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Comperation of pulping and bleaching behaviors of some agricultural residues1

Saim ATEŞa, İlhan DENİZb, Hüseyin KIRCIb, Celil ATİKc, Onur Tolga OKANb,*2

aKastamonu University, Faculty of Forestry, Department of Forest Industrial3

Engineering, 37200 Kastamonu, Turkey.4

bKaradeniz Technical University, Faculty of Forestry, Department of Forest Industrial5

Engineering, 61080 Trabzon, Turkey.6

cIstanbul University, Faculty of Forestry, Department of Forest Industrial Engineering,7

34473 Istanbul, Turkey.8

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*Corresponding author at; Karadeniz Technical University, Faculty of Forestry,21

Department of Forest Industrial Engineering,61080 Trabzon, Turkey. Tel: +90 462 37722

15 14; fax: +90 462 3257499. E-mail addresses: [email protected] (Onur T.23

OKAN).24

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Abstract1

In the present study, the characteristics of bleaching and beating of annual plants and2

agricultural waste, which constitute important raw material potential for the pulp and3

paper industry in Turkey, were determined, and the effects of this process on some paper4

properties were examined. First, chemical contents were determined for each raw material,5

and then evaluated for use in the pulp and paper industry. All raw materials studied were6

found to be suitable for use in the pulp and paper industry, according to the determined7

chemical content. Subsequently, the pulps obtained with different properties were first pre-8

treated with enzyme xylanase, and then bleached using with Elementary Chlorine Free9

(ECF) method, utilizing the DEpD bleaching sequence, which is both easy to apply, and10

highly effective. The bleaching behavior of each material was then determined. The11

highest ISO brightness value of 98.3% was obtained using soda-AQ pulps deriving from12

rye straw. This is followed by wheat straw (92.0%), reed (88.6%), corn stalks (87.6%),13

and rice straw (87.5%). Each unbleached pulp sample was beaten at a constant 300014

revolutions PFI (9000 rev. for hemp) and changes in freeness properties were15

determined. The hardest material to beating is hemp fibers, followed by reed, rye, corn,16

and cotton stalks. The best beatable pulps were rice straw, tobacco, wheat, sunflower,17

and barley stalks. Paper sheets from both unbleached and bleached pulps were tested.18

Keywords: Annual plants, Enzyme, ECF bleaching, Paper properties, Soda-AQ pulping19

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Introduction1

The use of agricultural residues in the paper industry, as a source of cellulose, is2

supported by many institutions, due in part to increasing environmental pressures3

(Camarero et al. 2004). The principal aim of those incentives is to minimize the4

environmental damage of the cellulose industry, in addition to reducing raw material5

pressure placed on forests (Pan et al., 1999). Moreover, another reason which makes the6

use of agricultural residues in the cellulose industry attractive is the fact that some7

countries have limited forest resources (Jimenez, 1999). When those countries that have8

an agricultural-dependent economy and limited forest sources are considered, the use of9

agricultural residues, and either cultured or uncultured annual stalks, for manufacturing10

pulp will offer a significant solution to the raw material problem (Okan et al, 2013).11

Being an agricultural-dependent country with limited forest resources, Turkey is still far12

away from utilizing the current potential of agricultural residues in the cellulose13

industry. In total, 38,247 hectares of agricultural fields are cultivated in Turkey. Of this14

cultivated area, the potential number of stalks (which include wheat, barley, corn, rye,15

cotton, and rice straw), usable for cellulose industry over last three years (2011, 2012,16

and 2013), is estimated at approximately 94 thousand metric tons. The worldwide17

tendency of increased demand-to-paper-and-cardboard-products persists, a constraint18

will occur in the production of wood-derived cellulose, and it will be inevitable to use19

the high growth potential of agricultural fibers in the cellulose industry in order to20

overcome this limitation (Fillat et al., 2012).21

Another important problem encountered by the paper industry concerns22

minimizing environmental pollution and developing technologies that create less23

pollution. After it was discovered that chlorine-containing components (for bleaching24

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pulp using conventional methods) react with the lignin (a residue in the pulp), which get1

converted into environmentally hazardous chlorinated phenolic compounds and2

poisonous carcinogenic compounds (such as dioxine and furan groups), exist in the3

waste water of bleaching process, social pressures were born to limit use of compounds4

containing chlorine: such as chlorine, chlorine dioxide, hypochloride, and chloride. All5

these facts led the pulp industry to develop new technologies which do not cause6

environmental problems in the production of bleached paper (Okan, 2013). However,7

the bleaching process of pulps (which are derived from annual plants) is difficult due to8

anatomic and chemical characteristics, therefore modern totally chlorine-free (TCF)9

bleaching procedures are not enough to reach a high brightness level in this type of pulp10

(Camamero et al., 2004). For this purpose, when it is compared with other11

environmentally friendly technologies used for bleaching pulps derived from annual12

plants, enzymatic procedures offer low-cost solutions by limiting the chlorine dioxide13

capacity (Stafford, 2000). The xylanase is a commercially available enzyme that is most14

often used for pretreatment of pulp bleaching. In a study with the bleaching stages15

determined as DC(EOP)(DED)(D:Chloride, C:Chlorine, E: Alkaline extraction, O:16

Oxygen, P:Peroxide), the total amount of chlorine could be reduced at rate of 15-23%17

with the use of the enzyme xylanase, without changing pulp quality in production plant18

conditions (Manji, 2006).19

In a current study, it was investigated whether the residual annual plants, which20

are cultivated all around Turkey, can be feasibly used as raw material in the paper21

industry. The resulting pulps, showing different characteristics, first exposed to pre-22

bleaching with the enzyme xylanase, followed by an easy to use, and remarkably more23

efficient ECF (Elementary chlorine-free bleaching) bleaching sequence (DEpD)24

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(D:Chloride, Ep: Alkaline-peroxide extraction). The bleaching characteristics of the1

resulting annual plant pulps were revealed. Also, the beating degrees of raw material2

were examined. Physical and optical properties of trial papers, which were made from3

those pulps, were determined. Thus, each annual plant or agricultural waste material4

will be evaluated in a production plant, either separately or altogether.5

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2. Materials and methods7

2.1. Material8

2.1.1. Raw Materials9

Cultivated areas were studied for each raw material, considering the location and10

potential of study areas in Turkey. The wheat, rye and barley straw were supplied from11

Konya, Cotton stalk was supplied from Adana, Tobacco and corn stalk were supplied12

from Samsun, Sunflower stalk was supplied from Tekirdağ, Rice straw was supplied13

from Çorum, Reed supplied was from Afyon and finally Hemp was supplied from14

Kastamonu province for this study. Initially, annual stalk samples were cleaned of15

leaves, root, soils, and other contaminants. Then, stalks were cut into 4-5cm pieces16

using a cutter. Raw material experiments were then conducted on the whole stalk. For17

hemp, only phloem fibers were used.18

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2.2. Method1

2.2.1 Analysis of raw material2

Annual plant samples were ground up and 60-80 mesh fractions were selected to3

determine the chemical composition, according to TAPPI T 264 om-88. Samples were4

first placed in a Soxhlet extraction, with alcohol-benzene extraction, according to T 2045

cm-97, then an acetone extraction according to SCAN CM:49-03. Holocellulose content6

was determined by Wise’s sodium chlorite method (Wise and Murphy 1946), and7

cellulose content according to Kurscher and Hoffner’s nitric acid method (Rowell8

1984). In addition, alpha cellulose (T 203 cm-99), lignin (T 222 om-02), silica (T 2079

CM-99), and ash (T 211 OM-93) contents were determined. Determination of 1%10

sodium hydroxide and water (hot and cold) solubility of annual plants were carried out11

following the standard procedures described in T 212 om-98 and T 212 OM-8812

respectively.13

2.2.2. Methods used for production and chemical analyses of pulp14

Kappa number described as the remaing lignin amount in pulp as a percentage of15

the total lignin content of the raw material. Easily bleachable pulp means the kappa16

number is below 15 (Danielewicz and Šlusarska 2006). In order to ensure the kappa17

numbers of pulps are within the category of easily and moderately bleachable pulps,18

previous studies were referenced (Jimenez et al.,1995; Lopez et al; 1996; Lopez et al.,19

2005; Rodriguez et al., 2008; Akgül and Tozluoğlu, 2009; Shakhes et al. 2011; Jahan20

and Rahman, 2012). Soda-AQ pulping method, the most suitable for agricultural21

residues (Eroğlu 1990), was choosed and applied to cooking plan as can be seen in22

Table 1.23

Table-124

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Cooking trials were performed in a thermostatically controlled, rotary, laboratory-1

type reactor characterized by a capacity of 15 liters, electrically heated, resistant to2

pressure of 25kg/m2, 4 rpm, with an automated temperature control table. The reactor3

was manually loaded and unloaded, and 600g of completely dry cut stalks were used for4

all of the cooking procedures. Determination of the kappa numbers and viscosities of5

pulp samples were carried out using the standard procedures described in T 236 om-996

and Scan-C 15:62 respectively.7

Handsheets of 60g/m2 were formed, and their some properties were evaluated in8

accordance with the TAPPI standard methods. The handsheets were conditioned in9

accordance with T 402 sp-98. The burst index of handsheets was measured by method T10

403 om-97, the tensile index of handsheets were determined by method T 404 cm-9211

and tear index was carried out by standard procedure described in T 414 om-98. ISO12

Brightness, yellowness, and opacity were calculated to the, ISO 2470-1, ASTM E313,13

ISO 2470 respectively, and the amount of bleaching yield was calculated using the dry14

solids content of the pulps.15

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2.2.3 Pulp bleaching17

2.2.3.1. Xylanase pretreatment (enzymatic procedure)18

A commercially available enzyme called endo-xylanase was used for the19

preliminary biological process prior to the elementary chlorine-free (ECF) bleaching20

sequence of pulps. Endo-xylanase was supplied from Sigma, and its activity was21

determined according to the DNS method (Bailey, 1988). The diluted sample of enzyme22

(30µl) was incubated in 300µl of 1% (w/v) common beech wood-xylane solution for 2023

minutes at 40°C. Activity of 1U xylanase was calculated as the enzyme catalyzed by24

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1mmol xylose per minute. Xylanase, 2 IU/g at ratio of 7:1 (solution/stalk), was applied1

to each pulp sample, which was obtained following the production of paper pulp, and2

was applied for 2 hours at pH = 4.8 and 48°C.3

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2.2.3.2. Elementary chlorine-free (ECF) bleaching procedure5

It was aimed to determine the bleachability characteristics of raw materials by6

applying DED bleaching sequence (D: Chloride, Ep : Alkaline-peroxide extraction)7

according to the easy to use and remarkably efficient conventional ECF (Elementary8

Chlorine-Free) bleaching method, following preliminary biological bleaching.9

Procedures of the bleaching sequence and application levels are given in detail in Table10

2.11

Table-212

2.2.4 Refining Process13

According to pre-trial results, reasonable PFI beating revolution was determined14

as 3000 for annual plants and also 9000 for hemp fibers. Each sample of unbleached15

pulp was beated totally 3000 revolution in the PFI beater under low load conditions, and16

beating characteristics were examined by SR° (Schopper Riegler degree) of the pulp.17

Because SR° value of hemp fibers were normally very low those fibers were beated18

with PFI as 9000 revolution.19

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2.2.5. Production of handsheets21

Paper samples obtained from pulp by using Rapid Köthen, which were made from22

different types of agricultural residues, were conditioned for 24 hours in an air-23

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conditioned room according to ISO 287 standards, and then some optical, and physical1

properties of each paper were determined according to TAPPI standard.2

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3. Results and discussion4

3.1. Chemical composition of raw material5

The average composition of raw materials is given in Table 3. Holocellulose is6

defined as the total content of carbohydrate materials. High holocellulose content,7

therefore, is considered desirable for the pulp and paper industry because it has been8

correlated with higher pulp yield (Shakhes et al., 2011).9

Table-310

The holocellulose content of wheat straw, barley, corn, tobacco, cotton, and11

sunflower stalks was similar to each other. Furthermore, there was a nearly identical12

holocellulose content of rye, rice straw, and reed. The holocellulose content of hemp13

was found to be higher than the other agricultural residues in this study. The14

holocellulose content in wheat straw, barley, corn, tobacco, cotton, and sunflower stalks15

are very close to those reported for wood species such as Pinus pinaster, Fagus16

sylvatica L, and Pinus sylvestris L (Alonso, 1976; Inari et al., 2007). The holocellulose17

content in rye, rice straw, and reed was similar to other wood species such as poplar and18

spruce (Law et al., 2001; Bertaud and Holmbom, 2004). The holocellulose content of19

rye (Secale cereale L), hemp (Cannabis sativa L.), sunflower (Helianthus annuus L),20

tobacco (Nicotiana tabacum L.), barley (Hordeum vulgare), and corn stalks (Zea mays L.)21

were close to that found in published literature (Lopez et al., 1996; Akgül and22

Tozluoğlu, 2009; Shakes et al., 2011). The lowest holocellulose contents were observed23

in wheat straw (Triticum aestivum L) and cotton stalks (Gossypium hirsitum L), while the24

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highest holocellulose contents were observed in rice straw, compared to that found in1

published literature (Deniz et al 2004; Rodriguez et al., 2008). The highest cellulose2

content was observed in hemp, but the lowest cellulose content was observed in cotton3

stalks and sunflower stalks. Additionally, the cellulose content of these raw materials4

was nearly identical to each other, with the exception of hemp. The amount of alpha5

cellulose, namely the fraction that is insoluble in 17.5% NaOH, was determined to be6

above 35%. According to Shakes et al (2010), the presence of 35% alpha cellulose7

content has a satisfactory effect on paper strength properties. Furthermore, the pulp8

yield strongly correlated with both holocellulose and alpha cellulose content. When9

examined Table 3, it can be seen that alpha cellulose content of wheat straw, barley, rye,10

corn, and sunflower stalks are significant differences compared to rice straw and reed.11

The alpha cellulose content of hemp was 72.29%, which was higher than the other12

agricultural residues samples.13

The desirable lignin content level is below 30%, because lignin was considered to14

be an undesirable polymer, and the removal during pulping and bleaching requires a15

high amount of energy and chemicals (Shakes et al., 2011). The lignin content of hemp16

was fairly low compared to other agricultural residues samples in this study, but no17

significant difference in lignin content was found in most other agricultural residues18

studied.19

Overall, high silica and ash content were found in agriculture samples. Compared20

to wood, this type of raw material commonly has silica and ash contents, which can21

cause problems in the manufacturing process. Ash content in trace elements also makes22

lower bleaching efficiency (Dutt et al. 2009).23

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The alcohol-benzene and acetone solubility of hemp and rice straw are lower than1

the other agricultural samples in this study. In the other eight agricultural samples,2

alcohol-benzene and acetone solubility contents were found to be very similar.3

According to Table 3, the content of 1% NaOH,hot and cold water solubilitytions4

of hemp was found to be fairly lower than the other agricultural residues samples.5

Barley, sunflower, tobacco, and wheat straw contain a significantly higher content of6

soluble compounds in both hot and cold water, and also 1% NaOH. Generally, the7

presence of extractives in wood increased the pulping effluent load and consumption of8

pulping reagents, and reduced the pulp yield (Azizi et al. 2010). For instance, as9

examined in Table 4, total yield of rye and rice straw is higher than wheat straw and10

barley stalk, although all cooking methods are the same. The reason for this is that11

wheat straw and barley stalk contain a considerably higher content of soluble12

compounds in 1% NaOH and hot and cold water, as compared to rye and rice straw.13

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3.2. Pulp properties obtained from annual plants with soda-AQ cooking method15

Screened yield, kappa numbers and viscosity values of bleachable (kappa number16

≤ 15) pulps, which are derived from annual plants using soda-AQ method, are given in17

Table 4.18

Table 419

It is obvious that cooking conditions vary when the cooking plan of each annual20

plant is examined. This fact is an important piece of criteria for the availability of21

relevant raw material. It is well known that the more lignin content in the pulp means22

the more bleaching chemicals and energy for removing it. When Table 4 is examined, it23

can be speculated that wheat, barley, rye, and rice straw are easily cooked raw materials,24

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while corn stalk is a moderately hard to cook material. Tobacco, cotton, and sunflower1

stalks are hard to cook raw materials. In bleaching, the term hard cooking conditions2

when used for a given pulping process, refers to the amount of lignin remaining in the3

unbleached pulp. Therefore cooking conditions have a remarkable effect on kappa4

numbers and viscosity. When figure 1 is examined, the lowest kappa values were5

obtained with rye (10.0), corn (10.14), reed (10.88), rice (11.2), wheat (12.60), and6

barley straw (12.7), among pulps which were cooked under the same conditions. When7

the viscosity value, indicating the depolimerization degree of cellulose, is examined, it8

was observed that easily cooked pulps have similar viscosites. However, harder cooking9

conditions were applied to obtaining economically bleachable pulps from tobacco,10

cotton, and sunflower stalks, which are among hard to cook pulps, and in conclusion11

this approach showed that the viscosities of those pulps were low (5.79cp, 6.07cp and12

7.49cp, respectively).13

Figure 114

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In a study conducted with tobacco stalks, it was found that for soda-AQ pulps16

which applied 20% active alkaline solution, 170°C, 90 minute cooking and 0.1% AQ17

conditions, the kappa number was 28.7 and viscosity was 46.0 cp, and it was not18

possible to bleach those pulps in an economic manner (Ateş et al., 2010). In another19

study conducted for producing economically bleachable paper pulp, it was found that20

for tobacco stalks, which were manufactured in conditions of 25% active alkali ratio,21

165°C pulping temperature, 180 minutes pulping time with the addition of 0.2% AQ,22

the kappa number was 20 (Shakhes et al., 2012). Based on cooking studies conducted23

on cotton stalks under various conditions, the kappa number was 33.1 and viscosity was24

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31.0 cp in the following conditions: 18% active alkali ratio, 0.075% AQ, solution to1

stalk ratio of 4:1, and 165°C (Ali et al., 2001). In a study conducted for obtaining2

bleachable pulps from sunflower stalk under different cooking conditions, the kappa3

number of pulps obtained from stalks was 25, under conditions of 16% active alkali,4

170°C with the addition of 0.13% AQ soda-AQ cooking (Khristova et al., 1998). In5

another study conducted for production bleachable soda-AQ pulp from corn stalks with6

or without preliminary hydrolysis, corn stalks applied a cooking procedure in different7

alkaline conditions (150°C, stalk/solution ratio of 6:1, AQ rate of 0.1%, and cooking8

time of 60 minutes). Based on those cooking conditions, the kappa number was 27.49

when 14% alkaline was applied, 24.8 when 16% alkaline was applied, and 21 when10

18% alkaline was applied (Jahan and Rahman, 2012).11

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3.3. Some physical properties of papers obtained from bleached and unbleached13

pulps14

Schopper Riegler degree (SR°), viscosity, gramage, and some physical and optical15

properties of paper obtained at an equal PFI beating stages of pulp papers, which are16

derived from annual plants with the soda-AQ method, are given in Table 5.17

Table 518

A comparison of pulps obtained from annual plants and agricultural residues,19

using the soda-AQ method, with regards to pulp freeness, is given in Figure 2. When20

Figure 2 is examined, the hardest material to beating is hemp fibers, followed by reed,21

rye, corn, and cotton stalks. The best beatable pulps are rice straw, tobacco, wheat,22

sunflower, and barley stalks. Therefore, pulps obtained from this group can be beat23

together.24

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Figure 21

In regards to Table 5, it is also observed that unbleached pulps can be more2

difficult to beat in comparison to bleached pulps. The underlying reason is that amount3

of xylane is low in pulps which have applied enzymatic pretreatment (Fillat, 2012). In4

other words, bleaching causes fibers to become more individual, and therefore cause5

more difficulty in beating. In studies investigating the effect of xylanase on beating the6

pulp, other investigators have found similar results (Wong et al., 1997; Roncero et al.,7

2003; Valls et al., 2010).8

The changes observed in the breaking length, burst, and tearing resistances of the9

handsheets (obtained from pulp after bleaching is performed) are demonstrated in10

Figure 3. As the figure indicates, resistance values were adversely influenced after11

pulps, obtained from hemp, cotton stalks, and reed fibers, were bleached. A mean12

reduction of 3.8 units was observed in the tearing index of hemp phloem, which is13

directly proportional to the length of the fiber. This is followed by reed with a reduction14

of 2.08 units, and cotton stalks with a reduction of 0.71 unit. Moreover, hemp, cotton,15

and tobacco stalks have higher rankings in terms of lignin residue in the paper pulp, and16

it is possible to speculate that when the lignin is removed from the stalks, the physical17

properties are adversely affected.18

An increase was observed in the resistance properties of paper pulps made from19

wheat straw, barley, rye, and rice straw (among cereal stalks) as well as corn, tobacco20

and sunflower stalks, when the pulp was bleached. Breaking length, burst, and tearing21

resistances increased at rates of 15.12%, 34.5% and 18.0%, respectively, as a22

consequence of the ECF bleaching method with pretreatment of xylanase (X+DEpD),23

particularly for the pulps obtained from rice straw.24

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Figure 31

Degradation occurs when bleaching is made under alkaline conditions. This leads2

to significant reduction on the viscosity (Camarero et al., 2004). Physical properties of3

the pulp are not only related to the amount of cellulose, but also to the ratio of hemi-4

cellulose. High amounts of cellulose usually give strong pulps, and a low ratio of5

cellulose to hemicellulose reduces the resistance of paper. (Brannvall, 2004). Briefly,6

the reactions of different annual plants to a bleaching sequence, which is applied under7

same conditions, are derived from the change of their effects on chemical compounds8

and fiber morphologies.9

3.4. Optical properties of papers as a result of ECF bleaching10

The brightness values of handsheets bleached in accordance with the XDEpD X11

(Xylanase) + D (chlorine dioxide) + Ep (Alkaline peroxide) + D (Chlorine dioxide)12

sequence, are given in Table 6.13

Table 614

Soda-AQ pulps produced from different annual plants under different cooking15

conditions (optimum, should the resultant kappa number be the same) were pretreated16

with enzyme xylanase, followed by bleaching with a DEpD bleaching sequence.17

Changes in brightness values of thepulps after the bleaching procedure is fully complete18

are given in Figure 4 and Table 6. When examining the table, it is shown that no19

remarkable change is observed in brightness properties. However, the effects of20

pretreatment with the enzyme can be clearly seen at the end of next bleaching stage. In21

other words, the results of this enzymatic procedure have small but remarkable effects22

on the brightness. When the literature is examined, it is found that this is similar to a23

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study conducted on the effects of pretreatment with xylanase on the brightness of paper1

pulp (Stafford et al., 2000; Ateş et al., 2008).2

Figure 43

When Table 6 is examined, it is obvious that brightness increases as long as4

bleaching advances. ISO Brightness values for fully bleached annual plant pulps are5

given in Figure 4. Accordingly, the highest ISO brightness value of 98.3% is obtained6

from soda-AQ pulps deriving from rye straw. This is followed by wheat straw (92.0%),7

reed (88.6%), corn (87.6%), and rice straw (87.5%). The weakest reaction to the8

XDEpD bleaching sequence was obtained from cotton, tobacco, and sunflower stalks,9

and the corresponding ISO brightness values were 61.0%, 68.4% and 71.9%,10

respectively.11

In a study conducted on wheat straw, which underwent a DEpD bleaching12

sequence with xylanase pretreatment, it was found that brightness increased as long as13

the bleaching stages advanced. ISO brightness of fully bleached wheat straw pulp was14

approximately 85%. It was reported in the same study that the XDEpD bleaching15

sequence is the best alternative to the DEpD bleaching sequence in terms of brightness16

and optical properties (Jimenez et al., 1995). Similar brightness values were determined17

in another bleaching study which involved the enzymatic pretreatment of paper pulps18

obtained from wheat straw pulps using the Biokraft method (Ateş et al., 2008a).19

4. Conclusions20

As a consequence of different cooking procedures for obtaining bleachable pulps21

from each of the primary agricultural residues, it was determined that tobacco, cotton,22

and sunflower stalks are not appropriate for obtaining bleachable pulp. When23

agricultural residues were examined with regards to beatability using the ECF bleaching24

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method with xylanase pretreatment, it was found that bleached pulps were usually more1

difficult to beat than unbleached pulps. It is understood that among all raw materials2

used, rice straw was the best type with regards to beatability. However, it can be3

speculated that reed, hemp, and cotton stalks are not suitable for ECF bleaching with4

enzymatic pretreatment. Generally no positive change was observed in the physical5

properties of agricultural residues after bleaching was completed. However, it was6

found that the ECF bleaching method with enzymatic pretreatment, similar to the7

beating process, was not a suitable method for reed, hemp, and cotton stalks due to the8

reduction in physical properties after bleaching was completed. When the brightness9

value was examined after the ECF method with enzymatic pretreatment was completed,10

an increase was observed for all types of pulps. However, considering bleaching11

efficiency, the best reaction to the XDEpD bleaching sequence was given by cotton12

(216%), wheat (167%), sunflower (154%), and reed (131%), while the weakest reaction13

to bleaching (as indicated by comparison to baseline unbleached brightness) was given14

by hemp, corn, and rye pulps, as indicated by corresponding increases at rates of 80, 99,15

and 160%, respectively.16

In brief, it was found that the type of agricultural residues appropriate for xylanase17

pretreated using ECF bleaching included rice, barley, wheat straw, and corn (in18

descending order) and unfavorable types were cotton, hemp, and reed.19

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Acknowledgment: The authors are grateful to Foundation for The Scientific and21

Technological Research Council of Turkey (TUBITAK) (Project No: 108 O 594) for22

financial support of this work.23

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6

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10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

23

Tabels1

Table 1: Cooking plan applied to production of pulp which is characterized as2

bleachable and derived from annual plants based on preliminary trials3

Annual plantNaOH

%

Temp.

oC

Time

min

AQ

(%)

Time to maximum

Temp (min.)

Wheat straw 16 160 40 0.1 60

Rice straw 16 160 40 0.1 60

Rye straw 16 160 40 0.1 60

Barley straw 16 160 40 0.1 60

Reed stalk 20 160 60 0.1 60

Corn stalk 16 160 60 0.1 60

Tobacco stalk 25 170 120 0.1 60

Cotton stalk 25 170 180 0.1 60

Sunflower stalk 20 170 180 0.1 60

Hemp 14 125 90 0.1 60

4

5

6

7

8

9

10

11

12

24

Table 2: Bleaching plan applied following preliminary biological bleaching1

Bleaching

Stages

Bleaching Conditions

Dosage Time

D1 %3 ClO2 120

EP

%1 NaOH

%0.5 MgSO4

%0.5 H2O2

180

D2 %1.5 ClO2 120

* Following assumptions were made: temperature is 75°C and the concentration is 72percent.3

45

6

7

8

9

10

11

12

13

14

15

16

17

18

19

25

Table 3: Chemical compositions of used agricultural residues.1

Whe

atst

raw

Bar

ley

stra

w

Rye

stra

w

Ric

e st

raw

Ree

d st

alk

Cor

n st

alk

Tob

acco

stal

k

Cot

ton

stal

k

Sunf

low

erst

alk

Hem

p

Components (%)

Holocellulose 69.84 66.01 76.95 79.39 78.85 69.92 64.29 62.79 66.85 86.08

Cellulose 50.70 49.30 51.65 55.30 56.65 55.70 50.95 47.30 47.80 80.70

α-cellulose 42.07 38.70 44.55 53.67 52.56 46.78 36.40 29.74 44.20 75.29

Lignin 22.33 19.47 17.25 23.77 22.79 18.16 15.15 23.79 14.43 6.42

Silica 7.33 6.88 2.07 15.67 1.23 2.98 0.94 0.34 0.44 1.24

Ash 11.63 10.97 4.01 15.44 4.17 7.75 14.44 4.99 7.99 3.62

Solubilities (%)

Acetone 5.37 5.39 4.51 3.02 2.98 8.10 5.58 3.84 4.86 1.62

Alcohol-

Benzene

9.33 8.71 7.44 2.21 3.26 8.57 8.06 8.36 7.48 1.59

1% NaOH 53.67 56.25 44.35 45.63 36.81 46.43 50.57 48.88 50.05 20.04

Hot water 14.71 16.25 15.72 13.81 9.80 16.82 21.56 17.91 24.26 5.85

Cold water 11.33 11.01 11.95 9.66 7.61 14.64 17.15 15.05 21.08 5.29

2

3

4

5

6

7

26

Table 4: Yield and chemical properties of pulps made from annual plants with soda-AQ1

method.2

Name ofsample

NaOH%

AQ%

Temp.oC

Time

min

ScreenYield(%)

Reject(%)

Totalyield(%)

Kappano

Visc.Cp

Wheat straw 16 0.1 160 40 37.1 0.8 37.9 12.6 24.62

Barley straw 16 0.1 160 40 32.6 1.4 34.0 12.7 24.92

Rye straw 16 0.1 160 40 43.5 0.4 43.9 10.0 28.88

Rice straw 16 0.1 160 40 41.2 1.4 42.6 11.2 26.75

Reed 20 0.1 160 60 42.3 0.2 42.5 10.8 37.48

Corn stalk 16 0.1 160 60 42.4 1.3 43.7 10.4 32.01

Tobacco stalk 25 0.1 170 120 22.9 2.4 25.3 13.4 5.79

Cotton stalk 25 0.1 170 180 17.8 1.4 19.2 17.6 6.07

Sunflower

stalk

20 0.1 170 180 31.1 0.5 31.6 13.7 7.49

Hemp 14 0.1 125 90 64.2 0.0 64.2 14.8 65.87

3

4

5

6

7

8

9

10

11

12

27

Table 5: SR°, viscosity, and some physical properties of pulps in constant beating stages1

RawMaterials

PFI (

rpm

)

SRo

Vis

cosi

ty(c

p)

Gra

mag

e(g

/m2 )

Den

sity

(kg/

m3)

Bul

kine

ss(g

/cm

3)

Tear

inde

x(m

Nm

2/g)

Bur

stin

dex

(kPa

m2/

g)B

reak

ing

leng

th(k

m)

Tens

ilein

dex

(Nm

/g)

Unbleached

Barley straw 3000 56.5 24.92 64.65 711.75 1.40 3.72 3.81 6.77 66.34

Hemp 9000 37.0 65.87 77.42 645.16 1.55 26.61 2.59 3.11 30.51

Sunflower

stalk3000 56.5 7.49 71.24 689.39 1.45 3.49 1.99 4.24 41.61

Rye straw 3000 35.3 28.88 72.45 679.18 1.47 6.47 3.38 6.03 59.14

Reed 3000 21.0 37.48 73.92 537.63 1.86 9.09 2.06 4.18 40.97

Tobacco stalk 3000 61.0 5.79 75.27 711.20 1.41 3.32 2.25 4.36 42.74

Wheat straw 3000 57.5 24.62 67.20 896.06 1.12 3.58 4.84 7.95 78.00

Corn stalk 3000 41.5 32.01 68.68 735.89 1.36 5.36 3.16 5.92 58.01

Rice straw 3000 65.5 26.75 69.76 611.02 1.64 4.89 3.42 6.02 59.00

Cotton stalk 3000 45.0 6.07 75.40 591.40 1.69 4.75 2.11 3.79 37.13

X+DEpD Bleached

Barley straw 3000 43.5 22.22 68.95 759.10 1.32 4.02 4.47 6.74 66.08

Hemp 9000 11 32.49 58.06 483.87 2.07 22.81 1.60 2.13 20.84

Sunflower

stalk3000 41.5 7.15 70.56 682.88 1.46 3.55 2.08 4.56 44.73

Rye straw 3000 24.0 29.40 74.60 699.34 1.43 6.87 3.71 6.37 62.49

Reed 3000 15.0 16.13 73.79 536.66 1.86 7.01 1.34 3.02 29.60

Tobacco stalk 3000 45.0 5.76 67.61 638.81 1.57 3.05 2.32 4.84 47.47

Wheat straw 3000 45.0 25.00 69.35 924.73 1.08 4.28 4.93 8.16 80.00

28

Corn stalk 3000 30.0 29.66 71.10 761.81 1.31 5.42 3.50 6.19 60.66

Rice straw 3000 53.5 29.85 62.90 550.98 1.81 5.77 4.60 6.93 67.97

Cotton stalk 3000 26.5 5.85 92.34 724.23 1.38 4.04 1.69 3.22 31.61

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

29

Table 6: Brightness properties of annual plant soda-AQ pulps following XDEpD1

bleaching2

Raw material Control X stageX + D1

stage

X + D1 + Ep

stage

X + D1 + Ep +

D2 stage

Wheat straw 34.5 36.70 62.34 76.06 92.0

Barley straw 39.0 42.06 62.05 74.17 86.0

Rye straw 47.8 48.62 72.51 85.09 98.3

Corn stalk 44.0 43.41 60.74 70.12 87.6

Sunflower

stalk

28.325.72 34.85 55.79 71.9

Rice straw 40.7 40.27 54.40 66.18 87.5

Tobacco stalk 31.2 30.85 44.43 56.81 68.4

Cotton stalk 19.3 17.02 35.35 42.71 61.0

Hemp 44.4 38.55 56.83 78.41 80.1

Reed 38.3 37.78 53.46 75.75 88.6

3

4

5

6

7

8

9

10

11

30

Figures1

2

3

Figure 1: Kappa numbers and viscosity values of annual plant and agricultural waste4

soda-AQ pulps5

6Figure 2: PFI beating behaviors of annual plant and agricultural waste soda-AQ pulps7

Kappa No

010203040506070

Schopper (SR°)

30

Figures2

3

4


soda-AQ pulps7


Viscosity (cp)

30

Figures3

4

5


soda-AQ pulps9


Viscosity (cp)

31

1

Figure 3: Change in the physical properties of annual plant pulps depending on the2

bleaching3

4

5

Figure 4: ISO Brightness properties of fully bleached annual plant pulps6

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

Tear Index (mNm2/g)

Burst Index (kPam2/g)

Breaking length (Km)

50

60

70

80

90

100

110ISO Brightness

31

2


bleaching5

5

6


Tear Index (mNm2/g)

Burst Index (kPam2/g)

Breaking length (Km)

ISO Brightness

31

3


bleaching7

6

7


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