Homopolymer and method for decomposing homopolymer from homopolymer composition containing shielding material

Abstract

Disclosed is a method for decomposing a homopolymer from a homopolymer composition containing the homopolymer and a shielding material. This method comprises a step for heating the homopolymer composition in the presence of a metal oxide. The homopolymer is derived from a cyclic monomer. According to the present invention, it is possible to efficiently decompose a homopolymer and reduce a possibility of side reactions occurring during the decomposition. Further, a cyclic monomer component can be recovered at a favorable yield.

Description

Method for decomposing homopolymers from homopolymer compositions containing homopolymers and shielding materials.

[0001] The present invention relates to a method for decomposing a homopolymer from a homopolymer composition comprising a homopolymer and a shielding material.

[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 biodegradable resin composition comprising a biodegradable resin and finely powdered titanium dioxide having photocatalytic function. Examples of biodegradable resins include polylactic acid or copolymers of lactic acid and other hydroxycarboxylic acids. According to this technology, a biodegradable resin composition exhibiting excellent degradability in a natural environment can be obtained by combining the decomposition of the biodegradable resin by microorganisms with the decomposition by the photocatalytic action of finely powdered titanium dioxide.

[0004] Patent Document 2 discloses a resin laminate formed by laminating a surface protective layer onto a resin molded body made of a thermoplastic resin. This surface protective layer is separable from the resin molded body, and the resin molded body contains a metal oxide having photocatalytic activity. Examples of resin molded bodies include polyolefins and polystyrene, and examples of metal oxides having photocatalytic activity include titanium oxide. When disposing of or recycling this resin laminate, the surface protective layer can be separated and exposed to sunlight or other light sources to promote the natural decomposition of the resin molded body through photocatalytic activity.

[0005] However, both the biodegradable resin composition described in Patent Document 1 and the resin laminate described in Patent Document 2 are intended to decompose under natural environmental conditions, and are specifically targeted at polymers used in disposable packaging materials and tableware. Therefore, decomposition under natural conditions takes a long time, and safety measures must be taken to prevent the polymer from being dispersed during the decomposition period. Furthermore, such decomposition under natural conditions is not considered efficient.

[0006] Japanese Patent Publication No. 2004-99739, Japanese Patent No. 4715303

[0007] The present invention aims to solve the above-mentioned problems, and its objective is to provide a method for decomposing homopolymers from a homopolymer composition containing a homopolymer and a shielding material, which can safely and efficiently decompose homopolymers.

[0008] The present invention relates to a method for decomposing a homopolymer from a homopolymer composition comprising a homopolymer and a shielding material, the method comprising the step of heating the homopolymer composition in the presence of a metal oxide, wherein the homopolymer is a polymer derived from a cyclic monomer.

[0009] In one embodiment, the shielding material is titanium oxide.

[0010] In one embodiment, the metal oxide is at least one compound selected from the group consisting of titanium oxide and magnesium oxide.

[0011] In one embodiment, the amount of the metal oxide is calculated based on the amount of the shielding material contained in the polymer composition.

[0012] In further embodiments, the amount of the shielding material contained in the polymer composition is determined by at least one method selected from the group consisting of graphite furnace atomic absorption spectrometry, colorimetric method, aluminum reduced iron(III) titration, atomic absorption spectrometry, X-ray diffraction (XRD), energy dispersive X-ray analysis, X-ray fluorescence analysis (XRF), inductively coupled radio frequency plasma emission spectrometry (ICP-AES), and inductively coupled radio frequency plasma mass spectrometry (ICP-MS).

[0013] In a further embodiment, the amount of the shielding material included in the polymer composition is calculated from the amount of ash obtained by thermal decomposition of the polymer composition.

[0014] In further embodiments, the amount of the metal oxide is calculated based on the following formula (I): Y = Z - X (I) where X is the amount of the shielding material relative to the total mass of the homopolymer composition (mass%), Y is the amount of the metal oxide relative to the total mass of the homopolymer composition and the metal oxide (mass%), and Z is 0.5 to 3.5% by mass.

[0015] In one embodiment, the temperature applied in the heating step is 265 to 325°C.

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

[0017] In one embodiment, the heating step is carried out under a nitrogen stream or under reduced pressure.

[0018] 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.

[0019] In one embodiment, the homopolymer composition is cut into pieces with a maximum side length of 20 mm or less.

[0020] In one embodiment, the homopolymer composition is in the form of a textile product.

[0021] 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.

[0022] 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.

[0023] The method of the present invention will be described below.

[0024] In the method of the present invention, a homopolymer composition comprising a homopolymer and a shielding material is heated in the presence of a metal oxide.

[0025] 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.

[0026] (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.

[0027] 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.

[0028] The homopolymer in the present invention may be composed of cyclic monomers. That is, the homopolymer may be obtained by polymerizing cyclic monomers.

[0029] 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.

[0030] 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.

[0031] (Polylactic acid) A preferred homopolymer in the present invention is polylactic acid.

[0032] As polylactic acid, polylactic acid having a high L-lactic acid content is preferably used because of its high melting point. The L-lactic acid content of the polylactic acid is preferably 96% or more, more preferably 98% or more, and still more preferably 98.6% or more. In the present invention, the polylactic acid constituting the homopolymer may be composed of only one type, or may be composed of a combination of two or more types.

[0033] The weight average molecular weight of polylactic acid is not particularly limited. In the present invention, the polylactic acid to be decomposed may have various weight average molecular weights depending on the molding processing method, shape and application of the molded article.

[0034] The above homopolymer composition may also contain any appropriate other components (additives), fillers and the like as necessary.

[0035] Examples of additives that can constitute the polymer composition include antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, antiblocking agents, antibacterial agents, compatibilizers, plasticizers, tackifiers, processing aids, lubricants, coupling agents, flame retardants, oxygen scavengers, foaming agents, coloring agents, and the like. The above additives can be added at any timing in the production process of the homopolymer, for example, in the form of liquid, powder, pellets, granules, or masterbatch. At least one type of additive that can constitute the polymer composition is used, and the content thereof can be appropriately selected by those skilled in the art.

[0036] The homopolymer composition of the present invention may have any form. For example, it may be spherical or strand-cut pellets, or a molded article molded by a known molding method (e.g., injection molding, extrusion molding, blow molding, injection blow molding, profile extrusion molding, inflation molding, press molding, melt spinning, solution spinning, vacuum molding, vacuum pressure forming, hot plate molding, etc.). The above molded articles include, for example, housings, containers, bags, tubes, cups, bottles, trays, long / short fibers, fabric products, and the like, and there are no particular limitations on the shape, size, thickness, and the like thereof.

[0037] Here, fiber products composed of the above homopolymer composition generally have a larger surface area per mass than other molded articles, which is preferable because they are easily brought into contact with the metal oxide described later. Such fiber products may be combined with other fibers such as natural fibers including cotton, hemp, wool, silk and tencel; regenerated fibers including rayon, cupra and polynosic; and semi-synthetic fibers including acetate, triacetate and promix by means of mixed weaving, mixed knitting, blended spinning, combined twisting or the like.

[0038] Furthermore, the homopolymer composition that can be used in the present invention preferably has a form cut such that the maximum side is 20 mm or less in order to increase the surface area by subdivision and accelerate the decomposition reaction of the homopolymer.

[0039] In the present invention, the content of the homopolymer contained in the homopolymer composition is not particularly limited. For example, based on the total mass of the polymer composition, it is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 99% by mass. When the content of the homopolymer contained in the polymer composition is less than 50% by mass, the decomposition of the homopolymer is inhibited by the decomposition of components other than the homopolymer, the target decomposition reactivity decreases, and the recovery rate of decomposition products (e.g., monomers) may decrease.

[0040] (Shielding material) The shielding material contained in the polymer composition is a material that, when kneaded into the homopolymer, does not absorb any of visible light, infrared light, and ultraviolet light, but reflects and / or scatters them. For example, it is preferable that the material has no specific absorption in the visible region, has high reflectivity, and has a large refractive index and is opaque.

[0041] Examples of shielding materials include inorganic compounds such as titanium oxide (titanium white), zinc white (zinc oxide), lithopone, lead white, and combinations thereof. Titanium oxide is preferable as a shielding material because it has a considerably high refractive index, thus has high hiding power, is thermally and chemically stable, and has high safety.

[0042] In the present invention, titanium oxide used as a shielding material refers to titanium (IV) oxide (TiO ２ ).

[0043] Possible crystalline structures of titanium dioxide include anatase type (tetragonal), rutile type (tetragonal, see figure), and brookite type (orthorhombic). In this invention, anatase type titanium dioxide is preferred because it exhibits the highest catalytic activity.

[0044] Furthermore, in order to enhance the catalytic activity of titanium dioxide, it is preferable to use a type with a large specific surface area. In this invention, the lower limit of the BET specific surface area of ​​titanium dioxide is preferably 5 m². ２ / g or more, more preferably 10m ２ It is 1 / g or more. Furthermore, by making the particle size of titanium dioxide even smaller, the specific surface area can be increased and the catalytic performance can be improved, but since nanoscale micronization is required, considering the burden during manufacturing, the stability during mixing with homopolymers, and the use of homopolymers, the upper limit of the BET specific surface area of ​​titanium dioxide is preferably 300 m². ２ / g or less, more preferably 200m ２ It is less than / g.

[0045] Regarding the content of the shielding material, we will explain the case where the shielding material contained in the homopolymer composition is titanium dioxide.

[0046] When the shielding material contained in the homopolymer composition is titanium dioxide, the titanium dioxide can function as a catalyst in the decomposition of the homopolymer contained in the composition, together with the metal oxides described later. For this reason, in the present invention, it is preferable that the amount of shielding material (titanium dioxide) contained in the homopolymer composition is measured.

[0047] The amount of shielding material (titanium dioxide) contained in the homopolymer composition can be measured using, for example, at least one method selected from graphite furnace atomic absorption spectrometry, colorimetric method, aluminum reduced iron(III) titration, atomic absorption spectrometry, X-ray diffraction (XRD), energy dispersive X-ray analysis, X-ray fluorescence analysis (XRF), inductively coupled radio frequency plasma emission spectrometry (ICP-AES), inductively coupled radio frequency plasma mass spectrometry (ICP-MS), and whiteness measurement. These methods are well known as qualitative and quantitative methods for titanium dioxide.

[0048] Alternatively, the amount of shielding material (titanium dioxide) included in the homopolymer composition may be calculated from the amount of ash obtained by thermal decomposition of the polymer composition. Although it is an approximation, the amount of ash can be used directly as the amount of titanium dioxide included in the homopolymer composition.

[0049] (Metal Oxides) The metal oxides in this invention are compounds in which a metal and oxygen are bonded. These metal oxides, in combination with the shielding material contained in the polymer composition, have catalytic activity and can promote the decomposition of homopolymers contained in the polymer composition.

[0050] 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, titanium oxide as a catalyst, strontium oxide, copper(I) oxide, copper(II) oxide, copper peroxide, paramelaconite, copper(III) oxide, and copper(IV) oxide, as well as combinations thereof.

[0051] Of the above metal oxides, it is preferable that the metal oxide contains titanium oxide and / or magnesium oxide as a catalyst, in that it can exhibit high catalytic function when combined with the above shielding material.

[0052] The titanium dioxide used as a catalyst here can be one that is commercially available for 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.

[0053] For titanium oxide as the catalyst in question, a lower content of impurities composed of other metals and other chemical substances such as sulfuric acid used in the production process results in higher catalytic activity and also higher dispersibility during homopolymer decomposition. Since a lower impurity content leads to a larger specific resistance value, the lower limit of the specific resistance value is preferably 2,000 Ω·cm or more, more preferably 5,000 Ω·cm or more. Although the specific resistance value can be further increased by increasing the purity through purification such as removal of coarse particles by a centrifugal separator, in consideration of the purification load and other factors, the upper limit of the specific resistance value is preferably 12,000 Ω·cm or less, more preferably 10,000 Ω·cm or less.

[0054] Furthermore, regarding titanium oxide used as a catalyst, the crystal structures of titanium oxide include anatase type (tetragonal), rutile type (tetragonal, see the figure), and brookite type (orthorhombic). Since the anatase type has the highest activity as a catalyst, it is preferable to use the anatase type. Since a larger specific surface area leads to higher catalytic activity, for titanium oxide as a catalyst, the lower limit of the BET specific surface area is preferably 5 m ２ / g or more, more preferably 10 m ２ / g or more. Further, reducing the particle diameter of titanium oxide to further increase the specific surface area will also improve the catalytic performance; on the other hand, it requires nanoscale micronization, and in consideration of the load incurred during production, for titanium oxide as a catalyst, the upper limit of the BET specific surface area is preferably 400 m ２ / g or less, more preferably 300 m ２ / g or less.

[0055] As magnesium oxide, for example, commercially available products for applications such as refractories, 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 can be used.

[0056] In addition, magnesium oxide preferably has a large specific surface area because it provides 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 m２ It is 1 / g or more. Furthermore, the upper limit of the BET specific surface area of ​​magnesium oxide in this invention is preferably 400 m². ２ / g or less, more preferably 200m ２ The BET specific surface area of ​​magnesium oxide is within this range, which allows for excellent dispersibility in homopolymers.

[0057] The amount of metal oxide blended in the present invention can preferably be calculated based on the following formula (I): Y = Z - X (I) where X is the amount of shielding material blended relative to the total mass of the homopolymer composition (mass%), Y is the amount of metal oxide relative to the total mass of the homopolymer composition and the metal oxide (mass%), and Z is 0.5 to 3.5% by mass.

[0058] (Heating) The homopolymer composition of the present invention is heated, for example, while 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.

[0059] The temperature applied for heating is preferably 265 to 325°C, more preferably 270 to 300°C. If the temperature is below 265°C, the yield of reaction products (e.g., monomers) obtained through the decomposition reaction of the homopolymer may be low. If the temperature 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, thermal decomposition of the homopolymer in the composition occurs in this temperature range, leading to side reactions and the formation of undesirable by-products.

[0060] In addition, the heating step of the present invention may be performed by heating the homopolymer composition and the metal oxide to the above temperature in a state where they are pre-mixed, or by adding the metal oxide to the reaction apparatus after the homopolymer composition has been heated to the above temperature in the reaction apparatus.

[0061] Furthermore, in the heating step described above, 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 process under reduced pressure.

[0062] 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 falls below 0.5 kPa, the vacuum level is too high, and homopolymers may overflow from the vacuum exhaust port and be discharged to the outside.

[0063] 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.

[0064] 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, monomers (e.g., cyclic monomers) that make up the homopolymer.

[0065] 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.

[0066] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to these examples.

[0067] In this example and comparative example １ H-NMR and thermogravimetric measurements were performed using the following methods.

[0068] (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)

[0069] (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.

[0070] (Example 1) 100 parts by mass of polylactic acid (Luminy, L130, manufactured by Total Corbion) which is a homopolymer, and 0.3 parts by mass of titanium oxide (TA301, manufactured by Fuji Titanium Industries Co., Ltd.) as a shielding material were kneaded in a twin-screw extruder at a cylinder temperature of 180 to 200°C to obtain a mixture (homopolymer composition) containing polylactic acid and a shielding material in pellet form.

[0071] Next, these pellets were fed into an extruder set to a cylinder temperature of 220°C and melt-spun to produce long fibers. 100 parts by mass of fabric woven using these long fibers as the raw material were placed in a reaction apparatus consisting of a three-necked flask equipped with a stirring mechanism, and heated to 280°C in the presence of a catalyst composition containing 0.3 parts by mass of titanium oxide (TA301 manufactured by Fuji Titanium Industries Co., Ltd.) and 1.0 part by mass of magnesium oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (the titanium oxide content in 100 parts by mass of the catalyst composition is 23.1 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.

[0072] The pressure inside the reaction apparatus was reduced to 4 kPa using a vacuum pump via a cooling trap. A few minutes after stirring began, the decomposition products were distilled off from the apparatus and trapped in the cooling trap. After holding it for 10 minutes, distillation from the system ceased.

[0073] The decomposition recovery rate calculated from the residue in the reactor was 94.0% by mass, indicating a high decomposition reaction yield.

[0074] Furthermore, the products collected in the cooling trap １ Analysis was performed using H-NMR measurements.

[0075] 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. １ Analysis of the relative abundances of each peak from the 1H-NMR spectrum revealed that the content of L,L-lactide or D,D-lactide was 89.6% by mass, and the content of D,L-lactide was 10.4% 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.

[0076] (Example 2) 100 parts by mass of polylactic acid (Luminy, L130, manufactured by Total Corbion) which is a homopolymer, and 0.3 parts by mass of titanium oxide (TA301, manufactured by Fuji Titanium Industries Co., Ltd.) as a shielding material were kneaded in a twin-screw extruder at a cylinder temperature of 180 to 200°C to obtain a mixture (homopolymer composition) containing polylactic acid and a shielding material in pellet form.

[0077] Next, these pellets were fed into an extruder set to a cylinder temperature of 220°C and melt-spun to produce long fibers. 100 parts by mass of fabric woven using these long fibers as the raw material were placed in a reaction apparatus consisting of a three-necked flask equipped with a stirring mechanism, and heated to 280°C in the presence of a catalyst composition containing 0.1 parts by mass of titanium oxide (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 oxide content in 100 parts by mass of the catalyst composition was 16.7 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.

[0078] The pressure inside the reaction apparatus was reduced to 4 kPa by a vacuum pump via a cooling trap. A few minutes after stirring began, the decomposition products were distilled off from the apparatus and trapped in the cooling trap. After holding it for 10 minutes, distillation from the system ceased.

[0079] The decomposition recovery rate calculated from the residue in the reactor was 90.7% by mass, indicating a high decomposition reaction yield.

[0080] Furthermore, the products collected in the cooling trap １ Analysis was performed using H-NMR measurements.

[0081] 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 peak from the 1H-NMR spectrum revealed that the content of L,L-lactide or D,D-lactide was 82.3% by mass, the content of D,L-lactide was 12.0% by mass, and the content of lactic acid or lactic acid polymer was 5.7% by mass. The crude lactide content (L,L-lactide, D,D-lactide, and D,L-lactide) was 94.3% by mass, indicating a high monomer recovery rate.

[0082] (Example 3) A fabric sample was used, which was woven from long fibers made of polylactic acid (Luminy, L130, manufactured by Total Corbion), a homopolymer, with titanium dioxide as a shielding material. 25 g of the above sample was placed in a crucible and heated to 600°C according to the direct ashing method of JIS K 7250-1, and the ash content was measured. The measurement result showed an ash content of 1.0 mass%. This content was interpreted as the content of the shielding material, and based on the following formula (1): Y = Z - X (1) (where X is the content of the shielding material in the fabric sample (1.0 mass%), and Z is 3.5 mass%), the content of the metal oxide to be added to this reaction system (Y value) was calculated to be 2.5 mass%.

[0083] The fabric was cut using a cutting machine to pieces no larger than 2.0 mm square. Then, 100 parts by mass of these cut pieces, along with 0.6 parts by mass of titanium dioxide (TA301 manufactured by Fuji Titanium Industries Co., Ltd.) and 1.8 parts by mass of magnesium oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), were used to create a catalyst composition (the titanium dioxide content in 100 parts by mass of the catalyst composition is 2.5 parts by mass, corresponding to the Y value mentioned above). This composition was fed into a twin-screw extruder, which served as the reaction apparatus, and kneaded and extruded under conditions of a cylinder temperature of 280°C. Two vents in the extruder were connected to a vacuum pump via a cooling trap, and the pressure inside the extruder was reduced to 4 kPa. After the start of extrusion, decomposition products were distilled off from the apparatus and trapped in the cooling trap, while residual components were discharged from the extruder die.

[0084] The decomposition recovery rate, calculated from the mass of residue discharged from the reaction apparatus die, was 93.5% by mass, indicating a high decomposition reaction yield.

[0085] Furthermore, the products collected in the cooling trap １ Analysis was performed using H-NMR measurements.

[0086] 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. Analysis of the relative abundances from the integral ratios of each peak in the 1H-NMR spectrum revealed that the content of L,L-lactide or D,D-lactide was 93.3% by mass, and the content of D,L-lactide was 6.7% 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.

[0087] According to the present invention, homopolymers contained in various homopolymer compositions including shielding materials, 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 fields.

Claims

1. A method for decomposing a homopolymer from a homopolymer composition comprising a homopolymer and a shielding material, comprising the step of heating the homopolymer composition in the presence of a metal oxide, wherein the homopolymer is polylactic acid, the shielding material is titanium oxide, and the metal oxide comprises magnesium oxide.

2. The method according to claim 1, wherein the amount of the metal oxide is calculated based on the amount of the shielding material contained in the homopolymer composition.

3. The method according to claim 2, wherein the amount of the shielding material contained in the homopolymer composition is an amount measured by at least one method selected from the group consisting of graphite furnace atomic absorption spectrometry, colorimetric method, aluminum reduced iron(III) titration, atomic absorption spectrometry, X-ray diffraction (XRD), energy dispersive X-ray analysis, X-ray fluorescence analysis (XRF), inductively coupled radio frequency plasma emission spectrometry (ICP-AES), and inductively coupled radio frequency plasma mass spectrometry (ICP-MS).

4. The method according to claim 2, wherein the amount of the shielding material contained in the homopolymer composition is calculated from the amount of ash obtained by thermal decomposition of the homopolymer composition.

5. The method according to claim 2, wherein the amount of the metal oxide is calculated based on the following formula (I): Y = Z - X (I) where X is the amount of the shielding material relative to the total mass of the homopolymer composition (mass%), Y is the amount of the metal oxide relative to the total mass of the homopolymer composition and the metal oxide (mass%), and Z is 0.5 to 3.5% by mass.

6. The method according to claim 1, wherein the temperature applied in the step of heating the homopolymer composition in the presence of a metal oxide is 265 to 325°C.

7. The method according to claim 1, wherein the step of heating the homopolymer composition in the presence of a metal oxide is carried out under a nitrogen stream or under reduced pressure.

8. The method according to claim 7, wherein the step of heating the homopolymer composition in the presence of a metal oxide is performed under reduced pressure, and the degree of vacuum under reduced pressure is 0.5 to 30 kPa.

9. The method according to claim 1, wherein the homopolymer composition is cut into pieces with a maximum side length of 20 mm or less.

10. The method according to claim 1, wherein the homopolymer composition is in the form of a textile product.