Harvest date affects colour and soluble solids concentrations (SSC) of <Emphasis Type="Italic">Uapaca kirkiana</Emphasis> (Muell. Arg.) fruits from natural woodlands

Uapaca kirkiana (Muell. Arg.) is a woodland fruit tree that is native to parts of eastern, central and southern Africa. Unripe fruits are harvested from wild and semi-wild sources by dislodging them from trees. Ripe fruits are gathered from the ground after abscission. Utilization of the fruits is affected by problems such as variability of fruit quality and high perishability. Quality attributes of fruits harvested on 1 and 17 November, and 3 December 2003 and kept at 25–30°C, have been evaluated. On the second and third harvests, fruits were also stored in polythene bags to investigate a common incubation method to hasten ripening. Fruit weight and colour before and after ripening, and the soluble solids concentrations (SSC) of ripe fruits were measured. The redness (a*) values at harvest increased from 3.5 to 5.3 units from 1 November to 3 December. Over this period there was a significant decline in both lightness (L*; 63.8 to 58.9 units) and yellowness (b*, 39.6 to 36.4 units). Skin colour became darker during storage as reflected by the decreasing lightness (L* values from 63.8 to 44.5 units), yellowness (b* values from 36.6 to 20.1 units) and increasing redness (a* values from 3.5 to 8.8 units). Fruits harvested on 17 November and 3 December did not darken during storage as much as fruits harvested on 1 November. Fruits harvested on 3 December lost less weight (13.7%) during storage than those harvested on 1 November (34.0%), while the respective SSC measured 6 days after harvest were 18.1% and 9.9%. Fruits kept in polythene bags had 5.3% lower SSC than those kept on plates. The results demonstrate the benefits of delaying fruit harvest to improve quality attributes such as fruit skin colour at harvest and during storage, to reduce weight loss and to obtain higher SSC during storage.     

Modelling of pH effects and CIE L*a*b*colour spaces of beech wood-inhabiting fungi by NIRS

A combination of statistical techniques of analyses were used to evaluate the potential of International Commission on Illumination (CIE) lightness (L*), redness (a*) and yellowness (b*) colour space system and near-infrared spectroscopy (NIRS) to assess surface changes in relation with progressive decay of beech (Fagus grandifolia Ehrh.) by wood-inhabiting lignicolous fungi Inonotus hispidus, Trametes versicolor and Xylaria polymorpha. pH effects based modelling predictions of beech earlywood and latewood tissues were also included. Multivariate analysis techniques included response surface optimization, sample-specific standard error of prediction (SEP) method and projection to latent structures partial least squares (PLS) regression. Strong statistical relationships were derived for pH predictions with R² values ranged: from 0.77 to 0.84 for I. hispidus; from 0.77 to 0.84 for T. versicolor and from 0.83 to 0.91 for X. polymorpha. R² values for CIE-based L*a*b* colour space measurements ranged: from 0.43 to 0.69 (L*), 0.66 to 0.76 (a*), 0.42 to 0.53 (b*) for I. hispidus; from 0.59 to 0.69 (L*), 0.69 to 0.79 (a*), 0.64 to 0.79 (b*) for T. versicolor; and from 0.51 to 0.75 (L*), 0.89 to 0.94 (a*), 0.85 to 0.89 (b*) for X. polymorpha. Multivariate technical analysis (response surface analysis, sample-specific SEP, PLS regression) of CIE L*a*b* system and NIRS results should be able to characterize pH effects and surface changes of wood spalted by lignicolous fungi as a quick and reliable non-destructive method relevant to wood-spalting concerns and the forest products industry.     

Progress of discoloration in green,freshly cut veneer sheets of black alder (Alnus glutinosa L.) wood

Abstract

Black alder wood has a great potential for more wide-spread use in the woodworking industry. This study describes the colour changes that appeared the first few hours after cutting thin veneer sheets from fresh, unseasoned black alder wood. CIELab coordinates were recorded for 50 spots at time intervals from 0 to 140 minutes exposure of the fresh-cut surfaces. The most pronounced change was increased lightness developing from 20 to 60 minutes after cutting. A model for total colour change as function of exposure time was developed. Redness of veneer sheets increased only slightly, i.e. the expected transfer to orange discoloration of the surface did not occur. The reason for this was probably that part of the free water in the wood was squeezed out during veneer production. The findings of this study give useful information about the colour change that appeared directly after veneer cutting, advising to avoid excess water on wood surface and ensuring quick surface drying.     

Change in fracturing and colouring of solid spruce and ash wood after thermal modification

Effects of different thermal treatments (maximum treatment temperatures of 200, 210 and 220°C for 2.5 hours) on solid spruce (Picea abies L. Karst.) and ash (Fraxinus excelsior L.) were investigated in this study. The fracture behaviour in radial/longitudinal as well as in tangential/longitudinal and the change of the wood colour (CIEL*a*b* colour space) on all principal anatomical surfaces (cross sectional, radial and tangential) were analysed. The specific fracture energy and the maximum breaking load decreased almost significantly after all thermally treated samples in comparison to the untreated (standard dried) sample. The wood colour changed also significantly, in particular the lightness decreased with increasing intensity of thermal treatment on all investigated surfaces. A comparison of the percentage loss of the different fracture and colour values has shown a strong correlation between the maximum breaking load and the lightness after several thermal treatments, in both investigated crack propagation systems, on all measured surfaces and for both analysed species.     

Colour responses from wood,thermally modified in superheated steam and pressurized steam atmospheres

Abstract

In this study, two different methods were used to produce thermally modified wood. One was carried out in a typical kiln drying chamber using superheated steam (SS) and the other used pressurized steam in an autoclave cylinder (PS). Overall, both processes followed the same principles and the wood was not treated with any chemicals. Two wood species were studied, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Treatments in the autoclave were carried out under pressure using temperatures of 160°C, 170°C and 180°C. Temperatures of 190°C and 212°C were used in treatments in the chamber at normal air pressure. The colour was measured using L*C*H colour space. Results for both species showed that similar L* (lightness) can be reached at lower (20–30°C) temperatures using PS compared with SS treatment. The hue angle of PS-treated wood was smaller than that of SS-treated wood. No significant difference in C* (chroma) was detected. The difference in E value between PS- and SS-treated wood was smaller for Norway spruce than for Scots pine. The residual moisture content was about 10% higher in wood treated by the PS process compared with the SS process.     

Surface quality sensing of trembling aspen (Populus tremuloides Michx.) veneer products by near infrared spectroscopy

Abstract

The potential of near infrared spectroscopy (NIRS) to estimate wood moisture content (MC), surface energy characteristics and adhesive bond strength were evaluated on aspen (Populus tremuloides Michx.) veneer subjected to different drying times. For samples dried progressively at 103°C, the best MC prediction model was for the total MC range (0–100%) with an R² value of 0.68. However, exposure at 180°C produced surface colour changes, and the CIE L*a*b* colour parameters measuring colour changes were better estimated using the 400–900 nm spectral data than the 1100–2400 nm spectral data. Increased exposure time at 180°C resulted in lower wettability and, hence, larger contact angles, especially when ethylene glycol was used as probe solvent. Lap shear strength tests on veneers showed that adhesion by phenol formaldehyde resins was impaired by the high temperature exposure; however, the lap shear strength test had high variability so there was not always a clear relationship between contact angle and lap shear strength test.     

防止兰考泡桐木材变色的初步试验

对多种化学药品配方防止兰考泡桐(Paulownia elongata)木材变色的效果进行了试验,并观测了处理前后材色的变化,探索到4种对防止变色有一定作用的配方。同时,初步观察了干燥条件和木材含水率对变色的影响,讨论了各种处理方法对防止兰考泡桐材变色的适用性。     

Coloring characteristics of in situ lignin during heat treatment

To investigate the effects of lignin on the discoloration of Black locust (Robinia pseudoacacia) wood during heat treatment, chromatic indexes of the extractive-free wood samples are examined at different moisture contents (MC) under oxygen and nitrogen environment, respectively. The organic acids are produced during heat treatment, resulting in pH decrease in the samples. Components absorbing visible light are formed during heat treatment, and oxygen and moisture contents have obvious effects on the decrease in L*, increase in a* value, yellowness (b*) and total color difference (ΔE) of the samples. It is found that the β-5, C _α C _β unsaturated bond, the conjugated carbonyl group, quinones structures, α, β-unsaturated ketone and α-C?=?O in lignin increased after heat treatment. The formation of condensation products, the low-molecular-weight phenolic substances and the oxidation products in lignin result in the increment of the light absorption within the entire visible region.     

Discolouration of birch wood: analysis of extractives from discoloured surface of vacuum-dried European white birch (Betula pubescens) board

A discolouration that appeared on the surfaces of a European white birch (Betula pubescens) board during vacuum drying was studied by means of colour measurements (CIEL*a*b*), elemental analysis and the analysis of extractives. The discoloured surface layer of the dried board contained substantially more methanol-soluble extractives than did the light-coloured part (50.7 mg g⁻¹ vs. 26.7 mg g⁻¹ dry wood), and the colour difference (ΔE* _ab 20.0) between the two extracts was notable. Characterization by means of GC and ¹³C NMR spectroscopy showed that the extracts contain sugars (mainly glucose and fructose), low-molecular-weight phenolic compounds, proanthocyanidins, Brauns’ lignin and fatty acid esters. Concentrations of sugars, low-molecular-weight phenols, proanthocyanidins and Brauns’ lignin were higher in the discoloured surface layer than in the light-coloured part. The yellowness of the surface layer was associated with the accumulation of low-molecular-weight phenolic extractives, and the redness with Brauns’ lignin and possibly proanthocyanidins.     

Colour alteration and chemistry changes in oak wood (Quercus pedunculata Ehrh) during plain vacuum drying

The formation of chromophore groups from a phenolic compound oxidized with air and the formation of dark materials from hydrolysable extractives are considered as causes of discoloration. In this work, the colour changes, antioxidant capacity, and Fourier Transform Infrared Spectra of dust-wood are investigated in European oak wood under different plain vacuum drying conditions. The conductive heat source is maintained at four temperatures (46, 61, 70 and 80°C), and vacuum in the chamber is controlled at three different intervals (60–100, 150–200, and 250–300?mbar). Drying kinetics and temperature profiles are presented. The results suggest that degradation of extractives allows yellowing in wood and temperature improves lightness under these special drying conditions (plain vacuum). Furthermore, the presence of carbonyl groups in surfaces is related to the loss in antioxidant potency.     

The Effect of Bark Condition,Delivery Time and Climate-adapted Wet Storage on the Moisture Content of Picea abies (L.) Karst. Pulpwood

The wet-base moisture content (MC) in outer sapwood of Norway spruce (Picea abies (L.) Karst.) pulpwood in different wood management programmes from the forest to the mill was studied from the point of view of three objectives: (1) the importance of rapid raw material delivery, (2) the effect of bark condition as a result of harvesting during the late dormant season and the growing season, and (3) the possibilities for retaining the pulpwood MC using climate-adapted wet storage. The reduction in MC after felling was significant in the pulpwood stored without wet storage. When not wet-stored, pulpwood with a high degree of bark damage dried out more rapidly than wood with a low degree of bark loss. In pulpwood, wet-stored in accordance with climate-adaptation, the MC remained or increased during storage. The shorter the drying time before wet storage, i.e., faster delivery to the mill, the more significant the increase in MC. The increase in MC during wet storage was more significant in pulpwood with a low degree of bark damage. Climate-adapted wet storage reduced the variation of the MC. When conducted with fresh pulpwood, i.e., drying time shorter than 4 weeks (low bark loss) or 2 weeks (high bark loss), a more homogeneous MC distribution was gained.     

Effects of log storage and drying on birch (<Emphasis Type="Italic">Betula pendula</Emphasis>) wood proanthocyanidin concentration and discoloration

In conventional drying, sawn birch (Betula sp.) timber darkens and reddens from the inside while the layer a few millimetres under the yellowish surface remains light in color. Lack of information concerning the chemical basis of the discoloration hinders the development of a reliable solution for this problem. In this study, the role of soluble proanthocyanidins in discoloration of birch wood was investigated because the polymerization and oxidation of these compounds are known to yield insoluble reddish compounds. Different periods of log storage affected the synthesis of soluble proanthocyanidins during conventional drying. Concentration of proanthocyanidins also correlated with changes in the color of birch wood. Discoloration appeared differently in conventionally dried and vacuum-dried wood, which indicates that the discoloration mechanism in these drying methods may differ chemically, and/or the compounds that take part in discoloration may be different at different drying temperatures.     

Wood colour variation in sapwood and heartwood of young trees of Tectona grandis and its relationship with plantation characteristics, site, and decay resistance

? Wood colour of Tectona grandis produced from fast-growth plantations is highly variable and the causes of this variation are relatively unknown.

? With the purpose of understanding the colour variation, different fast-growth plantations were sampled with different growth rates, tree ages, and sites.

? Wood colour was measured with a CIELab system, where three variables are estimated: coordinate L* for lightness, coordinate a* defines redness and coordinate b* defines yellowness.

? Results showed only a negative correlation between L* and a*. L* and a* were negatively and positively respectively correlated with pith distance in heartwood, but not for b*. No correlations were found between L* and b* in sapwood and plantation characteristics, while a* was positively correlated with age and height of tree and growth rate. In heartwood, tree age and diameter at breast height were correlated with all colour parameters, but tree height and plantation density were correlated with a* and b*. Cluster site had correlation with L*. Multiple correlation analysis showed that the heartwood is increasing darker (L*) and redder (a*) when the trees are older and bigger. Correlation coefficient shown that sapwood and heartwood with lighter colour (L*) is less resistance to fungal attack, but redness colour (a*) increasing decay resistance.

     

Relationship of selected cell characteristics and colour of silver birch wood after two different drying processes

Abstract

Change in the colour of silver birch wood is a serious problem in the mechanical wood industry. Here, colour was correlated with microscopic characteristics of wood, such as cell types and dimensions, by drying processes. In conventional drying, with lower temperature than in vacuum drying used here, the most important factor causing darkened wood was wide latewood. In vacuum drying, thickness of the vessel walls affected wood darkening, as did broad rays and large amount of axial parenchyma. Axial and terminal parenchyma cells contained very small amounts of phenolics, but after drying at elevated temperature, a thin dark layer could be observed on the innerside of their walls. Phenolics were abundant in ray parenchyma; these compounds darkened at elevated temperatures, less in conventional drying than in vacuum drying. Phenolics were observed only inside cells, mainly in the parenchyma, but in vacuum-dried wood also in fibres and vessels. Anatomical characteristics are known to be affected by both environmental and genetic factors. Thus it might be possible to influence the colour reaction of birch wood during the drying process by choosing wood according to growing-site conditions, or by choosing the seed source for birch plantations according to given anatomical characteristics.     

Effects of UV light irradiation on colour stability of thermally modified, copper ethanolamine treated and non-modified wood: EPR and DRIFT spectroscopic studies

A series of experiments were carried out to investigate the colour stability of chemically treated and thermally modified wood compared to non-modified wood during long term artificial UV light irradiation. One set of wood samples was vacuum-pressure impregnated with alkaline (pH 9.8) copper (II) ethanolamine aqueous solution, while another set of samples from the same wood block was thermally modified at 210°C and −0.90 bar for 2 h. The treated and modified wood samples along with the non-modified ones were exposed to artificial UV light with the wave length in the region of UVA (315–400 nm) and UVB (280–315 nm) intermittently for 500 h. Colour measurements were carried out throughout the irradiation period at an interval of 100 h according to CIEL*a*b* system, where the results are presented in terms of ΔE, ΔL*, Δa* and Δb* values. Better photo-stability in terms of colour changes was recorded for both treated and modified woods compared to the non-modified one. By means of EPR and DRIFT spectroscopic study it was shown that some degree of colour stability of treated and modified woods, achieved during artificial UV light irradiation, resulted from lignin modifications and monomers of phenolic compounds.     

Characterization of Brauns’ lignin from fresh and vacuum-dried birch (Betula pendula) wood

Brauns’ lignins present in the methanol extracts of fresh birch (Betula pendula) xylem and of sawn birch board subjected to vacuum drying were characterized by ¹H and ¹³C NMR spectroscopy (1D and 2D), IR spectroscopy, gel permeation chromatography (GPC) and colour measurements (CIELab) in order to find out whether Brauns’ lignin could contribute to the colour change of sawn timber that occurred during vacuum drying. The two Brauns’ lignin samples contained about equal amounts of syringylpropane and guaiacylpropane units linked with β-O-4 and β–β side-chain structures. Molecular weight of the Brauns’ lignin of vacuum-dried birch board (acetylated: 5,200 g mol⁻¹) was higher than that of the Brauns’ lignin of fresh birch wood (acetylated: 4,400 g mol⁻¹). The Brauns’ lignin of vacuum-dried wood was also clearly darker and more prominently yellow and red; between the Brauns’ lignin samples was 23.59. The differences in the molecular weights and colours suggest that the Brauns’ lignin underwent a chemical change during vacuum drying of the wood and that this change may have affected the colour of the wood.     

Grouping of <Emphasis Type="Italic">Tectona grandis</Emphasis> (L.f.) clones using wood color and stiffness

Commercial Tectona grandis plantations using clones have attracted considerable interest for lumber production in tropical regions where small areas are frequent. However, studies on wood properties are limited. Therefore, the purpose of this study is to group clones with similar wood color characteristics using the CIELab system, and mechanical resistance by dynamic stiffness (Ed) in order to obtain different types of clones for different climate and edaphic conditions. It was found that lightness (L*), yellowness (b*), redness (a*), and Ed are similar to those found for other plantation trees. These wood characteristics are significantly influenced by clone and site. Variance due to clone and site went from 31 to 53% and from 2.95 to 24.22%, respectively. Another source of variance was distance from pith, with the exception of parameter b*, which was not affected. Finally, clones were grouped (using multivariate analysis) according to color and mechanical resistance. This analysis established 4 groups by color and 5 groups by Ed. Clone clustering will allow us to choose or use clones with similar wood properties according to site and environmental conditions increasing area production and wood quality uniformity.     

Element content and pH value in American black cherry (<Emphasis Type="Italic">Prunus serotina</Emphasis>) with regard to colour changes during heartwood formation and hot water treatment

Element content and pH value in wood tissues of veneer grade logs of P. serotina Ehrh. were investigated with regard to wood colour variations, measured in the CIEL*a*b* system. The average pH value of heartwood tissue was about pH 4.0 and medium colour parameters of veneer sheets were determined at L* = 73, a* = 9.8, and b* = 23.5. Optical emission spectroscopy (ICP-OES) analyses showed differences in the element contents between two regional forest sites coming from Pennsylvania and West Virginia, USA, respectively. The latter is mainly characterised by higher variations of micro-element content in the transition zone (influencing heartwood formation) and also pH value of wood tissue, which contributes to higher variations in colour response of industrially produced veneer sheets. Investigations under industrial conditions underline the correlation between length and intensity of heat treatment in veneer production and colour development: with increasing duration and temperature of hot water treatment, veneer surfaces become darker and wood colour is intensified (ΔL = 3.6, Δa = 2.1, comparing 12 and 72 h of hot water treatment at 60°C). However, no equalisation of wood colour was achieved by modifying the treatment conditions. Artificial radiation by UV–visible light, quickly and extensively darkens and intensifies wood colour (ΔL = 16, Δa = 3.5, and Δb = 4.0 after 15 h of artificial radiation), but variations in wood colour deriving from different treatment conditions during veneer production, were not reduced.     

FeCl2处理麻栎木材化学变色工艺及变色机理研究

通过化学试剂与木材中木质素、抽提物等成分发生反应,可以改变木材的颜色,从而达到对木材表面修饰的目的。以氯化亚铁(FeCl2)为变色剂,通过浸渍的方式获得了变色麻栎(Quercus acutissima)单板。利用正交试验研究了亚铁离子的质量分数、处理温度、处理时间以及干燥温度对麻栎单板变色的影响,获得了最佳处理工艺;利用色差仪对麻栎表面的色度系数进行了测试,并通过紫外漫反射光谱和红外光谱对麻栎变色的原因进行了探究。实验结果表明:经氯化亚铁溶液处理后,麻栎单板表面变为蓝黑色,颜色均匀,纹理清晰;影响麻栎单板变色的各因素主次顺序为氯化亚铁质量分数>干燥温度>处理温度>处理时间。氯化亚铁对麻栎进行化学变色处理的优化工艺参数为:氯化亚铁质量分数为1.0%、处理时间为10 min、处理温度为80℃、干燥温度为40℃。碱抽提可以去除麻栎单板表面大部分可以与铁离子发生变色反应的木质素或酚类物质,碱抽提后的麻栎不再发生明显的变色反应;麻栎与铁离子的变色反应,主要发生在木材的酚羟基和芳香环取代基上,木材中的酚类物质与铁离子络合反应是其变色的主要原因。     

木材干燥变色的研究现状及其发展趋势

木材在干燥过程中产生的干燥变色导致木材使用价值和利用率的降低,这已经引起了国内外研究者的普遍关注。就近年来木材在干燥过程中诱发变色的研究进展予以评述,为木材干燥变色的深入研究以及木材资源的高效利用提供参考。