Induced Discoloration of Buerger Maple during Drying Process

Induced Discoloration of Buerger Maple during Drying ProcessGao JianminZhang BiguangChang JianminCollege of Material Sciences and Technology, Beijing Forestry University, Beiing 100083, P. R. ChinaABSTRACT Buerger maple (Liquidambar formosana Hance) is a kind of wood that is easily discolored. This paper tries toobtain satisfactory color and a broad prospect in the utilization of buerger maple by induced discoloration. The authors analyze themechanism of induced discoloration of buerger maple based on the analysis of visual physical parameter, the infrared spectrum (IRS)and the scanning electron microscope (SEM) under different drying conditions. The result shows that it is feasible to inducediscoloration during the drying process. The wood color tends to be red and fuscous during inducing discoloration of buerger maple.The induced discoloration mechanism is: 1) the high temperature and humidity accelerates the oxidation reaction of polyphenol,leuco- fancy pigment and tannin, which changes the wood color to red; 2) the hydroxy ( OH) is oxidized and the carbonyl( C O),carboxyl ( COOH), ester and ketone groups form during the high temperature steaming, which results in wood piece discoloration.KEY WORDS buerger maple, drying process, induced discoloration1 Introductionchromophoric groups and the auxochromic group ofColor is one of the indexes in evaluating the woodwood, according to different chemical componentsurface property and quality, and affects its application.extractives.Recently, there have been reports on wood inducedIn order to obtain a beautiful color and raise itsdiscoloration both in China and abroad. Li and Liu etcapplication value, many engineers and technicians(1998) conducted the research effects of heatinghave conducted extensive research and practical workon the dye of wood (Yu 1999), surface decoration oftreatment on the coloration of different wood species.wood products and wood based panel, etc. Wood is aThe Japanese researcher Matsuyama (1985) carried)ut research on wood discoloration， color tonekind of material that is readily discolored, caused bystorage environment and processing conditions.adjustment and tinting under high pressure.Sshlstedt-Persson(2003) studied discolorationDiscoloration is regarded as preliminary behavior ofrot, which is considered as a kind of defect in timberreaction of the succus and thermal extractives of thepineand spruce.McCurdy (2003) researchedprocessing (Li 1998). Up to now much attention hasbeen paid to the discoloration mechanism anddiscoloration on the sapwood veneer of radiate pinetechniques of anti-discoloration. Wood stain isunder different dry schedules. Yeo and Smith (2003)complex physical and chemical process. Because ofstudied the effects of temperature and moisturevarieties of factors related to wood discoloration,content during drying on discoloration of mapleveneer. These research results supported the study ondiscolorationshavedifferent effects on woodapplication. In fact， some physical and chemicalwood induced discoloration. Now, China faces theshortage of quality wood resources, and it has becomediscolorations do not have any negative influence onthe physical, mechanical and practical properties; formore and more important to sufficiently utilize theexample, the color of Betula costata after highlimited wood resource， to prevent the timbertemperature drying is similar to that of cherry woodprocessing defect and to promote wood property and(Liu 1994). If the wood stain is considered as a kind ofquality. The study on wood induced discoloration is awood dyeing process, a new research direction fornew field in wood science and technology. It has wide,wood science and technology may be developed.profound and practical significance in the utilizationWood discoloration can be well-controlled to make aof limited wood resources.Buerger maple (L. formosana Hance) is a kind ofbeautiful color without using dyestuff and woodrotting in the coloring process. Such research is calledfast-growing wood in south China and has arwood induced discoloration. Theinducedexiguous structure with a light color and beautifulgrain. But it cannot be used sufficiently because itdiscoloration is a process that giveswooddiscolors and中国煤化工It is verywell-proportioned and beautiful coloration throughdifficult to prec N M H discolorationphysical and chemical methods inducing the activityHof chemical substances in wood, modulatingduring the dryIng" process Decause 1l will begin to"Author for correspondence. Email: gaojm@ bjfu.edu.cnForestry Studies in China, 6(2): 50-55.Gao Jianmin et al: Induced Discoloration of Buerger Maple during Drying Process51discolor when relative humidity reaches to 50%. IfAutonomous Region. The length of test sample isbuerger maple has an ideal color after drying, it willabout 1 m, and the diameter is 30- -50 cm, both endsbe used more widely and practically.were sealed with wax. Arriving in laboratory, the2 Materials and experimental devicessamples were reserved in a freezer.The properties of buerger maple were tested2.1 Materialsaccording to the method of GB 1929-80, test resultsTest wood is taken from Fuhe,Luoding, .are shown in Table 1.Guangdong Province and Hezhou, Guangxi ZhuangTABLE 1 Results of basic properties of buerger mapleTest Number of DensityNatural dryCoefficient of shrinkageShrinkWood speciestimes_ samples (g cm 3) density l(g- cm 3) Tangential section Radial section VolumedifferenceBuerger maple26[0.5630.6520.3930.1660.5462.367600.6380.3650.1830.5381.995from Guangxi2.2 Experimental devicesuniformly.The experiments were carried out in the Wood生s0[Drying Lab of Beijing Forestry University. The majordevices include electrical heating blast drier(101C-1B); conditioner(302A); .automaticchromatism meter (TC-PIIG); electronic balance;50357911511923252Time /hSEM (Hitatch S-520); IR (FTS-20).- 40°C←60°C + 80C3 Experimental process and discussion✧100°C 一120°C - 140°C3.1 The inducing discoloration of buerger maple+ 160°Cunder different drying conditionsFIGURE 1 Discoloration of buerger maple at differentThe test samples are prepared in the dimension oftemperatures200mmx40mmX20mmandarepreservedinthe3.1.2 Discoloration of buerger maple underfreezer after they are weighed. One side is chosen asdifferent temperatures and humiditiesthe test side, and the integrated chromatism ( E) isExperiment is carried out in conditioner 302A, andtaken from the three test spots on it. The samples arethe results are shown in Figs. 2- 4。put into the test device, andE is taken for each hourwith automatic chromatism meter. If E and theweight of the sample keep the same value within twosuccessive tests, the experiment will be terminated.31.3????.??????The curve is drawn according to the changes of F一φ=50%→-φ=70%←φ=90%with the time.巴01357911315171921232527 .3.1.he discoloration of buerger maple inTime/different temperatureFIGURE 2 Discoloration of buerger maple under'he discoloration experiment of buerger mapledifferent humidities at40 Cat different temperatures is carried out in the electricalheating blast drier 101C-1B， and the effects o1humidity on wood discoloration is excluded in罗s0[experiment. The result is shown in Fig. 1.Fig.1 shows the discoloration of buerger maple at+φ=50%◆φ=70%different temperatures. We find that buerger maple804335911315171921232527starts to discolor obviously at 80°C， and with the中国煤化工increase of the temperature, the value of E increasesand the wood discolors quickly, but it does not changeFIGURE 3MH.CNMHGapleunderditferent humidities at 60飞.Forestry Studies in China, Vol.6, No.2, 200452experiment ended when the chromatism unchanged.罗50[The average chromatism curve is drawn according to月30test resuts. The discoloration results of buerger maple- + φ=50%←φ= 70%are shown in Fig.6.04357913151719212252Time hFIGURE4Discoloration of buerger maple underdifferent humidities at 80By observing the experiment process: 1) Humiditplays a more important role than temperature duringthe discoloration of buerger maple as Fig. 2 shows.FIGURE5 Experimental device of high temperatureThe color sample starts to change whent=40 C andsteaming0 = 50% which indicates; it difficult to prevent1: thermometer; 2: exhaust hole; 3: wood sample; 4: water enter;buerger maple from discoloration in drying; 2) Highs: water; 6: temperature adjuster: 7: electrical resource; 8:temperature and humidity can induce the buergerelectrical heater; 9: indicatior of water level; 10: netmaple to discolor. Fig. 4 shows that the inducingdiscoloration efeet is ideal when t=80 C and 0=g 5070%. The surface of wood sample changes to red and共#the inside of wood is pink showing that the condition+ Sample1-■ - Sample2- Sample3of inducing discoloration is high temperature and82012345678910111213humidity.The testing result shows that the value ofchromatism quickly grows with the increase ofFIGURE 6 The inducing discoloration of buergerhumidity at a constant temperature, and the color ismaple under high temperature steaminguniform. The humidity plays an important role more3.2.3 Analysis of inducing discoloration resultsnan the temperature during the discoloration ofThe analysis of experimental process and testbuerger maple. Because it is difficult to achieve highresults show that: 1) the value of chromatism ( E)temperature under the high humidity condition, thevaries quickly at the high temperature (96-99 C)test of inducing discoloration of buerger maple isinducing discoloration of buerger maple.Thecaught out with the high temperature steaming.maximum range of chromatism reaches 20, and the3.2 The inducing discoloration of buerger maplevariation curves are considerably smooth; 2) Woodin high temperature steaming pretreatmentcolor changes red in surface and pink in inside, while3.2.1 Experimental devicethe color is uniform and bright. This result shows thatThe experiment was performed in the experimentalthe high temperature (96 99 C) steam has thedevice of high temperature steaming, which consistsoptimum inducing discoloration effect, because highof boiler, heater, temperature adjuster, indicator oftemperature steam can make the water-solublewater level, thermometer, electrical resource, and thechromatism substance (such as polyatomic phenol,net. The net in the inter space of boiler is used to layleuco-fancy pigment and tannin) accelerate difusionthe wood sample. The temperature adjuster is used toand oxydic reaction.control the temperature of water in boiler. The3.3 Analysis of visual physics parametersexperimental device is shown in Fig.5.3.3.1 Visual physics parameters3.2.2 Experimental processThe standard chromatility system issued in 1976 byPut the wood samples on the net, to fll the waterIE (L'ab) is adopted to appraise the woodinto the boiler, keep the water level 50 mm apart fromcoloration accurately and quantitatively (Liu 1994).the net. The boiler is covered, while water is heated,L: lightness, where the entire white object is as 100,the temperature raises to 99The temperature ofand the entire black object is as 0;water is controlled within the range from 96 to 99a°: red or green index. if a' is a positive value andand sufficient steam insured in the top of boiler.increases, it e中国煤化工red, if a isThe average chromatism and discoloration werenegative value|YHCNMHGecolortendsmeasured every hour in the experiment. Theto green;Gao Jianmin et al: Induced Discoloration of Buerger Maple during Drying Process53b : yellow or blue index,if b" is a positive value andfinished. The results are shown in Figs.7 and 8.increases, it means the color tends to yellow, if b" is .3.3.3 Results and discussionnegative value and decreases, it means the color tendsThe experimental results show that the colorto blue.hue-angle Ag increases with the decrease of the redAg: color hue-angle, Ag° = arctan (b"/a" ) (Liuor green index a', the changing trend to red is very1994).significant; the color hue-angle Ag decreases with theIt is evident that the inducing discoloration effect isdecline of the yellow or blue index b，the changingoptimum with the high temperature and humidity ortrend to blue is very significant. This result indicatesthe high temperature steam pretreatment of buergerthat the red tonality of buerger maple increases, andmaple, through the research of drying process anthe yellow tonality decreases during the inducinghigh temperature steaming pretreatment to inducediscoloration under high temperature and humidity,discoloration. Therefore, the visual physics parameterespecially in high temperature (96- 99 ) steamingis analyzed during the discoloration.pretreatment. In other words, the variation tendency of复68}◆wood color trends to red and fuscous colors during theinducing discoloration of buerger maple.58一3.4 The analysis of the infrared spectrum (IRS) of53-discolored buerger mapleBuerger maple samples discolored under4301different conditions are grinded into the wood powerRed or green index aof 200 mesh. The samples are analyzed with IRS afterthe wood power is dried under low-temperature and6vacuum condition. Results are shown in Figs. 9 -11.57.100 [! 52-9080号4714 12023262970Yellow or blue index b*60FIGURE7The variation curve ofAg witha andb of50buerger maple in high temperature steaming3070-1 S00 1001300 200 200 3000 3500 400 430065}60-Wavenumber /cm'FIGURE 9Infrared spectrum (IRS) of buerger maple (t55古一方-891011=40 C)Red or green index a"婴，706st4016方18192021k 30Yellw or blue index b*20FIGURE 8 The variation curve of Ag witha" andb" ofbuerger maple(t=80 andO= 70%)0 500 1000 1500 2000 23500 10000 3500 4000 4500Wavenumber /cm 13.3.2 Experimental processThe integrated chromatism ( E) is tested by theFIGURE 10Infrared spectrum (IRS) of buergerautomatic chromatism meter during the inducingmaple under the condition of saturated streamdiscoloration. The visual physics parameters (L*, a*Fig. 9 is the infrared cnectrum_ (IRS) of theand b ) are obtained at same time. The color hue-angleun-discolored中国煤化工of samplesAg is calculated according to the visual physicaltreated with thqMYHCNMHGg,andunderparameters and the curve of the color hue-angle Ag ishigh temperature and humidity condition varies.54Forestry Studies in China, Vol.6, No.2, 2004greatly. The absorbing peaks corresponding to thebuerger maple is not infected by epiphyte in thespecial groups are different. TheOH decreasesinduced discoloration.while the C O，COOH, esters and ketonesincreases. That is to say, treated with the hightemperature steaming, under high temperature anhumidityconditions,OHisoxidizedto C O， COOH, esters and ketones, which makethe sample discolor.100厂90上05050 t40500 00015002000 29003003900 4000 4500Wavenumber /em~FIGURE 11Infrared spectrum (IRS) of buerger maple (t=80 C and 0= 70%)FIGURE 12 The s: scanning electron microscope (SEM)3.5 SEM of the discolored buerger maplepicture of discolored buerger maple sampleThe infection of sample can be found through theanalyses of SEM of buerger maple. The discoloredThe induced discoloration mechanism of buergersamples under different conditions are cut into 5 mmmaple during the dryingprocess is: 1) The highx 5 mm x 2 mm, dried in the desiccator. After the testtemperature and humidity accelerate the oxidationside is recut and gilded, the surface is observed underreaction of the water-solubility material of buergerSEM (Fig.12).maple (polyatomic phenol, leuco-fancy pigment andAs is shown in Fig. 12, 1) Mycelium is not found,tannin etC.), and the wood becomes red color; 2) Thewhich means that buerger maple is not infected byhydroxy ( OH) is oxidized and transmitted to theepiphyte during induced discoloration; 2) Crystal iscarbonyl( C O), carboxyl ( COOH), ester, ketonenot found or evidenced in the pictures after inducingand so on during the high temperature steamingdiscoloration. This phenomenon shows that thpretreatment, and the discoloration occurs in buergerorganic crystal disappeares because the crystal ismaple.concerned with the chemical reaction in the inducinghe wood drying technology for buerger maple todiscoloration of buerger maple.be induced discoloration is as follows: buerger mapleis treated immediately by inducing it to discolor with4 Conclusionsthe high temperature steaming pretreatment afterAccording to the experimental results of inducedbeing fallen. And then buerger maple is dried. Sodiscoloration of buerger maple, we can see that it isbuerger maple's color will become even and sightlyfeasible to induce buerger maple discoloration duringred.the drying process, and it may transmit to red or pinkLiterature citedcolor. Secondly, the conditions of buerger maplediscoloration are the high temperature and humidityLi J, Liu Y X. 1998. Coating and physic visual appraise ofand the latter plays a more important role than thewood (in Chinese). Harbin: Northeast Forestry Universityformer during buerger maple discoloration. The highPresstemperature steaming pretreatment is the optimalLi J 1994. Science of wood (in Chinese). Harbin: Northeastfactor to induce discoloration. Third, the variation ofForestry University Presswood color trends to red and fuscous colors accordingLi J. 1998. Woo中国煤化工: Northeastto the analysis of visual physical parameters duringForestry Univerinducing discoloration of buerger maple. Finally, theLiu Y X. 1994YHC N M H Gvironment (in.Gao Jianmin et al: Induced Discoloration of Buerger Maple during Drying Process55Chinese). Harbin: Northeast Forestry University PressTreatment of extractives and sap from pine and spruce. 8thMatsuyama M 1981. Discoloration and mix coloration ofInternational IUFRO Wood Drying Conference. Brasov,Sugi sap wood (in Japanese). Wood Industry. 36(1):8- 13RomaniaMatsuyama M.1985. Mix coloration of Sugi sap wood fromYeo H, Smith W B.2003. Effect of temperature and moistureYoshino (in Japanese). Wood Industry. 40 (9): 408- -413content on the discoloration of hard maple lumber. 8thMcCurdy M.2003. Measurement of colour development inPinus radiate sapwood boards during at various schedules.8th Intermational IUFRO Wood Drying Conference. Brasov,Yu z M.1999. Study on wood dye and pervading mechanismof dying solution (in Chinese). Doctor' s thesis. Beijing:Mu J. 1999. Study on discoloring of buerger maple duringBeijing Forestry Universitydrying process (in Chinese). Master' s thesis. Bejing: BeijingForestry University(Received January 20, 2004 Accepted March 15, 2004)Sshlstedt-Persson M. 2003. Colour responses to heat -中国煤化工MHCNMH G.