JP7585736B2 - Biodegradable resin composition, biodegradable molded body, method for disposing of polyamide resin, and composition - Google Patents

Description

The present invention relates to a biodegradable resin composition, a biodegradable molded body, a method for disposing of polyamide resin, and a composition. In particular, the present invention relates to a biodegradable polyamide resin and its decomposition products.

Polyamide resins have excellent physical and chemical properties. For this reason, they are widely used in a variety of applications, including electrical and electronic equipment components and packaging materials for food and medicine. For example, Patent Document 1 discloses a so-called high-barrier container in which a layer containing a transition metal salt such as organic cobalt is provided in a polyamide resin, and the polyamide resin is catalytically oxidized to absorb oxygen, thereby imparting oxygen absorption properties in addition to gas barrier properties.

JP 2002-321774 A

As described above, polyamide resins are used in various applications, but as part of efforts to protect the environment in recent years, it is required that polyamide resins be biodegradable. In particular, resin compositions containing general-purpose aliphatic polyamide resins such as polyamide 6 and polyamide 66 would be highly useful if they had biodegradability.
The present invention aims to solve such problems, and to provide a resin composition using a polyamide resin, which has excellent biodegradability, a biodegradable molded body, a method for disposing of the resin composition, a method for disposing of the molded body, and the composition.

In view of the above problems, the present inventors have conducted research and found that the above problems can be solved by blending a cobalt salt with a specific type of polyamide resin.
Specifically, the above problems were solved by the following means.
<1> A polyamide resin and a cobalt salt are included, and the polyamide resin contains 10 to 40 mol % of structural units derived from xylylenediamine, 5 to 50 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, 0 to 30 mol % of structural units derived from an aromatic dicarboxylic acid, 0 to 40 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, 0 to 40 mol % of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, and 0 to 80 mol % of structural units derived from an aromatic dicarboxylic acid. and 0 to 80 mol % of structural units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms, wherein the total of the structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, the structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, the structural units derived from a lactam having 4 to 10 carbon atoms, and the structural units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms is 10 to 80 mol %, and the total of the structural units does not exceed 100 mol %.
<2> The polyamide resin contains 10 to 40 mol% of structural units derived from xylylenediamine, 10 to 50 mol% of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, 0 to 40 mol% of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, and 10 to 40 mol% of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, and the total of the structural units does not exceed 100 mol%. The resin composition according to <1>.
<3> The polyamide resin contains 10 to 40 mol% of structural units derived from xylylenediamine, 10 to 50 mol% of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, and 10 to 40 mol% of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, and the total of the structural units does not exceed 100 mol%. The resin composition according to <1>.
<4> The resin composition according to <3>, wherein the molar ratio of the xylylenediamine-derived structural unit and the aliphatic diamine-derived structural unit having 2 to 20 carbon atoms in the polyamide resin is 20:80 to 80:20.
<5> The resin composition according to <3> or <4>, wherein the α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms is adipic acid, and the aliphatic diamine having 2 to 20 carbon atoms is 1,6-hexamethylenediamine.
<6> The polyamide resin contains 10 to 40 mol% of structural units derived from xylylenediamine, 10 to 40 mol% of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, and 20 to 80 mol% of structural units derived from a lactam having 4 to 10 carbon atoms, and the total of the structural units does not exceed 100 mol%. The resin composition according to <1>.
<7> The resin composition according to <6>, wherein the molar ratio of the xylylenediamine-derived structural unit and the lactam-derived structural unit having 4 to 10 carbon atoms in the polyamide resin is 20:80 to 70:30.
<8> The resin composition according to <6> or <7>, wherein the α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms is adipic acid, and the lactam having 4 to 10 carbon atoms is ε-caprolactam.
<9> The resin composition according to any one of <1> to <8>, wherein the mass ratio of the xylylenediamine structure in the polyamide resin is 5 to 60 mass%; here, the mass ratio of the xylylenediamine structure is a value calculated by [(mass of the xylylenediamine structure in the polyamide resin)/(total mass of the polyamide resin)]×100.
<10> The resin composition according to any one of <1> to <9>, wherein the cobalt salt includes a carboxylate of cobalt.
<11> The resin composition according to any one of <1> to <9>, wherein the cobalt salt includes cobalt stearate.
<12> The resin composition according to any one of <1> to <11>, wherein the content of the cobalt salt is 10 to 2000 ppm by mass based on cobalt atoms relative to 100 parts by mass of the xylylenediamine-based polyamide resin.
<13> The resin composition according to any one of <1> to <12>, wherein when the resin composition is stored for 28 days under an environment of 55°C and a relative humidity of 90%, a reduction rate of the number average molecular weight of the resin composition ((Mn of polyamide resin after storage/Mn of polyamide resin before storage) x 100) is 20% or less.
<14> The resin composition according to any one of <1> to <13>, wherein the resin composition has a biodegradability of 5% or more after storage for 90 days in a compost environment; wherein the biodegradability (%) is [(total amount of _CO2 generated during storage for 90 days in a compost environment)/(theoretical amount of carbon dioxide generated calculated from the composition formula)]×100.
<15> A biodegradable molded article formed from the resin composition according to any one of <1> to <14>.
<16> The molded body according to <15>, wherein the molded body is a fishing net.
<17> A method for disposing of a polyamide resin, comprising biodegrading the resin composition according to any one of <1> to <14> or the molded article according to <15> or <16>.
<18> A composition comprising a decomposition product of a polyamide resin and a cobalt salt, wherein the polyamide resin comprises 10 to 40 mol% of structural units derived from xylylenediamine, 5 to 50 mol% of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, 0 to 30 mol% of structural units derived from an aromatic dicarboxylic acid, 0 to 40 mol% of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, 0 to 40 mol% of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, and 0 to 80 mol% of structural units derived from an aromatic dicarboxylic acid. and 0 to 80 mol % of structural units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms, wherein the total of the structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, the structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, the structural units derived from a lactam having 4 to 10 carbon atoms, and the structural units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms is 10 to 80 mol %, the total of the structural units does not exceed 100 mol %, and the number average molecular weight of the composition is less than 1,000.

The present invention makes it possible to provide a resin composition using a polyamide resin, a highly biodegradable resin composition, a biodegradable molded article, a method for disposing of the resin composition, a method for disposing of the molded article, and the composition.

Hereinafter, an embodiment of the present invention (hereinafter, simply referred to as the present embodiment) will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to the present embodiment.
In this specification, the word "to" is used to mean that the numerical values before and after it are included as the lower limit and upper limit.
In this specification, various physical properties and characteristic values are those at 23° C. unless otherwise specified.
In this specification, ppm means ppm by mass.

The biodegradable resin composition of the present embodiment contains a polyamide resin and a cobalt salt, and the polyamide resin contains 10 to 40 mol % of structural units derived from xylylenediamine, 5 to 50 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, 0 to 30 mol % of structural units derived from an aromatic dicarboxylic acid, 0 to 40 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, 0 to 40 mol % of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, and 0 to 80 mol % of structural units derived from an aromatic dicarboxylic acid. The present invention is characterized in that the total of the structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, the structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, the structural units derived from a lactam having 4 to 10 carbon atoms, and the structural units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms is 10 to 80 mol %, and the total of the structural units does not exceed 100 mol %. By adopting such a configuration, it is possible to provide a resin composition with excellent biodegradability. The reason for this is presumed to be as follows.
For example, if the resin is left in a compost environment for a long period of time to biodegrade, microorganisms act on the resin and reduce the molecular weight of the resin. As a result, microorganisms can easily penetrate further into the resin, and biodegradation progresses, decomposing the resin into oligomers, monomers, and further low molecules. However, polyamide resins generally have a strong degree of amide bond and are usually crystalline resins, so they are not easily affected by microorganisms and are less likely to reduce in molecular weight. Therefore, polyamide resins are not easily decomposed by microorganisms. In this embodiment, polyamide resins are synthesized using xylylenediamine in addition to aliphatic monomers containing at least one of α,ω-linear aliphatic dicarboxylic acids having 4 to 7 carbon atoms, α,ω-linear aliphatic dicarboxylic acids having 8 to 22 carbon atoms, aliphatic diamines having 2 to 20 carbon atoms, lactams having 4 to 10 carbon atoms, and aliphatic aminocarboxylic acids having 3 to 9 carbon atoms, to effectively promote biodegradation. That is, it was speculated that by using xylylenediamine as a part of the raw material monomer, the NH ₂ -CH ₂ -benzene ring moiety of xylylenediamine was first oxidatively decomposed by cobalt, and cleaved between the benzyl moiety and NH _2. As a result, it was speculated that the reduction in the molecular weight of the polyamide resin was promoted, and biodegradation was promoted.
Hereinafter, the resin composition of the present embodiment will be described in detail.

<Polyamide resin>
The polyamide resin used in the present embodiment is composed of 10 to 40 mol % of structural units derived from xylylenediamine, 5 to 50 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, 0 to 30 mol % of structural units derived from an aromatic dicarboxylic acid, 0 to 40 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, 0 to 40 mol % of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, and 0 to 80 mol % of structural units derived from an aromatic dicarboxylic acid. The structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, the structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, the structural units derived from a lactam having 4 to 10 carbon atoms, and the structural units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms total 10 to 80 mol %, and the total of the structural units does not exceed 100 mol %.
In this way, by using a polyamide resin synthesized using xylylenediamine in addition to an aliphatic monomer containing at least one of an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, an aliphatic diamine having 2 to 20 carbon atoms, a lactam having 4 to 10 carbon atoms, and an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms, biodegradation can be effectively promoted.
Here, the total of the structural units derived from xylylenediamine, α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, aromatic dicarboxylic acid, α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, aliphatic diamine having 2 to 20 carbon atoms, lactam having 4 to 10 carbon atoms, and aliphatic aminocarboxylic acid having 3 to 9 carbon atoms (hereinafter, sometimes referred to as "structural unit X") does not exceed 100 mol%, but the total of the structural units X is preferably 90 to 100 mol%, more preferably 95 to 100 mol%, even more preferably 97 to 100 mol%, and even more preferably 99 to 100 mol% of all the structural units constituting the polyamide resin.

The polyamide resin used in the present embodiment contains a structural unit derived from xylylenediamine. By containing xylylenediamine, the biodegradation of the polyamide resin can be effectively promoted.
The xylylenediamine preferably contains 0 to 100 mol% metaxylylenediamine and 0 to 100 mol% paraxylylenediamine, more preferably contains 10 to 100 mol% metaxylylenediamine and 0 to 90 mol% paraxylylenediamine, even more preferably contains 30 to 100 mol% metaxylylenediamine and 0 to 70 mol% paraxylylenediamine, and even more preferably contains 70 to 100 mol% metaxylylenediamine and 0 to 30 mol% paraxylylenediamine. By containing metaxylylenediamine, crystallization tends to be delayed and moldability is further improved. In addition, in the xylylenediamine, the total of metaxylylenediamine and paraxylylenediamine preferably accounts for 95 mol% or more, more preferably accounts for 99 mol% or more, and even more preferably accounts for 100 mol%.
In the polyamide resin used in this embodiment, the proportion of the xylylenediamine-derived structural units (preferably meta-xylylenediamine) in all structural units is 10 to 40 mol%. The upper limit of the proportion of the xylylenediamine-derived structural units in all structural units is preferably 38 mol% or less, more preferably 35 mol% or less, and may be 30 mol% or less. The lower limit of the proportion of the xylylenediamine-derived structural units in all structural units may be 15 mol% or more, or even 20 mol% or more.

The polyamide resin used in this embodiment contains a structural unit derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms. In order to obtain high strength as a biodegradable resin composition or a molded article thereof, it is desirable to maintain the molar balance of amino groups and carboxyl groups derived from diamines, dicarboxylic acids, and aminocarboxylic acids. By containing such a dicarboxylic acid, the molar balance of amino groups and carboxyl groups is maintained even when xylylenediamine is introduced, and the effect of improving the strength of the biodegradable resin composition or a molded article thereof tends to be further improved. When the number of carbon atoms is smaller, the thermal stability tends to be inferior, and when the number of carbon atoms is larger, the biodegradable resin composition or a molded article thereof tends to be inferior.
Examples of the α,ω-straight-chain aliphatic dicarboxylic acid having 4 to 7 carbon atoms include succinic acid, glutaric acid, adipic acid, and pimelic acid, with adipic acid being preferred.
In the polyamide resin used in this embodiment, the proportion of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms (preferably adipic acid) in all structural units is 5 to 50 mol%, but is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 22 mol% or more. The upper limit is preferably 40 mol% or less, more preferably 37 mol% or less, and even more preferably 32 mol% or less. By setting it in such a range, a resin composition with better biodegradability can be obtained.
The polyamide resin used in the present embodiment may contain only one type of constitutional unit derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, or may contain two or more types. When two or more types are contained, it is preferable that the total amount is in the above range.

The polyamide resin used in the present embodiment may contain a structural unit derived from an aromatic dicarboxylic acid.
Examples of aromatic dicarboxylic acids include phthalic acid compounds such as isophthalic acid, terephthalic acid, and orthophthalic acid, and naphthalenedicarboxylic acids such as 1,2-naphthalenedicarboxylic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid, 1,7-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid, among which phthalic acid compounds are preferred, and isophthalic acid is more preferred.
In the polyamide resin used in this embodiment, the proportion of structural units derived from aromatic dicarboxylic acids (preferably isophthalic acid) in all structural units is 0 to 30 mol%, preferably 20 mol% or less, more preferably 10 mol% or less, even more preferably 5 mol% or less, and may be 1 mol% or less.
The polyamide resin used in the present embodiment may contain only one type of aromatic dicarboxylic acid-derived structural unit, or may contain two or more types. When two or more types are contained, the total amount is preferably within the above range.

The polyamide resin used in the present embodiment may contain a structural unit derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms.
Examples of α,ω-linear aliphatic dicarboxylic acids having 8 to 22 carbon atoms include suberic acid, azelaic acid, sebacic acid, 1,11-undecanedioic acid, 1,12-dodecanedioic acid, 1,13-tridecanedioic acid, 1,14-tetradecanedioic acid, 1,15-pentadecanedioic acid, 1,16-hexadecanedioic acid, 1,17-heptadecanedioic acid, 1,18-octadecanedioic acid, 1,19-nonadecanedioic acid, 1,20-eicosanediic acid, 1,21-heneicosanediic acid, and 1,22-docosanediic acid, with sebacic acid and 1,12-dodecanedioic acid being preferred.
The proportion of structural units derived from α,ω-linear aliphatic dicarboxylic acids having 8 to 22 carbon atoms in all structural units in the polyamide resin used in this embodiment is 0 to 40 mol%, preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, even more preferably 5 mol% or less, and may be 1 mol% or less.
The polyamide resin used in the present embodiment may contain only one type of constitutional unit derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, or may contain two or more types. When two or more types are contained, it is preferable that the total amount is in the above range.

The polyamide resin used in this embodiment may contain a structural unit derived from an aliphatic diamine having 2 to 20 carbon atoms.
The aliphatic diamine having 2 to 20 carbon atoms may be an alicyclic diamine having 3 to 20 carbon atoms, but is preferably a linear or branched aliphatic diamine having 2 to 20 carbon atoms, more preferably an α,ω-linear aliphatic diamine having 2 to 20 carbon atoms, and even more preferably an α,ω-linear aliphatic diamine having 3 to 10 carbon atoms.
Examples of aliphatic diamines having 2 to 20 carbon atoms include 1,4-tetramethylenediamine, 1,5-pentamethylenediamine, 2-methylpentanediamine, 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine, 1,10-decamethylenediamine, 1,12-dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, and 1,3-diaminocyclohexane. Examples of the aminocyclohexane include 1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminomethyl)decalin, and bis(aminomethyl)tricyclodecane. Of these, 1,4-tetramethylenediamine, 1,5-pentamethylenediamine, 2-methylpentanediamine, 1,6-hexamethylenediamine, 1,7-heptamethylenediamine, 1,8-octamethylenediamine, 1,9-nonamethylenediamine, 1,10-decamethylenediamine, and 1,12-dodecamethylenediamine are preferred, and 1,6-hexamethylenediamine is more preferred.
In the polyamide resin used in this embodiment, the proportion of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms (preferably 1,6-hexamethylenediamine) in all structural units is 0 to 40 mol%. When the polyamide resin used in this embodiment contains structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, the proportion is preferably 5 mol% or more, more preferably 10 mol% or more, and even more preferably 15 mol% or more. The upper limit is preferably 35 mol% or less, more preferably 30 mol% or less, and even more preferably 25 mol% or less.
The polyamide resin used in the present embodiment may contain only one type of constitutional unit derived from an aliphatic diamine having 2 to 20 carbon atoms, or may contain two or more types. When two or more types are contained, it is preferable that the total amount is in the above range.

The polyamide resin used in this embodiment may contain a structural unit derived from a lactam having 4 to 10 carbon atoms.
The lactam having 4 to 10 carbon atoms is preferably a lactam having 4 to 8 carbon atoms, and more preferably a lactam having 6 carbon atoms (ε-caprolactam).
In the polyamide resin used in this embodiment, the proportion of structural units derived from lactams having 4 to 10 carbon atoms (preferably ε-caprolactam) in all structural units is 0 to 80 mol%. When the polyamide resin used in this embodiment contains structural units derived from lactams having 4 to 10 carbon atoms, the proportion is preferably 5 mol% or more, more preferably 10 mol% or more, even more preferably 20 mol% or more, even more preferably 25 mol% or more, even more preferably 30 mol% or more, and even more preferably 37 mol% or more. The upper limit is preferably 77 mol% or less, more preferably 65 mol% or less, and even more preferably 55 mol% or less.
The polyamide resin used in the present embodiment may contain only one type of constitutional unit derived from lactam having 4 to 10 carbon atoms, or may contain two or more types. When two or more types are contained, it is preferable that the total amount is in the above range.

The polyamide resin used in this embodiment may contain a structural unit derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms.
Examples of the aliphatic aminocarboxylic acid having 3 to 9 carbon atoms include aminobutanoic acid, aminopentanoic acid, aminocaproic acid, and aminocaprylic acid, with aminocaproic acid being preferred.
In the polyamide resin used in the present embodiment, the proportion of structural units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms in all structural units is 0 to 80 mol%, preferably 60 mol% or less, more preferably 40 mol% or less, even more preferably 20 mol% or less, still more preferably 10 mol% or less, even more preferably 5 mol% or less, and may be 1 mol% or less.
The polyamide resin used in the present embodiment may contain only one type of constitutional unit derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms, or may contain two or more types. When two or more types are contained, it is preferable that the total amount is in the above range.

The polyamide resin used in this embodiment also has a total of 10 to 80 mol% of structural units derived from α,ω-linear aliphatic dicarboxylic acids having 8 to 22 carbon atoms, structural units derived from aliphatic diamines having 2 to 20 carbon atoms, structural units derived from lactams having 4 to 10 carbon atoms, and structural units derived from aliphatic aminocarboxylic acids having 3 to 9 carbon atoms. The lower limit is preferably 15 mol% or more, more preferably 20 mol% or more, and may be 25 mol% or more. By setting the content at or above the lower limit, biodegradability tends to be further improved. The upper limit is preferably 77 mol% or less. By setting the content at or below the upper limit, strength tends to be further increased.

Next, a preferred embodiment of the polyamide resin used in the present embodiment will be described.
A first embodiment of the polyamide resin used in this embodiment contains 10 to 40 mol% of structural units derived from xylylenediamine (preferably meta-xylylenediamine), 10 to 50 mol% of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms (preferably adipic acid), 0 to 40 mol% of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, and 10 to 40 mol% of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms (preferably 1,6-hexamethylenediamine), and the total of the structural units does not exceed 100 mol%.
In the first embodiment of the polyamide resin, it is preferable that the polyamide resin contains 10 to 40 mol% of structural units derived from xylylenediamine, 10 to 50 mol% of structural units derived from a linear α,ω-aliphatic dicarboxylic acid having 4 to 7 carbon atoms, and 10 to 40 mol% of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, and the total of the structural units does not exceed 100 mol%.
In the first embodiment of the polyamide resin, the total of the xylylenediamine-derived structural units, the structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, the structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, and the structural units derived from an aliphatic diamine having 2 to 20 carbon atoms (preferably the total of the xylylenediamine-derived structural units, the structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, and the structural units derived from an aliphatic diamine having 2 to 20 carbon atoms) is preferably 90 to 100 mol%, more preferably 95 to 100 mol%, even more preferably 97 to 100 mol%, and even more preferably 99 to 100 mol% of all the structural units constituting the polyamide resin.

In the first embodiment of the polyamide resin, the molar ratio of the xylylenediamine-derived structural units and the aliphatic diamine-derived structural units having 2 to 20 carbon atoms in the polyamide resin is preferably 20:80 to 80:20, more preferably 30:70 to 75:25, even more preferably 40:60 to 70:30, and even more preferably 45:55 to 65:35.

In the first embodiment of the polyamide resin, the polyamide resin may be a copolymer of a xylylenediamine-derived structural unit, a C4-7 α,ω-straight-chain aliphatic dicarboxylic acid-derived structural unit (preferably adipic acid), a C2-20 aliphatic diamine-derived structural unit (preferably 1,6-hexamethylenediamine), and an α,ω-straight-chain aliphatic dicarboxylic acid-derived structural unit having 8-22 carbon atoms, which is included as necessary, or two or more polyamide resins containing these structural units, but a copolymer is preferred.
In the first embodiment of the polyamide resin, the molar ratio ((A):(B)) of a blend of a polyamide resin (A) (e.g., MXD6) containing a structural unit derived from xylylenediamine and a structural unit derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms and a polyamide resin (B) (e.g., polyamide 66 or polyamide 610) containing a structural unit derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms and a structural unit derived from an aliphatic diamine having 2 to 20 carbon atoms, or a copolymer (e.g., MXD6/PA66, MXD6/PA610) composed of the same amount of raw material monomers is preferably 80:20 to 20:80, more preferably 80:20 to 30:70, even more preferably 70:30 to 40:60, and even more preferably 60:50 to 40:50. By setting it in such a range, there is a tendency to obtain a biodegradable resin composition or a molded body thereof having superior biodegradability.

A second embodiment of the polyamide resin used in this embodiment contains 10 to 40 mol % of structural units derived from xylylenediamine, 10 to 40 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms (preferably adipic acid), and 20 to 80 mol % of structural units derived from a lactam having 4 to 10 carbon atoms (preferably ε-caprolactam), and the total of the structural units does not exceed 100 mol %.
In a second embodiment of the polyamide resin, the sum of the xylylenediamine-derived structural units, the C4-C7 α,ω-linear aliphatic dicarboxylic acid-derived structural units, and the C4-C10 lactam-derived structural units is preferably 90-100 mol %, more preferably 95-100 mol %, even more preferably 97-100 mol %, and even more preferably 99-100 mol % of all structural units constituting the polyamide resin.

In the second embodiment of the polyamide resin, the molar ratio of the xylylenediamine-derived structural units to the lactam-derived structural units having 4 to 10 carbon atoms in the polyamide resin is preferably 10:90 to 70:30, more preferably 20:80 to 70:30, even more preferably 30:70 to 65:35, and even more preferably 60:40 to 50:50.

In the second embodiment of the polyamide resin, the polyamide resin may be a copolymer of a structural unit derived from xylylenediamine, a structural unit derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms (preferably adipic acid), and a structural unit derived from a lactam having 4 to 10 carbon atoms (preferably ε-caprolactam), or may be a blend of two or more polyamide resins containing these structural units, but is preferably a copolymer.
In the second embodiment of the polyamide resin, a blend of a polyamide resin (A) (e.g., MXD6) containing a structural unit derived from a xylylenediamine and a structural unit derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms and a polyamide resin (C) (e.g., polyamide 6) containing a structural unit derived from a lactam having 4 to 10 carbon atoms, or a copolymer (e.g., MXD6/PA6) composed of the same amount of raw material monomers, the molar ratio ((A):(C)) is preferably 20:80 to 75:25, more preferably 30:70 to 75:25, even more preferably 30:70 to 65:35, even more preferably 35:65 to 65:35, and even more preferably 60:40 to 50:50. By making it in such a range, there is a tendency that a biodegradable resin composition or a molded body thereof having excellent biodegradability can be obtained.

The polyamide resin used in this embodiment may satisfy the first and second embodiments of the polyamide resin. For example, it may be a blend of polyamide resin (A), polyamide resin (B), and polyamide resin (C), or a copolymer composed of the same amount of raw material monomers. The molar ratio of polyamide resin (A), polyamide resin (B), and polyamide resin (C) is preferably 80:20 to 20:80, more preferably 80:20 to 30:70, even more preferably 80:20 to 40:60, even more preferably 80:20 to 50:50, even more preferably 80:20 to 51:49, and even more preferably 65:35 to 41:49.
The polyamide resin used in this embodiment preferably satisfies at least the requirements of the first embodiment.

The polyamide resin used in this embodiment may contain structural units or terminal groups other than structural units derived from xylylenediamine, structural units derived from α,ω-linear aliphatic dicarboxylic acids having 4 to 7 carbon atoms, structural units derived from aromatic dicarboxylic acids, structural units derived from α,ω-linear aliphatic dicarboxylic acids having 8 to 22 carbon atoms, structural units derived from aliphatic diamines having 2 to 20 carbon atoms, structural units derived from lactams having 4 to 10 carbon atoms, and structural units derived from aliphatic aminocarboxylic acids having 3 to 9 carbon atoms. In this embodiment, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more of the polyamide resin is composed of structural units derived from xylylenediamine, structural units derived from α,ω-linear aliphatic dicarboxylic acids having 4 to 7 carbon atoms, structural units derived from aromatic dicarboxylic acids, structural units derived from α,ω-linear aliphatic dicarboxylic acids having 8 to 22 carbon atoms, structural units derived from aliphatic diamines having 2 to 20 carbon atoms, structural units derived from lactams having 4 to 10 carbon atoms, or structural units derived from aliphatic aminocarboxylic acids having 3 to 9 carbon atoms.

The polyamide resin used in this embodiment preferably has a mass ratio of the xylylenediamine structure of 5 to 60 mass %. This configuration allows for a well-balanced improvement in the reduction of the molecular weight of the resin and the biodegradability of the decomposition products. Here, the mass ratio of the xylylenediamine structure is a value calculated from [(mass of the xylylenediamine structure in the polyamide resin)/(mass of the entire polyamide resin)]×100. The xylylenediamine structure refers to the portion represented by "-HN-CH ₂ -benzene ring-CH ₂ -NH-".
The lower limit of the mass ratio of the xylylenediamine structure is more preferably 10% by mass or more, even more preferably 15% by mass or more, and may be 16% by mass or more. By setting it to the lower limit or more, the molecular weight of the resin due to oxidative decomposition tends to progress more easily. In addition, the upper limit of the mass ratio of the xylylenediamine structure is preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. By setting it to the upper limit or less, the aromatic decomposition products that are not easily biodegradable are reduced, and the biodegradability of the resin tends to be further improved.

The content of the polyamide resin in the resin composition of the present embodiment is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more in the resin composition. By making it equal to or more than the lower limit, the physical properties of the polyamide resin tend to be fully exhibited. The upper limit is the amount at which all components other than the cobalt salt become polyamide resin.
The resin composition of the present embodiment may contain only one type of polyamide resin, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Cobalt salts>
The resin composition of the present embodiment contains a cobalt salt. By containing the cobalt salt, biodegradation of the resin composition of the present embodiment is promoted when the resin composition is placed in a compost environment. In particular, the cobalt salt hardly has any adverse effect on the polyamide resin before being placed in a compost environment, and therefore is preferable in that it is unlikely to impair the inherent performance (particularly strength) of the resin composition when the resin composition is used.
The type of cobalt salt is not particularly limited, and may be either a divalent salt or a trivalent salt, with a divalent salt being preferred.
The cobalt salt is preferably a cobalt carboxylate. The use of a carboxylate tends to more effectively promote the reduction in molecular weight due to oxidative decomposition at the benzyl position. The reduction in molecular weight of the polyamide resin promotes subsequent biodegradation by microorganisms.
In the case of a cobalt carboxylate, the carboxylic acid is preferably an aliphatic carboxylic acid. The aliphatic carboxylic acid is not particularly specified because it does not significantly affect the oxidative decomposition behavior of the resin by cobalt, but either a linear or branched aliphatic carboxylic acid can be preferably adopted, and a linear aliphatic carboxylic acid is more preferable. The carbon number of the aliphatic carboxylic acid is not particularly specified because it does not significantly affect the oxidative decomposition behavior of the resin by cobalt, but it is preferably 2 or more, may be 10 or more, and is preferably 40 or less, more preferably 30 or less, and even more preferably 24 or less. In particular, an aliphatic dicarboxylic acid having an even number of carbon atoms is preferable.
Specific examples of aliphatic carboxylic acids include acetic acid, neodecanoic acid, lauric acid, neodecanoic acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, and melissic acid. From the viewpoint of physical properties, acetic acid, neodecanoic acid, and stearic acid are preferred, and stearic acid is more preferred.
In this embodiment, the cobalt salt is preferably cobalt stearate, and the cobalt stearate is preferably (C ₁₇ H ₃₅ COO) ₂ Co.

The content of the cobalt salt (preferably cobalt stearate) in the resin composition of this embodiment is preferably 10 ppm by mass or more, more preferably 50 ppm by mass or more, and even more preferably 80 ppm by mass or more, based on the cobalt atom, relative to 100 parts by mass of the polyamide resin. By making it equal to or more than the lower limit, the polyamide resin can be more effectively decomposed to a molecular weight that is easily biodegradable. In addition, the content of the cobalt salt in the resin composition of this embodiment is preferably 2000 ppm by mass or less, more preferably 1800 ppm by mass or less, even more preferably 1500 ppm by mass or less, even more preferably 1200 ppm by mass or less, even more preferably 1000 ppm by mass or less, and even more preferably 800 ppm by mass or less, based on the cobalt atom, relative to 100 parts by mass of the polyamide resin. By making it equal to or less than the upper limit, there is a tendency that deterioration and poor appearance during the preparation of the polyamide resin can be effectively suppressed.
The resin composition of the present embodiment may contain only one type of cobalt salt, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Other Ingredients>
The resin composition of this embodiment may contain other components other than the polyamide resin and the cobalt salt, as long as the purpose and effect of this embodiment are not impaired. Specific examples of the other components include thermoplastic resins other than polyamide resins, antioxidants, heat stabilizers, hydrolysis resistance improvers, weathering stabilizers, matting agents, UV absorbers, nucleating agents, plasticizers, dispersants, flame retardants, antistatic agents, coloring inhibitors, gelling inhibitors, colorants, release agents, surface activators, dyes, and the like. For details of these, please refer to the descriptions in paragraphs 0130 to 0155 of Japanese Patent No. 4894982, the descriptions in paragraph 0021 of Japanese Patent Publication No. 2010-281027, and the descriptions in paragraph 0036 of Japanese Patent Publication No. 2016-223037, and the contents of these are incorporated herein.
Examples of thermoplastic resins other than polyamide resins include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polycarbonate resins, polyoxymethylene resins, polyether ketones, polyether sulfones, thermoplastic polyether imides, etc. In the resin composition of this embodiment, it is possible to have a configuration that does not substantially contain thermoplastic resins other than polyamide resins. "Substantially does not contain" means, for example, that in the resin composition of this embodiment, the content of thermoplastic resins other than polyamide resins is 5% by mass or less of the mass of polyamide resin.
The resin composition of the present embodiment may contain a filler such as a glass resin composition or carbon fiber, but is preferably substantially free of the filler. The term "substantially free of the filler" means that the amount of the filler is 3% by mass or less of the resin composition of the present embodiment, for example.
In addition, the resin composition of the present embodiment can be given any surface property by performing a plasma treatment. For details, refer to the descriptions in paragraphs 0019 to 0022 of JP-A-06-182195, the contents of which are incorporated herein by reference.

<Characteristics and properties of resin composition>
The resin composition of the present embodiment preferably has a molecular weight that decreases when placed under constant temperature conditions. Specifically, when stored for 28 days under an environment of 55° C. and 90% relative humidity, the reduction rate of the number average molecular weight of the resin composition ((Mn of polyamide resin after storage/Mn of polyamide resin before storage)×100) is preferably 20% or less, more preferably 15% or less, even more preferably 10% or less, and even more preferably 7% or less. The lower limit of the reduction rate is ideally 0%, and even if it is 0.01% or more, the required performance is sufficiently met.
The resin composition of the present embodiment has biodegradability. Biodegradability refers to the ability to be ultimately decomposed into water and carbon dioxide by microorganisms and includes, for example, those in which a decrease in molecular weight is observed when stored for a certain period of time in a compost environment.
The resin composition of this embodiment preferably has a biodegradability of 5% or more after storage for 90 days in a compost environment, more preferably 10% or more, even more preferably 20% or more, even more preferably 35% or more, and even more preferably 60% or more. The upper limit of the biodegradability is ideally 100%, but even if it is, for example, 80% or less, the required performance is sufficiently met. Here, the biodegradability (%) is [(total _CO2 generation during storage for 90 days in a compost environment) / (theoretical carbon dioxide generation calculated from the composition formula)] × 100.
The resin composition of the present embodiment preferably has a number average molecular weight of 8,000 or more, more preferably 10,000 or more. The upper limit of the number average molecular weight is not particularly limited, but is, for example, 100,000 or less, and further 50,000 or less. The number average molecular weight here is that before biodegradation.

<Method of producing resin composition>
As a method for producing the resin composition of the present embodiment, any method may be adopted.
For example, a polyamide resin, a cobalt salt, and other components that are added as necessary are mixed using a mixing means such as a V-type blender to prepare a lump-sum blend, which is then melt-kneaded in a vented extruder and pelletized.

The heating temperature during melt kneading can usually be selected appropriately from the range of 180 to 360°C. If the temperature is too high, decomposition gas is likely to be generated, which may cause extrusion defects such as strand breakage. Therefore, it is desirable to select a screw configuration that takes shear heat generation, etc. into consideration.

<Molded body>
The resin composition of the present embodiment is molded into a biodegradable molded article. The biodegradable molded article may be a part or a finished product.
In the present embodiment, the manufacturing method of the molded body is not particularly limited, and any molding method generally used for resin compositions can be used. Examples include injection molding, ultra-high speed injection molding, injection compression molding, two-color molding, gas-assisted hollow molding, molding using a heat-insulating mold, molding using a rapid heating mold, foam molding (including supercritical fluid), insert molding, IMC (in-mold coating molding) molding, extrusion molding, sheet molding, thermoforming, rotational molding, lamination molding, press molding, blow molding, etc. Also, a molding method using a hot runner system can be used.

The molded article of the present embodiment is widely used in automobile and other transport machinery parts, general machine parts, precision machine parts, electronic and electrical equipment parts, office equipment parts, building materials and housing-related parts, medical devices, leisure and sporting goods (e.g., fishing lines), agricultural, forestry and fishery products, play equipment, medical products, food packaging films, everyday items such as clothing, defense and aerospace products, and the like.
In particular, the resin composition and molded article of this embodiment are preferably used for food packaging films, filter cloths, leisure sports goods (for example, fishing lines), and fishing nets, since they have excellent biodegradability, and are more preferably used for fishing nets.

The resin composition of this embodiment and the biodegradable molded article of this embodiment can be disposed of by biodegradation. The resin composition and the biodegradable molded article of this embodiment can be decomposed to the molecular level by the action of microorganisms, and ultimately turned into carbon dioxide and water, which can be circulated back into the natural world. This is therefore advantageous in that they can be disposed of naturally without destroying nature. In other words, this specification also discloses a method for disposing of polyamide resin, which includes biodegrading the resin composition or the biodegradable molded article of this embodiment.

The number average molecular weight of the biodegradable resin composition of this embodiment is reduced by storing it at 55°C and a relative humidity of 90% for 28 days. The composition after the number average molecular weight is reduced (low Mn composition) is a composition containing a decomposition product of a polyamide resin and a cobalt salt, and the polyamide resin contains 10 to 40 mol% of xylylenediamine-derived structural units, 5 to 50 mol% of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, 0 to 30 mol% of structural units derived from an aromatic dicarboxylic acid, 0 to 40 mol% of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, 0 to 40 mol% of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, and 0 to 80 mol% of structural units derived from an aromatic dicarboxylic acid. The composition contains 0-80 mol % of structural units derived from a lactam having 4-10 carbon atoms and 0-80 mol % of structural units derived from an aliphatic aminocarboxylic acid having 3-9 carbon atoms, and the total of the structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8-22 carbon atoms, the structural units derived from an aliphatic diamine having 2-20 carbon atoms, the structural units derived from a lactam having 4-10 carbon atoms, and the structural units derived from an aliphatic aminocarboxylic acid having 3-9 carbon atoms is 10-80 mol %, the total of the structural units does not exceed 100 mol %, and the number average molecular weight of the composition is less than 1000. The number average molecular weight of the low Mn composition is preferably 950 or less, and more preferably 900 or less. The lower limit of the number average molecular weight is the better, but 150 or more is practical, and even 300 or more satisfies the required performance.

The present invention will be described in more detail below with reference to examples. The materials, amounts, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.
If the measuring instruments used in the examples are difficult to obtain due to discontinuation or the like, measurements can be made using other instruments with equivalent performance.

Raw material <Synthesis of MXD6/PA6 copolymer, 70/30 (mass ratio)>
A precisely weighed amount of adipic acid (32.3 mol) and ε-caprolactam (35.4 mol) were placed in a jacketed reactor equipped with a stirrer, a partial condenser, a cooler, a thermometer, a dropping tank and a nitrogen gas inlet tube, and the atmosphere was fully replaced with nitrogen. The temperature was raised to 170°C under a small amount of nitrogen gas flow, and the adipic acid and ε-caprolactam were dissolved and made into a uniform fluid state. Metaxylylenediamine (32.3 mol) was dropped into the reactor while stirring for 160 minutes. During this time, the pressure inside the reaction system was kept at normal pressure, the internal temperature was continuously raised to 250°C, and water distilled with the dropping of metaxylylenediamine was removed from the system through the partial condenser and the cooler. After the dropping of metaxylylenediamine was completed, the liquid temperature was kept at 250°C and the reaction was continued for 10 minutes. Thereafter, the pressure inside the reaction system was continuously reduced to 600 Torr over 10 minutes, and the reaction was continued for 20 minutes. During this time, the reaction temperature was continuously raised to 260°C. After the reaction was completed, the inside of the reactor was pressurized with nitrogen gas at 0.3 MPa, and the polymer was taken out as a strand from a nozzle at the bottom of the polymerization tank, cooled with water, and cut into pellets to obtain pellets of a molten polymerized product. The obtained pellets were charged at room temperature into a tumbler (rotary vacuum tank) having a jacket for heating a heat medium. While rotating the tumbler, the inside of the tank was reduced in pressure (0.5 to 10 Torr), the circulating heat medium was heated to 150°C, and the pellet temperature was raised to 130°C and maintained at that temperature for 3 hours. Thereafter, nitrogen was introduced again to return to normal pressure, and cooling was started. When the temperature of the pellets reached 70°C or less, the pellets were taken out of the tank to obtain a solid-phase polymerized product.
The mass ratio of the xylylenediamine structure in the obtained polyamide resin was 38.1 mass %.

<Synthesis of MXD6/PA6 copolymer, 56/44 (mass ratio)>
The synthesis was carried out in the same manner as in the synthesis example of the MXD6/PA6 copolymer, 70/30 (mass ratio), except that the raw materials adipic acid was changed to 24.8 mol, ε-caprolactam to 50.5 mol, and metaxylylenediamine to 24.7 mol.
The mass ratio of the xylylenediamine structure in the obtained polyamide resin was 30.3 mass %.

<Synthesis of MXD6/PA6 copolymer, 28/72 (mass ratio)>
The synthesis was carried out in the same manner as in the synthesis example of the MXD6/PA6 copolymer, 70/30 (mass ratio), except that the raw materials adipic acid was changed to 11.6 mol, ε-caprolactam to 76.8 mol, and metaxylylenediamine to 11.6 mol.
The mass ratio of the xylylenediamine structure in the obtained polyamide resin was 15.2 mass %.

<Synthesis of MXD6/PA66 copolymer, 56/44 (mass ratio)>
A precisely weighed adipic acid (50.0 mol) was placed in a jacketed reactor equipped with a stirrer, a partial condenser, a cooler, a thermometer, a dropping tank and a nitrogen gas inlet tube, and the atmosphere was fully replaced with nitrogen. The temperature was raised to 170°C under a small amount of nitrogen gas flow, and the adipic acid was dissolved and made into a uniform fluid state. A diamine mixture of metaxylylenediamine (26.8 mol) and hexamethylenediamine (23.2 mol) was dropped into the reactor over a period of 160 minutes while stirring. During this time, the pressure inside the reaction system was kept at normal pressure, the internal temperature was continuously raised to 250°C, and water distilled with the dropping of metaxylylenediamine was removed from the system through the partial condenser and the cooler. After the dropping of metaxylylenediamine was completed, the liquid temperature was kept at 250°C and the reaction was continued for 10 minutes. Thereafter, the pressure inside the reaction system was continuously reduced to 600 Torr over a period of 10 minutes, and the reaction was continued for 20 minutes. During this time, the reaction temperature was continuously raised to 260°C. After the reaction was completed, the inside of the reactor was pressurized with nitrogen gas at 0.3 MPa, and the polymer was taken out as a strand from a nozzle at the bottom of the polymerization tank, cooled with water, and cut into pellets to obtain pellets of a molten polymerized product. The obtained pellets were charged at room temperature into a tumbler (rotary vacuum tank) having a jacket for heating a heat medium. While rotating the tumbler, the inside of the tank was reduced in pressure (0.5 to 10 Torr), the circulating heat medium was heated to 150°C, and the pellet temperature was raised to 130°C and maintained at that temperature for 3 hours. Thereafter, nitrogen was introduced again to return to normal pressure, and cooling was started. When the temperature of the pellets reached 70°C or less, the pellets were taken out of the tank to obtain a solid-phase polymerized product.
The mass ratio of the xylylenediamine structure in the obtained polyamide resin was 30.3 mass %.

PA6: Polyamide 6: Ube Industries, PA6 "1022B"
PA66: Polyamide 66: Toray Industries, PA66 "CM3001-N"
Cobalt stearate (StCo): Kanto Chemical Co., Ltd., product number: 07423-02

2. Examples 1 to 4 and Comparative Examples 1 to 6
<Production of Resin Composition (Compound)>
The polyamide resin and cobalt stearate were weighed out and blended in a tumbler to obtain the composition shown in Table 1 or Table 2 described later, and the blend was fed into a twin-screw extruder (TEM26SS, manufactured by Shibaura Machine Co., Ltd.) from its base, melted, and pelletized. The temperature of the twin-screw extruder was set to 260° C. In Tables 1 and 2, the content of cobalt stearate (StCo) is the amount of cobalt atoms (ppm by mass) relative to 100 parts by mass of the polyamide resin.

<Molecular weight reduction after storage at 55°C for 28 days>
The resulting polyamide resin pellets were stored at 55° C. and a relative humidity of 90% for 28 days. The number average molecular weight was measured before and after storage.
In addition, "Mn (%) after 28 days" is an index showing the rate of decrease in the number average molecular weight of the polyamide resin, and is a value expressed as (Mn of polyamide resin after storage/Mn of polyamide resin before storage) x 100.

The number average molecular weight (Mn) was measured according to the following gel permeation chromatography (GPC) method.
The GPC measurement was performed using a Shodex GPC SYSTEM-11 manufactured by Showa Denko K.K. Hexafluoroisopropanol (HFIP) was used as the solvent, and 10 mg of the polyamide resin sample was dissolved in 10 g of HFIP and used for the measurement. The measurement conditions were two HFIP-806M GPC standard columns (column size 300 x 8.0 mm I.D.) manufactured by the same company, two HFIP-800 reference columns, a column temperature of 40°C, and a solvent flow rate of 1.0 mL/min. PMMA (polymethyl methacrylate) was used as the standard sample, and the number average molecular weight (Mn) was obtained using SIC-480II manufactured by the same company as the data processing software.

<Biodegradability>
The biodegradability was measured according to JIS K 6953-1 (aerobic compost biodegradability test method). 10 g of the resin composition (pellets) was mixed with 60 g of compost with a dry mass of 45 to 50% by mass. This mixture was placed in a compost environment at 58±2°C and 100% relative humidity, and the air was saturated with water and gas with carbon dioxide removed was passed through for a 90-day biodegradation test. The amount of carbon dioxide generated was measured, and the biodegradability was calculated from the total theoretical amount of carbon dioxide generated according to the following formula.
Biodegradability (%) = [(total amount of _CO2 generated during storage for 90 days in a compost environment) / (theoretical amount of carbon dioxide generated calculated from the composition formula)] x 100
The theoretical amount of carbon dioxide generated was calculated from the composition formula according to the following formula using the total organic carbon (TOC) amount of the test material previously measured with a CHN analyzer and a sample weight of 10 g.
Theoretical carbon dioxide generation amount (g) = [(total organic carbon amount (TOC) of test material / 100)] x 3.67 x 10
The compost was made using a YK-11 manufactured by Yawata Bussan Co., Ltd. The amount of carbon dioxide was measured using a non-dispersive infrared analyzer (LI-830 manufactured by LI-COR Co., Ltd.) and the CHN analyzer was a PE2400 series II manufactured by PerkinElmer Co., Ltd.

In Tables 1 and 2, MXDA represents meta-xylylenediamine, ε-CL represents ε-caprolactam, and HDA represents hexamethylenediamine.
In Tables 1 and 2, StCo is shown as the amount of cobalt atoms (ppm by mass) relative to 100 parts by mass of the polyamide resin.

As is clear from Table 1, when the resin compositions of the present invention (Examples 1 to 4) were stored for 28 days at 55°C and a relative humidity of 90%, the cobalt salt acted to effectively reduce the number average molecular weight of the polyamide resin. Furthermore, when the resin compositions were stored for 90 days in a compost environment, the decomposition of the polyamide resin proceeded more effectively due to biodegradation in addition to the oxidative decomposition action of the cobalt salt.
In contrast, as is clear from Table 2 above, when no structural unit derived from xylylenediamine was included (Comparative Examples 1 and 2) or when no cobalt salt was included (Comparative Examples 3 to 6), almost no decrease in the number average molecular weight of the polyamide resin was observed even after storage at 55° C. and a relative humidity of 90% for 28 days. Furthermore, biodegradation did not progress.

Claims (13)

Contains a polyamide resin and a cobalt salt,
The polyamide resin contains 10 to 30 mol % of structural units derived from xylylenediamine, 5 to 50 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, 0 to 10 mol % of structural units derived from an aromatic dicarboxylic acid, 0 to 10 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, 0 to 10 mol % of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, 0 to 50 mol % of structural units derived from a lactam having 4 to 10 carbon atoms, and 0 to 10 mol % of structural units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms;
the total content of the constitutional units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, the constitutional units derived from an aliphatic diamine having 2 to 20 carbon atoms, the constitutional units derived from a lactam having 4 to 10 carbon atoms, and the constitutional units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms is 10 to 80 mol %,
the total amount of the xylylenediamine-derived structural units, the C4-C7 linear aliphatic dicarboxylic acid-derived structural units, and the C4-C10 lactam-derived structural units is 90-100 mol % of all structural units constituting the polyamide resin;
A biodegradable resin composition in which the total amount of the structural units does not exceed 100 mol %. The resin composition according to claim 1 , wherein the molar ratio of the xylylenediamine-derived structural unit and the lactam-derived structural unit having 4 to 10 carbon atoms in the polyamide resin is 20:80 to 75:25. 3. The resin composition according to claim 1 , wherein the α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms is adipic acid, and the lactam having 4 to 10 carbon atoms is ε-caprolactam. The resin composition according to any one of claims 1 to 3 , wherein the mass ratio of the xylylenediamine structure in the polyamide resin is 5 to 60 mass%; here, the mass ratio of the xylylenediamine structure is a value calculated from [(mass of the xylylenediamine structure in the polyamide resin)/(total mass of the polyamide resin)]×100. The resin composition according to any one of claims 1 to 4 , wherein the cobalt salt comprises a carboxylate of cobalt. The resin composition according to any one of claims 1 to 4 , wherein the cobalt salt comprises cobalt stearate. The resin composition according to any one of claims 1 to 6 , wherein the content of the cobalt salt is 10 to 2000 ppm by mass based on cobalt atoms relative to 100 parts by mass of the xylylenediamine-based polyamide resin. 8. The resin composition according to claim 7, wherein when the resin composition is stored for 28 days under an environment of 55 °C and a relative humidity of 90%, a reduction rate of the number average molecular weight of the resin composition ((Mn of polyamide resin after storage/Mn of polyamide resin before storage) x 100) is 20% or less. The resin composition according to any one of claims 1 to 8 , wherein the resin composition has a biodegradability of 5% or more after storage in a compost environment for 90 days; wherein the biodegradability (%) is [(total amount of _CO2 generated during storage in a compost environment for 90 days)/(theoretical amount of carbon dioxide generated calculated from the composition formula)]×100. A biodegradable molded article formed from the resin composition according to any one of claims 1 to 9 . The molded article according to claim 10 , wherein the molded article is a fishing net. A method for disposing of a polyamide resin, comprising biodegrading the resin composition according to any one of claims 1 to 9 or the molded article according to claim 10 or 11 . A composition comprising a decomposition product of a polyamide resin and a cobalt salt,
The polyamide resin contains 10 to 30 mol % of structural units derived from xylylenediamine, 5 to 50 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 4 to 7 carbon atoms, 0 to 10 mol % of structural units derived from an aromatic dicarboxylic acid, 0 to 10 mol % of structural units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, 0 to 10 mol % of structural units derived from an aliphatic diamine having 2 to 20 carbon atoms, 0 to 50 mol % of structural units derived from a lactam having 4 to 10 carbon atoms, and 0 to 10 mol % of structural units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms;
the total content of the constitutional units derived from an α,ω-linear aliphatic dicarboxylic acid having 8 to 22 carbon atoms, the constitutional units derived from an aliphatic diamine having 2 to 20 carbon atoms, the constitutional units derived from a lactam having 4 to 10 carbon atoms, and the constitutional units derived from an aliphatic aminocarboxylic acid having 3 to 9 carbon atoms is 10 to 80 mol %,
the total amount of the xylylenediamine-derived structural units, the C4-C7 linear aliphatic dicarboxylic acid-derived structural units, and the C4-C10 lactam-derived structural units is 90-100 mol % of all structural units constituting the polyamide resin;
The total amount of the structural units does not exceed 100 mol %,
A composition, wherein the composition has a number average molecular weight of less than 1000.