JP4527508B2 - Degradation evaluation method for polyamide - Google Patents

Description

  The present invention relates to a method for measuring the degree of degradation of a polyamide.

  Polyamide has an amide bond, and the polymer chains are linked by a hydrogen bond between NH and CO, and thus exhibits high crystallinity and a high melting point. Polyamide is excellent in abrasion resistance, elasticity, chemical resistance, and dyeability, and is used in large quantities as a fiber material, as well as excellent mechanical properties, abrasion resistance, heat resistance, and oil resistance. Widely used in engineering plastics such as machine parts and electrical parts, and other molded products.

  As described above, the polyamide material is a high molecular compound having excellent characteristics, but gradually deteriorates with time due to external force, chemical change, or the like. Understanding how much such deteriorated polyamide material has deteriorated, what factor it has deteriorated, and how strong it is, such as the durability of the polyamide material, etc. This is very important for evaluation and elucidation of the degradation mechanism of polyamide.

  Polyamide degradation includes chemical factors that cause polymer chains to undergo chemical changes or bond cleavage by the action of ultraviolet rays, heat, or hydrolysis in addition to degradation due to mechanical factors that cause the polymer chains to be broken by external forces such as shearing. Deterioration due to Due to these various actions, the polyamide material is deteriorated, and as a result, its mechanical strength and the like are lowered.

  In general, the degree of deterioration of polyamide is evaluated based on strength measured by a strength test such as a tensile test (for example, ASTM-D638-84) using a test piece having a predetermined shape and size.

  However, in order to perform the strength test as described above, it is necessary to prepare a test piece having a predetermined shape and size, the measurement operation is complicated, and an actual polyamide molded product has a curved surface. In many cases, therefore, the test piece cannot be prepared. In this case, there is a practical problem that the strength test cannot be performed. Further, in the above-described strength test, it is impossible to pinpoint only the deteriorated portion of a test piece that is locally deteriorated (for example, a polyamide material that is deteriorated only on the surface). Furthermore, in the above strength test, it is possible to determine whether the strength deterioration of the polyamide material is due to physical (mechanical) factors such as mechanical shearing, or due to chemical factors such as hydrolysis. Can not.

As a method for evaluating the deterioration of the polyamide due to chemical factors, a method of quantifying a substance produced by chemically changing the polyamide due to the chemical deterioration can be considered. As a method for quantifying a specific substance in polyamide, for example, a method of measuring the absorbance in the characteristic absorption wavelength region of the substance by visible ultraviolet absorption spectrum analysis is known (for example, Patent Document 1 below). However, this method requires that the substance produced by the chemical change has a characteristic absorption wavelength region characteristic of the substance, and the absorbance in the characteristic absorption wavelength region is weak or the characteristic absorption wavelength region of polyamide. Many problems remain to be solved, such as being unable to adopt when interfering with.
JP-A-9-281046

  The present invention can be applied to any test piece shape, can measure the local deterioration degree, and can accurately and easily prevent deterioration due to chemical factors such as hydrolysis and thermal factors due to oxygen. An object of the present invention is to provide a method for evaluating the degree of deterioration of a polyamide-based resin that can be evaluated.

The inventors of the present invention have a correlation between the amount of the terminal carboxyl group of the polyamide chain caused by chemical degradation due to hydrolysis of polyamide and the like and thermal degradation by oxygen and the mechanical strength, and the carboxyl group is Although the ultraviolet absorption cannot be measured simply by esterification or thioesterification, the amount of the terminal carboxyl group is determined by derivatizing the carboxyl group with a specific alcohol compound or thioalcohol compound and measuring the ultraviolet absorption of the specific group. Has been found to be accurately quantified, and the present invention has been completed.
That is, this invention is invention of the degradation degree evaluation method of a polyamide-type resin, General formula (I):

（式中、Ｒ^１は、炭素数１〜１０のアルキレン基または炭素数１〜１０のハロゲン化アルキレン基、Ｒ^２、Ｒ^３、Ｒ^４、Ｒ^５、及びＲ^６は、それぞれ独立に、水素原子、ハロゲン原子、炭素数１〜２０のアルキル基、炭素数１〜２０のハロゲン化アルキル基、炭素数１〜２０のアルコキシ基、ヒドロキシル基、ニトロ基及びアリール基からなる群より選択される基であり、Ｒ^２、Ｒ^３、Ｒ^４、Ｒ^５、及びＲ^６は、互いに隣接基同士で縮合芳香族環を形成してもよい。）
で表されるアルコール化合物、
または
一般式（ＩＩ）：

(In the formula, R ¹ is an alkylene group having 1 to 10 carbon atoms or a halogenated alkylene group having 1 to 10 carbon atoms, R ² , R ³ , R ⁴ , R ⁵ , and R ⁶ are each independently hydrogen. A group selected from the group consisting of an atom, a halogen atom, an alkyl group having 1 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a hydroxyl group, a nitro group, and an aryl group R ² , R ³ , R ⁴ , R ⁵ , and R ⁶ may form a condensed aromatic ring with adjacent groups.
An alcohol compound represented by
Or general formula (II):

（式中、Ｒ^７は、炭素数１〜１０のアルキレン基または置換された炭素数１〜１０のアルキレン基、Ｒ^８、Ｒ^９、Ｒ^１０、Ｒ^１１、及びＲ^１２は、それぞれ独立に、水素原子、ハロゲン原子、炭素数１〜２０のアルキル基、炭素数１〜２０のハロゲン化アルキル基、炭素数１〜２０のアルコキシ基、ヒドロキシル基、ニトロ基及びアリール基からなる群より選択される基であり、Ｒ^８、Ｒ^９、Ｒ^１０、Ｒ^１１、及びＲ^１２は、互いに隣接基同士で縮合芳香族環を形成してもよい。）
で表されるメルカプト化合物、
とポリアミド系樹脂とを反応させ、反応生成物の可視紫外線吸光度を測定することにより、その特定波長の吸光度の推移を見てポリアミド系樹脂の劣化度を判定する。

(In the formula, R ⁷ is an alkylene group having 1 to 10 carbon atoms or a substituted alkylene group having 1 to 10 carbon atoms, R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² are each independently Selected from the group consisting of a hydrogen atom, a halogen atom, an alkyl group having 1 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a hydroxyl group, a nitro group, and an aryl group. And R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² may form a condensed aromatic ring with adjacent groups.
A mercapto compound represented by:
And the polyamide resin are reacted, and the visible ultraviolet absorbance of the reaction product is measured, and the degree of deterioration of the polyamide resin is determined by looking at the change in absorbance at the specific wavelength.

  Preferred examples of the alcohol compound of the formula (I) include benzyl alcohol, and preferred examples of the mercapto compound of the general formula (II) include benzyl mercaptan.

  The amount of the terminal carboxyl group can be accurately determined by derivatizing the terminal carboxyl group of the polyamide chain caused by chemical degradation due to hydrolysis of polyamide, etc. and thermal degradation by oxygen with a specific alcohol compound or thioalcohol compound. In addition, the degree of deterioration of the polyamide-based resin can be accurately and easily evaluated. Since the conventional degradation degree evaluation method is to evaluate the strength by a tensile test or the like, the cause of the degradation could not be judged, but the method of the present invention is a chemical degradation of the polyamide resin and a thermal degradation due to oxygen. Therefore, the method of the present invention makes it possible to analyze the cause and mechanism of deterioration of the polyamide-based resin. In addition, the method of the present invention can be carried out if there is a very small amount of polyamide sample regardless of the size and shape, for example, a polyamide resin molded product having a curved surface, for which it was impossible to measure the degree of deterioration conventionally. But the degree of degradation can be measured.

The present invention is described in detail below.
Polyamide degradation due to chemical factors can be considered as hydrolysis of polyamides, and polyamide degradation due to thermal factors can be attributed to oxidative degradation of polyamides. In that case, the amide bond in the polyamide chain is cleaved by hydrolysis, oxidative decomposition or the like, and the polyamide chain is lowered in molecular weight. As a result, it is considered that the mechanical strength of the polyamide is lowered.

  By this hydrolysis, the amide bond in the polyamide chain becomes an amino group and a carboxyl group. Therefore, by quantifying the carboxyl group contained in the polyamide resin, it is possible to evaluate and estimate the degree of chemical and thermal deterioration of the polyamide resin, and hence the degree of strength deterioration.

  The “polyamide resin” as used in the present invention means a resin containing one or more polyamides, for example, not only a single-component resin composed of one type of polyamide, but also a resin containing two or more types of polyamides, and A multicomponent resin such as a polymer blend containing polyamide and a polymer compound other than polyamide as a resin component, and a molded product such as a molded product or fiber thereof are also included. The polyamide chain may be chemically bonded to other polymer chains to form, for example, a block polymer or a graft polymer.

  The polyamide for which the degree of degradation is measured by the method of the present invention is not particularly limited as long as it has an amide bond in the polymer chain, and any of natural polymers and synthetic polymers can be used. Can be used.

  Examples of the synthetic polymer polyamide include nylon (trade name). Nylon can be obtained by condensation polymerization of a diamine compound and a dicarboxylic acid compound, or can be obtained by ring-opening polymerization of a lactam compound.

  Specific examples of the diamine compound include tetramethylene diamine, hexamethylene diamine, undecamethylene diamine, dodecamethylene diamine, 2,2,4- / 2,4,4-trimethylhexamethylene diamine, and 5-methylnona. Methylenediamine, p-phenylenediamine, m-xylylenediamine, p-xylylenediamine, 1,3-bisaminomethylcyclohexane, 1,4-bisaminomethylcyclohexane, bis-p-aminocyclohexylmethane, bis-p- Examples include aminocyclohexylpropane and isophoronediamine.

  Specific examples of the dicarboxylic acid include, for example, adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-dichlorohexanedicarboxylic acid, terephthalic acid, isophthalic acid, Naphthalenedicarboxylic acid, dimer acid, etc. are mentioned.

  Specific examples of the lactam compound include ε-caprolactam, enantolactam, ω-laurolactam, and the like.

  The above-mentioned constituents are used alone or in a mixture of two or more, or are further mixed with other monomers for polymerization, and the resin containing the polyamide homopolymer and / or copolymer thus obtained is the subject of the method of the present invention. It can be.

  A linear aliphatic polyamide or a polyamide having an aromatic ring in the main chain can be obtained from the above components.

  Of the polyamides obtained from the above components, a linear aliphatic polyamide is represented by the following formula.

（式中、ｍ、ｎ及びｘは、それぞれ独立に、１以上の整数を表す。）

(In the formula, m, n and x each independently represents an integer of 1 or more.)

  Usually, the polyamides of the above formulas (a) and (b) are called “nylon m (n + 2)” and “nylon (n + 1)”, respectively.

  Specific examples of the polyamide that can be used in the method of the present invention include nylon 6, nylon 66, nylon 610, nylon 11, nylon 12, nylon 116, nylon 612, and the like.

  In the method of the present invention, the degree of deterioration of the polyamide-based resin is evaluated by quantifying the amount of carboxyl groups generated at the ends of the decomposed polyamide chain.

  As a method for quantifying the content of a specific substance or functional group in polyamide, a method by visible ultraviolet absorption spectrum analysis for detecting characteristic absorption specific to the substance is known. In the method of the present invention, it is conceivable to detect characteristic absorption of the terminal carboxyl group caused by hydrolysis and thermal decomposition of polyamide. However, if the carboxyl group is left unmodified, it cannot be detected because the sensitivity is weak in the visible ultraviolet absorption spectrum analyzer. Therefore, as a method for quantifying the carboxyl group, a method has been invented in which the carboxyl group is modified with an atomic group or the like having a visible ultraviolet characteristic absorption suitable for detection, and the modified carboxyl group is detected.

  The present inventors diligently studied a method for easily detecting a carboxyl group in a deteriorated polyamide-based resin. As a result, the alcohol compound represented by the general formula (I) or the mercapto compound represented by the general formula (II) was used. It has been found that by modifying the carboxyl group, the degree of deterioration of the polyamide-based resin can be accurately and accurately quantified by visible UV absorption absorbance analysis.

Specific examples of the substituent in R ^{2 to} R ⁶ and R ^{8 to} R ¹² are as follows.
Examples of the halogen atom include fluorine, chlorine, bromine and iodine, and fluorine is preferred.

Examples of the alkyl group having 1 to 20 carbon atoms include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, isobutyl, 1-pentyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3 -Methylbutyl, 2,2-dimethylpropyl, 1,2-dimethylpropyl, hexyl and the like can be mentioned, and an alkyl group having 1 to 4 carbon atoms is particularly preferable. Alternatively, R ² and R ³ , R ³ and R ⁴ , R ⁴ and R ⁵ , R ⁵ and R ⁶ are combined together to form an alkylene group — (CH ₂ ) _n — (n is 1 to 20, Preferably an integer of 1 to 4.) or an aromatic ring. Similarly, each of R ⁸ and R ⁹ , R ⁹ and R ¹⁰ , R ¹⁰ and R ¹¹ , R ¹¹ and R ¹² is combined to form an alkylene group — (CH ₂ ) _n — (n is 1 to 20 , Preferably an integer from 1 to 4.) or an aromatic ring.

  Examples of the aryl group include a phenyl group, a naphthyl group, and an anthranyl group.

  As the alcohol compound represented by the formula (I) and the mercapto compound represented by the formula (II), commercially available products may be used, or they can be easily produced by a known chemical synthesis technique.

  The alcohol compound represented by the formula (I) and the mercapto compound represented by the formula (II) react selectively and quantitatively with the terminal carboxyl group in the deteriorated polyamide-based resin, and the following general formula (I ′) :

（式中、Ｒ１〜Ｒ６は前記と同義である。）
又は、下記一般式（ＩＩ'）：

(In the formula, R1 to R6 have the same meanings as described above.)
Or the following general formula (II '):

（式中、Ｒ７〜Ｒ１２は前記と同義である。）
で表されるように、エステル結合またはチオエステル結合を形成する。

(In the formula, R7 to R12 have the same meanings as described above.)
As shown, an ester bond or a thioester bond is formed.

  Since the alcohol compound represented by the formula (I) and the mercapto compound represented by the formula (II) have the property of absorbing visible ultraviolet rays in a wavelength region of 230 nm or more, they interfere with visible ultraviolet absorption (up to 230 nm) by the polyamide. It is possible to measure the absorbance without receiving.

  Table 1 below illustrates specific examples of the alcohol compound represented by the general formula (I) and the absorption wavelength thereof. Similarly, specific examples of the mercapto compound represented by the general formula (II) and the absorption wavelength thereof are illustrated in Table 2 below.

  The modification of the carboxyl group of the deteriorated polyamide resin with the alcohol compound represented by the formula (I) or the mercapto compound represented by the formula (II) can be performed by a known ester synthesis method. Can be done.

  A polyamide resin for measuring the degree of deterioration is dissolved in a solvent. The solvent is not particularly limited as long as it dissolves the polyamide-based resin and does not chemically react with the polyamide-based resin or the aldehyde compound. For example, a fluorine-based solvent such as hexafluoroisopropanol or 2,2,2-trifluoroethanol. Etc.

  Next, an alcohol compound represented by formula (I) or a mercapto compound represented by formula (II) is added thereto, and the carboxyl group in the polyamide resin and the alcohol compound or formula represented by formula (I) ( A derivatization reaction with the mercapto compound represented by II) is performed.

  This derivatization reaction is usually carried out at 10 to 100 ° C., preferably 10 to 50 ° C., more preferably 20 to 30 ° C., for 0.1 to 100 hours, preferably 3 to 24 hours.

  The coupling product obtained by the above coupling reaction is purified by a conventional method to obtain the ester compound of the above formula (I ′) or the thioester compound of (II ′).

  Next, the absorbance of the ester compound of the above formula (I ′) or the thioester compound of (II ′) is measured by a general visible ultraviolet absorbance measurement method. The measurement wavelength is not particularly limited as long as it does not interfere with the absorption wavelength of the polyamide-based resin, but the characteristic absorption wavelength of the alcohol compound or mercapto compound to be used is preferable. For example, as shown in Table 1 and Table 2, when benzyl alcohol is used as the alcohol compound, measurement is preferably performed at 285 nm, and when benzyl mercaptan is used as the mercapto compound, measurement is performed at 269 nm. Is preferred.

  The greater the absorbance at the characteristic absorption wavelength derived from the compound of formula (I) or (II) measured by visible UV absorbance measurement, the greater the amount of carboxyl groups in the polyamide resin, i.e. hydrolysis and heat. It means that the amide bond or the like of the polyamide is cleaved due to decomposition or the like and the deterioration of the polyamide resin is progressing. In fact, a close correlation was observed between the degree of deterioration of the polyamide-based resin evaluated by the method of the present invention and the strength test result measured by a tensile test or the like, which is a conventional deterioration evaluation method.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.
"Example: Evaluation of deterioration degree of nylon 6"
(1) Polyamide resin Nylon 6 was used as a polyamide resin. Nylon 6 used an undegraded one and a hydrolyzed product obtained by hydrolyzing it (hydrolyzed at 150 ° C. for 24 hours and 48 hours).
(2) Coupling reaction between nylon 6 and alcohol compound (derivatization reaction)
Benzyl alcohol was used as the alcohol compound. After 0.1 g of the above sample (nylon 6) is dissolved in 10 ml of hexafluoroisopropanol (HFIP), 10 ml of benzyl alcohol and a condensing agent dicyclohexylcarbodiimide (DCCI) are added, and HFIP is removed by an evaporator. Esterification with benzyl alcohol was carried out at room temperature for 16 hours. This reaction solution was precipitated in methanol, and the precipitated derivative was washed with chloroform and dried.
(3) Visible UV absorbance measurement of ester compound The ester compound obtained in (2) above was dissolved in hexafluoroisopropanol to prepare a sample for absorbance measurement at a concentration of 0.01 g / 10 ml, and this was measured at a measurement wavelength of 283 nm. Was measured. The result is shown in FIG.

Further, undegraded nylon 6 and hydrolyzed nylon 6 were subjected to a tensile strength test under the following conditions in accordance with ASTM-D638-84. The results of the tensile strength test are also shown in FIG.
Test piece thickness: 3.2 mm
Dumbbell parallel part length: 50mm
Test speed: 10 mm / min (distance between chucks: 114 mm)
Test temperature: 23 ° C

  From the results of FIG. 1, the tensile strength decreases as the absorbance increases, that is, as the amount of carboxyl groups generated by hydrolysis decreases, and the degradation degree of the polyamide-based resin is chemically reduced by the method of the present invention. It turns out that it can be evaluated accurately from the side.

  FIG. 2 shows a non-derivatized nylon 6 (absorption (1)), a derivatized undegraded nylon 6 (absorption (2)), and a hydrolyzed product obtained by hydrolyzing the derivatized nylon 6 That is, those hydrolyzed at 150 ° C. for 24 hours (absorption (3)), those hydrolyzed at 150 ° C. for 48 hours (absorption (4)), and those hydrolyzed at 150 ° C. for 72 hours (absorption (5)). The visible ultraviolet absorbance measurement is shown. In the visible ultraviolet absorbance measurement, the above nylon 6 was dissolved in hexafluoroisopropanol to prepare a sample for absorbance measurement at a concentration of 0.01 g / 10 ml, and the absorbance was measured.

  From the results shown in FIG. 2, the absorption that is not seen with nylon 6 (absorption (1)) without derivatization is observed at 283 nm as the deterioration of the polyamide-based resin proceeds (absorption (2) to absorption (5)). The absorbance of is increased. That is, it can be seen that the degradation degree of the polyamide-based resin can be accurately evaluated from the chemical aspect by the method of the present invention.

  According to the present invention, it is possible to analyze the cause and mechanism of deterioration of a polyamide-based resin. In addition, the method of the present invention can be carried out if there is a very small amount of polyamide sample regardless of the size and shape, for example, a polyamide resin molded product having a curved surface, for which it was impossible to measure the degree of deterioration conventionally. But the degree of degradation can be measured.

It is a graph which shows the visible ultraviolet light absorbency measurement result and the test result of a tensile test of undeteriorated and a deteriorated nylon 6. It is a graph which shows the visible ultraviolet light absorbency measurement result after derivatization of the hydrolysis degradation nylon 6. FIG.

Claims (3)

Formula (I):

(In the formula, R ¹ is an alkylene group having 1 to 10 carbon atoms or a halogenated alkylene group having 1 to 10 carbon atoms, R ² , R ³ , R ⁴ , R ⁵ , and R ⁶ are each independently hydrogen. A group selected from the group consisting of an atom, a halogen atom, an alkyl group having 1 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a hydroxyl group, a nitro group, and an aryl group R ² , R ³ , R ⁴ , R ⁵ , and R ⁶ may form a condensed aromatic ring with adjacent groups.
An alcohol compound represented by
Or general formula (II):

(Wherein R ⁷ is an alkylene group having 1 to 10 carbon atoms or a halogenated alkylene group having 1 to 10 carbon atoms, R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² are each independently hydrogen. A group selected from the group consisting of an atom, a halogen atom, an alkyl group having 1 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a hydroxyl group, a nitro group, and an aryl group R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² may form a condensed aromatic ring with adjacent groups.
A mercapto compound represented by:
A method for evaluating the degree of deterioration of a polyamide resin, which comprises reacting a polyamide resin with a resin and measuring the visible ultraviolet absorbance of the reaction product.   2. A process according to claim 1, wherein the alcohol compound of formula (I) is benzyl alcohol.   2. The process according to claim 1, wherein the mercapto compound of the general formula (II) is benzyl mercaptan.

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