas detection.

Eliminating trade-offs between optical scattering and mechanical durability in aerogels as outdoor passive cooling metamaterials.

Passive cooling is a promising approach for reducing the large energy consumption to achieve carbon neutrality. Foams/aerogels can be considered effective daytime cooling materials due to their good solar scattering and thermal insulation capacity. However, the contradiction between the desired high solar reflectivity and mechanical performance still limits their scalable production and real application. Herein, inspired by the "Floor-Pillar" concept in the building industry, a multi-structure assembly-induced ice templating technology was used to construct all-cellulosic aerogels with well-defined biomimetic structures. By using cellulose nanofibers (CNFs) as pillars and cellulose nanocrystals (CNCs) as floors and methyltrimethoxysilane (MTMS) as a crosslinking material, an all-cellulosic aerogel (NCA) exhibiting high mechanical strength (mechanical strength = 0.3 MPa at 80% compression ratio, Young's modulus = 1 MPa), ultralow thermal conductivity (28 mW m-1 K-1), ultrahigh solar reflectance (97.5%), high infrared emissivity (0.93), as well as excellent anti-weather function can be achieved, exceeding the performance of most reported cellulosic aerogels. Furthermore, the mechanisms of the improved mechanical strength and stimulated superior solar reflectance of NCA were studied in detail using finite element simulations and COMSOL Multiphysics. As a result, the NCA can achieve a cooling efficiency of 7.5 °C during the daytime. The building energy stimulus demonstrated that 44% of cooling energy can be saved in China annually if the NCA is applied. This work lays the foundation for the preparation of biomass aerogels for energy-saving applications.

Eco-friendly wood-plastic composites from laminate sanding dust and waste poly(propylene) food pails.

Plastic pollution caused by non-degradable petrochemical-based plastics has become a serious environmental problem in China, and the reasonable management of industrial waste and renewable resources remains a huge challenge. Here, we report environment-friendly wood-plastic composites (WPCs), prepared from decorative high-pressure laminate (HPL) sanding dust (filler) and waste thermoplastic food pails (matrix), as well as comprehensively evaluate the processability, mechanical and interfacial properties, indoor safety evaluation. The elemental composition and thermal stability of these two residue materials were suitable for the WPC manufacturing process. The content of HPL sanding dust in WPC was fixed at 60 wt%, and the amount of maleic anhydride grafted polypropylene (MAPP) added was 5 wt%-7 wt%, which maximized the utilization of waste resources, and can obtain impact strength as high as 5-6 kJ/m2, tensile strength of 35-42 MPa and flexural strength as high as 43-46 MPa. The developed WPCs had low formaldehyde emissions (≤1.53 mg/m3) and slightly improved flame retardancy. Finally, their lower cost (5,035 yuan/ton) and higher eco-efficiency (12.81 yuan/kg CO2) characteristics allowed them to be compatible with the current sustainable development requirements. This study provides a novel approach for the utilization of industrial waste and recyclable resources for sustainable replacement of wood-based products.

Dynamically Tunable All-Weather Daytime Cellulose Aerogel Radiative Supercooler for Energy-Saving Building.

A passive cooling strategy without any electricity input has shown a significant impact on overall energy consumption globally. However, designing tunable daytime radiative cooler to meet requirement of different weather conditions is still a big challenge, especially in hot, humid regions. Here, a novel type of tunable, thermally insulating and compressible cellulose nanocrystal (CNC) aerogel coolers is prepared via chemical cross-linking and unidirectional freeze casting process. Such aerogel coolers can achieve a subambient temperature drop of 9.2 °C under direct sunlight and promisingly reached the reduction of ∼7.4 °C even in hot, moist, and fickle extreme surroundings. The tunable cooling performance can be realized via controlling the compression ratio of shape-malleable aerogel coolers. Furthermore, energy consumption modeling of using such aerogel coolers in buildings in China shows 35.4% reduction of cooling energy. This work can pave the way toward designing high-performance, thermal-regulating materials for energy consumption savings.

A Branched Polyelectrolyte Complex Enables Efficient Flame Retardant and Excellent Robustness for Wood/Polymer Composites.

Wood/thermoplastic composites (WPCs) have been restricted in some fields of building construction and electrical equipment because of their inherent high flammability and lower toughness. In this work, a branched crosslinking network polyelectrolyte complex (PEC) has been designed by incorporation of polyethyleneimine (PEI), a cation polyelectrolyte end capped amine groups, into cellulose nanocrystals (CNC), and ammonium polyphosphate (APP) via self-assembling. The hydrogen bonding interactions, penetration, and mechanical interlock provided by PEC effectively enhance the interfacial bonding within matrix, wood fibers, and flame retardant. Interestingly, it generates abundant micropores on the inner structure of WPC. The excellent interfacial bonding performance and easy-to-move molecular chain successfully transfer the stress and induce energy dissipation, simultaneously giving rise to higher strength and toughness for WPC. As well as the PEC endows WPC with a promotion in both smoke suppression and UL-94 V-0 rate. Additionally, the peak heat release rate and total smoke release for WPC obviously reduce by 36.9% and 50.0% respectively in presence of 25% PEC. A simple, eco-friendly, and concise strategy exhibits prospects for fiber-reinforced polymer composites with effective flame retardancy and mechanical robust properties.

Mechanically adaptive nanocomposites with cellulose nanocrystals: Strain-field mapping with digital image correlation.

Strain-transfer plays a key role in overall modulus of mechanically adaptive nanomaterials. Herein, mechanically adaptive nanocomposites were prepared via introducing cellulose nanocrystal (CNC) percolating network into poly butyl methacrylate (PBMA) with polyethylene glycol (PEG) as a stabilizer. The prepared PBMA/CNC nanocomposites were soaked in deionized water at 23 °C and 37 °C for one week to investigate their mechanically adaption. The interactions between PEG, CNC, and PBMA were assessed by Fourier Transform infrared, X-ray diffraction, and X-ray photoelectron spectroscopy. Incorporation of PEG to CNC and PBMA/CNC nanocomposites on the morphological and thermal properties was also investigated. The mechanical adaption of PBMA/CNC nanocomposites after switching dry-to-wet state and surrounding temperature (soaked in deionized water at 23 °C and 37 °C for one week, respectively) was evaluated by mechanical testing. Meantime, digital image correlation (DIC) was firstly used to study strain transfer mechanism in mechanical adaption which was carried out in real-time synchronized with mechanical measurement. It indicated that PEG improved the dispersion of CNC in PBMA/CNC nanocomposite and its thermal properties. Furthermore, CNC with PEG modification bridged PBMA during crack propagation and promoted the stress and stain transfer in PBMA/CNC nanocomposites according to DIC analysis.

Physicochemical transformation of rice straw after pretreatment with a deep eutectic solvent of choline chloride/urea.

This study focused on the pretreatment with deep eutectic solvent of choline chloride (ChCl)/urea mixtures on rice straw and its chemical fractions of holocellulose, α-cellulose, and acid-insoluble-lignin (AIL). The pretreatment of ChCl/urea was significantly affected by the treated temperature prior to the treated time, and 130°C and 4h was an optimum condition for ChCl/urea pretreatment. The separation capacity of ChCl/urea on the chemical fractions was in an order of AIL (22.87%)> hemicellulose and amorphous cellulose (16.71%)>α-cellulose (9.60%). ChCl/urea had a higher selective solubility on lignin. The solubility of the whole fractionation of rice straw affected by ChCl/urea was a combination of solubilization on cellulose, hemicellulose and lignin. ChCl/urea pretreatment increased crystallinity index (CrI) of rice straw residue and α-cellulose, while had no obvious influence on CrI of holocellulose. The effect of structural properties of rice straw residue on enzymatic hydrolysis was also explored.