Effects of preheating temperature, preheating time and their interaction on the sandwich structure formation and density profile of sandwich compressed wood

Wu, Yanmei; Qin, Li; Huang, Rongfeng; Gao, Zhiqiang; Li, Ren

doi:10.1186/s10086-019-1791-7

Cited by 12 publications

(8 citation statements)

References 21 publications

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“…Therefore, the propagation of heat is faster in wood with lower density, lower thickness, and higher moisture content. The fast propagation of heat in the wood is an important factor in the densification process (Wu et al 2019). The internal parts quickly reach the appropriate temperatures so that the hydrogen bonds in the hemicelluloses, in the amorphous areas of the cellulose, and the lignin bonds achieve the appropriate stick-slap to reach visco-elastic deformation of the anatomical elements of the wood and thus adequate densification (Bao et al 2017).…”

Section: Discussion Thm Densification Process Evaluationmentioning

confidence: 99%

Effect of thermo-hydro-mechanical densification on the wood properties of three short-rotation forest species in Costa Rica

Moya

2020

BioRes

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Alnus acuminata, Vochysia ferruginea, and Vochysia guatemalensis are three low-density wood species used for reforestation in Costa Rica. The goal of this work was to study a thermo-hydro-mechanical densification process and test the characteristics of densified wood of these species. Twelve densifying treatments based on temperature, compression time, and use/no use of steam were tested. The variables of the densification process and the properties of the densified wood were determined. The results showed that the densification percentage was over 80% for wood of A. acuminata and over 70% for wood of V. ferruginea and V. guatemalensis. In the three species, the densification process was influenced by initial density. The influence of temperature during the densification process affected the heating rate and color change. An increase in the modulus of elasticity and modulus of rupture in static bending and in the hardness of the densified wood relative to the normal wood was observed, as well as a clear positive correlation of the properties with final density and maximum load, the latter being highly correlated with initial density. This showed that initial density was significant in the densification process and affects wood properties.

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Section: Discussion Thm Densification Process Evaluationmentioning

confidence: 99%

Effect of thermo-hydro-mechanical densification on the wood properties of three short-rotation forest species in Costa Rica

Moya

2020

BioRes

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“…Surface hardness of compressed wood is generally significantly related with wood density [17,34]. Since sandwich compression can selectively densify wood surface or interior where required while the other areas/ zones in wood are almost intact [17][18][19][20][21][22][23], much less wood compressing percent is required to improve the surface hardness than traditional wood compression. In wood sandwich compression, density of wood interior beside the surface can be significantly increased based on the requirement, which can accordingly increase the surface hardness of the compressed wood.…”

Section: Hardness Of the Sandwich Compressed Timbersmentioning

confidence: 99%

“…Since the compressed layer(s) and thickness are both adjustable, this technology can minimize wood volume loss caused by the compression. So far, sandwich compression has demonstrated great successes for poplar wood [18][19][20][21][22][23], which is a typical plantation diffuse-porous hardwood. By adjusting the preheating temperature and time, compressed layer(s) position and thickness are both controllable.…”

Section: Introductionmentioning

confidence: 99%

Sandwich compression of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa) wood: density distribution, surface hardness and their controllability

et al. 2021

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The sapwood and heartwood of plantation sugi wood (Cryptomeria japonica), and plantation hinoki (Chamaecyparis obtusa) wood were flat-sawn into timbers, then kiln-dried to a MC level below 12%. These timbers were further processed into specific sizes and wetted on the surfaces, preheated at 150 °C and radially compressed into sandwich compressed timbers. Density distribution, compressed layer(s) position and thickness, surface hardness were investigated. It was demonstrated that sugi and hinoki timbers were both applicable for sandwich compression. By controlling the preheating time, sugi heartwood timber, sugi sapwood timber and hinoki timber can be all sandwich compressed, which resulted in surfaces compressed timbers, interior compressed timbers and center compressed timbers. When sugi timbers were sandwich compressed, density only tremendously increased in the earlywood. The increased density of the compressed sugi earlywood was independent of compressed layer(s) position, compressing distance or annual growth width, while for hinoki timbers compression, density increased both in earlywood and latewood. Surface hardness of the uncompressed sugi sapwood was almost twice of that of the uncompressed sugi heartwood. Surface compression sharply increased the surface hardness of sugi heartwood and sugi sapwood. Interior compression and center compression also contributed to increased surface hardness for the compressed timbers, but to smaller extents. Surface hardness change due to the surface compression was consistent with the surface average density change of timbers. Compression layer(s) position exerted statistically significant effects on the surface hardness, while surface hardness of the compressed wood was almost unrelated to the original density of the used wood or average density of the sandwich compressed wood. However, bigger compressing distance led to bigger surface hardness for the surface compressed wood.

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“…By adjusting the parameters of preheating temperature and time, the compressed layer(s) in the direction of wood thickness can be softened and compressed, while the rest can be maintained. Our findings revealed that as results of preheating temperature elevation or preheating time extension, compressed layer(s) move gradually from wood surfaces to wood interior center, forming three types of sandwich compressed wood, namely surface compressed wood, internal compressed and central compressed wood [5–10]. It can also realize the directional control of the compression layer(s) position of sandwich compressed wood.…”

Section: Introductionmentioning

confidence: 99%

“…It can also realize the directional control of the compression layer(s) position of sandwich compressed wood. The yield stress gradients due to the gradient of hydrothermal distribution during compression are considered to be the cause of sandwich compressed wood formation [6,10]. After the wood was preheated for 0–600 s between the hot plates at 180°C, there was a significant linear correlation between the MC peak position in the high MC area of wood and the peak density of the compressed layer(s) in the sandwich compressed wood produced by preheating compression, and the moisture distribution on the wood thickness could be controlled by adjusting the preheating time, and finally the position and thickness of the compression layer(s) in the sandwich compressed wood can be controlled [8].…”

Section: Introductionmentioning

confidence: 99%

The relationship between the hydrothermal response of yield stress and the formation of sandwich compressed wood

Huang

Gao

2021

Jnl of Sandwich Structures & Materials

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The effects of yield stress of poplar ( Poplar × euramericana cv. ‘Neva’) on temperature (60–210°C), moisture content (oven dry-30%) and grain response mechanism and as well as its role in the formation of sandwich compressed wood were studied in this paper. The results showed that the yield stress of wood was significantly affected by moisture content(MC), temperature and their interaction. Compared with temperature, the relative change rate of yield stress was nearly 10 times higher for each 1% increase in MC than for each 1°C increase in temperature. The experimental data revealed that the relative change rate of yield stress depended on the softening effect of wood by moisture and temperature. The asymmetry of yield stress in different grain direction also depended on wood hydrothermal softening effect. Raising the temperature or increasing the MC could make wood radial vs tangential asymmetry decrease and radial vs radial tangential asymmetry disappear. In the process of hydrothermal compression, the yield stress gradient caused by the hydrothermal softening inside the wood was the main reason for the formation of sandwich compressed wood, and provided a scientific basis for the controllability of the position and thickness of the compressed layer(s).

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Effects of preheating temperature, preheating time and their interaction on the sandwich structure formation and density profile of sandwich compressed wood

Cited by 12 publications

References 21 publications

Effect of thermo-hydro-mechanical densification on the wood properties of three short-rotation forest species in Costa Rica

Effect of thermo-hydro-mechanical densification on the wood properties of three short-rotation forest species in Costa Rica

Sandwich compression of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa) wood: density distribution, surface hardness and their controllability

The relationship between the hydrothermal response of yield stress and the formation of sandwich compressed wood

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