KR100984044B1 - Method of preparing homogeneous cellulose solution by using a twin screw extruder - Google Patents

Abstract

The present invention is characterized in that the cellulose pulp is directly dissolved in a high concentration of N-methylmorpholine N-oxide (hereinafter referred to as NMMO) containing 5 to 15% by weight of water, thereby producing cellulose fibers and films. To prepare a homogeneous cellulose solution. More specifically, in a method for producing a cellulose solution in a twin screw extruder, the step of dissolving and homogenizing the cellulose powder executed in the twin screw extruder in an NMMO aqueous solution comprises at least one forward screw, at least one kneading screw and at least After passing through a twin screw extruder by a method including one reverse screw, it relates to a method characterized in that there is no device for producing a separate cellulose solution.

Cellulose, N-methylmorpholine N-oxide, twin screw extruder, cellulose fiber, cellulose film.

Description

Method of preparing homogeneous cellulose solution by using a twin screw extruder

1 is a block diagram schematically illustrating a cellulose solution manufacturing process by a cellulose direct dissolution method according to the prior art method.

Figure 2 is a block diagram for schematically illustrating a cellulose solution manufacturing process by the cellulose direct dissolution method according to the method of the present invention.

3 is a schematic view for explaining the dissolution mechanism of the twin screw extruder according to the present invention.

＊ Explanation of symbols for main parts of drawing

1 ---- Twin Screw Extruder 2 ---- Forward Screw

3 ---- kneading screw 4 ---- reverse screw

The present invention relates to a method for producing a uniform cellulose solution that can be used to prepare cellulose fibers and films, and the like, wherein the cellulose powder pulverized from sheet-like pulp is converted into a liquid high concentration N-methylmorpholine N-oxide (hereinafter, NMMO) using a coaxial twin screw extruder with a ratio of screw diameter to screw length (L / D) in the range 36 to 60 to mix, swell and dissolve, and the extruder is a suitable combination of a forward screw, a kneading screw and a reverse screw, etc. It is characterized by using a twin screw extruder.

Methods for preparing cellulose solutions using tertiary amine oxide solvents have been proposed in the patents and literature in a number of ways. Initially improved methods have been presented since a method for preparing a cellulose solution using the tertiary amine oxide solvent described above in US Pat. No. 2,179,181 has been presented.

In U.S. Patent No. 4,144,080, cellulose is added to a tertiary amine oxide having a water content of about 25.27% and a predetermined amount of isopropyl alcohol to swell at a certain temperature and a predetermined time to form a slurry, and then an excess amount of water is used by vacuum in an extruder. A method of evaporating and dissolving is proposed. Since such a method requires a relatively long complex step such as swelling, evaporation, and dissolution, problems such as deterioration of molecular weight (DP) and discoloration may occur due to decomposition of the prepared solution. The process is contrary to the trend of streamlining and low energy consumption.

In the US Patent No. 5,534,113, a swelling of cellulose and a low concentration of tertiary amine oxide in a Premixer is used to improve the moisture of the solution using a thin film evaporator, which is an improved evaporator. A method of increasing the evaporation efficiency in evaporation is presented. However, this method is also not economical in that it involves complicated processes such as swelling, evaporation, and dissolution from low concentration solvents.

In order to solve the above problems, US Patent No. 6,153,003 proposes a method for directly dissolving cellulose powder in a high concentration of tertiary amine oxide (water content of 5 to 15%) solvent. The method proposed here is a method for producing a cellulose solution by continuously swelling, mixing, dissolving, and defoaming a high concentration of solvent and cellulose supplied using a twin screw extruder in a short time. Problems such as degradation and discoloration can be solved to some extent in the dissolution step. However, the disadvantage of this method is that the screw diameter (L / D) is short compared to the length of the screw, so that the mixing, swelling and dissolution time are short. The cellulose powder granules, which are difficult to mix and form a film without swelling, remain undissolved even after they are discharged from the extruder, so that the stabilization time in the stabilization tank is required to be used as cellulose products such as cellulose fibers and films. It must go through. This process is an additional process that requires residence time in the solution process and is therefore considered to be a solution that can be denatured.

Efforts have been made to solve problems such as molecular weight degradation and discoloration of the prepared solution in the cellulose solution preparation method. Above all, it is the most ideal method to dissolve uniformly in a short residence time and low temperature. would. As described above, a method of preparing a cellulose solution using a tertiary amine oxide solvent is largely 1) a method of preparing by dissolving water after evaporating water in a solution through a swelling step with a low concentration of solvent, and 2) high concentration. It can be represented in two ways: by dissolving directly in a solvent and then going through a stabilization process. However, the point to be pursued in the prior art is to minimize the above-mentioned problems, to develop a technology that can produce a more economical and complete cellulose solution, and it will be a problem to be constantly solved for those in the field. .

The method of the present invention is a method for directly dissolving in a high concentration of solvent, the object of the present invention is to provide a method for producing a homogeneous cellulose solution without dissolving in a twin screw extruder in a more complete dissolution method, without going through a separate process. The method of the present invention employs a coaxial twin screw extruder having a ratio of screw diameter to screw length (L / D) in the range of 36 to 60, wherein the extruder is a twin screw with a suitable combination of a forward screw, a kneading screw and a reverse screw. An economical method for producing a uniform cellulose solution in a short time by producing a cellulose solution that is completely dissolved in the extruder section, 1) the apparent diameter of the pulverized cellulose powder is 1000 μm or less, preferably 300 μm or less 2) the moisture content of the ground cellulose powder is 7% or less, preferably 6% or less, and 3) the concentration of NMMO hydrate is 80-92 wt%, preferably 85-90 wt%, and 4) the cellulose in the solution. The content is 5 to 20% by weight, preferably 8 to 15% by weight, and 5) the viscosity of the prepared solution is characterized in that 5000 to 30000 Poise.

According to a suitable embodiment of the present invention, the method comprises the steps of making a cellulose sheet into a cellulose powder; And supplying cellulose powder and concentrated N-methylmorpholine N-oxide hydrate (NMMO) or tertiary amine oxide to a twin screw extruder; Mixing and swelling steps; Dissolution and homogenization step; And discharging and metering, wherein the dissolving and homogenizing section in which the dissolving and homogenizing of the cellulose powder in the NMMO aqueous solution in the twin screw extruder is carried out comprises at least one forward screw, at least A method for producing a cellulose solution comprising one kneading screw and at least one reverse screw is provided.

In addition, the number of reverse screws of the twin screw extruder is preferably 1 to 10.

It is also preferred that the continuous alignment of two or three forward screws, one kneading screw and one reverse screw is repeated at least once in the dissolution and homogenization section.

In addition, the ratio (L / D) of the length to the diameter of the twin screw extruder is preferably 36 to 60.

In addition, the concentration of NMMO hydrate is preferably 80 to 92 wt%.

Moreover, it is preferable that the temperature of the barrel of a twin screw compressor will be 40-130 degreeC.

The present invention provides a cellulose solution prepared by the above method. The solution thus prepared is used as a cellulose fiber and a film according to a conventional manufacturing method using a spinning dopant.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a block diagram schematically illustrating a process for preparing a cellulose homogeneous solution prepared by a conventional cellulose direct dissolution method. 1 illustrates a method of producing a uniform solution through a stabilization process after dissolution in a twin screw extruder by a direct dissolution method. This method has a problem of preparing a separate device by going through a stabilization process as described above. Details can be understood through some of the details of FIG. 2.

Figure 2 is a block diagram for schematically illustrating a process for producing a cellulose homogeneous solution prepared by the direct cellulose dissolution method according to the present invention. Wood pulp is used as a main raw material such as cellulose fiber or film, and the α-cellulose has a purity of 90% or more, preferably 92% or more. In order to prepare a uniform solution by increasing the penetration and dispersibility of NMMO, it is advantageous to grind the particle size to 1000 μm or less, preferably 300 μm or less. The particle size of cellulose has a great effect on solubility in dissolving using NMMO. When the swelling and dissolution proceeds after the contact step with the cellulose, the viscous NMMO solution first forms a coating on the outside because the reaction starts first outside the cellulose cluster. Thus, the cellulose that forms the coating prevents NMMO from penetrating into the inside. You get in the way. Therefore, the smaller the size of the cellulose particles, the faster the internal penetration of the NMMO. In the present invention, it was possible to grind using a sieve knife grinder. The cellulose powder thus pulverized is stored in a storage tank in which temperature and humidity are kept constant, and the moisture content of the cellulose powder is adjusted to 7% or less, preferably 6% or less, and then supplied to the twin screw extruder through a pulp metering feeder.

When the moisture content of the cellulose supplied to the twin screw extruder is high, aggregation may occur between the cellulose powders. This may make it difficult to diffuse into the solvent during the mixing and swelling process made in the twin screw extruder, making it difficult to produce a homogeneous cellulose solution. The amount of cellulose fed into the twin screw extruder may be 5 to 20 wt% with respect to the final cellulose solution but the amount can be adjusted as needed.

In order to dissolve the cellulose powder, 10-50 wt% NMMO hydrate (equivalent to low concentration NMMO) was used with a falling film evaporator to 80-92 wt% NMMO hydrate (where concentration wt% = [ NMMO / (NMMO + water)] x100) is supplied to the twin-screw compressor. At this time, the temperature of the reservoir and the oil pipe is maintained at 70 to 105 ℃, the solvent was maintained in the liquid phase, it can be supplied to the twin screw extruder at a constant flow rate using a geared pump. The feedstock is subjected to a series of melting processes in a twin screw extruder. If it is less than 70 ℃, the transportability is lowered by the progress of the solidification of the solvent, if it exceeds 105 ℃, decomposition of the solvent may proceed.

Figure 3 illustrates a process made in a twin screw extruder of the method for producing a cellulose solution according to the present invention.

Referring to FIG. 3, the twin screw extruder may be divided into four sections in which four processes are performed. First, an NMMO aqueous solution concentrated to 8 to 20 wt% in the feeding step and a cellulose powder having a size of 1000 μm or less are supplied. NMMO solvent and cellulose powder are supplied to the first and third barrels of the twin screw extruder 1, respectively. At this time, the cellulose powder is fed into the side forced feeder (side feeder (not shown)) mounted on the twin screw extruder 1 side. The direction of rotation of the screw of the twin screw extruder is co-rotating and the rotational speed (RPM) can be adjusted to 100 to 300 RPM. And the size of the extruder is preferably 36 to 60 in length / diameter ratio (L / D), the total number of barrels is suitable 8 to 15, preferably about 13.

The NMMO and cellulose powders fed to the first and third barrels, respectively, are subjected to mixing and swelling steps. As shown in Fig. 3, in the mixing and swelling section for performing the mixing and swelling process, a plurality of forward screws 2 of different pitches may be arranged at regular intervals. The NMMO and cellulose mixture mixed and swelled by the forward screw 2 are dissolved and homogenized. In the melting and homogenizing section, the forward screw 2, the kneading screw 3 and the reverse screw 4 are arranged in combination and in FIG. 3 an exemplary implementation of the alignment of the respective screws 2, 3 and 4 is shown. An example is shown. Referring to FIG. 3, two to three forward screws 2, one leading screw 3 and one reverse screw 4 can be continuously aligned and again the same type of screw alignment can be repeated again. have. According to the production method of the present invention, through the above dissolution and homogenization step, the mixture is properly stirred and the shear force of an appropriate size is applied to the mixture so that the solvent can be uniformly penetrated into the cellulose to be dispersed. And this prevents the generation of undissolved cellulose to allow homogeneous dissolution. The number and arrangement of forward screws 2, leading screws 3 and reverse screws 4 presented in FIG. 3 are exemplary and are not intended to limit the scope of the invention.

In the present invention, it can be seen that the proper arrangement of the type and number of screws in this section is a major step to rate the dissolving power of cellulose. In particular, the number of the reverse screw disposed in this section greatly affects the dissolving power, the number proposed in the present invention is 1 to 10, preferably 2 to 7 is suitable. If the number of the backscrew is less than one, the stirring and shearing force applied to the solution, the residence time is low, if more than 10, the solution is difficult to proceed smoothly in the forward direction of the extruder, it is difficult to control the internal pressure and the temperature for each barrel. The mixture in which the cellulose powder is uniformly dissolved is removed through the vacuum or natural degassing, and then subjected to a vent and metering process to obtain a homogeneous cellulose solution according to the present invention. The cellulose solution of the present invention has sufficient properties with spinning dope suitable for the production of fibers and films and the like.

Features and other advantages of the present invention as described above will become more apparent from the following examples.

In the Examples and Comparative Examples of the present invention, the properties of the cellulose solution were evaluated in the following manner.

(a) Homogeneity of cellulose solution

Evaluation of the solubility of the cellulose solution prepared in the present invention was sampled in the solution transfer line immediately after discharged from the twin screw extruder 100mm ^{2 in} the form of a film within 1mm and then evaluated by observing the tube through a polarizing microscope. The degree of dissolution was divided into 5 grades, and the state of complete dissolution was '1' and the state in which a large amount of undissolved powder was present was '5'. The intermediate state was divided into 2, 3, and 4 according to the extent of undissolved cellulose. The number of evaluations was carried out five times for each sample, and the average was measured.

b) weight average degree of polymerization (DPw)

The intrinsic viscosity [IV] of the dissolved cellulose was measured in a concentration range of 0.1 to 0.6 g / dl at 25 W 0.01 ° C with a 0.5 M cupriethyleneamine hydroxide solution made according to ASTM D539-51T using a Uberod viscometer. . Intrinsic viscosity is obtained by extrapolating specific viscosity according to concentration, and substituting this into Mark-Houwink's formula to obtain polymerization degree.

[IV] = 0.98 ㅧ 10 ^-2 DPw ^0.9

Example 1

A pulp sheet (Buckeye V-81) with a degree of polymerization (DPw) of 1,200 (α-cellulose content; 97%) was passed through a drying chamber, adjusted to a moisture content of 7.0 W 0.5%, followed by a 250 μm screen sieve. A cellulose powder having an apparent diameter of 200 μm or less was prepared through a grinder and transferred to a storage tank. At this time, the moisture content of the cellulose powder transferred to the storage tank was to be 4.5% or less. The weight of the cellulose powder was continuously measured through a loss-in-weight metering feeder and continuously fed to the twin screw extruder through a side feeder mounted on the third barrel of the twin screw extruder. A low concentration of 25 wt% NMMO was concentrated to a high concentration of 87 wt% in a thin falling film evaporator and fed to the first barrel of a twin-axial compressor through a reservoir, conduit and gear pump maintained at 90 ° C. At this time, the supply amount of cellulose powder and NMMO was supplied so that the cellulose concentration of the total solution weight was 11wt%. The twin screw extruder screw diameter is 48 mm, the rotational speed (RPM) is 180, and detailed conditions for other implementations are shown in Table 1 below. Sampling to evaluate the homogeneity and viscosity of the solution was carried out in a solution feed tube about 1 m away from the twin screw extruder.

[Example 2]

The same procedure as in Example 1 was conducted except for the detailed conditions related to the twin screw extruder and other implementations shown in Table 1 below.

Example 3

The same procedure as in Example 1 was conducted except for the detailed conditions related to the twin screw extruder and other implementations shown in Table 1 below.

Example 4

The same procedure as in Example 1 was conducted except for the detailed conditions related to the twin screw extruder and other implementations shown in Table 1 below.

Example 5

The same procedure as in Example 1 was conducted except for the detailed conditions related to the twin screw extruder and other implementations shown in Table 1 below.

Comparative Example 1

Unlike the example, the reverse screw was not applied to the dispersing section of the twin screw extruder, and the L / D was also carried out by a method having a different range from that of the example. It was carried out in the same manner as in Example 1 except for the detailed conditions relating to the twin screw extruder and other implementations shown in Table 2 below.

Comparative Example 2

It was carried out in the same manner as in Comparative Example 1 except for the twin screw extruder and other detailed conditions related to the implementation shown in Table 2.

Comparative Example 3

It was carried out in the same manner as in Comparative Example 1 except for the twin screw extruder and other detailed conditions related to the implementation shown in Table 2.

[Comparative Example 4]

It was carried out in the same manner as in Comparative Example 1 except for the twin screw extruder and other detailed conditions related to the implementation shown in Table 2.

TABLE 1

Condition Example 1 Example 2 Example 3 Example 4 Example 5 Cellulose degree of polymerization (DP) 1200 1200 1200 850 850 Extruder length / diameter ratio (L / D) 52 48 48 52 52 Powder Cellulose Moisture Content (%) 4.5 4.0 4.5 4.5 5.0 Reverse Screw Count 5 5 3 5 One Temperature
℃
Raw material supply section 70 70 80 70 70 Pyungyun & Mixing Section 80 80 90 80 80 Dissolution and Equalization Section 100 100 95 90 90 Defoaming and weighing section 105 105 105 100 100 Homogeneity of Solution (1 ~ 5) One One 2 One 2 Solution viscosity 18000 18200 19000 15200 14800 Degree of polymerization (DP) 1090 1100 1130 700 750

TABLE 2

Condition Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Cellulose degree of polymerization (DP) 1200 1200 850 850 Extruder length / diameter ratio (L / D) 34 48 48 48 Powder Cellulose Moisture Content (%) 4.5 7.5 7.5 4.0 Reverse Screw Count 3 5 One - Temperature
℃ Raw material supply section 70 70 70 70 Pyungyun & Mixing Section 80 80 80 80 Dissolution and Equalization Section 100 100 90 90 Defoaming and weighing section 105 105 100 100 Homogeneity of Solution (1 ~ 5) 5 3 5 3 Solution viscosity 18050 18000 16000 15400 Degree of polymerization (DP) 1126 1135 730 725

As described above, the present invention is a method of directly dissolving in a high concentration of solvent, the length / diameter ratio (L / D) of the twin screw extruder and the arrangement of the screw, specifically the forward screw, kneading screw and reverse screw It is possible to provide a method for producing a homogeneous cellulose solution without a separate process after the twin screw extruder by completely dissolved in the section using a properly combined twin screw extruder, the conventional cellulose solution It has the advantage of producing a homogeneous cellulose solution within a short time even with less process than the manufacturing method. Such a method of manufacturing a cellulose solution is more economical than the conventional technique. Since the prepared cellulose solution undergoes a short process, the degradation of solution properties such as polymerization decrease and discoloration is minimized. It may be applied in an economical and easy way in the manufacturing field.

While the invention has been described in detail only with respect to the described embodiments, it will be apparent to those skilled in the art that various modifications and variations are possible within the spirit of the invention, and such modifications and variations belong to the appended claims. .

Claims (9)

Making the cellulose sheet into cellulose powder; And supplying cellulose powder and concentrated N-methylmorpholine N-oxide hydrate (NMMO or tertiary amine oxide to a twin screw extruder; mixing and swelling; dissolving and homogenizing; and discharging and metering). The dissolution and homogenization section in which the step of dissolving and homogenizing the cellulose powder executed in the twin screw extruder in an NMMO aqueous solution is performed comprises at least one forward screw, at least one kneading screw and at least one reverse screw. Method for producing a cellulose solution. The method according to claim 1, wherein the number of reverse screws of the twin screw extruder is 1 to 10. The method of claim 1, wherein the dissolution and homogenization section has at least one repetition of successive alignments of two or three forward screws, one kneading screw, and one reverse screw. The method according to claim 1, wherein the ratio (L / D) of the length to the diameter of the twin screw extruder is 36 to 60. The method according to claim 1, wherein the concentration of NMMO hydrate is 80 to 92 wt%. The method according to claim 5, wherein the temperature of the barrel of the twin-screw compressor is 40 to 130 ° C. delete delete delete

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