JP2015206139A - Method for producing dissolved pulp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing dissolved pulp satisfying an ultrahigh purity (α cellulose content>97%), a high polymerization degree (η>700) and a high whiteness (ISO brightness>90).SOLUTION: Provided is a method for producing dissolved pulp immersing a bleach pulp into cold concentrated alkali, thus hemicellulose is removed to increase the purity of α cellulose, in which the step of immersing the bleach pulp into cold concentrated alkali is a treatment where the bleach pulp is immersed into a sodium hydroxide aqueous solution of 7.0 to 7.5 wt.% in the range of 15 to 100°C for 30 to 90 min.

Description

  The present invention relates to a method for producing dissolving pulp.

  Dissolving pulp is known as a pulp having a high refining degree and an α-cellulose content of 90% or more among chemical pulps. In the production of this dissolving pulp, cold alkali extraction is required even if it is a steaming method when obtaining ultra-high purity of α-cellulose.

  Patent document 1 makes it a subject to provide the method of improving the quality of the cellulose fiber used for formation of melt | dissolution pulp, a cellulose fiber is made into about 5%-about 30% (v: v) ammonia water, and about 0.00. A degumming solution containing 5% to 3% hydrogen peroxide (relative to OD fiber) at a temperature of about 50 ° C. to about 200 ° C. and a liquid and solid content of about 3: 1 to about 20: 1 Disclosed is a method for degumming cellulose fibers comprising the step of treating at a concentration (v / w).

Special table 2010-528191

  Even in the dissolving pulp manufacturing method to which the cellulose fiber degumming method of Patent Document 1 is applied, ultra high purity (α cellulose content> 97%), high degree of polymerization (η> 700), high whiteness ( It does not establish a method for producing dissolved pulp of ISO brightness> 90).

  In view of the above problems in the prior art, the present invention provides a method for producing a dissolving pulp of ultra high purity (α cellulose content> 97%), high degree of polymerization (η> 700), and high whiteness (ISO brightness> 90). The purpose is to provide.

  In the method for producing a dissolving pulp of the present invention, bleached pulp is immersed in a cold concentrated alkali to remove hemicellulose, and the purity of the dissolving pulp, that is, the content of α cellulose in the dissolving pulp (hereinafter referred to as “α cellulose purity” in this specification). In the method for producing dissolved pulp, the step of immersing the bleached pulp in a cold concentrated alkali is carried out at 15-100 ° C. in a 7.0-7.5 wt% aqueous sodium hydroxide solution. The treatment is characterized in that the treatment is immersed for 30 to 120 minutes, preferably 30 to 90 minutes.

  The temperature of the aqueous sodium hydroxide solution should be controlled within the range of 15-45 ° C, the temperature of the aqueous sodium hydroxide solution should be controlled within the range of 15-40 ° C, and the bleached pulp should be immersed for 45-90 minutes. desirable.

  After immersing the bleached pulp in cold concentrated alkali and thoroughly washing it with water, sodium metasilicate is added to the bleaching solution in a range of 0.2-0.5% by weight relative to the pulp to adjust the pH to 11-11.5. It is preferable to perform 0.2% or less hydrogen peroxide bleaching.

As a bleached pulp, a fiber fraction obtained by removing particles (soft cells) of 100 μm or less from a bleached kraft digested pulp derived from a bamboo material can be used.

  According to the method for producing a dissolving pulp of the present invention, it is possible to obtain a dissolving pulp having ultra-high purity (α cellulose content> 97%), high polymerization degree (η> 700), and high whiteness (ISO brightness> 90). it can.

It is explanatory drawing of the Example of the manufacturing method of the melt | dissolution pulp of this invention which shows the influence which the alkali concentration and reaction temperature at the time of melt | dissolution pulp preparation by LBKP * alkali treatment have on the alpha cellulose purity and intrinsic viscosity number of melt | dissolution pulp. It is explanatory drawing of the Example of the manufacturing method of the melt | dissolution pulp of this invention which shows the influence which the processing time and temperature by LBKP-alkali treatment have on alpha cellulose purity. It is explanatory drawing of the Example of the manufacturing method of the melt | dissolution pulp of this invention which shows the influence which the reaction temperature by LBKP-alkali treatment has on the alpha cellulose purity and viscosity of melt pulp after alkali treatment. It is explanatory drawing of the Example of the manufacturing method of the dissolving pulp of this invention which shows the influence of the temperature change in a LBKP-alkali process. It is explanatory drawing of the Example of the manufacturing method of the dissolving pulp of this invention which shows the influence which various bleaching processes have on the cellulose and whiteness in LBKP. It is explanatory drawing of the Example of the manufacturing method of the dissolving pulp of this invention which shows the influence of bleaching auxiliary agent addition in the bleaching by the hydrogen peroxide type | system | group of dissolving pulp. It is explanatory drawing of the Example of the manufacturing method of the dissolving pulp of this invention which shows the influence on the alpha cellulose purity which the neutralization method of an alkali treatment pulp gives. It is explanatory drawing of the Example of the manufacturing method of the dissolving pulp of this invention which shows the influence which the hydrogen peroxide bleaching before and behind LBKP-alkali processing has on the quality of dissolving pulp. It is an electron micrograph (500 times) of LBKP (A), NBKP (B), bamboo BKP (C) and bamboo fiber (D) bamboo soft cells (E).

Hereinafter, the manufacturing method of the dissolving pulp of this invention is demonstrated in detail.
In the method for producing dissolved pulp of the present invention, the step of immersing the bleached pulp in a cold concentrated alkali is a step of immersing the bleached pulp in a 7.0-7.5 wt% sodium hydroxide aqueous solution.
If it is less than 7.0 wt%, the α-cellulose purity does not sufficiently increase. Even if it exceeds 7.5 wt%, the increase in α-cellulose purity is negligible.

The temperature of the aqueous sodium hydroxide is in the range of 15-100 ° C. At higher temperatures, the alpha cellulose purity does not increase sufficiently. If it is 70 ° C. or higher, the purity slightly increases, but α cellulose is also decomposed.
When it exceeds 100 degreeC, alpha cellulose purity will fall.
More preferably, the temperature of the sodium hydroxide aqueous solution is controlled in the range of 15 to 45 ° C. This gives the highest alpha cellulose purity dissolving pulp. When it exceeds 45 degreeC, alpha cellulose purity will not fully raise.

  The time for immersing the bleached pulp in the aqueous sodium hydroxide solution is 30-90 minutes. If it is less than 30 minutes, the alpha cellulose purity does not rise sufficiently. When it exceeds 90 minutes, alpha cellulose purity will fall.

Most preferably, the temperature of the aqueous sodium hydroxide solution is controlled in the range of 15 to 45 ° C, and the bleached pulp is immersed for 45 to 90 minutes. This gives the highest alpha cellulose purity dissolving pulp.
If the temperature of the sodium hydroxide aqueous solution exceeds 45 ° C., the α-cellulose purity does not sufficiently increase. On the other hand, when the temperature is lower than 15 ° C., an effect corresponding to the cost required for cooling cannot be obtained. Moreover, when the immersion time exceeds 90 minutes, the α cellulose purity is lowered. On the other hand, if it is less than 45 minutes, alpha cellulose purity does not rise sufficiently.

At that time, it is necessary to add sodium metasilicate to the bleaching solution in the range of 0.2 to 0.5% by weight based on the pulp.
As a result, the reaction system can be made alkaline and has a buffering action. In addition, there is an effect that it can react with polyvalent metal ions and suppress disproportionate cleavage of hydrogen peroxide.
If it is less than 0.2%, the alkali cannot be sufficiently maintained and the bleaching effect is not sufficient, and if it exceeds 0.5%, the bleaching effect is hardly improved and is not effective.

As bleached pulp, hardwood, conifer, bamboo-derived ECF (Elemental Chlorine Free) and TCF (Total Chlorine Free) bleached pulp can be used.
In particular, a fiber fraction obtained by removing particles of 100 μm or less from bleached kraft digested pulp derived from bamboo material can be used.

Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
In a polypropylene bag, LBKP (craft pulp made from hardwood) was immersed for 60 minutes in aqueous sodium hydroxide solutions at various concentrations at a reaction temperature of 85 ° C. and 100 ° C. The treatment was performed in a drying cabinet or a water bath, and the reaction was started at a predetermined temperature ± 3 ° C. The temperature raising time was about 20 to 30 minutes. After the treatment, dilution and filtration with water were repeated 2-3 times to make the pH neutral. The obtained alkali-treated pulp was dried overnight at 60 ° C. with a forced circulation dryer. After drying, the sample was left at room temperature to obtain a dry dissolving pulp sample. The obtained dissolved pulp sample was pulverized with a cutter mill, and the water content was measured.

  The obtained dry dissolving pulp sample was subjected to α cellulose purity measurement and viscosity measurement. The α-cellulose purity was measured by measuring about 150 mg of absolute dryness with an accuracy of 0.1 mg, and a 20% sodium hydroxide aqueous solution and mili-Q water (ultra pure water) were added so as to be 17.5 wt% of sodium hydroxide. This was stirred with a stirrer for 30 minutes. Thereafter, 7.5 mL of miri-Q water was added and further stirred for 5 minutes. After stirring, suction filtration was performed with a glass fiber filter paper having a diameter of 47 mm (GF / C, manufactured by Advantec), which had been weighed in advance. The solution used for the alkali treatment was washed twice with a 7.0-7.5 wt% sodium hydroxide aqueous solution, and the washing was filtered through a glass fiber filter paper. The obtained alkali-extracted fiber was washed several times with mili-Q water, 10% acetic acid solution was added and suction filtered. After further washing with water, 10% acetic acid was again added to the filter paper and left for about 1 minute. Then, it aspirated and washed 6 times with water. The obtained filter paper and residue were dried overnight (or 4 hours or more) with a 105 ° C. dryer, allowed to cool to room temperature with a vacuum desiccator, and then weighed to determine the amount of α-cellulose recovered.

  Viscosity is measured by measuring a dissolved pulp sample of about 50 mg of absolute dryness with an accuracy of 0.1 mg, adding mili-Q water to a water content of 7.5 mL, and using a stirrer until the pulp is sufficiently dispersed. After stirring (˜30 minutes), 7.5 mL of 1 mol / L copper ethylenediamine solution (Kanto Chemical) was added and stirred for 15-20 minutes with a stirrer to dissolve. The viscosity of the 0.5 mol / L copper ethylenediamine solution after dissolution was taken in a Cannon Fenceke dynamic viscosity tube and kept at 25 ° C. for 5 minutes, and then the flow down time was measured to measure the viscosity. From the measurement results, the intrinsic viscosity was calculated according to JIS 8215: Intrinsic Viscosity Measurement.

  The results are shown in FIG. The α-cellulose purity increased up to a concentration of about 7.0 wt% of the sodium hydroxide solution regardless of whether the treatment temperature was 85 ° C. or 100 ° C. At a concentration of 7.0 wt% or more, the α cellulose purity was in a saturated state, and the effect of improving the α cellulose purity by making the sodium hydroxide solution concentration 7.0% or more was small. On the other hand, at the alkali concentration before saturation, a tendency that the α-cellulose purity was slightly higher under the treatment condition of 100 ° C. was observed.

  On the other hand, the viscosity tended to decrease as the alkali concentration increased. However, there was almost no effect due to the treatment temperature. However, the intrinsic viscosity constant was about 700 even under the processing conditions with the lowest viscosity, and it was judged that the viscosity was sufficiently high. From the above, it has been clarified that the alkali treatment of LBKP proceeds sufficiently by immersing in an aqueous solution having a sodium hydroxide concentration of about 7 wt% so that the pulp concentration is about 10% and performing the treatment for about 60 minutes. It was.

Example 2
The alkali treatment was performed in the same manner as in Example 1. However, the treatment temperature was changed from 15 ° C to 100 ° C. Further, the treatment time was changed from 0 minutes to 120 minutes. In the 85 ° C. reaction system, the temperature rose from room temperature to 85 ° C. by 25 minutes after the start of the treatment.
The α cellulose measurement method and the like were carried out in the same manner as in Example 1.

  The results at the treatment temperatures of 85 ° C. and 25 ° C. are shown in FIG. The treatment time of 0 minutes represents the alpha cellulose purity of LBKP used as a raw material. The α cellulose purity had reached 96% by the time the treatment time reached 25 minutes and the temperature of the treatment system reached 85 ° C. In addition, a maximum purity of 96.4% was obtained when the treatment time was 60 minutes, and thereafter a tendency for the α cellulose purity to gradually decline was observed.

  Since sufficiently high α-cellulose purity was obtained before the treatment system temperature reached 85 ° C., it was expected that the removal of hemicellulose from the pulp would proceed sufficiently even at lower temperatures. Therefore, alkali treatment was performed at room temperature (25 ° C.). As a result, the α-cellulose purity of LBKP was improved by about 10% in 45 minutes at 25 ° C. and reached 97.8%. It was revealed that when the treatment time was extended to 90 minutes, 97.7% was almost the same as the 45 minute treatment, or slightly decreased.

  Since extremely high α-cellulose purity was obtained at a treatment temperature of 25 ° C., the results of a more detailed examination of the treatment system temperature are shown in FIG. It was found that the treatment temperature of 15 ° C. showed the highest purity (> 98%), and the purity gradually decreased as the temperature increased. Furthermore, the purity dropped sharply from around the treatment temperature of 60 ° C., and there was a minimal value around 60-80 ° C. Thereafter, when the temperature was further raised, the purity gradually increased and recovered to 96% or more. Looking at the viscosity, it can be seen that unlike the case of α cellulose purity, there is almost no effect in the low to medium temperature range (˜70 ° C.). If the temperature is higher than that, a significant decrease in viscosity may occur.

  In general, when the alkali treatment temperature is low, the fibers are well swollen by alkali, and extraction of hemicellulose into an alkaline solution is performed efficiently. On the high temperature side, it is said that the decomposition of hemicellulose occurs and the purity of α cellulose in the pulp is improved. It is known that there is a minimum value of α cellulose purity in the middle temperature range as in this result. Based on these facts, we examined how α cellulose purity is affected when combining swelling and extraction of hemicellulose by low-temperature alkali treatment and decomposition of hemicellulose by high-temperature alkali treatment.

The first stage treatment was carried out at low temperature (4, 15, 22.5 ° C.) for 45 minutes, then raised to 85 ° C. over 25 minutes and then treated for 45 minutes, and raised from room temperature to 85 ° C. and held for 45 minutes Later, alkali treatment was carried out in a system that was treated at a low temperature (15, 30 ° C.) for 45 minutes. As a result, as shown in FIG. 4, when the temperature was changed, the α cellulose purity was higher than that when treated at 85 ° C. for 90 minutes, but considerably more than when treated at 15 ° C. for 90 minutes. Alpha cellulose purity was low. From the above, for the production of dissolving pulp by alkali treatment of LBKP, a 7.0-7.5 wt% sodium hydroxide aqueous solution is used at a low temperature range of 4-45 ° C., preferably about 15-40 ° C. It has been clarified that a dissolving pulp having the highest α-cellulose purity can be obtained when it is carried out for about 45 to 90 minutes.

Example 3
LBKP or alkali-treated LBKP (DP) was suspended in water at a pulp concentration of 10% in a polypropylene bag, a bleaching agent or an auxiliary agent was added, and then adjusted to a predetermined pH using sodium hydroxide or an aqueous sulfuric acid solution. The pulp and the bleaching reagent were well blended and then immersed in a predetermined 60 ° C. water bath for 120 minutes. After completion of the bleaching, the pulp was further diluted with water and filtered and washed. After washing, the sample was air-dried at 60 ° C. overnight, and this sample was used as a measurement sample for α cellulose purity, viscosity, and ISO whiteness.

  In the quality of dissolving pulp, whiteness is important as a value indicating the amount of lignin. It is generally necessary to aim for a whiteness of 90 or more, preferably 91 or more. First, as a preliminary study, LBKP was bleached. As a bleaching system, a mixed system of hypochlorous acid (pH 10.5), oxone (persulfate, pH 3.0), thiourea (pH 6.5 or 10.5) and hydrogen peroxide was prepared. Also, hydrogen peroxide (pH 10.6-12.4) alone or a system in which sodium metasilicate was added to hydrogen peroxide was prepared. The results are shown in FIG. During various bleaching treatments, the improvement in ISO whiteness was observed only in the hydrogen peroxide alone and hydrogen peroxide + metasilicic acid bleaching systems. The hypochlorous acid bleaching system caused a significant decrease in α cellulose purity, and the persulfate bleaching system was observed to decrease in viscosity. The thiourea bleaching system did not seem to affect the pulp. In the hydrogen peroxide bleaching, although an increase in whiteness was observed, a slight decrease in α cellulose purity accompanying a decrease in viscosity and a lower molecular weight of cellulose was observed. On the other hand, when sodium metasilicate, also known as a cellulose protective agent, was added together with hydrogen peroxide, only an increase in whiteness was observed, and a decrease in viscosity and α-cellulose purity was not observed.

  By treating with LBKP hydrogen peroxide + sodium metasilicate bleaching system, we were able to obtain high whiteness while maintaining viscosity and alpha cellulose purity, so we treated the sodium hydroxide solution at 85 ° C and 7.0 wt%. The dissolved pulp was bleached. In addition to sodium metasilicate, magnesium sulfate known as a hydrogen peroxide bleach-based cellulose protective agent was also studied. As shown in FIG. 6, the whiteness of the addition system of sodium metasilicate was as high as that of the non-addition system (ISO brightness> 91.5%). On the other hand, in the magnesium sulfate addition system, the result was that increase in whiteness was suppressed. This is because magnesium sulfate generally has a protective effect at a lower concentration than metasilicic acid, and has features such as chelating more metals to suppress side reactions, so magnesium sulfate is more powerful in polysaccharides. By coordinating, it is thought that the sugar residue browned in the pulp was also protected.

Example 4
Pulp having an alkali treatment temperature of 21 ° C. and 85 ° C. was prepared. In the case of washing with water, the alkali-treated pulp was diluted with water and filtered three times to obtain a neutral pH. In the case of neutralization with acid, the pulp concentration is concentrated from 10% to 30% by suction filtration, 5 wt% dilute sulfuric acid is added to lower the pH to 8-9, which is close to neutrality, and then washed twice with water. went. The α cellulose purity was measured in the same manner as in Examples 1 to 3.

In the examination so far, it has been found that it is necessary to perform a hydrogen peroxide bleaching treatment at about pH 11 after treating the pulp with a high concentration of alkali in order to obtain high whiteness. After alkali treatment, alkali can be dehydrated and recovered to some extent, but the alkali remaining in the pulp must be washed or neutralized. Therefore, it was investigated whether washing with water until neutral pH was good or neutralization with acid was good. In the dissolving pulp prepared at any treatment temperature, the α cellulose purity was higher by about 1% when the pH was lowered to near neutral by washing with water (FIG. 7). This was presumed to be due to the hemicellulose component extracted or partially decomposed and eluted by the alkali treatment, re-precipitated by neutralization and re-adsorbed to the cellulose. Therefore, washing with water rather than neutralization with acid seems to be suitable for producing high purity dissolving pulp.

Example 5
For alkali treatment, add 7.3 wt% sodium hydroxide aqueous solution so that LBKP is 10 wt% by dry weight, and stir well. After post-bleaching, treat at 18 ° C for 45 minutes at 45 ° C for pre-bleaching. It was. The pulp was washed as described above.
In the hydrogen peroxide bleaching before alkali treatment, a predetermined concentration of hydrogen peroxide and 1.0 wt% (vs. pulp) sodium metasilicate were added to adjust the pH in the system to 11-11.5. The pulp concentration was 10 wt%. In the case of post-bleaching, the hydrogen peroxide concentration was 0.1-0.375%, and the pre-bleaching was 0.5-1.5% (both in weight percent of pulp). Bleaching was performed at 60 ° C. for 120 minutes. The obtained dissolved pulp sample was washed and air-dried at 60 ° C., and then the α cellulose purity, intrinsic viscosity constant, and ISO whiteness were measured.

  Compared with the pre-bleaching, the post-bleaching showed better values in all of the α-cellulose purity, viscosity and whiteness (FIG. 8). When the hydrogen peroxide was 0.5% or less, the α cellulose purity and viscosity were not sufficiently increased. In the case of pre-bleaching, the limiting viscosity number was about 800, not limited to the hydrogen peroxide concentration, whereas in the case of post-bleaching, a tendency to decrease according to the hydrogen peroxide concentration was observed. In most cases, however, post-bleaching was higher than pre-bleaching. The alpha cellulose purity showed the highest value when 0.1 or 0.2% (vs. pulp) hydrogen peroxide was used in post-bleaching, and higher than that without bleaching (0% in FIG. 8). However, in other cases, purity tended to be slightly lower than when not bleached. With regard to whiteness, the highest value was obtained when 0.2% wt (vs. pulp) hydrogen peroxide was used. From the above, bleaching of dissolving pulp is optimally performed after alkali treatment with 0.2% hydrogen peroxide and sodium metasilicate as a cellulose protective agent, and bleaching at pH 11.5 and 60 ° C. for 120 minutes. It was judged.

  Further, when bleaching with hydrogen peroxide having a pulp concentration of 0.2%, bleaching was performed by changing the amount of sodium metasilicate added to 0.2 to 1.0%. There was almost no change in both constants. Therefore, since the sodium metasilicate aqueous solution is alkaline, sodium metasilicate may be added so that the pH becomes 11-11.5 within this concentration range.

Example 6
Bamboo BKP was obtained by immersing a sieve (diameter 30-cm, depth 8-cm) with an opening of 100 μm in a tarai filled with 8 L of water, and putting BKP corresponding to 100 g of absolutely dry on the sieve. The pulp was washed with a lab stirrer (manufactured by Yamato) for 4 hours at 50 rpm. The fine particles that passed through the sieve were subjected to suction filtration with a nylon mesh having an opening of 50 μm. This was a parenchyma. For the pulp remaining on the sieve, the above washing was repeated a total of 5 times to eliminate fine particles as much as possible. This fraction was used as bamboo fiber.

  NBKP (craft pulp made from softwood) is added to 7.0 wt% sodium hydroxide aqueous solution so that the pulp becomes 10 wt%, and after alkali treatment at 85 ° C for 60 minutes, the alkali is removed with a dehydrator. The pulp concentration was diluted to 10%, and the pH was adjusted to 11.5 with sulfuric acid. Hydrogen peroxide was added to this so that it might become 0.25% (vs. pulp), and bleaching was performed at 60 ° C. for 60 minutes. After bleaching, washing with water and air drying, the α cellulose purity and viscosity were measured.

  LBKP, NBKP (craft pulp made from softwood), TCF-LBKP, bamboo BKP, bamboo fiber and soft cells are added with pulp so that the pulp concentration becomes 10% in a 7.3 wt% sodium hydroxide aqueous solution. Hold at 50 ° C. for 50 minutes. After treatment, the pulp was washed with water until the pH was near neutral. The washed alkali-treated pulp was added so as to have a pulp concentration of 10%, hydrogen peroxide of 0.2%, and sodium metasilicate of 0.5 wt% (both with respect to pulp concentration). At this time, the pH of the reaction system was 11.3-11.4. After stirring well, this was left still in a 60 ° C. water bath for 120 minutes. After the bleaching treatment, the pulp was washed again with water, air-dried at 60 ° C., and the α-cellulose purity, viscosity, whiteness and the like were measured.

As shown in Table 1, the pulp used for dissolving pulp production in this example and the dissolved pulp quality after alkali treatment are shown in Table 1, and it is understood that the α cellulose purity of LBKP and NBKP hardly changes. On the other hand, bamboo BKP has a particularly low purity of 85%. This is because fibers with high α cellulose purity (92.6%) and low parenchyma cells (78.4%) are mixed at a ratio of about 60-50: 40-50. On the other hand, as for the pulp used for dissolving pulp production, the viscosity was high in LBKP, and NBKP and bamboo BKP were almost the same. There was no significant difference between bamboo fiber and parenchyma cells.

  Looking at Table 1, it can be seen from the results of the dissolving pulp prepared by alkali treatment that the purity of α-cellulose is improved only to about 92% for NBKP and bamboo soft cells. On the other hand, with respect to LBKP and bamboo fiber, a purity exceeding 97% was obtained, and in particular, bamboo fiber had a purity exceeding 98%, which was a quality that can be called pure cellulose. The α-cellulose purity of the bamboo BKP after the alkali treatment was similar to the value expected from the weight ratio of fiber to parenchyma, as with the untreated bamboo BKP. The viscosity was higher than that of the raw material pulp except for NBKP to which sodium metasilicate was not added at the time of bleaching. Moreover, the dissolving pulp produced from bamboo fiber and LBKP has a limiting viscosity number exceeding 700 mL / g, and is a high-grade dissolving pulp together with α cellulose purity. The whiteness of these dissolving pulps was 92.2 and 91.3, respectively, indicating a sufficient whiteness. From the above, it was found that bamboo fiber is most suitable for the production of the highest grade dissolving pulp, followed by LBKP.

SEM photographs of each BKP, fiber, and parenchyma are shown in FIG. Bamboo fiber and LBKP have an average fiber diameter of about 8-12 μm, whereas NBKP has a fiber diameter of 20-30 μm, and bamboo soft cells are not fibers but particles of 20 μm-100 μm in diameter. . Such a large difference in fiber shape may be one of the reasons why the α cellulose purity of NBKP and bamboo parenchyma cells has not improved.

Claims (6)

The step of immersing the bleached pulp in the cold concentrated alkali in the method for producing a dissolved pulp which is dehemicellulosed by immersing the bleached pulp in the cold concentrated alkali to increase the alpha cellulose purity is 7.0-7.5 wt%. A method for producing a dissolving pulp, characterized in that the bleaching pulp is immersed in an aqueous solution of sodium hydroxide at 15 to 100 ° C. for 30 to 120 minutes. The manufacturing method of the dissolving pulp of Claim 1 which manages the temperature of sodium hydroxide aqueous solution in the range of 15-45 degreeC. The manufacturing method of the dissolving pulp of Claim 1 or Claim 2 which manages the temperature of sodium hydroxide aqueous solution in the range of 15-40 degreeC, and immerses a bleached pulp for 45-90 minutes. The manufacturing method of the dissolving pulp as described in any one of Claims 1-3 which performs 0.2% or less of hydrogen peroxide bleaching by the weight with respect to a bleached pulp, after immersing a bleached pulp in a cold concentrated alkali. The method for producing a dissolving pulp according to claim 3 or 4, wherein sodium metasilicate is added to the bleaching solution in a range of 0.2 to 0.5% by weight with respect to the pulp. The method for producing a dissolving pulp according to any one of claims 1 to 5, wherein a fiber fraction obtained by removing particles of 100 µm or less from a bleached kraft cooking pulp derived from a bamboo material is used as the bleaching pulp.