JPH04325526A - Biodegradable resin molding and its production - Google Patents

Abstract

PURPOSE:To provide a molding which can easily be degraded or decomposed by organisms such as microbes, insects or plants or enzymes or the like secreted from such organisms and a process for producing the same. CONSTITUTION:A biodegradable resin molding made of poly-3-hydroxybutyric acid of a degree of crystallization of below 50%, and a process for producing a biodegradable resin molding comprising melting poly-3-hydroxybutyric acid and solidifying the melt by rapid cooling into a molding of a degree of crystallization of below 50%.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to poly-3-hydroxybutyric acid (Poly(3-hydroxybutyric acid)) which has excellent biodegradability.
roxybutyrate): Hereinafter also referred to as PHB)
molded products that have the property of being easily disintegrated or decomposed by living things such as microorganisms, insects, and plants, and enzymes secreted by these living things (hereinafter referred to as biodegradable). The present invention relates to a manufacturing method thereof.

0002

[Prior Art] Conventionally, processed molded products that disintegrate due to the action of microorganisms, etc. have been processed, such as film sheets, etc., in which polymers such as cornstarch are blended into resin to promote the disintegration of molded products by microorganisms, etc. are on the market, but there are concerns about environmental pollution because some parts of these molded products remain undegradable in the ecosystem.

On the other hand, PHB is known as a polymeric material with a biodegradable function that undergoes decomposition at the molecular level in the ecosystem, and is published in Journal of the Japanese Society of Agricultural Chemistry, Vol. 50,
9, 431-436 (1976), etc.

0004

[Problems to be Solved by the Invention] However, at present, PHB that fully utilizes the biodegradability of PHB or molded products with excellent biodegradability based on PHB as a main component have not yet been proposed. do not have. Specifically, regarding a method for molding a copolymer molded product containing hydroxybutyric acid units as a main component, JP-A-57-150393 discloses a melt molding method in which the polymer is cooled at a temperature exceeding the glass transition temperature of the polymer after melt extrusion. It is shown. However, the biodegradability of PHB molded products molded by such a molding method is still low, and there is still room for improvement.

As described above, PHB, which essentially has excellent biodegradability, has not fully demonstrated its properties, and there is a need for the development of molded products and molding methods that have excellent biodegradability. ing.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present inventors have conducted intensive research and found that the degree of crystallinity of PHB in a PHB resin molded product is greatly related to its biodegradability. The present inventors have now discovered that by lowering the crystallinity of PHB below a certain level, its biodegradability can be significantly improved, leading to the completion of the present invention. That is, the present invention provides a biodegradable resin molded article made of poly-3-hydroxybutyric acid (PHB) having a crystallinity of less than 50%.

[0007] In the present invention, PHB produced by a known method can be used without any particular restriction. Generally, PHB produced from PHB-producing bacteria is isolated by a known method such as extraction using chloroform, and has an average molecular weight of 10,000 or more, preferably 50,000 or more. Preferably used.

The resin molded article of the present invention may contain other resins to the extent that they do not adversely affect the biodegradability of the PHB. As such resin, any known polymer can be used as long as it is a polymer that can be melt-molded with PHB. Among these, polymers that are immiscible with PHB at the molecular level are preferred. That is, such a polymer does not affect the biodegradation function of PHB and tends to have an auxiliary effect on the biodegradation function in the sense of increasing the surface area. Specific examples of polymers suitable for use with PHB include thermoplastic resins such as polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polycaprolactone. Further, the blending ratio of the resin is preferably 50% by weight or less, preferably 20% by weight or less, based on PHB.

The most important feature of the resin molded article of the present invention is that the crystallinity is less than 50%, preferably 49.8% or less.
It consists of B. That is, by constructing a resin molded product with PHB having such a degree of crystallinity, the biodegradability of the PHB can be dramatically improved, and the collapse or decomposition of the resin molded product in the ecosystem can be achieved in a short period of time. can do.

[0010] Hitherto, there have been no reports of resin molded articles made of PHB in which the degree of crystallinity of PHB is less than 50%. For example, Macromolecules (Mac
romolecules), vol. 22, 694-697 (
1989), 55 obtained by casting method
PHB with crystallinity of around % is shown. However, the above literature also describes PH with a crystallinity of less than 50%.
B is not disclosed at all, and furthermore, the technical idea of the present invention that the biodegradability of PHB is significantly improved by reducing the degree of crystallinity to less than 50% is not disclosed at all.

In the present invention, the crystallinity of PHB is
This is a value measured by line diffraction method. That is, CuKα rays are used as the X-rays, and the diffraction intensity at 2θ from 6° to 40° is measured by the reflection concentration method. From this diffraction intensity curve, the degree of crystallinity can be determined by the following calculation.

Crystallinity (%) = P×100/(QR) (However, P
is the area of the peak portion based on the crystal, Q is the total area under the curve, and R is the area of the diffuse scattering portion. ) The above-mentioned area of the diffuse scattering portion represents the area under the straight line connecting two points with 2θ of 6° to 40°. When measuring crystallinity using this X-ray diffraction method, the orientation of the crystals has a large effect on the degree of crystallinity, so the molded product used as the measurement sample is generally unoriented or in the form of finely ground powder. used.

[0013] For resin compositions in which PHB is blended with other polymers, the analysis pattern of the resin composition is measured in advance, and then the analysis strength curve of the entire resin composition is determined using the analysis strength according to the blending ratio. By subtracting from PHB
An analytical curve based on is obtained, and the degree of crystallinity of PHB can be determined from the analytical curve using the above calculation formula.

[0014] In the present invention, the biodegradation function refers to a function that undergoes decomposition at the molecular level by an ecosystem, and specifically includes degrading enzymes such as biodegradation function depolymerase, depolymerase-producing bacteria, and specifically means that it is decomposed by PHB-degrading bacteria, depolymerase-containing substances, etc. Also,
The biodegradability of a resin molded article refers to the property that it can be easily disintegrated or decomposed by organisms such as microorganisms, insects, and plants, and enzymes secreted by these organisms due to the biodegradation function. Generally, such enzymes and/or bacterial cells are present in environments such as natural environments such as soil, partial natural environments such as landfills, municipal waste, excess sludge from sewage treatment plants, pig excrement, etc. As a treatment method, the resin molded article may be disintegrated or even decomposed in a rapid composting treatment environment under aerobic conditions, which is known as a treatment method.

The method for producing the molded article of the present invention is not particularly limited. The most typical manufacturing method is a biodegradable resin molded product characterized by melting poly-3-hydroxybutyric acid and then rapidly solidifying it to obtain a molded product with a PHB crystallinity of less than 50%. The manufacturing method is mentioned. That is, the present inventors discovered that PHB or PH containing the thermoplastic resin
It has been found that by immediately quenching and solidifying B and molding it after melting, a resin molded article exhibiting excellent biodegradability can be easily obtained with good reproducibility. The lower the quenching temperature is, the more preferable it is, but generally the molten resin is cooled to a temperature below the glass transition temperature of PHB, specifically to a temperature below 15°C, preferably below 5°C, more preferably below 0°C. Just go.

[0016] The molding method after the above-mentioned melting is not particularly limited. For example, various molding methods such as extrusion molding, injection molding, blow molding, casting, vacuum molding, melt spinning, calendar molding, and foam molding are used.

[0017] Furthermore, in the above molding method, for the rapid cooling, a cooling means appropriate for each molding method is appropriately employed. For example, when forming a film or sheet by extrusion molding, a pair or more chilled rolls whose surfaces are cooled to the cooling temperature by flowing a refrigerant inside are installed near the exit of the T-die of the extrusion molding machine. , T
A method such as rapidly cooling the molten material extruded from a die can be adopted. Furthermore, in injection molding, rapid cooling can be performed by flowing a refrigerant into a mold and setting the mold temperature to the cooling temperature.

[0018] In the above-mentioned quenching, the quenching time is appropriately determined within a range where the crystallinity of PHB is less than 50%, taking into account the thickness of the resin molded product, etc., with respect to the set cooling temperature. Good, but preferably for as short a time as possible. Generally, a time of 30 seconds or less, preferably 10 seconds or less is appropriate.

The resin molded product of the present invention can take any shape such as film, sheet, thread, tape, plate, structure, etc., but the biodegradability of the resin molded product is best exhibited. This is a thin molded product having a wall thickness of 2 mm or less in the form of a film, sheet, thread, tape, etc. whose crystallinity can be easily controlled by the manufacturing method described later. Specific examples of resin moldings include fibers, films, packing, cases, bottles, paper diapers, disposable packaging materials such as various foam containers, and other daily necessities, films for greenhouses, films for covering the ground, pots for seedlings, Agriculture and forestry materials such as strings, fertilizer bags, slow-release pesticide materials, fishing materials such as fishing nets and fishing lines, leisure goods such as leisure bags and fishing supplies packaging materials, drug delivery system materials, suture threads, osteosynthesis materials, Examples include medical materials such as sanitary products.

[0020]

[Effects] As shown in the Examples and Comparative Examples described below, the biodegradable resin molded product of the present invention is a highly crystalline resin molded product manufactured by ordinary melt molding, or a resin molded product obtained by casting. Compared to molded products, PHB has a higher biodegradability and can exhibit excellent biodegradability.

[0021] Therefore, when the resin molded article of the present invention is buried in soil and subjected to decomposition treatment by microorganisms, the resin molded article can be efficiently rendered harmless in a shorter period of time.

[0022] Furthermore, the method for producing a biodegradable resin molded article of the present invention allows the resin molded article having the above-mentioned good biodegradability to be easily obtained with good reproducibility, and the quenching conditions can be appropriately changed. This is also useful as a means for controlling the biodegradability of the resulting resin molded product within a certain range.

[0023]

[Examples] In order to explain the present invention more specifically, Examples are given below, but the present invention is not limited to these Examples.

Examples 1 and 2 and Comparative Examples 1 and 2 (1) Preparation of resin sheets with different crystallinity A cotton-like resin (fermented and synthesized using microorganisms: Alcaligenes eutrophus) was dissolved in a chloroform/hexane system. A product purified by reprecipitation treatment (molecular weight approximately 200,000) was dissolved in chloroform at a concentration of approximately 4% by weight/volume. This was transferred to a Petri dish and allowed to stand at room temperature to produce a cast film (thickness approximately 0.4 to 0.5 mm). Next, four test pieces of 16 x 12 mm were cut out from this sheet. The cut test pieces were held in a template and held in an oven at 190° C. for about 13 minutes to melt them. The above molten resin was rapidly cooled within 10 seconds by the cooling method shown in Table 1 to obtain molded bodies A to D shown in Table 1.

(2) Measurement of Crystallinity The crystallinity of each sample obtained in (1) above was measured under the following measurement conditions.

Measurement method: Reflection focusing method Diverging slit: 1° Scattering slit: 1° Measurement temperature: room temperature The degree of crystallinity of each sample was determined from the above-mentioned calculation formula from the intensity of the obtained diffraction curve. The results are shown in Table 1. Further, the diffraction curves of Sample A and Sample C are shown in FIGS. 1 and 2, respectively.

(3) Measurement of biodegradability PHB-degrading bacteria strain SC-17 isolated from soil was used to perform decomposition in a medium having the following composition.

[0028] Degradability evaluation medium (medium I) Inorganic salt solution
100ml
Yeast Extract
100 ppm p
H
7. Pour 100 ml of the above medium I into a 1500 cc Erlenmeyer flask, plug it with a cotton plug, and then
Sterilization was performed by autoclaving at 21° C. for 20 minutes. Next, the sample sheet prepared in (1) was sterilized with ethanol, weighed, and then introduced. Subsequently, 1 ml of a culture solution of a PHB-degrading bacterium strain SC-17 that had been cultured in advance was inoculated. After inoculation, microbial decomposition was performed using a rotary shaker at 30° C. and 180 rpm for 72 hours. Thereafter, the remaining sample sheet was taken out from the culture solution, washed with pure water, and vacuum-dried overnight at room temperature. The weight of the sample before decomposition (Xg) and the weight of the sample after decomposition and drying (Yg) were weighed, and the weight reduction rate calculated by the following formula was taken as the biodegradation rate.

Biodegradation rate (%)=(X-Y)×100/X The results of the above biodegradation rate are also shown in Table 1.

[0030]

[Table 1]

Example 3 and Comparative Example 3 (1) Preparation of resin sheets with different crystallinity Pellet-shaped P
HB (manufactured by Imperial Chemical Industries PLC, UK, product name: BX GV9 (
Extrusion molding was performed using EE)) as a raw material. The cylinder temperature was set at 185°C, and the sheet extruded from the T-die was rapidly cooled by passing it through a pair of chilled rolls installed near the outlet of the T-die and whose surface temperature was cooled to -10°C. Immediately after, the approximately 0.5 mm thick sheet that came out of the chilled roll was introduced into a cooling water tank at 0° C. to obtain a resin molded product (sample E) made of a PHB sheet.

On the other hand, for comparison, a resin molded product (sample F) was obtained by the same operation except that the temperature of the chilled roll was set at 60°C and the temperature of the water bath was set at about 30°C.

(2) Measurement of crystallinity degree A portion of each molded product obtained in (1) above was cooled with liquid nitrogen, and then ground into fine powder using a pulverizer, which was used as a sample for crystallinity measurement. . The degree of crystallinity was measured and calculated under the same measurement conditions as in Example 1, and the degree of crystallinity was determined. The results are shown in Table 2.

(3) Measurement of biodegradability A 16×12 mm sample for biodegradability evaluation was cut out from the sheet prepared in (1) above, and microbial degradability was measured in the same manner as in Example 1. The results are also shown in Table 2.

[0035]

[Table 2]

Example 4 and Comparative Example 4 (1) Preparation of resin molded products with different crystallinity Pellet-shaped P
HB (manufactured by Imperial Chemical Industries PLC, UK, product name: BX GV9 (
Using EE)) as a raw material, injection molding was performed to form a pot-shaped container (approximately 0.5 mm thick). Cylinder temperature 190℃,
The mold temperature was set at two cooling temperatures: -5°C (sample G) and 35°C (sample H), and molding was performed. Note that the holding time was 90 seconds.

(2) Measurement of crystallinity A portion of each molded product obtained in (1) above was cooled with liquid nitrogen, and then ground into fine powder using a pulverizer, and used as a sample for crystallinity measurement. . The degree of crystallinity was measured and calculated under the same measurement conditions as in Example 1. The results are shown in Table 3.

(3) Measurement of biodegradability Also, from the molded product obtained in (1) above, a 16 x 12 mm
A sample for biodegradability evaluation was cut out and subjected to microbial decomposition in the same manner as in Example 1, and the decomposition rate was calculated. The results are also shown in Table 3.

[0039]

[Table 3]

Example 5 (1) Preparation of resin sheets with different crystallinity Pellet-shaped P
HB (manufactured by Imperial Chemical Industries PLC, UK, product name: BX GV9 (
EE)) and 10% by weight of polystyrene as raw materials, extrusion molding was performed in the same manner as in Example 3 to obtain a resin molded product (sample) consisting of a PHB sheet with a thickness of about 0.5 mm. I) was obtained.

On the other hand, for comparison, a resin molded product (Sample J) was obtained by the same operation except that the temperature of the chilled roll was set at 60°C and the temperature of the water bath was set at about 30°C.

(2) Measurement of crystallinity degree A part of the molded product obtained in the above (1) was cooled with liquid nitrogen, and then ground into fine powder using a pulverizer to prepare a sample for crystallinity measurement. The crystallinity was measured in the same manner as in Example 1. Further, the crystallinity was calculated by reducing the X-ray analysis pattern of a sheet made of polystyrene alone obtained in the same manner as the above-mentioned sheet according to its blending ratio.

(3) Measurement of biodegradability Also, from the molded product obtained in (1) above, a 16 x 12 mm
A sample for biodegradability evaluation was cut out and subjected to microbial decomposition in the same manner as in Example 1, and the decomposition rate was calculated. The results are shown in Table 4.

[0044]

[Table 4]

[Brief explanation of the drawing]

FIG. 1 shows an X-ray diffraction curve of Sample A obtained in Example 1.

FIG. 2 shows an X-ray diffraction curve of Sample C obtained in Comparative Example 1.

Claims (2)

[Claims] 1. A biodegradable resin molded article made of poly-3-hydroxybutyric acid having a crystallinity of less than 50%. 2. A method for producing a biodegradable resin molded article, which comprises melting poly-3-hydroxybutyric acid and then rapidly solidifying it to obtain a molded article in which the crystallinity of the polyhydroxybutyric acid is less than 50%. .