CN108912671B

CN108912671B - Melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant and application thereof in PA6 resin

Info

Publication number: CN108912671B
Application number: CN201810901971.1A
Authority: CN
Inventors: 熊雷; 钟柔潮; 靳艳巧; 吕秋丰
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2018-08-09
Filing date: 2018-08-09
Publication date: 2020-04-10
Anticipated expiration: 2038-08-09
Also published as: CN108912671A

Abstract

The invention discloses an organic-inorganic double-coated red phosphorus flame retardant and application thereof in PA6 resin, and belongs to the field of high polymer materials. The invention mainly takes lignin, aldehyde, melamine, alkali, magnesium salt, red phosphorus and a dispersant as raw materials, and adopts Mannich reaction and chemical coprecipitation method to prepare the melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant. The organic-inorganic double-coated red phosphorus flame retardant can obviously improve red phosphorus, instability and surface properties and improve the compatibility with a high polymer material, the used lignin is a renewable biomass material and is cheap and easy to obtain, and good flame retardant synergistic effect is shown among red phosphorus, melamine modified lignin and magnesium hydroxide, and the flame retardant has good flame retardant and anti-dripping effects when used in PA6 resin.

Description

Melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant and application thereof in PA6 resin

Technical Field

The invention belongs to the field of high polymer materials, and particularly relates to a preparation method of a melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant and application of the melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant in PA6 resin.

Background

PA6 (nylon 6) is used as the most widely used engineering plastic in the world, and has the advantages of good mechanical property, stable chemical property, convenient molding and the like. However, the PA6 resin releases much heat during combustion, and flame droplets are easily generated to cause the spread of fire, thereby limiting the application range of the PA6 resin. Therefore, the flame retardant which can inhibit the combustion of the PA6 resin and prevent the dripping has great social and economic benefits and can further widen the application range of the PA6 resin is found.

The red phosphorus flame retardant belongs to a halogen-free flame retardant, and has the advantages of good flame retardant effect, good thermal stability, difficult volatilization, no generation of corrosive gas, good electrical insulation, insolubility in the application process, high melting point, low toxicity, small addition amount and the like. However, red phosphorus is easily exploded when existing in the form of dust, and can react to generate phosphine with highly toxic properties in a high-temperature environment, which all result in difficulty in carrying and storing, and greatly limit the application of red phosphorus. Therefore, the red phosphorus can exert larger flame retardant application value only after being coated on the surface. Red phosphorus coating can be classified into an inorganic coating method, an organic coating method, and an inorganic-organic coating method according to the difference of the coated red phosphorus substrate. The inorganic coating method is to coat red phosphorus with an inorganic material as a capsule material, and has some improvements in ignition point, moisture absorption, and amount of phosphine generated, but is deficient in compatibility with resin. The organic coating method uses organic polymer as a capsule material to coat red phosphorus, and has the advantages of less hydrogen phosphide generation amount, high ignition point of the product, good compatibility with resin and strong hygroscopicity. The organic-inorganic coating method is to carry out double coating on the red phosphorus by an organic method and an inorganic method, can integrate the advantages of organic coating and inorganic coating, overcomes the defects of the organic coating and the inorganic coating to a certain extent, and is an ideal process for preparing the microencapsulated red phosphorus at present.

The invention provides an organic-inorganic double-coated red phosphorus flame retardant prepared by using melamine modified lignin and magnesium hydroxide as capsule materials and red phosphorus as core materials, which not only can effectively utilize lignin which is a renewable resource and magnesium hydroxide which is an inorganic flame retardant to improve the instability and surface property of red phosphorus, but also can fully exert good flame-retardant synergistic effect among red phosphorus, melamine modified lignin and magnesium hydroxide, and is expected to be applied to PA6 resin and obtain good flame-retardant and molten drop-proof effects.

Disclosure of Invention

The invention aims to provide a preparation method of an organic-inorganic double-coated red phosphorus flame retardant, and the obtained flame retardant has the characteristics of good thermal stability, smoke abatement, molten drop resistance, good weather resistance, good compatibility with high polymers, high flame retardant efficiency and the like, and has a wide application prospect in PA6 resin.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention takes lignin, aldehyde, melamine, alkali, magnesium salt, red phosphorus and a dispersing agent as raw materials, and adopts a Mannich reaction and a chemical coprecipitation method to prepare the melamine modified lignin and hydroxide double-coated red phosphorus flame retardant. The process flow comprises the steps of preparing raw materials, synthesizing melamine modified lignin and preparing an organic-inorganic double-coated red phosphorus flame retardant, and specifically comprises the following steps:

(1) preparation of raw materials: weighing a certain amount of alkali, dissolving the alkali in deionized water to prepare an alkali solution with a certain concentration, and then adding lignin according to a certain proportion for dissolving.

Wherein the alkaline solution OH^-Concentration: 2-10wt% of lignin and alkaline solution OH^-The dosage ratio is as follows: 20-100 g/mol.

(2) Preparation of melamine modified lignin: the melamine modified lignin is prepared by adopting a Mannich reaction principle, and comprises the following specific steps: pouring the alkali solution of lignin into a three-neck flask provided with an electric stirrer, a thermometer and a reflux condenser, raising the temperature of an oil bath to 80-100 ℃, slowly adding a certain amount of aldehyde, and reacting for 1-3 h. Then slowly adding melamine with a certain proportion, and continuously reacting for 1-3h under heat preservation. The reaction conditions are as follows:

the dosage ratio of the aldehyde to the lignin is as follows: 0.05-0.5mol/10 g; the dosage ratio of the melamine to the lignin is as follows: 6.3-25.2g/10 g; atmosphere: air, stirring speed: 200 and 400 rpm.

(3) Preparing an organic-inorganic double-coated red phosphorus flame retardant: the melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant is prepared by a chemical coprecipitation method, and comprises the following specific steps: pouring the product obtained in the step (2) into a beaker, adding a certain amount of red phosphorus and a dispersant, mechanically stirring to fully disperse the red phosphorus, slowly adding a certain amount of magnesium salt, controlling a certain temperature to continuously stir for a period of time, aging the product for a certain period of time, carrying out vacuum filtration, drying the filtered product in an oven, crushing and sieving to obtain a khaki powder product, and sealing and storing.

Wherein the dosage ratio of the red phosphorus to the lignin is as follows: 0.4-1.2g/g, the dosage ratio of the dispersant to the red phosphorus is as follows: 0.005-0.01g/g, magnesiumSalt Mg²⁺With alkaline solution OH^-The dosage ratio is as follows: 1/2mol/mol, reaction temperature: 80-100 ℃, reaction time: 0.5-2h, aging time: 12-24h, drying temperature: 80-100 ℃, drying time: 12-24h, stirring speed: 200 and 400 rpm.

The lignin in the step (1) is one or more of enzymatic hydrolysis lignin, alkali lignin, organic lignin and lignosulfonate.

The alkali in the step (1) is one or more of sodium hydroxide, potassium hydroxide and calcium hydroxide.

The aldehyde in the step (2) is one or more of formaldehyde, acetaldehyde and butyraldehyde.

The magnesium salt in the step (3) is one or more of magnesium nitrate, magnesium phosphate, magnesium chloride, magnesium acetate and magnesium sulfide.

The dispersant in the step (3) comprises one or more of sodium dodecyl benzene sulfonate, sodium hexametaphosphate, sodium dodecyl sulfate and OP-10.

The invention has the following remarkable advantages:

(1) the invention can adjust the yield, the appearance, the particle size and the flame retardant property of the reaction product by controlling the proportion of the reaction raw materials, the reaction temperature, the reaction time and the stirring speed. The yield of the melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant prepared by the production method can reach over 88 percent, and the average grain diameter of the product is about 10-20 mu m.

(2) The melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant synthesized by the invention has the advantages of good thermal stability, high flame retardant efficiency, smoke abatement, molten drop resistance, good weather resistance and good compatibility with high polymer materials, and has a flame retardant grade reaching UL 94V-0 grade when the addition amount of the melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant in PA6 resin is 15%, thereby having wide application prospects in flame retardance of PA6 resin.

Drawings

FIG. 1 is a process flow diagram of the practice of the present invention;

FIG. 2 is an SEM photograph of red phosphorus used and a flame retardant prepared in example 1, wherein (a) is red phosphorus and (b) is a flame retardant of the present invention;

FIG. 3 is a FTIR plot of the flame retardant prepared in example 1;

FIG. 4 is an SEM photograph of a burned carbon layer of a sample bar prepared in application example 1;

FIG. 5 is an SEM photograph of a burned carbon layer of a sample strip prepared in application example 2;

FIG. 6 is an SEM photograph of the burned carbon layer of the sample bar prepared in application example 3.

Detailed Description

In order to make the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.

Example 1

Weighing 8g (0.2 mol) of sodium hydroxide in a beaker, adding deionized water to prepare a sodium hydroxide solution with the concentration of 4wt%, and adding 10g of enzymatic hydrolysis lignin in alkali liquor to be heated, stirred and dissolved. Pouring the alkali solution of lignin into a three-neck flask provided with an electric stirrer, a thermometer and a reflux condenser, adding 16mL (0.2 mol) of 38wt% formaldehyde aqueous solution, reacting for 3 hours at 80 ℃, adding 12.6g (0.1 mol) of melamine, pouring the reaction product in the three-neck flask into a beaker after reacting for 3 hours, adding 6g of red phosphorus and 0.03g of sodium dodecyl benzene sulfonate, slowly adding 20.3g (0.1 mol) of magnesium chloride hexahydrate after the red phosphorus is fully dispersed, and stirring and reacting for 2 hours. And aging the suspension obtained by the reaction for 12h, carrying out vacuum filtration, drying the filtered product in an oven at 80 ℃ for 24h, crushing and sieving to obtain a yellowish brown powder product, and sealing and storing.

Example 2

Weighing 11.2g (0.2 mol) of potassium hydroxide in a beaker, adding deionized water to prepare a potassium hydroxide solution with the concentration of 4wt%, adding 12g of enzymatic hydrolysis lignin in alkali liquor, heating, stirring and dissolving. Pouring the alkali solution of lignin into a three-neck flask provided with an electric stirrer, a thermometer and a reflux condenser, adding 24mL (0.3 mol) of 38wt% formaldehyde aqueous solution, reacting for 2h at 90 ℃, adding 12.6g (0.1 mol) of melamine, after reacting for 2h, pouring the reaction product in the three-neck flask into a beaker, adding 8g of red phosphorus and 0.04g of sodium dodecyl benzene sulfonate, slowly adding 25.6g (0.1 mol) of magnesium nitrate hexahydrate after the red phosphorus is fully dispersed, and stirring and reacting for 1 h. And aging the suspension obtained by the reaction for 18h, carrying out vacuum filtration, drying the filtered product in a 90 ℃ oven for 18h, crushing and sieving to obtain a yellowish brown powder product, and sealing and storing.

Example 3

Weighing 16g (0.4 mol) of sodium hydroxide into a beaker, adding deionized water to prepare a sodium hydroxide solution with the concentration of 8wt%, and adding 20g of organic lignin into alkali liquor to be heated, stirred and dissolved. Pouring the alkali solution of lignin into a three-neck flask provided with an electric stirrer, a thermometer and a reflux condenser, adding 36mL (0.4 mol) of butyraldehyde, reacting for 1h at 100 ℃, adding 25.6g (0.2 mol) of melamine, after reacting for 1h, pouring the reaction product in the three-neck flask into a beaker, adding 12g of red phosphorus and 0.12g of sodium dodecyl sulfate, slowly adding 51.2g (0.2 mol) of magnesium nitrate hexahydrate after the red phosphorus is fully dispersed, and stirring and reacting for 0.5 h. And aging the suspension obtained by the reaction for 24h, carrying out vacuum filtration, drying the filtered product in an oven at 100 ℃ for 12h, crushing and sieving to obtain a yellowish-brown powder product, and sealing and storing.

Application example 1

Weighing 15 parts of the flame retardant obtained in the example 1 and 85 parts of PA6 resin, uniformly mixing, carrying out twin-screw extrusion granulation and injection molding to obtain a flame retardant property test sample strip (length multiplied by width multiplied by thickness =130 mm multiplied by 10 mm multiplied by 3.2 mm), wherein the vertical combustion test grade can reach UL 94V-0 grade (no molten drop), and the residual carbon rate of the flame retardant sample strip is 16.3% after the flame retardant sample strip is fully carbonized at 500 ℃ in a muffle furnace. The melt index of the extruded pellets at 230 ℃ under a 2.16Kg load was 18.8g/10min (the melt index of pure PA6 resin at 230 ℃ under a 2.16Kg load was 15.7g/10 min).

Application example 2

Weighing 15 parts of the flame retardant obtained in the example 2 and 85 parts of PA6 resin, uniformly mixing, carrying out twin-screw extrusion granulation and injection molding to obtain a flame retardant property test sample strip (length multiplied by width multiplied by thickness =130 mm multiplied by 10 mm multiplied by 3.2 mm), wherein the vertical combustion test grade can reach UL 94V-0 grade (no molten drop), and the residual carbon rate of the flame retardant sample strip is 16.7% after the flame retardant sample strip is fully carbonized at 500 ℃ in a muffle furnace. The extruded pellets had a melt index of 20.2g/10min at 230 ℃ under a 2.16Kg load.

Application example 3

Weighing 15 parts of the flame retardant obtained in the example 3 and 85 parts of PA6 resin, uniformly mixing, carrying out twin-screw extrusion granulation and injection molding to obtain a flame retardant property test sample strip (length multiplied by width multiplied by thickness =130 mm multiplied by 10 mm multiplied by 3.2 mm), wherein the vertical combustion test grade can reach UL 94V-0 grade (no molten drop), and the residual carbon rate of the flame retardant sample strip is 15.2% after the flame retardant sample strip is fully carbonized at 500 ℃ in a muffle furnace. The extruded pellets had a melt index of 16.9g/10min at 230 ℃ under a 2.16Kg load.

Comparative examples

Taking commercially available microencapsulated red phosphorus as a comparison, weighing 85 parts of PA6 resin and 15 parts of commercially available microencapsulated red phosphorus flame retardant, uniformly mixing, carrying out twin-screw extrusion granulation and injection molding to obtain a flame retardant property test sample strip (length multiplied by width multiplied by =130 mm multiplied by 10 mm multiplied by 3.2 mm), wherein the vertical combustion test grade is UL 94V-2 grade (molten drop exists), and the residual carbon rate of the flame retardant sample strip after being fully carbonized at 500 ℃ in a muffle furnace is 12.6%. The extruded pellets had a melt index of 12.2g/10min at 230 ℃ under a 2.16Kg load.

FIG. 2 is an SEM photograph of red phosphorus used and a flame retardant prepared in example 1, wherein (a) is red phosphorus, and (b) is a flame retardant. As can be clearly seen by comparing the two figures, the red phosphorus is a long irregular block with smooth surface, the coated red phosphorus has obviously enlarged size and rough surface, and a plurality of particles and needles cover the surface of the red phosphorus, which shows that the red phosphorus is tightly coated and has the average particle size of about 10-20 μm.

FIG. 3 is a FTIR plot of the flame retardant prepared in example 1. As can be seen, the flame retardant prepared is 3150 cm^-1A wide and strong absorption peak appears nearby, which is attributed to the N-H stretching vibration of melamine and is 580 cm^-1And a characteristic absorption peak of Mg-O appears nearby. In connection with fig. 2, it is shown that the red phosphorus surface is indeed double coated with melamine modified lignin and magnesium hydroxide.

FIGS. 4 to 6 are SEM images of the carbon layer after combustion of the sample strips prepared in application examples 1 to 3, respectively. As can be seen from the figure, the obtained carbon layer is uniform and compact, and the sample has good flame retardant property.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.

Claims

1. The preparation method of the melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant is characterized by comprising the following steps: the preparation method comprises the steps of preparing raw materials, synthesizing melamine modified lignin and preparing the organic-inorganic double-coated red phosphorus flame retardant, and comprises the following steps:

(1) preparation of raw materials: weighing a certain amount of alkali, dissolving the alkali in deionized water to prepare an alkali solution with a certain concentration, and then adding lignin according to a certain proportion for dissolving;

(2) preparation of melamine modified lignin: the melamine modified lignin is prepared by adopting a Mannich reaction principle, and comprises the following specific steps: pouring the alkali solution of lignin into a three-neck flask provided with an electric stirrer, a thermometer and a reflux condenser, raising the temperature of an oil bath to 80-100 ℃, slowly adding a certain amount of aldehyde, and reacting for 1-3 h; slowly adding melamine with a certain ratio, and continuously reacting for 1-3h under heat preservation;

preparing an organic-inorganic double-coated red phosphorus flame retardant: the melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant is prepared by a chemical coprecipitation method, and comprises the following specific steps: pouring the product obtained in the step (2) into a beaker, adding a certain amount of red phosphorus and a dispersant, mechanically stirring to fully disperse the red phosphorus, slowly adding a certain amount of magnesium salt, controlling a certain temperature to continuously stir and react for a period of time, aging the product for a certain time, performing vacuum filtration, drying the filtered product in an oven, crushing and sieving to obtain a khaki powder product, and sealing and storing; the dosage ratio of the red phosphorus to the lignin in the step (3) is as follows: 0.4-1.2g/g, the dosage ratio of the dispersant to the red phosphorus is as follows: 0.005-0.01g/g magnesium salt Mg²⁺With alkaline solution OH^-The dosage ratio is as follows: 1/2mol/mol, reaction temperature: 80-100 ℃, reaction time: 0.5-2h, aging time: 12-24h, drying temperature: 80-100 ℃, drying time: 12-24h, stirring speed: 200 and 400 rpm.

2. The method of claim 1, wherein: step (1) OH^-Concentration: 2-10wt%, the dosage ratio of lignin and alkali liquor is: 20-100 g/mol.

3. The method of claim 1, wherein: the lignin in the step (1) is one or more of enzymatic hydrolysis lignin, alkali lignin, organic lignin and lignosulfonate; the alkali in the step (1) is one or more of sodium hydroxide, potassium hydroxide and calcium hydroxide.

4. The method of claim 1, wherein: the reaction conditions in the step (2) are as follows: the dosage ratio of the aldehyde to the lignin is as follows: 0.05-0.5mol/10 g; the dosage ratio of the melamine to the lignin is as follows: 6.3-25.2g/10 g; atmosphere: air, stirring speed: 200 and 400 rpm.

5. The method of claim 1, wherein: the aldehyde in the step (2) is one or more of formaldehyde, acetaldehyde and butyraldehyde.

6. The method of claim 1, wherein: the magnesium salt in the step (3) is one or more of magnesium nitrate, magnesium phosphate, magnesium chloride, magnesium acetate and magnesium sulfide; the dispersant in the step (3) comprises one or more of sodium dodecyl benzene sulfonate, sodium hexametaphosphate, sodium dodecyl sulfate and OP-10.

7. A melamine modified lignin/magnesium hydroxide double-coated red phosphorus flame retardant prepared by the preparation method of any one of claims 1 to 6.