Modified composite PP foaming flame-retardant material and preparation method thereof

Abstract

The invention discloses a modified composite PP foaming flame-retardant material and a preparation method thereof, and belongs to the technical field of PP materials. Comprising the following raw materials in parts by weight: 70-80 parts of homo-polypropylene, 5-10 parts of nano-montmorillonite, 3-6 parts of maleic anhydride grafted polypropylene, 10-20 parts of a halogen-free synergistic flame retardant, 1-2 parts of an antioxidant, 0.1-0.2 part of an initiator, 3-5 parts of a foaming agent and 0.5-1.5 parts of zinc oxide. According to the invention, the halogen-free synergistic flame retardant is prepared, so that the problem that the traditional halogen flame retardant releases toxic gas and smoke during combustion is avoided; phosphorus, sulfur and aromatic rings are introduced into the halogen-free synergistic flame retardant as functional groups, so that a synergistic flame retardant mechanism is effectively formed; the flame retardant can be subjected to a cross-linking reaction with a matrix, so that migration and precipitation of the flame retardant are reduced, and long-acting flame retardance is realized; in conclusion, the PP foaming material which is efficient, flame-retardant, environment-friendly and safe is prepared, and the PP foaming material has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of PP material technology, specifically relating to a modified composite PP foam flame retardant material and its preparation method. Background Technology

[0002] With the rapid development of polymer materials science, polypropylene (PP) foam materials have been widely used in automotive interiors, building insulation, packaging, and transportation due to their lightweight, high specific strength, excellent thermal insulation and sound absorption properties, and good chemical corrosion resistance. However, traditional polypropylene foam materials have many inherent defects, which seriously limit their widespread application in many scenarios with higher performance requirements. On the one hand, polypropylene is a highly flammable hydrocarbon polymer with a low limiting oxygen index (LOI), resulting in severe dripping during combustion, rapid flame propagation, and the release of large amounts of black smoke and toxic gases, posing significant fire safety hazards. This makes it difficult for untreated PP foam materials to meet the stringent flame retardant requirements of fields such as electronics, aerospace, and high-speed rail transportation.

[0003] Currently, the mainstream methods for improving the flame retardant properties of PP foam materials in the industry mainly include physical blending with added flame retardants and chemical grafting modification. Commonly used additive flame retardants include halogenated and inorganic hydroxides. Among them, halogenated flame retardants, although highly efficient, produce a large amount of smoke and release toxic and corrosive gases during combustion, and are facing increasingly stringent environmental regulations. Inorganic flame retardants, represented by magnesium hydroxide and aluminum hydroxide, are environmentally friendly, but require very high addition levels (usually exceeding 50%) to achieve the desired flame retardant effect. This leads to a sharp deterioration in the melt flowability of the material, poor processing performance, and, more seriously, significantly damages the flexibility and mechanical strength of the foam material, causing the material to become brittle, increase in density significantly, and lose the lightweight advantage of foam materials.

[0004] Therefore, developing a modified composite PP foam flame-retardant material and its preparation method has important market prospects for promoting the industrial application of high-performance PP foam materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a modified composite PP foam flame retardant material and its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions: A modified composite PP foam flame retardant material comprises the following raw materials in parts by weight: 70-80 parts homopolymer polypropylene, 5-10 parts nano-montmorillonite, 3-6 parts maleic anhydride grafted polypropylene, 10-20 parts halogen-free synergistic flame retardant, 1-2 parts antioxidant, 0.1-0.2 parts initiator, 3-5 parts foaming agent, and 0.5-1.5 parts zinc oxide.

[0007] As a further technical solution, the antioxidant is one of antioxidant 1010, antioxidant 1076, antioxidant 3114 and antioxidant 1790.

[0008] As a further technical solution, the halogen-free synergistic flame retardant is prepared through the following steps: A1. Take a dry round-bottom flask, add the weighed p-hydroxybenzaldehyde and thiourea in sequence, add anhydrous ethanol as solvent, add 2-3 drops of glacial acetic acid as catalyst, add a stir bar, install a spherical condenser, turn on magnetic stirring, heat to 80-85℃ in an oil bath, keep warm and reflux for 4-6 hours, after the reaction is completed, after post-treatment, obtain intermediate product 1; A2. Take a dry round-bottom flask, add the weighed 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and intermediate product 1 in sequence, add ethanol as solvent to the flask, put in a stir bar, install a spherical condenser, turn on magnetic stirring, heat to 85-90℃ in an oil bath, keep it at the temperature and reflux for 6-7 hours. After the reaction is completed, after post-processing, intermediate product 2 is obtained. A3. In a fume hood, take a dry round-bottom flask, add the weighed intermediate product 2, then add N,N-dimethylformamide as a solvent, place a stir bar, install a spherical condenser, turn on the magnetic stirrer, and then add sodium hydroxide in batches. After stirring for 20-30 minutes in a water bath at 50-60℃, slowly add allyl chloride dropwise through a constant pressure dropping funnel. After the addition is complete, keep the mixture under reflux for 6-8 hours. After the reaction is complete, and after post-treatment, a halogen-free synergistic flame retardant is obtained.

[0009] As a further technical solution, the ratio of p-hydroxybenzaldehyde to thiourea in step A1 is 26.7-28.5g:7.6g.

[0010] As a further technical solution, in step A2, the ratio of the amount of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to intermediate product 1 is 45.5-47.1g:28.4g.

[0011] As a further technical solution, the ratio of intermediate product 2, sodium hydroxide and allyl chloride in step A3 is 71.6g:8.0g:16.8-17.2g.

[0012] The reaction formula for preparing the halogen-free synergistic flame retardant through the above steps is as follows: This invention prepares a halogen-free synergistic flame retardant in three steps. To ensure the smooth progress of the reaction, the amount of reactants needs to be strictly controlled in each step. Specifically, in step A1, the molar ratio of p-hydroxybenzaldehyde to thiourea is controlled to be close to 2:1, with the former in excess, so that both amino groups of the latter participate in the reaction. In step A2, the molar ratio of DOPO to intermediate 1 is controlled to be close to 2:1, with the former in excess, so that both imine groups of the latter participate in the reaction. Finally, in step A3, the molar ratio of allyl chloride to intermediate 2 is controlled to be close to 2:1, with the former in excess, so that both hydroxyl groups of the latter participate in the reaction.

[0013] As can be seen from the above reaction formula, the flame retardant prepared by this invention does not contain halogens and belongs to halogen-free flame retardants. Moreover, the multi-group in the flame retardant can play a multi-group role. Among them, the phosphorus element (phosphate ester structure) can decompose at high temperature to generate phosphoric acid and polyphosphoric acid, catalyzing the formation of aromatic rings into carbon, forming a dense heat-insulating carbon layer, and blocking heat. The sulfur element generates SO2 gas at high temperature, diluting the oxygen in the combustion zone. At the same time, the sulfur compound can promote the carbonization efficiency of the phosphorus-based flame retardant and enhance the density of the carbon layer. It forms a flame-retardant synergistic effect with phosphorus. Furthermore, the introduced aromatic ring is itself a "carbon-forming group", which can quickly form a stable carbon layer at high temperature, strengthening the flame-retardant effect of the condensed phase. It not only further improves the flame-retardant effect, but also belongs to a rigid group, which can significantly increase the thermal decomposition temperature of the material. Finally, one end of the flame retardant is a double bond, which can undergo a cross-linking reaction with the matrix at high temperature, making it difficult for it to precipitate or migrate in the substrate, thus making the flame-retardant effect more durable.

[0014] This invention also provides a method for preparing a modified composite PP foam flame-retardant material, comprising the following steps: B1. Place the homopolymer polypropylene in a forced-air drying oven to dry it, remove the moisture from the raw material, and avoid the rupture of the cells due to the presence of moisture during subsequent processing to obtain dried polypropylene. B2. Next, place the nano-montmorillonite and maleic anhydride-grafted polypropylene in a mixer and stir at low speed to achieve initial dispersion of montmorillonite. Then, add the dried polypropylene, halogen-free synergistic flame retardant, antioxidant and initiator to the mixer and stir at high speed to ensure uniform dispersion of each component. Finally, add the foaming agent and zinc oxide and continue mixing for 3-5 minutes to obtain the mixture. B3. The mixture is fed into a twin-screw extruder for melt blending, extruded through a die, air-cooled, and pelletized to obtain modified composite PP masterbatch; B4. The modified composite PP masterbatch is fed into a foaming molding machine. After the material has completed foaming, cooling and curing in the mold, it is demolded to obtain the modified composite PP foamed flame retardant material.

[0015] As a further technical solution, the drying temperature is 80-90℃ and the time is 2-3 hours.

[0016] As a further technical solution, the low-speed stirring speed is 300-500 rpm, and the time is 5-10 min.

[0017] As a further technical solution, the high-speed stirring speed is 1000-1500 rpm, and the time is 20-30 min.

[0018] The beneficial effects of this invention are: I. This invention produces a halogen-free synergistic flame retardant, which avoids the problem of traditional halogen-based flame retardants releasing toxic gases and fumes during combustion, and meets increasingly stringent environmental regulations. Second, the introduction of phosphorus, sulfur, and aromatic rings as functional groups in halogen-free synergistic flame retardants effectively forms a synergistic flame retardant mechanism; and the flame retardant has a double bond structure at the end, which can undergo cross-linking reaction with the matrix, reducing the migration and precipitation of the flame retardant and achieving long-lasting flame retardancy. In summary, this invention produces a PP foam material that is both highly flame-retardant and environmentally friendly, with promising prospects for industrial application. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 Preparation of halogen-free synergistic flame retardants: A1. Take a dry round-bottom flask, add 26.7g of p-hydroxybenzaldehyde and 7.6g of thiourea in sequence, add 100mL of anhydrous ethanol as solvent, add 2 drops of glacial acetic acid as catalyst, add a stir bar, install a spherical condenser, turn on magnetic stirring, heat to 80℃ in an oil bath, keep warm and reflux for 4h, after the reaction is completed, stop heating, cool, vacuum filter with a Buchner funnel, recrystallize and purify to intermediate product 1; A2. Take a dry round-bottom flask, add 45.5g of weighed 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 28.4g of intermediate product 1 in sequence, add 120mL of ethanol as solvent, place a stir bar, install a spherical condenser, turn on magnetic stirring, heat to 85℃ in an oil bath, keep the temperature under reflux for 6h, stop heating after the reaction is completed, cool, filter, filter the precipitated solid through a Buchner funnel under vacuum, filter the solid with ethanol through a Buchner funnel under vacuum, dry, and obtain intermediate product 2; A3. In a fume hood, take a dry round-bottom flask, add 71.6g of weighed intermediate product 2, then add N,N-dimethylformamide as a solvent, place a stir bar, install a spherical condenser, turn on magnetic stirring, and then add 8.0g of sodium hydroxide in four portions, each time in the same amount. After stirring for 20 minutes in a 50°C water bath, slowly add 16.8g of allyl chloride dropwise through a constant pressure dropping funnel. After the addition is complete, keep the mixture under reflux for 6 hours. After the reaction is complete, cool to room temperature, concentrate under reduced pressure using a rotary evaporator, and purify by column chromatography (silica gel, eluent gradient from pure petroleum ether to petroleum ether:ethyl acetate = 10:1). Remove the eluent by rotary evaporation to obtain a halogen-free synergistic flame retardant. A method for preparing a modified composite PP foam flame-retardant material includes the following steps: B1. Place 70 parts of homopolymer polypropylene in a forced-air drying oven and dry at 80°C for 2 hours to remove moisture from the raw material and prevent the cells from breaking due to moisture during subsequent processing, thus obtaining dried polypropylene. B2. Next, place 5 parts of nano-montmorillonite and 3 parts of maleic anhydride-grafted polypropylene in a mixer and stir at a low speed of 300 rpm for 5 minutes to achieve initial dispersion of montmorillonite. Then, add dried polypropylene, 10 parts of halogen-free synergistic flame retardant, 1 part of antioxidant and 0.1 parts of initiator to the mixer and stir at a high speed of 1000 rpm for 20 minutes to ensure uniform dispersion of each component. Finally, add 3 parts of foaming agent and 0.5 parts of zinc oxide and continue mixing for 3 minutes to obtain the mixture. B3. The mixture is fed into a twin-screw extruder (the temperature of each section of the extruder is controlled as follows: feeding section 160℃, compression section 175℃, homogenization section 180℃, die head 185℃, and the screw speed is set to 300r / min) for melt blending, extruded through the die head, air-cooled, and pelletized to obtain modified composite PP masterbatch. B4. The modified composite PP masterbatch is fed into a foaming molding machine (the parameters of the foaming molding machine are: barrel temperature 170℃, nozzle temperature 180℃, mold temperature 30℃, injection pressure 80MPa, holding pressure 40MPa, and holding time 5s). After the material completes foaming, cooling and curing in the mold, it is demolded to obtain the modified composite PP foamed flame retardant material.

[0021] Example 1 Preparation of halogen-free synergistic flame retardants: A1. Take a dry round-bottom flask, add 28.5g of p-hydroxybenzaldehyde and 7.6g of thiourea in sequence, add 100mL of anhydrous ethanol as solvent, add 3 drops of glacial acetic acid as catalyst, add a stir bar, install a spherical condenser, turn on magnetic stirring, heat to 85℃ in an oil bath, keep warm and reflux for 6h, after the reaction is completed, stop heating, cool, vacuum filter with a Buchner funnel, recrystallize and purify to intermediate product 1; A2. Take a dry round-bottom flask, add 47.1g of weighed 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 28.4g of intermediate product 1 in sequence, add 120mL of ethanol as solvent, place a stir bar, install a spherical condenser, turn on magnetic stirring, heat to 90℃ in an oil bath, keep the temperature under reflux for 7h, after the reaction is completed, stop heating, cool, filter, filter the precipitated solid through a Buchner funnel under vacuum, and filter the solid with ethanol through a Buchner funnel under vacuum, dry to obtain intermediate product 2; A3. In a fume hood, take a dry round-bottom flask, add 71.6g of weighed intermediate product 2, then add N,N-dimethylformamide as a solvent, place a stir bar, install a spherical condenser, turn on magnetic stirring, and then add 8.0g of sodium hydroxide in four portions, each time in the same amount. After stirring in a 60℃ water bath for 30 minutes, slowly add 17.2g of allyl chloride dropwise through a constant pressure dropping funnel. After the addition is complete, keep the mixture under reflux for 8 hours. After the reaction is complete, cool to room temperature, concentrate under reduced pressure using a rotary evaporator, and purify by column chromatography (silica gel, eluent gradient from pure petroleum ether to petroleum ether:ethyl acetate = 10:1). Remove the eluent by rotary evaporation to obtain a halogen-free synergistic flame retardant. A method for preparing a modified composite PP foam flame-retardant material includes the following steps: B1. Place 75 parts of homopolymer polypropylene in a forced-air drying oven and dry at 85°C for 3 hours to remove moisture from the raw material and prevent the cells from breaking due to moisture during subsequent processing, thus obtaining dried polypropylene. B2. Next, place 7.5 parts of nano-montmorillonite and 4.5 parts of maleic anhydride-grafted polypropylene in a mixer and stir at a low speed of 400 rpm for 10 minutes to achieve initial dispersion of montmorillonite. Then, add dried polypropylene, 15 parts of halogen-free synergistic flame retardant, 1.5 parts of antioxidant and 0.15 parts of initiator to the mixer and stir at a high speed of 1500 rpm for 30 minutes to ensure uniform dispersion of each component. Finally, add 4 parts of foaming agent and 1.0 part of zinc oxide and continue mixing for 5 minutes to obtain the mixture. B3. The mixture is fed into a twin-screw extruder (the temperature of each section of the extruder is controlled as follows: feeding section 170℃, compression section 185℃, homogenization section 190℃, die head 195℃, and the screw speed is set to 350r / min) for melt blending, extruded through the die head, air-cooled, and pelletized to obtain modified composite PP masterbatch. B4. The modified composite PP masterbatch is fed into a foaming molding machine (the parameters of the foaming molding machine are: barrel temperature 185℃, nozzle temperature 190℃, mold temperature 40℃, injection pressure 100MPa, holding pressure 50MPa, and holding time 8s). After the material completes foaming, cooling and curing in the mold, it is demolded to obtain the modified composite PP foamed flame retardant material.

[0022] Example 3 The only difference between this embodiment and Embodiment 2 is that, in this embodiment, a method for preparing a modified composite PP foam flame-retardant material includes the following steps: B1. Place 80 parts of homopolymer polypropylene in a forced-air drying oven and dry at 90°C for 3 hours to remove moisture from the raw material and prevent the cells from breaking due to moisture during subsequent processing, thus obtaining dried polypropylene. B2. Next, place 10 parts of nano-montmorillonite and 6 parts of maleic anhydride-grafted polypropylene in a mixer and stir at a low speed of 500 rpm for 10 minutes to achieve initial dispersion of montmorillonite. Then, add dried polypropylene, 20 parts of halogen-free synergistic flame retardant, 2 parts of antioxidant and 0.2 parts of initiator to the mixer and stir at a high speed of 1500 rpm for 30 minutes to ensure uniform dispersion of each component. Finally, add 5 parts of foaming agent and 1.5 parts of zinc oxide and continue mixing for 5 minutes to obtain the mixture. B3. The mixture is fed into a twin-screw extruder (the temperature of each section of the extruder is controlled as follows: feeding section 170℃, compression section 185℃, homogenization section 190℃, die head 195℃, and the screw speed is set to 350r / min) for melt blending, extruded through the die head, air-cooled, and pelletized to obtain modified composite PP masterbatch. B4. The modified composite PP masterbatch is fed into a foaming molding machine (the parameters of the foaming molding machine are: barrel temperature 185℃, nozzle temperature 190℃, mold temperature 40℃, injection pressure 100MPa, holding pressure 50MPa, and holding time 8s). After the material completes foaming, cooling and curing in the mold, it is demolded to obtain the modified composite PP foamed flame retardant material.

[0023] Comparative Example 1 The only difference between this comparative example and Example 3 is that in this comparative example, an equal amount of DOPO is used as a flame retardant to replace the halogen-free synergistic flame retardant, and the material is prepared accordingly.

[0024] Comparative Example 2 The only difference between this comparative example and Example 3 is that in this comparative example, an equal amount of magnesium hydroxide is used as a flame retardant to replace the halogen-free synergistic flame retardant, and the material is prepared accordingly.

[0025] The following performance tests were conducted on Examples 1, 2, and 3, and Comparative Examples 1 and 2: The oxygen index was determined according to GB / T 2406.2-2009 standard; The heat distortion temperature was determined according to GB / T 1634.2-2019 standard. After storing the samples outdoors for 300 days, the oxygen index was determined using the GB / T 2406.2-2009 standard. The measurement results are shown in Table 1: Table 1 As can be seen from the performance test results in Table 1, the PP foam material prepared by the embodiment of the present invention has higher flame retardancy and heat resistance than the comparative example, and can still maintain high flame retardancy after 300 days of long-term storage. Therefore, the present invention has important application value in the field of PP material technology.

[0026] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0027] The above description is merely an example and illustration of the present invention. Any modifications or additions made by those skilled in the art to the specific embodiments described, or any substitutions made in a similar manner, should fall within the protection scope of the present invention.

Claims

1. A modified composite PP foam flame-retardant material, characterized in that, It includes the following raw materials in parts by weight: 70-80 parts homopolymer polypropylene, 5-10 parts nano montmorillonite, 3-6 parts maleic anhydride grafted polypropylene, 10-20 parts halogen-free synergistic flame retardant, 1-2 parts antioxidant, 0.1-0.2 parts initiator, 3-5 parts foaming agent and 0.5-1.5 parts zinc oxide.

2. The modified composite PP foam flame-retardant material according to claim 1, characterized in that, The halogen-free synergistic flame retardant is prepared by the following steps: A1. In a flask, add p-hydroxybenzaldehyde, thiourea and anhydrous ethanol in sequence, add 2-3 drops of glacial acetic acid, start stirring, and reflux at 80-85℃ for 4-6 hours. When the reaction is complete, intermediate product 1 is obtained. A2. In a flask, add 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, intermediate product 1 and ethanol in sequence. Start stirring and reflux at 85-90℃ for 6-7 hours. When the reaction is complete, intermediate product 2 is obtained. A3. In a flask, add intermediate product 2 and N,N-dimethylformamide in sequence, start stirring, then add sodium hydroxide to the flask, stir for 20-30 minutes in a water bath at 50-60℃, then add allyl chloride dropwise. After the addition is complete, keep the mixture under reflux for 6-8 hours. Once the reaction is complete, a halogen-free synergistic flame retardant is obtained.

3. The modified composite PP foam flame-retardant material according to claim 2, characterized in that, In step A1, the ratio of p-hydroxybenzaldehyde to thiourea is 26.7-28.5g:7.6g.

4. The modified composite PP foam flame-retardant material according to claim 2, characterized in that, In step A2, the ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to intermediate 1 is 45.5-47.1 g: 28.4 g.

5. The modified composite PP foam flame-retardant material according to claim 2, characterized in that, In step A3, the ratio of intermediate product 2, sodium hydroxide, and allyl chloride is 71.6g:8.0g:16.8-17.2g.

6. The modified composite PP foam flame-retardant material according to claim 1, characterized in that, The antioxidant is one of antioxidant 1010, antioxidant 1076, antioxidant 3114 and antioxidant 1790.

7. A method for preparing modified composite PP foamed flame-retardant material, used to prepare the modified composite PP foamed flame-retardant material according to any one of claims 1-6, characterized in that, Includes the following steps: B1. Dry the homopolymer polypropylene to obtain dried polypropylene; B2. Next, place nano-montmorillonite and maleic anhydride-grafted polypropylene in a mixer and mix at low speed. Then, add dried polypropylene, halogen-free synergistic flame retardant, antioxidant and initiator to the mixer and mix at high speed. Finally, add foaming agent and zinc oxide and continue mixing for 3-5 minutes to obtain the mixture. B3. The mixture is fed into a twin-screw extruder for melt blending, extruded through a die, air-cooled, and pelletized to obtain modified composite PP masterbatch; B4. The modified composite PP masterbatch is fed into a foaming molding machine. After the material has completed foaming, cooling and curing in the mold, it is demolded to obtain the modified composite PP foamed flame retardant material.

8. The preparation method of the modified composite PP foamed flame-retardant material according to claim 7, characterized in that, The drying temperature is 80-90℃, and the time is 2-3 hours.

9. The preparation method of the modified composite PP foamed flame-retardant material according to claim 7, characterized in that, The low-speed stirring speed is 300-500 rpm, and the time is 5-10 min.

10. The preparation method of the modified composite PP foamed flame-retardant material according to claim 7, characterized in that, The high-speed stirring speed is 1000-1500 rpm, and the time is 20-30 min.

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