Moisture-dependent orthotropic viscoelastic properties of Chinese fir wood during quenching in the temperature range of 20 to −120°C

Holzforschung ◽  
2019 ◽  
Vol 74 (1) ◽  
pp. 10-19 ◽  
Author(s):  
Zhu Li ◽  
Jiali Jiang ◽  
Jianxiong Lyu
Keyword(s):  
Cell Wall ◽  
Viscoelastic Properties ◽  
Wood Cell Wall ◽  
Bound Water ◽  
Free Water ◽  
Chinese Fir ◽  
High Temperature Side ◽  
Temperature Spectrum ◽  
Β Relaxation ◽  
Temperature Side

AbstractAn understanding of wood’s moisture-dependent viscoelastic properties under various temperature conditions is important for assessing its utilization and product quality. In this study, we investigated the influence of moisture content (MC) on the orthotropic viscoelasticity of Chinese fir wood (Cunninghamia lanceolata [Lamb.] Hook.) during quenching ranging from 20 to −120°C. The storage modulus (E′) and loss factor (tan δ) of the longitudinal (L), radial (R) and tangential (T) specimens were determined for nine MC levels ranging from 0.6 to 60.0%. The results showed that E′ generally decreased with increasing amount of bound water in all orthotropic directions, regardless of the temperature. In contrast, a sharp increase in E′ was observed at temperatures below 0°C when free water was present, due to the formation of ice within the cell lumens. The γ-relaxation and β-relaxation were observed in the temperature spectrum. A comparison demonstrates that the β-relaxation showed evident grain orientation. When only bound water was present in the wood cell wall, one clear γ-relaxation was found for all orthotropic directions. In contrast, only the high-temperature side of the γ-relaxation was observed in the three anatomic directions in specimens with free water, which might be related to the amorphous wood cell wall coupling with the frozen free water during the quenching process. In addition, the differences in peak temperatures of the γ-relaxation among the three main directions diminished with increasing bound water.

scholarly journals The Study of Bound Water Status and Pore Size Distribution of Chinese Fir and Poplar Cell Wall by Low-Field NMR

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Huimin Cao ◽  
Jianxiong Lyu ◽  
Yongdong Zhou ◽  
Xin Gao
Keyword(s):  
Cell Wall ◽  
Low Temperature ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Adsorption Isotherms ◽  
Bound Water ◽  
Chinese Fir ◽  
Fast Growing ◽  
Pore Size Distributions

With the increasing shortage of timber resources and the advancement of environmental protection projects, many artificial fast-growing forests are planted and used as raw materials in China. There are significant differences in the properties of natural forest wood and artificial fast-growing forest wood, and the properties of wood mainly depend on the change in the status of bound water in the cell wall. In this study, the fiber saturation point (FSP) and pore size distributions within the cell wall of six species of fast-growing forest wood were studied by low-temperature nuclear magnetic resonance (NMR) technology. The effects of species, growth rings, and extractives on the FSP and pore structure were analyzed. The water vapor sorption experiments were performed, and the adsorption isotherms of the samples were fitted through the Guggenheim-Anderson-de Boer (GAB) equation. According to the least-square regression of the adsorption isotherms and combined with the low-temperature NMR experiments, the content and proportion of the different types of bound water were analyzed. The results showed that the average FSP of each Chinese fir was about 40% and that of each poplar was about 35%. There is about a 10% difference between the FSP measured by NMR technology and the adsorption bound water content obtained by adsorption isothermal. The pore size distribution results show that in all samples, the proportion of pores larger than 10.5 nm is very low, about 10%; the proportion of 1.92-10.5 nm pores is about 30%; and the proportion of pores smaller than 1.92nm is more than 50%. This work will be helpful to the study of the wood moisture status and provide reference data for wood modification.

Orthotropic Viscoelastic Properties of Chinese Fir Wood Saturated with Water in Frozen and Non-frozen States

2021 ◽  
Vol 71 (1) ◽  
pp. 77-83
Author(s):  
Zhu Li ◽  
Jiali Jiang ◽  
Jianxiong Lyu ◽  
Jinzhen Cao
Keyword(s):  
Viscoelastic Properties ◽  
Initial Temperature ◽  
Loss Modulus ◽  
Viscoelastic Behavior ◽  
Free Water ◽  
Chinese Fir ◽  
Enhancement Effect ◽  
Wood Industry ◽  
Order Of Magnitude ◽  
Water Saturated

Abstract In order to better understand the differences in orthotropic viscoelastic properties of Chinese fir (Cunninghamia lanceolata) in frozen and non-frozen states, the storage modulus (E′) and loss modulus (E″) of the longitudinal, radial, and tangential specimens were investigated under water-saturated conditions with temperatures ranging from −120°C (or 30°C) to 280°C. Results revealed that the order of magnitude in E′ for each orientation was consistent for temperatures below 0°C, while the anisotropy in E′ was reduced due to the enhancement effect of ice. Frequency-dependent γ-relaxation was observed at approximately −96°C for all orthotropic directions. A sharp discontinuity in E′ occurred at approximately 0°C for each specimen, together with the corresponding sharp peak in the E″ spectrum. Furthermore, the frozen free water had an effect on the orthotropic viscoelastic behavior in the water-saturated specimens within the range of −120°C to 280°C. Specimens with a frozen history leveled off at the initial temperature ramping phase for each orientation, while a frozen history reduced the decline in stiffness of the wood specimens. Similar to the variations in E′, the dramatic loss of water increased the complexity of the E″ values. The loss of free water also had a pronounced effect on the viscoelastic properties during the temperature ramping process. Thus, in the wood industry, it necessary to consider the variations in the orthotropic viscoelastic performance of specimens under water-saturated conditions during the water loss process.

Dynamic viscoelastic properties of Chinese fir (Cunninghamia lanceolata) during moisture desorption processes

Holzforschung ◽  
2016 ◽  
Vol 70 (6) ◽  
pp. 547-555 ◽  
Author(s):  
Tianyi Zhan ◽  
Jiali Jiang ◽  
Hui Peng ◽  
Jianxiong Lu
Keyword(s):  
Cell Wall ◽  
Viscoelastic Properties ◽  
Loss Factor ◽  
Loss Modulus ◽  
Polymer Networks ◽  
Chinese Fir ◽  
Cunninghamia Lanceolata ◽  
Unstable State ◽  
Factor Ratios ◽  
Moisture Desorption

Abstract The viscoelasticity of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) during moisture desorption processes were examined at 30°C and two relative humidity (RH) modes: RHramp-down mode from 85 to 0% RH, and RHisohume mode at 0, 30, and 60% RH, respectively. Dynamic viscoelastic properties were determined in a multi-frequency range of 1, 2, 5, 10, and 20 Hz. In both RH modes, desorption of water resulted in increasing stiffness and decreasing damping. The reduction in moisture content caused an unstable state in the cell wall due to the formation of free volumes in cell wall and rearrangement of hydrogen bonds within the polymer networks. Higher ramping rates resulted in greater destabilization, and the unstable state was more pronounced at a lower frequency. The ratio of storage modulus at 1 and 20 Hz remained unchanged during both RH modes. The ratios of loss modulus and loss factor at 1 and 20 Hz increased during the RHramp-down and decreased during the RHisohume period. The changes of loss modulus or loss factor ratios at two frequencies were suitable for evaluation of the unstable state. The instability was aggravated with reducing RH and slightly recovered at constant RH.

scholarly journals Effect of Heat Treatment on Water Absorption of Chinese fir Using TD-NMR

2018 ◽  
Vol 9 (1) ◽  
pp. 78 ◽  
Author(s):  
Yulei Gao ◽  
Kang Xu ◽  
Hui Peng ◽  
Jiali Jiang ◽  
Rongjun Zhao ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Water Absorption ◽  
Bound Water ◽  
Treated Wood ◽  
Free Water ◽  
Scientific Basis ◽  
Transport Processes ◽  
Chinese Fir ◽  
Frequency Coding ◽  
Heat Treated

Knowledge of the dynamic changes in the water absorption process of heat-treated wood is important for providing a scientific basis for the reasonable application of heat-treated wood, especially for outdoor applications. Nuclear magnetic resonance (NMR) techniques provide detailed information about the moisture components and moisture transport processes in wood, which are not available with other methods. In this work, water absorption of untreated and heat treated Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) heartwood was investigated using various NMR methods. The heat treatment temperatures were varied between 160 °C and 220 °C. According to the spin-spin relaxation time (T2), there were two components of water in the samples heat-treated at 160 °C and 180 °C as well as the untreated sample, while three components of water were found in the samples heat-treated at 200 °C and 220 °C, and the mass of each component was calculated by the integral peak areas of the T2 curve. The amount of bound water and free water in heat-treated samples were less compared to the untreated ones, and the water absorption decreased correspondingly, due to the increasing heat-treated temperature. The results obtained by one dimensional frequency coding indicated that the heat treatment made wood difficult to be accessed by moisture. Besides, NMR images revealed that the free water absorption in latewood was faster than in earlywood, but earlywood could absorb more water than latewood.

Influence of hygrothermal condition on dynamic viscoelasticity of Chinese fir (Cunninghamia lanceolata). Part 1: moisture adsorption

Holzforschung ◽  
2018 ◽  
Vol 72 (7) ◽  
pp. 567-578 ◽  
Author(s):  
Tianyi Zhan ◽  
Jiali Jiang ◽  
Jianxiong Lu ◽  
Yaoli Zhang ◽  
Jianmin Chang
Keyword(s):  
Cell Wall ◽  
Wood Cell Wall ◽  
Mechanical Analysis ◽  
Thermal Softening ◽  
Chinese Fir ◽  
Moisture Adsorption ◽  
Dynamic Viscoelasticity ◽  
Time Periods ◽  
The Difference ◽  
The Relationship

AbstractThe dynamic viscoelasticity of Chinese fir was investigated by dynamic mechanical analysis (DMA), while the influence of the moisture adsorption (MAds) was the focus of the study. The specimens were climatized at 30, 40, 50, 60, 70 and 80°C under two relative humidity (RH) modes. The RHrampmode included 0, 30, 60 and 90% RH with varied ramping rates (0.5, 1.0 and 2.0% RH min−1), while the RHisohumemethod worked with constant RHs of 30, 60 and 90%, respectively, for 60, 120 or 240 min. During the MAdsprocess, a decrease in stiffness and an increase in damping of the wood were seen and were attributed to the combination of the plasticization, mechano-sorptive (MS) effects and heating. High temperatures accelerate the MAdspace and intensify the plasticization and MS effects. In RHrampexperiments, the glass transition RH (RHg) of xylan was visible, as determined by the maximum of damping. The values of RHgvaried from 60 to 90% at 50°C or above. In the RHisohumemode, the thermal softening of hemicelluloses and lignin occurred for shorter time periods under more severe hygrothermal (HT) levels between 40–60°C and 70–80°C, respectively. During MAds, the MS effect diminished as the wood approached a new equilibrium moisture content (EMC). The MAdstimes to new EMCs became shorter at the expense of intensifying the unstable arrangement of the wood cell wall. Severe HT levels led to great residual instabilities in the wood cell wall, which could be evaluated by the relationship between the extent of the MS effect and the difference between the MC and EMC.

Determine the Moisture Distribution in Sewage Sludge by Drying Differential

2014 ◽  
Vol 665 ◽  
pp. 404-407 ◽  
Author(s):  
Wan Yu ◽  
Pei Sheng Li
Keyword(s):  
Sewage Sludge ◽  
Interstitial Water ◽  
Bound Water ◽  
Free Water ◽  
High Accuracy ◽  
Moisture Distribution ◽  
Municipal Sewage ◽  
Municipal Sewage Sludge ◽  
Hot Air ◽  
Critical Water Content

Moisture distribution in sewage sludge was considered as the essential of thermal drying. Some methods were given in literatures to test the moisture distribution, but there was no standard method to determine the critical water content between different kinds of water. The municipal sewage sludge was dried by hot air in this work. Based on the drying curve, the derivative of drying rate with respect to dry basis moisture content was brought out to analyze the moisture distribution in sewage sludge. Results show that this method can easily determine the free water, interstitial water, surface water and bound water with a high accuracy. The present work can provide new insight to determine the moisture distribution in sewage sludge, which was still lacking in the literatures.

Dynamic Study on Vacuum Pyrolysis Reaction of Chinese Fir Sawdust Biomass

2012 ◽  
Vol 512-515 ◽  
pp. 375-378
Author(s):  
Su Wen Yang ◽  
Jian Min Yi ◽  
Ke Qiang Qiu ◽  
Xin Deng ◽  
Jian Shan Chen
Keyword(s):  
Heating Rate ◽  
Free Water ◽  
Chinese Fir ◽  
Peak Temperature ◽  
Gravimetric Analysis ◽  
Water Desorption ◽  
Exponential Factor ◽  
Pyrolysis Reaction ◽  
Temperature Range ◽  
Vacuum Pyrolysis

This thesis does thermal gravimetric analysis（TGA）studies on Chinese fir sawdust biomass by integrated thermal analyzer under vacuum conditions. Through the analysis on lostmass curve at different heating rate of 10, 15, 20 and 30°C/min, we found the process of Chinese fir sawdust vacuum pyrolysis can be mainly divided into three stages: evaporation of free water and combined water desorption, rapid lostmass of pyrolysis and slow decomposition of residues. The lostmass major temperature range is between 250 ~ 450°C, the peak temperature is between 365 ~ 400°C. When the pyrolysis temperature is 500°C, vacuum pyrolysis reaction of Chinese fir sawdust has basically completed. As the heating rate rises, the lostmass curve is moving to the right, the peak temperature is shifting to higher temperature, and the temperature range of thermal decomposition reaction widens significantly. According to experimental datas, we tried to obtain the vacuum pyrolysis dynamic parameters of Chinese fir sawdust, and the results are that the apparent activation energy of vacuum pyrolysis reaction of Chinese fir sawdust biomass is 128.34kJ/mol, with the pre-exponential factor being 6.42×109 and reaction order being 1.08, similar to first order reaction.

Acetyl Group Distribution in Acetylated Wood Investigated by Microautoradiography

Holzforschung ◽  
2001 ◽  
Vol 55 (3) ◽  
pp. 270-275 ◽  
Author(s):  
Marie Rosenqvist
Keyword(s):  
Cell Wall ◽  
Weight Gain ◽  
Acetic Anhydride ◽  
Wood Cell Wall ◽  
Environmental Scanning Electron Microscopy ◽  
Environmental Scanning ◽  
Accurate Information ◽  
Concentration Gradients ◽  
Good Opportunity ◽  
Acetyl Group

Summary Sapwood of Scots pine (Pinus silvestris L.) was acetylated with 14C- and 3H-labelled acetic anhydride. The distribution of acetyl groups was investigated with microautoradiography and microautoradiographs were evaluated with ESEM, Environmental Scanning Electron Microscopy. The investigation showed that the impregnation of wood with radioisotope-labelled substances provides a good opportunity to investigate the location of substances covalently bonded to the wood material. Introduced 14C-labelled acetyl groups show an even distribution in the wood cell wall, with no discernible concentration gradients at acetylation levels of about 5, 15 and 20% weight gain. 3H-labelled acetyl groups show an even distribution in the wood cell wall at 15 and 20% weight gain, with no discernible concentration gradients. At the 5% weight gain level, however, an uneven distribution of 3H-labelled acetyl groups over the cell wall is observed. Nevertheless, the unevenness is random and no concentration gradient is discernible at this level. 3H with a relatively high resolution, 0.5–1 μm, compared to 14C with a resolution of 2–5 μm, gives more accurate information about where exactly the acetyl groups are situated in the wood cell wall. Acetic anhydride was evenly distributed when a full impregnation procedure was used. The chemical and physical properties of acetic anhydride allow a uniform penetration into the pine cell wall and a complete acetylation takes place when the specimens are heated.

Sign in / Sign up

Export Citation Format

Share Document