Recycling method of thermoplastic polyurethane

Abstract

To provide a recycling method of thermoplastic polyurethane capable of decomposing thermoplastic polyurethane in a short period of time by action of a microorganism, melting the decomposed thermoplastic polyurethane and reusing as a thermoplastic resin.SOLUTION: A recycling method of thermoplastic polyurethane includes steps of: causing thermoplastic polyurethane including a urea bond to act on a microorganism capable of decomposing thermoplastic polyurethane including a urea bond, in a medium in which the microorganism is cultured; and turning the thermoplastic polyurethane after the microorganism has acted on into pellets. The culture medium includes saccharide and amino-acid groups.SELECTED DRAWING: Figure 15

Description

Technical Field

[0001] The present invention relates to a method for recycling thermoplastic polyurethane.

Background Art

[0002] The hardly decomposable thermoplastic polyurethane (TPU) used as the skin material of an instrument panel is a polyurethane having a urea bond in the hard segment and a polyether-based polyurethane in the soft segment, and a microphase separation structure is formed as shown in FIG. 18. For this reason, the surface becomes very dense, and the material has excellent heat resistance and abrasion resistance.

[0003] The urea bond has a symmetric conjugate structure with a carbonyl group (=CO) in the middle as shown in the following formula (1). And as shown in the following formulas (2) and (3), by polarizing, the molecular binding force becomes large and it has the property of being difficult to decompose. Also, against an external attack, as shown in the following formula (4), the valence electrons move and a relaxation action works, showing the property of being difficult to decompose.

[0004]

Chemical formula

[0005]

Chemical formula

[0006]

Chemical formula

[0007]

Chemical formula

[0008] Furthermore, as shown in Fig. 19, the polyether-based polyurethane of the soft segment of thermoplastic polyurethane contains a polyester group with high cohesive force. Therefore, in the process of melting and solidifying, the terminal groups form hydrogen bonds with urethane groups and undergo partial cross-linking, resulting in a stronger and more difficult-to-decompose structure.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The thermoplastic polyurethane used as the skin material of the instrument panel is molded by the powder slush method using powder with a particle shape of about 100 μm as shown in Fig. 20 as the raw material. The molding method by the powder slush method is a method of charging thermoplastic polyurethane powder into a heated mold, rotating the mold while gelling and adhering the resin to the mold surface, and cooling and solidifying to form a mold.

[0011] The characteristics of the thermoplastic polyurethane powder used for powder slush molding are that the width of the molecular weight distribution of the material is very small and is made. Therefore, due to the low viscosity of the raw material in the molding temperature range, the melting sensitivity is very high, and the skin can be molded in a lower temperature range of 30 to 40 °C than before without deteriorating the heat resistance of the film. In addition, it is characterized by very high adhesion to the mold and a high-quality appearance with good transferability.

[0012] As shown in Fig. 19, the formed thermoplastic polyurethane sheet forms a pseudo-crosslinked structure by hydrogen bonds at the end during the process of melting and solidifying, resulting in high heat-resistant material properties. When the melting characteristics are confirmed by thermal analysis, the thermoplastic polyurethane raw material powder melts uniformly at around 200°C as shown in Fig. 21. In contrast, the slash molded product does not melt uniformly even at around 300°C and shows the characteristics of carbonizing and decomposing as it is. Therefore, the molded body of thermoplastic polyurethane cannot be reused as a thermoplastic resin by melting the waste material, and it is currently being treated as thermal recycling.

[0013] In order to solve this problem, the present inventors selected microorganisms that show degradability against thermoplastic polyurethane (hereinafter, also simply referred to as "microorganisms", "decomposing bacteria" or "urethane-decomposing bacteria"), and considered performing the decomposition treatment of thermoplastic polyurethane by this. As a result, it was found that the decomposing bacteria adsorb to the urea bond in the molecule and cause a decomposing action, and accordingly, the intermolecular force (van der Waals force) between the hard segments in the thermoplastic polyurethane molecule is relaxed, and the partial crosslinked structure by the terminal hydrogen bond is disturbed, and it can be changed to a material property that is easy to melt (see Patent Document 1).

[0014] A schematic diagram showing the change in the molecular structure of thermoplastic polyurethane after the action of the decomposing bacteria is shown in Fig. 22, and the melting characteristics by thermal analysis are shown in Fig. 23. In addition, for the decomposition of thermoplastic polyurethane, the Sinomonas Atrocyanea ES2231 strain specified by the accession number NITE P-03613 was used. Fig. 24 shows a photograph of the state where the ES2231 strain is adsorbed on the thermoplastic polyurethane. By the action of the microorganisms, the waste material of the molded body that showed the property of being hardly soluble could be changed to the property of showing thermoplasticity in the same state as the initial raw material, but it took 3 weeks (21 days) to obtain the thermoplastic property. Therefore, shortening the decomposition time is necessary for practical use, and it is extremely necessary to see whether it has the property of being injection moldable and how the mechanical material physical properties change due to the decomposition.

[0015] Therefore, an object of the present invention is to provide a method for recycling thermoplastic polyurethane that can decompose thermoplastic polyurethane in a short period of time by the action of microorganisms and further melt the decomposed thermoplastic polyurethane for reuse as a thermoplastic resin.

Means for Solving the Problems

[0016] The method for recycling thermoplastic polyurethane according to an embodiment of the present invention includes: a step of allowing a microorganism having the ability to decompose thermoplastic polyurethane containing a urea bond to act on the thermoplastic polyurethane containing a urea bond in a medium for culturing the microorganism; a step of pelletizing the thermoplastic polyurethane after the action of the microorganism; and the medium contains saccharides and amino acids, which is a method for recycling thermoplastic polyurethane.

Effects of the Invention

[0017] According to the present invention, it is possible to provide a method for recycling thermoplastic polyurethane that can decompose thermoplastic polyurethane in a short period of time by the action of microorganisms and further melt the decomposed thermoplastic polyurethane for reuse as a thermoplastic resin.

Brief Description of the Drawings

[0018]

Figure 1A

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Embodiments for Carrying Out the Invention

[0019] The present inventors considered improving the degradability of microorganisms showing degradability to thermoplastic polyurethane with respect to thermoplastic polyurethane. In particular, an attempt was made to improve the degradability of thermoplastic polyurethane by improving the growth property of the degrading bacteria in the culture solution rather than the adsorptivity of the microorganisms to thermoplastic polyurethane. Two effects are expected for this. 1) By increasing the growth of the degrading bacteria, the amount of the released degrading enzyme increases, improving the thermoplastic polyurethane degradability. 2) The growth rate of the degrading bacteria becomes faster, the time until the logarithmic phase is shortened, and the expression of the thermoplastic polyurethane degradability is accelerated.

[0020] In addition, in the above Patent Document 1, when culturing thermoplastic polyurethane-degrading bacteria, it is disclosed that an inorganic salt liquid medium (Nakajima-Kambe, Toshiaki et al.) having the composition shown in Table 1 below is used. This inorganic salt liquid medium is a culture medium capable of enhancing the adsorbability and fixability of thermoplastic polyurethane-degrading bacteria to thermoplastic polyurethane.

[0021]

Table 1

[0022] The inventors first conducted various studies on culture media capable of improving the growth of microorganisms having thermoplastic polyurethane-degrading ability. Then, they further examined whether the thermoplastic polyurethane-degrading ability could also be improved by using a culture medium capable of improving the growth of microorganisms having thermoplastic polyurethane-degrading ability.

[0023] As a result, it was found that in order to enhance the growth of microorganisms having thermoplastic polyurethane-degrading ability and further improve the thermoplastic polyurethane-degrading ability, it is effective to use a culture medium containing saccharides and amino acids.

[0024] <Recycling method of thermoplastic polyurethane> The recycling method of thermoplastic polyurethane according to an embodiment of the present invention includes a step of allowing a thermoplastic polyurethane containing a urea bond to act on the microorganism in a medium for culturing a microorganism having the ability to decompose the thermoplastic polyurethane containing a urea bond, and a step of pelletizing the thermoplastic polyurethane after the action of the microorganism, and the culture medium contains saccharides and amino acids, which is a recycling method of thermoplastic polyurethane.

[0025] (Microorganisms having the ability to decompose thermoplastic polyurethane) The microorganism used in the recycling method of thermoplastic polyurethane according to an embodiment of the present invention may be any microorganism having the ability to decompose a thermoplastic polyurethane containing a urea bond. For example, microorganisms belonging to the genus Pseudomonas or microorganisms belonging to the genus Sinomonas can be mentioned. At least one or more microorganisms belonging to these genera may be used.

[0026] Examples of microorganisms having thermoplastic polyurethane-degrading ability and belonging to the genus Pseudomonas include, for example, the microorganism specified by the accession number NITE P-03612 (Pseudomonas Hibiscicola MS4102 strain). The said microorganism was deposited under the above accession number at the Patent Microorganisms Depositary, National Institute of Technology and Evaluation (2-5-8 Kazusa Kamashima, Kisarazu City, Chiba Prefecture) on February 24, 2022. In addition, mutants of the Pseudomonas Hibiscicola MS4102 strain can be used in the present invention as long as they have the same thermoplastic polyurethane adsorption and degradation ability.

[0027] Examples of microorganisms having thermoplastic polyurethane-degrading ability and belonging to the genus Sinomonas include, for example, the microorganism specified by the accession number NITE P-03613 (Sinomonas Atrocyanea ES2231 strain). The said microorganism was deposited under the above accession number at the Patent Microorganisms Depositary, National Institute of Technology and Evaluation (2-5-8 Kazusa Kamashima, Kisarazu City, Chiba Prefecture) on February 24, 2022. In addition, mutants of the Sinomonas Atrocyanea ES2231 strain can be used in the present invention as long as they have the same thermoplastic polyurethane adsorption and degradation ability.

[0028] The above-mentioned Pseudomonas Hibiscicola MS4102 strain and Sinomonas Atrocyanea ES2231 strain are microorganisms selected by the present inventors from soil, and also have the ability to degrade thermoplastic polyurethane containing urea bonds.

[0029] (Medium) The saccharides added to the medium are not particularly limited, and examples thereof include soluble starch and glucose. The amino acids added to the medium are not particularly limited, and examples thereof include peptone and casamino acids.

[0030] Examples of the culture medium that can be used in the method for decomposing urethane according to the embodiment of the present invention include the R2A medium having the composition shown in Table 2 below.

[0031]

Table 2

[0032] As described above, the R2A medium contains amino acids such as casamino acids and peptone, and nutrients such as glucose, and can enhance the growth property and urethane-decomposing ability of urethane-decomposing bacteria.

[0033] When culturing microorganisms having the ability to decompose thermoplastic polyurethane using a medium containing saccharides and amino acids as described above, the induction period of the microorganisms is shortened, and the growth rate in the logarithmic phase can be improved. Conventionally, a medium capable of improving the adsorptivity of microorganisms to thermoplastic polyurethane, such as an inorganic salt liquid medium, has been selected. However, the present inventors have found that improving the growth property of microorganisms can express the decomposition action of thermoplastic polyurethane in a shorter time.

[0034] By enhancing the growth property of the microorganisms, aggregation of the microorganisms during growth can be suppressed, and the microorganisms can be finely dispersed in the medium and allowed to act on thermoplastic polyurethane in a suspended state. By allowing the microorganisms to act on thermoplastic polyurethane in a finely dispersed and suspended state in the medium, urethane-decomposing enzymes (esterase, lipase, hydrolase, etc.) generated during the growth of the microorganisms can act uniformly on the surface of thermoplastic polyurethane, and the decomposition rate can be improved.

[0035] (Step of allowing microorganisms to act on thermoplastic polyurethane) The thermoplastic polyurethane may be a hardly decomposable one containing a urea bond, and examples thereof include waste materials of instrument panels of automobiles. As a method of allowing a microorganism to act on a thermoplastic polyurethane containing a urea bond, for example, there is a method of adding and culturing a thermoplastic polyurethane having a urea bond in a medium inoculated with the microorganism. When the thermoplastic polyurethane is in the form of a sheet, for example, it is preferably ground into small pieces of irregular shape about 5 mm to 10 mm. This can enhance the decomposition effect by the microorganism, and further facilitates the use of the thermoplastic polyurethane after the action of the microorganism as a thermoplastic resin for material recycling. The method for grinding the thermoplastic polyurethane (waste material) is not particularly limited, and for example, it can be ground using a rotary grinder (for example, SM300 manufactured by Retch). As shown in Fig. 16, the rotary grinder can grind the waste material between the rotary cutting blade and the screen.

[0036] The temperature at which the microorganism acts on the thermoplastic polyurethane may be a temperature suitable for the growth of the microorganism. For example, it can be about 20°C to 40°C. Note that the temperature at which the microorganism acts on the thermoplastic polyurethane may be appropriately selected according to the type of the microorganism. For example, when the microorganism is Sinomonas atrocyanea ES2231 strain, the decomposition efficiency is high and optimal when it acts at 30°C.

[0037] The time for allowing the microorganism to act on the thermoplastic polyurethane is not particularly limited, and it may be carried out until the thermoplastic polyurethane is sufficiently decomposed in consideration of the type and amount of the microorganism to be allowed to act. The longer the time for allowing the microorganism to act, the more the decomposition of the thermoplastic polyurethane progresses, but if the time is too long, the cost for decomposing the thermoplastic polyurethane will increase. Also, as will be described later, if the time for allowing the microorganism to act (the time for decomposing the thermoplastic polyurethane) is too long, not only the melting start temperature but also the boiling start temperature of the thermoplastic polyurethane will decrease, leading to a deterioration in the material physical properties of the recycled product when performing material recycling. Therefore, it is preferable to select an appropriate time so that the melting start temperature of the thermoplastic polyurethane decreases and the boiling start temperature does not decrease too much. For example, when the Sinomonas Atrocyanea ES2231 strain acts on thermoplastic polyurethane in R2A medium at 30°C, the time for the microorganism to act is preferably about 6 hours.

[0038] (Process of pelletizing thermoplastic polyurethane) The thermoplastic polyurethane (degraded product) decomposed by the action of the microorganism as described above can be melted more easily than the thermoplastic polyurethane before decomposition. When material recycling of the thermoplastic polyurethane (degraded product) is carried out, for example, it can be melted with a twin-screw kneader and pelletized into a size of about 3 mm to 5 mm suitable for injection molding.

[0039] In addition, when the thermoplastic polyurethane after the action of the microorganism is pelletized and recycled as a raw material for injection molding, there may be cases where appearance defects such as peeling marks occur due to poor peelability between the resin and the mold on a part of the surface of the molded product. This is considered to be due to an extreme decrease in the melt viscosity at the interface between the resin and the mold and poor mold release property of the resin from the mold.

[0040] In order to improve the fluidity of the thermoplastic polyurethane at the mold interface and the mold release property from the mold, it is preferable to add a lubricant to modify the properties of the material when pelletizing the thermoplastic polyurethane after the action of the microorganism. There are also various types of lubricants. In particular, in order to exhibit an effect on highly polar thermoplastic polyurethane, the types are limited, and there are concerns that the addition amount will increase and it will also affect the mechanical properties of the material.

[0041] Generally, lubricants include external lubricants that bleed to the surface of the resin to reduce the friction at the interface of the mold, and internal lubricants that act inside the resin to reduce the friction between particles. As lubricants used for thermoplastic polyurethanes, acrylic lubricants with good compatibility and bleeding properties with respect to the material are known. Acrylic lubricants have a compatible part and an incompatible functional group with respect to thermoplastic polyurethanes, and have the dual nature of internal lubricants and external lubricants. Also, montan-based and amide-based waxes have poor compatibility with thermoplastic polyurethanes and have a high effect as external lubricants. The types and characteristics of lubricants are shown in FIG. 17.

[0042] In the method for recycling thermoplastic polyurethane according to an embodiment of the present invention, when pelletizing the powder of thermoplastic polyurethane after the action of microorganisms, for example, with a twin-screw kneader, it is preferable to add a lubricant. By adding a lubricant to the thermoplastic polyurethane after decomposition, the fluidity of the thermoplastic polyurethane can be improved, and the mold release property at the mold interface during material recycling can be significantly improved. It is preferable to add an ester-based montan wax (main component: calcium butylene glycol ester of montanic acid) having both internal and external activity characteristics to the thermoplastic polyurethane after the action of the microorganisms. Thereby, the fluidity of the thermoplastic polyurethane can be improved, and furthermore, the appearance quality of the molded product can be improved when material recycling is performed.

[0043] As described above, in the method for recycling thermoplastic polyurethane according to an embodiment of the present invention, microorganisms having a decomposing ability are used for a hardly decomposable thermoplastic polyurethane having a urea bond or a pseudo-crosslinked structure to relax the cohesive force of the urea bond or the ester bond, and melt characteristics (fluidity) reusable as a thermoplastic resin can be imparted. Furthermore, when recycling and molding as a thermoplastic resin, by improving the mold release property at the interface with the mold, a molded product with high appearance can be obtained.

[0044] The recycling method of the thermoplastic polyurethane according to the embodiment of the present invention includes the aspects described below. (1) A step of allowing a microorganism having the ability to decompose a thermoplastic polyurethane containing a urea bond to act on the thermoplastic polyurethane containing a urea bond in a medium for culturing the microorganism; A step of pelletizing the thermoplastic polyurethane after the action of the microorganism; and the culture medium contains saccharides and amino acids, A recycling method of thermoplastic polyurethane. (2) The microorganism contains at least one kind of microorganism belonging to the genus Pseudomonas or the genus Sinomonas, The recycling method of the thermoplastic polyurethane according to (1) above. (3) The microorganism belonging to the genus Pseudomonas is the Pseudomonas Hibiscicola MS4102 strain identified by the accession number NITE P-03612, The recycling method of the thermoplastic polyurethane according to (2) above. (4) The microorganism belonging to the genus Sinomonas is the Sinomonas Atrocyanea ES2231 strain identified by the accession number NITE P-03613, The recycling method of the thermoplastic polyurethane according to (2) above. (5) The saccharides are saccharides containing soluble starch and / or glucose, The recycling method of the thermoplastic polyurethane according to (1) or (2) above. (6) The amino acids are amino acids containing peptone and / or casamino acids, The recycling method of the thermoplastic polyurethane according to (1) or (2) above. (7) In the step of pelletizing the thermoplastic polyurethane, a lubricant is added. The recycling method of the thermoplastic polyurethane according to (1) or (2) above. (8) The lubricant is an ester-based montan wax. The method for recycling the thermoplastic polyurethane according to (7) above.

Examples

[0045] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples.

[0046] -Examples- [Evaluation of microbial growth] The comparison of growth due to differences in the culture solutions of thermoplastic polyurethane-decomposing bacteria was carried out as follows.

[0047] (Microorganisms) As the microorganism having the ability to decompose thermoplastic polyurethane, the microorganism specified by the accession number NITE P-03613 (strain: Sinomonas Atrocyanea ES2231 strain) was used.

[0048] (Culture medium) As the culture medium for carrying out the urethane decomposition method of the present invention, the R2A medium "Dai-go" manufactured by Shioya MS Co., Ltd. (sold by Fujifilm Wako Pure Chemical Corporation) (having the composition described in Table 2 above) was used. For comparison, an inorganic salt liquid medium (Nakajima-Kambe, Toshiaki et al.) having the composition shown in Table 1 above was used.

[0049] (Culture) The pre-culture solution was obtained by inoculating the Sinomonas Atrocyanea ES2231 strain into 100 mL of the R2A medium or the inorganic salt liquid medium and performing shaking culture. The culture conditions at this time were 30 °C, 140 rpm, and 1 day. Subsequently, 1 mL of each of the pre-culture solutions obtained above was added to 100 mL of the R2A medium or the inorganic salt liquid medium, respectively, and shaking culture was performed at 140 rpm. The culture temperature was changed to 20 °C, 30 °C, and 40 °C for evaluation, respectively. After a certain period of time had elapsed since the start of cultivation, the culture broth was collected, and the absorbance (OD660) was measured to evaluate the growth of the degrading bacteria up to 48 hours later. The results are shown in FIGS. 1A and 1B.

[0050] As shown in FIGS. 1A and 1B, it was found that the degrading bacteria (ES2231 strain) had a shorter lag phase and a higher growth rate when cultured in R2A medium than when cultured in an inorganic salt liquid medium. Also, the culture temperature was most stable at 30°C. It is considered that the degradation effect is enhanced by allowing viable cells with activity before reaching the stationary phase, where the growth rate is constant and saturated, to act on the thermoplastic polyurethane.

[0051] When the inorganic salt liquid medium was used, aggregation of the degrading bacteria occurred in the medium, and the transparency of the liquid medium was high. On the other hand, when the R2A medium was used, the degrading bacteria grew in a finely dispersed manner in the medium, and the liquid medium was turbid. The difference in the growth state of the degrading bacteria is also thought to affect the degradability of the thermoplastic polyurethane. That is, it is considered that when the degrading bacteria are finely dispersed in the medium, the degradability becomes uniform and the degradability of the thermoplastic polyurethane is stabilized.

[0052] [Evaluation of the Degradability of Thermoplastic Polyurethane by Microorganisms] The degradability of the thermoplastic polyurethane degrading bacteria was compared according to the difference in the culture solution as follows. The results are shown in FIG. 2.

[0053] (Microorganisms) The ES2231 strain was used in the same manner as in the growth evaluation performed above. Also, the ES2231 strain was inoculated into R2A medium or an inorganic salt liquid medium and pre-cultured (100 mL, 30°C, 140 rpm, for 1 day).

[0054] (Thermoplastic Polyurethane) As the material to be recycled (thermoplastic polyurethane), waste material from an instrument panel was processed with a crusher (Rotary Crusher SM300 manufactured by RETSCH) to obtain a size of 0.5 cm 2 ~1 cm2 Irregularly shaped objects crushed to a certain degree were used.

[0055] (Decomposition of thermoplastic polyurethane) 1 mL of each preculture solution obtained by preculturing in the same manner as above and the crushed thermoplastic polyurethane prepared as described above were each added to 100 mL of R2A medium or inorganic salt liquid medium, and shake-cultured at 30 °C and 140 rpm. Then, the weight of each thermoplastic polyurethane was measured 6 hours, 1 day, 7 days, and 21 days after the start of decomposition (cultivation), and the weight loss rate (%) was calculated by comparing with the weight before the start of cultivation. The weight of the thermoplastic polyurethane was measured after taking it out of the culture medium, washing, and drying it. The results are shown in Figure 2.

[0056] As shown in Figure 2, when using the R2A medium (「new medium」 in Figure 2), the decomposing bacteria showed a higher thermoplastic polyurethane decomposing ability compared to when using the inorganic salt liquid medium (「conventional medium」 in Figure 2). This effect was also observed in the short time range of 6 hours after the start of decomposition (cultivation). It is presumed that this may be due to the change in the growth property of the decomposing bacteria due to the difference in the medium. Under the conventional conditions, an inorganic salt liquid medium was used with the aim of improving the adsorption property of the decomposing bacteria to the thermoplastic polyurethane and growing the decomposing bacteria using urethane as a nutrient source to improve the decomposing ability. In contrast, the R2A medium used this time aims to add a nutrient source to the medium and improve the growth property of the decomposing bacteria. And from the results of the above growth property evaluation, it has been confirmed that by using the R2A medium, the induction period of the growth of the decomposing bacteria becomes shorter and the growth rate in the logarithmic phase also becomes faster. Also, the growth property of the decomposing bacteria is not aggregated like in the case of using the conventional inorganic salt liquid medium, but is finely dispersed in a suspended state. Therefore, it is considered that the difference in the growth property of the decomposing bacteria may affect the decomposing ability of the thermoplastic polyurethane.

[0057] [Evaluation of the melting characteristics of thermoplastic polyurethane after the action of microorganisms] For each of the thermoplastic polyurethanes (degraded products) on which the degrading bacteria were allowed to act using the R2A medium or the inorganic salt liquid medium as described above, the melting characteristics were evaluated by thermal analysis. The results are shown in FIGS. 3 and 4. In addition, the following can be read from the obtained melting characteristics. Melting start temperature: It represents the magnitude of the intermolecular binding force (van der Waals force). Boiling start temperature: It is a characteristic value that depends on the molecular weight. When the molecular weight decreases, the boiling point decreases. That is, the degree of progress of material degradation associated with molecular cleavage can be judged.

[0058] FIG. 3 shows the comparison of the melting start temperature, and FIG. 4 shows the comparison of the boiling start temperature. In both cases, it was confirmed that the characteristic temperature of the thermoplastic polyurethane was lower when using the R2A medium, indicating a high decomposition effect. In addition, when reusing the thermoplastic polyurethane after the action of the degrading bacteria as a thermoplastic resin, it is necessary to find the optimal conditions that lower the melting start temperature in a short decomposition time and do not cause the boiling start temperature related to decomposition to decrease too much.

[0059] [Examination of the time for microorganisms to decompose thermoplastic polyurethane in the R2A medium] From the evaluation performed above, it was found that by allowing the Sinomonas Atrocyanea ES2231 strain to act on the thermoplastic polyurethane in the R2A medium as a degrading bacterium, it is possible to shorten the decomposition time of the thermoplastic polyurethane and lower the melting characteristics (melting start temperature and boiling start temperature).

[0060] In addition, it is preferable that the melting start temperature is lowered for improving the moldability in material recycling, but if the boiling start temperature is lowered too much, it will lead to a decrease in the material physical properties of the recycled product. Therefore, a suitable decomposition time (the time for the action of microorganisms), during which the thermoplastic polyurethane changes to a characteristic that is easy to melt while suppressing the influence on the material properties due to decomposition as much as possible, that is, material properties suitable for material recycling, was investigated. Specifically, the thermoplastic polyurethane was decomposed under the same conditions as in the above-mentioned "Evaluation of the decomposing ability of thermoplastic polyurethane by microorganisms", except that the decomposition time was changed to 4 hours, 6 hours, 12 hours, and 24 hours, and the melting characteristics of the thermoplastic polyurethane (decomposed product) after decomposition were analyzed by thermal analysis.

[0061] Fig. 5 shows a graph summarizing the change in the melting start temperature, and Fig. 6 shows a graph summarizing the change in the boiling start temperature. As shown in Fig. 5, a decrease in the melting start temperature was observed when the decomposition time was 6 hours or more. That is, setting the time for the action of microorganisms to 6 hours or more is a decomposition condition under which an improvement in moldability can be expected. On the other hand, as shown in Fig. 6, no decrease in the boiling start temperature indicating deterioration of the material properties was observed until the decomposition time reached 6 hours, but a decrease in the boiling start temperature was observed when it exceeded 6 hours, and a decrease in the material properties due to decomposition was a concern. From the above results, it was found that in order to obtain a recycled thermoplastic polyurethane material with good moldability and little decrease in material properties, it is a suitable condition to set the decomposition time to 6 hours.

[0062] [Confirmation of MFR (Melt Flow Rate) of Thermoplastic Polyurethane after Decomposition] In order to evaluate the moldability of the thermoplastic polyurethane (decomposed product) obtained by allowing the decomposing bacteria (ES2231 strain) to act for 6 hours in the R2A medium as described above, the MFR (Melt Flow Rate) values at 175 °C, 180 °C, and 185 °C were measured. Also, for comparison, the MFR value of the thermoplastic polyurethane before the action of the decomposing bacteria was measured. The results are shown in Fig. 7. In general, the MFR value is a numerical value for evaluating the fluidity of a resin during melting. In the JIS (ISO) standard, it is standardized in K7210-1:2014 (ISO1133-1:2011). The measurement of the MFR value is carried out by filling pellets (or powder) into a cylinder (heating furnace), waiting for a predetermined preheating time, then applying a certain load to the melted resin, and measuring the amount of resin extruded per 10 minutes from a die installed at the bottom of the cylinder. The numerical value is expressed in the unit of MFR (g / 10 min). Also, it is evaluated that the resin with a larger MFR value has better (faster) fluidity, and conversely, the resin with a smaller MFR value has poor (slow) flow.

[0063] As shown in Fig. 7, the thermoplastic polyurethane before the action of the decomposing bacteria (「undecomposed TPU」 in Fig. 7) had poor resin fluidity and did not have the characteristics that could be reused as a thermoplastic resin. In contrast, the thermoplastic polyurethane (「TPU after decomposition」 in Fig. 7) after the action of the decomposing bacteria for 6 hours (decomposed) had improved melting characteristics, and it was found that it had the characteristics that could be reused as a thermoplastic resin (melting characteristics that could be molded by injection molding) when the resin temperature was 180 °C or higher. Note that the thermoplastic polyurethane on which the decomposing bacteria acted in the R2A medium showed an MFR value similar to that of PP (polypropylene) generally used for injection molding when the temperature was 180 °C or higher.

[0064] [Attempts at injection molding using the decomposed thermoplastic polyurethane] Using the thermoplastic polyurethane (decomposed product) obtained by allowing the decomposing bacteria (ES2231 strain) to act for 6 hours in the R2A medium as described above, injection molding was carried out under the conditions shown in Fig. 8. Also, the appearance photos of the molded products obtained thereby are shown in Figs. 9 and 10.

[0065] As shown in Figs. 9 and 10, peeling marks of the resin were formed on a part of the surface of the obtained molded products, and there were parts where defects in appearance occurred. This phenomenon is thought to be caused by an extreme decrease in the melt viscosity at the interface between the resin and the mold, and poor mold release of the resin. These events are also thought to be due to the characteristics of the thermoplastic polyurethane material developed for slash molding. The presumed factors are described below. 1) Thermoplastic polyurethane has a high polarity and is easily adsorbed to the mold surface. 2) It has a very high melt sensitivity for slash molding, and the viscosity change due to temperature is large (because the molecular weight distribution width of the material is narrow). 3) The fluidity at the mold interface is particularly poor (interaction between melt viscosity change and adhesion).

[0066] [Evaluation of Material Property Modification by Adding Lubricant to Thermoplastic Polyurethane after Degradation] As described above, when injection molding is performed using the thermoplastic polyurethane (degraded product) obtained by allowing the degrading bacteria to act for 6 hours in R2A medium, appearance defects may occur. Therefore, lubricant was added to the thermoplastic polyurethane after the action of the degrading bacteria to examine how the MFR value changes. The results are shown in Fig. 11. The graph shown at the top of Fig. 11 is a graph showing the MFR values at 190 °C when no lubricant was added and when various lubricants were added. The graph shown at the bottom of Fig. 11 is a graph showing the MFR values at each temperature when no lubricant was added and when various lubricants were added. The degradation of thermoplastic polyurethane was carried out by allowing the degrading bacteria (ES2231 strain) to act for 6 hours in R2A medium in the same manner as above. As lubricants, montan wax, amide wax, and acrylic lubricants were used with varying addition amounts. The addition amount of montan wax was 1 mass%, the addition amounts of amide wax were 1 mass% and 3 mass%, and the addition amount of acrylic lubricant was 3 mass%.

[0067] As shown in Fig. 11, the montan wax-based lubricant showed a greater change with a smaller addition amount than the acrylic lubricant. This is thought to be because the intermolecular bonds (van der Waals forces) of the thermoplastic polyurethane are weakened by the action of the decomposing bacteria, making it easier for the added lubricant to migrate to the surface and forming a uniform lubricant layer at the interface with the mold, thereby reducing the interfacial friction and improving the fluidity. Even with a small addition amount of 1% by mass of montan wax, a great effect was obtained in improving the fluidity of the thermoplastic polyurethane after decomposition. On the other hand, acrylic lubricants have a high adsorptivity with thermoplastic polyurethane molecules and the migration of the lubricant layer to the interface with the mold is slow, so the effect is considered to be low.

[0068] Fig. 12 shows a diagram summarizing the types of lubricants added to the thermoplastic polyurethane after the action of the decomposing bacteria and the evaluation of the moldability. As shown in Fig. 12, as lubricants, wax-based ones had a greater effect on the appearance defects (peeling phenomenon) of the molded products. This is due to the action on the mold interface by the lubricants, and wax-based lubricants that are easily transferred to the surface of the thermoplastic polyurethane, especially montan wax, are effective.

[0069] Fig. 13 shows an appearance photo of a molded product (recycled product) with high appearance obtained when injection molding was performed under Condition 1 of the cylinder temperature of the conditions shown in Fig. 8 using a thermoplastic polyurethane (decomposed product) whose moldability was improved by adding a lubricant (1% by mass of montan wax). Fig. 14 also shows the evaluation results of the mechanical properties when a lubricant (1% by mass of montan wax) was added to the thermoplastic polyurethane (decomposed product) obtained by allowing the decomposing bacteria (ES2231 strain) to act in the R2A medium for 6 hours as described above. As shown in Fig. 14, it was confirmed that the mechanical properties did not change significantly depending on the presence or absence of the lubricant and had properties applicable to various fields including automotive applications.

[0070] [Material Recycling of Thermoplastic Polyurethane] In the method for recycling thermoplastic polyurethane according to an embodiment of the present invention, a material production process as shown in FIG. 15 has been established. That is, from the decomposition of thermoplastic polyurethane, the flow of kneading, pelletizing, injection molding, and productization of the material (decomposed product) can be realized in a small space in a short period of time, enabling material production at low cost.

Claims

1. A step of allowing a thermoplastic polyurethane containing a urea bond to act on a microorganism in a medium for culturing the microorganism having the ability to decompose the thermoplastic polyurethane containing a urea bond; A step of pelletizing the thermoplastic polyurethane after allowing the microorganism to act thereon; characterized by comprising: wherein the medium contains saccharides and amino acids; A method for recycling a thermoplastic polyurethane.

2. The microorganism contains at least one microorganism belonging to the genus Pseudomonas or the genus Sinomonas; The method for recycling a thermoplastic polyurethane according to Claim 1.

3. The microorganism belonging to the genus Pseudomonas is the Pseudomonas Hibiscicola MS4102 strain identified by the accession number NITE P-03612; The method for recycling a thermoplastic polyurethane according to Claim 2.

4. The microorganism belonging to the genus Sinomonas is the Sinomonas Atrocyanea ES2231 strain identified by the accession number NITE P-03613; The method for recycling a thermoplastic polyurethane according to Claim 2.

5. The saccharides are saccharides containing soluble starch and / or glucose; The method for recycling a thermoplastic polyurethane according to Claim 1 or 2.

6. The amino acids are amino acids containing peptone and / or casamino acids; The method for recycling a thermoplastic polyurethane according to Claim 1 or 2.

7. In the step of pelletizing the thermoplastic polyurethane, a lubricant is added; The method for recycling a thermoplastic polyurethane according to Claim 1 or 2.

8. The lubricant is an ester-based montan wax; The method for recycling a thermoplastic polyurethane according to Claim 7.

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