KR20050059972A - Production method of biodegradable plastic and apparatus for use in production thereof - Google Patents

Abstract

The present invention provides a method for producing biodegradable plastics for synthesizing polylactic acid directly from lactic acid, and a device for use thereof, without adopting a conventional synthetic route for synthesizing polylactic acid from lactic acid through lactide. This greatly shortens the synthesis time of the polylactic acid, thereby reducing the manufacturing cost.

The method for producing a biodegradable plastic of the present invention is characterized by obtaining lactic acid as a raw material and polylactic acid as a main component of the biodegradable plastic by dehydrating and condensation polymerization of the lactic acid in the presence of a metal catalyst and under high temperature and reduced pressure.

Description

Production method of biodegradable plastic and apparatus for use in production

The present invention relates to a method for producing biodegradable plastics based on lactic acid and an apparatus used therein.

Although a method for producing polylactic acid, which is a main component of biodegradable plastics, is known from lactic acid as a raw material, the conventional production method is, as shown in FIG. 1, by dehydrating polycondensation of lactic acid under high temperature pressurization, thereby lactic acid is lactic acid. Synthetic routes for obtaining polylactic acid via

Biodegradable plastics have the function and performance as plastics in normal use, but they are easily decomposed and harmless in the natural environment when they are discarded after use. They are not contaminated with natural environment. It is expected to be used in the field and is extremely useful material.

However, the conventional manufacturing method has only been used in a fertilizer bag (compost bag), agricultural multi-film, etc. until now due to the drawback of high manufacturing cost and not enough strength and performance compared to general-purpose plastics. In addition, it is beginning to be used in the medical field such as a surgical suture because of better biocompatibility.

The present invention has been made for the purpose of providing such a biodegradable plastic at low cost, and does not adopt a route for synthesizing polylactic acid from the lactic acid through the lactic acid, and as shown in FIG. Provided are methods and devices for synthesizing lactic acid. This greatly shortens the synthesis time of the polylactic acid, thereby reducing the manufacturing cost.

This method yields lactic acid by lactic acid fermentation of starch represented by corn starch. Using the lactic acid as a raw material, polylactic acid, which is a main component of biodegradable plastics, is obtained by dehydrating polycondensation of the lactic acid in the presence of a metal catalyst and under high temperature and reduced pressure.

The steam generated by the dehydration polycondensation is discharged out of the system, the amount of steam discharged is measured, and the end point of the reaction is detected to obtain polylactic acid, which is a main component of the biodegradable plastic.

As the metal catalyst, zinc chloride and / or stannous chloride is suitable. That is, lactic acid is used as a raw material, and the lactic acid is promoted in the presence of zinc chloride or / and stannous chloride and under reduced pressure at high temperature to promote polyhydric acid as a main component of biodegradable plastics.

Preferably, when using zinc chloride and stannous chloride as a catalyst, the amount of the zinc chloride added is selected from the range of 0.1 to 0.3% by weight, and the amount of the tin chloride added is from the range of 0.1 to 1% by weight. Choose from.

In addition, the dehydration polycondensation temperature is selected in the range of 180 to 220 ℃, the vacuum degree during dehydration condensation polymerization is preferably selected in the range of -0.05 to -0.08Mpa.

In the combination, the dehydration polycondensation reaction is remarkably slowed when the total weight percentage of zinc chloride and stannous chloride is less than 0.4% by weight, and above 1% by weight, only the dehydration reaction proceeds. The reactant may be carbonized. In order to avoid this, if the vacuum degree of the apparatus is increased, the condensation polymerization reaction is accelerated, but the generation of lactide proceeds, and a problem such as a decrease in the amount of polylactic acid occurs.

For this reason, it is preferable that the total addition amount at the time of using a zinc chloride and a tin tin chloride together is 0.4 to 1 weight%, the addition amount of zinc chloride is a range of 0.1 to 0.3 weight%, and the addition amount of a tin chloride It is preferable that it is 0.3 to 0.7 weight%.

As a specific example, the weight average molecular weight of polylactic acid is 110,000 when zinc chloride and tin tin are used in combination, and zinc chloride is 0.1% by weight and tin is 0.1% by weight, and zinc chloride is 0.2%. The weight average molecular weight of polylactic acid when% and stannous chloride are 0.5 wt% is 120,000.

In addition, when using only zinc chloride as a catalyst, the addition amount is preferable in the range of 0.2 to 0.8% by weight, and the weight average molecular weight of the resulting polylactic acid is 80,000 to 100,000.

In the case where only stannous chloride is used as a catalyst, the amount of addition is preferably in the range of 0.3 to 1% by weight, and the weight average molecular weight of the resulting polylactic acid is 100,000 to 120,000.

However, it can be seen that when one of such zinc chloride and stannous chloride is used alone, it takes a long time for polymerization. Therefore, if the reaction time is ignored, these catalysts can be used alone.

It was confirmed by this that when zinc chloride and stannous chloride were used together as a catalyst, the polymerization time was shortened, the molecular weight of the resulting polylactic acid was increased, and the yield of polylactic acid was increased.

Next, based on FIG. 3 and FIG. 4, the apparatus used for the manufacturing method of the said biodegradable plastics is demonstrated.

The apparatus includes an airtight container 1 into which lactic acid as a raw material and a metal catalyst are introduced, a pressure reduction device 2 for depressurizing the inside of the airtight container 1, a heating means 3 for heating the airtight container 1, and It is equipped with the stirring apparatus 4 which stirs lactic acid in the airtight container 1.

The said airtight container 1 consists of the container main body 1a opened upward, for example, and the opening and closing lid 1b which seals or opens the said opening part.

For example, the ceiling plate, that is, the lid 1b of the container 1 is provided with an inlet port 5 for injecting lactic acid and a catalyst as a raw material and an exhaust port 6 connected to the decompression device 2.

The heating means 3 is formed of an electric heater which is in contact with the periphery of the hermetic container body 1a and is arranged to surround it.

Further, a discharge cylinder 7 communicating with a space in the airtight container 1 for discharging the polylactic acid synthesized is provided on the bottom plate of the airtight container 1, that is, the bottom plate of the container body 1a. The product outlet 8 is provided at the outer end of the discharge cylinder 7.

Then, the screw shaft 9 is coaxially installed in the discharge cylinder 7, and the screw shaft 9 receives the polylactic acid in the airtight container 1 when the product discharge port 8 is opened. Eject through.

3 and 4 show an example of the operating structure of the screw shaft 9. As shown in the drawing, the stirring device 4 is formed of the stirring blade root 4a, the motor 4c is connected to the upper end of the rotating shaft 4b of the stirring blade root 4a, and the motor 4d is provided. The rotary shaft 4b and the stirring blade root 4a are rotated.

The motor 4c is disposed outside the airtight container 1, for example, above the container ceiling plate, that is, above the lid 1b, and directly connects the rotary shaft 4b to the drive shaft of the motor 4c. And vertically in the center of the airtight container 1.

The screw shaft 9 is coaxially installed at the lower end of the rotating shaft 4b, and the screw shaft 9 is inserted into the discharge cylinder 7.

On the other hand, the motor 4c is supported by the support 10, the support 10 is supported by the fluid pressure cylinder 11, and as shown in FIG. 3, the contracting operation of the fluid pressure cylinder 11 is shown. By lowering the support 10 and the motor 4c, thereby lowering the screw shaft 9 together with the rotary shaft 4b and the stirring blade root (4a). That is, the screw shaft 9 is pushed into the product outlet 8 in the discharge cylinder 7, and the end surface of the screw shaft 9 is brought into contact with the end 12 formed in the connection mounting portion with the product outlet 8. To close the product outlet (8).

In the state where the said outlet 8 is closed, the stirring blade root 4a is reversed in the positive direction by the motor 4c, the lactic acid in a container is stirred, and high temperature by the decompression device 2 and the heating means 3 is carried out. Promote the dehydration polycondensation under reduced pressure.

In addition, as shown in FIG. 4, the support 10 and the motor 4c are pushed up by the extending operation of the fluid pressure cylinder 11, and thus, together with the rotating shaft 4b and the stirring blade root 4a. Raise the screw shaft 9. That is, the screw shaft 9 is pulled up in the discharge cylinder 7 and separated from the end 12 to open the product outlet 8.

In the state where the outlet 8 is open, the motor 4c is reversely driven to reverse the rotation shaft 4b to reverse the screw shaft 9. The polylactic acid thus synthesized is returned to the product outlet 8 and discharged from the product outlet 8.

In other words, a predetermined amount of lactic acid and a catalyst are introduced into the polymerization apparatus (airtight vessel 1), and the inside of the vessel 1 is decompressed by the pressure reduction device 2 while the stirring apparatus 4 is operated, and at the same time, the heating means ( It heats to 180-220 degreeC by 3). As the reaction proceeds, water, i.e., water vapor, is generated inside the container 1, but by discharging the water vapor to the outside of the system by the decompression device 2, the production rate of lactide decreases and a large amount of polylactic acid is produced. do.

In addition, a water vapor sensor 13 is inserted in the middle of the piping to the decompression device 2, and the amount of water vapor generated by the measuring device 14 is measured to determine the progress of the reaction, and the reaction is terminated when the calculated amount of water vapor is reached. do.

The polylactic acid, which is a main component of the biodegradable plastic thus obtained, is discharged to the outside through the discharge cylinder 7 and the product outlet 8. The method for recovering the metal catalyst from this discharged polylactic acid is based on known techniques.

According to the present invention, polylactic acid can be synthesized directly from the lactic acid, as shown in FIG. 2, without adopting a conventional synthetic route for synthesizing polylactic acid from the lactic acid shown in FIG. 1 via lactide. In addition, the synthesis time of polylactic acid is greatly shortened, and manufacturing cost is reduced.

In addition, the reaction time is reduced by about 50% compared with the conventional polymerization method, and the oxygen partial pressure in the polymerization apparatus is small, so that even if the heating temperature is slightly changed, the product is not carbonized and high-quality polylactic acid is obtained.

1 illustrates a chemical formula showing a synthetic route of a conventional polylactic acid.

Figure 2 shows the chemical formulas showing the synthetic route of polylactic acid according to the invention.

3 is a cross-sectional view showing the apparatus used in the method for producing a biodegradable plastic of the present invention with the outlet closed.

4 is a cross-sectional view of the apparatus with the outlet open.

[Description of the code]

Reference Signs List 1: airtight container, 1a: container body, 1b: cap body, 2: pressure reducing device, 3: heating means, 4: stirring device, 4a: stirring blade root, 4b: rotating shaft, 4c: motor, 5: lactic acid and catalyst Inlet, 6: Exhaust port, 7: Exhaust cylinder, 8: Product outlet, 9: Screw shaft, 10: Motor support, 11: Hydraulic cylinder, 12: End, 13: Water vapor sensor, 14: Water vapor meter

Claims (7)

A method for producing a biodegradable plastic, comprising lactic acid as a raw material and polylactic acid as a main component of the biodegradable plastic obtained by dehydration and polycondensation polymerization of the lactic acid in the presence of a metal catalyst and under high temperature and reduced pressure. The lactic acid is used as a raw material, and the lactic acid is dehydrated and condensation-polymerized in the presence of a metal catalyst and under high temperature and reduced pressure, the steam generated by the dehydration and condensation polymerization is discharged out of the system, and the amount of water vapor discharged is measured to measure the end point of the reaction. Method of producing a biodegradable plastic, characterized in that to obtain a polylactic acid as a main component of the biodegradable plastic by detecting. The process for producing a biodegradable plastic according to claim 1 or 2, wherein the metal catalyst is zinc chloride and / or stannous chloride. The biodegradability according to claim 3, wherein when zinc chloride and stannous chloride are used together as a catalyst, the amount of zinc chloride added is 0.1 to 0.3% by weight, and the amount of stannous chloride is 0.1 to 1% by weight. Method of Making Plastics. The method for producing a biodegradable plastic according to claim 1 or 2, wherein the dehydration condensation polymerization temperature is 180 to 220 deg. C, and the vacuum degree during dehydration condensation polymerization is -0.05 to -0.08 Mpa. A biodegradable plastic comprising a hermetic container into which lactic acid as a raw material is introduced, a decompression device for depressurizing the inside of the hermetic container, heating means for heating the hermetic container, and a stirring device for stirring the lactic acid in the hermetic container. Manufacturing equipment. 7. The airtight container according to claim 6, further comprising a discharge cylinder having a discharge port in the airtight container, a screw shaft coaxially installed in the discharge cylinder, and wherein the screw shaft discharges the polylactic acid in the airtight container through the discharge port when the discharge port is opened. Biodegradable plastic manufacturing apparatus characterized in that.