Dimensional Stability and Mechanical Properties of Plantation Poplar Wood Esterified Using Acetic Anhydride

Plantation poplar (Populus ussuriensis) wood was esterified using acetic anhydride without catalysts to improve its dimensional stability. The effects of acetylation temperature (100 °C, 120 °C, and 140 °C) on the dimensional stability, mechanical properties, microstructure, and functional groups of the resulting acetylated wood were systematically investigated. Results showed that the wood acetylated at 100 °C and 120 °C had an improved dimensional stability and comparable mechanical properties to those of the control wood. Wood acetylated at 140 °C had an improved dimensional stability and decreased mechanical properties as compared to those of the control wood. Scanning electron microscopic (SEM) analysis showed that the wood acetylated at 140 °C had obviously different microstructures than the control wood and the wood acetylated at 100 °C and 120 °C. The changes of functional groups in the acetylated wood were revealed by Fourier transform infrared spectroscopy (FTIR). The –OH groups of cellulose, hemicellulose, and lignin all were shown to participate in the acetylation reaction

Effect of Vacuum Heat Treatment on Larch Earlywood and Latewood Cell Wall Properties

The aim of this study was to evaluate the hygroscopicity and nanomechanics of earlywood (EW) and latewood (LW) larch after thermal modification under vacuum conditions. Wood samples were heat-treated in a vacuum atmosphere at 180–220 °C for 6 h, then their cell wall properties were observed using dynamic water vapor sorption (DVS), imaging Fourier-transform infrared (FTIR) microscopy, and nanoindentation. The results showed that the vacuum heat treatment reduced the hygroscopicity of EW and LW and increased hysteresis between the adsorption and desorption branches of the isotherm. Compared with EW, the treatment temperature had a more pronounced influence on the hygroscopicity of LW. The Hailwood-Horrobin model was found to accurately fit the experimental data. Imaging FTIR microscopy revealed degradation of hemicellulose, cross-linking, condensation reactions, and redistribution of lignin in the cell wall. The elastic modulus for the heat-treated EW and LW cell walls increased at first and then decreased as the treatment temperature increased; the increase in LW was more intense than that in EW. Cell wall hardness also markedly increased after heat treatment. Our analysis suggests that vacuum heat treatment decreases hygroscopicity and alters the chemical composition distribution of cell walls, thus improving wood cell wall mechanics

Synthesis and Characterization of Biobased Melamine Formaldehyde Resins from Bark Extractives

In this study, bark alkaline extractives from the mountain pine beetle (<i>Dendroctonus ponderosae</i> Hopkins) infested lodgepole pine (<i>Pinus contorta</i> Dougl.) was used to partially replace 30 wt % of melamine in formulating the biobased bark extractive–melamine formaldehyde (MF) resin. Results showed that the addition of the bark extractives and the type of solvent system used for resin formulation significantly affected the initial molecular weight, molecular structure, viscosity, curing behavior, postcuring thermal stability, and bonding performance of the resulting resins. The bark extractive–MF resins exhibited similar dry and wet bonding strengths to the laboratory made control MF resins formulated in the same type of solvent system. The liquid-state ¹³C NMR study showed that bark extractives were reactants and incorporated into the resulting biobased MF resin structures. Bark extractives obtained from the mountain pine beetle infested lodgepole pine showed promise as a suitable partial replacement for melamine in MF resin formulations

Effect of Vacuum Heat Treatment on the Chemical Composition of Larch Wood

The effects of vacuum heat treatment were studied relative to the chemical composition of larch wood. The samples were heat-treated in vacuum at 160 °C, 200 °C, and 240 °C for 4 h, and the chemical changes were investigated by wet chemical analysis, elemental analysis, calorific value determination, and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). The relative percentage contents of lignin and extractives increased after heat treatment. Additionally, the relative percentage contents of holocellulose, cellulose, and hemicelluloses decreased as a result of the thermo-vacuum treatment. Elemental analysis showed a slight reduction in the contents of hydrogen and oxygen. Vacuum heat treatment also increased the calorific value compared with untreated samples

Characterization of Modified Phenol Formaldehyde Resole Resins Synthesized in Situ with Various Boron Compounds

In this study, three different boron compounds were used together with alkaline catalyst to synthesize phenol formaldehyde (PF) resole resins in situ. The resin curing behavior, molecular structure, bonding performance, and properties of resin-impregnated wood were investigated. Results showed that boron compound-modified PF resins had a lower degree of polymerization than the control PF resin made in the laboratory. The curing kinetics, molecular structure, and functional groups of the modified resins varied depending on the type of boron compounds used. The thermal stability of cured modified PF resins was slightly lower than that of laboratory-made control PF resin. Boron compound-modified PF resins exhibited dry and wet bonding strengths comparable to the those of the laboratory-made control PF resin. Wood impregnated using modified PF resins had comparable dimensional stability, mechanical properties and improved fire resistance than the wood impregnated using lab made control PF resin regardless the type of boron compounds used

Low carbon research of science and technology park in southern cities

Climate change is a major global issue of general concern to the international community. As a developing country focusing on environmental protection, China has adopted a series of relevant policies and measures to address global warming, namely, achieving carbon peak by 2030 and carbon neutrality by 2060. It can be said that carbon peaking is China's national policy to actively respond to climate change, and is also an independent commitment based on scientific demonstration; Carbon neutrality is an action goal based on China's national conditions and is also a long-term development strategy with a long-term vision. In order to realize the important long-term strategy of “carbon neutrality” at an early date, low-carbon buildings will gradually come into people's lives. This paper first analyzes the crisis and challenges we are facing under the background of the current era, and expounds how to solve the energy crisis. In this paper, we propose that green and low-carbon buildings will make a significant contribution to solving the problem of carbon pollution. Then, we studied the low carbon scheme of science and technology parks in southern cities through literature review, and case study. Next, taking the project of Block H01-01, Unit PDC1-0401, Lingang New Area of Shanghai Free Trade Zone as an example, we 、analyzed the technical characteristics of the project's climate responsive design and the integrated design of renewable energy buildings, and elaborated its project functions. While satisfying people's demands for scientific research and comfortable living, it also responded to the call of the national “double carbon” goal and completed the task of “strengthening building energy conservation and continuously improving building energy efficiency” in the key work of energy conservation, emission reduction and carbon reduction in Shanghai. Finally, it is concluded that green and low-carbon buildings can make outstanding contributions to the realization of “double carbon” goals in the future, and at the same time provide a more powerful guarantee for human living environment and quality of life

Towards a bright future: The versatile applications of organic solar cells

Due to the mechanical flexibility, light weight, aesthetics, absorption tunability and environmental friendliness, organic solar cells (OSCs) have superior application potential over their inorganic counterparts including silicon and perovskite solar cells (PSCs). Thanks to these benefits, the past decade have witnessed the rapid growth of flexible OSCs, semitransparent OSCs and indoor OSCs. In this progress report, we firstly overview the recent advance of the applications of the three promising OSCs. Subsequently, we sketch the critical points for the three classes of OSCs and highlight the efforts paid by the research community to address these issues. Besides, we discuss some popular strategies to afford great performance of each kind of OSC, respectively, and underline the corresponding breakthrough directions. Last but not least, we present the remaining challenges for advancing the commercial applications of these three classes of OSCs