Application of a novel de-watering process to control kiln brown stain in radiata pine

Kreber, B.; Stahl, Mario; Haslett, A. N.

doi:10.1007/s001070050468

Cited by 12 publications

(7 citation statements)

References 6 publications

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“…Decreasing the MC down to 37.5% should preclude the alternative mechanism of KBS proposed by Franich et al (2019a). The present results support those found previously (Kreber et al 2001;McDonald et al 2000). Kreber et al (2001) reported that KBS was not formed in Pinus radiata sapwood in a cyclic high-pressure treatment of green wood involving the use of compressed air (10 MPa; 85 cycles) followed by oven drying.…”

Section: Discussionsupporting

confidence: 91%

“…Previous studies with different treatments have reported that KBS was prevented with various drying regimes. McDonald et al (2000) and Kreber et al (2001) dried Pinus radiata sapwood using sap displacement with water exchanges or high pressure compressed air treatment cycles, respectively. McCurdy et al (2006) found that colour formation in Pinus radiata sapwood, occurred both Fig.…”

Section: Discussionmentioning

confidence: 99%

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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: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

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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“…Beyer et al (2006) found heat induces thermal processes which usually lead to non-beneficial effects such as yellowing, discoloration, or unpleasant odor. In earlier studies discoloration of birch had been investigated using colorimetric methods, with results indicating a notable color change occurring during kiln drying, of which temperature appeared to be the most important parameter (Kreber and Haslett, 1997;Luostarinen and Verkasalo, 2000;Kreber et al, 2001;Luostarinen and Luostarinen, 2001;Mononen et al, 2002;Sundqvist, 2002;Mononen et al, 2004). During drying, for some species (mainly softwoods), hydrophilic and lipophilic extractives migrate towards the surface and become distributed on the board surface causing a brown stain.…”

Section: Causes Of Wood Discoloration 41 Heatmentioning

confidence: 97%

Causes of color changes in wood during drying

et al. 2010

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The forest industry operates in a dynamic and global market where change and competition are the rule rather than the exception. The color of wood is one of the most attractive features for the modern wood industry. Even when wood is chosen for its structural qualities, attractive and decorative colors are usually an important factor. In many applications, particularly in furniture, decorative products, decorative veneers and fl ooring, accurate matching of the color of different samples is required. Wood attributes and properties are important because they have a direct bearing on market opportunities and consumer acceptance for many types of manufactured wood products. The aim of this review is to identify causes of wood discoloration and advances in drying technology to overcome this problem. Wood discoloration is a complex phenomenon, mainly affected by heat, light, physiological and biochemical reactions, as well as from attack by microorganisms.

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“…Importantly, in spite of the green wood material having been subjected to many cycles of high pressure and decompression, the cell structure and wood anatomy was unchanged from that of the fresh, green state. A practical benefit of the compressed air “incubation–decompression” process was the elimination of kiln brown-stain [ 14 ]. This process, resulting in improved quality of the output wood material, seemed a good candidate process to rival conventional drying.…”

Section: Introductionmentioning

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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Application of a novel de-watering process to control kiln brown stain in radiata pine

Cited by 12 publications

References 6 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

Causes of color changes in wood during drying

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

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