JP2001064441A - Biodegradable plastic holding product and its degradation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inexpensive plastic molding product satisfying fixed strength conditions of plastic molding product, not eluting an exogenous internal secretion disturbance chemical substance in a degradation process, readily degradable under a natural environment. SOLUTION: This biodegradable molding product is obtained by molding a solution comprising 5-20 wt.% of carboxymethylethyl cellulose(CMEC), 0.8-2 wt.% of glycerol fatty acid ester, 39-75 wt.% of ethanol and 18-46 wt.% of methylene chloride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biodegradable plastic composition which can be decomposed by soil microorganisms and the like, and whose glucoside bond is hydrolyzed by a bacterium extracellular enzyme into carbon dioxide gas and water. It relates to goods and the like.

[0002]

2. Description of the Related Art One of the results of recent technological innovation is the use of synthetic polymer materials such as plastics. That is, plastics have been used for clothing, food packaging materials, building materials, agricultural multi-films, etc. because they are light, durable, beautiful, easy to process, and chemically stable (do not corrode). According to annual statistics, plastic production in Japan is enormous at 12,580 thousand tons (“Biodegradable Plastic Handbook”,
1992 statistics in p.33 "Table 1", edited by Yoshiharu Toi:
(NTS Corporation), the types of which are phenolic resin, melamine resin, epoxy resin, urethane foam,
Polyethylene, vinyl chloride, etc. have no spare time. Among these plastics, polycarbonate resin is used for tableware, and vinyl chloride is used for multi-films for agriculture and sheets and films for tunnel cultivation. It has become indispensable. Vinyl chloride is also used in seedling pots.

[0003] However, in recent years, some problems have been pointed out from the viewpoint of treating wastes and using them as recyclable resources, even in the case of synthetic polymer materials having one aspect which are excellent materials.

[0004] For example, the advantage of a synthetic polymer material that is chemically stable as a product highlights the disadvantage that it is not easily decomposed in the case of waste disposal.
Environmental conservation, securing of disposal sites, and the effects on the safety of animal and plant growth and health, including humans, have become problems due to the huge amount of disposal. By the way,
The amount of waste of polymer materials is about 56% at 3,910,000 tons discharged as general waste and about 44% at 3,010,000 tons as industrial waste (see “Biodegradable” above). Plastic Handbook ”, p. 33,“ Table 1 ”
(Statistics 1999), about 12% of municipal and industrial wastes are recycled and processed, about 51% are incinerated, and the remaining 37% are disposed of by land reclamation. Decomposable Plastic Handbook ”, p. 36)
However, there is a problem in recent years that the number of landfill sites is decreasing.

As another disposal method of waste plastics, an incineration method is known. However, chlorine-containing organic compounds and the like have a problem that dioxin is generated due to incineration conditions, and have strong acute toxicity.

[0006] For the purpose of solving the above-mentioned problem of disposal of synthetic polymer materials, many biodegradable plastics which do not require landfill disposal or incineration have already been proposed (for example, JP-A-5-320418). No. 5, JP-A-5
No. 5065, Japanese Patent Application Laid-Open No. 9-205895), biodegradable plastics that have been proposed to date include, for example, those using biocellulose or pullulan produced by microorganisms, and conventional petroleum-based plastics containing starch. , Those using plant-derived cellulose, those using chitin which is a shell component of crustaceans and insects such as shrimp and crab, and synthetic polymers such as polybutyric acid and polyvinyl alcohol.

[0007]

By the way, plastics are not easily decomposed in the environment and are considered to be high in safety. It has been pointed out that sexual endocrine disrupting chemicals (generally referred to as “environmental hormones”) elute (for example, bisphenol A elutes from polycarbonate). The food chain, which causes river and coastal pollution by disturbing chemicals, is taken up by fish and shellfish and seagrass and finally enters the mouth of human beings. Dioxin, which may be generated by incineration, is also one of these endocrine disrupting chemicals, and these endocrine disrupting chemicals have serious effects on the endocrine system, immune system, reproductive system, brain and nervous system of animals, including humans. Is a major problem ("Environmental Scientific Materials and Learning Disabilities"; Yoichi Kuroda, "Science", 68, 4).
70, 1998: Iwanami Shoten).

[0008] The conventionally proposed biodegradable plastics are very expensive in terms of price, and thus have a problem that they are unlikely to be used in place of conventional products. Is considered to be decomposed by microorganisms, but the safety of decomposition products generated during the decomposition has not been studied, and it is not necessarily safer than conventional general plastics. Is difficult to say ("Biodegradable plastics using biomass"; Masafumi Nishiyama and Jun Hosokawa, "Industrial Materials", 38, 4
7, p. 1990).

The present inventor has been able to satisfy the predetermined strength conditions required for biodegradable plastics, that is, plastic molded products, which are currently strongly sought to be solved from the background and the various prior arts, and to satisfy the requirements. The purpose of the present invention is to provide a plastic composition or the like which is inexpensive in terms of treatment and disposal and does not elute endocrine disrupting chemicals during the decomposition process and can be easily decomposed even in a natural environment.

[0010]

SUMMARY OF THE INVENTION The features of the present invention which have been attained to achieve the above-mentioned object are as set forth in the appended claims.

[0011] The invention of the biodegradable plastic molded article according to claim 1 proposed in the present application mainly comprises carboxymethylethylcellulose (hereinafter abbreviated as "CMEC") and a plasticizer having no benzene ring in structure. It is characterized by comprising a plastic composition.

The above-mentioned CMEC has a basic skeleton of cellulose and is partially ether-bonded with a carboxymethyl group and an ethyl group, and has the property of being chemically stable and not easily hydrolyzed. However, such a stable C
The present inventors have noticed that MEC has a property of easily dissolving when reacted with an alkali metal salt in a neutral or alkaline aqueous solution having a pH of 6.0 or more, and have accomplished the present invention.

In the above invention, a plasticizer having no benzene ring is used because most of the chemicals suspected to be "exogenous endocrine disrupting chemicals" commonly called "environmental hormones" Phthalic acid plasticizers, one of the plasticizers for plastics, have this benzene ring ("Environment Agency's policy on the problem of endogenous endocrine disrupters"about"
Environment Agency: May 1998). Therefore, in the present invention, a plasticizer which does not have a benzene ring and which is unlikely to generate the above-mentioned suspected chemical substance in the decomposition process is used. Examples of such a plasticizer include those having a chain chemical structure such as glycerin and glycerin fatty acid ester.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the above description, "biodegradable" does not mean physical or chemical decomposition, nor does it decompose in an in-vivo environment. It refers to the property of being easily degraded biologically by microorganisms that grow in it, and is generally decomposed into water and carbon dioxide by the decomposition of cellose by cellulase produced by soil microorganisms.
The method of using the microorganism in the present invention is not limited to the case where the microorganism is used in a natural environment, and may be a method used in a wastewater treatment facility such as an activated sludge method.

[0015] Carboxymethylethylcellulose (CME) which is a main component of the plastic composition in the present invention is used.
C) is a substance whose acute toxicity, subacute toxicity, chronic toxicity, and safety have been confirmed by reproductive tests ("Applied pharmacology" (1976) 11, (1), p139-152, "Applied pharmacology"). (1977) 13, (3), p411-420, "Applied pharmacology"
(1985) 30, (4), p677-685).

In the structure of the present invention, CMEC has a number average molecular weight of about 1.4 × 10 ⁻⁴ and a weight average molecular weight of 4.
In many cases, it is better to be about 9 × 10 ⁻⁴ ,
It is not limited to this.

As the plasticizer, a glycerin fatty acid ester such as a medium-chain fatty acid triglyceride is preferably used, but is not limited thereto, and may be any as long as it satisfies the above conditions.

The biodegradable plastic composition of the present invention can contain at least one of known extenders, stabilizers, antioxidants, pigments, and ultraviolet absorbers. It is preferred that they do not contain exogenous endocrine disrupting chemicals and do not produce such chemicals during the degradation process. Specifically, those having no benzene ring are preferably used.

The above-mentioned biodegradable plastic composition can be formed into a biodegradable plastic molded article by various known methods, for example, a sheet used for an agricultural vegetation sheet, a tunnel cultivation sheet, and the like. Materials, pots for seedlings and the like are particularly preferred. Also,
It can also be used as a sheet material for curing used in architectural works, interior works, etc., a film material, a sheet material for bags used for containers, shopping bags and the like.

The above-mentioned biodegradable plastic molded article is obtained by dissolving a composition comprising carboxymethylethylcellulose (CMEC), the above-mentioned plasticizer, and other additives as necessary in a solvent (solvent). Can be manufactured. For example, carboxymethylethylcellulose (CMEC) having 5 to 20% by weight, a plasticizer at 0.8 to 2% by weight, and an organic solvent dissolving these at 78 to 94% by weight are preferable. Preferred examples of the solvent include ethanol and methylene chloride. Typical examples of the dissolving solution include those prepared in 5 to 20% by weight of CMEC, 0.8 to 2% by weight of glycerin fatty acid ester, 39 to 75% by weight of ethanol, and 18 to 46% by weight of methylene chloride.

The biodegradable plastic molded article of the present invention comprises:
In addition to being molded from only the biodegradable plastic composition, it can also be a composite plastic molded article that is composited with paper. This composite plastic molded product is, for example,
It can be produced by impregnating paper with a solution obtained by dissolving CMEC and the above-mentioned plasticizer or the like in a solvent or coating the paper surface. Further, a sheet material obtained by dispersing and suspending the crushed pulp in the above-mentioned solution and making paper may be used.

In the above, the term "paper" is not particularly limited and includes a broad range, and includes recycled paper, sheets of cotton and the like. Generally, cellulosic materials are suitable.

As the dissolution solution, the same solution as described above can be used, and it can contain at least one of a extender, a stabilizer, an antioxidant, a pigment, and an ultraviolet absorber.

The present invention also proposes a method for rapidly decomposing the above-mentioned composition or molded article by contacting it with a decomposition solution, for which purpose carboxymethylethylcellulose (CMEC) is used prior to biodegradation. Pretreatment of bringing the molded article into contact with the decomposition solution of the above. As the decomposition solution, a buffer solution having a pH of 6 to 8 containing an alkali metal,
For example, a sodium phosphate buffer having a pH of 6.5 to 7.5 and a concentration of 1 mM to 100 mM can be exemplified. The molded article is decomposed so as to be finely fragmented by being brought into contact with the decomposition solution. be able to. If the pH of this buffer solution is less than 6.0 or more than 8.0, no decomposition occurs or it becomes very slow.

As the decomposition solution, a neutral or alkaline aqueous solution containing an alkali metal hydroxide can be used in place of the above buffer solution. A hydroxide solution of an alkali metal such as potassium hydroxide is added, and the pH is 6.8 to 7.
A solution adjusted to 4 is typically exemplified. In order to perform the decomposition in a short time, it is preferable to use a 100 mM sodium phosphate buffer solution having a pH of about 7.4.

The above-mentioned decomposition solution can be brought into contact with the above-mentioned molded article by spraying, dipping, or the like. For example, when the above-mentioned molded article is used as a sheet material for covering the soil surface, it is used as it is. The pretreatment for decomposition can be performed only by spraying the decomposition liquid on the sheet.

On the other hand, when the molded article is pre-processed and decomposed by immersing the molded article in a solution, the liquid containing the substance fragmented by the pre-treatment is left on the soil or sprayed on the soil, The fragmented substance can be more easily biodegraded by microorganisms in the soil. The decomposition treatment can also be performed by a sewage treatment facility having a general biological treatment step.

Further, a particularly excellent advantage of the present invention is that by rapidly decomposing a seedling pot, seedlings can be grown quickly and with a small number of working steps.
That is, seed pots are used for the initial stage of growing various plants, but are usually taken out of the pots and replanted for the next growing process. However, there is a problem that this replanting operation is troublesome and that the remaining pot must be disposed of. In order to solve this problem, for example, a pot for seeds and seedlings using a biodegradable plastic containing starch or the like as a main component has been proposed (JP-A-9-205895). It takes several months or more to biodegrade. On the other hand, in the above invention of the present application, the pot can be rapidly decomposed in a very short time of several hours to several tens of hours only by immersing the seedling pot in the decomposition solution, When planted inside, the advantage is obtained that the growth and elongation of the root of the plant are not hindered.

[0029]

EXAMPLES The present invention will be further described below with reference to examples.
The following tests were performed as follows. (Film tensile strength test) A Strograph M-2 type (manufactured by Toyo Seiki Seisaku-sho, Ltd.), which is a film tensile strength measuring device, was used.

Example 1 CMEC 8% (w / w), glycerin fatty acid ester 1.6% (w / w), ethanol 45.2% (w / w)
w), a solution prepared so as to contain 45.2% (w / w) of methylene chloride was degassed, and then poured into a Teflon-coated tray to produce films having a thickness of 0.1 mm and 0.2 mm.

The tensile strength of the produced 0.1 mm thick film was 260 kg / cm ² , and the tensile strength of the 0.2 mm film was 370 kg / cm ² .

Comparative Example 1 The glycerin fatty acid ester concentration of the plasticizer was 2.1% (w
/ W) and a film was produced in the same manner as in Example 1 except that 2.2% (w / w) was used.
Glycerin exudes to the film surface and sticks to the film surface, which is unsuitable for use as a film product.

Comparative Example 2 The concentration of the glycerin fatty acid ester of the plasticizer was 0.7% (w
A film was produced in the same manner as in Example 1 except that the ratio was changed to / w). The resulting product film was poor in plasticity and lacked flexibility, and was unsuitable as a film product.

Example 2 (Disassembly Test Example) The film having a thickness of 0.1 mm produced in Example 1 was placed on the soil surface and exposed to a natural environment. Although it remained in its original condition for about one month, fragmentation progressed as soon as cracks occurred after a longer period.

Example 3 (Test Example of Acceleration of Decomposition by Pretreatment Decomposition) The film prepared in Example 1 was treated with a decomposition solution of 10 mM
It was immersed in a sodium phosphate buffer solution (pH 7.4) and its decomposition and degradability were observed.

As a result, decomposition starts about 10 minutes later,
It began to fragment finely in about 5 hours, and decomposed almost completely in 24 hours.

Example 4 (Test Example of Acceleration of Decomposition by Pretreatment Decomposition) "Hyponex solution 1" which is commercially available as a horticultural fertilizer and contains potassium dihydrogen phosphate and potassium hydroxide as components
-10-5 "(guaranteed component amount (%): total nitrogen amount 5% [ammonia nitrogen 19.5%, nitrate nitrogen 0.90%],
Water-soluble phosphoric acid 10.0%, water-soluble potassium 5.0%, water-soluble magnesia 0.05%, water-soluble manganese 0.001%, water-soluble boron 0.005%: manufactured by Hyponex Japan Co., Ltd.) Was diluted 200 times with tap water, and then the film of Example 1 was immersed in this solution to observe its degradability.

As a result, decomposition starts about 15 minutes later,
It began to fragment finely in about 5 hours, and decomposed almost completely in 24 hours.

Example 5 (Preparation of Composite Sheet) The solution prepared in Example 1 was immersed in a 27 cm × 20 cm recycled paper having a thickness of 0.05 mm, and then naturally dried for about 12 hours to obtain CMEC and A composite biodegradable plastic molded sheet based on paper impregnated with glycerin fatty acid ester was prepared.

The prepared sheet had a tensile strength of 260
kg / cm ² .

Example 6 (Disassembly test example) When the film having a thickness of 0.1 mm produced in Example 5 was placed on the soil surface and exposed to a natural environment under the same conditions as in Example 2, it took about 3 months. It existed in its original condition. Thereafter, cracks gradually occurred, but fragmentation did not proceed for a long time because paper was used as the base material, and the soil surface was protected.

Example 7 A seedling pot having a thickness of 0.1 mm (having the same shape as that of a commercially available product) was prepared using the solution prepared in Example 1 above. It was confirmed that the pot did not leak even if filled with water.

Next, this pot was used for the decomposition solution of Example 3 (10 mM sodium phosphate buffer solution (pH 7.4)).
After being immersed in the pot for 30 minutes, the pot was filled with a hole dug in the ground, filled with water in the pot, and the amount of water was observed over time. As a result, the water in the pot disappeared in about half a day.

From these results, according to the seed and seedling pot of this example, the pot is decomposed very quickly only by immersing the seed and seedling in the decomposition solution while planting the seed and seedling together with the pot in the ground. It was confirmed that. Therefore, since the water from outside can reach the roots of the seedlings without replanting, it can be seen that the seedlings do not die. In other words, when seedlings are planted together with the seedling pot, if the pot is pre-treated by immersing the pot in a decomposing solution such as a sodium phosphate buffer solution as described above, the pot is quickly decomposed and the seedlings are grown. It turns out to be effective. Also, there is no need to dispose of the pot.

Example 8 The film having a thickness of 0.1 mm prepared in Example 1 was immersed in a paint diluting solution (Rock Paint: trade name) which is a general diluting solution of an oil paint used in a construction site. When its degradability was observed over time, no decomposition was observed for 2 days or more.

Therefore, it was found that this film has a property that it can be used as a curing sheet used, for example, at the time of painting at a construction site.

The same test was carried out on a water-based paint used at a similar construction site, but no decomposition was observed in the same manner, and it was found that the water-based paint had properties that could be used as a curing sheet when applying the water-based paint.

[0048]

As described above, according to the present invention, a plastic composition comprising CMEC, which forms the skeleton of molded plastic, is easily decomposed biologically by microorganisms in soil and is contained together with CMEC. , The use of chemicals that do not contain exogenous endocrine disrupting chemicals and do not produce such chemicals in the decomposition process as plasticizers that make up molded articles has resulted in the disposal of plastic products, which has recently become a problem. The effect that processing can be performed safely is produced.

In addition, according to the composite biodegradable plastic molded article formed by impregnating or coating a paper as a base material with a solution, the shape retention by the paper is reinforced, and the shape retention is improved. The present invention has an effect that it can be suitably used for required applications, for example, prevention of the occurrence of weeds in a field, a rice field, or the like, and application of a sheet material covering a soil surface for early cultivation of crops by a heat retaining effect.

Further, the above biodegradable plastic composition,
When the molded article is disposed of, for example, by a simple pretreatment of contacting it with a decomposition solution, the composition and the molded article can be fragmented quickly.

Further, when used as an agricultural sheet material or film material and biodegraded in soil, there is an advantage that carbon dioxide generated by decomposition of cellulose is used for photosynthesis of plants.

According to the invention of the present application, it is possible to provide particularly excellent agricultural sheet materials such as agricultural vegetation sheets, tunnel cultivation sheets, seedling pots and the like. Also, in particular, after pretreatment such as immersion in a seed decomposition solution for seeds and seeds having the above-described configuration, if this is planted in a growing soil or the like while seeds and seedlings are planted, subsequent replanting work can be unnecessary, and seeds and seeds can be grown. An excellent effect that work can be simplified is achieved.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 101/16 C08L 101/00 A F term (Reference) 2B024 DB03 2B027 NC24 NC43 NC51 ND09 NE05 2B029 EB11 EC06 EC09 4F071 AA09 AC10 AE04 AE19A AF52 AG12 AH01 BA02 BB01 BB02 BC01 BC02 4J002 AB031 EH046 FD026 GA00

Claims (6)

[Claims] 1. A carboxymethyl ethyl cellulose (C)
A biodegradable plastic molded article comprising a plastic composition containing, as a main component, MEC) and a plasticizer having no benzene ring in its structure. 2. The carboxymethyl ethyl cellulose (CMEC), the plasticizer, and if necessary, a bulking agent,
3. A biodegradable plastic molded article according to claim 1, wherein a plastic composition containing a stabilizer, an antioxidant, a pigment, and an ultraviolet absorber is dissolved in a solvent, and the solution is used to mold the biodegradable plastic molded article according to claim 1. Manufacturing method of plastic molded products. 3. Carboxymethyl ethyl cellulose (C)
MEC), plasticizers and, if necessary, extenders, stabilizers,
The plastic composition containing an antioxidant, a pigment, and an ultraviolet absorber is dissolved in a solvent, and this solution is impregnated into a paper substrate or coated on the surface of the paper substrate. A biodegradable plastic molded product as described. 4. The biodegradable plastic molded article according to claim 1, wherein the molded article is used for agricultural vegetation sheets, tunnel cultivation sheets, and seedling pots. 5. A biodegradable plastic, which is subjected to a pretreatment in which the molded article according to claim 1 is brought into contact with a decomposition solution of carboxymethylethylcellulose (CMEC) before biodegradation by microorganisms. How to disassemble molded products. 6. The seedling pot according to claim 4, wherein a desired plant is planted in the filled seedling medium, is brought into contact with a decomposition solution of carboxymethylethylcellulose (CMEC), and then the seedling is put together with the seedling pot in growing soil or A method of growing seeds and seedlings, wherein the seedlings are directly planted in a growing pot.