The Dielectric Properties of Wood V TitleProperties of the Chemicl Constitu Dielectric Anisotropy of Wood Author(s) NORMOTO, Misto; YAMADA, Tdshi Cittion Wood reserch : bulletin of the Woo University (1972), 52: 31-43 ssue Dte 1972-01-31 URL http:hdl.hndle.net243353414 Right Type Deprtmentl Bulletin Pper Textversion publisher Kyoto University
The Dielectric Properties of Wood V* On the Dielectric Properties of the Chemicl Constituents of Wood nd the Dielectric Anisotropy of Wood Misto NORMOTO** nd Tdshi YAMADA** Abstrct--n this pper, the dielectric properties of the chemicl constituents of wood were mesured over wide temperture nd frequency rnges in order to elucidte the dielectric nisotropy of wood. n the cse of cellulose nd mnnn the only one temperture dispersion ws observed. The dispersion would be due to the rottionl motions of methylol groups in the morphous regions since the dispersion did not OCcur in xyln. On the other hnd, the two dispersions were observed in lignin. The dispersion in high temperture rnge would be due to the motions of crbonyl groups to which wter molecules re ttched by hydrogen bonds, while the one in low temperture rnge would be due to the motions of methylol groups. The tempertures corresponding to the mximum dielectric loss fctor for wood in the longitudinl direction coincided with tht of cellulose nd they were in higher rnge thn those for wood in the trnsverse directions. These fcts, therefore, show tht the dielectric relxtion processes of wood in the longitudinl direction re governed by those of cellulose, while the relytion processes of wood in the trnsverse directions re considerbly influenced by those of lignin.. ntroduction t is well known tht there exist vritions in the mgnitudes of dielectric constnt of wood in the three principl directions, nd tht the mgnitude of dielectric constnt decreses generlly in the order, longitudinl, rdil, nd tngentil directions. Although mny rguments on the dielectric nisotropy of wood hve been presented, there re mny problems remining unsolved. Especilly, the reports which discussed the dielectric nisotropy in connection with the relxtion processes hve pprently not been published. n the previous pper ll, it ws reported tht the dielectric nisotropy of wood in the longitudinl nd trnsverse directions is closely relted to different modes of dipolr motions in both directions since the distribution for relxtion times in the longitudinl direction differs very much from tht in the trnsverse directions. The present pper dels with the effect of grin ngles in the three principl plnes on the dielectric properties of wood nd the dielectric properties of the chemicl constituents of wood in order to elucidte * Previous Pper, Wood Reserch, No. 51, 12 (1971). ** Division of Wood Physics. - 31- the dielectric nisotropy of wood in
WOOD RESEARCH No. 52 (1972) more detil.. Experimentl Wood (HOONOK, HNOK nd Lwson Cypress) nd the chemicl constituents of wood (cellulose, mnnn, xyln, nd lignin) were used s smples. The chrcteristics of the smples re shown in Tble 1. The mesurements t oven-dried condition nd low moisture content were performed over phosphorus pentoxide nd silic gel, respectively. The instruments nd the methods of mesurement were ll the sme to the ones lredy refered to in the previous ppers 2,3l. The smple disks of the chemicl constituents of wood were pressed to 20 mm dimeter nd bout 1 mm thickness under the pressure. The mesurements of dielectric constnt nd of loss fctor were mde over the frequency rnge from 300 Hz to 9.4 GHz nd over the temperture rnge from -70 to 80 C. Specimen Tble 1. HOONOK (Mgnoli obovt THUNB.) HNOK (Chmecypris obtus ENDL.) Lwson Cypress (Cupressus lwsonin MURR.) Cellulose (Merk) Mnnn (devil's tongue) Beech xyln Beech MWL Bmboo MWL The chrcteristics of the smples. Moisture content Specific grvity (%) 0.51 11.3 0.-39 8.2 1.25 1.19 1.28 0 1. 26 0 1.21 1.21 0 0 0 0.84 0 0.90 Direction Three principl plnes Three principl plnes LR plne. Results nd Discussion 3-1. The effect of grin ngle on the dielectric properties of wood As mentioned in the introduction, in the three principl directions the mgnitude of dielectric constnt decreses generlly in the order, longitudinl (L), rdil (R), tngentil (T) directions. KRONER et l. 4l nd NAKAT0 5 ) reported tht the dielectric nisotropy is minly cused by the mcroscopic structures of wood, wheres SKAAR suggested tht the nisotropy my be scribed to the moleculr structures of cell w1l 6 ). n the previous ppero, it ws reported tht the dielectric nisotropy is cused only by the mcroscopic structures in very high frequency region in which the deformtion polriztions contribute to dielectric constnt, while the nisotropy is cused by the moleculr structures of wood substnce s - 32-
NORMOTO, YAMADA: The Dielectric Properties of Wood well s the mcroscopic structures of wood cell becuse the mgnitude of dielectric constnt in L-direction is greter thn tht in R- or T- direction. The grin ngle dependences of the dielectric constnt nd loss fctor of wood in LR, LT nd RT plnes re discussed in this section. The report which dels with the effect of grin ngle on the dielectric pro perties of wood hs not hitherto been known. ngle on dielectric constnt (' (8) HOONOK nd over-dried HNOK Figs. 1'"'-'4 show the effect of grin nd dielectric loss fctor ( (8) of ir dried in the three principl plnes t 10 khz nd 7 LT plne LR plne RT plne 6 f- 5 > - \.l. 4 eq( ' f- 3 l- f- 4-eq( 2) 1 1 2-90 60 30 0 0 30 60 9090 60 30 0 T L L R R T 8 (in degrees) Fig. 1. The effect of grin ngle on dielectric constnt of HOONOK. 23 C, 10 khz, 11.3 %m.c. 1.00 LT plne LR plne RT plne 0.75 "w 050 0 0.25 0 0 90 60 30 0 0 30 60 90 90 60 30 \ 0 T L L R R T 8 ( in degrees) Fig. 2. The effect of grin ngle on dielectric loss fctor of HOONOK. 23 C, 10 khz, 11.3 %m.c. - 33-
WOOD RESEARCH No. 52 (1972) 4.---------, 2.0 0.28,0 LT plne LR plne RT plne 0 \ 0-3 \ \ 0 eq.( ) \ o..1.j 2 0 o - o o 0 \..) \ -\..l. 1.8 \ 0.20 " o \ eq.(z) V \.\ r 60 30, 0030 60 909060 L L R R (8) (in degrees) 30 Fig. 3. The effect of grin ngle on dielectric constnt of HNOK. 30 C, 10 khz, 0 %m.c. o T \ \ 1.6 0 30 60 90 0. 12 (8) (in degrees) Fig. 4. Dielectric constnt nd dielectric loss fctor of Lwson Cypress for grin ngles in LR plne. 20 C, 9.4 GHz, 8.2 %m.c. those of ir-dried Lwson Cypress in LR plne t 9.4 GHz, respectively. The vlues of E' (B) nd E" (B) for HOONOK in LR nd LT plnes t 10 khz decresed with incresing grin ngle except smll grin ngles, wheres those for Lwson Cypress t 9.4 GHz in LR plne decresed monotonously in mgnitude s grin ngle incresed. n RT plne it seemed tht E' (B) nd E" (B) decresed slightly in mgnitude with decresing grin ngle. The following empiricl epution held for E'(B) in LR nd LT plnes. E' (B) = (E' (0) -E'( ~ ))cos 2B+E'( ~ ), (1) rc 0<B<2' where E' (0) is the dielectric constnt in L-direction nd E' (rc2) is tht in R- or T-direction. the empiricl equtions. The solid lines in Figs. 1 nd 4 represent the curves clculted from The curves greed well with the empiricl vlues, especilly with vlues t very high frequency. On the other hnd, the theoreticl eqution for E' (B) in LR nd LT plnes cn be obtined by pplying the theory7) on the dielectric constnt for lmellr mixture consisting of two kinds of dielectrics to wood. (+ l)et' Et' cos 2 B+ (Et' -) (+ 1) sin 2 B' = :1 (Et' - 1), - 34- (2)
N ORMOTO, YAMADA: The Dielectric Properties of Wood where r is the specific grvity, rl the specific grvity of wood substnce, nd f]' the dielectric constnt of wood substnce. n the eqution (2), it is ssumed tht the dielectric constnts in the longitudinl nd trnsverse directions cn be represented by WENER'S equtions. The broken lines in Figs. 1 nd 4 represent the theoreticl curves clculted by the eqution (2). Although the clculted curves did not gree well with the experimentl vlues, the curves showed qulittively tht the vlue of f' (8) decreses with incresing grin ngle even in the region of smll grin ngle. As mentioned bove, in the low frequency region in which only the orienttion polriztion contributes to loss fctor, f!! (8) versus 8 curve hd mximum in the region of smll grin ngle, while in very high frequency region in which the deformtion polriztion contributes minly to dielectric constnt the vlues of f'(8) decresed monotonously with incresing grin ngle. These fcts show tht the dielectric nisotropy of wood substnce would be cused by the orienttion polriztion due to the rottionl motions of the dipoles, nd tht the mgnitude of dielectric constnt of wood substnce tkes its mximum vlue t the smll grin ngle. Figs. 5 nd 6 show f' versus frequency curves nd f' versus temperture curves for oven-dried HOONOK t the three different grin ngles in LT plne, 2.2 2.5 2.0 1.8 2.0 1.6 345 6 Qog f (f in Hz) Fig. 5. Dielectric constnt of oven-dried HOONOK for three grin ngles in LT plne s function of frequency t -70 C. 1.5-50 o Fig. 6. Dielectric constnt of oven-dried HOONOK for three grin ngles in LT plne s function of temperture t 100 khz. - 35-
WOOD RESEARCH No. 52 (1972) 0.075 f- 0.10 ::: 0050f- W 0.05 3 4 5 gog f (f in Hz) Fig. 7. Dielectric loss fctor of oven-dried HOONOK for three grin ngles in LT plne s function of frequency t -70 C. e=90 (T) 6 0'-------1.------.1..--------' -50 0 T (OC) Fig. 8. Dielectric loss fctor of oven-dried HOONOK for three grin ngles in LT plne s function of temperture t 100 khz. respectively. E' decresed in mgnitude with incresing frequency nd with decresing temperture. Figs. 7 nd 8 show Ell versus frequency curves nd Ell versus temperture curves for oven-dried HOONOK t the three different grin ngles in LT plne, respectively. The frequency nd temperture corresponding to f.1 mximum shifted to higher frequency nd lower temperture rnges with incresing grin ngle, respectively. From these results, it is evident tht the dielectric nisotropy of wood depends on the mcroscopic structures of wood s well s the relxtion process of dipoles. 3-2. The dielectric properties of the chemicl constituents of wood The dielectric properties of the chemicl constituents of wood re discussed in this section in order to explin the nisotropy of the dielectric relxtion process of wood in the longitudinl nd trnsverse directions. dielectric properties of cellulose hve been presented. on the dielectric properties of the hemicelluloses nd lignin. Fig. 9 shows the results of Ell s function of temperture t severl frequencies for dry cellulose. frequency nd temperture rnges studied. Mny reports on the However, there is no report The only one bsorption ws observed within the The temperture corresponding to the loss mximum fm shifted to lower temperture region nd the vlue of 1m decresed with decresing frequency. Fig. 10 shows the results of Ell s function of frequency t severl tempertures for dry cellulose. The frequency corresponding to Ellmx shifted to lower frequency nd the vlue of E"mx decresed with - 36-
NORMOTO, YAMADA: The Dielectric Properties of Wood 0.2 02 0.1 YJKHz 10KHz -----o::=r:=:.~ 3 KH Z \--KHZ '-- 300Hz OL.- --L ---l. ---' -50 0 T (Oe) Fig. 9. Dielectric loss fctor of cellulose s function of temperture t respective frequencies. 01 3 4 5 6 ~og f (fin Hz) -43-58 -70 OL----L--l...------L.l...-_~ 2 Fig. 10. Dielectric loss fctor of cellulose s function of frequency t respective tempertures. 7 decresing temperture. ije, the logrithm of the frequency n order to determine the energy of pprent ctivtion plotted ginst the reciprocl of bsolute temperture lit. corresponding to loss mximum log fm ws The logfm-lit plots for cellulose gve the stright line nd the vlue of ije clculted from the slope of this line ws bout 10 kclmole. The existence of the dielectric bsorption in cellulose hs been shown by mny uthors S - 10 ). SHDA et 1. 9) mesured the dielectric properties of the three cellulose fibers nd reported tht the dipoles in the morphous region nd on the surfce of the crystllite provide the chief contribution to this dispersion since the order of the mgnitude of (Eo' - Ec') for the smples prllels tht of the ccesibility of the smples. MKHALOV et 1. 10 ) investigted the dielectric relxtions of cellulose nd its derivtives nd suggested tht the dispersion my be due to the movement of methylol groups in the less ordered zones of the polymers. Fig. 11 shows the results of E" s function of temperture t vrious frequencies for dry mnnn. The loss peks t respective frequencies for mnnn were lmost identicl in the loction with those of cellulose. Hence, there ws no gret difference between the vlues of the ctivtion energy for cellulose nd mnnn. Fig. 12 shows the results of E" s function of frequency t severl tempertures for dry mnnn. Fig. 13 shows E" versus temperture curves t respective frequencies for dry beech xyln nd Fig. 14 shows E" versus frequency curves t respective tempertures for dry beech xyln. those for cellulose nd mnnn. The behviors of E" for xyln differed very much from The bsorption occured in cellulose nd mnnn - 37-
WOOD RESEARCH No. 52 (1972) 0.15 0.16 10ce -5 MHz 28 0.12-25 ~O.O ~ \l.j -40 0.08-69 0.05 0.04 01-------L------.1..--------' -50 0 T (OC) Fig. 11. Dielectric loss fctor of mnnn s function of temperture t respective frequencies. 2 3 4 5 6 Qog f (f in Hz) Fig. 12. Dielectric loss fctor of mnnn s function of frequency t respective ternpertures. 0.100r----------------. 300Hz 0.075 0.075, \lj 0.050 0.025 1KHz 3KHz MHz 10KHZ ----.::e-::::.-::::je::; ~~300KHz 100 KHZ 30KHz ~0.050 0.025 0L...------L------.1..---.,------ -50 0 T (OC) 3 4 5 Qog f (f in Hz) 6 Fig. 13. Dielectric loss fctor of beech xyln s function of temperture t respective frequencies. Fig. 14. Dielectric loss fctor of beech xyln s function of frequency t respective tempertures. did not occur in xyln. t seems, therefore, tht the relxtion process ppered in cellulose nd mnnn would be due to the rottionl motions of metylol groups. Fi.gs. 15 nd 16 show E" versus temperture curves t vrious frequencies for dry milled wood lignin (MWL) nd for MWL contining smll mount of. wter, respectively. As is evident from the figures, the two bsorptions were observed, lthough the mgnitude of f" ws very smll compred with those of cellulose - 38-
NORMOTO, YAMADA: The Dielectric Properties of Wood o 0 006 0.02L- L- --:- --::'::-- ~ -50 50 Fig. 15. Dielectric loss fctor of beech MWL s function of temperture t respective frequencies. 0100.------------------, 0075 0075 _o----c>---..._~ MHz ~OO50 ~ u; 00::0 0025 0025 3 KHz 300Hz OL-----'-------'---------' -50 0 ~ Fig. 16. Dielectric loss fctor of beech MWL s function of temperture t respective frequencies. 0.84 %m.c. OL.------l.------.L..--------' -50 0 50 T("C ) Fig. 17. Dielectric loss fctor of beech MWL nd bmboo MWL s function of temperture t 300 Hz. -0- beech MWL, 0 %m.c. -e- bmboo MWL, 0 %m.c. 0 beech MWL, 0.84 %m.c.... bmboo MWL, 0.90 %m.c. nd mnnn. For convenience, the bsorptions re clled the low temperture bsorption nd the high temperture one, respectively. The mgnitude of the low temperture bsorption ws greter thn tht of the high temperture one. When the results of Fig. 15 is compred with those in Fig. 16, it is evident tht the high temperture bsorption increses in mgnitude by dsorption of smll mount of wter, wheres the low temperture bsorption is not influenced remrkbly by dsorption of smll mount of wter. n Fig. 17 (:.11 for beech nd bmboo MWLs s function of temperture t 300 Hz is shown. As is shown in the figure, it is - 39-
WOOD RESEARCH No. 52 (1972) 006e ~T'C ~~~t~'9 ~~~t~7 _ 002 ~006t~-O ~~~t ~-28 002 0.06 ~-69 0.02 006 - ~~~t ~~~t 002 ~ J.J 006 - ~~~t 0.02 006-0.02 ~-12 ~-29 ~-46 ~o-o-69 2 3 4 5 6 7. og f (f in Hz) Fig. 18. Dielectric loss fctor of beech MWL s function of frequency t respective tempertures. 0 %m.c. 2 3 4 5 6 7 fog f (f in Hz) Fig. 19. Dielectric loss fctor of beech MWL s function of frequency t respective tempertures. 0.84 %m.c. evident tht the high temperture bsorption is influenced remrkbly by dsorption of smll mount of wter. Figs. 18 nd 19 show Ell s function of frequency for beech MWL t 0% nd 0.84% moisture content, respectively. Figs. 20 nd 21 show those for bmboo MWL t 0% nd 0.90% moisture content, respectively. The two frequency bsorptions were observed nd for convenience the bsorptions re clled the high frequency bsorption nd the low frequency one, respectively. The two loss peks shifted to lower frequency region with decresing temperture nd the mgnitude of the bsorptions decresed with decresing temperture. The low frequency bsorption incresed remrkbly in mgnitude by dsorption of smll mount of wter, while the high frequency one ws not influenced by it. n the cse of lignin it seems tht the motions of the dipoles such s OH, OCH 3, CO nd CH 2 0H groups re die1ectriclly ctive. However, since it is reported tht from the results of the dielectric mesurements for metylcellu10se nd cellu10setricette the relxtion processes due to the motions of OH nd OCH 3 groups do not occur within the frequency nd temperture rnges studied O ), the motions of two dipoles, CO nd CH 2 0H groups, cn contribute eventully to dielectric loss. Furthermore, the mesurement of the dielectric properties of nylon nd polyethylene terephth1te W showed tht CO groups cn only contribute to - 40-
NORMOTO, YAMADA: The Dielectric Properties of Wood 010r-------------, 0.06 ~00C 0.06 ~~~[~-8 ~:[~-24 ~-18 ~v ~.~~t ~-40 ~~~t~-56 ~:~ ~~-~~-70 002 ~-37 ~-47 ~-68 2 345 6 7 P09 ; : fin Hz) 2! 3 1! 4 5 ~ 09 f (f in Hz ) [ 6 7 Fig. 20. Dielectric loss fctor of bmboo MWL s funclion of frequency t respective tempertures. 0 %m.c. Fig. 21. Dielectric loss fctor of bmboo MWL s function of frequency t respec tive tempertures. 0.90 %m.c. dielectric loss by the dsorption of wter, nd therefore this dielectric loss is due to the motion of CO groups to which wter molecules re ttched by hydrogen bonds. The high temperture bsorption in lignin would be due to the motions of CO-H 2 0 complexes, since this relxtion process hs sme chrcters s tht of nylon nd polyethylene terephthlte. Hence, it my be concluded tht the high temperture bsorption is ttributed to the motion of CH 2 0H groups. As the bsorption due to CH 2 0H groups of lignin occurs in lower temperture region compred with tht of cellulose nd mnnn, CH 2 0H groups in lignin is more mobile thn tht in cellulose nd mnnn. Fig. 22 shows E" s function of frequency for HOONOK in three principl directions, cellulose, nd beech MWL t -58 C. As is evident from the figure, the nisotropy in the relxtion process could not be observed in the trnsverse directions. The frequency corresponding to the loss pek 1m for HOONOK in L direction coincided with tht of cellulose nd tht it ws in lower frequency rnge thn those in R- nd T-directions by one decde. Therefore, it seems tht the di electric properties of wood in the trnsverse directions re considerbly influenced by those of lignin, since 1m for MWL ws in higher frequency region thn tht - 41-
WOOD RESEARCH No. 52 (1972) 015 0.10 Cellulose 020 HOONOK (L) w 010 cellulose HOONOK (Ll HOONOK ~ (R)~ - (T) 2 3 4 log f (f in Hz) Fig. 22. Dielectric loss fctor vs. frequency curves for HOONOK, cellulose nd beech MWL t -58 C. 5 T ("C) ech MWL HOONOK (T) 0 50 Fig. 23. Dielectric loss fctor of HOONOK, cellulose nd beech MWL s function of temperture t 300 khz. of cellulose. Fig. 23 shows f.!! s function of temperture for HOONOK in T nd L-directions, cellulose, nd beech MWL t 300 khz. The behvior of f.!! for HOONOK in L-direction ws similr to tht of cellulose, wheres the behvior of f.!! for HOONOK in T-direction ws considerbly influenced by tht of lignin. From the results in sections 3-1 nd 3-2, it my be concluded tht the dielectric properties of wood re governed by those of cellulose nd mnnn in the longitudinl direction nd re considerbly influenced by those of lignin in the trnsverse directions. Furthermore, it my be concluded tht there re two stble orienttionl positions long the directions of microfibrils for ech CH20H dipole of cellulose in the disordered region. Acknowledgement The uthors wish to thnk Prof. T. HGUCH, Dr. A. SATO, nd Mr. E. MAE KA W A of our institute for their helpful dvice nd for supplying the smples. References 1) M. NORMOTO nd T. YAMADA, Wood Reserch, No. 51, 12 (1971). 2) M. NORMOTO nd T. YAMADA, J. Jpn Wood Res. Soc., 15, 56 (1969). 3) M. NORMOTO nd T. YAMADA, Wood Reserch, No. 46, 1 (1969). 4) K. KRONER und L. PUNGS, Holzforsch., 6, 13 (1952). 5) K. NAKATO nd S. KADTA, J. Jpnese Forestry Soc., 36, 95 (1954). 6) C. SKAAR, New York Stte College of Forestry, Technicl Publiction, No. 69, 6 (1948). - 42-
NORMOTO, YAMADA: The Dielectric Properties of Wood 7) O. WENER, Phys. Z., 5, 332 (1904). 8) W. TRAPP und L. PUNGS, Ho17forsch, 10, 144 (1956). 9) Y. SHDA et., J. Appi. Polymer Sci., 1, 227 (1959). 10) G. P. MKHALOV et., Polymer Sci. USSR, 11, 628 (1969). 11) N. G.MCCRUM, B. E. READ nd G. WLLAMS, Anelstic nd Dielectric Effects in Polymeric Solids, John Wiley & Sons, London-New York-Sydney, (1967). - 43-