Journal of Scientific & Industrial Research Vol. 63, February 2004, pp. 125- 133

Morphological , anatomical and chemical characteristics of Leucaena leucocephala and its impact on pulp and paper making properties

R S Malik , Dharm Dutt' , C H Tyagi , A K Jindal and L K Lakharia

Department of Paper Technology, Indian Inst itute of Technology Roorkee, Saharan pur C llnpus, Saharanpur 24700 I

Received: 30 June 2003; accepted: 02 December 2003

. SC;lrcity of cellulosic fibrou s raw material s in India has compelled to search for fas t growing and high pu lp yielding trees. which can he grown In all types of soIl s like semi and arid regions. Anatomical, morphologica l, and chemical studies of L. 1(, IICOCl'lllwlll

show that It can sustain an ade4lIate supply of raw mate ri als for the pu lp and paper industry. With some drawbacb , like the presence 01 Ca or Mg oxalates L. lellcoc('lJ/wla has porous wood structures, longer fibre than that of other hard woods, hi\.!h holocellulose and a.-cellu lose and low lignin content wi th xylan type hemicellulose. Anatomy, morphology, and proximate che~llical analysis of L. lell["()cel llwia arc directly rellected to good quality and quantity of pulp, shorter cooking cyc le and chemical dosing.

Keywnrds : L l' IIC(/{! )J({ lellcacepilala, Pulp and paper

Introduction Indian pulp and paper industry is faci ng an acu te short­

age of good qual ity of wood fibre and has to spend heav i Iy on imported wood fibe r each year. If they do not over­come this seri olls lack of domestic wood fibre as well as revamp the obso lete paper machine and improve the qual­ity of products to mach imports then the pulp and paper industry will stagnate and dec line in competiti ve scenario. This inadequate supply of wood and hi gh prices has led them to defer expansion plans. Although among hardwood eucalyptus species have been well accepted as a paper maki ng raw material s, yet ot her comparatively faster grow­ing exotic species are being introduced and grown on waste land to make a sustainable suppl y of wood fibre so that Indian pulp and paper industry can face important chal­lenges, particularl y in cop ing with strong competiti on from import to some extent.

Can a new kind of tree so lve such diverse and funda­mental problems as the shortage of arable land the nudation of forests the increase in so il erosion and fl ooding the decreasi ng fertility of soil and demand for milk? The an­swer incredibly enough , seems to be yes. The miracle tree that has attracted much attention of farmers and paper

* Author for correspondence E-mail: malik_iitr 0! yahoo.com

makers is L. /eucocep/w/a and is loca ll y known as Ku­babul or Su-babul , Ipi l-ip il in Philippines and Lamotra in Indonesia. It is orig inall y a nati ve of Central America, it has already travelled other lands li ke, Hawaii , Austra lia, and the Philippines and now poised for a break through in India. Su-babul appears to be fastest growi ng tree ever introduced in India. In irrigated conditi ons, it can shoot­up to a height of 13 ft in just six months, a height which not even the euca lyptu s can achieve in less than few years. It yields not less than 30 t of green fodde r, enri ched in protein per acre of irri gated land enough to feed six cross bred cows. It can also tolerate drought and highl y alka­line soil. The water requirement of this miracle tree is only 2Uac/4 weeks and thus, it can convenientl y be taken up in social fores try programme in almost all areas of the country. Su-babul is a leguminous plant which fixes ni ­trogen from the air directl y in to the soil and add up to 200 kilos of nitrogen per acre which is more than ten­times over average consumption of nitrogenous fert ili zer per ac re l

.

In present context look ing the astoni shing propert ies of Su-babul efforts were made to in ves ti gate anatomica l, morphological and chemical studies and their suitability to make chemical grade pulp in order to manufacture va lue added quality papers.

126 J SCI IND RES VOL 63 FEBRUARY 2004

Table 1- Morpho logical characteri sti cs of L. lellcoCl'II/w /a

S I No ParalllclCrs L. lellweeplwlll E. globllles ll

I Fibre length (L). III 0.96 076

2 Fibre width (D). !lm 23.33 15

3 Lumen widt h(d),pm 12.9(J 8.7

4 Cell wal l thi ckness(w), pill 10.45 3.3

5 Vesse l length (I ). pill 377.57

() Vessel di alll (W). p m 159. 39

7 Felting power, UD. (fibre) 4 1.27 50.67

X Felting power, I/W (vessel) 2.36 () Run kel ratio, 2w/d. (fiber) 1.65 0.78

10 Ri gidity coefficient. 2wID (fihre) O.R9 0.44

11 Fl ex ibilit y coelTicient, (li /D ) x 100 (l'ihre) 55.29 55.30

12 Fihre. per cent 64.5

J] Vessel . pCI' cent 8.5

14 Parenchyma. p CI' cent 9.0

I S Ray ce ll s. pCI' ce llt 18

Experimental Procedure

Preparation of Thin Wood Samples - Thin wood sec ti ons of L. lell('ocep //{/l([ of 2S 11m thi ckness were cut in c ross and

longitudinal direc ti on on Slade Beltz Microtome. Micro­photographs I a and I b in transverse view at a magnifica­

ti on of 260X and Microphotograph s 2a and 2b in radial

view at a magni f ica ti on of 100X were taken. Micropho­

tographs of wh o le kraft pulp at a magnificati on of 100X we re taken and a re shown in Microphotograph 3. The cross and radi a l sect ion s of L. leueocephala we re

de lignified by Cross and Bevan method. The micropho­

tographs o f de ligni fied cross and long itudinal sect ions are shown in Microphotog raph 4a and 4b whi ch are taken at magn ifi cation of 200X . In another se t the cross and long i­

tudinal sec tions were treated with 22 per cent KOH for 20 min in order to remo ve hemi cellul ose. The micropho­tograph o f hemicellul ose free c ross and long itudin a l sec­tions were taken at a magnifi cati on of200X and are shown

in Mic rophograph Sa and Sb. The cross and long itudina l sections L. lellc() cep/wl([ we re treated with 8 per cent

NaOH for 20 min and washed with 0 . 1 per cent N HCI for 30 min to convert -COON a group to -COOH and micro­photogra phs were ta ken at a magnifi cation of 200X and are shown in microphotograph 6a and 6b. The c ross and

long itudinal sec t ion were treated with 0.5 per cent NaOH 1'0 1' 30 min and was hed with 0.1 pe r cent N HC I to remove

E. grandi.I·" E. l l' relicorn l'.I' 1I E. 1711111.1'1(/ 11 P k('sim"

0.84 O.lO 1.07 ) ~') _ . . l-

19 15 19 -+0.7

10. 1 6.3 12 .1 34.35

4.4 4 .2 3.4 5.X5

44.2 1 55.33 56.32 72.03

0.87 133 0 .56 1.47

0.46 0.56 0. 36 0.59

53. 16 420 63. 68

-COOCH group but not -COOH group and microphoto­g raphs at

la magnificat ion of 200X were taken and are

shown in Microphograph 7a and 7b:!·5 .

Infra-red Spectrosc()py of Treated W()od Section - The infra­

red spec tra of de lignified , hemicellul ose free, conve rted -

COON a group to -COOH group and -COOC H free but

not -COOH group and sections cut long itud in a lfy and ra­

dially were taken wi th Perkin E lmar Spectrophotomcte r and shown in Figure I .

Bauer McNett Fibre Classilication - Bauer McNett fibre clas­s ification of kraft pulp o f L. leuencephal{[ was carried out using mes h size +28 , +48, + I 00 and +200. The M icro­photographs of each fraction are shown in Microphoto­g raphs 8- 11 .

Fiber Morphology - Wood chips of L. lellCoCel'hala were treated with potassium chl orate and hyd rochl ori c ac id in order to separate cellul os ic fibres togcther by di sso lving middle lame lla. The glass slides for fibre microscopy were prepared as per BlS 528S- 1969 .Fiber length , fibre w idth. ce ll wall thickness, lumen diamete r were de te rmined . The res ults are reported in TJbl e I .

Proximat.e Chemical Analysis - The dried wood chips were powdered in wood mill and the frac tion passes th rough -

MALIK el al. : MORPHOLOGICAL. ANATOMICAL & CHEM ICAL CHARACTERISTICS OF L. LEUCOCEPHALA 127

Mi cro photograph I (a) - Transverse view of Lellcaell (t

lellcocephal(l (Magn 260 X)

Mi crophotograph (2a)- Radial view of Leucaena lellcocl'phala

showing crystalliferous parcnchyma (Magn 100 X)

Microphotograph (3)- Unbroken crystalliferous parenchyma cclls in Kraft pulp of Lel/caella lellcocephala (Magn 100 X)

Microphotograph ( I b) - Longituuinal view of LCII('(Ima

ICllcicephala (Magn 100 X)

Microphotograph (2b)- Tangential view of Lell caell(l ICllcOcclJ/lCl la

showing crystalliferous parenchyma in the form of rays (Magn 100 X)

Microphotograph (4a) - Deli gnified cross secti on of Llicacl/(I

lellcocephala (Magn 200 X)

12~ J SCI IND RES VOL 63 FEBRUARY 2004

Micropholo~raph (4b)- Deli gnified longitudinal section of Leucaena leucocephala (Magn 200 X)

Mi crophotograph (5b)- Hemi cellulose free longitudinal section of Leucacna leucocephala

(Magn 200 X)

~ ., - . I . \ ..

Microphotograph (6b)-Longi tLIdinal section of Lcucacna Icucocephala shuws the co nversion of

-COON a to COOH (Magn 200 X)

Mi crophotograph (5a)-Hcmi ce llulose free c ross section of Leucaena leucocephal ,i (Magn 200 X)

Microphotograph (6a)-Cross sec ti on of LClicaena leucucephala shows the convcrsion of -COONa to COOH

(Magn 200 X)

Microphotograph (7a)- Rcmova l of -COOCH hut not COOH group in the cruss sec ti on of LeucaenC1

leu cocephala (Ma~n 200 X)

l ,

MALIK el at.: MORPHOLOGICAL, ANATOMICAL & CHEMICAL CHARACTERISTICS OF L. LEUCOCEPHALA 129

Microphotograph (7b )- Removal of -COOC H but not COOH group in the longitudinal section of Leucaena

leucocephala

// '\ -. f< ,$ --~"'.

I ...,

1, l '.

\ ~ 1% ,. ! !i(' " ~,

,/ "

" "

""4t;

i <" '; i1

i -',

t . ~'

t "-'\

Microphotograph (8)-+28 fraction showing long slender fibres and epidermal cells (Magn 100 X)

'* l, /'

./ , t? \

, L

-. iN

.,;,

,~.."., ill'

.. Microphotograph(9)-+48 frac tion showing fairly long

fibres and lot o f epidermal cell s (Magn 100 X) Microphotograph( I 0)-+ I 00 fract ion showing short fibres and

epidermal cell bundles (Magn 100 X)

Microphotograph ( 11 )- +200 fracti on showing thin walled parenchymatous cells (Magn 100 X)

130

100

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<>0

40

26

0 . 10,)

;ro

60

A ~o

20·

Q' ..., 100

f<C d " ,>

i1. .. <>0 L>

" ::: 'Ii 40 :;.. ::

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J SCI INO RES VOL 63 FEBRUARY 2004

"", ~ .... ; . - '.

......

-- CROSS SECTION

- -- • . RADIAL SEC1l0N

200.1 11100 liIM .

Wave lellg1h, Cln .. , .....• •.. ...: •.... _ ••.. _ ....•.... _-> 1200 1000

Figure I - Radial sections of L. lellcoceplia/a (A) Oeligni fied (B) Treated (C) Untreated (0) Treated with 22 per cent KOH for 20 min

L·1

MALI K e/ al.: MORPHOLOGICAL, ANATOMICAL & CHEMICAL CHARACTERISTICS OF L. LEUCOCEPHALA 13

W mesh s ize and retained on +80 mesh size were se lected

for proximate chemical ana lys is. The results are reported

in Table 2.

Results and Discussion Microphotographs I a and I b show that the paren­

chymatous ce ll s frequently contain extraneous mate ri a l such as, c rystal s, s ilica, gum, res ins, tannins, o il s, latex, co louring mate ria ls, and nitrogenous mate ri a ls like alka­

lo ids. Sap wood porti on of the L. leucocephala consists of carbohydrates in the form of starch grain s, which is

confirmed by iodine test. A deep red colour is developed when iodine so lution is applied on cross-secti on of L. leucocephala w hich shows the presence of abundant starch granules in storage cell s, i.e., wood parenchynatous and ray cells. The radial and tangential views (Microphoto­graphs 2a and 2b) show the presence of crystalliferous

parenchymatous in the form of ray cell s. Calcium and

potassium are th e pre d o minatin g m e ta ls in L. leucocephala . Most of the calcium present as calc ium

oxalate c rysta ls depos ited in the ce ll wall and lumen of

parenchyma and bound to the carboxylic groups of pectin and xy lem . The xy lem cell s are arranged in storied pat­tern , which are surrounded by lati c iferous ce lls .

Microphotograph 3 shows unbroken crysta lliferous

parenchyma cell s in kraft pulp (~fL. leucocephala, it indi­cates that during de lignifi cation this crystalliferous cell

in the atmosphere of high a lka li concentration and at very

high te mperature remains unaffected . The c rysta lli ferous

cell s still remain attached with fibres when theseare sub­jected to mechanical attrition and increased the alkalinity

of pulp. It is refl ected in an increase in a lum consumpti on

during acid siz ing process. Figure I shows the spectra of de lignified cross and

radi a l sec tions and sections treated for remova l of hemi­

cellul ose from L. leucocepha/a. When the samples were

treated to effect of de lignificati on the bands at 1595 and 1510 cm,l di sappear, some changes are also observed in

the region near 1250 c m,l. There is one broad band neat 1230 cm,l and thi s band shifted its pos iti on s lightl y aftet de l ignification(,7.

When the sec ti ons were treated for hemicellul ose remo val the band at 1730 cm,l is weakened. Some ch ange~ are a lso observed in the reg ion fro m 1200 to 1300 c m,l.

Wood secti on of L. leucocep//(//a treated with 8 per cenl

NaOH for 20 min at room temperature has brought about partial removal of band near 1730 cm·l. The 1730 c rn ,l

band can be comple te ly e liminated w hen these sect ion

were treated with 22 per cent KOH.

It has been noted that the relative intens ities of the parallel cellulose bands near 3350, 1430, and I 160 Clll i

are weaker in the spectra of the c ross-section than in the

spec tra of the radi a l sections. The re lative intensit ies 01 the perpendicular bands at 13 17 c m,l (Cellul ose) and I73C

Table 2- Proximate chemical ana lysis or L. 1(, lIcoc('flhala

SI No Parameters L. lellcOCelJ/w la E. glohllles" E. gralldis l1 E. l('relicon/es" Mrso re hrhrid' l E. m/JIIs{(;"

I Bulk densit y, kg/m' 2 16 205 .1 222. 1 236.7 227 273 2 Basic densit y, kg/m 1

(on dry basis) 529 525 53l) 578 525 575

3 Moisture, per cent 12.2

4 Co le! water soluble, per cent 3.45 1.6 I 2.06 2.37 2.n 55l)

5 Hot water solu ble, per cent 5.98 2.2 1 3.58 2.79 3.64 12.43 6 Ethanol: benzene soluble,

rer cellt ( 1.2 v/v) 2.55 2.30 2.69 2. 12 2.02 9.27

7 I r er celli NaO H so luble 13.26 14.58 15.67 14.69 13.90 12.43 g Lign in , per cent 19.55 2 1.1 l) 286l) 30.6H 29. IH 34. 15 9 Holocellu lose, rer cent 76.58 73.27 68 .87 65.49 69 .40 55 ,64 10 a-ce llulose, per cent 58.70 48.66 40.26 39l)9 43.30 35.n II p-ccllulose, rer cent 5.65 16.76 9.72 8.32 10.80 11.32 12 y-cellul me. per cent 12.23 7.85 18.l.\9 17.2l.\ 15.30 H. 55 13 Pelllosan, per cent 17.2 1 17,64 12.88 12. 11 13.69 13.03 14 Ash. per cent 0.85 0.30 0.28 0.40 0.5 1 0. 24

15 Si li ca, per cent 055

132 J SCI IND RES VOL 63 FEBRUARY 2004

cm·1 (Xy lan ) are stronger in the spectra of cross sec tions than that of rad ial sec tions, These differences in the re la­tive intens ities are readily explained in tenn of fibre ori­entati ons in these secti ons2

• In the spectral region near 1000 cnyl , there are some striking differences between the spec tra of cross-secti on and radial secti on. The ab­sorption max ima in the c ross-sec tion were observed at 966 em·l. This frequency is lowe r than the max ima ob­served in the radia l sections. These differences in the 1000 un·1 region can be inte rpre ted based on fiber and fibril ori ental ionx.

Microphographs 8-11 show Bauer McNett fibre clas­sification of kraft pulp of L. leucocephala at 220 CSF +28 frac ti ons show 19.2 per cent of the pulp and it con­sists of long sl ender fib res with epidermal cells . +48 frac­ti ons show 47.5 per cent of pulp and the fibers are fairly long wi th lot o f epidermal ce ll s. + I 00 fractions constitute about 8.5 per cent of total pul p and fibers a re short with lot epidermal ce ll s bundles. +200 fractions show 6.5 per cent of pulp . The short broken fibers are very few with thin wa lled parenchymatous cells are clearly visible.

Table I sh ows the morpho logical characte ristics of L. /ellc()cephala. Vessels, parenchyma and ray cells are 8.5,9.0 and 18 per cent, respecti vely. Vessel length is twice the width o f vesse l dia and felting power is only 2.36. It means those vesse l e le me nts acts as filler and it does not take part in bond formation. If they are present in excess then they may cause linting, i.e., e levating of fibres from Ihe surface o f paper sheet problem in dryer secti on and it ea n be e liminated by incre<'II;i ng dry strength additi ves based on charge of the system. The feltin g power of L. /ellcocep/w/({ fibre is 4 1.27 which is comparable to fe lt­ing power of all other eucalyptus species but it is lesser than P kesiya. ft indicates that the tendency of fiber fl oc­culati on is less and sheet is so formed hav ing uniform formati on. T he runkel ratio o f L. leucocephala is 1.65 compared to 1.47 for Pinus kesiya. Runke l rat io and fibre to vessel ratio influences the basic density of wood5.(,. It is d irec tl y re lated to the deg ree of fibre collapsibility, conformability, and the re lative fibre bonded area. It, in turn , im parts it s direct influence on surface and other mechani cal stre ngth properties o f paper. The low density wood fibres or fibres having low cell wall thickness and wide lumen are flexibl e and form ribbon readily on press­ing, whereas hig h densi ty wood fibres or fibres of thick­ened ce ll wall with narrow lumen are cy lindrical, rig id , and do not form ribbon readily on pressing. The fibres of L. /el/cocephala are comparatively rig id than that of P kesiva and these provide less surface area for bonding.

Therefore, all properties like tens ile and double-fo ld w ill be lower than that of P kesiya. Tear index is a func ti on of cell wall thickness and fibre length . The fibre length of P kesiya is about the twice the length o f L. /ellcocep/7% but cell wall thickness is twice the ce ll wa ll thickness of P kesiya. Rigidity coeffic ient 2W ID of L. lel/cocepha/a shows that the fibres are more rig id than that of euca lyp­tus spec ies and P. kes iya .

Table 2 shows the proximate che mical anal ys is o r L leucocephala. The bulk dens ity and packing de ns ity of L leucocephala is comparable to those o f eucal yptu s spe­c ies. However, co ld and water so lu ble are s lig htl y on higher side than those of eucalyptus species. O ne per cent NaOH solution is comparati vely low th an those o f euca­lyptus spec ies. It means that the logs o f L. /cuwcep//(//o can be stored for a longer pe ri od in wood yard and would not be decayed by heat, lig ht or fun g i. The li g nin content which determines chemical dose and cook ing cycle is only 19.55 per cent, whereas in eucal yptu s spec ies it va ri es be tween 2 1.1 8 - 34. 15 per cent. It in d icates that L. leucocepha/a requires lesser cook ing dose and shorte r cooking cyc le to pro du ce c he mi ca l g rad e pulp. Ho locellulose contents in euca lyptus species vary among 55.64 to 73.27 per cent , compared to 76.58 per cent in L leucocephala. Mechanical properti es o f paper or viscos­ity are directly influenced by a cellul o"e conte nts which is 58 .70 per cent in L leucocephala. whereas in euca lyp­tus spec ies it varies between 35 .78 - 48.66 per cent .

~ and y Cellulose - S hort chai n length polymers are removed during pulping and bleaching ope ration due to hydrolysis and peeling reactions . It directl y influences pulp yi e ld and mechani ca l streng th prope rti es. ~ and y celluloses are 17 .88 per cent in L. leucocephala. it vari es between 19.87 - 28.6 1 per cent in va ri ous eucalyptus spe­cies. Ash conte nt in L. leucocephala is 0.85 per cent due to the presence of oxalates.

Conclusions (i) Anatomical studies of L. leLtc()cepha/a shows the

presence of crysta lli ferous parenchyma in the form of ray or axial parenchymatous ce lls . Most of the calcium and magnes ium present as calcium and magnes ium oxalate crystals depos ited in the ce ll wall and lumen of parenchyma and bound to the carboxylic groups o f pectin and xylem.

( ii ) These crystalliferous cell s remain unaffected dur­ing pulping and still remain attached with fibres when they are subjected to mechanica l attrition and increased in the alkalinity of pulp . [t is reflected as

MALI K 1'1 al.: MORPHOLOGICAL. ANATOM ICAL & CHEM ICAL CHARACTER ISTICS OF L. LF:UC()CEPHALA I ~:\

an inc rease in alum consumpti on during acid siz­

IIlg process . ( iii) The infra red spectra of wood sections have been

recorded both in the untreated state and after treat­

ment for removal of li gnin and hemice llulose. It is obse rved th at L. /e ll (;oce phala is g rea te r in g'lu co mann a n co nt e nt. It indi ca tes th a t L. /ell eocephala shows the c haracte ri st ic of hard

wood . The application of microspectroscopic tech­niques to determine the position of various e nti­

ties, such as xylan in the cell wall appears feasible

now that these entities can be assoc iated with dis­

tinct absorption bands. ( iv) Vessels , parenchyma and ray ce ll s in L.

leucocepha/a are 8.5, 9.0 and 18 per cent , respec­tively. The felting power of vessels is only 2 .36 and it indicates that vessel e lements ac t as filler

and it does not take part in bond formation . (v) I f vesse ls are present in excess then they may cause

linting, i.e .. e levat ion of" fibres from the surface of

paper sheet problem in dryer section and it can be

e limina ted by increas ing dry strength additives based on c harge of the system.

(v i) The felting power of L. lellcocephala fibre is 41 .27

which indicate that the tendency of fibre floccula­tion in head box is less and sheet is so formed hav­

in g unifo rm formation . Th e runkel ratio of L. /eucocep/wla is 1.65 compared to 1.47 for Pinus kesiva . It indicates that the fibres of L. leucocepha/a are comparative ly ri gid than that of P kesiya and it

provides less surface area for bonding . Therefore,

all properties like tensil e and double fold will be lower than that of P kesiva .

(vi i) The lignin content which determines chemical dose and cook ing cycle is only 19.55 per cent, whereas

in eucalyptus species it varies between 2 1.18 - 34.1 5

per cent. It indicates that L. /eucocepha/a requires

lesser cook ing dose and shorter cook ing cyc le to produce c hemical grade pulp.

(v iii) Holoce llul ose co nte nt is 76.58 per cen t in L /eucocep/w/a . It is directly re lated to pulp yield. Mechanical properties of paper or viscosity are directly influenced by ex cellul ose contents to some

extent which is 58 .70 per cent in L /ellcocep/w/u. whereas in eucalyptus species it varies among 35.78 to 48 .66 per cent.

( ix) Ash content in L. leuc()cepha/o is 0.85 per cent

due to the presence of oxa lates.

References I Murthy Y S S, Shah CD & Pare J L, IPPTA. 22 (3) ( 1085)

2 Ott E & Spurlin H M, High IlOi\'I!lel".I" . Vo l V, second ed , Cellu­lose, Part I. Chap Y, (lntem:ience Publi shers. Inc. NewYurk). 1954.

3 Junes E J. 7ill'pi. 32 (1949) I (i7.

4 Casey J P. Pulp alld I}({I '('/". Vol I . (Interscience Puhlisher~.

Inc, Newyurk) 1954. pp :\ -4.

5 Hagg lund E. Lindberg B & McPherson J. lIela ClU:1II SWI/{I. 10 ( 1956) 1160.

G Dadswell H L and Watson A J, In 1301111 'sfOl"lllalioll o/papel". (B ritish Paper and Board Maker's Association Lundon ) 1962, 537-72.

7 Hergert H L. Ligllill. K Y Sarkanan & C H Ludwig. Tappi puhl (lnterscience Publishers. Inc, New York) . 1971. 267.

8 Liang C Y. Bassell K H. McGinnes E A & Marchessault R H. Tappi. 43 ( 1<)(i0) I 2.

9 Swanson J W. Tappi . 39 (5) ( 195(i) 257.

10 Clark J D A. Paller Trade .l. liS (26) ( 1942) 3(1.

II Project repurt on' Be.l"l available Il'chl1ologr .fiJi' a 3DO TPf) hleached hal"dwood !,{(I,I of" hrighille.l".\· C)O I}(' I" celli hy Y. Panwar 1'1 al. (Institute ur Paper Technulugy. University or Roorkee, Roorkee) 200 I.

12 Norad projeci by Cri Hah P Reuben. Tanz<l ni a, 1992.