JP5651932B2 - Biodegradable resin composition - Google Patents

Description

  The present invention relates to a biodegradable resin composition containing, as a main component, a hardly hydrolyzable biodegradable resin such as polylactic acid. More specifically, the degradability of the biodegradable resin is enhanced. The present invention relates to a biodegradable resin composition, a molded body such as a container formed of the biodegradable resin, and a method for decomposing the biodegradable resin in the biodegradable resin composition.

  Recently, biodegradable resins have attracted attention from various viewpoints in various fields. In particular, since biodegradable resins such as polylactic acid are hardly hydrolyzable and stable even when contacted with water, various molded articles using such hardly hydrolyzable biodegradable resins are available. It is used for practical use. For example, Patent Document 1 proposes a lactic acid resin composition containing polylactic acid as a main component and a molded product thereof.

  By the way, a molded body made of a biodegradable resin such as polylactic acid is hardly hydrolyzable, so it takes time to decompose due to the action of an enzyme. Particularly in a molded body such as a container, the surface of the molded body is affected by the action of the enzyme. Since the decomposition proceeds, it takes a long time until the biodegradable resin forming the molded body is completely decomposed, and the property of biodegradability is not fully utilized.

In order to solve such problems, the present applicant has previously proposed a biodegradable resin composition in which an aliphatic polyester such as polyethylene oxalate is blended with a biodegradable resin such as polylactic acid (patent document). 2).
Aliphatic polyesters such as polyethylene oxalate blended in this biodegradable resin composition are easily hydrolysable and easily hydrolyze to release acid when mixed with water. It functions as an agent. That is, since the released acid accelerates the hydrolysis of the biodegradable resin, the degradation of the biodegradable resin by the enzyme can be significantly accelerated. Further, when a molded body such as a container formed of this biodegradable resin composition is mixed with an enzyme aqueous solution, cracks are generated in the molded body due to hydrolysis of the aliphatic polyester. Easily penetrates into the molded body, leading to the degradation of the biodegradable resin from within the molded body. As a result, the degradation of the biodegradable resin by the enzyme is significantly accelerated even in the form of molded products. There is an advantage of being.

JP-A-11-116788 WO2008-038648

  However, in a biodegradable resin composition containing an aliphatic polyester that functions as an ester decomposition accelerator, decomposition of the decomposition accelerator starts when it comes into contact with moisture, so that its use is significantly limited. For example, when this biodegradable resin composition is molded into a container and used for use, if water is present in the container contents, its components are decomposed by hydrolysis of the decomposition accelerator in the container contents. This causes fatal problems such as the acid being released and the quality of the contents of the container being deteriorated, or in some cases, the decomposition of the biodegradable resin composition may cause the container itself to collapse. The current situation is that its practical application is hindered.

Therefore, the object of the present invention is to allow the biodegradable resin to be rapidly decomposed and to effectively suppress the decomposition of the decomposition accelerator when it comes into contact with moisture, in the form of a molded body such as a container. It is providing the biodegradable resin composition which can be used.
Another object of the present invention is to provide a molded article, for example, a container, molded using the above-described biodegradable resin composition.
Still another object of the present invention is to provide a method for decomposing a biodegradable resin contained in the biodegradable resin composition.

According to the present invention, it contains a hardly hydrolyzable biodegradable resin, an ester decomposition accelerator, and an ester decomposition inhibitor having a non-hydrolyzable ester group ,
The hardly hydrolyzable biodegradable resin is polylactic acid, polyhydroxyalkanoate, polycaprolactone, polybutylene succinate, cellulose acetate, or a copolymer or blend thereof,
The ester decomposition accelerator is polyoxalate or polyglycolic acid,
The ester decomposition inhibitor is a polymer containing a methyl ester group or an acetate group as the non-hydrolyzable ester group,
The ester decomposition inhibitor is contained in an amount of 0.01 to 5.6 parts by weight and the ester decomposition accelerator in an amount of 0.01 to 30 parts by weight per 100 parts by weight of the biodegradable resin. A biodegradable resin composition is provided.

In the biodegradable resin composition of the present invention, the ester degradation inhibitor is at least one selected from the group consisting of polyvinyl acetate, ethylene vinyl acetate copolymer or a partially saponified product thereof and polymethyl methacrylate. Preferably there is.

  According to the present invention, the above-described biodegradable resin composition is heated to a temperature equal to or higher than the glass transition point (Tg) of the ester decomposition accelerator and the ester decomposition inhibitor in a solvent in the presence of a catalyst. By this, the method characterized by decomposing | disassembling the hardly hydrolysable biodegradable resin contained in this resin composition is provided.

In the decomposition method of the biodegradable resin in the present invention,
(1) An enzyme is used as the catalyst, and the ester decomposition accelerator and ester decomposition inhibitor are those having a glass transition point (Tg) lower than the deactivation temperature of the enzyme. And decomposing the biodegradable resin by heating to a temperature below the deactivation temperature of the enzyme,
(2) The biodegradable resin composition is used in the form of a molded body,
Is preferred.

  In the biodegradable resin composition of the present invention, an ester decomposition accelerator, specifically, a component that releases an acid or an alkali that can be easily hydrolyzed by contact with moisture to act as an ester decomposition catalyst is blended. Therefore, the degradation of the hardly hydrolyzable biodegradable resin in the composition can be promoted, and the degradation of the biodegradable resin by a catalyst such as an enzyme can be remarkably accelerated. That is, a molded body such as a container molded by this biodegradable resin composition can be quickly disintegrated, and it is extremely advantageous in avoiding environmental destruction such as an increase in dust, and a used molded body is recovered. Thus, the biodegradable resin can be reused and recycled.

  In addition, since the ester decomposition inhibitor for suppressing the decomposition of the ester (decomposition of the biodegradable resin) by the ester decomposition accelerator is blended with the ester decomposition accelerator, the composition is simply in contact with moisture. It is possible to effectively suppress the decomposition of the decomposition accelerator in the formed state, for example, it is possible to effectively prevent the decomposition of the biodegradable resin and the collapse of the molded body in a state of being molded into a molded body such as a container.

  Furthermore, in the decomposition method of the present invention, the biodegradable resin in the biodegradable composition molded into a molded body such as a container is decomposed in a solvent in the presence of a catalyst such as an enzyme. At this time, since the ester decomposition accelerator and the ester decomposition inhibitor are heated to a temperature equal to or higher than the glass transition point, the mobility of the ester decomposition accelerator and the ester decomposition inhibitor is enhanced. As a result, the enzyme uses the ester decomposition accelerator. It is hydrolyzed and the restraint by the ester degradation inhibitor is relaxed or eliminated, and the effect of inhibiting the ester degradation is lost. The resin can be decomposed in a very short time.

The measurement result of FT-IR in the film before hydrolysis of Reference Example 1 is shown. The measurement result of FT-IR in the film before hydrolysis of Reference Example 5 is shown. Experiment of Experimental Example 2 in which the amount of oxalic acid eluted into water was measured when an ester decomposition inhibitor (partially saponified polyvinyl acetate) was blended with a blend containing polylactic acid and an ester decomposition accelerator (polyethylene oxalate) The figure which shows a result. The figure which shows the experimental result of Experimental example 2 which measured the oxalic acid elution amount in water when an ester decomposition inhibitor (polyvinyl acetate) was mix | blended with the blend containing polylactic acid and ester decomposition accelerator (polyethylene oxalate). . The figure which shows the experimental result of Experimental example 2 which measured the oxalic acid elution amount in water when an ester decomposition inhibitor (polymethylmethacrylate) was mix | blended with the blend containing polylactic acid and ester decomposition accelerator (polyethylene oxalate). . The figure which shows the experimental result of Experimental example 3 which measured the weight change when the decomposition | disassembly by the enzyme of the composition of this invention was performed at the temperature higher than Tg of an ester decomposition accelerator and lower than Tg of an ester decomposition inhibitor. The figure which shows the experimental result of Experimental example 4 which measured the weight change when the decomposition | disassembly by the enzyme of the composition of this invention was performed at temperature higher than Tg of an ester decomposition accelerator and an ester decomposition inhibitor. The figure which shows the gradient conditions of HPLC (high performance liquid chromatograph).

  The biodegradable resin composition of the present invention contains a hardly hydrolyzable biodegradable resin as a main component, is blended with an ester degradation accelerator and an ester degradation inhibitor, and further contains known additives as necessary. These components are prepared by melt kneading with an extruder or the like.

<Biodegradable resin>
In the present invention, the biodegradable resin used is hardly hydrolyzable. For example, an aqueous dispersion having a concentration of 10 mg / 10 ml is prepared from a sample obtained by freeze-pulverizing and pulverizing the biodegradable resin. After 1 week of incubation at 0 ° C., the TOC (total organic carbon content) of the remaining liquid is 5 ppm or less. Furthermore, water-soluble polyester is not included. Specific examples of such a hardly hydrolyzable biodegradable resin include polylactic acid, polyhydroxyalkanoate, polycaprolactone, polybutylene succinate, and cellulose acetate. These are copolymers. It can also be used in the form of blends.

  The polylactic acid may be 100% poly-L-lactic acid or 100% poly-D-lactic acid, or may be a melt blend of poly-L-lactic acid and poly-D-lactic acid, It may be a random copolymer or block copolymer of L-lactic acid and D-lactic acid.

Furthermore, the above-described biodegradable resin is a copolymer obtained by copolymerizing various aliphatic polyhydric alcohols, aliphatic polybasic acids, hydroxycarboxylic acids, lactones, etc., as long as the properties of the biodegradable resin are not impaired. It can also be used in the form of a coalescence.
Examples of such polyhydric alcohols include ethylene glycol, propylene glycol, butanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, and polyethylene glycol.
Examples of the polybasic acid include succinic acid, adipic acid, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, and terephthalic acid.
Examples of the hydroxycarboxylic acid include glycolic acid, hydroxypropionic acid, hydroxyvaleric acid, hydroxycaproic acid, and mandelic acid.
Examples of the lactone include caprolactone, butyrolactone, valerolactone, poropiolactone, undecalactone, glycolide, and mandelide.

  The biodegradable resin described above should have a molecular weight sufficient to form a film from the viewpoint of moldability, and generally has a weight average molecular weight of 5,000 to 1,000,000, particularly 10 In the range of 1,000,000 to 500,000.

  In the present invention, polylactic acid is optimal from the viewpoint of being suitably applied in the field of packaging materials such as containers.

  The above-described biodegradable resin is hardly hydrolyzable and requires a very long time for its decomposition. Therefore, the following ester degradation accelerator is blended, and the inconvenience caused by the accelerated ester degradation is avoided. In order to do this, an ester decomposition inhibitor described below is blended.

<Ester degradation accelerator>
An ester decomposition accelerator does not exhibit ester degradation by itself, but releases an acid that functions as a catalyst for ester decomposition when mixed with moisture . In the present invention, polyoxalate or polyglycolic acid is used. Is done. Such ester degradation accelerators are usually dispersed uniformly throughout the biodegradable resin and are used to rapidly accelerate hydrolysis of the biodegradable resin by acids released from the ester degradation accelerator. Those having a weight average molecular weight of about 1,000 to 200,000 are used.

Polyoxalate and polyglycolic acid used as ester decomposition accelerators have a pH (25 ° C.) of 3 or less in an aqueous solution or aqueous dispersion having a concentration of 0.005 g / ml, and when mixed with water It is easily hydrolyzed to release acid .
Such polyoxalate and polyglycolic acid may be used as a copolymer, used alone or in combination of two or more.
Examples of the components forming the copolymer include polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, bisphenol A, and polyethylene glycol; succinic acid, adipine Acids, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, anthracene dicarboxylic acid and other dicarboxylic acids; glycolic acid, L-lactic acid, D-lactic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxy Hydroxycarboxylic acids such as valeric acid, hydroxycaproic acid, mandelic acid, hydroxybenzoic acid; glycolide, caprolactone, butyrolactone, valerolactone, polo Examples include lactones such as piolactone and undecalactone.

  In the present specification, a polymer obtained by polymerizing oxalic acid as at least one monomer in a homopolymer, copolymer, or blend is referred to as polyoxalate.

  In particular, the above-mentioned polyoxalate and polyglycolic acid are easily hydrolyzable biodegradable resins, and are also preferably used in that they have biodegradability by themselves.

  In addition, the above-described ester decomposition accelerator is preferably one whose glass transition point (Tg) is lower than the deactivation temperature (usually about 50 ° C.) of the enzyme used for the decomposition of the biodegradable resin. By using the one having such a low glass transition point, it becomes possible to accelerate the degradation of the biodegradable resin by an enzyme more rapidly.

In the present invention, such an ester decomposition accelerator is used in an amount of 0.01 to 30 parts by weight, particularly 1 to 10 parts by weight per 100 parts by weight of the biodegradable resin . If the amount of the ester decomposition accelerator used is too small, it may be difficult to promote the decomposition of the biodegradable resin. If it is used in an excessive amount, it may be used as a preparation stage or a molded product of this resin composition. This is because the biodegradable resin may start decomposing at the stage of use.

<Ester degradation inhibitor>
The ester decomposition inhibitor has hydrogen bonding to the ester group as an interaction with the ester group of the polyester whose decomposition is to be suppressed. Various compounds containing a non-hydrolyzable methyl ester group or an acetate group can be used. used. That is, this compound is hardly hydrolyzable, and like the above-mentioned hardly hydrolyzable biodegradable resin, the pH of the aqueous solution or aqueous dispersion is at a neutral level and does not release an acid by hydrolysis. It may be water-soluble.

  Such an ester decomposition inhibitor has a high affinity with a biodegradable resin or an ester decomposition accelerator when dispersed in the biodegradable resin composition, and may be compatible. For this reason, not only the release of acid due to hydrolysis of the ester group can be effectively suppressed, but also the degradation of the biodegradable resin by acid or alkali can be effectively suppressed. Degradation of the biodegradable resin at the stage can be effectively suppressed.

  Further, this ester decomposition inhibitor is preferably a polymer having a polymer form from the viewpoint of moldability and the like, and those having a weight average molecular weight of about 1,000 to 1,000,000 are suitable, and in particular, the glass transition point (Tg) thereof. Like the ester decomposition accelerator, those lower than the deactivation temperature (usually about 50 ° C.) of the enzyme used for the decomposition of the biodegradable resin are suitable. By using a material having such a low glass transition point, the action of the ester decomposition inhibitor can be reduced or eliminated by heating in the decomposition step, and the decomposition of the biodegradable resin by the enzyme can be accelerated more rapidly. This is because it becomes possible.

In the ester decomposition inhibitor used in the present invention , the ester group is a methyl ester group (—COO—CH ₃ ) or an acetate group (—OOC—CH ₃ ) , and specifically, polyvinyl acetate, ethylene acetate A vinyl copolymer or a partially saponified product thereof, polymethyl methacrylate, polymethyl acrylate and the like are preferably used, and these can be used alone or in combination of two or more. That is, when the above-mentioned one having a methyl ester group or an acetate group is blended in a biodegradable resin composition as an ester decomposition inhibitor, hydrolysis of the biodegradable resin is effectively suppressed. In addition, the ester decomposition accelerator can be hydrolyzed to effectively suppress the release of acid and the like. The reason why the methyl group of such a methyl ester group or an acetate group exhibits a function of inhibiting the decomposition of the ester is not clearly elucidated, but the present inventors, the methyl group bonded to the ester group, It is thought that it may form hydrogen bonds with ester groups in biodegradable resins and ester decomposition accelerators.

  For example, as shown in Experimental Example 1 described later (see Table 1), the above-mentioned ester decomposing agent, polyvinyl acetate, partially saponified polyvinyl acetate (saponification degree 60%) and polymethyl methacrylate When a composition blended with polylactic acid is immersed in an aqueous sodium hydroxide solution, the amount of lactic acid eluted by hydrolysis of polylactic acid is significantly reduced, while ethylene vinyl alcohol having no ester group as described above is used. Copolymer (saponification degree 99% or more) has a large amount of lactic acid elution. Experimental Example 1 is an accelerated test under alkaline and heating conditions. In Reference Example 2, the partially saponified product of polyvinyl acetate (saponification degree 60%) is water-soluble and has low alkali resistance. Therefore, the decomposition inhibitor is decomposed and hydrolysis of the substrate cannot be suppressed, and lactic acid is eluted. The amount is thought to have increased.

  That is, from this experimental result, in polyvinyl acetate having an acetate group and polymethyl methacrylate having a methyl ester group, the methyl ester group or the acetate group forms a hydrogen bond with the oxygen atom of the carbonyl group of the ester group of polylactic acid, As a result, it is believed that the ester group of polylactic acid is protected from alkali and its hydrolysis is suppressed. On the other hand, an ethylene vinyl alcohol copolymer having no methyl ester group has a strong hydrogen bond strength (hydrogen bond strength between OH groups), and thus no interaction with polylactic acid is observed. As a result, it is considered that hydrolysis of polylactic acid in an aqueous alkaline solution cannot be suppressed.

1 and 2 show the measurement results of FT-IR in the pre-hydrolysis films of Reference Examples 1 and 5. This shows a spectrum obtained by second-order differentiation of the peak due to the stretching vibration of the carbonyl group of Reference Examples 1 and 5, and the peak of the carbonyl group of the polylactic acid of Reference Example 5 (1743 cm ⁻¹ ) is the polyvinyl acetate of Reference Example 1. It was found that the carbonyl group of polylactic acid interacted with polyvinyl acetate because it was shifted to a low wavenumber range (1736 cm ⁻¹ ).
In general, hydrolysis of a polyester is caused by hydrolysis of an ester group by nucleophilic attack or electrophilic attack on a carbonyl group. That is, it is considered that hydrolysis was suppressed by blending with a component having an interaction with the carbonyl group.

  In Experimental Example 2, which will be described later, polylactic acid, polyethylene oxalate (ester decomposition accelerator) and polyvinyl acetate were blended in various blending amounts shown in Table 2, and formed into a film. The amount of oxalic acid eluted when immersed is measured. According to this experimental result (see FIG. 3), it can be seen that hydrolysis of polyethylene oxalate, which is an ester decomposition accelerator, is also effectively suppressed by the addition of polyvinyl acetate having an acetate group. That is, the use of the above-described ester decomposition inhibitor having a methyl ester group or an acetate group can effectively suppress the hydrolysis of the ester decomposition accelerator. From this, the methyl ester group or the acetate group is It is believed that a hydrogen bond is formed with the oxygen atom of the ester group (carbonyl group) of the decomposing agent and the hydrolysis is effectively suppressed.

  As described above, the use of an ester decomposition inhibitor having a methyl ester group or an acetate group can effectively prevent hydrolysis of a hardly hydrolyzable biodegradable resin, and can also be achieved by hydrolysis of an ester decomposition accelerator. The release of acid can also be effectively prevented.

In the present invention, the ester decomposition inhibitor is used in such an amount that the ester decomposition ability is sufficiently exerted, and 0.01 to 5.6 parts by weight, particularly 0.01 , per 100 parts by weight of the biodegradable resin. Used in an amount of up to 5 parts by weight.

<Other ingredients>
The biodegradable resin composition of the present invention can also contain various resin additives in addition to the components described above, for example, in an amount that does not impair the moldability and biodegradability of the biodegradable resin. , Plasticizers, light stabilizers, antioxidants, UV absorbers, flame retardants, colorants, pigments, fillers, mold release agents, antistatic agents, fragrances, foaming agents, antibacterial / antifungal agents, nucleating materials, etc. It is also possible to blend other thermoplastic resins if necessary.

<Application>
The biodegradable resin composition of the present invention containing the various components described above can be used as molded articles having various shapes by molding methods known per se, such as extrusion molding, injection molding, and compression molding. Can be suitably used also in the field of packaging materials.

  For example, in the field of packaging materials, the above-described biodegradable resin composition can be used as a packaging film or sheet. In particular, the film can be used as a bag-like container ( Can be used as a pouch). Further, the film or sheet can be used as a cup-shaped or tray-shaped container by vacuum forming, pressure forming, stretch forming, plug assist forming, or the like. Furthermore, it can be used as a test tube-shaped preform by injection molding or the like, and can be used as a bottle-shaped container by blow molding using this preform.

  In the molded products of various shapes as described above, if necessary, they were laminated with other resins by molding using an extruder equipped with a multilayer multiple die or a co-injector equipped with a plurality of injection gates. It can also be used as a multilayer structure.

<Disassembly method>
A molded body such as a container molded using the biodegradable resin composition of the present invention may be supplied to a decomposition tank as it is upon disposal, but this is appropriately cut into small pieces by cutting, crushing, or the like. After that, it is supplied to the decomposition tank and decomposed.

  This decomposition treatment is performed in an appropriate solvent in the presence of a catalyst. As such a catalyst, a water-containing solid acid catalyst, for example, an activated clay having a high specific surface area obtained by acid treatment of smectite clay such as acid clay or bentonite can be used, but an enzyme is used. Is preferred. That is, not only from the viewpoint of environmental impact and waste treatment, but also when an enzyme is used as a catalyst, the enzyme quickly penetrates into the molded body (waste) and also from the inside of the molded body. This is extremely advantageous in that the biodegradable resin is decomposed and can be decomposed in a short time until the molded body completely disintegrates.

  Examples of such enzymes include protease, cellulase, cutinase, lipase and the like, and these enzymes may or may not be immobilized. For example, protease K manufactured by Wako Pure Chemical Industries, Ltd. is used in the form of an aqueous solution. Moreover, microorganisms may be put in and the extracellular enzyme may be used, and the culture medium component and nutrient component which the microorganism requires may be added.

  In order to prevent the pH of the enzyme reaction solution from changing, the solvent during the decomposition treatment as described above can be performed, for example, by exchanging the reaction solution or using a buffer solution as the reaction solution. Suitable buffers include glycine-HCl buffer, phosphate buffer, Tris-HCl buffer, acetate buffer, citrate buffer, citrate-phosphate buffer, borate buffer, tartaric acid buffer, glycine- A sodium hydroxide buffer solution etc. are mentioned. Further, a solid neutralizing agent may be used in place of the buffer solution, and water may be used as the solvent. Examples thereof include calcium carbonate, chitosan, and deprotonated ion exchange resin. This can be done by adding a neutralizing agent to the reaction solution. Moreover, you may add organic solvents, such as ethanol, as needed.

That is, it is preferable to perform the decomposition treatment by mixing and stirring the waste of the molded body of the biodegradable resin composition with the enzyme aqueous solution in the decomposition tank. At this time, the amount of the enzyme used varies depending on the activity of the enzyme used, but generally it may be an amount of about 0.01 to 10 parts by weight per 100 parts by weight of the hardly hydrolyzable biodegradable resin. The decomposition treatment is performed by putting the compact waste into the charged enzyme aqueous solution and stirring it.
In the case of using the above-described solid acid catalyst, since the solid acid catalyst contains water, the solid acid catalyst is dispersed in an appropriate organic solvent, and the compact waste is put into this dispersion. Is good.

  In such a decomposition treatment, the temperature should be higher than the glass transition point (Tg) of the ester decomposition accelerator and ester decomposition inhibitor contained in the biodegradable resin composition described above.

  That is, in the biodegradable resin composition of the present invention, ester decomposition inhibitor is blended together with an ester decomposition accelerator, and therefore, simply mixing the catalyst solution or catalyst dispersion and the molded product waste produces biodegradation. The decomposition of the decomposition resin itself proceeds slowly, and it takes a considerable time until the biodegradation resin is completely decomposed to the monomer level and the shape of the molded body is completely destroyed. For example, in the experimental result of Experimental Example 3 described later (see FIG. 6), the decomposition rate in the composition of the present invention in which the ester decomposition inhibitor is blended is only PLA at a temperature lower than the Tg of the decomposition inhibitor. It can be seen that it is considerably slower than the composition in which is incorporated.

  On the other hand, in the composition of the present invention in which the ester decomposition inhibitor is blended, when heated to a temperature higher than the glass transition point (Tg) of the ester decomposition accelerator and the ester decomposition inhibitor, This is shown in the experimental results (FIG. 7). Incidentally, in Experimental Example 4, an experiment was also conducted using polymethyl methacrylate (PMMA) having a glass transition point (Tg) of 72 ° C. as an ester decomposition inhibitor, and the heating temperature in this case was 45 ° C. It is lower than the Tg of this PMMA. For this reason, it turns out that the decomposition | disassembly rate is not accelerated | stimulated.

  As described above, in the present invention, the biodegradable resin is decomposed by heating to a temperature higher than the Tg of the ester decomposition accelerator and ester decomposition inhibitor blended in the composition, thereby degrading the enzyme. Hydrolyzes the ester decomposition accelerator, further loses the ability to inhibit ester decomposition, fully performs the function of the ester decomposition accelerator, and is decomposed to the same level as when no ester decomposition inhibitor is blended. The decomposition rate can be increased. That is, by heating to a temperature equal to or higher than Tg, the mobility of the molecules of the ester decomposition accelerator and the ester decomposition inhibitor is enhanced, and the enzyme hydrolyzes the ester decomposition accelerator, thereby hydrogen bonding of the ester decomposition accelerator. Therefore, the decomposition of the biodegradable resin is promoted by the release of acid and the like due to hydrolysis of the ester decomposition accelerator. In addition, since the easily hydrolyzable ester decomposition accelerator is hydrolyzed prior to the decomposition of the biodegradable ester resin to release acid or the like, a large number of cracks are generated in the molded body. As a result, the catalyst solution ( In particular, the enzyme aqueous solution) penetrates into the molded body, the biodegradable resin proceeds on the surface and inside the molded body, and the degradation can be completed in an extremely short time.

  In addition, when performing a decomposition process using an enzyme as a catalyst, it is natural that the heating temperature should be lower than the deactivation temperature of the enzyme (usually about 50 ° C.). As the agent and the ester promotion inhibitor, it is necessary to select one having a glass transition temperature (Tg) lower than the deactivation temperature of the enzyme.

  As described above, when the decomposition is performed and the molded body is completely disintegrated, the biodegradable resin is decomposed into monomers or oligomers constituting the resin, and the liquid in the decomposition tank may be discarded. If necessary, the monomer or oligomer can be recovered by a separation operation such as distillation or extraction and reused for the synthesis of the biodegradable resin.

The invention is illustrated by the following experimental example.
The various measurements performed in the experimental examples are based on the following methods.

<Synthesis of polyethylene oxalate (hereinafter also abbreviated as “PEOx”)>
A 1 L separable flask equipped with a mantle heater, a stirrer, a nitrogen inlet tube, and a condenser tube was charged with 354 g (3.0 mol) of dimethyl oxalate, 223.5 g (3.6 mol) of ethylene glycol, and 0.30 g of tetrabutyl titanate under a nitrogen stream. While the methanol was distilled off from 110 &ordm; C, the internal temperature was heated to 170 &ordm; C and reacted for 9 hours. Finally, 210 ml of methanol was distilled off. Thereafter, the mixture was stirred at an internal temperature of 150 &ordm; C under a reduced pressure of 0.1-0.5 mmHg for 1 hour, and reacted at an internal temperature of 170 ° C. to 190 &ordm; C for 7 hours. Ηinh of the composite was 0.12. The obtained PEOx had a melting point (mp) and a glass transition temperature (° C.) of mp 172 ° C. and Tg 25 ° C.
The solution viscosity (ηinh) was measured using a synthesized PEOx that was vacuum-dried overnight at 120 ° C., and this was mixed with m-chlorophenol / 1,2,4-trichlorobenzene = 4/1 (weight ratio) mixed solvent. It was immersed and dissolved at 150 ° C. for about 10 minutes to form a solution having a concentration of 0.4 g / dl, and then the melt viscosity was measured at 30 ° C. using an Ubbelohde viscometer. (Unit dl / g)

<Measurement of melting point (mp) and glass transition temperature (° C.)>
A sample amount of 5 to 10 mg was added to an aluminum pan, sealed, and measured using a differential scanning calorimeter DSC (manufactured by Seiko Instruments Inc .: DSC6220). Measurement conditions were measured at a heating rate of 10 ° C./min from 0 ° C. to 200 ° C. in a nitrogen atmosphere, and a melting point and a glass transition temperature were obtained.

<Production of film>
Various materials were dry blended and kneaded with a microkneader (manufactured by Toyo Seiki Seisakusho Co., Ltd.) at a molding temperature of 190 ° C. and a screw rotation speed of 50 rpm to produce pellets. The pellet was melted at 190 ° C. for 5 minutes and then heated and pressed (hot pressed) at a pressure of 40-50 kgf / cm ² to prepare a film.

<FT-IR measurement>
This was performed using FTS7000SERIES manufactured by Digilab Japan. Performed by the total reflection measuring method (ATR method) to the film, measurement ^frequency: was 600cm ^-1 ~4000cm -1.

<Measurement of lactic acid elution amount>
The film produced by the above method was cut into 2 cm × 2 cm and a weight of 60 mg, 10 ml of 3% NaOH aqueous solution was placed in a 25 ml vial, and left at 50 ° C. for 20 minutes. After 20 minutes, 1.5 ml of 2 mol / l HCl aqueous solution was added to acidify the pH, 2 ml of the liquid was taken out, and the amount of lactic acid eluted was measured by HPLC described later.

<Measurement of oxalic acid elution amount>
The film produced by the above method was cut into 2 cm × 2 cm and weighed 70-80 mg, 10 ml of ultrapure water was added to a 25 ml vial, and left at 40 ° C. for one week. One week later, 2 ml of the remaining solution was taken out, and the oxalic acid elution amount was measured by HPLC described later.

<HPLC (High Performance Liquid Chromatograph)>
JASCO GULLIVER series was used for the HPLC system. The analytical conditions were as follows. The column was Waters Atlantis dC ₁₈ 5 μm, 4.6 × 250 mm in a column oven maintained at 40 ° C., and a gradient was applied as shown in FIG. 8 with 0.5% phosphoric acid and methanol at a flow rate of 1 mL / min. Then, 50 μl of sample was injected using it as a mobile phase. 210 nm UV absorption was used for detection, and oxalic acid or L-lactic acid (manufactured by Wako Pure Chemical Industries, Ltd.) purified as a standard sample was used.

<Measurement of film degradation rate and degradability test>
48ml of CLE enzyme solution (Cryptococcus sp. S-2 lipase showing lipase activity of 653U / ml (Independent Administrative Institution Liquor Research Institute: JP 2004-73123)) added to 10ml of pH7 60mmol / l phosphate buffer Thus, a decomposition solution was prepared. The lipase activity was measured using paranitrophenyl laurate as a substrate. Here, 1 U of lipase activity is defined as the amount of enzyme when 1 μmol / min of paranitrophenol is released from paranitrophenyl laurate.
The film produced by the above method was cut into 2 cm × 2 cm and weighed 60-80 mg, 10 ml of the above-mentioned decomposition solution was put into a 25 ml vial, and shaken at a predetermined temperature (37 or 45 ° C., 100 rpm) for 7 days. In order to avoid an extreme decrease in pH, 7 days were divided into 2 days, 2 days, and 3 days, and the decomposition solution was changed. Seven days later, the film was taken out and dried in a 45 ° C. oven overnight, and the weight was measured. The degradation rate of the film was determined by {(initial film weight) − (film weight after 7 days) / initial film weight} × 100.

<Appearance evaluation>
Visually evaluate the appearance of the film produced by the above method, ◯ for a good film, △ for a film (gel-like material) produced on a part of the film, and x for a film produced on the entire film. did.

(Experimental example 1)
Polylactic acid (PLA) (Natureworks 4032D (mp160 ° C, Tg58 ° C)) as a base material, polyvinyl acetate (PVAc) (ACROS ORGANICS: Tg30 ° C, Mw101600)), polymethyl methacrylate (PMMA) ) (Wako Pure Chemical Industries, Ltd .: Tg72 ° C), saponification degree 60mol% polyvinyl alcohol (PVA60) (Kuraray CP9000: Tg40 ° C), ethylene content 32mol% ethylene-vinyl alcohol copolymer (EVOH32) (Kuraray) F101: mp 178 ° C., Tg 57 ° C.) were blended in the blending amounts shown in Table 1 to produce films of Reference Examples 1-5. Table 1 shows the measurement results of the lactic acid elution amount of the obtained film.

(Experimental example 2)
Films of Examples 1 to 13 and Comparative Examples 1 to 5 were prepared by blending the materials used in Experimental Example 1 with the blending amounts shown in Table 2. The results of oxalic acid elution amount, decomposition rate measurement, and appearance evaluation of the obtained film are shown in Table 2 and FIGS.
In addition, in said Example, Example 2, 5, 7-12 is an example outside the range of this invention. Moreover, in Example 13, the degradation rate after 7 days indicating enzyme degradability is a low value, because this is because an enzyme having a low deactivation temperature (enzyme decomposition temperature) is used. When an enzyme having a high pH is used, as shown in Example 4, the degradation rate after 7 days becomes a high value.

(Experimental example 3)
100 parts by weight of polylactic acid (PLA) (Natureworks 4032D: mp 160 ° C., Tg 58 ° C.) as a base material, 5.5 parts by weight of polyethylene oxalate (PEOx) as a decomposition accelerator, and polymethyl methacrylate (PMMA) as a decomposition inhibitor ) (Wako Pure Chemical Industries, Ltd .: Tg 72 ° C.), saponification degree 60 mol% polyvinyl alcohol (PVA60) (Kuraray CP9000: Tg 40 ° C.), respectively. The film was subjected to a degradability test under the condition of ° C. The results are shown in FIG.

(Experimental example 4)
Experimental Example 3 except that the decomposition solution was kept at 45 ° C. and a film containing 5.5 parts by weight of polyvinyl acetate (PVAc) (manufactured by ACROS ORGANICS: Tg 30 ° C., Mw 101600) as a decomposition inhibitor was prepared. The decomposability test was conducted in the same manner as above. The results are shown in FIG.

Claims (7)

It contains a hardly hydrolyzable biodegradable resin, an ester decomposition accelerator, and an ester decomposition inhibitor having a non-hydrolyzable ester group ,
The hardly hydrolyzable biodegradable resin is polylactic acid, polyhydroxyalkanoate, polycaprolactone, polybutylene succinate, cellulose acetate, or a copolymer or blend thereof,
The ester decomposition accelerator is polyoxalate or polyglycolic acid,
The ester decomposition inhibitor is a polymer containing a methyl ester group or an acetate group as the non-hydrolyzable ester group,
The ester decomposition inhibitor is contained in an amount of 0.01 to 5.6 parts by weight and the ester decomposition accelerator in an amount of 0.01 to 30 parts by weight per 100 parts by weight of the biodegradable resin. A biodegradable resin composition. 2. The biodegradable resin composition according to claim 1 , wherein the ester decomposition inhibitor is at least one selected from the group consisting of polyvinyl acetate, ethylene vinyl acetate copolymer, or a partially saponified product thereof, and polymethyl methacrylate. object. The molded object shape | molded using the biodegradable resin composition of Claim 1 or 2 . The molded article according to claim 3 , which is a container. The biodegradable resin composition according to claim 1 is heated in a solvent in the presence of a catalyst to a temperature equal to or higher than a glass transition point (Tg) of the ester decomposition accelerator and the ester decomposition inhibitor. A method comprising decomposing a hardly hydrolyzable biodegradable resin contained in a resin composition. An enzyme is used as the catalyst, and the ester decomposition accelerator and ester decomposition inhibitor are those having a glass transition point (Tg) lower than the deactivation temperature of the enzyme. The method according to claim 5 , wherein the biodegradable resin is decomposed by heating to a temperature lower than the deactivation temperature. The method according to claim 5 or 6 , wherein the biodegradable resin composition is used in the form of a molded body.

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