CN117186256A - A toughened starch-based one-component intumescent flame retardant and its preparation method and application - Google Patents

Abstract

The invention discloses a toughened starch-based single-component intumescent flame retardant, and a preparation method and application thereof. The method takes starch, hexa-phosphate, amino acid and other substances as raw materials, and adopts a hydrothermal one-pot method to prepare the toughening starch-based single-component intumescent flame retardant, so that the preparation process is simple, the synthesis condition is mild, most of the raw materials are renewable biomass materials, and the environment is protected and pollution is avoided; the prepared starch-based single-component intumescent flame retardant has the advantages of good thermal stability, high flame retardant efficiency, excellent anti-dripping and smoke suppression performances, excellent mechanical properties, small particle size and good compatibility with polylactic acid, can retain the self degradation capability of the polylactic acid, simultaneously effectively realizes the toughening of the polylactic acid material, and greatly expands the application range of the polylactic acid material.

Description

A toughened starch-based one-component intumescent flame retardant and its preparation method and application

Technical field

The invention belongs to the technical field of biodegradable and flame-retardant composite materials, and specifically relates to a toughened starch-based single-component intumescent flame retardant and its preparation method and application.

Background technique

In recent decades, with the rapid development of the polymer industry, polymers represented by plastics, rubber and fibers have been widely used in all aspects of life. While people enjoy the convenience brought by polymer materials, they also bring about a serious environmental problem - white pollution. The degradation cycle of traditional polymers under natural conditions is as long as hundreds of years, and degradation will also cause serious chemical pollution. Therefore, promoting a degradable biomass polymer material has become an increasingly urgent task. Among the current mainstream degradable polymer materials, polylactic acid (PLA) is widely used because of its good mechanical properties, easy processing, high transparency, non-toxic and harmless, good biocompatibility and biodegradability. In electronics, textiles, packaging, 3D printing, medical and construction materials.

PLA is a thermoplastic biomass-based degradable plastic polymerized from lactic acid monomers. Currently, lactic acid is mostly produced through biological fermentation, so PLA is a truly biomass-based degradable plastic. However, because the ester bonds contained in PLA are easily broken when burned by a fire source, and the structure of the molecular chain can also cause the production of flammable volatile substances, the limiting oxygen index of pure PLA is only 19.5%. This greatly limits the application of PLA in fields with high requirements for flame retardancy, such as electronic products, automobile industry, and building materials. Therefore, flame retardant modification of PLA is an important part of expanding its widespread application.

Traditional PLA flame retardants include halogen flame retardants, phosphorus flame retardants, nitrogen flame retardants, metal compound flame retardants, etc. As the country's requirements for environmental protection and green development continue to increase, the use of flame retardants that are harmful to the environment, such as halogen flame retardants, has been banned and replaced by intumescent flame retardants composed of carbon sources, acid sources, and gas sources. agent. Among them, biomass-based intumescent flame retardants are widely favored due to their advantages of being green, environmentally friendly, low in additive amounts, and having good compatibility with PLA matrix.

Contents of the invention

The object of the present invention is to provide a toughened starch-based single-component intumescent flame retardant and its preparation method and application. The synthesis process of the flame retardant is green and environmentally friendly, the reaction conditions are mild, the operation is simple, and the flame retardant is The PLA matrix has good compatibility, which can effectively improve the flame retardant, smoke suppression, anti-droplet, degradability and toughness-enhancing properties of polylactic acid, which is of great significance to the promotion and use of PLA materials.

In order to achieve the above objects, the present invention adopts the following technical solutions:

A toughened starch-based one-component intumescent flame retardant, the preparation method of which includes the following steps:

(1) Add water-soluble starch to deionized water and disperse it evenly through stirring and ultrasonic vibration to obtain a starch suspension;

(2) Add an appropriate amount of dilute acid solution to the starch suspension obtained in step (1), stir and react for 4 hours in a nitrogen environment at 45°C, and then wash, filter, and vacuum dry to obtain soluble starch;

(3) Grind the soluble starch obtained in step (2) and disperse it in deionized water, then heat it to 90°C and stir to completely dissolve it to obtain a starch solution;

(4) Ultrasonically heat the starch solution obtained in step (3) to 90°C, and slowly add hexavalent phosphate and acetic anhydride dropwise under stirring conditions. After the addition is completed, ultrasonicate for 1.0-1.5h, and then continue at 90°C. Stir and react for 7.0-10.0h to obtain a phosphated starch solution;

(5) Add an appropriate amount of amino acid to the phosphated starch solution obtained in step (4), stir and react at 70°C for 12.0-18.0 hours, and obtain an amino acid phosphated starch solution;

(6) Add an appropriate amount of Al ³⁺ -containing compound to the amino acid phosphated starch solution obtained in step (5), and continue the stirring reaction at 70°C for 7.0-10.0h;

(7) Add sodium carbonate solution to the reaction solution in step (6), adjust the pH to neutral, let it stand for 12 hours, and then wash and filter, vacuum dry, crush, and sieve to obtain the toughened starch. Based on one-component intumescent flame retardant.

Further, the water-soluble starch in step (1) is any one of potato starch, corn starch, wheat starch, sweet potato starch, etc.

Further, the dosage of the dilute acid solution in step (2) is converted based on 100-200mL per 10g of water-soluble starch; the concentration of the dilute acid solution is 2-3wt%, and the acids used are formic acid, hydrochloric acid, and citric acid. one of them.

Further, the dissolution temperature of the soluble starch obtained in step (2) is 90-95°C.

Further, the hexavalent phosphate in step (4) is sodium hexametaphosphate and/or sodium phytate.

Further, the amino acid in step (5) is one or more of tryptophan, threonine, glycine, alanine, glutamic acid, and arginine.

Further, the Al ³⁺ -containing compound described in step (6) is one or more of aluminum nitrate, aluminum sulfate, aluminum hydroxide, and aluminum chloride.

Further, for every 10 g of water-soluble starch, 0.02-0.1 mol of hexavalent phosphate, 10-15 mL of acetic anhydride, 0.06-0.3 mol of amino acid, and 0.02-0.1 mol of Al ³⁺ -containing compound are used.

Further, the frequency of the ultrasonic vibration described in steps (1) and (4) is 40KHz.

Further, the stirring speed in steps (1)-(6) is 300-500 rpm.

Further, the concentration of the sodium carbonate solution in step (7) is 5wt%.

The starch-based one-component intumescent flame retardant prepared above can be used to prepare toughened flame-retardant polylactic acid. Specifically, the toughened starch-based one-component intumescent flame retardant and polylactic acid are mixed in a mass ratio of 90 :10 Stir and mix, extrudate through a twin-screw extruder and injection molding to prepare toughened flame-retardant polylactic acid.

Starch is polymerized from glucose monomers. It is a high-carbon, polyhydroxyl polysaccharide that forms a large amount of charcoal layer when burned. The hydroxyl groups it contains will catalyze the charcoal layer to become denser, reducing the amount of outside air entering the interior. It also hinders the mass and heat transfer process during PLA combustion, which can effectively reduce the combustion characteristics of PLA, so it can be used as a good biomass carbon source for intumescent flame retardants.

Sodium hexametaphosphate is easily soluble in water and is a white crystal. It is mainly used in the food industry as a quality improver, pH regulator, metal ion chelating agent, adhesive and expanding agent. The phosphoric acid and hydroxyl groups contained in sodium hexametaphosphate can accelerate the dehydration of the carbon source to form a dense carbon layer. At the same time, the phosphoric acid group will also form a protective layer of phosphorus pentoxide after burning, which plays a similar role to the carbon layer, so it can be used as Good acid source for intumescent flame retardants.

Sodium phytate contains six phosphate groups and the phosphorus content is as high as 28%. During the combustion process of PLA, the phosphoric acid and hydroxyl groups contained in sodium phytate can accelerate the dehydration of the carbon source to form a dense carbon layer. At the same time, the phosphate groups After burning, the pellet will also form a protective layer of phosphorus pentoxide, which plays a similar role to the carbon layer, so it can be used as a good biomass acid source for intumescent flame retardants.

Amino acids are a class of substances widely distributed in animals and plants. They contain amino groups in their structure and can react with acidic solutions under certain conditions. At the same time, the amino groups in amino acids will produce a lot of inert gases during the combustion process, which can effectively reduce the concentration of flammable substances produced by the thermal decomposition of PLA. It can also have a good smoke suppression effect, so it can be used as a good producer of intumescent flame retardants. Material nitrogen source.

By rationally designing the reaction route, the present invention proposes a method of chemically modifying starch through six-membered phosphate, amino acids, and aluminum ions, and using ultrasonic vibration, catalyst catalysis, pH control and other means to improve the concentration of phosphorus and nitrogen elements on starch. Grafting degree, and a starch-based single-component intumescent flame retardant that combines three sources of carbon source, acid source, and nitrogen source is directly generated through a hydrothermal one-pot method.

The significant advantages of the present invention are:

(1) All the synthesis steps of the present invention are carried out in the aqueous phase, and the hydrothermal one-pot method is used. The required product can be directly obtained without separating the intermediate product. The preparation process is simple, the reaction conditions are mild, and industrial production is easy to achieve.

(2) The starch-based one-component intumescent flame retardant prepared by the present invention has good thermal stability and good compatibility with the PLA matrix, and can be well dispersed in the PLA matrix and only needs to be added in a small amount. It achieves high-efficiency flame retardancy, making its flame retardant grade reach UL94V-0, and at the same time, it can effectively improve its anti-melting and smoke suppression effects.

(3) The high-toughness, completely biodegradable flame-retardant polylactic acid composite material prepared by using the starch-based single-component intumescent flame retardant obtained by the present invention has good mechanical properties, and its tensile strength and elongation at break are compared with pure PLA. Both have been improved, and the impact strength has been greatly improved.

(4) The raw materials used in the present invention are all completely biodegradable materials, causing no damage to the environment and no pollution. At the same time, they will not affect the degradation performance of the PLA matrix itself, and can achieve the unification of flame retardant and degradable properties.

Description of the drawings

Figure 1 is a process diagram for preparing toughened starch-based one-component intumescent flame retardant in Example 1.

Figure 2 is an FT-IR diagram of the toughened starch-based one-component intumescent flame retardant prepared in Example 1.

Figure 3 is an SEM image (B) of the carbon layer after burning the flame retardant prepared in Example 1 (A) and the sample prepared in Application Example 1.

Figure 4 is an SEM image (B) of the carbon layer after burning the flame retardant prepared in Example 2 (A) and the sample prepared in Application Example 2.

Figure 5 is an SEM image of the carbon layer after combustion of the sample prepared in Comparative Example 1.

Figure 6 is an SEM image of the carbon layer after combustion of the sample prepared in Comparative Example 2.

Figure 7 is an SEM image of the carbon layer after combustion of the sample prepared in Comparative Example 3.

Detailed ways

A toughened starch-based one-component intumescent flame retardant, the preparation method of which includes the following steps:

(1) Add 10g of water-soluble starch to deionized water and disperse it evenly through 300-500 rpm stirring and 40KHz ultrasonic vibration to obtain a starch suspension;

(2) Add 100-200mL of dilute acid solution with a concentration of 2-3wt% to the starch suspension obtained in step (1), stir and react at 300-500 rpm for 4 hours in a nitrogen environment at 45°C, and then wash and pump. Filter and vacuum dry to obtain soluble starch;

(3) Grind the soluble starch obtained in step (2) and disperse it in deionized water, then heat it to 90°C and stir at 300-500 rpm to completely dissolve it to obtain a starch solution;

(4) Place the starch solution obtained in step (3) into an ultrasonic cleaning machine, heat it to 90°C, and slowly add 0.02-0.1 mol of hexavalent phosphate and 10 -15mL acetic anhydride, ultrasonic for 1.0-1.5h after the dropwise addition, then continue the stirring reaction at 90°C at 300-500 rpm for 7.0-10.0h to obtain a phosphated starch solution;

(5) Add 0.06-0.3 mol of amino acid to the phosphorized starch solution obtained in step (4), and stir and react at 300-500 rpm at 70°C for 12.0-18.0 hours to obtain an amino acid phosphated starch solution;

(6) Add 0.02-0.1 mol of Al ³⁺ -containing compound to the amino acid phosphated starch solution obtained in step (5), and continue the stirring reaction at 70°C at 300-500 rpm for 7.0-10.0 h;

(7) Add 5wt% sodium carbonate solution to the reaction solution in step (6), adjust the pH to neutral, let it stand for 12 hours, and then wash and filter, vacuum dry, pulverize, and sieve to obtain the above-mentioned sodium carbonate solution. Tough starch-based one-component intumescent flame retardant.

Wherein, the water-soluble starch is any one of potato starch, corn starch, wheat starch, sweet potato starch, etc. The acid used is one of formic acid, hydrochloric acid, and citric acid. The hexavalent phosphate is sodium hexametaphosphate and/or sodium phytate. The amino acid is one or more of tryptophan, threonine, glycine, alanine, glutamic acid, and arginine. The Al ³⁺ -containing compound is one or more of aluminum nitrate, aluminum sulfate, aluminum hydroxide, and aluminum chloride.

In order to make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

Example 1:

Weigh 5g (0.03mol) potato starch and add it to a 250mL beaker filled with 150mL deionized water. Disperse it evenly through magnetic stirring (500rpm, the following magnetic stirring speeds are based on this speed) and 40KHz ultrasonic vibration to obtain a starch suspension. liquid. Weigh 2.67g (0.014mol) of citric acid and dissolve it in 97.33mL of deionized water solution to prepare a 2.67% citric acid solution. Then add it to the obtained starch suspension and stir for 4 hours in a nitrogen environment at 45°C. , soluble starch is obtained after washing, suction filtration and vacuum drying. The obtained soluble starch was ground and dispersed in 100 mL of deionized water, heated to 90°C and stirred until dissolved to obtain a starch solution. Weigh 18.5g (0.02mol) sodium phytate and 7mL acetic anhydride and add to the obtained starch solution, stir, disperse and ultrasonic for 1.0h, then stir and react at 70°C for 10.0h, then add 6.13g (0.03mol) to the solution ) tryptophan, continue to stir and react at 70°C for 12.0h, then add 13.2g (0.02mol) aluminum sulfate to the solution, continue to stir and react at 70°C for 8.0h. Finally, 5wt% sodium carbonate solution was added to the solution to adjust the pH to neutral. It was left to settle for 12 hours, washed, filtered, vacuum dried, pulverized, and passed through a 200-mesh sieve to obtain a toughened starch-based single-component intumescent flame retardant. agent.

Example 2:

Weigh 5g (0.03mol) corn starch into a 250mL beaker containing 150mL deionized water, and disperse it evenly through magnetic stirring and ultrasonic vibration to obtain a starch suspension. Add 20 mL, 3wt% hydrochloric acid solution to the obtained starch suspension, stir and react for 4 hours in a nitrogen environment at 45°C, and obtain soluble starch after washing, suction filtration, and vacuum drying. The obtained soluble starch was ground and dispersed in 100 mL of deionized water, heated to 90°C and stirred until dissolved to obtain a starch solution. Weigh 12.2g (0.02mol) sodium hexametaphosphate and 7mL acetic anhydride and add it to the obtained starch solution, stir, disperse and ultrasonic for 1.0h, then stir and react at 70°C for 10.0h, then add 4.41g (0.03mol) to the solution. Glutamic acid, continue the stirring reaction at 70°C for 12.0h, then add 2.34g (0.03mol) aluminum hydroxide to the solution, and continue the stirring reaction at 70°C for 8.0h. Finally, 5wt% sodium carbonate solution was added to the solution to adjust the pH to neutral. It was left to settle for 12 hours, washed, filtered, vacuum dried, pulverized, and passed through a 200-mesh sieve to obtain a toughened starch-based single-component intumescent flame retardant. agent.

Application example 1:

Weigh 10 parts (mass parts) of the starch-based one-component intumescent flame retardant prepared in Example 1, stir and mix with 90 parts (mass parts) of PLA, extrudate through a twin-screw extruder and injection molding. Vertical combustion (UL-94), limiting oxygen index (LOI), tensile, and impact standard specimens were prepared for testing.

Application example 2

Weigh 10 parts (mass parts) of the starch-based single-component intumescent flame retardant prepared in Example 2 and 90 parts (mass parts) of PLA, stir and mix, extrudate through a twin-screw extruder and injection molding to prepare Vertical combustion (UL-94), limiting oxygen index (LOI), tensile, and impact standard specimens were obtained for testing.

Comparative example 1 (pure sample)

Polylactic acid particles were injection molded to prepare vertical combustion (UL-94), limiting oxygen index (LOI), tensile, and impact standard specimens for testing.

Comparative Example 2 (starch)

Weigh 10 parts of potato starch (parts by mass), stir and mix with 90 parts (parts by mass) of PLA, then extrude it through a twin-screw extruder and injection mold it to produce vertical combustion (UL-94), limiting oxygen Index (LOI), tensile, and impact standard specimens were used for testing.

Comparative example 3 (commercially available flame retardants)

Weigh 10 parts (mass parts) of ammonium polyphosphate purchased on the market (phosphorus content 30% to 32%, nitrogen content 14% to 16%), 5 parts of potato starch (mass parts) and 85 parts (mass parts) of PLA are stirred and mixed, extruded through a twin-screw extruder and injection molded to prepare vertical combustion (UL-94), limiting oxygen index (LOI), tensile, and impact standard splines for test.

The vertical combustion splines, limiting oxygen index splines, tensile splines, and impact splines prepared above were tested for combustion performance and mechanical testing in accordance with ASTM D3801, ASTM D2863-97, GB/T 1843-2008, and GB/T 1843-2008. Performance test, the test results are shown in Table 1.

Table 1 Combustion performance and mechanical properties table

It can be seen from Table 1 that the flame retardant properties and mechanical properties of the materials obtained in Application Example 1 and Application Example 2 are relatively close. Compared with Comparative Example 1, its flame retardant properties and mechanical properties have been greatly improved, and the limiting oxygen index has increased. About 61%; the UL-94 vertical combustion level has also been improved from NR to V-0; the impact strength, elongation at break and tensile strength have increased by 35%, 3.0% and 39% respectively, while maintaining the high tensile strength of the polylactic acid material In the case of high strength, it also effectively achieves the toughening of polylactic acid materials.

Comparing with Comparative Examples 2 and 3, it can be seen that the material prepared by the application example has higher flame retardant efficiency, improves the mechanical properties of polylactic acid, and realizes multi-functional modification of polylactic acid materials.

Figure 2 is an FI-IR diagram of the starch-based one-component intumescent flame retardant prepared in Example 1. It can be seen from the figure that compared with pure starch, five new peaks appear on the infrared spectrum of starch-based one-component intumescent flame retardant, namely 3630cm ^-1 , 1150cm ^-1 , 3530cm ^-1 , 1520cm ^-1 and 486cm ^-1 , corresponding to the hydroxyl group and -OP- bond of sodium phytate, the hydroxyl group on starch, the NH ₃ ⁺ and Al-O bond on tryptophan, which indicates that sodium phytate, tryptophan and Al ³⁺ were successfully grafted onto starch.

Figures 3 and 4 are respectively the SEM image (A) of the flame retardant prepared in Examples 1 and 2 and the SEM image (B) of the carbon layer after burning of the sample prepared in the application example. As can be seen from the figure, the microscopic morphology of the obtained flame retardant is small spheres, so it can be well dispersed in the PLA matrix, thereby improving the mechanical properties of the PLA composite material. The charcoal layer after combustion is dense and compact, which can effectively isolate heat and mass transfer, and has a good flame retardant effect.

Figures 5-7 are respectively SEM images of the carbon layer after burning of the polylactic acid strips prepared in Comparative Examples 1-3. It can be seen from the picture that the carbon layer has many holes and cannot block the heat source well, so it cannot achieve the ideal flame retardant effect.

From the above example analysis, we can know:

(1) Most of the raw materials used in the toughened starch-based one-component intumescent flame retardant prepared by the present invention are completely biodegradable materials, which can be degraded into non-toxic and harmless small molecular substances under natural conditions. . The toughened starch-based single-component intumescent flame retardant added to the polylactic acid matrix in the present invention will not affect its degradation performance, but can accelerate the natural degradation rate of polylactic acid to a certain extent. This is due to the sodium phytate Both sodium hexametaphosphate and sodium hexametaphosphate have good hydrophilicity, which can improve the water absorption performance of polylactic acid. It is easier to catalyze the cleavage of ester bonds in polylactic acid in the natural environment. At the same time, starch, amino acids, etc. can be decomposed and utilized by microorganisms, further Accelerate the degradation of polylactic acid matrix.

(2) The toughened starch-based one-component intumescent flame retardant prepared by the present invention is microspherical and has small particle size, and can be well dispersed into the polylactic acid matrix. At the same time, the raw materials used such as starch, hexavalent phosphate, amino acids, etc. will form intermolecular hydrogen bonds with the active groups in the polylactic acid matrix, which enables the resulting flame-retardant polylactic acid composite material to maintain high tensile strength. It also improves its toughness, making an important contribution to the wider application of polylactic acid materials.

(3) The flame retardant prepared by the present invention is a biomass-based material, has good compatibility with polylactic acid materials, and is well dispersed in the polylactic acid matrix. Therefore, it can be achieved with only a small amount of addition. Effectively flame retardant, while the introduction of aluminum ions effectively suppresses droplets and smoke emissions during combustion.

The above are only preferred embodiments of the present invention, and all equivalent changes and modifications made in accordance with the patentable scope of the present invention shall fall within the scope of the present invention.

Claims (10)

1. A method for preparing a toughened starch-based one-component intumescent flame retardant, which is characterized in that it includes the following steps: (1) Add water-soluble starch to deionized water and disperse it evenly through stirring and ultrasonic vibration to obtain a starch suspension; (2) Add dilute acid solution to the starch suspension obtained in step (1), stir and react for 4 hours in a nitrogen atmosphere at 45°C, and then wash, filter, and vacuum dry to obtain soluble starch; (3) Grind the soluble starch obtained in step (2) and disperse it in deionized water, then heat it to 90°C and stir to completely dissolve it to obtain a starch solution; (4) Ultrasonically heat the starch solution obtained in step (3) to 90°C, and slowly add hexavalent phosphate and acetic anhydride dropwise under stirring conditions. After the addition is completed, ultrasonicate for 1.0-1.5h, and then continue at 90°C. Stir and react for 7.0-10.0h to obtain a phosphated starch solution; (5) Add amino acids to the phosphorized starch solution obtained in step (4), stir and react at 70°C for 12.0-18.0 hours, and obtain an amino acid phosphated starch solution; (6) Add the Al ³⁺ -containing compound to the amino acid phosphated starch solution obtained in step (5), and continue the stirring reaction at 70°C for 7.0-10.0h; (7) Add sodium carbonate solution to the reaction solution in step (6), adjust the pH to neutral, let it stand for 12 hours, and then wash and filter, vacuum dry, crush, and sieve to obtain the toughened starch. Based on one-component intumescent flame retardant. 2. The preparation method according to claim 1, characterized in that: the water-soluble starch in step (1) is any one of potato starch, corn starch, wheat starch, and sweet potato starch. 3. The preparation method according to claim 1, characterized in that: the dosage of the dilute acid solution in step (2) is converted by using 100-200mL per 10g of water-soluble starch; the concentration of the dilute acid solution is 2 -3wt%, the acid used is one of formic acid, hydrochloric acid, and citric acid. 4. The preparation method according to claim 1, characterized in that: the hexavalent phosphate in step (4) is sodium hexametaphosphate and/or sodium phytate. 5. The preparation method according to claim 1, characterized in that: the amino acid in step (5) is one of tryptophan, threonine, glycine, alanine, glutamic acid, and arginine. or more. 6. The preparation method according to claim 1, characterized in that: the Al ³⁺ -containing compound in step (6) is one or more of aluminum nitrate, aluminum sulfate, aluminum hydroxide, and aluminum chloride. 7. The preparation method according to claim 1, characterized in that: every 10g of water-soluble starch uses 0.02-0.1mol hexavalent phosphate, 10-15mL acetic anhydride, 0.06-0.3mol amino acid, 0.02-0.1mol containing Al ^{3 +} compound. 8. The preparation method according to claim 1, characterized in that: the concentration of the sodium carbonate solution in step (7) is 5wt%. 9. A toughened starch-based one-component intumescent flame retardant prepared by the method of any one of claims 1 to 8. 10. The application of the toughened starch-based single-component intumescent flame retardant as claimed in claim 9 in the preparation of toughened flame-retardant polylactic acid, characterized in that: the toughened starch-based single component The components intumescent flame retardant and polylactic acid are mixed at a mass ratio of 90:10, and then extruded and injection molded to obtain toughened flame retardant polylactic acid.