Journal of Scientific & Industrial Research

Vo1.58, October 1999, pp 799-806

Pulping of Casuarina glauca with ASAM - An Environmental Friendly Process

Nadia Shukry, Samira F EI-Kalyoubi and EI-barbary M Hassan Cellulose and Paper Department, National Research Centre, Dokki , Cairo, Egypt

Received: 19 April 1999; accepted: 14July 1999

ASAM pulping process has been experimented on Casuarilla glauca. The pulping parameters such as methanol concentration, cooking time, chemical charge, and a lkali rati o, affectin g the chemi cal and physical propert ies of the pulp are de termined .. For ASAM

I cooks, NaOH is the supporting a lk al i, while in AS AM II pulping, Na2CO) is the supporting alkali. The best ASAM I pulping is

achieved at 22.5 and 25 per cent chemi cal charge with 0.7 and 0.8 a lkali ratio while the best ASAM II pulping is achieved at 27.5 per

cent chemi cal charge and 0 .6 alkali rati o. When both the pure a lk al ies were used, somc changes in the pulp propert ies were observed by

vary ing the ratio of NaOH :Na2CO). Pulp- and papermaking properti es of Casuarina cooked by the ASAM process are observed to be

superior to Casuarina pulp obtained by the kraft process.

Introduction soft- and hardwoods have been reported earlier I1 3-23 Not ASAM pulping process, alkaline sulphite reinforced much is reported about Casuarina. The present study

by addition of anthraquinone and methanol , is an ap- aims at investigating the possibility of producing ASAM proach to pollution free pulp production. Unbleached pulps from Casuarina glauca. Casuarina is a hardwood ASAM pulps are characterized by low kappa number and represents the most important genus of trees in the with high yield and viscosity and can ,therefore, be Egyptian forestry. bleached by TCF bleach sequences 1-'. Such bleach se-quences contribute to the fulfillment of the requirements Experimental Procedure of environmental regulations for AOX. Pulping trial s have been carried out in stainless steel

ASAM process is derived from the industrially estab- rotating pressure reactors , immersed in a temperature lished alkaline sulphite anthraquinone (AS/ AQ) method. controlled oil bath. In each experiment, 100 g od wood The use of Na

2SO, and an alkali shows that the process chips (5x2.5xO.25 cm) and the cooking liquor were mixed

combines the depolymerizing characteristics of kraft in the reactors at room temperature. The cooking liquor ..,.. pulping with the hydrophilicity-creating properties of the is composed of Na2S03, a supporting alkali (NaOH in

sulphite process6•7.The redox reactions taking place by the case of ASAM I and Na2CO, in the case of ASAM

AQ lead to strong lignin fragmentation and dissolution II) , AQ, methanol, and water. At the end of the cook, the while the carbohydrates are protected against degrada- pulp was washed carefully with water, stirred and then tion . This allows extending the delignification towards screened. The pulp was then weighed and the yield ex-very low kappa numbers without deterioration of the pressed as per cent of od pulp remaining after treatment. strength properties of pulpx-Io. The mechanism of metha- For wood analys is and pulp testing the following meth-nol action in ASAM pulping should be to increase the . ods were applied: efficiency of AQ in retarding carbohydrate degradation . On the other hand, methanol can decrease the swelling Klason lignin: Tappi T 222 os-74 of the lignocellulosic material s and the so lubil ity of Hemicellulose: Tappi T 223m-58 NaOH and Na

2S0

3 in the system, leading to low pH, Kappa numbe: Tappi T 236-cm85

which acts against the activation potential of AQ. There- RI O. Zellcheming IV/39/67 fore , an appropriate adjustment of methanol concentra- Paper: sheet formation : Scan-standard method tion in the cooking liquor has to be performed ". The Tensile strength: Zellcheming standard optimum methanol charge depends on the type of the Bursting strength: Tappi standard 403 raw material used l2

. Studies on ASAM pulping ofsom~ _____ I.earing strength: Tappi standard 414

800 ] SCIIND RES VOL.58 OCTOBER 1999

Table 1- Some analytical data or Ca.worina g/a/lca

Kl ason lignin Hollocellu lose Hemicellulose Ash Densi ty

24.40 per cent 8 1.40 " 15.50 1.54

0.76 g/enr1

Results and Discussion Table I g ives some ana lyt ical data o n Casua rino.

Casuarina is a hardwood and ha rd wood requ ires higher

meth 'lnol charges in the cook ing I iquor than softwood 12 .

However, an adequate amount of methanol has to be used

so that the effectiveness of AQ in accele rating li gnin dissolution I II during cooking can be granted. T herefore,

cooking tria ls using cooking liquors conta in ing diffe r­

ent concentrations of Na2S01' NaOH or a2CO" and diffe rent concentrati ons of methan o l (20, 25, 32 .5 , and

40 per cent) were performed and the e ffec t of va ry ing

the methanol charge on the pulp properti e. was s tudi ed . It was found that by usin g 25 per cent methan ol the

select ivity of the cooking liquors atta in it s op timum ef­

fect , where the most favourable y ie ld to kappa number

relationship exists ,i. e., low kappa number accompan ied by high sc reened y ie ld . Lower or hi gher meth ano l con­centrati on results in comp a rat ively un sat isfac tory

delignification (high kappa number or hig h rejec ts).

Another series of tria ls have been performed in order to dete rmine the su itabl e cook ing time at I 75"C. By us­

ing cook ing liquors hav ing 25 per cen t methano l and

different concentrat ions o f Na,SO" NaOH or Na.,CO, and cooking for different time inte;'val s, it has bee ,~ ob~ served that the kappa number attained minimum va lues when the cooking time was 180 min . Longer cooking times (up to 220 min ) were accompan ied by li gnin con­

densat ion reactions, expressed as s imultaneous inc rease in kappa number and yie ld.

Afte r determining the opt imum methano l charge (25 per cent) and cooking time ( 180 min ) the fo ll owing pulping tria ls were perfol111ed to study the effec t o f va ry­

ing the concentrations of Na2S01, NaOH or Na2CO, on

the de lig ni f ication process. It may be noted th at in all the experiments, 0. 1 per cent AQ was used. Tab le 2 con­

tains the applied pulping condi ti ons.

Effect of Chemical Charge and Alkali Ratio on ASAM Pulp Properties

Tables 3-6 illustrate the results obtained by cooking

Casuarina with 20 to 30 per cent chem ica ls at 0.6-0 .8 a lka li ratio . The results g iven in Table 3 show that in­c rease the chemical charge of ASAM I cooks from 20 to

Table 2 - ASAM pulping conditions of Cas /lrina

Chemica l charge as aOH, ( per cent 0 d wood) Alkali ratio (Na2S0.1/total alka li ) AQ ( per cent 0 d wood )

20, 22.5,25 , 27.5 ,30

0.6,0.7 , 0.8 0. 1

Methanol charge 25 (on total liquor, v/v) Liq uor : wood 4 : I M ax imum cooking temperature (lC) 175 HealUp ti me (min) 75 Cooking time at maxi mum 180 temperature (min)

30 per cent at diffe rent alkali ratios leads to decreased pu lp y ie lds, rejects and pentosan per cent. It is also ev i­

dent th at raising the chemica l charge from 20 to 27.5 per cen t is accompanied by decreased kappa number. Thirty

per cent chem ica l c harge acts negati ve ly on the kappa

number (Tab le 3). T he de li g nificat ion is a lso enhanced

ri se when ri se in the che mi cal charge is assoc iated w it h

inc rease the a lkali rat io . Table 4 shows that 20 per cent

c hemical charge is fa voured at 0.6 a lkal i ratio , 22.5 at 0.7 and both 25 and 27.5 per cent at 0.8 . However, in­c rease in the a lka l i ratio shifts the pH towards lower

values and ra ises the amollnt of rejects . This means that the defiberization point is favoured by low a lk a li rat io.

O n the o ther hand, bri ghtness is improved at hi gh a lka li ratio.

Table 5 show that 25 per cen t c hemical c harge has to

be used so th at the de li gnification of ASAM II can be

compared with that of ASAM I. Contrary to ASAM I

the delignificatio n is enhanced at low a lka li ratio . How­e ver, it seems that an a lkali ratio of 0.6 is the most suit­

ab le ratio fo r ASAM II cooks. Lowe r rati os , i.e. 0.55 and 0.5 g ive unsati sfac tory de li gnification (Table 6).

At a chemica l charge of 27.5 per cen t and an a lkali rati o 01'0.6, ASAM I and ASAM II pulps possess a lmos t the same kappa number ( 14.9 and 14.6). However, pulp y ie ld of ASAM II cook is hi gher than that of ASAM I (54.9 per cent, 49 .8 per cen t). T he results show the pro­

tective e ffec t o f Na2CO, on the carbohydrates. In gen­

e ral , ASAM JI cooks possess re lati ve ly lowe r pH and

bri ghtness, higher kappa numbers and pulp y ields than ASAM I cooks (Tables 4-6). Moreover, the bri gh tness of ASAM II pulps improves by increase in the alkali rati o.

From the above results, it can be proved that ASAM I optimum pu lpi ng condit ion s o f Casuarina can be achieved by using 22.5-25 per cent chemical charge at

SHUKRY el at.: PULPING OF CASUA RINA GLAUCA WITH ASAM 80 1

Tab le 3 - Effect of chemical charge on ASAM I pu lping

Chemical Alkali Yi eld (per cent on raw material) Kappa Pentosan * charge ratio Screened Rejects Total no . per cent

per cent

20.0 52.7 0.40 53 .1 19.3 22.5 52.5 0.06 52.6 16.3 9.41 25.0 0.6 50.3 50.3 15 .7 10.09 27 .5 49 .8 49.8 14 .9 8.98 30.0 49.5 49 .5 14.9 9.09

20.0 52.7 1.20 53 .9 21.2 22.5 53 .0 0.10 53.1 13.4 10.50 25 .0 0 .7 51.3 0.30 51.6 13.4 10.25 27.5 50.2 0.30 50.5 12.4 9.44 30.0 51.6 51.6 15 .9 8.76

20.0 51.7 0.80 52.5 19.6 22.5 53.0 0.97 53 .9 14.4 9.24 25.0 0.8 51.6 0.70 52.3 11.8 9. 19 27.5 49.6 0.50 50.1 11.4 8.5 1 30.0 47 .8 0.30 48.1 15.0 7.42

* Based on raw materi al

Table 4 - Effect of alkali ratio on ASAM I pulping

Chemical

charge per cent

Alkali Yield (per cent on raw materi al ) Kappa End Brightness ratio Screened Rejects

0.6 52.7 0.40 20.0 0.7 52.7 1.20

0.8 5 1.7 0 .80

0 .6 52.5 0 .06 22.5 0.7 53.0 0. 10

0.8 53 .0 0.90

0.6 50.3 25 .0 0.7 51.3 0.30

0.8 5 1.6 0.7

0.6 49.8 27 .5 0.7 50.2 0.30

0.8 49.6 0.50

0.7 and 0.8 alkali ratios, respec ti vely. ASAM II is suc­cessful at 27 .5 per cent and 0.6. Table 7 presents these results with control kraft cooks carried out at common pulping conditions . It is ev ident th at kappa number, screened yie ld , and brightness per cent of ASAM pulps are superior to those of kraft. However, high reject in ASAM cooks is due to relatively low alkalinity of the ASAM pulping liquors.

Total no. pH per cent

53.1 19.3 11.4 53 .9 21.2 10.8 52.5 19.6 10.6

52.6 16.3 11.6 34. 1 53.1 13.4 10.1 35.7 53.9 14.4 9.8 36. 1

. 50.3 15.7 11.8 3 1.8 51.6 13.4 10.8 33.4 52.3 11.8 9.9 39.9

49.5 14.9 12 .1 32.9 50.5 12.4 10.6 34.5 50. 1 11.4 I 1.1 41.4

ASAM Pulping Under Varied Ratios of NaOH:NaZCOj

Table 8 contains the result of ASAM I and ASAM II cooks carried out at the optimum conditions mentioned earli er: 25 per cent at 0 .8 and 27.5 per cent at 0.6, when the cooking is achieved by both alkalies, instead of one alkali . Table 8 a lso shows that the addition of Na2C03 to NaOH is not advantageous for the kappa number, Rill and· brightness and the increase in the kappa

802 J SCI IND RES VOL.58 OCTOBER 1999

Tab le 5 - Effect of chemical charge on ASAM II pulping

Chemical Alkali Yi eld (per cent on raw material) Kappa Pentosan* charge ratio Screened Rejects Total no. per cen t

per cent

20.0 35.0 2 1.9 56.9 32.8 22 .5 39.2 15.2 54.4 29.0 8.62 25 .0 0.6 47 .5 5.3 52.8 2 1.7 7.79 27.5 53.0 1.9 54.9 14.6 9.68 30.0 55.1 2.2 57.3 27 .0 9.40

20.0 49.5 7.2 56.7 33. 1 22.5 49.1 3.8 52.9 24.8 6.93 25.0 0.7 49 .5 6.7 56.2 28 .5 9. 18 27 .5 52.5 1.6 54.1 19.8 7.80 30.0 54.9 0.1 55.0 23.2 8.43

20.0 52.9 3.7 56.6 31.9 22.5 53.2 2.7 55.9 31.3 8.90 25.0

0.8 49.5 5.2 54.7 32.4 8.93

27.5 52.5 0.5 52.7 18.8 8. 14 30.0 55.9 0.5 56.4 27 . 1 9.40

* Based on raw material

Tabie 6 - Effect of alkali ratio on ASAM II pu lping

Chemical Alka li Yield (per cent on raw materi al) Kappa End Brightness charge ratio Screened Rejects

per cent

0.6 35.0 21.9 20.0 0.7 49.5 7.2

0.8 52.9 3.7

0.6 39.2 15.2 22 .5 0.7 49. 1 3.8

0 .8 53.2 2.7

0.6 47.5 5. 3 25.0 0.7 49.5 6.7

0 .8 49.5 5.2

0 .50 44 .0 I 1.1 0.55 50.2 4.7

27 .5 0.60 53 .0 1.9 0.70 52.5 1.6 0.80 52.2 0.5

number is m ore pronounced , w hen the ra ti o NaOH:Na CO ,decreases. The observation that the end 2 ,

pH of ASAM pulping liquors containing both a lkalies is hig her than that with NaOH, on ly suggests that com­plete participation of NaOH in the delignification proc­ess is hindered in the presence of Na2CO,.Table 8 also shows that an increase (but less pronounced) in the kappa number occurs as the ratio NaOH:Na

2CO, decreases. L

Total no. pH per cent

56.9 32.8 10.4 56.7 33. 1 9.5 56.6 3 1.9 10.2

54.4 29 .0 10.6 52.9 24.8 9 .6 55 .9 31.3 9.4

52.8 2 1.7 10.8 28 56.2 28.5 9 .9 54.7 32.4 10.0 37.7

55.1 27.7 0.6 54.9 28 .2 10.6 54.9 14.6 10.8 29.4 54. 1 19.8 9.7 32.7 52.7 18.1 9.8 38.4

However, the sa me kappa number as the ASAM II cook

but at 0 per cent rej ect, high R i ll and brightness could be ob tain ed by us in g equa l a mounts o f NaOH a nd Na2CO, in the cook ing liquor (NaOH: Na

2CO,= I). From

these results , it is evi dent that addition o f Na?CO, to ASAM I cook is not advantageous. On the other hand, the presence of NaOH in AS AM IT cook improves the delignification process, especiall y when the value of

SHUKRY et lIl.: PULPING OF CASUA RINA GLAUCA WITH ASAM ~03

Table 7 - Comparison of AS AM and kraft pulping of C(l.W(lr;na

Pulping conditions Cooking Yield (per cent on raw material) Kappa End Brightnes~

time, (min) Screened Rejects Total no. pH per cent

ASAMI Chemical charge = 22.5 per cent 180 53.0 0.1 53.1 13.4 10.1 35.7 Alkali ratio =0.7 Chemical charge = 25 per cent 180 51.6 0.7 52.3 11.8 9.9 39.9 Alkali rat io =0.8

AS AM II Chemical charge = 27 .5 per cent 180 53.0 1.9 54.9 14.6 10.8 24.9 Alkali ratio =0.6

Kraft 90 50.2 50.2 20.6 13.2 Active alkali = 18 per cen t 120 46.8 46.8 19.3 13.5 Sulphidity = 25 per cent 150 49.0 49.0 17.2 13.6 Maximum temp. = 160°c 180 49 .3 49.3 16.3 13.8 28.9 Liquor : wood =4 : I

Table 8 - Results of ASAM cooks carri ed out at different NaOH :NalCO, ratios

Chemicals ratio Chemical charge Yield (per cent on raw material)

Kappa End Brightness NalS0,:NaOH:Na2CO,

per cent Screened

/ Alkali ratio

80: 20 : 00 5 1.6 80: 15: 05 25/0.8 53.7 80: 10: 10 56.8 80: 05: 15 57 .2

60: 00: 40 53.0 60: 10 : 30 54.4 60: 20: 20 27.5/0.6 54.0 60: 30 : 10 52.7

Papermaking Properties of Unbleached ASAM Pulps ASAM pulps prepared by different chemical charges

and alkali ratios were subjected to beating in a lokro mill for varying durations and the physica l characteri s·· tics of the pulps have been studied . It is like ly that the physical changes in the fibrous structure of the different pulps due to beating are more or less affected by those pulping parameters rather than by the amount of res idual lignin or pentosan content of the pulps . In the case of ASAM I pulps (Table 9) increase in the chemical charge and alkali ratio makes the pulp beat eas ier. The best beat­ing has been achieved at 27 .5 per cent chemical charge and 0 .8 alkal i ratio . In the case of ASAM II pul ps the best beating has been found at 25 pe r cent chemical charge and 0 .8 alkali ratio , although this pulp possesses

Rejects Total no. pH RIO per cent

0.7 52.3 11.8 9.9 89.0 39.4 0.4 54.1 17.6 11.5 0.1 56.9 21.6 I 1.2 87.9 34.4 1.4 58.6 25 .7 11.0

1.9 54.9 14.6 10.8 89.8 29.4 1.0 55.4 19.4 11.2

54.0 14.6 11.6 91.6 31. 1 0.3 53.0 15.3 12.0

very high kappa number (Table 10).Despite their high kappa number ASAM II pulps beat easier or have al­most the same beating response as ASAM I pu lps.

Figure I shows the beating respon se of three ASAM pulps possessi ng the same kappa number together with a kraft pulp. ASAM pulps are prepared by using 27.5 per cent chemical charge and 0 .6 a lkali ratio. It has been found that the beati ng of pulp prepared by I : I ::NaOH:Na2CO] is superior to the other two pu lps. Moreover, it is ev ident that the kraft pulp beats almost s imilar to those ASAM pulps, especially to low beating degrees .

It has also been found that the required beating time for ASAM I pulps to develop their optimum sheet form­ing qual ities depends on the chemical charge rather than the alkali rati o. Use of low and moderate chemical charges (22.5 and 25 per cent) permits prolongation of

804 J SCI IND RES VOL.58 OCTOBER 1999

the beating time. After 40 min beating, no deterioration of the strength properties bserved . When the chemical charge increases to 27 .5 per cent the strength properties attain maximum values and after that deteri orati on of the properties takes place (Table 9). However, in most cases and within the experimented beating times and degrees, the tear factor is improved by increase in beat­ing, which ind icates that the amount of inter-fibre bond­ing is compatible with the developed fibre length , al­though beat ing degrees of -50 "SR were reached.

ASAM I pulps and pul ps prepared by both a lkali es appear to possess stronger fibre-to-fib re bonding and longer fibres thah ASAM f1 pul ps, as shown from the data of breaking length , burst and tear (Tables 9-11 ).In

2 0

. 20

Na,SO, : NaOH: Na,CO,

• 60 40 00

" 60 : 20 20

+60: 0040

• Kraft pulp

30 ~ o so Beating time, min.

Figure 1- Beal ing behaviour of ASA M pul ps r repared by di f­\'erenl Na1SO), NJOH and Na1CO) concelllratl ons at 27 .5 per cent chemica l charge

Table 9 - Parcrmaki ng prorcl1ies of di fferent ASAM I pulps

Chemical charge / Alkal i ratio

22.5/ 0 .6

22.5 / 0.7

22.8 /0.8

25.0 / 0.6

25 .0 /0.7

25.0/0.8

27.5/ 0.6

27.5/ 0 .7

27 .5/0.8

Kappa no.

16.3

13.4

14.4

15.7

13.4

I U';

14.9

12 .4

11.4

Pentosan, per cent

9.4 1

10.5

9.24

9. ()l)

10.25

9. 19

8.98

9.44

X.5 1

Beating Ti me, Degree,

mill °SR 20 29 35 4 1 40 50

20 30 40

16 20 40

20 33 38

15 20 33

20 40 50

20 32 40

16 20 30

16 20 30

23 36 49

33 38 45

28 46 50

27 37 46

36 35 38

3 1 4 1 46

30 36 54

33 39 55

. Breaking length, (m)

5 139 5649 67 12

4769 5097 5209

3751 5242 6355

5265 5656 769 1

3626 7273 6593

4289 4988 48Tl

5 146 5423 4846

3329 755 1 5836

4240 (i034

6 12

Burst factor

26.80 33.53 37.5 1

22.37 27.73 35 .1 2

24 .49 29 .28 4 1.38

29.38 33.47 52.65

24.09 4 1.77 5 1.9 1

27.33 2(i.42

25.59

27.63 29.89 29.97

23 .68 39.58 3 1.98

24.03 35.69 35.8 l

Tear factor

129.36 14 8.90 142.96

125.50 14 3.40 144.20

143.90 149.40 155.30

125.50 162.40 172.00

122. 10 155.00 160.80

135. 10 147.00 135. 10

148.90 153.20 139.1 0

147.40 150.20 153. 10

139.50 142.10 145.30

,

~

SHUKRY el al.: PULPING OF CASUA RINA CLAUCA WITH ASAM 805

Table 10 - Papermaking properties of difrerent ASAM II pulps

Chemic'al charge Kappa no. Pentosan , Beati ng Breaking Burst Tear IAlkali ratio per cent Time, Degree, length , (m) factor factor

min °SR

18 28 4280 35.66 120.5 25 .010.6 21.7 7.79 23 37 4980 34.99 126.8

28 48 5387 42.95 139.4

25 .010.8 32.4 8.93 15 39 3742 25.48 98.1 20 48 3843 29.62 11 8.3

20 30 4587 26.0 1 135.7 27.5/0.6 14.6 9.68 27 42 4964 32.78 137.0

35 52 5745 28,.18 140.3

27.5/0.7 19.8 7.8 19 32 5163 30.02 113.4 30 49 5597 37 .66 122.3

18 34 5192 35 .9 1 99 .5 27.5/0 .8 18.8 8. 14 25 42 5403 35.70 114.3

35 61 6129 49.88 122.5

• Tablc II - Papennaking properti es of ASAM pulps with differen t

Na2S0,: NaOH : Na2CO, ratios

Chemicals rat io Kappa Pcntos3 n Beating Breaking length, Burst Tear Na2S0 .1: NaOH :Na2COJ no . per cent Time, min Degree, (m) factor factor

°SR

80: 10 : 10 16 35 59 17 38.60 133 .2

2 1.6 8.95 2 1 42 6446 48.96 157 .7 Chemical charge =25 per ccnt 26 49 6803 50.09 151.8

60 : 20: 20 13 29 5798 36.77 150.4 Chemical chargc =27.5 pcr cent 14.6 8.77 20 42 5782 56.09 152.6

28 52 6936 5 1.52 155.4

Tab le 12 - Papermaking properti es of ASAM pu lps in comparison with kraft pulp

ASAM I ASAM II Breaki ng length , 769 1 6 129 111

Burst factor 52 .65 49.90 Tear rac tor 172 140.3

genera l, the different ASAM a lternatives are superi or to kraft pulps with regard to break ing length and burst. On the other hand, comparab le tear factors are obtained for the different pu lp types (Table 12).

Conclusions ASAM pulping experiments carried out on Casuorino

glauca revealed the suitability of thi s process for pro-

ASAM (NaOH + a2CO.l) Kraft 6936 4837

56.09 27.17 157.7 1576

ducing high quality paper pulp from this wood. The effect of me than o l c harge, cooki ng time, che mical charge, and a lka li ratio on the de lignification process of Casuarina has been studi ed . Twenty five per cent methanol and 180 min cooki ng time result in adequate de lignifi cation. By using NaOH as the supporting al­ka li , ASAM I, increase in the chemical charge from 20 to 30 per cent .improves the de li gnification but at the

806 J SCI IND RES VOL.58 OCTOBER 1999

expense of the yield and pentosan content. Using 22.5 and 25 per cent chemical charge with 0.7 and O. 8 alkali ratio , respectively, the optimum delignification is achieved. In ASAM II pulping, adequate delignification is achieved at high chemical charges and low alkali ratio. In general, ASAM II pulps possess relati vely lower bright­ness and! higher kappa numbers, than ASAM I pulps. At a given kappa number, ASAM II pulp y ield is higher than that of ASAM I, indicating the protective effect ofNa,C0

1

on the carbohydrates. Optimum ASAM II del ignification is obtained using 27.5 per cent che mica l c harge at 0.6 alkali ratio. ASAM pUlping could also be achieved by mixing NaOH with Na,C0

1 in different ratios, whereas

some pulp c haracteri st ics are improved and others are deteriorated. The physical c hanges in the fibrous struc­ture of unbleached ASAM pulps due to the beating proc­ess are more or less affected by the chem ica l charge and alka li ratio rather than by the amount of res idual lignin or pentosan content of the pulps. AS AM alte rnatives are stronger than kraft pulp as compared to break ing length and burst. Tear is almost the same for both pu lp types.

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23 Pall R, Gause E & Zimmermann M , Holz Roh-We!'ksi , 52 ( 1994) 267.