Effects of different heat treatment media on odorous constituents, chemical decomposition and mechanical properties of two hardwoods.

With China's increasing dependence on foreign wood, African wood has gradually become a potential imported species, but its use is seriously affected by problems such as unpleasant odors. In this study, we investigate the effect of heat treatment medium on odor-causing VOCs, decomposition of structural polymers, Modulus of Rupture (MOR) and Modulus of Elasticity (MOE) of hardwood. Samples of "Afrormosia" and "Newtonia" wood were heated under air and palm oil for two hours at 160 °C, 180 °C, and 200 °C, respectively. Then, the nature of the odor of each VOC emitted by the wood before and after heat treatment was identified using the GCMS method. The decomposition of hemicelluloses, cellulose and lignin in wood samples was examined using a ThermoGravimetric Analyzer coupled to Fourier Transform InfraRed spectrometry (TGA-FTIR). The 3-point bending test was used to evaluate MOR and MOE. The results indicate that the main VOCs responsible for unpleasant smells are acetic acid and hexanal; the reduction in hexanal emissions after heat treatment is mainly due to the treatment temperature, while the reduction in acetic acid emissions depends on the heat treatment medium and is due to the chemical interactions between palm oil and acetic acid; thus, the heat treatment under palm oil reduces the percentage area of VOCs with unpleasant odors in Afrormosia and Newtonia wood better than the heat treatment under air. Based on TGA-3D FTIR analysis and mechanical results, the reduction in MOR is greater in heat treatment under air because the said treatment induces a greater loss of woody matter, which was characterized by higher H2O and CO emissions during heat treatment of wood under palm oil than during heat treatment of wood under air. On the other hand, palm oil more than air, promotes lignin deacetylation, which is characterized by the fact that the 1050 cm-1 wavelength peak was far higher in samples treated with palm oil than in those treated under air; and this might explain why heat treatment under palm oil reduces MOE more than heat treatment under air.

How do the main components influence the VOCs emission characteristics and formation pathways during moso bamboo heat treatment?

Bamboo heat treatment will cause plenty of release of volatile organic compounds (VOCs) into the atmosphere which are important precursors for ozone (O3) formation. In this study, dewaxed bamboo was heat-treated at 180 °C for 2 h to investigate the emission characteristics and the formation pathways of VOCs during heat treatment by removing different main components. The results showed that aldehydes (22.61%-57.54%) and esters (14.64%-38.88%) are the primary VOCs released during heat treatment. These compounds mainly originate from the degradation of hemicellulose, lignin, cellulose, and the linkage bonds between them in bamboo. During the bamboo heat treatment, the degradation of CO, CH, and CO bonds in hemicellulose results in the release of 5-hydroxymethylfurfural, 3-furfural, and 1-(+)-ascorbic acid 2,6-dihexadecanoate. The breakage of benzene ring group and the CO and CH bonds of lignin leading to the emission of VOCs including m-Formylphenol, Vanillin, and Syringaldehyde. The degradation of aliphatic CH, CC, and CO bonds in the amorphous region of cellulose contributes to an enhanced release of alcohols, olefins, and alkanes. It is calculated that acids (28.92%-59.47%), esters (10.10%-22.03%) and aldehydes (17.88%-39.91%) released during heat treatment contributed more to Ozone Formation Potential (OFP).

Effects of Heat Treatment on Color, Dimensional Stability, Hygroscopicity and Chemical Structure of Afrormosia and Newtonia Wood: A Comparative Study of Air and Palm Oil Medium.

In recent years, China is increasingly dependent on imported wood. Afrormosia and Newtonia are some of the imported species with good utilization potential. However, both of them also have problems with poor dimensional stability. In order to make better use of these two types of wood, the influence of heat treatment under air and palm oil conditions on the color, dimensional stability, and hygroscopicity of Afrormosia and Newtonia was investigated. The Afrormosia and Newtonia wood samples were heated in air or palm oil medium for two hours at 160 °C, 180 °C and 200 °C, respectively. Then, the color, weight changes, swelling, moisture absorption and chemical structure were evaluated for each case. As results, the heat treatments with air or palm oil increased the dark color of Newtonia and Afrormosia wood and this increase was proportional to the treatment temperature. The tangential and radial swelling coefficient for air heat treatment of Afrormosia wood at 200 °C were, respectively, reduced by 24.59% and 19.58%, while this reduction for Newtonia was 21.32% and 14.80%. The heat treatment in palm oil further improved the stability and hygroscopicity of the wood, showing that the Afrormosia samples treated by palm oil at 200 °C underwent a decrease of its tangential and radial swelling coefficient, respectively, by 49.34% and 45.88%, whereas the tangential and radial swelling coefficient of Newtonia treated under the same conditions were reduced by 42.85% and 33.63%, respectively. The heat treatments of Afrormosia and Newtonia samples under air at 200 °C diminished the water absorption by 21.67% and 22.12%. The water absorption of Afrormosia and Newtonia heat-treated under palm oil at 200 °C was reduced, respectively, by 39.40% and 37.49%. Moreover, the FTIR analysis showed the decrease of hydroxyl groups in proportion to the wood treatment temperature.

Improved CEEMDAN, GA, and SVR Model for Oil Price Forecasting.

Accurate prediction of crude oil prices (COPs) is a challenge for academia and industry. Therefore, the present research developed a new CEEMDAN-GA-SVR hybrid model to predict COPs, incorporating complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN), a genetic algorithm (GA), and support vector regression machine (SVR). First, our team utilized CEEMDAN to realize the decomposition of a raw series of COPs into a group of comparatively simpler subseries. Second, SVR was utilized to predict values for every decomposed subseries separately. Owing to the intricate parametric settings of SVR, GA was employed to achieve the parametric optimisation of SVR during forecast. Then, our team assembled the forecasted values of the entire subseries as the forecasted values of the CEEMDAN-GA-SVR model. After a series of experiments and comparison of the results, we discovered that the CEEMDAN-GA-SVR model remarkably outperformed single and ensemble benchmark models, as displayed by a case study finished based on a time series of weekly Brent COPs.

Characterization of the structural and dynamic changes of cell wall obtained by ultrasound-water and ultrasound-alkali treatments.

It is well-known that ultrasound has been studied for its cavitation, mechanical and thermal effects. As a pretreatment technology, ultrasonic alkali treatment has attracted much attention in the field of biomass biochemical transformation. In this study, the structural and dynamic changes of wood cell walls during ultrasound-water, alkali, and ultrasound-alkali treatments were investigated by stereoscopic microscopy, confocal Raman microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. The results indicated that the ultrasound-water, alkali, and ultrasound-alkali treatments had the effect of removing extractives from conduits. The uniform self-shrinking samples with shrinkage conduits were obtained by the alkali and ultrasound-alkali treatments. All of the treatments affected the relative content, structure and distribution of the chemical components in the wood cell walls. Compared with water-immersion samples, the relative content of hemicellulose of the treated samples reduced from 32.31% to 7.02% for ultrasound-8% NaOH treated samples. For the signal intensity of lignin, ultrasound-water treated and ultrasound-alkali treated samples displayed a more significant reductions than the alkali treated samples in the cell wall region. The crystal zone and amorphous zone of cellulose coexisted before and after the treatment, for all of the treated samples, and particularly for the ultrasound-assisted treated samples, the crystallinity increased from 38.15% for water-immersion samples to 57.42% for ultrasound-8% NaOH treated samples.

The effect of ultrasonic intensity on physicochemical properties of Chinese fir.

Cavitation intensity is affected by ultrasonic intensity (UI) and is a key parameter to describe experimental results during ultrasonic treatment. The relationship between the UI and physicochemical properties of Chinese fir was investigated. In this study, four frequencies (25, 28, 40, and 59 kHz) were used at the same intensity of 240 W and the same duration of 35 min. The UI during the ultrasonic treatment was determined, and the chemical components were determined. The chemical structure, crystallinity, morphology, and extractives of wood were respectively analyzed by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and gas chromatography-mass spectrometry (GC-MS). The results showed that higher crystallinity was associated with a larger integrated area under the curve of the ultrasonic intensity (UIA). The largest UIA was observed at 25 kHz, followed by those at 40, 59, and 28 kHz. The relative content of hemicellulose was strongly affected by the ultrasonic treatment. No chemical reactions were observed in the wood, whereas the ultrasonic treatment affected the torus of the bordered pits and facilitated the migration of extractives. In general, the higher the UIA, the stronger the effect of the cavitation was. The most significant changes in the physicochemical properties were observed at 25 kHz. The instantaneous ultrasonic intensity (IUI) changed over time, and the UIA was closely associated with changes in the physicochemical properties of the wood. The results of this study demonstrate that UI has a significant influence on the physicochemical properties of wood.

Effects of Combined Acid-alkali and Heat Treatment on the Physiochemical Structure of Moso Bamboo.

To improve the performance of bamboo and increase its utilization value, this study aimed at investigating the effects of impregnation pretreatment and thermal treatment on the structural changes of bamboo. The samples were pretreated in sodium hydroxide or zinc chloride solution, and then treated at 160 °C. The pretreated and control samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), and Fourier transform infrared spectroscopy (FTIR). The results showed that the cellulose crystallinity and intensity of samples pretreated by ZnCl2 could be reduced, but the crystal structure remained the same. As for samples pretreated in NaOH, the crystal structure of fiber was destroyed and the crystallinity was increased significantly. High temperature treatment has little effect on the thermal stability of bamboo. However, after treatment with NaOH and ZnCl2, the thermal degradation temperature changed obviously and moved to a lower temperature. ZnCl2 pretreatment had influence on the chemical structure of bamboo, while NaOH pretreatment had greater influence on the chemical structure of bamboo.

The numerical simulation and experimental study of heat release in a heat storage system with various diameters of aluminum tubes.

Phase change materials (PCMs) can be used to store solar energy. The heat released from PCMs is directly influenced by the efficiency of thermal energy storage and the scope of application. In this study, paraffin was used as the PCM, and was encapsulated in an aluminum tube. The temperature of the inner PCM was measured, and the heat release process of the PCM was simulated. The results indicate that the melt temperature of the PCM ranged from 45 °C to 60 °C, and the latent heat was 177 J/g. The heat release processes of the PCM in different aluminum tubes included three stages: 1) the stage during which no phase change occurred at temperatures above the melt temperature and at a rapidly decreasing temperature; 2) the stage during which phase change occurred at very slowly decreasing temperatures; 3) the stage during which no phase change occurred at temperatures lower than the melt temperature. The temperature of the PCM decreased when the radius of the aluminum tube increased. The temperature results obtained via simulation were similar to the actual temperature data. The total energy released from the PCM increased linearly with the time required to complete the energy release process of the PCM in aluminum tubes with different diameters, as well as with the increase in the aluminum tube diameter. The diameter of the PCM exerted no significant influence on the energy release rate. The relationship between the tube diameter and the time required to complete heat release, and the relationship between the amount of heat released, the diameter of the aluminum tube, and the release time, were established. These equations could predict actual values and provide theoretical guidance for heat release in heat storage systems. They could also be used as a guide in practical production.

Effects of zinc chloride-silicone oil treatment on wood dimensional stability, chemical components, thermal decomposition and its mechanism.

The hygroexpansion and anisotropy of wood limit its application in construction and wood products industry. Zinc chloride-silicone oil was use to decrease the hygroscopicity and improve the dimensional stability of wood at 80 °C, 140 °C, 160 °C and 180 °C. The effects of the treatment on the dimensional stability, chemical structure, thermal degradation, morphology of wood were evaluated, and the mechanism was determined. Results indicated that the zinc chloride-silicone oil treatment at 80 °C improved the dimensional stability and decreased the hygroscopicity of wood. The tangential, radial, and volumetric swelling coefficients of the treated wood decreased by 9.7%, 33.5%, and 18.2%, respectively, relative to those of the untreated wood. Zinc chloride-silicone oil treatment also changed the chemical structure of wood by degrading the wood components and decreasing the moisture absorption groups. Moreover, zinc chloride-silicone oil treatment significantly influenced the thermal degradation of wood, as samples treated with zinc chloride-silicone oil at 140 °C, 160 °C and 180 °C presented sharp peaks around 511 °C, 501 °C and 473 °C. The control group exhibited a more common derivative thermogravimetric curve with a sharp peak at 375 °C. In addition, the silicone oil could impregnate wood, occlude moisture passage, and prevent the movement of moisture in wood. This method can be applied in building and wood industries to expand the applications of wood products.

Effects of the ultrasound-assisted pretreatments using borax and sodium hydroxide on the physicochemical properties of Chinese fir.

This work investigated the physicochemical properties of Chinese fir after ultrasound-assisted pretreatments with borax and sodium hydroxide additives in an aqueous solution. TGA, FTIR, and XRD were used to analyze the thermal degradation processes, changes in chemical structures, and crystallinity of the treated samples, respectively. Additionally, the release of volatiles from wood pyrolysis was measured on-line by the TG-FTIR apparatus. In thermal analysis, all samples showed main degradation stages at 220-500 °C, and alkaline compounds could efficiently shift the process to lower temperatures with lower maximum weight loss rate (MWLR) and more residues. From TG-FTIR, it was observed that CO2 was the primary gas product from pyrolysis in the alkaline-treated samples, while there were more carbonyl compounds released in the control and deionized water groups. Due to the destruction and removal of hemicellulose and lignin after alkaline treatments, the related peaks changed greatly. Changes in the ester groups caused by saponification also accounted for one of the most significant differences between samples. Moreover, except for the deionized water group without sonication, the crystallinity of the samples increased from 6.34% to 11.29%. Overall, comparing the samples treated with or without ultrasound, the results showed that the ultrasound treatment did influence the samples' physicochemical properties, and its' effects varied by the basicity of the solution. This in-depth investigation offers a better understanding of ultrasound-assisted and alkaline pretreatments of wood materials.

Effects of Ultrasound Pretreatment on Eucalyptus Thermal Decomposition Characteristics As Determined by Thermogravimetric, Differential Scanning Calorimetry, and Fourier Transform Infrared Analysis.

Samples were pretreated by ultrasound at 300 W and 28 kHz in three different solutions. The thermal degradation characteristics of the samples were then characterized via thermogravimetric, differential scanning calorimetry, and Fourier transform infrared analysis in a nitrogen environment. The characteristic of gas product release, the formation mechanisms of the main products, and the mechanistic basis for the effects of ultrasound on wood components were studied. The results showed that the gaseous products are the same with ultrasound pretreatment but the amounts are changed. The gaseous products mainly constitute of CO, H2O, CO2, CH4, and CH3COOH, and more gaseous products were produced at 361 °C than at 308 °C. The reaction rates for specimens pretreated in aqueous soda solution proceeded faster than specimens pretreated in aqueous acetic acid solution and distilled water. Moreover, the maximum FTIR spectra absorbance appeared around 341 °C for specimens pretreated in aqueous soda solution but appeared around 369 °C for the control sample and samples pretreated in distilled water or acetic acid solution. The heat flows for specimens pretreated in aqueous soda solution, compared to control group, was much lower. Additionally, hydroxyl and hydroperoxy radicals provided by ultrasound cavitation in alkaline conditions act to intensify the overall rates of reactions.

Influence of ultrasound-assisted extraction on the pyrolysis characteristics and kinetic parameters of eucalyptus.

In this study, the influence of ultrasound-assisted extraction on eucalyptus samples with special focus on pyrolysis characteristics and kinetic parameters was explored. Ultrasound and Soxhlet extraction were used to pretreat samples respectively, then samples were assayed by component analysis, TG-FTIR, and kinetic analysis. Ultrasound-assisted extraction did change the physiochemical characteristics of eucalyptus samples, particularly in regards to the quantity of extractives obtained. In TG and DTG curves, ultrasound-extracted samples reflected lower residual weight ratio (17.77%) and higher maximum weight loss rate (-22.92%/min), and were accompanied by a slight shift in the weight loss rate peak to lower temperature (366°C). The volatiles produced during pyrolysis and the discrepancies of product distribution between experimental and controlled groups were explored based on TG-FTIR spectra. According to kinetic analysis results, ultrasound-treated samples showed higher activation energy at the primary portion of thermal degradation with an average of 206.09kJ/mol.

Influence of ultrasound pretreatment on wood physiochemical structure.

As an initial step to increase the use of renewable biomass resources, this study was aimed at investigating the effects of ultrasound pretreatment on structural changes of wood. Samples were pretreated by ultrasound with the power of 300W and frequency of 28kHz in aqueous soda solution, aqueous acetic acid, or distilled water, then pretreated and control samples were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The results shown that ultrasound pretreatment is indeed effective in modifying the physiochemical structure of eucalyptus wood; the pretreatment decreased the quantity of alkali metals (e.g., potassium, calcium and magnesium) in the resulting material. Compared to the control group, the residual char content of samples pretreated in aqueous soda solution increased by 10.08%-20.12% and the reaction temperature decreased from 361°C to 341°C, however, in samples pretreated by ultrasound in acetic solution or distilled water, the residual char content decreased by 12.40%-21.45% and there were no significant differences in reactivity apart from a slightly higher maximum reaction rate. Ultrasound pretreatment increased the samples' crystallinity up to 35.5% and successfully removed cellulose, hemicellulose, and lignin from the samples; the pretreatment also increased the exposure of the sample to the treatment solutions, broke down sample pits, and generated collapses and microchannels on sample pits, and removed attachments in the samples.