A melamine standard substance based on a polyamide substrate, and a preparation method and application thereof

Abstract

This invention discloses a melamine standard substance based on a polyamide substrate, its preparation method, and its application, belonging to the field of standard substance preparation technology. The melamine standard substance provided by this invention comprises the following components in parts by weight: 89-99 parts polyamide resin, 1-10 parts melamine cyanurate, 0.05-0.35 parts antioxidant, and 0.1-1.1 parts lubricant; the relative viscosity of the polyamide resin is ≤2.55; the antioxidant is at least one of phosphite antioxidants and hindered phenolic antioxidants; the lubricant is polyethylene wax; the apparent viscosity of the polyethylene wax at 140°C is 550-660 cps. The melamine standard substance provided by this invention exhibits excellent stability when the melamine content is in the range of 300-1000 mg / kg, and there are no significant differences within and between samples of the obtained standard substance.

Description

Technical Field

[0001] This invention relates to the field of standard substance preparation technology, specifically to a melamine standard substance based on a polyamide substrate, its preparation method, and its application. Background Technology

[0002] Food contact materials refer to various materials that come into direct contact with or may come into contact with food, and their safety is crucial for ensuring food quality and human health. An increasing number of plastic products are used in the food packaging industry. Melamine, a common contaminant in food contact materials, can migrate from plastics into food, posing a potential risk to human health. Current research on plastic-based melamine reference materials for food contact materials largely focuses on liquids such as dairy powders and methanol / water, while plastic-based reference materials are relatively scarce. Because plastics have a condensed structure, the migration patterns of melamine differ significantly from those in traditional liquid and powder forms, limiting the accurate assessment and control of melamine migration in plastic-based materials. Furthermore, the European Chemicals Agency has listed melamine as a Substance of Very High Concern, and existing melamine control measures in the electrical and electronic equipment (EIE) sector are also on the list. Since most EIE products are made of plastics, traditional dairy and liquid melamine reference materials have different forms and control limits, failing to meet the requirements for melamine control in the EIE sector. Therefore, there is an urgent need to develop plastic-based melamine reference materials.

[0003] Patent CN109883782A discloses a melamine-containing milk powder standard substance and its preparation method. It involves dissolving melamine and milk powder separately, mixing them to form a homogeneous solution, and then drying and pulverizing the solution to obtain the standard substance. However, this method directly adds melamine to the milk powder and falls under the food industry, making it unsuitable for studying the melamine content in plastics used in the electronics and electrical industries. Patent CN1233711C discloses a molecular composite melamine cyanurate flame retardant and its preparation method, focusing on the preparation method of the melamine cyanurate flame retardant but not on the study of melamine standard substances in polymer materials. Patent CN111040248A discloses a preparation method of melamine cyanurate (MCA) flame retardant and its application in PA6, focusing on the preparation method of the flame retardant and its application as a flame retardant in PA6, but not on the study of homogeneous and stable standard substances or the accurate content of melamine.

[0004] Therefore, the aforementioned publicly available literature mainly focuses on the research of melamine standard materials in food and the preparation and flame-retardant application of melamine cyanurate flame retardants, without reporting on the research of melamine standard materials in plastic substrates. Current technology still has some problems and limitations in the development of melamine standard materials for plastic substrates in the electronics and electrical fields, requiring further improvement and refinement. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a melamine standard material based on polyamide substrate with excellent stability, its preparation method and application.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a melamine standard material based on a polyamide substrate, the melamine standard material comprising the following components in parts by weight: 89-99 parts of polyamide resin, 1-10 parts of melamine cyanurate, 0.05-0.35 parts of antioxidant, and 0.1-1.1 parts of lubricant;

[0007] The relative viscosity of the polyamide resin is ≤2.55;

[0008] The antioxidant is at least one of phosphite antioxidants and hindered phenolic antioxidants;

[0009] The lubricant is polyethylene wax with an apparent viscosity of 550-660 cps at 140°C.

[0010] This invention provides a melamine standard reference material based on a polyamide substrate. By selecting appropriate mass fractions and component types, the resulting melamine standard reference material exhibits excellent stability within the melamine content range of 300-1000 mg / kg, and shows no significant intra- and inter-sample differences. Specifically, by selecting the relative viscosity of the polyamide resin within the range of this invention, good uniformity and stability are ensured for products with melamine content in the 300-1000 mg / kg range. The introduction of phosphite antioxidants and / or hindered phenolic antioxidants allows for synergistic effects with other components, resulting in good thermal stability and improved aging resistance, further enhancing the stability of the melamine standard reference material. The introduction of polyethylene wax within a specific apparent viscosity range as a lubricant allows for synergistic effects with other substances, improving the dispersibility of melamine cyanurate and ensuring the uniformity of melamine migration within the melamine standard reference material, thereby improving the uniformity and stability of the results.

[0011] The polyamide resin can be any point value or any two points within a range of 89-99 parts, for example, 90-99 parts, or 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 parts, etc.; the melamine cyanurate can be any point value or any two points within a range of 1-10 parts, for example, 2-10 parts, or 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc.; the number of parts of the antioxidant can be any point value or any two points within the range of 0.05-0.35 parts, for example, it can be 0.1-0.3 parts, or 0.05 parts, 0.08 parts, 0.1 parts, 0.12 parts, 0.15 parts, 0.18 parts, 0.2 parts, 0.22 parts, 0.25 parts, 0.28 parts, 0.3 parts, 0. 32 parts, 0.35 parts, etc.; the number of parts of the lubricant can be any point value or any two-point range value between 0.1 and 1.1 parts, for example, it can be 0.5-1 part, or 0.1 part, 0.12 parts, 0.15 parts, 0.18 parts, 0.2 parts, 0.22 parts, 0.25 parts, 0.28 parts, 0.3 parts, 0.32 parts, 0.35 parts, 0.38 parts, 0.4 parts, 0.42 parts, 0.45 parts, 0 0.48 portions, 0.5 portions, 0.52 portions, 0.55 portions, 0.58 portions, 0.6 portions, 0.62 portions, 0.65 portions, 0.68 portions, 0.7 portions, 0.72 portions, 0.75 portions, 0.78 portions, 0.8 portions, 0.82 portions, 0.85 portions, 0.88 portions, 0.9 portions, 0.92 portions, 0.95 portions, 0.98 portions, 1 portion, 1.02 portions, 1.05 portions, 1.08 portions, 1.1 portions, etc.

[0012] In a preferred embodiment of the melamine standard material of the present invention, the antioxidant has a mass percentage between 0.08% and 0.5%, and the lubricant has a mass percentage between 0.1% and 2%.

[0013] The relative viscosity of the polyamide resin was tested according to ISO 307-2019. Specifically, the method for detecting and calculating the relative viscosity is as follows: Weigh 0.5g of polyamide resin, transfer it to a 50mL volumetric flask, add 40mL of 96% concentrated sulfuric acid, and sonicate until the polyamide resin is completely dissolved. Cool the solution to 25°C, dilute it to the mark with concentrated sulfuric acid, and mix it evenly. Measure the flow time of the 0.01g / mL polyamide resin solution at 25°C through an Ubbelohde viscometer, and record it as t1. Measure the flow time of the concentrated sulfuric acid solvent using the same viscometer, and record it as t2. t1 / t2 is the relative viscosity.

[0014] The apparent viscosity of the polyethylene wax at 140°C was obtained according to ASTM D1986-14.

[0015] In a preferred embodiment of the melamine standard material of the present invention, the polyamide resin is at least one of polyamide 6 and polyamide 66.

[0016] The present invention has found that, based on polyamide substrates, when polyamide 6 and polyamide 66 are further selected as the polyamide substrates, the obtained melamine standard material exhibits superior uniformity and stability.

[0017] In a preferred embodiment of the melamine standard material of the present invention, the polyamide resin has a relative viscosity of 1.65-2.45.

[0018] The present invention has found that the relative viscosity of polyamide resin has a certain impact on the stability and uniformity of the product. When the relative viscosity of polyamide resin is further selected to be 1.65-2.45, the overall performance of the product is even better.

[0019] For example, the relative viscosity of the polyamide resin can be any point value or any two-point range between 1.65 and 2.45, such as 1.68-2.4, or 1.65, 1.68, 1.70, 1.72, 1.74, 1.76, 1.78, 1.80, 1.82, 1.84, 1.86, 1.90, 1.92, 1.94, 1.96, 1.98, 2.00, 2.02, 2.04, 2.06, 2.08, 2.10, 2.12, 2.14, 2.16, 2.18, 2.20, 2.22, 2.24, 2.26, 2.28, 2.30, 2.32, etc.

[0020] 2.34, 2.36, 2.38, 2.40, 2.42, 2.45, etc.

[0021] In a preferred embodiment of the melamine standard material of the present invention, the antioxidant is at least one of antioxidant 168, antioxidant 608, and antioxidant PEP36.

[0022] This invention has found that both phosphite antioxidants and hindered phenolic antioxidants can effectively improve the aging resistance, uniformity, and stability of products. For example, the hindered phenolic antioxidants can be hindered phenol 1010 and hindered phenol 1098, etc., and the phosphite antioxidants can be antioxidants 168, 608, PEP36, etc. However, when further selecting phosphite antioxidants 168, 608, and PEP36, the prepared melamine standard material is more stable and uniform.

[0023] As a preferred embodiment of the melamine standard material of the present invention, the polyethylene wax has an apparent viscosity of 570-580 cps at 140°C.

[0024] The present invention has found that further selecting the apparent viscosity of polyethylene wax at 140°C within the above-mentioned range can better ensure the uniformity of melamine migration in melamine standard materials.

[0025] In a second aspect, the present invention provides a method for preparing the melamine standard substance, the method comprising the following steps: mixing the components uniformly, melt extruding, and granulating to obtain the melamine standard substance.

[0026] In a preferred embodiment of the preparation method described in this invention, the temperature of the melt extrusion is 210-250℃ and the rotation speed is 250-350rpm.

[0027] The method for preparing melamine standard material provided by this invention is simple to operate and beneficial to actual production.

[0028] In a third aspect, the present invention provides the application of the melamine standard material in evaluating the amount of melamine migration in plastic materials.

[0029] The melamine standard material provided by this invention has excellent uniformity and long-term and short-term stability. Furthermore, by further pulverizing or injection molding the standard material in different forms, it can be used to evaluate the requirements for melamine control under the REACH regulation in plastic materials used in electronic and electrical applications.

[0030] The beneficial effects of this invention are:

[0031] This invention provides a melamine standard reference material based on a polyamide substrate. By selecting appropriate mass fractions and component types, the resulting melamine standard reference material exhibits excellent stability within the melamine content range of 300-1000 mg / kg, and shows no significant intra- and inter-sample differences. Furthermore, the melamine standard reference material provided by this invention can be prepared in different forms, thus meeting the application requirements for evaluating melamine migration in plastic materials. In addition, the preparation method of the melamine standard reference material provided by this invention is simple to operate and beneficial for practical production applications. Detailed Implementation

[0032] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and comparative examples. The purpose of this description is to provide a detailed understanding of the invention, not to limit its scope. All other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of this invention. Unless otherwise specified, the experimental reagents and instruments designed in the embodiments and comparative examples of this invention are commonly used reagents and instruments; and the raw materials used in the parallel experiments of the embodiments and comparative examples of this invention are consistent.

[0033] The raw materials used in the various embodiments, comparative examples, and effect examples of this invention are as follows:

[0034] Polyamide resin 1: PA66, PA66 EPR 24, relative viscosity is 2.36, Henan Shenma Co., Ltd.;

[0035] Polyamide resin 2: PA6, PA6 M2400, relative viscosity is 2.4, Sinopec Baling Petrochemical;

[0036] Polyamide resin 3: PA12, PA12 VESTAMID L1940 NC, relative viscosity 1.68, Evonik Degussa (China) Investment Co., Ltd.;

[0037] Polyamide resin 4: PA66, PA66 EP158NH, relative viscosity 2.53, Zhejiang Huafeng Group Co., Ltd.;

[0038] Polyamide resin 5: PA66, PA66 EPR 27, relative viscosity is 2.65, Henan Shenma Co., Ltd.;

[0039] Melamine cyanurate (MCA): Purity ≥ 99.5%, Sichuan Fine Chemical Research and Design Institute;

[0040] Melamine hydrobromide (MHB): Purity ≥99%, Wuhan Xingzhongcheng Technology Co., Ltd.;

[0041] Antioxidant 1: Antioxidant 608, a phosphite antioxidant, commercially available;

[0042] Antioxidant 2: Antioxidant PEP36, a phosphite antioxidant, commercially available;

[0043] Antioxidant 3: Antioxidant 1098, hindered phenolic antioxidant, commercially available;

[0044] Antioxidant 4: Antioxidant 412s, a thioester antioxidant, commercially available;

[0045] Lubricant 1: Polyethylene wax AC-540A, apparent viscosity (@140℃) 575cps, Honeywell, USA;

[0046] Lubricant 2: Polyethylene wax, AC 5120, apparent viscosity (@140℃) 600cps, Honeywell, USA;

[0047] Lubricant 3: Polyethylene wax, AC 580, apparent viscosity (@140℃) 650cps, Honeywell, USA;

[0048] Lubricant 4: Polyethylene wax, AC 629, apparent viscosity (@140℃) 200cps, Honeywell, USA;

[0049] Lubricant 5: Polyethylene wax, AC 725P, apparent viscosity (@140℃) 1400cps, Honeywell, USA.

[0050] Examples 1-10 and Comparative Examples 1-9

[0051] The present invention provides a melamine standard substance in the embodiments and comparative examples, wherein the component (parts by mass) content of the melamine standard substance is shown in Table 1-2;

[0052] Table 1

[0053]

[0054] Table 2

[0055]

[0056]

[0057] The preparation method of the melamine standard material provided in Example 1 is as follows:

[0058] (1) Weigh each component according to the component content in Table 1 and mix them evenly;

[0059] (2) Melt extrusion and granulation were carried out by twin-screw extruder and injection molding machine at a processing temperature of 240℃ to obtain melamine standard material;

[0060] Granulation process parameters: Feed rate controlled at 450 kg / h; temperature control for each zone as follows: Zone 1 120±10℃, Zone 2 220±10℃, Zone 3 240±10℃, Zone 4 240±10℃, Zone 5 240±10℃, Zone 6 240±10℃, Zone 7 240±10℃, Zone 8 240±10℃, Zone 9 240±10℃. Injection molding process parameters: Injection temperature 240℃, injection speed 35 mm / s, injection pressure 40 MPa, injection time 6 s, holding pressure 45 MPa, holding time 20 s, melt speed 55 mm / s, melt pressure 60 MPa, back pressure gauge controlled at 10-15 MPa, cooling time 15 s.

[0061] The preparation methods of the melamine standard substances in Examples 2-10 and Comparative Examples 1-9 are consistent with those in Example 1.

[0062] Example of effect

[0063] The homogeneity and stability of the melamine standard materials prepared in Examples 1-10 and Comparative Examples 1-9 were tested. Ten groups of melamine standard materials prepared in Examples 1-10 and Comparative Examples 1-9 were randomly selected, pulverized with liquid nitrogen, and subjected to migration experiments using methanol as the extraction solvent, in accordance with GB / T 22388-2008. Quantitative analysis of melamine was performed using chromatography and chromatography-mass spectrometry.

[0064] 1. Homogeneity: Each group of samples was tested twice, and the test results were analyzed using one-way ANOVA (F test). If the F value was less than the specified limit (F0.05(9,10)=3.02), it indicated that there was no significant difference within and between samples, and the samples were homogeneous.

[0065] 2. Stability: Stability is another important parameter for evaluating standard substances. When examining whether there is a difference between the average values ​​of two sets of data, the independent samples t-test can be used to evaluate the stability of the standard substance. If the relationship between the statistic t and ta at the significance level a and degrees of freedom f = n1 + n2 - 2 is t < ta(f), then the characteristic value of the standard substance is considered to have not changed significantly; otherwise, the characteristic value of the standard substance is considered to have changed significantly. After sealing and storing the standard samples at room temperature in the dark for 6 months, 10 sets of samples were randomly selected from the standard samples, and migration experiments were performed using methanol as the extraction solvent. Melamine was quantitatively tested using chromatography and chromatography-mass spectrometry. The test results were analyzed using the t-test. If the t value is less than the specified limit (t0.05(20+20-2) = 2.024), it proves that the standard substance has not changed significantly.

[0066] The statistical value t is obtained using the following formula:

[0067] In the formula The average of n measurements:

[0068]

[0069] Note: To ensure the accuracy of the mean and standard deviation, n ≥ 6;

[0070] If t < significance level a (usually a = 0.05) and the critical value ta(n-1) with n-1 degrees of freedom, then there is no significant difference between the mean and the standard / reference value.

[0071] The test results are shown below:

[0072] 1) The homogeneity test results of the melamine standard material prepared in Example 1 are shown in Table 3, and the stability test results are shown in Table 4.

[0073] Table 3

[0074]

[0075] Table 4

[0076]

[0077] 2) The homogeneity test results of the melamine standard material prepared in Example 2 are shown in Table 5, and the stability test results are shown in Table 6.

[0078] Table 5

[0079]

[0080] Table 6

[0081]

[0082] 3) The homogeneity test results of the melamine standard material prepared in Comparative Example 5 are shown in Table 7, and the stability test results are shown in Table 8.

[0083] Table 7

[0084]

[0085] Table 8

[0086]

[0087]

[0088] 4) The F-values, total average values ​​of stability tests, total average values ​​of homogeneity tests, and t-values ​​of the melamine standard substances obtained from Examples 1-10 and Comparative Examples 1-9 are recorded in Table 9.

[0089] Table 9

[0090]

[0091] As can be seen from Table 7, the standard samples of each embodiment of the present invention have excellent uniformity and stability. After multiple sampling and testing, the melamine migration test results of multiple samples are very close, and the F value is ≤0.95. During the long-term storage of 6 months, the melamine migration test results in the standard samples are still stable and close to the first test results, with a t value ≤0.86, indicating that the standard samples have good stability.

[0092] The mass fractions of components in Comparative Examples 1-4 are outside the scope of this invention, resulting in significantly worse stability and uniformity of the obtained melamine standard substances, with F values ​​all greater than 3.02 and t values ​​all greater than 2.02. In Comparative Example 5, the parameters of the polyamide resin are outside the range given in this invention, resulting in a melamine content in the product exceeding 1000 mg / kg. This is mainly due to increased relative viscosity of the resin, and the shear heating during processing leading to a final temperature rise, which promoted melamine production. Furthermore, the stability and uniformity of the resulting product did not meet the requirements. In Comparative Example 6, when MHB was used instead of MCA, the obtained product exhibited melamine hydrobromic acid... The weak salt binding force leads to a high free melamine content. During processing, severe resin degradation causes severe foaming, making granulation difficult and significantly reducing the uniformity and stability of the resulting product. In Comparative Example 7, the stability of the product is significantly worse, with a t-value greater than 2.02. In Comparative Examples 8-9, when the apparent viscosity of the polyethylene wax is outside the range given in this invention, the melamine content in the resulting product is higher than 1000 mg / kg. This is mainly due to the mismatch between the lubricant and the components in the system, which causes the decomposition of melamine cyanurate. Furthermore, the uniformity and stability of the product are also significantly worse.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A melamine standard material based on a polyamide substrate, characterized in that, The melamine standard material comprises the following components in parts by weight: 89-99 parts polyamide resin, 1-10 parts melamine cyanurate, 0.05-0.35 parts antioxidant, and 0.1-1.1 parts lubricant; The relative viscosity of the polyamide resin is ≤2.55; the relative viscosity of the polyamide resin is tested according to ISO 307-2019; the method for detecting and calculating the relative viscosity is as follows: weigh 0.5g of polyamide resin, transfer it to a 50 mL volumetric flask, add 40 mL of 96% concentrated sulfuric acid, ultrasonically vibrate until the polyamide resin is completely dissolved, cool the solution to 25℃, dilute it to the mark with concentrated sulfuric acid, and mix it evenly. Test the flow time of the 0.01g / mL polyamide resin solution at 25℃ through the Ubbelohde viscometer, and record it as t1. Test the flow time of the solvent concentrated sulfuric acid through the same viscometer, and record it as t2. t1 / t2 is the relative viscosity. The antioxidant is at least one of phosphite antioxidants and hindered phenolic antioxidants; The lubricant is polyethylene wax; the apparent viscosity of the polyethylene wax at 140°C is 550-660 cps; the apparent viscosity of the polyethylene wax at 140°C is obtained by testing with reference to ASTM D1986-14.

2. The melamine standard material according to claim 1, characterized in that, The polyamide resin is at least one of polyamide 6 and polyamide 66.

3. The melamine standard material according to claim 1, characterized in that, The relative viscosity of the polyamide resin is 1.65-2.

45.

4. The melamine standard material according to claim 1, characterized in that, The antioxidant is at least one of antioxidant 168, antioxidant 608, and antioxidant PEP36.

5. The melamine standard material according to claim 1, characterized in that, The apparent viscosity of the polyethylene wax at 140°C is 570-580 cps.

6. The method for preparing the melamine standard substance according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: mixing the components evenly, melt extruding, and granulating to obtain melamine standard material.

7. The preparation method according to claim 6, characterized in that, The temperature of the melt extrusion is 190-250℃, and the rotation speed is 250-350rpm.

8. The application of the melamine standard material as described in any one of claims 1-5 in evaluating the migration amount of melamine in plastic materials.

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