Catalyst composition for decomposing homopolymer and method for decomposing homopolymer using same

Abstract

Disclosed are: a catalyst composition for decomposing a homopolymer; and a method for decomposing a homopolymer using the catalyst composition. This catalyst composition is for decomposing a homopolymer, and contains at least titanium oxide and a metal oxide other than titanium oxide. Furthermore, this method for decomposing a homopolymer includes a step of heating the homopolymer in the presence of the catalyst composition. The present invention enables a homopolymer to be efficiently decomposed, while reducing the likelihood of side reactions occurring during the decomposition. In addition, the monomer component can be recovered in good yield.

Description

Catalyst composition for decomposing homopolymers and method for decomposing homopolymers using the same

[0001] The present invention relates to a catalyst composition for decomposing homopolymers and a method for decomposing homopolymers using the same.

[0002] Methods for decomposing polymers have been studied for some time. Many polymers decompose when heated to 400-600°C, but controlling the reaction is difficult, and various reactions occur in rapid succession, raising concerns about the safety of the reaction products, and the decomposition yield is not always high. Therefore, there is a need for a reaction that is energetically advantageous, operates at a lower temperature, and has a high decomposition yield. This is especially true for homopolymers composed of a single monomer, as controlling the decomposition reaction would allow for the reuse of the recovered monomer.

[0003] Patent Document 1 discloses a technique for recovering lactide from polylactic acid, a homopolymer obtained by polymerization of the cyclic monomer lactide, in the presence of a catalyst made of tin or a tin compound. Patent Document 2 discloses a technique for recovering the monomer lactide from polylactic acid, a homopolymer obtained by polymerization of the cyclic monomer lactide, in the presence of monobutyltin, by heating the mixture to 120-230°C. However, these methods use tin-based catalysts, raising concerns about adverse environmental impacts, and the development of safer catalysts is desired.

[0004] Patent Document 3 discloses a technique for recovering lactide from a lactic acid oligomer, which is a homopolymer obtained by polymerization of the cyclic monomer lactide, using ferrous oxide as a catalyst. Patent Document 4 discloses a technique for recovering lactide from the same lactic acid oligomer using alkali metal hydroxides or alkoxides, and salts with carboxylic acids as catalysts. However, these methods are merely techniques for monomer dissociation from oligomers with low molecular weight and do not suggest polymer decomposition.

[0005] Patent Document 5 discloses a method for recovering lactide by adding an alkaline earth metal compound to a lactic acid polymer, which is a homopolymer obtained by polymerizing lactide (cyclic monomer), and then heating it. However, the recovery rate of the method described in Patent Document 5 is low, at less than 60%.

[0006] Patent Document 6 discloses that polycaprolactone, a homopolymer obtained by polymerization of the cyclic monomer caprolactone, is depolymerized after a foaming process using a depolymerizing agent such as an esterase.

[0007] JP-A-9-77904 JP-A-11-209370 JP-A-8-119961 JP-A-6-65230 International Publication No. 03 / 091238 International Publication No. 2021 / 123299

[0008] The present invention aims to solve the above-mentioned problems, and its objective is to provide a catalyst composition for decomposing homopolymers and a method for decomposing homopolymers using the same, which can decompose homopolymers safely and efficiently.

[0009] The present invention relates to a catalyst composition for decomposing homopolymers, which contains at least titanium dioxide and a metal oxide other than titanium dioxide.

[0010] In one embodiment, the monomer constituting the homopolymer is a cyclic monomer.

[0011] In one embodiment, the resistivity of the titanium oxide is 2,000 Ω·cm or more and 12,000 Ω·cm or less.

[0012] In one embodiment, the titanium dioxide is anatase-type titanium dioxide, and 5m ２ / g or more 400m ２ It has a BET specific surface area of ​​less than or equal to / g.

[0013] In one embodiment, the metal oxide contains magnesium oxide.

[0014] In a further embodiment, the magnesium oxide is 3m ２ / g or more 400m２ It has a BET specific surface area of ​​less than or equal to / g.

[0015] In one embodiment, the titanium dioxide content in 100 parts by mass of the catalyst composition is 10 to 75 parts by mass.

[0016] In one embodiment, the homopolymer is polylactic acid.

[0017] The present invention also relates to a method for decomposing a homopolymer, comprising the step of heating the homopolymer in the presence of the catalyst composition.

[0018] In one embodiment, 0.5 to 3.5 parts by mass of the catalyst composition is used per 100 parts by mass of the homopolymer.

[0019] In one embodiment, the temperature applied in the heating step is 265 to 325°C.

[0020] In one embodiment, the heating step is carried out under an inert gas stream or under reduced pressure.

[0021] In a further embodiment, the heating step is carried out under reduced pressure, and the vacuum level under reduced pressure is 0.5 to 30 kPa.

[0022] In one embodiment, the homopolymer is contained within a textile product.

[0023] In a further embodiment, the textile product is cut to a size having a maximum side of 20 mm or less.

[0024] According to the present invention, homopolymers can be efficiently decomposed. The present invention also reduces the possibility of side reactions occurring during decomposition, and allows for the recovery of monomer components in good yield.

[0025] The following describes exemplary embodiments of this disclosure. However, this disclosure is not limited in any way to the embodiments described below. In this specification, numerical ranges indicated using "~" indicate a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. Also, unless otherwise explicitly stated, the units of the numbers before and after "~" are the same. Furthermore, the upper and lower limits described individually can be combined in any way.

[0026] (1) Catalyst composition First, the catalyst composition of the present invention will be described.

[0027] The catalyst composition of the present invention can be used to decompose homopolymers as described later. The catalyst composition of the present invention contains titanium dioxide and a metal oxide other than titanium dioxide. According to this catalyst composition, homopolymers can be decomposed at lower concentrations and temperatures than without a catalyst or with other catalysts. Furthermore, the catalyst composition is less prone to side reactions and can achieve a high monomer recovery rate.

[0028] (Titanium Oxide) The titanium oxide constituting the catalyst composition of the present invention is titanium(IV)(TiO) ２ Titanium dioxide can be commercially available for use in applications such as paints for houses and automobiles, inks for food packaging materials, pigments for synthetic resins in refrigerators and washing machines, colorants for pharmaceuticals such as capsules and tablets, colorants for foods such as chocolate and gum, matting agents for synthetic fibers such as nylon and polyester, and colorants for cosmetics.

[0029] In the present invention, titanium dioxide exhibits higher catalytic activity and greater dispersibility during homopolymer decomposition when it contains fewer impurities, such as other metals or other chemical substances like sulfuric acid used in the manufacturing process. Since a lower impurity content results in a higher resistivity, the lower limit of the resistivity of titanium dioxide is preferably 2,000 Ω·cm or higher, and more preferably 5,000 Ω·cm or higher. The resistivity can be further improved by increasing purity through purification, such as removing coarse particles using a centrifuge. However, considering the burden of purification, the upper limit of the resistivity of titanium dioxide is preferably 12,000 Ω·cm or lower, and more preferably 10,000 Ω·cm or lower.

[0030] Examples of usable crystal structures of titanium dioxide include anatase type (tetragonal), rutile type (tetragonal, see the figure), and brookite type (orthorhombic). In the present invention, anatase-type titanium dioxide is preferred because it has the highest activity as a catalyst.

[0031] Note that, in order to enhance the catalytic activity of titanium dioxide, it is preferable to use one having a larger specific surface area. The lower limit of the BET specific surface area of titanium dioxide in the present invention is preferably 5 m ２ / g or more, more preferably 10 m ２ / g or more. Further, reducing the particle size of titanium dioxide can further increase the specific surface area and improve the catalytic performance, but this requires nanoscale micronization. Therefore, considering the load during production, the upper limit of the BET specific surface area of titanium dioxide is preferably 400 m ２ / g or less, more preferably 300 m ２ / g or less.

[0032] The content of titanium dioxide contained in 100 parts by mass of the catalyst composition of the present invention is preferably 10 to 75 parts by mass, more preferably 20 to 70 parts by mass. When the content of titanium dioxide in the catalyst composition is within this range, excellent dispersibility in homopolymers and high decomposition reactivity can be obtained.

[0033] (Metal Oxide) The metal oxides other than titanium dioxide constituting the catalyst composition of the present invention are compounds in which metal and oxygen are bonded. These metal oxides, in combination with titanium dioxide, can exhibit high catalytic activity for the decomposition of homopolymers described later.

[0034] Examples of metal oxides include iron(II) oxide, magnetic iron oxide, iron(III) oxide, sodium oxide, lithium oxide, potassium oxide, calcium oxide, magnesium oxide, beryllium oxide, aluminum oxide, gallium oxide, indium oxide, thallium oxide, zinc oxide, nickel oxide, barium oxide, strontium oxide, copper(I) oxide, copper(II) oxide, copper peroxide, paramelaconite, copper(III) oxide, copper(IV) oxide, and combinations thereof.

[0035] Among the above metal oxides, it is preferable that the above metal oxide contains magnesium oxide, since it can exhibit high catalytic function when combined with titanium oxide.

[0036] Commercially available magnesium oxide may be used, for example, for applications such as refractory materials, various additives, fillers for resins, optical materials, electronic component applications, phosphor raw materials, various target material raw materials, raw materials for superconducting thin film substrates, and protective film raw materials for color plasma display panels.

[0037] Furthermore, magnesium oxide preferably has a large specific surface area because it has high catalytic activity. The lower limit of the BET specific surface area of magnesium oxide in the present invention is preferably 3 m ２ / g or more, more preferably 10 m ２ / g or more. Further, the upper limit of the BET specific surface area of magnesium oxide in the present invention is preferably 400 m ２ / g or less, more preferably 200 m ２ / g or less. When the BET specific surface area of magnesium oxide contained in the catalyst composition falls within such a range, excellent dispersibility in homopolymers can be provided.

[0038] The content of metal oxides other than titanium oxide contained in 100 parts by mass of the catalyst composition of the present invention is preferably 25 to 90 parts by mass, more preferably 35 to 80 parts by mass. When the content of the metal oxide contained in the catalyst composition falls within such a range, excellent dispersibility in homopolymers and high decomposition reactivity can be obtained.

[0039] The catalyst composition of the present invention may further contain other components. Examples of other components include dispersants. Dispersants can improve, for example, the mixing efficiency into polymers.

[0040] Examples of dispersants include polymeric dispersants such as polycarboxylates, naphthalene sulfonic acid formalin condensate, polyethylene glycol, partially alkyl polycarboxylates, polyethers, and polyalkylene polyamines; surfactant-type dispersants such as alkyl sulfonic acids, quaternary ammonium compounds, higher alcohol alkylene oxides, polyhydric alcohol esters, alkyl polyamines, and polyglycerins; and inorganic dispersants such as sodium tripolyphosphate, as well as combinations thereof.

[0041] Alternatively, the catalyst composition may be used as a catalyst composition masterbatch that has been previously kneaded into the above polypolymer at a high concentration. The concentration of the catalyst composition in the homopolymer is preferably 5 to 150 parts by mass per 100 parts by mass of homopolymer.

[0042] The content of other components in 100 parts by mass of the catalyst composition of the present invention is not particularly limited and can be appropriately selected by those skilled in the art.

[0043] The catalyst composition of the present invention can be used, for example, to decompose homopolymers as described later.

[0044] (2) Method for Decomposing Homopolymers Next, the method for decomposing homopolymers according to the present invention will be described.

[0045] In the method of the present invention, the homopolymer is heated in the presence of the catalyst composition.

[0046] According to the method of the present invention, homopolymers can be decomposed at lower concentrations and temperatures than without a catalyst or with other catalysts. Furthermore, such a method for decomposing homopolymers is less prone to side reactions and can achieve a high monomer recovery rate.

[0047] (Homopolymer) In the present invention, homopolymer refers to a polymer compound composed of repeating units (monomers) of the same type, and examples include polyethylene, polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, polytetrafluoroethylene, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polycaprolactone, polylactic acid, polyamide 6, polyamide 12, and polydimethylsiloxane.

[0048] Furthermore, the homopolymer may, for example, have a fibrous form and may be part of a product (textile product) that contains it as a base material.

[0049] The homopolymer described above may also take the form of a polymer composition that coexists with any other suitable components (additives) or fillers, as needed.

[0050] Additives that may constitute a polymer composition include antioxidants, heat stabilizers, light stabilizers, UV absorbers, antiblocking agents, antimicrobial agents, compatibilizers, plasticizers, tackifiers, processing aids, lubricants, coupling agents, flame retardants, oxygen scavengers, foaming agents, colorants, and the like. These additives can be added at any time during the homopolymer manufacturing process, for example, in the form of liquids, powders, pellets, granules, or masterbatches. The polymer composition may contain at least one additive, and its content can be appropriately selected by those skilled in the art.

[0051] The homopolymer in the present invention may be composed of cyclic monomers. That is, the homopolymer may be obtained by polymerizing cyclic monomers.

[0052] Cyclic monomers include monomers such as cyclic lactones, cyclic lactams, cyclic ethers, and lactides. Examples of cyclic lactones include caprolactone, valerolactone, nonalactone, butyrolactone, and propiolactone. Examples of cyclic lactams include propiolactam, butyrolactam, valerolactam, caprolactam, laurolactam, enantractam, and undecanelactam. Examples of cyclic ethers include ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, dioxane, and dioxanone. Lactides are cyclic compounds having two ester bonds within a molecule formed by the dehydration condensation of the hydroxyl and carboxyl groups of two hydroxy acid molecules. Examples include glycolides, 3,6-dimethyl-1,4-dioxane-2,5-dione (derived from 2-hydroxypropionic acid (lactic acid)), and 1,6-dioxacyclodecane-2,7-dione (derived from 4-hydroxybutanoic acid). Among these, so-called lactides derived from lactic acid can be optically active substances, and include L-lactide, D-lactide, and meso-lactide.

[0053] By polymerizing these, homopolymers such as polycaprolactone, polyvalerolactone, polynonalactone, polybutyrolactone, polypropiolactone, polypropiolacrum, polybutyrolactam, polyvalerolactum, polycaprolactam, polylaurolactam, polyenanthractam, polyundecanelactum, polyethylene oxide, polypropylene oxide, polybutylene glycol, polyoxytetramethylene glycol, polydioxane, polydioxanone, polylactic acid, and polyhydroxybutanoic acid can be obtained. Homopolymers polymerized from cyclic monomers are less prone to side reactions in the decomposition reaction of the present invention and are easy to recover monomers from, making them suitable targets for homopolymers in which the catalyst composition of the present invention is used.

[0054] (Polylactic acid) A preferred homopolymer in the present invention is polylactic acid.

[0055] As for polylactic acid, polylactic acid with a high L-lactic acid content is preferably used because it has a high melting point. The L-lactic acid content of the polylactic acid is preferably 96% or more, more preferably 98% or more, and even more preferably 98.6% or more. In the present invention, the polylactic acid constituting the homopolymer may consist of only one type, or it may be composed of a combination of two or more types.

[0056] The weight-average molecular weight of polylactic acid is not particularly limited. In this invention, the polylactic acid to be decomposed may have various weight-average molecular weights depending on the molding method, shape, and application of the molded product.

[0057] The homopolymer to be decomposed in this invention may have any form. For example, it may be spherical or strand-cut pellets, or it may be a molded product formed using known molding methods (e.g., injection molding, extrusion molding, blow molding, injection blow molding, shape extrusion molding, inflation molding, press molding, melt spinning, solution spinning, vacuum forming, vacuum pressure forming, hot plate forming, etc.). The above-mentioned molded product includes, for example, housings, containers, bags, tubes, cups, bottles, trays, long and short fibers, fabric products, etc., and is not particularly limited in terms of its shape, size, thickness, etc.

[0058] Here, textile products containing the above homopolymer are generally preferred because they have a larger surface area per unit mass than other molded articles, making them more readily in contact with the catalyst composition of the present invention. Such textile products may be compounded with other fibers such as natural fibers like cotton, linen, wool, silk, and Tencel; regenerated fibers like rayon, cupro, and polynosic; and semi-synthetic fibers like acetate, triacetate, and Promix, through weaving, knitting, blending, or twisting.

[0059] Furthermore, the homopolymer used in the decomposition method of the present invention is preferably cut to a maximum length of 20 mm or less in order to increase the surface area through subdivision and accelerate the decomposition reaction of the homopolymer.

[0060] (Heating Process) The homopolymer of the present invention is heated, for example, while it is charged in a reaction apparatus. The reaction apparatus is not particularly limited, but examples include batch or continuous tank type reactors, reactors, mill rolls, mixers, single-screw or twin-screw extruders, etc. The reaction apparatus is preferably equipped with heating means such as an electric heater or a heat transfer medium.

[0061] The amount of catalyst composition that can be used in the heating step is preferably 0.5 to 3.5 parts by mass, more preferably 0.5 to 2.0 parts by mass, per 100 parts by mass of the homopolymer. If the amount of catalyst composition is less than 0.5 parts by mass, the catalytic promoting effect in the decomposition reaction decreases, which may result in a lower yield of reaction products (e.g., monomers) obtained through the decomposition reaction. In particular, the reaction promoting effect may decrease in the optimal temperature range where the catalytic effect can be expected. If the amount of catalyst composition exceeds 3.5 parts by mass, the efficiency of the decomposition reaction plateaus, not only resulting in wasted catalyst, but also making secondary reactions and side reactions of decomposition more likely due to overactivation of the decomposition reaction by the catalyst, which may result in a lower yield of reaction products (e.g., monomers) obtained through decomposition.

[0062] The temperature applied in the heating step is preferably 265 to 325°C, more preferably 270 to 300°C. If the temperature applied in the heating step is below 265°C, the yield of reaction products (e.g., monomers) obtained through the decomposition reaction may be low. If the temperature applied in the heating step is above 325°C, the yield of reaction products (e.g., monomers) obtained through the decomposition reaction may also be low. This is because, regardless of the presence or absence of the catalyst composition, this temperature range is where thermal decomposition of the homopolymer occurs, leading to side reactions and making it easier for undesirable by-products to be generated.

[0063] In addition, the heating step of the present invention may be performed by heating the homopolymer and the catalyst composition to the above temperature in a state where they are already combined, or by adding the catalyst composition to the reaction apparatus after the homopolymer has been heated to the above temperature in the reaction apparatus.

[0064] Furthermore, the reaction apparatus may be operated at atmospheric pressure, but it may also be carried out under an inert gas atmosphere such as nitrogen, or under an inert gas flow or under reduced pressure. Since the reaction products obtained through the decomposition reaction (e.g., monomers) may undergo secondary chemical reactions and degradation if continuously heated, it is preferable to quickly discharge them from the system and recover them. In other words, it is preferable to carry out the reaction under reduced pressure.

[0065] In the case of the above-mentioned reduced pressure, the vacuum level inside the reaction apparatus is preferably 0.5 to 30 kPa. If it exceeds 30 kPa, the efficiency of discharging the reaction products obtained through the decomposition reaction to the outside of the system is poor, and if it is less than 0.5 kPa, the vacuum level is too high, and homopolymers may overflow from the vacuum exhaust port and be discharged to the outside.

[0066] The time required for the heating step is not particularly limited, but is preferably 2 to 60 minutes, and more preferably 5 to 30 minutes. If the heating step is performed for less than 2 minutes, the catalytic effect may not be sufficiently expressed, and the yield of the decomposition reaction may decrease. If the heating step is performed for more than 60 minutes, the decomposition reaction may be over-activated by the catalyst, making secondary reactions and side reactions of decomposition more likely, and the yield of the reaction product (e.g., monomer) obtained through decomposition may decrease.

[0067] After the heating process described above, reaction products are generated in the reaction system from the decomposition of the homopolymer. These reaction products are, for example, the monomers that make up the homopolymer (e.g., cyclic monomers).

[0068] The monomers produced by the decomposition are separated and purified using means known to those skilled in the art and recovered. The recovered monomers can also be reused as materials for forming homopolymers again.

[0069] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples.

[0070] In this example and comparative example １ H-NMR and thermogravimetric measurements were performed using the following methods.

[0071] (１ (H-NMR measurement) Analysis of decomposition reaction products was performed using a Bruker AV-600 under the following analytical conditions. １ The measurement was performed by 1H-NMR. Deuterated chloroform was used as the solvent for the NMR measurement, and tetramethylsilane was used as the internal standard. (1) Measurement temperature: 23°C (2) Sample concentration: 0.01 g / 0.6 mL (3) Number of accumulations: 8 (4) Relaxation time: 2 seconds (5) Solvent: Deuterated chloroform (6) Chemical shift standard: Hydrogen atom signal of the methyl group of tetramethylsilane in the internal standard sample (0.0 ppm)

[0072] (Thermogravimetric Analysis) The decomposition reaction yield under a nitrogen atmosphere was determined by thermogravimetric analysis under a nitrogen atmosphere using a TG-DTA8122 instrument manufactured by Rigaku Corporation. The temperature was raised from room temperature to a predetermined temperature at a rate of 10°C per minute, and then held for 10 minutes.

[0073] (Example 1) Using polylactic acid (Luminy, L130, manufactured by Total Corbion) as a homopolymer, 100 parts by mass of a fabric woven from long fibers produced by melt spinning was placed in a reaction apparatus consisting of a three-necked flask equipped with a stirring mechanism. The apparatus was heated to 280°C in the presence of a catalyst composition containing 0.3 parts by mass of titanium dioxide (TA301, manufactured by Fuji Titanium Industries Co., Ltd.) and 0.5 parts by mass of magnesium oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (the titanium dioxide content in 100 parts by mass of the catalyst composition was 37.5 parts by mass). After 5 minutes, the fabric began to melt, and after 10 minutes it was completely melted, so the reaction apparatus was stirred. The pressure inside the reaction apparatus was reduced to 4 kPa by a vacuum pump via a cooling trap. A few minutes after the start of stirring, decomposition products were distilled off from the apparatus and trapped in the cooling trap, and after being held for 10 minutes, distillation from the system ceased.

[0074] The decomposition recovery rate calculated from the residue in the reactor was 90.9% by mass, indicating a high decomposition reaction yield. Furthermore, the product recovered in the cooling trap １Analysis was performed using 1H-NMR measurements. Peaks of lactic acid and lactic acid polymers were observed around 1.59 ppm, and peaks originating from L,L-lactide or D,D-lactide were observed around 1.68 ppm. Additionally, a peak originating from D,L-lactide was observed around 1.72 ppm. １ Analysis of the relative abundances of each component based on the integral ratio of each peak obtained from the 1H-NMR spectrum revealed that L,L-lactide or D,D-lactide accounted for 82.2% by mass, D,L-lactide for 11.9% by mass, and lactic acid or lactic acid polymer for 5.9% by mass. The crude lactide content (L,L-lactide, D,D-lactide, D,L-lactide) was 94.1% by mass, indicating a high monomer recovery rate.

[0075] (Example 2) Using polylactic acid (Luminy, L130, manufactured from a homopolymer) as a raw material, 100 parts by mass of a fabric woven from long fibers produced by melt spinning was placed in a reaction apparatus consisting of a three-necked flask equipped with a stirring mechanism. The apparatus was heated to 280°C in the presence of a catalyst composition containing 0.3 parts by mass of titanium dioxide (TA301, manufactured by Fuji Titanium Industries, Ltd.) and 2.7 parts by mass of magnesium oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (the titanium dioxide content in 100 parts by mass of the catalyst composition was 10 parts by mass). After 5 minutes, the fabric began to melt, and after 10 minutes it was completely melted, so the reaction apparatus was stirred. The pressure inside the reaction apparatus was reduced to 4 kPa by a vacuum pump via a cooling trap. A few minutes after the start of stirring, decomposition products were distilled off from the apparatus and trapped in the cooling trap, and after being held for 10 minutes, distillation from the system ceased.

[0076] The decomposition recovery rate calculated from the residue in the reactor was 92.4%, indicating a high decomposition reaction yield. Furthermore, the product recovered in the cooling trap １ Analysis was performed using 1H-NMR measurements. A peak originating from L,L-lactide or D,D-lactide was observed around 1.68 ppm. A peak originating from D,L-lactide was also observed around 1.72 ppm. No peaks attributable to lactic acid or lactic acid polymers were observed. １Analysis of the relative abundances of each peak from the 1H-NMR spectrum revealed that L,L-lactide or D,D-lactide accounted for 88.6% by mass, and D,L-lactide accounted for 11.4% by mass. The crude lactide content (L,L-lactide, D,D-lactide, and D,L-lactide) was 100% by mass, indicating a very high monomer recovery rate.

[0077] (Examples 3-14) Catalyst compositions (catalyst compositions 1-11) of Examples 3-14 were prepared by mixing titanium oxide (TA301 manufactured by Fuji Titanium Industries Co., Ltd.) and metal oxides in the mass ratios shown in Table 1.

[0078] Next, the mixture was obtained in pellet form by kneading the homopolymer polylactic acid (Luminy, L130, manufactured by Total Corbion) and the catalyst composition in a twin-screw extruder at a cylinder temperature of 180 to 200°C.

[0079] Subsequently, the pellets were subjected to thermogravimetric analysis to determine the decomposition and recovery rate. The results are shown in Table 1.

[0080] In addition, the thermogravimetric analysis involved heating to 280°C. By heating polylactic acid (Luminy, L130, manufactured by Total Corbion), a homopolymer, to 280°C in the presence of the above catalyst composition, a high decomposition and recovery rate was obtained.

[0081]

[0082] As shown in Table 1, in all of the polylactic acid samples used in Examples 3 to 14, monomers were recovered with excellent decomposition and recovery rates.

[0083] (Comparative Examples 1-9) Catalyst compositions 1-9 (catalyst compositions 13-21) were prepared by mixing titanium oxide (TA301 manufactured by Fuji Titanium Industries Co., Ltd.) and metal oxides in the mass ratios shown in Table 2.

[0084] Next, the homopolymer polylactic acid (Luminy, L130, manufactured by Total Corbion) and the catalyst composition were kneaded in a twin-screw extruder at a cylinder temperature of 180 to 200°C to obtain a mixture in pellet form.

[0085] Subsequently, the pellets were subjected to thermogravimetric analysis to determine the decomposition and recovery rate. The results are shown in Table 2.

[0086] For thermogravimetric analysis, the sample was heated to 280°C.

[0087]

[0088] As shown in Table 2, Comparative Examples 1 to 9 show that when the amount of catalyst composition deviates from 0.5 to 3.5 parts by mass per 100 parts by mass of homopolymer, and when the titanium dioxide content in 100 parts by mass of catalyst composition deviates from 10 to 75 parts by mass, the decomposition recovery rate is less than 80% by mass, which is a low value.

[0089] (Examples 15-19 and Comparative Examples 10-12) Catalyst compositions were prepared by mixing 25 parts by mass of titanium oxide (TA301, manufactured by Fuji Titanium Industries Co., Ltd.) with 75 parts by mass of magnesium oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), which is a metal oxide.

[0090] Next, the homopolymer polylactic acid (Luminy, L130, manufactured by Total Corbion) and the catalyst composition were kneaded in a twin-screw extruder at a cylinder temperature of 180 to 200°C to obtain a mixture in pellet form.

[0091] Subsequently, the pellets were subjected to thermogravimetric analysis to determine the decomposition and recovery rate. The heating temperatures used for the thermogravimetric analysis were 230 / 250 / 260 / 270 / 280 / 290 / 300 / 320 / 350°C. The results are shown in Table 3.

[0092]

[0093] As shown in Table 3, polylactic acid could be decomposed with a high decomposition recovery rate of over 80% by mass at heating temperatures of 270 / 280 / 290 / 300 / 320°C, whereas the decomposition recovery rate was low at heating temperatures of 230 / 250 / 350°C.

[0094] According to the present invention, various homopolymers obtained as waste generated during the manufacturing process or as waste after consumption can be efficiently decomposed. This makes it useful in a wide range of fields, including the disposal and recycling of industrial or household waste, as well as in the apparel and resin molding industries.

Claims

1. A catalyst composition for decomposing a homopolymer into monomers, comprising at least titanium dioxide and a metal oxide other than titanium dioxide, wherein the homopolymer is polylactic acid, the metal oxide contains magnesium oxide or calcium oxide, and the content of titanium dioxide in 100 parts by mass of the catalyst composition is 10 to 75 parts by mass.

2. The catalyst composition according to claim 1, wherein the resistivity of the titanium oxide is 2,000 Ω·cm or more and 12,000 Ω·cm or less.

3. The titanium dioxide is anatase-type titanium dioxide, and 5m ２ / g or more 400m ２ The catalyst composition according to claim 1, having a BET specific surface area of ​​less than or equal to / g.

4. The catalyst composition according to claim 1, wherein the metal oxide contains magnesium oxide.

5. The magnesium oxide is 3 m ２ / g or more 400m ２ The catalyst composition according to claim 4, having a BET specific surface area of ​​less than or equal to / g.

6. A method for decomposing a homopolymer into monomers, comprising the step of heating the homopolymer in the presence of a catalyst composition according to any one of claims 1 to 5, wherein the homopolymer is polylactic acid.

7. The method according to claim 6, wherein 0.5 to 3.5 parts by mass of the catalyst composition is used per 100 parts by mass of the homopolymer.

8. The method according to claim 6, wherein the temperature applied in the heating step is 265 to 325°C.

9. The method according to claim 6, wherein the heating step is carried out under an inert gas stream or under reduced pressure.

10. The method according to claim 9, wherein the heating step is performed under reduced pressure, and the degree of vacuum under reduced pressure is 0.5 to 30 kPa.

11. The method according to claim 6, wherein the homopolymer is contained in a textile product.

12. The method according to claim 11, wherein the textile product is cut to a size having a maximum side of 20 mm or less.

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