PRODUCED USING THE SAME

Technical Field

The present invention relates to a method for producing fiber pulp using bamboos, and more particularly to a method for producing good-quality fiber (dissolving) pulp using bamboos, which comprises longitudinally splitting the bamboo, transversely cutting the split bamboo to short lengths, dissolving hemicellulose from the cut material by prehydrolysis, and bleaching the prehydrolyzed material with a bleaching agent causing low environmental pollution, and thus has a high pulp production yield and does not emit environmental pollutants such as dioxin, as well as pulp produced thereby.

Generally, papermaking and dissolving pulps are recognized to be produced using wood.

As used herein, the term "dissolving pulp" refers to fiber pulp that can be used later to produce fibers.

In other words, because the dissolving pulps consist mostly of wood pulps, and producing pulp as the raw material of paper while conserving forests due to the lack of wood resources and maintaining the environment have recently became a great problem, effects to produce pulp using non- woody plant fibers and the like are being conducted.

Background Art

The present invention relates to a method for producing pulp, and more particularly to a method for producing

dissolving pulp (i.e., fiber pulp) which can be used later to produce fibers.

In other words, because the dissolving pulps consist mostly of wood pulps, and producing pulp as the raw material of paper while conserving forests due to the lack of wood resources and maintaining the environment have recently became a great problem, effects to produce pulp using non- woody plant fibers and the like are being conducted.

Such non-woody plants include paper mulberry bast fibers, hemps, cottons, and Manila hemps, and Korea Patent Publication Nos. 98-9651 and 93-2604 disclose a method for pulp using rice-straw.

All such efforts can be considered as efforts to conserve trees, which can prevent environmental pollution. In other words, these efforts aim to conserve trees by absorbing pollutants and carbon dioxide contained in the atmosphere through photosynthetic action while producing and supplying oxygen.

The development of industry and civilization really led to a great improvement in the quality of life of mankind, but involved a rapid increase in energy use, so that the emission of greenhouse gas was also rapidly increased, and thus the contamination of the global environment and side effects thereof became very severe. In typical examples thereof, the depletion of the ozone layer in the South Pole becomes very rapidly severe, and misfortunes caused by a rapid change in weather, global warming and ecosystem destruction occur in the whole world.

Such environment pollution phenomena very rapidly progressed to reach a state that threatens the survival of

mankind, and thus the Tokyo Protocol on the reduction of greenhouse gas emissions, which has been delayed due to the noncooperation of some of highly developed countries, became effective. Accordingly, in manufactures in various countries, efforts to reduce greenhouse gas emissions are urgently required, and in severe cases, additional expenses for purchasing greenhouse gas emission rights are expected.

Meanwhile, rayon corresponding to high-grade fiber utilizes dissolving pulp produced from wood as a raw material.

Regarding the pressure for the reduction of greenhouse gas emissions as described above, a tree is a reproducible natural material, but it requires a period of a few years to a few ten years until it reaches a usable level. For this reason, the regulation for the use of wood is tightened and the pressure for the development of an eco-friendly material that can substitute for wood is being actualized.

One mean for solving this problem, which has recently received great attention, is a non-woody plant that eliminates the need for the felling of wood.

In other words, when this non-woody plant is used to produce pulp, there will be a great advantage in that wood, which is consumed in large amounts, needs to be felled.

Among the non-woody plants, a bamboo, which receives attention and is used as a raw material in the present invention, is produced in large amounts in Southeast Asia countries such as China and Myanmar and sufficiently grows to a usable degree only within about five months.

Recently, in China, a technology for producing dissolving pulp using a bamboo having antibacterial activity

and for producing rayon fiber using the dissolving pulp was developed.

However, this technology has shortcomings in that it does not consider the compact structure of the bamboo, so that the pulping of the bamboo is not satisfactorily achieved, and it consumes large amounts of chemicals and energy, and has low yield because a bleaching process is conduced in strong conditions. In addition, it causes the decomposition and destruction of fiber, making the fiber weak. A chlorine bleaching process using elemental chlorine provides the cause of dioxin generation.

Also, because bleaching powder that acts as the cause of the corrosion of an apparatus is used as a bleaching chemical, the durability of the production apparatus is highly problematic.

In addition, this processing problem acts as the cause of increasing chemical amount, energy consumption and production cost per unit pulp production.

Disclosure of Invention

The present invention has been made to solve the above- described problems occurring in the prior art, and it is an object of the present invention to provide a method for producing good-quality fiber (dissolving) pulp using a bamboo, which comprises longitudinally splitting the bamboo, transversely cutting the split bamboo to short lengths, dissolving hemicellulose from the cut material by prehydrolysis, and bleaching the prehydrolyzed pulp with a bleaching agent causing low environmental pollution, and thus has a high pulp production yield and does not emit

environmental pollutants such as dioxin, as well as pulp produced thereby.

Another object of the present invention is to provide a method for producing dissolving (fiber) fiber using bamboos, which allows the production of pulps having various qualities according to the intended use thereof by applying a technology capable of optionally controlling the degree of polymerization of the fiber pulp, and also can produce byproduct xylose using a method wherein xylose which forms a significant portion of hemicellulose dissolved during a prehydrolysis process is recovered and purified from a solution and cooked waste isolated from the pulp after prehydrolysis, as well as pulp produced thereby.

To achieve the above objects, the present invention provides a method for producing fiber pulp using a bamboo, comprising: a leaf removal step of removing the leaves of the bamboo; a longitudinal splitting step of longitudinally splitting the bamboo to have a width of 1.5-3 mm; a transverse cutting step of transversely cutting the split bamboo to a length of 10-30 mm to produce bamboo chips; a screening step of filtering out small fragments or impurities from the cut bamboo chips; a washing step of washing the bamboo chips with water to remove impurities, contaminants or dust; a prehydrolysis step of subjecting the washed bamboo chips to prehydrolysis using water or steam, and adding sulfur dioxide or sulfuric acid according to the degree of required prehydrolysis to promote the prehydrolysis so as to dissolve hemicellulose from the bamboo chips; a cooking step of introducing the bamboo chips into a digester, in which the ratio of a chemical liquor consisting of water, alkali and

anthraquinone to the weight of the bamboo chips is adjusted to 1:3.5-6.0 (bamboo: chemical liquor), and the bamboo chips are cooked at high temperature in said liquor ratio, thus softening and pulping the bamboo chips; a contaminant removal step of removing contaminants with the bamboo using a centrifugal cleaner; a selection step of removing contaminants from the cooked pulp using a pressure screen, and feeding back an incompletely cooked portion of the bamboo into the digester; a washing and concentrating step, in which a decker is used to wash the pulp so as to remove the chemicals and to squeeze water so as to concentrate the pulp; a bleaching step of bleaching the washed and concentrated pulp; an acid treatment and washing step of removing metal ions present on the surface and inside the pulp; and a sheet preparation step of preparing the pulp into a sheet or a roll. In addition, the present invention provides fiber pulp produced by said method.

Brief Description of Drawings FIG. 1 is a flowchart showing sequentially the steps of a preparation method according to the present invention. FIG. 2 shows a general centrifugal cleaner.

Best Mode for Carrying Out the Invention The present invention is similar to the prior art, in that it relates to a method for preparing fiber pulp.

However, the present invention is remarkably different from the prior art, in that non-woody plant bamboo is used to produce pulp, the consumption of chemicals and energy is reduced by treating the bamboo in the production of the pulp

so as to make prehydrolysis and cooking easy, the generation of hazardous substances such as dioxin which can be generated in a bleaching process is minimized, xylose (also used as the raw material of gum) contained in hemicellulose dissolved during the inventive prehydolysis step can be produced, and thus wood present on the globe needs not to be felled, and the pulp prepared from the bamboo has surprisingly good quality. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

As shown in the flowchart of FIG. 1, the inventive method for producing fiber (dissolving) pulp comprises a first step (bamboo leaf removal step) of removing the leaf of the bamboo. In other words, the bamboo leaf contains a large amount of extracts unnecessary to produce pulp, but has a small amount of essential fibrous material.

Thus, because the bamboo leaf is of help to prepare pulp, but rather can act as the cause of increasing the consumption of drugs, the bamboo leaf is removed before introduction into a process for producing dissolving pulp.

In other words, in the inventive method for producing the bamboo pulp, the bamboo leaf is not used and only the bamboo stalk is used. Then, a second step (longitudinal splitting step) of longitudinally splitting the bamboo to a width of 1.5-3 mm is conducted.

Due to the compact structure of the bamboo, chemicals are significantly difficult to penetrate the bamboo, compared to wood.

Thus, crushing must be conducted to initiate the production of pulp. For this purpose, the bamboo is first longitudinally split into half, and the split bamboo is additionally split to a narrower width. In this step, the bamboo is preferably split to a width of 1.5-3 mm.

This longitudinal splitting is a significantly characteristic step of the present invention, and when the bamboo is split at random without considering orientation, fibrous material will not be uniformly split, but rather the fibrous material itself can be broken.

This reduces the strength of the produced pulp to reduce the quality thereof.

For this reason, in the inventive production method, the bamboo is used after it is longitudinally split several times to have narrow width.

It is also possible to use a method of splitting the bamboo in a one-step process using a device mounted with a plurality of blades. Then, a third step (cutting step) of transversely cutting the longitudinally split bamboo to a length of 10-30 mm is conducted.

In other words, in order to produce small bamboo chips which are easily filled and packed in a digester, the split bamboo is transversely cut to a length of 10-30 mm using a cutter.

If the length of the bamboo chips is too large, they cannot be effectively packed into the digester, and if the bamboo is cut to an excessively short length, large damage to fiber can occur, resulting in the reduction in the strength

of the pulp.

Then, a fourth step (screening step) of filtering out small fragments or impurities from the cut bamboo chips is conducted. In other words, even if small fragments which are generated in the step of cutting the bamboo are prepared into pulp, the pulp is in a state in which the fibrous material is broken. Thus, these small fragments can weaken the strength of the pulp and increase the consumption of chemicals. Also, contaminants during the cutting step are not of any help to produce the pulp.

Accordingly, if these small fragments and contaminants are all used in the production of the fiber (dissolving) pulp, they will not be of any help for the yield (production rate) of the pulp and will adversely affect the quality of the pulp. For this reason, these are removed by screening.

Then, a fifth step (washing step) of washing the bamboo chips with water to remove impurities, contaminants and dust from the bamboo chips is conducted. In other words, the contaminant, dust and the like attached to the bamboo chips are removed with water.

This can reduce the consumption of unnecessary chemicals in a cooking process and allows pure pulp to be obtained, thus improving the quality of the produced pulp. Then, a sixth step (prehydrolysis step) is conducted, the washed bamboo chips are subjected to prehydrolysis using water or steam, and sulfur dioxide or sulfuric acid is added to the chips depending on the degree of required prehydrolysis to promote the prehydrolysis so as to dissolve hemicellulose from the bamboo chips.

In other words, to maximize the yield of fiber (dissolving) pulp in the bamboo chips while dissolving hemicellulose, the bamboo chips are subjected to prehydrolysis . This hydrolysis is performed with liquid water or steam using sulfur dioxide or sulfuric acid as a catalyst.

This prehydrolysis aims to dissolve hemicellulose from the bamboo chips, and thus if an acid is used alone, acid hydrolysis can severely occur to severely destroy cellulose. For this reason, the acid must be controlled to a suitable liquor ratio according to operation circumstances.

In this step, the ratio of the amount of liquid water and catalyst to the amount of the bamboo chips is preferably controlled within the range of 1.5-7 : 1 depending on the degree of required hydrolysis.

In other words, the prehydrolysis is performed in a state in which the ratio of the water-containing liquor to the bamboo chips is 1.5-7:1.

In this step, hemicellulose among the chemical components of the bamboo is decomposed while generating organic acid, which leads to the hydrolysis of the bamboo.

Thus, the desired polymerization degree and the hydrolysis degree of hemicellulose must be controlled using a characteristic in that, as said liquor ratio increases, the hydrolysis smoothly progresses.

In other words, regarding the liquor ratio, if the weight of the bamboo chips is 1 on an oven-dry weight basis, volume of the aqueous solution (if chemicals such as catalysts are contained, a state in which the chemicals are dissolved in water) is 1.5-7.

Also, the use of said liquor ratio aims to easily bring the bamboo chips into uniform contact with chemicals during the reaction and to control the extent of the reaction by allowing the intensity (concentration) of chemicals in contact with the bamboo chips to vary depending on the liquor ratio.

Also, although the conditions of the prehydrolysis step may slightly vary depending on the required quality, the prehydrolysis is preferably conducted at a temperature of 100-200 ^° C for 40-300 minutes.

Such conditions were determined through many experiments conducted by the applicant.

As used herein, the term "oven-dry weight" means the mass of the bamboo chips that excludes the content of moisture in the bamboo chips.

To calculate the oven-dry weight, the moisture content of the bamboo chips is measured, and on the basis of the measured value, the weight of only the bamboo chip is calculated. Meanwhile, in the sixth step (prehydrolysis) of the present invention, xylose may additionally be extracted.

In other words, bamboo contains pentosans in a high amount corresponding to 22%, and the pentosans are dissolved in the prehydrolysis step to produce the fiber (dissolving) pulp.

These pentosans have been disposed of as waste in the prior art, but xylose that forms the significant portion of the pentosans can be used as an important raw material for producing furfural, xylitor, or a sweetening agent. In other words, the xylose dissolved in the sixth step

(prehydrolysis step) is obtained by concentrating a solution isolated from the pulp after the prehydrolysis, using a heat exchange system or waste heat.

To the concentrated solution, methanol or ethanol is added to precipitate xylose through an alkanol precipitation method or a neutralization method.

In addition, the xylose may also be dissolved in a seventh step (cooking step) to be described later.

In other words, the xylose dissolved in the cooking step is recovered by separating alkali and a xylose solution and subjecting the xylose solution to the same dissolution method as described above.

Then, a seventh step (cooking step) is conducted, in which the bamboo chips are introduced into a digester, in which the bamboo chips are cooked at high temperature in a liquor ratio of 1:3.5-6.0 (bamboo chips: chemical liquor) that indicates the ratio of a chemical liquor consisting of water, alkali and anthraquinone to the bamboo chips, thus softening and pulping the bamboo chips. The use of the prior sulfite process for the cooking of the bamboo chips has problems in that the fiber becomes weak and the yield of the pulp is low.

Thus, in the present invention, a soda-AQ process is applied in order to promote delignification and to prevent the decomposition of alpha-cellulose and also to increase the yield of the pulp.

In other words, the soda-AQ process comprises adding a liquor consisting of alkali (mainly NaOH) , anthraquinone and water in a liquor ratio of 3.5-6.0 : 1 with respect to the oven-dry weight of the bamboo chips.

Also, in the soda-AQ process, the amount of alkali (as Na ₂ O) added to water is preferably 10-30 % based on the oven- dry weight of the bamboo chips (i.e., mass excluding the content of moisture in the bamboo chips), and the anthraquinon (AQ) is preferably added in an amount of 0.01-2%.

The cooking temperature in this cooking step is preferably 140-180 ^° C , and the cooking time is preferably controlled within the range of 90-200 minutes depending on the polymerization degree and the quality of pulp to be produced.

That the xylose can also be extracted in this step is already described above in the sixth step (prehydrolyiss step) , and thus the description thereof will be omitted herein. Then, an eighth step (contaminant removal step) is conducted, in which contaminants introduced together with the bamboo is removed using a centrifugal cleaner.

In other words, the centrifugal cleaner shown in FIG. 2 is used to remove contaminants introduced in the process together with the bamboo.

Briefly, the centrifugal cleaner is a cone-shaped device as shown in FIG. 2, and is used to remove contaminants from the cooked pulp. The contaminants to be removed mainly include sand, metal pieces and glass pieces, which can be introduced in each of the steps.

The centrifugal cleaner is used considering the fact that the specific gravity of pulp when completely wetted with water approaches 1, whereas the specific gravity of the above-mentioned contaminants is higher than 1. Accordingly, when the pulp is introduced into an inlet

10 in FIG. 2, it rotates along the inner wall of the centrifugal cleaner 100 by the force of a pump while moving to the bottom 30, in which the rotating force applies centrifugal force. According to this action, relatively light pulp moves inward and is discharged through accepts 20, and heavy contaminants move outward and are discharged to the bottom 30.

In addition, the centrifugal cleaner 100, which is generally used to remove contaminant having a specific gravity higher than that of pulp during the production of the pulp, is called "forward cleaner", and the centrifugal cleaner, which is used to removed contaminants (styrofoam, plastic, etc.) having a weight lower than that of pulp in the recycling of waste paper, is called "reverse cleaner". Because the above-described centrifugal cleaner is well known in the art, the present invention is not limited thereto and may also utilize a variety of other centrifugal cleaners.

Then, a ninth step (selection step) is conduced, in which contaminants are removed from the cooked pulp using a pressure screen, and an incompletely cooked portion of the pulp is fed back into the digester.

In other words, the pressure screen is used to remove non-dissociated fibers and contaminants. A fraction passed through the screen is sent to the following step, a fraction remaining on the screen is filtered through a vibrating screen, and a fraction remaining on the vibrating screen is wasted and a fibrous or incompletely cooked portion is fed back into the digester as shown in FIG. 1.

Then, a tenth step (washing and concentrating step) is conducted, in which a decker is used to wash the pulp to remove the chemicals, and the pulp is concentrated by squeezing water. The decker (not shown) is a machine that serves to wash the pulp and, at the same time, to concentrate the pulp by squeezing water. Using this decker, the pulp is washed and concentrated to a concentration suitable for bleaching.

In this step, the washing operation is repeated at least three times in order to remove fine powders and parenchyma cells as much as possible.

Then, an eleventh step (bleaching step) , which is very important in the present invention, is conducted.

In order words, in order to eliminate environmental problems such as the generation of environmental hormone dioxin, an ECF (elementary chlorine-free) or TCF (total chlorine-free) bleaching process is used.

As bleaching stages in this step, DED, DEDD, DEDP, DEZP, DEOP, DEOZ and PEOZ can be selectively applied. A bleaching process, the number of bleaching stages, and bleaching conditions, are determined depending on the degree of required bleaching.

In the above description of the bleaching stages, D means chlorine dioxide bleaching, E means alkaline extraction, P means peroxide bleaching, 0 means oxygen bleaching, and Z means ozone bleaching.

If the content of metal ions in the pulp is high, the metal ions will be inactivated by treating the pulp with a chelating agent (EDTA, DTPA, DTPMPA, etc.) to increase bleaching efficiency before conducting the bleaching of the

pulp .

Herein, the chelating agent is a chemical for making the reactivity of metal ions impotent, and if large amounts the metal ions are present in the pulp, they will remarkably deteriorate the performance of a bleaching chemical used for bleaching.

For this reason, if the content of the metal ions is large so that it reduces bleaching efficiency, the pulp is treated with the chelating agent before conducting the bleaching of the pulp.

As an example of a bleaching method using the bleaching stages, the bleaching stages of DEDD indicate that bleaching is conducted in four sequential steps of: (1) chlorine dioxide bleaching, (2) alkaline extraction, (3) chlorine dioxide bleaching, and (4) chlorine dioxide bleaching.

In other words, various bleaching stages listed above indicate that a pulp producer may selectively the bleaching stages depending on the brightness or chemical purity required in the pulp to be produced, or the preference of a worker.

Regarding the purpose for increasing the number of the bleaching stages, when the brightness or chemical purity is greatly required, the number of the bleaching stages may be increased or the amount of chemicals used may be increased. Also, even if the same level is required, a method of reducing the amount of a chemical used in each stage and increasing the number of the stages can be used in order to minimize adverse effects on pulp (pulp damage and decomposition, etc) . Accordingly, even if the quality of the same level is

required, it is possible to control the number of the bleaching stages or the amount of chemicals used, and it is difficult to express this control as an absolute numerical value, because the state of pulp supplied into the bleaching process varies depending the degrees of prehydrolysis and pulping or cooking conducted in the above-described steps.

However, when the fiber (dissolving pulp) is bleached, it is preferable that the content of lignin in the pulp produced in the digester be first measured and, based on the measured content, the amount of addition of bleaching chemicals be calculated so as to increase or decrease the amount depending on the required quality.

Thus, the present invention can prevent the generation of dioxin, an environmental pollutant, using said bleaching agent, and has excellent bleaching effects.

Then, a twelfth step (acid treatment and washing step) of removing metal ions from the surface and inside the pulp is conducted.

In other words, to remove metal ions present on the surface and inside the fiber (dissolving) pulp, the pulp us adjusted to pH 3-5, treated with acid at room temperature for

20-110 minutes and washed with clean water until it reaches the natural pH range.

The treatment time is preferably increased or decreased depending on the content of the metal ions and the extent of removal difficulty.

Finally, a thirteen step (sheet preparation method) of preparing the sheet into a sheet or a roll is conducted.

Also, the scope of the present invention encompasses all fiber (dissolving) pulps produced using bamboos according

to the above-described method, and the pulps may be in the form of sheet or rolls.

Also, the sheet-shaped pulp is preferably prepared to have a thickness of 0.1-3 mm, and the roll-shaped pulp is preferably prepared by preparing the pulp into a web having a thickness of 0.1-1.5 mm and winding the web into a roll shape. In other words, the roll-shaped pulp is preferably prepared in a form thinner than the sheet-shaped pulp, because it should be wound on a roll. Hereinafter, Examples of the present invention will be described with reference to the accompanying drawings. Example 1

A Myanmar bamboo was split to a width of about 2 mm and then cut to a length of 15-25 mm. The cut material was screened through a 60-mesh screen to remove contaminants and small bamboo fragments, followed by washing.

400 g (on a oven-dry weight basis) of the washed bamboo was placed in a digester into which water was added to make a liquor ratio of 6:1. Then, a stainless weight is laid on the bamboo such that the bamboo could be sufficiently immersed in water.

After the digester was covered with a lid and screwed, the bamboo was subjected to prehydrolysis at 170 ^° C for 90 minutes. After completion of the prehydrolysis, the content within the digester was washed and then placed again into the digester, into which 16% active alkali (calculated as Na ₂ O) and 0.1% anthraquinone were added so as to adjust the liquor ratio to 4:1. Then, the bamboo was cooked at 170 ^° C for 120 minutes.

The cooked pulp was washed and subjected to a four- stage bleaching of DEDD, and the properties of the resulting pulp are shown in Table 1 below.

Table 1: Results of prehydrolysis and pulping tests of bamboo

*Kappa number is used to indicate the amount of lignin remaining in the pulp produced in the digester, and is used as a standard for determining the amount of addition of chemicals in bleaching, and is calculated from the consumed amount of potassium permanganate through oxidation-reduction titration.

Example 2

The treatment of bamboo and most of conditions were the same as in Example 1, but the prehydrolysis and bleaching conditions were as follows:

The liquor ratio in the prehydrolysis was adjusted to 4:1, and the prehydrolysis was conducted at 170 ^° C for 100 minutes . The cooked and washed pulp was subjected to a four- stage bleaching of DEDP, and the properties of the resulting pulp are shown in Table 2 below.

Table 2: Results of prehydrolysis and pulping tests of

bamboo

Industrial Applicability As described above, according to the present invention, it is possible to produce fiber (dissolving) pulp in more mild conditions by making prehydrolysis and cooking easy through longitudinal splitting and transverse cutting. Also, the soda-AQ process, in which anthraquinone is used as a catalyst in a cooking step, is applied for the pulping of bamboo, so that the present invention can have great effects on delignification, the improvement in pulp quality and the increase in pulp yield.

Also, an environmental problem can be solved by applying an ECF and TCF bleaching process, and it is possible to optionally control the content of alpha-cellulose and the degree of polymerization depending on the properties of rayon to be produced, by controlling the prehydrolysis, cooking and bleaching conditions. In addition, the use of waste as resources and the increase in economic efficiency can' be achieved by recovering xylose dissolved in a fiber (dissolving) pulp-manufacturing process and using the recovered xylose as a raw material for preparing xylitol, a sweetening agent, furfural, etc.