Drying Characteristics of Eucalyptus urophylla × E. grandis with Supercritical CO2

Zhang, Jing-Wen; Liu, Honghai; Yang, Hang; Yang, Lin

doi:10.3390/ma13183989

Cited by 14 publications

(12 citation statements)

References 36 publications

(43 reference statements)

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“…The 70 °C/60 °C lowtemperature schedule took 103 h to reduce the MC of scCO 2 pre-treated boards down to 10% and was discontinued after 2 weeks as this timeframe was too long to manage the throughput of subsequent weeks. These results agree with those of Zhang et al (2020) who found that water removal from Eucalyptus urophylla × E. grandis was nine times faster using scCO 2 treatment (30 MPa) than conventional kiln-drying.…”

Section: Drying Timessupporting

confidence: 92%

Effect of supercritical CO2 pre-treatment and kiln-drying of fresh green Pinus radiata sapwood on kiln brown stain and drying stress

et al. 2022

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High pressure (20 MPa), cyclic, supercritical carbon dioxide (scCO2) treatments can reduce the moisture content of green Pinus radiata sapwood from 150–200% to 35–40%. Such treatments can be used as a dewatering pre-treatment before the kiln-drying of timber. Kiln-drying can utilise various temperature and humidity schedules, targeting around 10% moisture content, with a final stress-relieving steam-conditioning step. After scCO2 treatment and kiln-drying of samples, kiln brown stain was evaluated using the CIE L*a*b* colour space while drying stress was assessed by stress-cup measurements. The most significant results of scCO2 pre-treatment of Pinus radiata sapwood followed by kiln-drying plus steam-conditioning were as follows: Drying from green (36 h from a moisture content (MC) of 164%) using a conventional temperature schedule (90 °C/60 °C) took 2–5 times longer than kiln-drying scCO2 pre-treated boards (37.5% MC) to a target of 10% MC. Colour measurements proved that kiln brown stain does not occur. The use of a steam-conditioning step in reducing internal drying stresses was important irrespective of whether or not there was a scCO2 pre-treatment step. Over all drying schedule combinations, internal drying stress of both green and scCO2 pre-treated timber was similar after kiln-drying plus steam-conditioning. However, using only 90 °C/60 °C schedule data, with steam-conditioning, drying stresses were lower using kiln-drying without the scCO2 pre-treatment. This was surprising since the scCO2 step reduced the moisture content to around 37.5% without significant moisture gradients and so a secondary kiln-drying to 10% moisture content could have been expected to yield lower internal stress levels by preventing large moisture gradients to develop during drying. This result confirms the efficacy of the steam-conditioning step following standard kiln-drying. The colour data demonstrating the prevention of kiln brown stain using kiln-drying schedules offers a path to increasing timber quality for interior applications.

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Section: Drying Timessupporting

confidence: 92%

Effect of supercritical CO2 pre-treatment and kiln-drying of fresh green Pinus radiata sapwood on kiln brown stain and drying stress

et al. 2022

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“…The first term describes the internal work of plasticity along the shear plane, where τ γ is shear yield stress and γ is the shear strain along the shear plane. The value of γ can be calculated according to Equation (6), assuming that Φ c corresponds to the shear angle:…”

Section: Methodology For Determination Of Materials Properties From the Cutting Testmentioning

confidence: 99%

“…Several methods of drying wood are commonly used in the modern wood industry with air drying, kiln drying and vacuum drying recognized as the most frequent [1][2][3][4]. Alternative methods using super-critical drying, higher temperature schedules, low pressures, assistance of microwaves, among others, were developed to shorten time of this process [5,6]. Nevertheless, a consequence of each drying event is a change of the native material properties that can occur to a different extent depending on the wood species and process settings-particularly exposure time and treatment temperature.…”

Section: Introductionmentioning

confidence: 99%

Effect of the Drying Method of Pine and Beech Wood on Fracture Toughness and Shear Yield Stress

et al. 2020

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The modern wood converting processes consists of several stages and material drying belongs to the most influencing future performances of products. The procedure of drying wood is usually realized between subsequent sawing operations, affecting significantly cutting conditions and general properties of material. An alternative methodology for determination of mechanical properties (fracture toughness and shear yield stress) based on cutting process analysis is presented here. Two wood species (pine and beech) representing soft and hard woods were investigated with respect to four diverse drying methods used in industry. Fracture toughness and shear yield stress were determined directly from the cutting power signal that was recorded while frame sawing. An original procedure for compensation of the wood density variation is proposed to generalize mechanical properties of wood and allow direct comparison between species and drying methods. Noticeable differences of fracture toughness and shear yield stress values were found among all drying techniques and for both species, but only for beech wood the differences were statistically significant. These observations provide a new highlight on the understanding of the effect of thermo-hydro modification of wood on mechanical performance of structures. It can be also highly useful to optimize woodworking machines by properly adjusting cutting power requirements.

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“…In-depth studies of combining dewatering sequences and a final drying step using temperatures typical of conventional kiln drying of industrially important Eucalyptus species showed significant advantage in speed of conversion from green to dry compared with current commercial practice and in the final dry material quality [ 23 , 24 , 25 ]. Whereas carbon dioxide supercritical fluid-to-gas phase change dewatering was straightforward when applied to radiata pine and some other softwoods, application of the process to difficult-to-dry timbers such as the eucalypts might have greater commercial impact by minimising product quality loss, which results from material distortion and volumetric collapse when green eucalypt wood is conventionally kiln dried.…”

Section: Review Of Science Studies On Dewatering Green Wood Using mentioning

confidence: 99%

Dewatering Green Sapwood Using Carbon Dioxide Undergoing Cyclical Phase Change between Supercritical Fluid and Gas

Franich

Meder²,

Behr

2020

Molecules

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Conventional kiln drying of wood operates by the evaporation of water at elevated temperature. In the initial stage of drying, mobile water in the wood cell lumen evaporates. More slowly, water bound in the wood cell walls evaporates, requiring the breaking of hydrogen bonds between water molecules and cellulose and hemicellulose polymers in the cell wall. An alternative for wood kiln drying is a patented process for green wood dewatering through the molecular interaction of supercritical carbon dioxide with water of wood cell sap. When the system pressure is reduced to below the critical point, phase change from supercritical fluid to gas occurs with a consequent large change in CO2 volume. This results in the efficient, rapid, mechanical expulsion of liquid sap from wood. The end-point of this cyclical phase-change process is wood dewatered to the cell wall fibre saturation point. This paper describes dewatering over a range of green wood specimen sizes, from laboratory physical chemistry studies to pilot-plant trials. Magnetic resonance imaging and nuclear magnetic resonance spectroscopy were applied to study the fundamental mechanisms of the process, which were contrasted with similar studies of conventional thermal wood drying. In conclusion, opportunities and impediments towards the commercialisation of the green wood dewatering process are discussed.

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Drying Characteristics of Eucalyptus urophylla × E. grandis with Supercritical CO2

Cited by 14 publications

References 36 publications

Effect of supercritical CO2 pre-treatment and kiln-drying of fresh green Pinus radiata sapwood on kiln brown stain and drying stress

Effect of supercritical CO2 pre-treatment and kiln-drying of fresh green Pinus radiata sapwood on kiln brown stain and drying stress

Effect of the Drying Method of Pine and Beech Wood on Fracture Toughness and Shear Yield Stress

Dewatering Green Sapwood Using Carbon Dioxide Undergoing Cyclical Phase Change between Supercritical Fluid and Gas

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