A biomass-based highly flame-retardant MPP pipe and preparation method thereof

Abstract

The present invention discloses a method for preparing a biomass-based highly flame-retardant MPP pipe, and belongs to the technical field of flame-retardant pipes. The biomass-based highly flame-retardant MPP pipe comprises, by weight, 64 to 69 parts of polypropylene, 11 to 16 parts of modified flame retardant powder, 12 to 17 parts of filler, 1 to 3 parts of lubricant and 0.5 to 1 part of antioxidant. The modified flame retardant powder is obtained by grafting carboxymethyl chitosan with N-aminoethyl-3-aminopropyltriethoxysilane. In the preparation process of the MPP pipe of the present invention, carboxymethyl chitosan modified by silane coupling agent KH-793 is added to improve the flame retardant properties of the MPP pipe.

Description

Technical Field

[0001] The present invention belongs to the technical field of flame-retardant pipes, and in particular relates to a biomass-based highly flame-retardant MPP pipe and a preparation method thereof. Background Art

[0002] MPP pipes are generally divided into two types: trenchless and excavation. MPP trenchless pipes are also called MPP jacking pipes or dragging pipes. MPP pipes are made of modified polypropylene (MPP) as the main material and are suitable for use in medium and low voltage transmission line cable pipes within 10 kilovolts. They are resistant to high temperatures and are widely used. However, the existing MPP pipes still have certain problems. For example, in the process of large-scale power transmission, heat energy accumulates and flammability is likely to occur, which brings certain inconveniences to the use of MPP pipes. Therefore, it is urgent to improve their flame retardant properties.

[0003] Carboxymethyl chitosan is a high-grade chitosan derivative obtained by chemically modifying marine chitosan. It is a natural bio-adjuvant product with good biodegradability and biocompatibility. Carboxymethyl chitosan has a large amount of carbon and nitrogen sources. During the combustion process, it can be carbonized in the polymer to hinder the combustion, promote the formation of an expanded carbon layer, and help inhibit the heat exchange in the matrix. However, the number of hydroxyl and amino groups in carboxymethyl chitosan is too large, and it has certain hydrophilic and oleophobic properties, and its compatibility with polypropylene (PP) is poor. Therefore, it is necessary to modify carboxymethyl chitosan to exert excellent flame retardant properties. Carboxymethyl chitosan is not only a common chitosan derivative, but also a low-cost polysaccharide polymer with the characteristics of biodegradability, biocompatibility, environmental friendliness and non-toxicity. Carboxymethyl chitosan has a large amount of carbon source and a certain amount of nitrogen source. It will undergo a ring-opening reaction at high temperature to form an aromatic cross-linked structure, that is, a carbon layer is formed in the condensed phase. However, due to the hydrophilic and oleophobic properties of carboxymethyl chitosan and its poor compatibility with polypropylene (PP), if it is directly added, it will not have a good flame retardant effect.

[0004] In view of the above problems, it is of great significance to develop a new flame retardant and MPP pipe with high efficiency flame retardant properties using carboxymethyl chitosan. Summary of the invention

[0005] In view of the deficiencies of the above prior art, the present invention provides a biomass-based highly flame-retardant MPP pipe and a preparation method thereof. During the preparation of the MPP pipe, carboxymethyl chitosan modified by silane coupling agent KH-793 is added to make the prepared MPP pipe have high flame retardant properties, which is specifically achieved through the following technologies.

[0006] A biomass-based highly flame-retardant MPP pipe comprises, by weight, 64 to 69 parts of polypropylene, 11 to 16 parts of modified flame retardant powder, 12 to 17 parts of filler, 1 to 3 parts of lubricant and 0.5 to 1 part of antioxidant.

[0007] The modified flame retardant powder is obtained by grafting carboxymethyl chitosan with N-aminoethyl-3-aminopropyltriethoxysilane.

[0008] The silane coupling agent selected in the present invention is N-aminoethyl-3-aminopropyltriethoxysilane (KH-793), which has rich carbon source, nitrogen source and silicon source. On the one hand, the amount of C in carboxymethyl chitosan is increased, and a silicon source is additionally introduced. Carboxymethyl chitosan undergoes a ring-opening reaction at high temperature and self-condenses in the matrix to form an aromatic ring cross-linked structure, that is, a carbon layer is generated in the condensed phase, which is beneficial to inhibit heat exchange in the matrix, thereby achieving the effect of interrupting polymer combustion; on the other hand, KH-793 further increases the barrier The amount of nitrogen source in the flame retardant, amino group can release a large amount of gas in the form of NH3 during thermal decomposition, dilute the concentration of combustible gas, and further improve the flame retardant properties of carboxymethyl chitosan. In addition, the silicon source introduced by the coupling agent will migrate to the surface of the melt during combustion to form a dense and stable silicon layer (the main component is SiO2), which plays a role in blocking thermal oxygen. In general, under the joint action of carboxymethyl chitosan and KH-793, the application of carboxymethyl chitosan-based flame retardant in MPP pipes has been better reflected.

[0009] Preferably, the filler is a mixture of talc and powdered quartz.

[0010] Preferably, the lubricant is at least one of calcium stearate, methyl stearate or butyl stearate.

[0011] Preferably, the antioxidant is a hindered phenol antioxidant and / or a phosphite antioxidant.

[0012] Preferably, the preparation method of the modified flame retardant powder comprises the following steps:

[0013] P1. Dry the carboxymethyl chitosan, dissolve it in an acetic acid solution, and adjust the pH value to acidic to obtain solution A; add N-aminoethyl-3-aminopropyltriethoxysilane to the acetic acid solution and dissolve it to obtain solution B;

[0014] P2. Under the protection of inert gas, the solution A and the solution B are mixed to obtain a solution C, which is then heated, stirred, filtered under reduced pressure, washed, dried, crushed, ground, and sieved to obtain a modified flame retardant powder.

[0015] The present invention adopts carboxymethyl chitosan as a raw material, which is widely available and inexpensive, and then a silane coupling agent (N-aminoethyl-3-aminopropyltriethoxysilane, KH-793) is acted on the carboxymethyl chitosan to obtain a carboxymethyl chitosan grafted silane coupling agent composite material. After acting on an MPP pipe, high flame retardant performance can be obtained. The method of the present invention can not only solve the problem of normal use of subsequent MPP pipes, but also reduce the cost of flame retardants, which meets the use requirements of power technology.

[0016] Preferably, the mass percentage of carboxymethyl chitosan in solution A is 1 to 1.5%.

[0017] Preferably, the mass percentage of N-aminoethyl-3-aminopropyltriethoxysilane in solution B is 1.5-2%.

[0018] Preferably, the mass ratio of carboxymethyl chitosan to N-aminoethyl-3-aminopropyl triethoxysilane in solution C is (8-12.5):(2.5-8.1). Further preferably, the mass ratio of carboxymethyl chitosan to N-aminoethyl-3-aminopropyl triethoxysilane in solution C is 10:5.69.

[0019] Preferably, in step P1, the drying temperature is 100-120° C., and the drying time is 5-8 hours.

[0020] Preferably, the pH values ​​of solution A and solution B in step P1 are both 3-6.

[0021] Preferably, the heating and stirring in step P2 are divided into two stages. The first stage is heating to 40-60° C. and stirring time is 2-4 h; the second stage is heating to 60-80° C. and stirring time is 0.5-1 h.

[0022] Preferably, in step P2, the drying temperature is 60-80° C. and the drying time is 24-30 hours.

[0023] Preferably, the inert gas in step P2 is nitrogen or argon.

[0024] The method for preparing any of the above-mentioned biomass-based highly flame-retardant MPP pipes comprises the following steps:

[0025] S1, stirring and mixing polypropylene and modified flame retardant powder, and continuing to stir and mix at temperature I to obtain mixture I; stirring and mixing fillers and lubricants, stirring and mixing at temperature II, adding antioxidants, continuing to stir and mix, and obtaining mixture II after heat and pressure maintenance;

[0026] S2, mixing mixture I and mixture II, heating to temperature III, stopping stirring, and cooling to obtain mixture III;

[0027] S3, extruding and granulating the mixture III, and then thermoplasticizing and molding it through a mold to obtain an MPP pipe.

[0028] Preferably, in step S1, temperature I is 70-90°C; temperature II is 100-120°C.

[0029] Preferably, the pressure of the pressure-maintaining step S1 is 8 to 11 MPa, and the pressure-maintaining time is 8 to 16 minutes.

[0030] Preferably, in step S2, the mass ratio of mixture I to mixture II is 1:(1-2).

[0031] Preferably, the temperature III in step S2 is 110-130°C.

[0032] Compared with the prior art, the present invention is beneficial in that:

[0033] 1. The carbon source and nitrogen source in carboxymethyl chitosan can delay or stop the thermal degradation of the polymer in the condensed phase, interrupt the generation process of combustible volatiles, thereby reducing the flammability of the material and stopping or delaying combustion. However, the number of hydroxyl and amino groups in carboxymethyl chitosan is too large, and its compatibility with MPP organic materials is poor. It cannot improve the flame retardant properties of MPP pipes well when used alone. Therefore, the present invention adopts silane coupling agent KH-793 to graft and modify carboxymethyl chitosan, improves the disadvantage of poor organic compatibility of carboxymethyl chitosan, improves the flame retardant properties of carboxymethyl chitosan, and thus improves the flame retardant properties of MPP pipes;

[0034] 2. The MPP pipe of the present invention has excellent flame retardant properties, the limiting oxygen index is above 42%, and the Vicat softening point temperature is not less than 152°C;

[0035] 3. Carboxymethyl chitosan is a derivative of common chitosans and a low-priced polysaccharide polymer. With the increasing prominence of environmental resource issues, people have a deeper understanding of carboxymethyl chitosan and how to use it has attracted more and more attention. Flame retardant materials prepared with carboxymethyl chitosan as raw materials can not only produce low-priced, efficient and useful flame retardants, but also expand the application field of carboxymethyl chitosan, which is of great significance to the effective utilization of biomass-based materials and the significant improvement of the ecological environment in my country. DETAILED DESCRIPTION

[0036] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0037] A biomass-based highly flame-retardant MPP pipe comprises, by weight, 64 to 69 parts of polypropylene, 11 to 16 parts of modified flame retardant powder, 12 to 17 parts of filler, 1 to 3 parts of lubricant and 0.5 to 1 part of antioxidant.

[0038] Wherein, the modified flame retardant powder is obtained by grafting carboxymethyl chitosan with N-aminoethyl-3-aminopropyl triethoxysilane (KH-793);

[0039] Optionally, the filler is a mixture of talcum powder and powdered quartz, and the mass ratio of talcum powder to powdered quartz is 2:1;

[0040] Optionally, the lubricant is at least one of calcium stearate, methyl stearate or butyl stearate;

[0041] Optionally, the antioxidant is a hindered phenol antioxidant and / or a phosphite antioxidant; further preferably, the antioxidant is antioxidant 1010;

[0042] The preparation method of the modified flame retardant powder comprises the following steps:

[0043] P1. Dry carboxymethyl chitosan at 100-120°C for 5-8h, and dissolve it in acetic acid solution, the mass ratio of carboxymethyl chitosan to acetic acid is 1:70, to obtain solution A, the mass percentage of carboxymethyl chitosan in solution A is 1.41%; add N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) to acetic acid solution and dissolve it, the mass ratio of N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) to acetic acid solution is 1:50, to obtain solution B, the mass percentage of N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) in solution B is 1.96%; the pH values ​​of solution A and solution B are both 3-6;

[0044] P2. Under the protection of nitrogen or argon, solution A and solution B are mixed in a mass ratio of (59-86):(14-41) to obtain solution C, in which the mass ratio of carboxymethyl chitosan to N-aminoethyl-3-aminopropyltriethoxysilane is (8-12.5):(2.5-8.1). The solution is heated to 40-60°C, stirred for 2-4 hours, then heated to 60-80°C, and the reaction is continued with stirring for 0.5-1 hour. The solution is filtered under reduced pressure, washed, dried at 60-80°C for 24-30 hours, crushed, ground, and sieved to obtain a modified flame retardant powder.

[0045] The method for preparing a biomass-based highly flame-retardant MPP pipe using the modified flame retardant powder comprises the following steps:

[0046] S1. Stir and mix polypropylene and modified flame retardant powder, place at 70-90° C. and continue to stir and mix to obtain mixture I; mix a mixture of talcum powder and powdered quartz and calcium stearate, place at 100-120° C. and stir and mix evenly, add antioxidant 1010, continue to stir and mix, keep warm, and maintain pressure at a pressure of 8-11 MPa for 8-16 minutes to obtain mixture II;

[0047] S2, mixing mixture I and mixture II in a mass ratio of 1:(1-2), heating to 110-130° C., stopping stirring, and cooling to obtain mixture III;

[0048] S3, extruding and granulating the mixture III, and then thermoplasticizing and molding it through a mold to obtain an MPP pipe.

[0049] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] Example 1

[0051] A biomass-based highly flame-retardant MPP pipe, comprising, by weight, 67 parts of polypropylene, 13 parts of modified flame retardant powder, 17 parts of a mixture of talcum powder and powdered quartz, 2 parts of calcium stearate and 1 part of antioxidant 1010;

[0052] The preparation method of the modified flame retardant powder comprises the following steps:

[0053] P1. Dry carboxymethyl chitosan at 110° C. for 6 h, dissolve it in a 2% acetic acid solution, the mass ratio of carboxymethyl chitosan to the acetic acid solution is 1:70, and obtain solution A; add N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) to a 2% acetic acid solution and dissolve it, the mass ratio of N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) to the acetic acid solution is 1:50, and obtain solution B; the pH values ​​of solution A and solution B are both 4;

[0054] P2. Under argon protection, solution A and solution B were mixed in a mass ratio of 71:29 to obtain solution C, in which the mass ratio of carboxymethyl chitosan to N-aminoethyl-3-aminopropyltriethoxysilane was 10:5.69. The solution was heated to 50°C and stirred rapidly for 3 hours. The solution was then heated to 70°C and stirred for 0.5 hours. After reduced pressure filtration, the obtained carboxymethyl chitosan grafted N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) slurry was washed three times with deionized water and anhydrous ethanol, respectively. The filter cake was then placed in a vacuum drying oven at 80°C and dried for 24 hours. The dried filter cake was crushed, ground, and sieved through a 200-mesh sieve to obtain a modified flame retardant powder.

[0055] This embodiment also provides a method for preparing a biomass-based highly flame-retardant MPP pipe using the modified flame retardant powder, comprising the following steps:

[0056] S1. Put polypropylene and modified flame retardant powder into a high-speed mixer and stir and mix them, set the stirring speed to 700 r / min, then heat at 80° C., continue stirring and mixing for 40 minutes to obtain a mixture I; stir and mix a mixture of talcum powder and powdered quartz and calcium stearate, stir and mix them at 110° C., add antioxidant 1010, continue stirring and mixing for 30 minutes, keep warm, and maintain pressure at 9 MPa for 10 minutes to obtain a mixture II;

[0057] S2, mixing mixture I and mixture II in a mass ratio of 1:1, heating at 120° C., stirring, and cooling to 50° C. to obtain mixture III;

[0058] S3. Extruding and granulating the mixture III through a twin-screw extruder, and then thermoplasticizing and molding the mixture through a mold to obtain an MPP pipe; wherein the temperature of the barrel zone 1 is set to 180°C, the temperature of the zone 2 is set to 190°C, the temperature of the zone 3 is set to 200°C, the temperature of the zone 4 is set to 210°C, and the screw speed of the extruder is set to 120r / min.

[0059] Example 2

[0060] This embodiment provides a biomass-based highly flame-retardant MPP pipe, which includes, by weight, 64 parts of polypropylene, 16 parts of modified flame retardant powder, 17 parts of a mixture of talcum powder and powdered quartz, 2 parts of calcium stearate, and 1 part of antioxidant 1010;

[0061] The preparation method of the modified flame retardant powder comprises the following steps:

[0062] P1. Carboxymethyl chitosan was dried at 100°C for 8 hours and dissolved in a 2% acetic acid solution, the mass ratio of carboxymethyl chitosan to the acetic acid solution being 1:70, to obtain solution A; N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) was added to a 2% acetic acid solution and dissolved, the mass ratio of N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) to the acetic acid solution being 1:50, to obtain solution B; the pH values ​​of solution A and solution B were both 4;

[0063] P2. Under nitrogen protection, solution A and solution B were mixed in a mass ratio of 71:29 to obtain solution C, in which the mass ratio of carboxymethyl chitosan to N-aminoethyl-3-aminopropyltriethoxysilane was 10:5.69. The solution was heated to 40°C and rapidly stirred for 4 hours. The solution was then heated to 80°C and stirred for 1 hour. After vacuum filtration, the obtained carboxymethyl chitosan grafted N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) slurry was washed three times with deionized water and anhydrous ethanol, respectively. The filter cake was then placed in a vacuum drying oven at 80°C and dried for 28 hours. The dried filter cake was crushed, ground, and sieved through a 200-mesh sieve to obtain a modified flame retardant powder.

[0064] This embodiment also provides a method for preparing a biomass-based highly flame-retardant MPP pipe using the modified flame retardant powder, comprising the following steps:

[0065] S1. Put polypropylene and modified flame retardant powder into a high-speed mixer and stir and mix them, set the stirring speed to 700 r / min, and then continue to stir and mix them at 90° C. for 40 min to obtain a mixture I; stir and mix a mixture of talcum powder and powdered quartz and calcium stearate, stir and mix them at 100° C. until they are evenly mixed, add antioxidant 1010, continue to stir and mix for 30 min, keep warm, and maintain the pressure at a pressure of 11 MPa for 16 min to obtain a mixture II;

[0066] S2, mixing mixture I and mixture II at a mass ratio of 1:1, heating to 110° C. and then stopping stirring, and cooling to 50° C. to obtain mixture III;

[0067] S3. Extruding and granulating the mixture III through a twin-screw extruder, and then thermoplasticizing and molding the mixture through a mold to obtain an MPP pipe; wherein the temperature of the barrel zone 1 is set to 180°C, the temperature of the zone 2 is set to 190°C, the temperature of the zone 3 is set to 200°C, the temperature of the zone 4 is set to 210°C, and the screw speed of the extruder is set to 120r / min.

[0068] Example 3

[0069] This embodiment provides a biomass-based highly flame-retardant MPP pipe, which includes, by weight, 69 parts of polypropylene, 11 parts of modified flame retardant powder, 17 parts of a mixture of talcum powder and powdered quartz, 2 parts of calcium stearate, and 1 part of antioxidant 1010;

[0070] The preparation method of the modified flame retardant powder comprises the following steps:

[0071] P1. Carboxymethyl chitosan was dried at 120°C for 5 hours and dissolved in a 2% acetic acid solution, the mass ratio of carboxymethyl chitosan to the acetic acid solution being 1:70, to obtain solution A; N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) was added to a 2% acetic acid solution and dissolved, the mass ratio of N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) to the acetic acid solution being 1:50, to obtain solution B; the pH values ​​of solution A and solution B were both 4;

[0072] P2. Under nitrogen protection, solution A and solution B were mixed in a mass ratio of 71:29 to obtain solution C, in which the mass ratio of carboxymethyl chitosan to N-aminoethyl-3-aminopropyltriethoxysilane was 10:5.69. The solution was heated to 60°C and stirred rapidly for 2 hours. The solution was then heated to 60°C and stirred for 1 hour. After vacuum filtration, the obtained carboxymethyl chitosan grafted N-aminoethyl-3-aminopropyltriethoxysilane (KH-793) slurry was washed three times with deionized water and anhydrous ethanol, respectively. The filter cake was then placed in a vacuum drying oven at 60°C and dried for 30 hours. The dried filter cake was crushed, ground, and sieved through a 200-mesh sieve to obtain a modified flame retardant powder.

[0073] This embodiment also provides a method for preparing a biomass-based highly flame-retardant MPP pipe using the modified flame retardant powder, comprising the following steps:

[0074] S1. Put polypropylene and modified flame retardant powder into a high-speed mixer and stir and mix them, set the stirring speed to 700 r / min, and then continue to stir and mix them at 70° C. for 40 min to obtain a mixture I; stir and mix a mixture of talcum powder and powdered quartz and calcium stearate, stir and mix them at 120° C. until they are evenly mixed, add antioxidant 1010, continue to stir and mix for 30 min, keep warm, and maintain the pressure at 8 MPa for 8 min to obtain a mixture II;

[0075] S2, mixing mixture I and mixture II at a mass ratio of 1:1, heating to 130° C. and then stopping stirring, and cooling to 50° C. to obtain mixture III;

[0076] S3. Extruding and granulating the mixture III through a twin-screw extruder, and then thermoplasticizing and molding the mixture through a mold to obtain an MPP pipe; wherein the temperature of the barrel zone 1 is set to 180°C, the temperature of the zone 2 is set to 190°C, the temperature of the zone 3 is set to 200°C, the temperature of the zone 4 is set to 210°C, and the screw speed of the extruder is set to 120r / min.

[0077] Example 4

[0078] This embodiment is basically the same as Example 1, except that in step P2 of the method for preparing the modified flame retardant powder, solution A and solution B are mixed in a mass ratio of 86:14 to obtain solution C, and the mass ratio of carboxymethyl chitosan to N-aminoethyl-3-aminopropyl triethoxysilane in solution C is 12.11:2.75.

[0079] Example 5

[0080] This embodiment is basically the same as Embodiment 1, except that in step P2 of the method for preparing the modified flame retardant powder, solution A and solution B are mixed in a mass ratio of 59:41 to obtain solution C, and the mass ratio of carboxymethyl chitosan to N-aminoethyl-3-aminopropyl triethoxysilane in solution C is 8.31:8.04.

[0081] Comparative Example 1

[0082] This comparative example is basically the same as Example 1, except that the manufacturing material of the biomass-based highly flame-retardant MPP pipe does not include a flame retardant, that is, the manufacturing material of the biomass-based highly flame-retardant MPP pipe provided in this comparative example includes the following weight components:

[0083] 80 parts of polypropylene, 17 parts of a mixture of talc and powdered quartz, 2 parts of calcium stearate and 1 part of antioxidant 1010.

[0084] Comparative Example 2

[0085] This comparative example is basically the same as Example 1, except that in the preparation method of the modified chitosan quaternary ammonium salt powder, in step P2, solution A and solution B are mixed in a mass ratio of 91:9 to obtain solution C, and the mass ratio of carboxymethyl chitosan to N-aminoethyl-3-aminopropyl triethoxysilane in solution C is 12.82:1.76.

[0086] Comparative Example 3

[0087] This comparative example is substantially the same as Example 1, except that the silane coupling agent KH-793 is replaced by an equal mass of silane coupling agent KH-570.

[0088] Application Example 1

[0089] Limiting oxygen index test

[0090] The limiting oxygen index (LOI) refers to the minimum oxygen concentration required for a material to burn with a flame in a mixed gas flow of oxygen and nitrogen under specified conditions. The higher the LOI value, the better the flame retardant performance. Although the LOI test cannot reflect the large-scale combustion behavior of the material, it has been widely used in industry to evaluate the flame retardant properties of polymer materials. The LOI value is calculated according to the following formula:

[0091]

[0092] Where: [O2] represents the oxygen flow rate, in L / min; [N2] represents the nitrogen flow rate, in L / min.

[0093] The specific steps are as follows: The MPP pipes in Examples 1 to 5 and Comparative Examples 1 to 3 are processed into standard test specimens (width b is about 10 mm, height h is about 3 mm, and length l is about 125 mm). The LOI value of the specimen is measured by an oxygen index meter, the specimen to be tested is fixed on a combustion rack, the flow rates of N2 and O2 are adjusted to a certain fixed value, the specimen to be tested is ignited, and it is observed whether the specimen to be tested can self-extinguish within 3 minutes. If it cannot self-extinguish, the flow rate of N2 is increased, and if it cannot be ignited, the flow rate of O2 is increased. Repeat the test until it self-extinguishes to determine the limiting oxygen index of the specimen. The test results are shown in Table 1.

[0094] Application Example 2

[0095] Vicat softening point test

[0096] The MPP pipes of Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to a Vicat softening point test according to ISO 306-2022 standard to obtain the temperature at which the MPP pipes of Examples 1 to 5 and Comparative Examples 1 to 3 began to soften rapidly, wherein the load gravity was 10N and the heating rate was (120±10)°C / h. The test results are shown in Table 1.

[0097] Table 1 Test results of Examples 1 to 5 and Comparative Examples 1 to 3

[0098] Group Limiting oxygen index (%) Vicat softening point(℃) Example 1 45.1 158.7 Example 2 46.5 160.8 Example 3 43.7 154.2 Example 4 43.1 153.9 Example 5 42.3 152.3 Comparative Example 1 20.7 145.2 Comparative Example 2 30.1 150.6 Comparative Example 3 35.2 151.9

[0099] It can be seen from Table 1 that the limiting oxygen index of Examples 1 to 5 is all above 42%, and the Vicat softening point temperature is not less than 152°C, which indicates that the MPP pipe to which the modified flame retardant of the present invention is added has excellent flame retardant properties, and the limiting oxygen index and Vicat softening point of Example 2 are the highest, which is due to the fact that a large number of modified flame retardants are added to the MPP pipe of Example 2.

[0100] The limiting oxygen index and Vicat softening point of Examples 1 to 3 are better than those of Examples 4 to 5. This is because the difference between Examples 1 to 3 and Examples 4 to 5 is that the mass ratio of carboxymethyl chitosan to N-aminoethyl-3-aminopropyltriethoxysilane is 10:5.69, so the prepared MPP pipe has excellent flame retardant properties; and even if the amount of modified flame retardant added to the MPP pipe of Example 3 is small, the flame retardant property is still better than that of Examples 4 to 5.

[0101] The limiting oxygen index and Vicat softening point of Comparative Example 1 are significantly lower than those of Example 1. This is because the solution adopted in Comparative Example 1 is not to add a flame retardant, so the flame retardant performance of the obtained MPP pipe is poor.

[0102] Compared with Comparative Example 1, the limiting oxygen index and Vicat softening point of Comparative Example 2 are slightly improved, but compared with Example 1, the limiting oxygen index and Vicat softening point are still significantly reduced. This is because the amount of silane coupling agent used in Comparative Example 2 is relatively small. Therefore, although the prepared MPP pipe has certain heat resistance, its flame retardant performance is not ideal.

[0103] Compared with Example 1, the limiting oxygen index and Vicat softening point of Comparative Example 3 are improved, but compared with Example 1, the limiting oxygen index and Vicat softening point are still significantly reduced. This is because KH-570 is used in Comparative Example 3 to graft and modify carboxymethyl chitosan, and the modified flame retardant obtained has poor flame retardant effect, so the flame retardant performance of the prepared MMP pipe is general.

[0104] The above specific embodiments describe the implementation of the present invention in detail, but the present invention is not limited to the specific details in the above embodiments. Within the scope of the claims and technical concept of the present invention, the technical solution of the present invention can be modified and changed in many simple ways, and these simple modifications all belong to the protection scope of the present invention.

Claims

1. A biomass-based highly flame-retardant MPP pipe, characterized in that: By weight, it comprises 64-69 parts of polypropylene, 11-16 parts of modified flame retardant powder, 12-17 parts of filler, 1-3 parts of lubricant and 0.5-1 parts of antioxidant; The modified flame retardant powder is obtained by grafting carboxymethyl chitosan with N-aminoethyl-3-aminopropyl triethoxysilane; the mass ratio of the carboxymethyl chitosan to the N-aminoethyl-3-aminopropyl triethoxysilane is (8-12.5): (2.5-8.1).

2. The biomass-based highly flame-retardant MPP pipe according to claim 1, characterized in that: The preparation method of the modified flame retardant powder comprises the following steps: P1. Dry the carboxymethyl chitosan, dissolve it in an acetic acid solution, and adjust the pH value to acidic to obtain solution A; add N-aminoethyl-3-aminopropyltriethoxysilane to the acetic acid solution and dissolve it to obtain solution B; P2. Under the protection of inert gas, the solution A and the solution B are mixed to obtain a solution C, which is then heated, stirred, filtered under reduced pressure, washed, dried, crushed, ground, and sieved to obtain a modified flame retardant powder.

3. The biomass-based highly flame-retardant MPP pipe according to claim 1, characterized in that: The filler is a mixture of talcum powder and powdered quartz.

4. The biomass-based highly flame-retardant MPP pipe according to claim 1, characterized in that: The lubricant is at least one of calcium stearate, methyl stearate or butyl stearate.

5. The biomass-based highly flame-retardant MPP pipe according to claim 1, characterized in that: The antioxidant is a hindered phenol antioxidant and / or a phosphite antioxidant.

6. The biomass-based highly flame-retardant MPP pipe according to claim 2, characterized in that: The pH values ​​of the solution A and the solution B in step P1 are both 3-6.

7. The biomass-based highly flame-retardant MPP pipe according to claim 2, characterized in that: In step P2, the heating and stirring are divided into two stages. In the first stage, the mixture is heated to 40-60° C. and stirred for 2-4 h; in the second stage, the mixture is heated to 60-80° C. and stirred for 0.5-1 h.

8. The method for preparing the biomass-based highly flame-retardant MPP pipe according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Stir and mix polypropylene and modified flame retardant powder, and continue to stir and mix at 70-90° C. to obtain mixture I; stir and mix filler and lubricant, and stir and mix at 100-120° C., add antioxidant, continue to stir and mix, and after heat and pressure maintenance, obtain mixture II; S2, mixing mixture I and mixture II, heating to 110-130° C., stopping stirring, and cooling to obtain mixture III; S3, extruding and granulating the mixture III, and then thermoplasticizing and molding it through a mold to obtain an MPP pipe.

9. The method for preparing the biomass-based highly flame-retardant MPP pipe according to claim 8, characterized in that: In step S2, the mass ratio of the mixture I to the mixture II is 1:(1-2).

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