CHAPTER 5 Bleaching and Characterization of …shodhganga.inflibnet.ac.in/bitstream/10603/6212/10/10...165 CHAPTER 5 Bleaching and Characterization of Treated and Untreated Bamboo

165

CHAPTER

5

Bleaching and Characterization of Treated and Untreated

Bamboo Pulps

5.1 Introduction

Conventional kraft pulping removes approximately 90-95% of the lignin from

wood. Further delignification results in an increased degree of carbohydrate degradation

and dissolution, causing significant loss in yield and pulp strength. Kraft pulps,

containing residual lignin, are delignified further using alternative delignification

procedures that do not cause significant yield loss (Sixta et al., 2006; Gullichsen and

Fogelholm, 2000). Chlorine is well-recognized as an effective delignification agent for

kraft pulps; it oxidizes and degrades residual lignin in such a way that a substantial

portion of the lignin is easily removed from the pulp by a subsequent alkali extraction.

The effluents from chlorine bleaching contain chlorinated organic compounds, typically

measured as absorbable organic halides (AOX) (Froass, 1996).

The bleaching of pulp with elemental chlorine and chlorine based chemicals has

become a major global environmental concern (Brunner and Pulliam, 1993). The

discharge of chlorinated phenolics (formed during bleaching with chlorine) in mill

effluents became an issue in early 1970’s when measurement techniques become

available and high concentration of chlorinated phenolics was detected in fish stock

receiving bleach plant effluent. Conventional pulp bleaching of softwoods produces

about 5 kg of organically bound chlorine per tonne of pulp, with almost all of this

discharged as effluent. Consequently environmental regulatory authority became active

and finalized norms and guidelines to reduce the discharge of chloro-organics in mill

effluents. Typical goals were to produce 1.5 to 2.5 kg AOX per tonne of pulp after

recognizing the toxic effect of chlorinated phenolics, generated during bleaching of pulp

with chlorine based chemicals. Efforts have been made by researchers and technology

suppliers to develop technologies which can reduce the kappa number of pulp and

improve pulp washing to minimize the carry over of organic matters along with pulp

166

going to bleach plant as both the factors govern the consumption of bleach chemicals.

Bleaching chemicals are quite expensive and they result in increased cost of bleaching

operation. Therefore minimization of chemical usage during pulp bleaching is beneficial

for both environmental improvement and mill economics. In addition, minimal water

usage is the additional benefit while the volume of effluents is reduced by reducing kappa

number of pulp prior to bleaching (Wang et al., 1995; Malinen and Fuhrman, 1995;

Pryke and Reeve, 1997).

5.1.1 Alternatives for use in Bleaching Stages to Reduce Pollution

Several other measures have already been taken to reduce the amount of AOX

released into the environment. For example, the incorporation of chlorine dioxide (ClO2),

ozone (O3) and hydrogen peroxide (H2O2) into pulp bleaching sequences has significantly

reduced the problem (Johnston et al., 1997). For the same amount of Cl2, ClO2 produces

only one-fifth the amount of AOX and more efficient pulping methods prior to bleaching

helps to reduce the amount of lignin which reaches the bleaching stages.

A great part of the effort put into these environmental actions in the last few years

has been directed towards the reduction of chemical reagents in the pulp bleaching. The

application of biotechnology to the pulp and paper industry has been an object of many

research studies (Eriksson, 1998; Tortter, 1990). Years ago, microorganisms began to

be used in the treatment of effluents, the fermentation of sulphate liquors, the preparation

of starch for paper sizing and the prevention/ control of slime buildup on paper machines.

Now a day, research is more focused on improving tree species, pulping, modifying

fibers and bleaching. An interesting approach is the use of lignin-degrading fungi, not in

a pre-bleaching stage but as an alternative bleaching process. This alternative has already

been proven to reduce by 72% the required bleaching agents for Kraft pulp (Fujita et al.,

1991). The investigation of how these microorganisms degrade a polymer of the

structural complexity of lignin has been the object of many research studies. The lignin-

degrading capacity of these fungi is now known to be due to extracellular oxidative

enzymes that function together with low molecular weight cofactors (Barr and Aust,

1994; Kuhad et al., 1997). Secreted by the fungi in response to low levels of key

nutrients such as C, N or S, these enzymes are mainly lignin peroxidase (LiP) (Tien and

167

Kirk, 1983), manganese peroxidase (MnP) (Glenn and Gold, 1985), manganese-

independent peroxidase (MIP) (Jong et al., 1992), laccase (Eggert et al., 1995), H2O2-

generating oxidases (Kuwahara et al., 1984) and hemicellulolytic enzymes such as

xylanases (Casimir-Schenkel et al., 1995). The role of each of these enzymes is still

unclear since the lignin-degrading species differ in the range of ligninolytic enzymes they

produce. MnP activity is detected in active biobleaching cultures of different strains

(Moreira et al., 1997), and has been correlated with the biobleaching ability of different

white-rot fungi. Kondo et al. (1994) proved the bleaching ability of purified MnP in in-

vitro systems, provided that Mn2+, Tween 80, malonate and H2O2 were supplied in

adequate concentrations. Moreover, the use of MnP avoids operational problems related

to the need of a mediator, as in the case of a laccase based bleaching with the larger

associated benefits related to economical and environmental points of view. However, an

application of MnP on a pilot or an industrial scale is still lacking, which would be the

first step to involve industrial partners in the uses of this enzyme.

5.1.2 Bleaching Chemicals and Bleaching Sequences

Chemicals commonly used for pulp bleaching include oxidants (chlorine, chlorine

dioxide, oxygen, ozone and hydrogen peroxide) and alkali (NaOH). Hydrogen peroxide is

commonly used as a bleaching agent, and is simply called peroxide". These chemicals are

mixed with pulp suspensions and the mixture is retained at a prescribed pH, temperature

and concentration for a specific minimum period of time (Akida, 2001). The pulp is

normally bleached with elemental chlorine and hypochlorite, which leads to the

formation of variety of chlorinated phenolic compounds. In aqueous chlorine system,

chlorine can exist in three different forms, depending on the pH of the solution. These are

molecular chlorine (Cl2), hypochlorous acid (HOCl) and its anion (OCl-). In the region up

to pH 5, a concentration dependent equilibrium exists between molecular chlorine and

hypochlorous acid, while at higher pH values hypochlorous acid and its anion are both

present in proportions directly determined by the pH of the solution. Two pH regions are

of particular interest for bleaching chemistry (Dence and Reeve, 1996). The pre-

chlorination of pulp is carried out at pH 2, and the purpose of this operation is to make

the bulk of the residual lignin soluble in both water and alkali. There is no color

168

improvement of pulp accomplished at this stage as well as in the following alkali-wash,

but the subsequent hypochlorite bleaching stage is greatly facilitated because of the

decreased residual lignin content. The optimum region for the hypochlorite bleaching is

pH 8 to 9, and the effect of the bleaching at this pH differs significantly from that of pre-

chlorination. The difference between the effects of pre-chlorination and hypochlorite

bleaching is probably due to the difference in the nature of the reacting chlorine species.

At the lower pH, molecular chlorine, a species much more reactive than hypochlorous

acid, directs the reaction, while in the hypochlorite bleaching, hypochlorous acid, or a

reactive intermediate derived from it, probably plays the role of the primary attacking

species (Sarkanen, 1962).

With increasing environmental awareness and recognition of the adverse and

toxic effects of these chlorinated phenolic compounds, most of the pulp mills in

developed countries have adopted modified pulping and bleaching processes to reduce

the discharge of chlorinated phenolic compounds. In India, due to economic

considerations molecular chlorine and its compounds are used for producing bleached

grade paper. The most common bleaching sequences adopted by the Indian pulp and

paper mills are CEH or CEHH. Use of chlorine dioxide, hydrogen peroxide and oxygen

reinforced alkali extraction which is also limited to very few mills and are producing

rayon grade pulp and papers with high brightness quality. The small and medium scale

pulp mills are normally using CEHH sequence for bleaching of the pulp to the required

brightness level and a few mills use only hypochlorite. The bleaching chemicals are

applied in multistage sequences wherein chemicals are mixed with pulp and allowed a

period of retention for bleaching reactions to complete. The spent chemicals and

dissolved impurities are removed by washing of pulp (Keski-Santti, 2007). The various

bleaching chemicals used in pulp bleaching are given in Table-5.1. Oxygen is another

effective delignifying agent which is widely used to enhance the extraction stage and it is

being used in advance of chlorine in order to reduce the carryover of organic matter to

bleach plant (Sjostrom, 1993; Johansson and Clark, 1995). The hypochlorite and ClO2

are mainly used for brightening of pulp. CEH is the traditional sequence used by the

Indian paper industries to produce bleached pulp. But with increasing environmental

pressure to reduce or eliminate organo-chlorine, the use of chlorine is decreasing rapidly

169

with oxygen, peroxide and ClO2 providing more environmentally compatible bleaching

(Gullichsen and Fogelholm, 2000; Ansari et al., 2007). Non wood pulps are easier to

bleach than wood pulps. Shorter bleaching sequences and lower chemical charges are

used to bleach non woods. Globally, most non woods still are bleached using chlorine in

a typical CEH (Chlorination-Extraction-Hypochlorite) or CEHH (Chlorination -

Extraction – Hypochlorite - Hypochlorite) bleaching sequence.

Table 5.1: Chemicals Used in Pulp Bleaching.

Oxidants Form Advantages Disadvantages

Chlorine Gas Effective, economical

delignification. Good

practical removal

Can cause loss of pulp strength

if used improperly. Organo

chlorine formation.

Hypochlorite Ca(OCl2), NaOCl

solution 40 gpl as Cl2

Easy to make and use Can cause loss of pulp strength

if used improperly. Cholorform

formation

Chlorine dioxide 7-10 g/l ClO2 solution in

water

Achieves high brightness

without pulp degradation.

Good particle removal.

Must be made on site.

Expensive. Some organo

chlorine formation

Oxygen Gas used with NaOH

solution

Low chemical cost. Provides

chloride-free effluent from

recovery

Used in large amounts requires

expensive equipment. Can

cause loss of pulp strength.

Hydrogen peroxide 2-5% solution Easy to use low capital cost Expensive, poor particle

bleaching.

Ozone Gas in low concentration

in oxygen

Effective, provides chloride-

free effluent for recovery

Expensive, Degrades pulp.

Poor particle bleaching

Reductant

Hydrosulfite (for

mechanical pulps

only)

Solution of Na2S

2O

4 or

made onsite from NaBH4

solution plus SO2

Easy to use. Low capital

cost.

Decomposes readily. Limited

brightness gain

Alkali Sodium

Hydroxide

5-10% NaOH solution Effective and economical Darkens pulp

In this chapter fungal treated and untreated bamboo kraft pulps from non

destructured and destructured samples were subjected to conventional CEHH bleaching to

170

study the effect of fungal treatment on bleaching chemical consumption. The strength and

optical properties of the fungal treated and untreated pulps after bleaching were evaluated

to estimate the effect of fungal treatment on the pulp properties.

5.2 Materials and Methods

5.2.1 Bleaching Conditions and Sequences

Kraft pulp of bamboo samples were bleached by the CEHH bleaching sequence.

All the bleaching experiments were carried out in the laboratory, using batch vessels

immersed in water bath at constant temperature. The conditions maintained during

bleaching are given in Table 5.2 and also detailed in text below.

Table 5.2: Conventional Bleaching Conditions for All Bleaching Sequences.

Conditions Stages

C E HI HII

Chemical charges Kappa no.× 0.22 × 0.60 3.5% Kappa no.× 0.22 × 0.24 Kappa no.× 0.22 × 0.16

Pulp consistency% 3 10 10 10

Temperature0C 30 60 45 45

Time (minutes) 30 60 120 120

pH 2.0 10 9 9

Chlorination (C): Chlorine was dissolved in water by bubbling slowly from a chlorine

cylinder. The chlorine water strength was determined by pipetting out 5 ml of the chlorine

water into a 250 ml conical flask containing 10 ml of 10% potassium iodide and 20 ml

distilled water. The top of the pipette was kept under the surface of this solution to prevent

escape of chlorine. The iodine liberated was titrated against 0.2N sodium thiosulfate using

starch indicator.

R×0.2×35.5

Chlorine, g/l =

5

Where, R = volume in ml of thiosulfate used in the titration

171

Freshly prepared chlorine water was added to 3% consistency pulps in capped

plastic jar at pH 2. Reaction time maintained was 30 minutes at 30°C. At the end of

reaction, pulps were washed and subjected to alkali extraction. For CEHH sequences total

chemical charge was calculated on the basis of kappa number and 60% of the total chlorine

demand was utilized in the C stage, while 40% of total chlorine demand was divided in

each H stage. The kappa factor was 0.22 for each sample.

Extraction (E): Laboratory grade sodium hydroxide pellets were dissolved in distilled

water. After the solution was cooled down, the clear liquid was decanted and titrated as

given in 4.3.2.1.

Chlorinated pulps were extracted with NaOH (3.5%) at 60°C temperature, 10%

consistency and 60 minutes time. After the end of reaction time, the pulps were washed

using terylene cloth.

Hypo-chlorination (H): The calcium hypochlorite solution was prepared by dissolving

bleaching powder (calcium hypochlorite) in water. 1 kg of bleaching powder was added to

10 liters of water into a plastic bucket, thoroughly agitated, closed with a lid and set aside

for settling, for overnight. The supernatant liquor was filtered through a terylene cloth over

a Buchner funnel using suction. The available chlorine in hypochlorite was determined

iodometrically. 5 ml of hypochlorite solution was pipetted into a 250 ml conical flask

containing 10 ml of 10% acetic acid and titrated against 0.2N thiosulfate using starch as a

indicator.

R×0.2×35.5

Chlorine, g/l =

5

Where, R = volume in ml of thiosulfate used in the titration

The hypochlorite, 1st and 2

nd stages were performed in polyethylene bags at

reaction time 120 minutes, pulp consistency 10%, pH 9 and temperature 45°C. For H stage

40% of total chlorine demand was utilized by dividing again in 60% and 40% ratio in two

stage of hypo-chlorination. After the end of reaction pulps were washed using terylene

cloth.

172

5.2.2 Hand Sheet Preparation and Testing

Hand sheets were prepared of both treated and untreated bamboo pulp samples

with the help of laboratory sheet former. The experimental details for preparation and

testing for strength properties of bleached pulp sheets have been discussed in details in

4.3.4.

Optical Properties: The most important properties of fully bleached pulps are the optical

properties, i.e. the light scattering coefficient and the opacity. Opacity characterizes the

ability of paper to hide text or pictures on the back side of the sheet. Brightness is

reflectance of paper using blue light. Blue light is used because papermaking fibres have

a yellowish color and because the human eye perceives blue color as brightness.

“Lorentzen & Wettre – Elrepho” was used to measure optical properties.

The intrinsic reflectance factor measured at an effective wavelength of 457 nm

with a reflectometer conforming to the requirements described in AS/NZS 1301.436s-91 -

Measurement of diffuse reflectance factor and calibrated against ISO reference standards.

Units of brightness are a ratio, expressed as a percentage of the radiation reflected by a

body to that reflected by a standard reflecting diffuser under the same conditions.

5.3 Results and Discussion

Pulps obtained from kraft pulping of treated and untreated bamboo samples (non

destructured and destructured) were bleached by CEHH sequences. The kappa factor was

0.22 for each sample. Bleached pulps obtained from bleaching of NDC, DC, NDT and DT

were used to prepare hand sheets to evaluate the strength and optical properties (Fig. 5.1).

On the basis of pulp kappa number and assuming uniform kappa factor for all the pulp

samples, utilization of bleaching chemicals (as chlorine) was found to reduce 5kg/t in

destructured control (DC), 12kg/t in non destructured treated (NDT), 23kg/t in destructured

treated (DT) samples when compared from non destructured control (NDC) sample.

5.3.1 Strength and Optical Properties of Bleached Pulps

The effect of bleaching on pulp yield, strength and optical properties in each

sample was studied and evaluated for effect of fungal treatment on brightness of pulp.

173

Table 5.3 shows the effect of fungal treatment and cooking time on the strength and

optical properties of bamboo bleached pulps.

The properties of bleached pulp sheets from NDC, NDT, DC and DT bamboo

samples were compared to find out the variation in tear index, tensile index, burst index,

brightness and opacity. The tear index is influenced by fiber length, while tensile and

burst index are influenced by both fiber length and extent of hydrogen bonding.

Table 5.3: Strength and Optical Properties of Bleached Treated/Untreated Bamboo

Non destructured and Destructured Pulps Obtained at Various Cooking Time.

S.

No.

Pulp

Samples

Yield% Tensile

Index,

N.m/g

Tear Index,

mNm2/g

Burst

Index,

K.Pa.m2/g

Brightness%

Opacity%

1 NDC 1

NDC 2

NDC 3

NDC 4

45.39

43.93

43.76

42.40

56.98

68.05

70.74

66.78

19.50

19.80

19.96

19.57

3.97

4.91

4.90

4.16

74.02

74.08

74.53

74.76

97.44

98.10

98.19

95.94

2 DC 1

DC 2

DC 3

DC 4

47.45

47.69

45.85

44.18

68.69

67.56

66.73

59.42

10.17

10.69

10.43

10.19

4.10

4.33

4.45

4.31

75.00

75.32

76.43

75.97

93.96

94.42

93.99

94.44

3 NDT 1

NDT 2

NDT 3

NDT 4

44.72

43.45

43.37

38.80

58.50

66.13

69.54

63.72

18.57

18.72

18.23

15.53

4.28

4.97

4.53

4.14

76.64

80.06

79.80

79.97

94.05

98.51

99.21

98.14

4 DT 1

DT 2

DT 3

DT 4

44.88

44.35

43.33

42.30

62.19

61.76

61.67

59.11

6.73

6.45

5.95

5.90

4.64

4.26

4.39

4.05

84.03

85.33

84.28

84.20

92.51

92.75

94.59

94.73

5.3.1.1 Brightness and Opacity

Table 5.3 and Fig. 5.2 show the effect of fungal treatment and cooking time on the

brightness of the finally bleached pulps. Generally brightness value of unbleached pulps

is lower than bleached pulps. The brightness value depends on pulping processes and

pulping conditions because they can reduce and remove lignin content in wood and non-

wood fiber. The residual lignin, remains in unbleached pulp, has major effect on

174

brightness value. If a comparison is made between NDC, DC, NDT, DT bleached pulps

brightness was increased in following order.

NDC < DC < NDT < DT

The final brightness of NDC bleached pulps when compared with NDT showed a

different pattern. In case of NDC pulps, brightness increased in pulps cooked from 30

minutes to 120 minutes. The maximum brightness was 74.76% in the bleached pulp

cooked for 120 minutes. Whereas in case of NDT pulp, highest brightness observed was

80.06% in the bleached pulp cooked upto 60 minutes cooking time. At the same time

when the brightness is compared with NDC, the brightness is comparatively 5.98 units

more in NDT.

In case of DC and DT, when brightness values were compared a different pattern

was observed. Brightness values of DC pulps increased upto 90 minutes. After 90

minutes a slight decrease in brightness was observed. In case of DT maximum brightness

was observed in the pulps of 60 minutes cooking time period. However decrease in

brightness was observed from 60 to 120 minutes cooking. The highest observed

brightness was 85.33% in DT pulp of 60 minutes and 76.43% in DC pulp of 90 minutes

cooking.

If a comparison is made between NDC and DT, brightness properties of DT are

higher than NDC. At the optimum cooking time period i.e. 30 minutes, when the

brightness value of NDC is compared with DT, the brightness is comparatively 10.01

units more in DT. The lower kappa number and higher brightness in DT pulp indicates

that fungal treatment makes a chemical change in lignin, which helps remove the lignin

easily in the subsequent bleaching stages (Dube and Kothari, 1983; Kirk and Shimada,

1985; Akhtar et al., 1993).

Table 5.3 and Fig. 5.3 show the effect of fungal treatment and cooking time on the

opacity of the finally bleached pulps. No significant effect of fungal treatment was

observed on opacity of NDC, NDT, DC and DT pulps at all the cooking time periods.

Whereas opacity values were slightly lower in DT pulp sheets compared to NDC pulp

sheets. In case of DT pulp samples, fibers are degraded slightly more than NDC pulp

175

samples. This is due to harsh treatment by chemicals during cooking where the treated

fibers are exposed for longer time.

5.3.1.2 Tensile Index

The variations in tensile index for NDC, DC, NDT and DT bleached pulps are

shown in Table 5.3 and Fig. 5.4. When tensile index of NDC compared with NDT

bleached pulp samples for all the four cooking time periods, it showed increase in tensile

index upto 90 minutes cooking. However reduction in tensile properties of both bleached

NDC and NDT pulps were observed after 90 minutes cooking. The maximum tensile

obtained were 70.74 N.m/g in NDC and 69.54 N.m/g in NDT bleached pulp of 90

minutes cooking.

Tensile index of DC when compared with DT show decreasing pattern from

bleached pulp of 30 minutes to 120 minutes cooking. Tensile index decreased from 68.69

N.m/g to 59.42 N.m/g in case of DC and 61.19 N.m/g to 58.11 N.m/g in case of DT with

increasing cooking time.

A comparison between NDC and DT pulps shows 5.21 N.m/g higher tensile in

DT pulp than NDC pulp at optimum cooking time period i.e. 30 minutes.

5.3.1.3 Tear Index

The variation in tear index after bleaching shown in Table 5.3 and Fig. 5.5, for

NDC, NDT, DC and DT pulp samples, is explained below:

Tear index of NDC when compared with NDT did not show much difference in

the pulps cooked from 30 to 120 minutes. In NDC maximum tear index obtained was

19.96 mNm2/g in 90 minutes cooked pulp. Whereas; in case of NDT maximum tear index

was 18.72 mNm2/g for 60 minutes cooked pulp. In case of NDT there was a decrease in

tear index of bleached pulps cooked for 90 and 120 minutes subsequently.

In case of DC and DT, when the tear values of bleached pulps of all cooking time

periods are compared, a different pattern is observed. In DT pulps, highest observed tear

index was 6.73 mNm2/g of 30 minutes pulp. However a drop in tear values was then

observed. If a comparison is made between DC and DT, tear index of DC are higher than

DT. At the same time when the tear index values are compared with corresponding

176

brightness, the drop in brightness is comparatively more in DC than DT. The variation in

tear index was due to harsh treatment of bleaching chemical.

Tear index of NDC bleached pulps when compared with DT bleached pulps, of all

the four cooking time periods, show more drop in tear properties. In NDC, maximum tear

index obtained was 19.96 mNm2/g of 90 minutes pulp. However, in case of DT

maximum tear index observed was 6.73 mNm2/g of 30 minutes pulp. The tear index was

lower in DT pulp sheets than NDC pulp sheets.

5.3.1.4 Burst index

Table 5.3 and Fig. 5.6 show the effect of bleaching chemicals on burst index of all

the pulp samples. Burst index of NDC bleached pulp observed at 30 minutes of cooking

time was 3.97 K.Pa.m2/g, whereas this value increased to 4.28 K.Pa.m

2/g in the case of

NDT. In case of NDC the maximum burst index observed was 4.91 K.Pa.m2/g in the

bleached pulp of 60 minutes cooking time periods. However, reduction in burst index

properties was observed in the pulps after 60 minutes. In case of NDT, burst index

increased from 4.28 K.Pa.m2/g to 4.97 K.Pa.m

2/g in 30 to 60 minutes. There is no

significant difference in the burst properties of NDT and NDC bleached pulps. However

brightness of NDT is more than NDC.

In case of DC and DT, when burst values are compared, a different pattern is

observed in all bleached pulps of different cooking time periods. In DC, highest burst

observed was 4.45 K.Pa.m2/g in the pulp of 90 minutes. Whereas in DT, highest burst

observed was 4.64 K.Pa.m2/g in the pulp of 30 minutes. However a drop in burst values

was then observed in both the pulp samples. This is mainly due to exposure of the fibers

to bleaching chemicals for longer time. When a comparison is made in between NDC and

DT bleached pulps of 30 minutes cooking time period, less burst value is observed in

NDC than DT. Whereas other burst values are more in NDC than DT bleached pulp. This

is due to harsh treatment of bleaching chemical.

5.4 Conclusion

To achieve the desired brightness, all pulp samples extracted at four different

cooking times i.e. 30 minutes, 60 minutes, 90 minutes and 120 minutes, were bleached

177

using CEHH sequences. Bleaching chemical charge was calculated on the basis of kappa

number and kappa factor. The Kappa factor for each pulp sample was 0.22. On the basis of

kappa number at same kappa factor it was observed that saving of bleaching chemical was

5kg/t in destructured control (DC), 12kg/t in non destructured treated (NDT), 23kg/t in

destructured treated (DT), when compared from non destructured control (NDC). Although

conventional bleaching of chemical pulp using chlorine is the most economic one, it is not

possible to achieve higher brightness without sacrificing pulp strength. Hypochlorite

extensively degrades the cellulose. With conventional CEHH sequences, the target

brightness is achieved at the cost of drastic reduction in strength properties (Ates et al.,

2008). The investigation has shown that brightness of destructured treated samples was

10.01% ISO points more than non destructured control pulp. Fungal treatment makes a

chemical change in lignin, which helps to remove the lignin easily in the subsequent

bleaching stages. Opacity of all pulp samples was more than 90% and there was a little

effect of fungal treatment on opacity observed. The strength properties of the pulp samples

did not show much difference among them. If a comparison is made between strength

properties of unbleached sheets with bleached sheets, tensile, tear and burst properties

shows 8-10% reduction due to harsh chemical treatments given for bleaching purpose.

178

(a) (b)

d

(c) (d)

Fig. 5.1: Bleached Pulp Sheets of (a) NDC, (b) DC, (c) NDT and (d) DT.

179

Fig. 5.2: Brightness of Bleached NDC, DC, NDT and DT Pulps in Relation to

Cooking Time (Minutes).

Fig. 5.3: Opacity of Bleached NDC, DC, NDT and DT Pulps in Relation to Cooking

Time (Minutes).

180

Fig. 5.4: Tensile Index of Bleached NDC, DC, NDT and DT Pulps in Relation to

Cooking Time (Minutes).

Fig. 5.5: Tear Index of Bleached NDC, DC, NDT and DT Pulps in Relation to

Cooking Time (Minutes).

181

Fig. 5.6: Brust Index of Bleached NDC, DC, NDT and DT Pulps in Relation to

Cooking Time (Minutes).

182

5.5 References

Akhtar, M., Attridge, M.C., Myers, G.C. and Blanchette, R.A. 1993.

Biomechanical pulping of loblolly pine chips with selected white rot fungi.

Holzforschung, 47(1): 36-40.

Akida, K. 2001. Indirect adaptive model predictive control of a mechanical pulp

bleaching process using a smart delay time predictor. A thesis, Master of Science

in Engineering, In the Department of Electrical and Computer Engineering. The

University of New Brunswick, Khaled Akida. 62p.

Ali, M. and Sreekrishnan, T.R. 2001. Aquatic toxicity from pulp and paper mill

effluents: A review. Adv. Environ. Res., 5(2): 175-196.

Ansari, P.M., Sengupta, B., Karforma, H.K., Gupta, S.K., Jwala, H. 2007.

Development of standards of AOX for small scale pulp and paper mills. Central

Pollution Control Board. Programme Objective Series Probes/104/2006-2007. pp.

1-9. Avilable at: www.cpcb.nic.in/newitems/34.pdf.

Ates, S., Ni, Y. and Imamoglu, S. 2008. Pretreatment by Ceriporiopsis

subvesmispora and Phlebia subserialis of wheat straw and its impact on

subsequent soda AQ and kraft AQ pulping. Roumanian Biotechnological Letters,

13(5): 3914-3921.

Barr, D.P. and Aust, S.D. 1994. Mechanisms white-rot fungi use to degrade

pollutants. Environ. Sci. Technol., 28(2): 78A-87A.

Brunner, F.L. and Pulliam, T.L. 1993. An analysis of the environmental impact on

pulping and bleaching technologies. Tappi J., 76(7): 65–74.

Casimir-Schenkel, J., Davis, S., Fiechter, A., Gygin, B., Murray, E., Perrolax, J.

and Zimmermann, W. 1995. Pulp bleaching with thermostable xylanase of

Thermomonospora fusca. US Patent No. 5407827.

Dence, C.W. and Reeve, D.W. 1996. Pulp bleaching – principles and practice. Ist

edition. TAPPI Press, Atlanta, USA. 868p.

Dube, H.C. and Kothari, I.L. 1983. Lignin and its degradation by fungi. Ind. Bot.

Reptr., 2: 101-106.

183

Eggert, C., Temp, U., Dean, J.F.D. and Eriksson, K.E. 1995. A fungal metabolite

mediates degradation of non-phenolic lignin structures and synthetic lignin by

laccase. FEBS Letter, 391(1-2): 144–148.

Eriksson, K.E.L. 1998. Past successes and future possibilities for biotechnology in

the pulp and paper industry. In: 7th International Conference on Biotechnology in

the Pulp and Paper Industry, 16-19 June 1998. Proceedings. Vancouver, Canada.

pp. A1–A4.

Froass, P.M. 1996. Structural changes in lignin during kraft pulping and chlorine

dioxide bleaching. PH.D. Thesis. Institute of Paper Science and Technology,

Atlanta, Georgia. 260p.

Fujita, K., Kondo, R., Sakai, K., Kashino, Y., Nishida, T. and Takahara, Y. 1991.

Biobleaching of kraft pulp using white-rot fungus IZU-154. Tappi J., 74(11):

123–127.

Glenn, J.K. and Gold, M.H. 1985. Purification and properties of an extracellular

Mn(II)-dependent peroxidase from the lignin-degrading basidiomycete,

Phanerochaete chrysosporium. Arch. Biochem. Biophys., 242(2): 329–341.

Gullichsen, J. and Fogelholm, C.J. 2000. Chemical pulping, papermaking science

and technology, Book 6A, Fapet Oy, Jyvaskyla. 693p.

Johansson, N.G. and Clark, F.M. 1995. Alkaline extraction, E+P and P bleach

plant operations short course. Course Notes. Tappi Press, Atlanta, GA, pp. 1-23.

Johnston, P.A., Stringer, R.L., Santillo, D., Stephenson, A.D., Labounskaia, I. and

McCartney, H.M.A. 1997. Towards zero-effluent pulp and paper production: the

pivotal role of total chlorine free bleaching. Environmental Science and Pollution

Research, 4 (3): 130-135.

Jong, E., Field, J.A. and Bont, J.A.M. 1992. Evidence for a new extracellular

peroxidase: manganese inhibited peroxidase from the white-rot fungus

Bjerkandera sp. BOS55. FEBS Letter, 299(1): 107–110.

Keski-Säntti, J. 2007. Neural networks in the production optimization of a kraft

pulp bleach plant. Ph.D. Thesis, Faculty of Technology, University of Oulu,

Finland. 103p.

184

Kondo, R., Harazono, K. and Sakai, K. 1994. Bleaching of hardwood kraft pulp

with manganese peroxidase secreted from Phanerochaete sordida YK-624. Appl.

Environ. Microbiol., 60(12): 4359–4363.

Kirk, T. K. and Shimada, M. 1985. Lignin biodegradation: the microorganisms

involved and the physiology and biochemistry of degradation by white-rot fungi.

In: Higuchi, T. (ed.). Biosynthesis and biodegradation on wood components.

Academic Press, NY. pp. 579-605.

Kuhad, R.C., Singh, A. and Eriksson, K.E. 1997. Microorganisms and enzymes

involved in the degradation of plant fiber cell walls. Adv. Biochem. Eng.

Biotechnol., 57: 45-125.

Kuwahara, M., Glenn, J.K., Morgan, M.A. and Gold, M.H. 1984. Separation and

characterization of two extracellular H2O2-dependent oxidases from ligninolytic

cultures of Phanerochaete chrysosporium. FEBS Letter, 169(2): 247–250.

Malinen, R. and Fuhrman, A. 1995. Recent trends in bleaching of chemical pulp.

Paperi ja Puu, 77(3): 78-83.

Moreira, M.T., Feijoo, G., Sierra-Alvarez, R., Lema, J.M. and Field, J.A. 1997.

Biobleaching of oxygen delignified kraft pulp by several white rot fungal strains.

J. Biotechnol., 53(2-3): 237–251.

Pryke, D.C. and Reeve, D.W. 1997. A survey of ClO2 delignification practices in

Canada. Tappi Journal, 80(5): 153-161.

Sarkanen, K.V. 1962. The Chemistry of Delignification in pulp Bleaching,

Cellulose Research Institute, Syracuse University, N.Y., U.S.A. pp. 219-231.

Avilable at: www.iupac.org/publications/pac/5/1/0219/pdf.

Sixta, H., Suess, H.Y., Potthast, A., Schwanninger, M., and Krotscheck, A. 2006.

Pulp bleaching. In: Sixta, H. (ed.). Handbook of Pulp, Vol 2, Wiley-VCH Verlag

GmbH, Weinheim, 609p.

Sjostrom, E. 1993. Wood chemistry fundamentals and applications. Academic

Press Inc., San Diego. 293p.

Tien, M. and Kirk, T.K. 1983. Lignin-degrading enzyme from the hymenomycete

Phanerochaete chrysosporium Burds. Science, 221(4611): 661–663.

185

Tortter, P. C. 1990. Biotechnology in the pulp and paper industry: A review (Part

I). Tappi J., 73(5):198–204.

Wang, R.X., Tessier, P.J.C. and Bennington, C.P.J. 1995. Modeling and dynamic

simulation of a bleach plant. AICHE Journal, 41(12): 2603-2613.