Preparation method of phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material

Abstract

The invention discloses a preparation method of a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material, which comprises the following steps: adding a maleic anhydride modified DOPO phosphorus-containing flame retardant and zinc hydroxystannate into a nylon 6 resin matrix, feeding into a twin-screw extruder, directly blending and granulating to obtain resin master batch, drying the resin master batch, and then carrying out injection molding to obtain the phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material. The phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material is obtained; the flame-retardant nylon 6 is prepared from the following components in parts by mass: 90 to 98 parts of nylon 6, 1 to 5 parts of maleic anhydride modified 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO (9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) phosphorus-containing flame retardant and 1 to 5 parts of zinc hydroxystannate. The halogen-free flame-retardant nylon 6 composite material prepared by the invention greatly enhances the flame-retardant efficiency of DOPO (9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), and is combined with the smoke suppression effect of zinc hydroxystannate, so that the flame-retardant grade of the composite material is V-0 grade under the condition of low addition amount, the limit oxygen index reaches 32.6%, the total heat release amount is reduced by 62%, and the heat release peak value is reduced by 43.6%.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of halogen-free flame-retardant nylon polymer materials, and particularly relates to a method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material. Background Art

[0002] Engineering plastic nylon 6 is a polymer compound, also known as PA6, polyamide 6, and nylon 6, with a chemical formula of (C6HNO) n It has not been flame retardant modified, and its flame retardancy is low. Vertical combustion can only reach UL94 V-2 level, and the oxygen index is about 24. It produces dripping during the combustion process, which is very easy to cause a fire. Especially in the field of electronic products, there are many fires caused by nylon, causing great losses. At present, the application of nylon materials in the electronics industry is becoming more and more popular. Therefore, it is urgent to improve the flame retardancy of nylon 6.

[0003] The research on flame retardant nylon must first solve the problem of flame retardant selection, and generally the main considerations are flame retardant efficiency, product performance, toxicity and other aspects. Although traditional halogen flame retardants have high flame retardant efficiency, they are prone to emit toxic smoke and gas during the combustion process, which is very harmful to the environment and is increasingly being banned. Traditional inorganic hydroxides have the disadvantage of large addition amounts affecting the mechanical properties of the material. Therefore, it is very important to develop new, efficient, halogen-free, environmentally friendly, flame retardant systems or flame retardant synergistic enhancement systems that are halogen-free and have high flame retardant efficiency. Both phosphorus-based and tin-based flame retardants have the advantages of being environmentally friendly and safe and non-toxic, and can achieve the improvement of material flame retardant properties at low addition amounts, which can meet the above needs. Therefore, a phosphorus-based synergistic flame retardant system has been developed for nylon 6 flame retardancy, such as a new phosphorus-nitrogen halogen-free flame retardant nylon 6 and its preparation method disclosed in Chinese patent application CN104177824A, which adopts phosphorus-nitrogen synergistic flame retardancy. Tin-based flame retardants are often used as synergistic flame retardants. For example, Chinese patent application CN108948734A discloses a high-glow-wire-temperature flame-retardant reinforced PA6 composite material and its preparation method, which uses a combination of tin-based and brominated flame retardants to increase the ignition temperature of nylon 6. However, technologies for phosphorus-tin synergistic flame retardancy in nylon 6 have yet to be reported.

[0004] While additive flame retardants are simple to prepare, and flame-retardant polymers can be produced through blending processes, they suffer from poor compatibility with the matrix and are prone to migration and precipitation, resulting in decreased flame retardancy. Therefore, achieving flame retardancy levels (Limiting Oxygen Index > 28%) often requires large addition levels. Therefore, in recent years, researchers have been committed to achieving a significant improvement in the flame retardant properties of nylon 6 at low addition levels through reactive flame retardants. For example, Chinese patent application CN104744690A discloses a flame retardant nylon 6 and a preparation method thereof, which uses the reaction of nylon polymerization monomers caprolactam and aminomethylphenylphosphinic acid to prepare reactive flame retardant nylon. The patent claims that the addition of aminomethylphenylphosphinic acid to the polymerization system of flame retardant nylon 6 allows the flame retardant and nylon 6 to be perfectly combined, thereby improving the flame retardant properties of nylon 6 at low addition levels. Chinese patent application CN105153414A discloses a permanent flame retardant nylon 6 material and a preparation method thereof, which uses a two-step reaction method to prepare intrinsically flame retardant nylon 6. The patent claims that the resulting flame retardant nylon 6 material has the characteristics of low flame retardant addition and long-lasting flame retardant effect, a limiting oxygen index of more than 30%, a vertical burning test reaching UL94V-0 level, and excellent mechanical properties. However, these monomer-based reactive flame retardant technologies generally suffer from complex reactions and high costs, which hinder the industrial production of nylon 6 and make it difficult to achieve industrialization. Therefore, it is very important to improve the reactivity of flame retardants and nylon 6 macromolecules to enhance flame retardant efficiency. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, the present invention provides a method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material, which can solve the problems of poor compatibility between additive phosphorus-based flame retardants and nylon 6, resulting in limited improvement in the flame retardant performance of the composite material at low addition amounts, as well as high cost and complex reactions of the bulk reaction type.

[0006] The technical solution adopted by the present invention is as follows: A method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material comprises adding a DOPO phosphorus-containing flame retardant and zinc hydroxystannate to a nylon 6 resin matrix, feeding the mixture into a twin-screw extruder, directly blending and granulating the mixture to prepare a resin masterbatch, drying the resin masterbatch, and then injection molding the composite material to obtain the phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material. The composite material comprises, by weight, 90 to 98 parts of nylon 6, 1 to 5 parts of a maleic anhydride-modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO phosphorus-containing flame retardant, and 1 to 5 parts of the zinc hydroxystannate. The DOPO phosphorus-containing flame retardant is maleic anhydride-modified 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and its preparation method is as follows: (1) Add the flame retardant intermediate DOPO (9,10-dihydro-9-oxa-10-phospha-10-phenanthrene oxide) and a toluene-tetrahydrofuran mixed solvent to a reaction vessel equipped with a condenser and a magnetic stirrer at room temperature, and stir magnetically until completely dissolved to obtain a DOPO / toluene / tetrahydrofuran solution; (2) Under nitrogen protection, add maleic anhydride / toluene / tetrahydrofuran solution to DOPO / toluene / tetrahydrofuran solution, and react with heating and stirring for 20 hours at a heating temperature of 80°C to 100°C; (3) After the reaction is completed, the mixture is cooled to room temperature, filtered, and the filtered precipitate is washed with tetrahydrofuran, then vacuum-dried for 8 to 10 hours and cooled to room temperature to obtain a white powder product, which is the DOPO phosphorus-containing flame retardant.

[0007] Furthermore, in the toluene-tetrahydrofuran mixed solvent described in step (1), the volume ratio of toluene to tetrahydrofuran is 1:1, and the volume ratio of DOPO to the toluene-tetrahydrofuran mixed solvent is 1 g / mL to 2 g / mL; and in the maleic anhydride / toluene / tetrahydrofuran solution, the proportion of maleic anhydride is 0.5 g / mL to 2 g / mL.

[0008] Furthermore, in step (2), when the maleic anhydride / toluene / tetrahydrofuran solution is added to the DOPO / toluene / tetrahydrofuran solution, the molar ratio of DOPO to maleic anhydride is controlled to be 1:1 to 1:1.2.

[0009] Furthermore, the granulation temperature of the blending granulation is 200-250°C.

[0010] Furthermore, the injection molding temperature is 220-280°C.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention combines reactive extrusion technology with the addition of zinc hydroxystannate (ZHS) to enhance the flame retardancy of the material through tin-based compounding. By designing the molecular structure of phosphorus-based flame retardants, phosphorus-based flame retardants with anhydride groups are synthesized, and compounded with tin-based flame retardants. This allows the successful preparation of flame-retardant nylon 6 composite materials with excellent mechanical properties at low addition levels. This method does not require a specialized nylon 6 reaction unit; flame retardant modification can be completed in an extruder, resulting in a simple reaction. The anhydride groups of the modified phosphorus-containing flame retardant provide reactive sites that react with the amino groups of nylon 6 during the extrusion process, enhancing its flame retardancy. Furthermore, compounding with tin-based compounds enhances the flame retardancy of the nylon 6 material.

[0012] 2、The application utilizes the dehydration reaction of the anhydride groups in the melt extrusion and the macromolecular chains containing polar groups (-NH2, -OH) under high temperature and shearing effect to form a macromolecular phosphorus flame retardant system, and the method is simple in process and wide in adaptability, the prepared macromolecular phosphorus system is strong in sustained action and high in flame retardant efficiency, and the problems of easy migration and large addition amount of small molecule flame retardants are solved.

[0013] 3、The flame-retardant nylon 6 composite material utilizes the reaction of the anhydride groups of the modified phosphorus-containing flame retardant and the amino groups of nylon 6, realizes the compatibility of the polymer system and the flame retardant in the melt extrusion process, simultaneously improves the flame retardant performance of the material through the compounding of tin-based compounds, realizes the synchronous improvement of the flame-retardant grade V-0 of nylon 6 and the limiting oxygen index > 30% and the decrease of the CO2 release amount under the low addition amount of the flame retardant, and thus realizes the goal of the intrinsic non-toxic, efficient and long-term flame-retardant of the material.

[0014] 4、Under the high temperature and shearing effect, the maleic anhydride of the phosphorus flame retardant and the macromolecular chains of nylon 6 containing polar groups -NH2 and -OH are in-situ reacted on line, the flame retardant efficiency of DOPO is greatly enhanced, and the smoke suppression effect of zinc hydroxystannate is combined, the prepared phosphorus / tin synergistic flame-retardant nylon 6 composite material has excellent performance, the flame-retardant grade of the composite material is V-0 grade under the low addition amount, the limiting oxygen index reaches 32.6%, the total heat release amount is decreased by 62%, and the heat release peak value is decreased by 43.6%.

[0015] 5、The application can solve the problem of the limited improvement of the flame retardant performance of the composite material under the low addition amount due to the poor compatibility of the additive type phosphorus flame retardant and nylon 6, and the problem of high cost and complex reaction of the in-situ reaction type, can prepare the nylon 6 composite material with the flame-retardant grade, and widens the application field of nylon 6. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is the UL-94 vertical combustion behavior photo of the flame-retardant nylon 6 composite material prepared in examples 1-3 and comparative examples 1-3; Figure 2 It is the residual carbon picture of the cone test of examples 1-3 and comparative examples 1-3; Figure 3 It is the thermal gravimetric curve of examples 1-3 and comparative examples 1-3; Figure 4 It is the heat release peak curve of comparative example 1 (PA6) and example 3 (5wt% DOPO-MA / 5wt% ZHS) composite material; Figure 5 It is the total heat release curve of comparative example 1 (PA6) and example 3 (5wt% DOPO-MA / 5wt% ZHS) composite material; Figure 6 The CO2 release curves of the composite materials of Comparative Example 1 (PA6) and Example 3 (5wt% DOPO-MA / 5wt% ZHS) are shown. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments. The following embodiments are for further explanation of the present invention, but not for limiting the scope of protection of the present invention. Example 1

[0018] A method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material, comprising the following steps: (1) Add DOPO (9,10-dihydro-9-oxa-10-phospha-10-phenanthrene oxide) and a toluene-tetrahydrofuran mixed solvent (volume ratio 1:1) to a three-necked flask equipped with a condenser and a magnetic stirrer. The mixing ratio of DOPO to the toluene-tetrahydrofuran mixed solvent is 160 g / 260 mL. Dissolve DOPO completely under stirring to obtain a DOPO / toluene / tetrahydrofuran solution. Add maleic anhydride to the toluene-tetrahydrofuran mixed solvent (volume ratio 1:1) and mix well to obtain a maleic anhydride / toluene / tetrahydrofuran solution. The mixing ratio of maleic anhydride to the toluene-tetrahydrofuran mixed solvent is 86 g / 60 mL. (2) Under nitrogen protection, maleic anhydride / toluene / tetrahydrofuran solution was added to DOPO / toluene / tetrahydrofuran solution within 1 hour. The molar ratio of DOPO to maleic anhydride in the mixed solution was 1:1.2. The mixed solution was heated at 80°C with stirring for 20 hours. (3) After the reaction mixture is cooled to room temperature, it is filtered, and the filtered precipitate is washed with tetrahydrofuran. The washed precipitate is then placed in a vacuum oven for vacuum drying for 8 to 10 hours, and cooled to room temperature to obtain a white powder product, which is maleic anhydride-modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO phosphorus-containing flame retardant (abbreviated as modified phosphorus-containing flame retardant DOPO-MA); (4) The modified phosphorus-containing flame retardant DOPO-MA was added to the nylon 6 resin matrix, which included 98 parts by weight of nylon 6 (PA6), 1 part of the modified phosphorus-containing flame retardant DOPO-MA, and 1 part of zinc hydroxystannate. The mixture was blended and granulated in a twin-screw extruder at 220°C to prepare PA6 / DOPO-MA (97 / 3) resin pellets. The resin masterbatch was dried and injection molded in an injection molding machine at 220°C to obtain a flame-retardant nylon 6 composite material. Example 2

[0019] A method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material, comprising the same steps as in Example 1, except that: the modified phosphorus-containing flame retardant DOPO-MA and zinc hydroxystannate (ZHS) are added to a nylon 6 resin matrix, comprising, by weight, 92 parts of nylon (PA6), 3 parts of the modified phosphorus-containing flame retardant DOPO-MA, and 5 parts of zinc hydroxystannate; the mixture is blended and granulated in a twin-screw extruder at 220° C. to prepare PA6 / DOPO-MA / tin-based small molecule (92 / 3 / 5) resin pellets; the resin masterbatch is dried and injection molded in an injection molding machine at 220° C. to obtain a flame-retardant nylon 6 composite material. Example 3

[0020] A method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material, wherein the method and steps are the same as those in Example 1, except that: The modified phosphorus-containing flame retardant DOPO-MA and zinc hydroxystannate were added to a nylon 6 resin matrix, comprising, by weight, 90 parts of nylon (PA6), 5 parts of the modified phosphorus-containing flame retardant DOPO-MA, and 5 parts of zinc hydroxystannate. The mixture was blended and granulated at 220° C. in a twin-screw extruder to prepare PA6 / DOPO-MA / tin-based small molecule (90 / 5 / 5) resin pellets. The resin masterbatch was dried and injection molded at 220° C. in an injection molding machine to obtain a flame-retardant nylon 6 composite material. Comparative Example 1

[0021] The preparation method of pure nylon 6 comprises the following steps: drying 100 parts of a nylon 6 matrix in a vacuum oven at 80°C for 24 hours, blending and granulating the matrix in a twin-screw extruder at 220°C to prepare resin particles, and then drying the resin masterbatch and injection molding the matrix in an injection molding machine at 220°C to obtain a flame-retardant nylon 6 composite material. Comparative Example 2

[0022] The preparation method of the nylon 6 / DOPO composite material comprises the following steps: drying 95 parts of a nylon 6 matrix in a vacuum oven at 80°C for 24 hours, mixing the matrix with 5 parts of DOPO, and then blending and granulating the matrix in a twin-screw extruder at 220°C to prepare resin particles; and drying the resin masterbatch and injection molding the matrix in an injection molding machine at 220°C to obtain a flame-retardant nylon 6 / DOPO composite material. Comparative Example 3

[0023] The preparation method of nylon 6 / DOPO-MA composite material comprises the following steps: drying 95 parts of nylon 6 matrix in a vacuum oven at 80°C for 24 hours, mixing with 5 parts of modified phosphorus-containing flame retardant DOPO-MA, and then blending and granulating the mixture in a twin-screw extruder at 220°C to prepare resin particles; and drying the resin masterbatch and injection molding it in an injection molding machine at 220°C to obtain a flame-retardant nylon 6 / DOPO composite material.

[0024] The flame retardant nylon 6 composite materials of Example 1, Example 2, Example 3 and the flame retardant composite material of the comparative example were subjected to the UL-94 vertical burning test. The UL-94 vertical burning behavior photos are shown in FIG. Figure 1 .from Figure 1 It can be seen that the flame retardant grade of the nylon 6 composite material obtained by compounding and mixing the present invention can be improved to V-0 grade, and the melt dripping thereof is significantly suppressed.

[0025] The combustion carbon residues of Examples 1-3 and Comparative Examples 1-3 were tested by cone measurement. The carbon residue pictures are shown in Figure 2 .from Figure 2 As can be seen, after complete combustion, the PA6 of Comparative Example 1 exhibits almost no carbon layer, leaving only a thin layer of ash. This suggests that the near absence of residual carbon is a major factor in PA6's poor flame retardancy. The carbon layer of PA6 / 5wt% DOPO in Comparative Example 2 is thin and loose. The carbon layer formed by PA6 / 3wt% DOPO-MA in Comparative Example 3 is relatively dense, but relatively small. In contrast, Examples 1 (PA6 / 1wt% DOPO-MA / 1wt% ZHS), Example 2 (PA6 / 3wt% DOPO-MA / 5wt% ZHS), and Example 3 (PA6 / 5wt% DOPO-MA / 5wt% ZHS), all of which incorporate the flame retardant of this invention, form denser and more numerous carbon layers, preventing oxygen from contacting the material and hindering combustion. This demonstrates the condensed-phase flame retardancy of DOPO-MA and ZHS.

[0026] The thermogravimetric TGA method was used to obtain the thermogravimetric curves of the flame retardant nylon 6 composite materials of Examples 1-3 and the materials of Comparative Examples 1-3. Figure 3 .from Figure 3 It can be seen that the carbon residue content of PA6 increased after the flame retardant was added in Examples 1 to 3, and the carbon residue content increased compared with Comparative Examples 1 to 3, especially in Example 3, indicating that the introduction of ZHS can increase the carbon residue content of the matrix to a certain extent. However, for all Examples and Comparative Examples, the addition of flame retardant (whether only DOPO, DOPO-MA, or DOPO-MA / ZHS) did not affect the thermal stability of PA6, ensuring the thermal stability of PA6 during processing.

[0027] The peak heat release, total heat release and CO2 release curves of the flame retardant composite materials of Example 3 (5wt% DOPO-MA / 5wt% ZHS) and Comparative Example 1 (PA6) were obtained by cone test method. Figure 4 The peak heat release curve Figure 5 Total heat release curve, Figure 6 CO2 release curve. Figures 4 to 6It can be seen that the introduction of 5wt% DOPO-MA / 5wt% ZHS significantly reduced the total heat release of PA6, which decreased by about 40%, from 159.1 of pure PA6 to 96.543MJ / m 2 The heat release rate per unit area is significantly lower than that of pure PA. The combination of DOPO-MA and ZHS effectively reduces the peak heat release of PA6. At the same time, the release of CO2 is reduced. This is mainly because the presence of DOPO-MA affects the efficiency of carbon oxidation during combustion, so that part of the carbon source cannot be fully oxidized into CO2, but exists in the form of CO or other carbon-based products.

[0028] Table 1 shows the vertical combustion grades of the embodiments and comparative examples as well as their limiting oxygen index values, molten droplets, residual carbon amounts, and CO2 release amounts.

[0029] Table 1 Vertical combustion behavior and carbon residue of PA6 and its composites

[0030] As can be seen from Table 1, the halogen-free flame retardant method of the present invention can significantly improve the UL-94 grade and limiting oxygen index of the material. The limiting oxygen index is increased to 32.6% by the synergistic combination of phosphorus and tin, which is a flame retardant grade. The amount of residual carbon is also increased, and the release of CO2 is significantly suppressed, with a decrease of 51.8%, which has a significant smoke suppression effect. At the same time, combined with its actual combustion behavior, total heat release and the decrease in heat release peak, it can be seen that the flame retardant properties of the phosphorus-tin synergistic halogen-free flame retardant nylon 6 composite material prepared by the method of the present invention are significantly improved, and it can be used in fields with higher flame retardant requirements.

Claims

1. A method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material, characterized in that: The method comprises adding a DOPO phosphorus-containing flame retardant and zinc hydroxystannate to a nylon 6 resin matrix, feeding the mixture into a twin-screw extruder, directly blending and granulating the mixture to prepare a resin masterbatch, drying the resin masterbatch, and then injection molding the mixture to obtain the phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material. The composition comprises, by weight, 90 to 98 parts of nylon 6, 1 to 5 parts of a maleic anhydride-modified 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO phosphorus-containing flame retardant, and 1 to 5 parts of zinc hydroxystannate. The DOPO phosphorus-containing flame retardant is maleic anhydride-modified 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and its preparation method is as follows: (1) Add the flame retardant intermediate DOPO (9,10-dihydro-9-oxa-10-phospha-10-phenanthrene oxide) and a toluene-tetrahydrofuran mixed solvent to a reaction vessel equipped with a condenser and a magnetic stirrer at room temperature, and stir magnetically until completely dissolved to obtain a DOPO / toluene / tetrahydrofuran solution; (2) Under nitrogen protection, add maleic anhydride / toluene / tetrahydrofuran solution to DOPO / toluene / tetrahydrofuran solution, and react with heating and stirring for 20 hours at a heating temperature of 80°C to 100°C; (3) After the reaction is completed, the mixture is cooled to room temperature, filtered, and the filtered precipitate is washed with tetrahydrofuran, then vacuum-dried for 8 to 10 hours and cooled to room temperature to obtain a white powder product, which is the DOPO phosphorus-containing flame retardant.

2. The method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material according to claim 1, characterized in that: In the toluene-tetrahydrofuran mixed solvent described in step (1), the volume ratio of toluene to tetrahydrofuran is 1:1, and the volume ratio of DOPO to the toluene-tetrahydrofuran mixed solvent is 1 g / mL to 2 g / mL; in the maleic anhydride / toluene / tetrahydrofuran solution, the proportion of maleic anhydride is 0.5 g / mL to 2 g / mL.

3. The method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material according to claim 1, characterized in that: In step (2), when the maleic anhydride / toluene / tetrahydrofuran solution is added to the DOPO / toluene / tetrahydrofuran solution, the molar ratio of DOPO to maleic anhydride is controlled to be 1:1 to 1:1.

2.

4. The method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material according to claim 1, characterized in that: The granulation temperature of the blending granulation is 200-250°C.

5. The method for preparing a phosphorus-tin synergistic halogen-free flame-retardant nylon 6 composite material according to claim 1, characterized in that: The injection molding temperature is 220-280°C.

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