A method for studying the migration rule of styrene in air in ABS plastic toys based on static headspace technology

Abstract

This invention discloses a method for studying the migration law of styrene in ABS plastic toys in the air based on static headspace technology. It relates to the technical field of styrene migration law research in ABS plastic toys. The key technical points are: studying the migration law of styrene in ABS plastic toys based on Fick's first law and the law of conservation of mass; constructing a migration model of styrene in ABS plastic toys; obtaining the diffusion coefficient and distribution coefficient of styrene using curve fitting; and then predicting the migration law and maximum migration amount of styrene in ABS plastic toys in the air using the fitted formula. This method has the advantages of being fast, simple, time-saving, and labor-saving, effectively reducing the safety risks of plastic toys and improving detection efficiency, which is of great significance for protecting children's healthy growth.

Description

Technical Field

[0001] This invention relates to the field of styrene migration law research in ABS plastic toys, and more specifically, it relates to a method for studying the migration law of styrene in ABS plastic toys in the air based on static headspace technology. Background Technology

[0002] ABS is a rigid plastic polymerized from acrylonitrile, butadiene, and styrene, widely used in the production of interlocking building blocks, model toys, and other plastic toys. Styrene easily remains in plastic toys as unpolymerized monomers, migrating into the air and being inhaled by children, posing a health hazard. Long-term exposure to styrene can irritate and numb the eyes and upper respiratory tract, and may cause obstructive pulmonary disease and reproductive disorders. It has been classified as a Group 2B carcinogen by the International Agency for Research on Cancer (IARC). Therefore, styrene is listed in the US Toxic Substances Control Act (TSCA) and the Washington List of Substances of Very High Concern for Children (CHCC). The EU Toy Safety Directive harmonizes standard EN71-9, which sets the migration limit for styrene in children's toys at 0.75 mg / L.

[0003] However, current research on the migration behavior of styrene in plastic toys mainly focuses on its migration in solution, and there are no methods for studying the migration behavior of styrene in plastic toys in the air. Summary of the Invention

[0004] The purpose of this invention is to provide a method for studying the migration behavior of styrene in ABS plastic toys in the air based on static headspace technology. This method combines curve fitting to obtain the distribution coefficient and diffusion coefficient of styrene in ABS plastic toys at a specific equilibrium temperature, establishes a migration model, and effectively studies the migration behavior of styrene in plastic toys in the air.

[0005] 1. The above-mentioned technical objective of this invention is achieved through the following technical solution: a method for studying the migration law of styrene in ABS plastic toys in the air based on static headspace technology, comprising the following steps:

[0006] S1. Determine the total amount of styrene in ABS plastic;

[0007] S2. Determine the migration amount of styrene;

[0008] S3. Obtain a model of the migration law of styrene in ABS plastic in air, and obtain the diffusion coefficient D and partition coefficient K of the model;

[0009] S4. Predict the maximum migration of styrene at phase equilibrium.

[0010] The present invention is further configured as follows: the specific operation for determining the total amount of styrene in ABS plastic in S1 is as follows: ABS plastic is crushed to 1 mm, 0.1 g is weighed into a 20 mL headspace vial, 2 mL of N,N-dimethylformamide is added, shaken to dissolve, sealed, placed in a headspace sampler, and the total amount of styrene in ABS plastic is determined by gas chromatography-mass spectrometry.

[0011] The present invention is further configured as follows: the specific operation for determining the migration amount of styrene in S2 is as follows: prepare an ABS plastic sample of 5cm*4mm*4mm, seal four of its surfaces with wax, leaving two 5cm*4mm surfaces in the vertical direction, place the sample in a headspace vial, with the unsealed side in contact with the bottom of the headspace vial, and migrate within the headspace vial at a specific equilibrium temperature for a migration time of 10 to 150 minutes, and determine the migration amount of styrene by gas chromatography-mass spectrometry.

[0012] The present invention is further configured such that, in the headspace injection method of S2, the equilibrium temperature is preferably 40°C.

[0013] The present invention is further configured such that the working conditions of the headspace bottle in S2 are:

[0014] (1) The metering loop temperature is 60℃;

[0015] (2) The transmission line temperature is 80℃;

[0016] (3) The quantitative loop is 1000 μL.

[0017] The present invention is further configured such that the instrument operating conditions for determining the migration amount of styrene by gas chromatography-mass spectrometry in S2 are as follows:

[0018] (1) The injection port temperature is 250℃;

[0019] (2) The heating program is as follows: hold at 40℃ for 5 minutes, then increase the temperature to 250℃ at 5℃ / min, and hold for another 5 minutes;

[0020] (3) The flow rate of helium is 1.5 mL / min.

[0021] The present invention is further configured as follows: the specific operation of obtaining the migration law model of styrene in ABS plastic in air in S3 and obtaining the diffusion coefficient D and the distribution coefficient K of the model is as follows: combining Fick's first law and the mass conservation relationship, the migration amount at different migration times is curve fitted, and combined with the total amount measured in step (1), the migration law model of styrene in ABS plastic in air is obtained, and the diffusion coefficient D and the distribution coefficient K of the model are obtained.

[0022] The present invention is further configured such that: in step S3, by combining Fick's first law and the law of conservation of mass, a migration law model of styrene in ABS plastic in air is obtained, and the diffusion coefficient D and partition coefficient K of the model are obtained in the following specific process:

[0023] S31. The migration process of styrene in S3 is described by Fick's first law as shown in equation (1):

[0024]

[0025] In the formula, J is the diffusion flux, g / (m 2 s); m s S is the mass of styrene in the sample, in grams; S is the base area of ​​the sample, in centimeters. 2 t is the migration time, in seconds; D is the diffusion coefficient of styrene in the sample, in cm. 2 / s;c s and c s * , respectively, represent the concentrations of styrene at the sample center and sample interface, in g / mL; h is the height of the sample, in cm;

[0026] S32. When the migration of styrene in the air in S3 reaches equilibrium, equation (2) can be obtained.

[0027]

[0028] In the formula, c g * is the concentration of styrene at the gas phase interface, in g / mL; K is the partition coefficient of styrene in the sample;

[0029] S33. Since the diffusion rate of styrene in the gas phase is much greater than that in the sample, it is assumed that the concentration of styrene at the gas phase interface is the same as that in the gas phase, i.e., equation (3).

[0030]

[0031] S34. According to the law of conservation of mass, we can obtain equation (4) in the headspace bottle.

[0032] m = m s +m g =c s V s +c g V g (4)

[0033] In the formula, m is the total mass of styrene in the sample before volatilization, in grams; m s m g These represent the mass of styrene in the headspace vial sample and in the gas phase, respectively, in grams; Vs V g It is the volume of the sample and the volume of the gas phase in the headspace vial;

[0034] S35. According to the law of conservation of mass, the mass of styrene that decreases from the sample per unit time in the headspace vial is equal to the mass of styrene that increases in the gas phase, which gives equation (5).

[0035]

[0036] The present invention is further configured such that by combining equations (1)-(5), equation (6) can be obtained.

[0037]

[0038] in, γ=V g +KV s .

[0039] The present invention is further configured such that, based on the initial conditions, t = 0, c g =0, solving equation (6) yields equation (7).

[0040]

[0041] The present invention is further configured such that: based on equation (7), combined with the curve fitting method, the distribution coefficient K and diffusion coefficient D can be calculated when the total amount of styrene in the sample is known, using the curve fitting formula measured at different equilibrium times.

[0042] The present invention is further configured such that the specific operation of predicting the maximum migration amount of styrene at phase equilibrium in S4 is as follows: using the diffusion coefficient D and the partition coefficient K obtained in S3, and given the total content of styrene, the maximum migration amount of styrene at phase equilibrium can be calculated by combining the fitted equation.

[0043] In summary, this invention has the following beneficial effects: Taking ABS plastic toys containing styrene as the research object, this invention studies the migration law of styrene in ABS plastic in the air based on static headspace technology combined with gas chromatography-mass spectrometry, and establishes a rapid and effective method for studying the migration law of styrene in the air. By combining curve fitting method to construct a migration model to obtain diffusion coefficient and partition coefficient, the maximum migration amount of styrene can be predicted by using diffusion coefficient and partition coefficient given the total styrene content. This method has the advantages of being fast, simple, time-saving and labor-saving, and can effectively reduce the safety risks of plastic toys and improve detection efficiency, which is of great significance for protecting children's healthy growth. Attached Figure Description

[0044] Figure 1This is the migration curve of styrene in the headspace vial in an embodiment of the present invention. Detailed Implementation

[0045] The following is in conjunction with the appendix Figure 1 The present invention will be described in further detail below.

[0046] Example 1: A method for studying the migration pattern of styrene in ABS plastic toys in air based on static headspace technology, comprising the following steps:

[0047] 1. Crush ABS plastic to 1 mm, weigh 0.1 g into a 20 mL headspace vial, add 2 mL of N,N-dimethylformamide, shake to dissolve, seal, place in a headspace sampler, and determine the total amount of styrene in the ABS plastic by gas chromatography-mass spectrometry.

[0048] 2. Prepare an ABS plastic sample of 5cm*4mm*4mm, seal four of its surfaces with wax, leaving two 5cm*4mm surfaces in the vertical direction, place the sample in a headspace vial, and allow it to migrate within the headspace vial at a specific equilibrium temperature for 10–150 min. Determine the amount of styrene migrated using gas chromatography-mass spectrometry.

[0049] 3. Combining Fick's first law and the law of conservation of mass, curve fitting was performed on the migration amount at different migration times. Combined with the total amount measured in step (1), the migration law model of styrene in ABS plastic in air was obtained: diffusion coefficient D and distribution coefficient K.

[0050] 4. Using the diffusion coefficient D and partition coefficient K obtained in step (3), the maximum migration amount of styrene at phase equilibrium can be predicted given the total styrene content.

[0051] Example 2:

[0052] (1) Instruments and experimental conditions

[0053] Instruments and reagents

[0054] Static headspace sampler (7697A, Agilent Technologies, USA); Gas chromatography system (7890B, Agilent Technologies, USA); Mass selection detector (5977A, Agilent Technologies, USA).

[0055] Styrene standard stock solution: Weigh an appropriate amount of styrene (purity not less than 98%) standard substance (accurate to 0.1 mg), and prepare a solution with a mass concentration of 100 mg·L⁻¹ using tetrahydrofuran. -1 The stock solution.

[0056] Instrument operating conditions

[0057] The equilibrium temperature was 40℃, the quantitative loop temperature was 60℃, the transfer line temperature was 80℃, the equilibrium time was 10-150 min, and the quantitative loop volume was 1000 μL. A DB-5MS capillary column (30 m × 320 μm × 0.25 μm, Agilent) was used. The helium flow rate as the carrier gas was 1.5 mL / min. The injection port temperature was set to 250℃. The temperature program was: hold at 40℃ for 5 minutes, then increase to 250℃ at 5℃ / min, and hold for another 5 minutes. The quantitative ion for styrene was m / z 104, and the auxiliary qualitative ions were m / z 78 and 51.

[0058] (2) Experimental methods

[0059] a) Determine the total amount of styrene

[0060] The ABS plastic sample was crushed to 1 mm, 0.1 g was weighed into a 20 mL headspace vial, 2 mL of N,N-dimethylformamide was added, the vial was shaken to dissolve, sealed, and placed into a headspace sampler. The total amount of styrene in the ABS plastic was determined by gas chromatography-mass spectrometry.

[0061] b) Determine the migration amount of styrene

[0062] Prepare a 5cm*4mm*4mm ABS plastic sample, seal four of its surfaces with wax, leaving two 5cm*4mm surfaces in the vertical direction, place the sample in a headspace vial, and allow it to migrate within the headspace vial at a specific equilibrium temperature for 10–150 min. The amount of styrene migrated is determined by gas chromatography-mass spectrometry.

[0063] (3) Research on migration patterns

[0064] When an ABS plastic sample is placed in a headspace vial, styrene will gradually evaporate from the sample into the headspace vial and reach equilibrium. To simplify the calculation, it is assumed that the styrene is uniformly distributed in the sample, and the concentration of styrene at the center of the sample is used instead of the concentration of styrene in the sample; it is assumed that the partition coefficient K and diffusion coefficient D are constant throughout the migration process; it is assumed that the styrene enters the air on the side of the sample that is not sealed with wax; and it is assumed that the entire process conforms to Fick's law.

[0065] The migration process of styrene can be described using Fick's first law, i.e., equation (1).

[0066]

[0067] In the formula, J is the diffusion flux, g / (m 2 s); ms is the mass of styrene in the sample, in g; S is the base area of ​​the sample, in cm². 2 t is the migration time, in seconds; D is the diffusion coefficient of styrene in the sample, in cm. 2 / s;cs and c s * , respectively, represent the concentrations of styrene at the sample center and sample interface, in g / mL; h is the height of the sample, in cm.

[0068] When equilibrium is reached, equation (2) can be obtained.

[0069]

[0070] In the formula, c g * It represents the concentration of styrene at the gas phase interface, in g / mL.

[0071] Since the diffusion rate of styrene in the gas phase is much greater than that in the sample, it is assumed that the concentration of styrene at the gas phase interface is the same as that in the gas phase, i.e., equation (3).

[0072]

[0073] According to the law of conservation of mass, we can obtain equation (4) for the headspace bottle.

[0074] m = m s +m g =c s V s +c g V g (4)

[0075] In the formula, m is the total mass of styrene in the sample before volatilization, in grams; m s m g These represent the mass of styrene in the headspace vial sample and in the gas phase, respectively, in grams; V s V g It refers to the volume of the sample and the volume of the gas phase within the headspace vial.

[0076] According to the law of conservation of mass, the mass of styrene that decreases from the sample per unit time in the headspace vial is equal to the mass of styrene that increases in the gas phase, which gives equation (5).

[0077]

[0078] Combining equations (1)-(5), we obtain equation (6).

[0079]

[0080] in, γ=V g +KV s .

[0081] (37) Based on the initial conditions, t = 0, c g=0, solving equation (6) yields equation (7).

[0082]

[0083] As can be seen from equation (7), by combining the curve fitting method and using the curve fitting formulas obtained at different equilibrium times, the distribution coefficient K and diffusion coefficient D can be calculated when the total amount of styrene in the sample is known.

[0084] according to Figure 1 The fitted equation is

[0085]

[0086] That is y=0.001(1-e -0.028x Substituting the data, we obtain the distribution coefficient of styrene in air at an equilibrium temperature of 40℃ as K = 460, and the diffusion coefficient as D = 4.05 × 10⁻¹² m² / s.

[0087] (4) Prediction of maximum migration

[0088] Based on the above measurements, the total amount of styrene in ABS plastic is 11.87 mg / kg. According to the fitted equation, the maximum migration amount of styrene in ABS plastic can be calculated to be 0.026 mg / kg.

[0089] In summary, this patent studies the migration law of styrene in ABS plastic toys based on Fick's first law and the law of conservation of mass. It constructs a migration model of styrene in ABS plastic toys, obtains the diffusion coefficient and distribution coefficient of styrene by combining curve fitting method, and then predicts the migration law and maximum migration amount of styrene in ABS plastic toys in the air through the fitted formula. This method has the advantages of being fast, simple, time-saving and labor-saving, and can effectively reduce the safety risks of plastic toys and improve detection efficiency, which is of great significance for protecting children's healthy growth.

[0090] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for studying the migration patterns of styrene in ABS plastic toys in air based on static headspace technology, characterized by: Includes the following steps: S1. Determine the total amount of styrene in ABS plastic; S2. Determine the migration amount of styrene; S3. Obtain a model of the migration law of styrene in ABS plastic in air, and obtain the diffusion coefficient D and partition coefficient K of the model: The specific steps for obtaining the migration law model of styrene in ABS plastic in air in S3, and obtaining the diffusion coefficient D and distribution coefficient K of the model are as follows: Combining Fick's first law and the mass conservation relationship, the migration amount at different migration times is curve-fitted, and combined with the total amount measured in S1, the migration law model of styrene in ABS plastic in air is obtained, and the diffusion coefficient D and distribution coefficient K of the model are obtained. In step S3, combining Fick's first law and the law of conservation of mass, a migration model of styrene in ABS plastic in air is obtained, and the specific process of obtaining the diffusion coefficient D and the partition coefficient K of this model is as follows: S31. The migration process of styrene in S3 is described by Fick's first law as shown in equation (1): （1） In the formula, J is the diffusion flux, g / (m 2 s); m s S is the mass of styrene in the sample, in grams; S is the base area of ​​the sample, in centimeters. 2 ; t is the migration time, in seconds; D is the diffusion coefficient of styrene in the sample, in cm. 2 / s; c s and c s * , respectively, represent the concentrations of styrene at the sample center and sample interface, in g / mL; h is the height of the sample, in cm; S32. When the migration of styrene in the air in S3 reaches equilibrium, equation (2) can be obtained. （2） In the formula, c g * is the concentration of styrene at the gas phase interface, in g / mL; K is the partition coefficient of styrene in the sample; S33. Since the diffusion rate of styrene in the gas phase is much greater than that in the sample, it is assumed that the concentration of styrene at the gas phase interface is the same as that in the gas phase, i.e., equation (3). （3） S34. According to the law of conservation of mass, we can obtain equation (4) in the headspace bottle. （4） In the formula, m is the total mass of styrene in the sample before volatilization, in grams; m s m g These represent the mass of styrene in the headspace vial sample and in the gas phase, respectively, in grams; V s V g It is the volume of the sample and the volume of the gas phase in the headspace vial; S35. According to the law of conservation of mass, the mass of styrene that decreases from the sample per unit time in the headspace vial is equal to the mass of styrene that increases in the gas phase, which gives equation (5). （5）； Combining equations (1) and (5), we can obtain equation (6). （6） in, ; ; Based on the initial conditions, t=0, =0, solving equation (6) yields equation (7). （7）； According to equation (7), combined with the curve fitting method, the distribution coefficient K and diffusion coefficient D can be calculated using the curve fitting formulas measured at different equilibrium times when the total amount of styrene in the sample is known. S4. Predict the maximum migration of styrene at phase equilibrium.

2. The method for studying the migration law of styrene in air in ABS plastic toys based on static headspace technology according to claim 1, characterized in that: The specific procedure for determining the total amount of styrene in ABS plastic in S1 is as follows: ABS plastic is crushed to 1 mm, 0.1 g is weighed into a 20 mL headspace vial, 2 mL of N,N-dimethylformamide is added, shaken to dissolve, sealed, and placed into a headspace sampler. The total amount of styrene in ABS plastic is determined by gas chromatography-mass spectrometry.

3. The method for studying the migration law of styrene in air in ABS plastic toys based on static headspace technology according to claim 1, characterized in that: The specific procedure for determining the migration amount of styrene in S2 is as follows: Prepare an ABS plastic sample of 5cm*4mm*4mm, seal four of its surfaces with wax, leaving two 5cm*4mm surfaces in the vertical direction, place the sample in a headspace vial with the unsealed side in contact with the bottom of the headspace vial, and allow it to migrate within the headspace vial at a specific equilibrium temperature for 10~150min. The migration amount of styrene is determined by gas chromatography-mass spectrometry.

4. The method for studying the migration law of styrene in air in ABS plastic toys based on static headspace technology according to claim 3, characterized in that: In the headspace sampling method described in S2, the equilibrium temperature is 40°C.

5. The method for studying the migration law of styrene in air in ABS plastic toys based on static headspace technology according to claim 3, characterized in that: The operating conditions of the headspace bottle in S2 are as follows: (1) The metering ring temperature is 60℃; (2) The transmission line temperature is 80℃; (3) The quantitative loop is 1000 μL.

6. The method for studying the migration law of styrene in air in ABS plastic toys based on static headspace technology according to claim 3, characterized in that: The instrument operating conditions for determining the migration of styrene by gas chromatography-mass spectrometry in S2 are as follows: (1) The injection port temperature is 250℃; (2) The heating program is as follows: hold at 40℃ for 5 minutes, then increase the temperature to 250℃ at 5℃ / min, and hold for another 5 minutes; (3) The flow rate of helium is 1.5 mL / min.

7. The method for studying the migration law of styrene in air in ABS plastic toys based on static headspace technology according to claim 1, characterized in that: The specific operation for predicting the maximum migration amount of styrene at phase equilibrium in S4 is as follows: using the diffusion coefficient D and partition coefficient K obtained in S3, and given the total styrene content, the maximum migration amount of styrene at phase equilibrium can be calculated by combining the fitted equation.

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