A low-smoke-density flame-retardant polyethylene material, a preparation method and application thereof

Abstract

The application discloses a low-smoke-density flame-retardant polyethylene material and a preparation method and application thereof, and relates to the technical field of polymer materials; the low-smoke-density flame-retardant polyethylene material comprises polyethylene, a compatilizer, a hydroxide flame retardant, borate whiskers and strontium carbonate; the borate whiskers and the strontium carbonate are compounded and the component proportion is optimized in the system, the flame-retardant efficiency is improved, the formation of a barrier carbon layer is promoted during combustion, the smoke density can be greatly reduced, and the material has excellent mechanical properties; the tensile strength of the material is greater than 13 MPa; the elongation at break of the material is greater than 330%; the flameless smoke density of the material is less than 280; and the flame-retardant performance is V-0 grade.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a low-smoke-density flame-retardant polyethylene material, its preparation method, and its application. Background Technology

[0002] Fatal accidents at fire scenes are mainly caused by asphyxiation from dense smoke and toxic gases. Moreover, dense smoke significantly reduces visibility, delaying the opportunity for firefighting and rescue. Therefore, reducing the amount of smoke and toxic gases produced when plastics burn has always been a key research topic in the field of flame retardancy.

[0003] According to the building electrical fire protection design code, high flame-retardant and low-smoke cables are required for densely populated areas, high-rise buildings, and special locations. Medium- and high-voltage armored cables need excellent mechanical properties and crack resistance. Existing halogen-free cable materials generally fill a polyethylene resin matrix with more than 40% flame retardant, which can improve flame retardancy and suppress the spread of fire, but the material's smoke density fails to meet requirements. Significantly increasing the amount of flame retardant with both flame-retardant and smoke-suppressing properties, or introducing a large amount of smoke suppressant, can reduce the material's smoke density to some extent, but this will cause the material's mechanical strength and crack resistance to fail to meet requirements.

[0004] Patent CN106336562A describes a flame-retardant polyethylene cable material and its preparation method. It combines linear low-density polyethylene, modified linear low-density polyethylene, a composite flame-retardant synergist, a solvent, aluminum hydroxide, and magnesium hydroxide, which can significantly reduce the amount of flame retardant used. While ensuring the flame-retardant effect of the cable material, it also ensures the mechanical properties, processing properties, and resistance to environmental stress cracking of the cable material. However, it fails to effectively control the smoke density of the material. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing flame-retardant polyethylene materials that fail to effectively reduce smoke density while ensuring mechanical properties, and to provide a low-smoke-density flame-retardant polyethylene material.

[0006] Another objective of this invention is to provide a method for preparing a low-smoke-density flame-retardant polyethylene material.

[0007] Another object of the present invention is to provide an application of the above-mentioned low smoke density flame-retardant polyethylene material in the preparation of cable sheaths.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] This invention protects a low-smoke-density flame-retardant polyethylene material, comprising the following components in parts by weight:

[0010]

[0011]

[0012] This invention employs a compound of borate whiskers and strontium carbonate as a smoke suppressant added to a PE matrix, with optimized component ratios. This significantly reduces the smoke density of polyethylene materials and minimizes the loss of mechanical properties and crack resistance. Strontium carbonate, acting as a char-forming agent, promotes char formation during combustion and catalyzes the reaction between borate and hydroxide flame retardants, forming a more robust and stable heat-resistant carbon layer containing boron compounds. This strengthens the condensed phase carbon layer, making it less prone to forming a loose carbon layer that decomposes and produces smoke. This not only improves flame retardant efficiency but also prevents the carbon layer itself from peeling off and decomposing to form smoke, providing a protective barrier and preventing the diffusion of small solid particles, thus reducing smoke density. Furthermore, the use of borate whiskers with a whisker structure enhances the carbon layer strength, resulting in a continuous and dense carbon layer, improving the barrier effect and strengthening the smoke suppression. Simultaneously, the use of a hydroxide-based flame retardant not only improves flame retardant performance but also reduces smoke generation as the hydroxide decomposes upon heating to form water vapor.

[0013] In some embodiments, the polyethylene is metallocene linear low-density polyethylene (LLDPE). Furthermore, when LLDPE is used as the matrix resin, it produces less smoke during combustion and exhibits superior mechanical properties, making it advantageous for modification with flame retardants and smoke suppressants.

[0014] In some embodiments, the metallocene linear low-density polyethylene content that enables the achievement of the present invention can be 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, or 40 parts.

[0015] In some embodiments, the compatibilizer content that enables the present invention to achieve its purpose can be 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, or 15 parts.

[0016] In some embodiments, the content of the hydroxide flame retardant that can achieve the purpose of the present invention can be 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, or 40 parts.

[0017] In some embodiments, the content of borate whiskers that can achieve the purpose of the present invention can be 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, or 10 parts.

[0018] In some embodiments, the strontium carbonate content that enables the achievement of the present invention can be 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, or 10 parts.

[0019] In some embodiments, the mass ratio of the borate whiskers to strontium carbonate is (0.3-6):1. Under this preferred ratio of aluminum borate whiskers to strontium carbonate, the mechanical properties and smoke suppression properties can be balanced, resulting in a lower smoke density of polyethylene material while ensuring the mechanical properties of the material.

[0020] Preferably, the mass ratio of the borate whiskers to strontium carbonate is (1-5):1.

[0021] More preferably, the mass ratio of the borate whiskers to strontium carbonate is (2-4):1. In some embodiments, the total amount of the borate whisker agent and strontium carbonate accounts for 5-16% of the mass fraction of the polyethylene material. Preferably, the borate whisker agent and strontium carbonate account for 8-14.5% of the mass fraction of the polyethylene material, more preferably 10-13%.

[0022] In some embodiments, the total amount of the borate whiskering agent and strontium carbonate used to achieve the purpose of the present invention is 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, or 16% of the mass fraction of the polyethylene material.

[0023] In some embodiments, the borate whiskers have an average length of 5-40 μm and a diameter of 0.5-5 μm. Preferably, the aspect ratio of the borate whiskers is >30.

[0024] In some embodiments, the strontium carbonate has a particle size D90 ≤ 20 μm. This invention optimizes the particle size of strontium carbonate, which is beneficial for improving the mechanical properties and flame retardant properties of the material. In some embodiments, the borate whiskers are aluminum borate whiskers and / or magnesium borate whiskers.

[0025] In some embodiments, the hydroxide flame retardant is magnesium hydroxide and / or aluminum hydroxide. Magnesium hydroxide and aluminum hydroxide flame retardants not only possess flame-retardant properties but also have filling and smoke-suppressing functions.

[0026] Preferably, the hydroxide flame retardant is magnesium hydroxide or a compound hydroxide flame retardant with a magnesium hydroxide content of not less than 50 wt%; magnesium hydroxide, in addition to dehydration during combustion, can also promote char formation in materials, significantly improving the smoke suppression effect. More preferably, the magnesium hydroxide content in the hydroxide flame retardant is not less than 70 wt%.

[0027] In some embodiments, the compatibilizer is a maleic anhydride graft.

[0028] Preferably, the maleic anhydride graft is PE-grafted maleic anhydride and / or POE-grafted maleic anhydride; more preferably, the maleic anhydride graft is PE-grafted maleic anhydride.

[0029] The low-smoke-density flame-retardant polyethylene material of the present invention can be supplemented with conventional additives in the art, with the amount of conventional additives not exceeding 10 wt%. These conventional additives include, but are not limited to, antioxidants, lubricants, plasticizers, silane coupling agents, and color masterbatches.

[0030] In some of these embodiments, 0.1-3 parts of an antioxidant are also included.

[0031] This invention protects a method for preparing a low-smoke-density flame-retardant polyethylene material, comprising the following steps: mixing and stirring metallocene linear low-density polyethylene, a compatibilizer, a filler-type inorganic flame retardant, and a smoke suppressant, then kneading and extruding the mixture to obtain the low-smoke-density flame-retardant polyethylene material.

[0032] In some embodiments, the stirring speed is 1000-2000 rpm.

[0033] In some of these embodiments, the mixing temperature is 120-140°C.

[0034] In some of these embodiments, the extrusion temperature is 140-150°C.

[0035] This invention protects the application of a low-smoke-density flame-retardant polyethylene material in the preparation of cable sheaths.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] This invention provides a low-smoke-density flame-retardant polyethylene material. The invention utilizes a compound of borate whiskers and strontium carbonate as a smoke suppressant added to the PE matrix, with optimized component ratios. This significantly reduces the smoke density of the polyethylene material and minimizes the loss of mechanical properties and crack resistance. Strontium carbonate, acting as a char-forming agent, promotes char formation during combustion and catalyzes the reaction between borate and hydroxide flame retardants, forming a more robust and stable heat-resistant carbon layer containing boron compounds. This strengthens the condensed phase carbon layer, making it less prone to forming a loose carbon layer that decomposes and produces smoke. This not only improves flame-retardant efficiency but also prevents the carbon layer itself from peeling off and decomposing to form smoke, while also providing a protective barrier against the diffusion of small solid particles, thus reducing smoke density. Through the synergistic effect of borate whiskers and strontium carbonate, flame-retardant efficiency is improved, while simultaneously adsorbing smoke and promoting char formation, resulting in a significant reduction in smoke density. Tests show that the manufactured material has a tensile strength greater than 13 MPa, an elongation at break greater than 330%, a smokeless density of less than 280, and a flame retardant rating of V-0. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0039] The raw materials used in the following examples and comparative examples are as follows:

[0040] Metallocene linear low-density polyethylene (LLDPE): Model number LLDPE ENGAGE 3518PA, manufactured by ExxonMobil.

[0041] PE grafted with maleic anhydride: model number MC-218, produced by Nengzhiguang Company.

[0042] Magnesium hydroxide: Model number H-5, manufactured by Huber Corporation, USA.

[0043] Aluminum hydroxide: Model number OL-104LEO, manufactured by Huber Corporation, USA.

[0044] Aluminum borate whiskers: Model NP-BW02-S, manufactured by Jia Ying Chemical Technology Co., Ltd.

[0045] Magnesium borate whiskers: Produced by Shanghai Kaishefeng Industrial Co., Ltd.

[0046] Calcium carbonate whiskers: Model number NP-CW2, produced by Jia Ying Chemical Technology Co., Ltd.

[0047] Strontium carbonate (SrCO3): This is a high-purity strontium carbonate produced by Nanjing Jinyan Strontium Industry Co., Ltd., with a purity of >99%.

[0048] Zinc borate: Model HT-207, produced by Taixing New Materials Co., Ltd.

[0049] Antioxidant: Antioxidant 1010, produced by BASF.

[0050] The following examples and comparative methods for preparing low-smoke-density flame-retardant polyethylene materials include the following steps:

[0051] Each raw material component is added to a high-speed mixer in proportion and mixed evenly at a speed of 1500 rpm. The final mixture is then fed into an internal mixer and granulated by extrusion through a two-stage single-screw extruder. The internal mixer temperature is controlled at 130℃ and the single-screw extruder temperature is controlled at 145℃ to obtain low-smoke density flame-retardant polyethylene material.

[0052] Examples 1-13

[0053] This embodiment provides a series of low smoke density flame-retardant polyethylene materials, the components of which are shown in Table 1.

[0054] Table 1. Components (parts by weight) of Examples 1-13

[0055]

[0056] Comparative Examples 1-6

[0057] This comparative example provides a series of flame-retardant polyethylene materials, the composition of which is shown in Table 2.

[0058] Table 2. Components (parts by weight) of Comparative Examples 1–6

[0059]

[0060]

[0061] Performance testing

[0062] The granules from Examples 1-13 and Comparative Examples 1-6 were pressed into tablets at 180°C for 10 minutes on a flat vulcanizing machine at a pressure of 15 MPa, with a tablet thickness of 1 mm. After being placed at room temperature for 16 hours, the tablets were tested for conventional mechanical properties, smoke density, and flame retardancy.

[0063] Experimental methods:

[0064] 1. Mechanical properties: The tensile strength and elongation at break are tested according to the test method of standard GB / T 1040.2.

[0065] 2. Smoke density: Cut a 1mm thick sample into 100*100mm pieces and test the flameless smoke density according to the test method in standard GB / T8323.2-2008.

[0066] 3. Flame Retardant Performance: The granules were pressed into 3mm sheets, and 125mm×12.5mm×3mm specimens were prepared for UL 94 vertical burning tests. The tests were conducted according to the standard ASTM 3801 method. The UL 94 flammability rating is divided into four levels: V-0, V-1, V-2, and NR. The flame retardant performance of the four levels, V-0, V-1, V-2, and NR, decreases sequentially, with V-0 being the best.

[0067] The experimental results are shown in Table 3.

[0068] Table 3

[0069]

[0070]

[0071] The tensile strength of the material in this embodiment of the invention is greater than 13.7 MPa; the elongation at break is greater than 332%; the smoke density without flame is less than 279; and the flame retardant performance is rated V-0. In particular, when the mass ratio of aluminum borate whiskers to strontium carbonate is (2-4):1, not only is the tensile strength greater than 14 MPa and the elongation at break greater than 360%, but the smoke density of the material is also significantly reduced, with the smoke density without flame being less than 253, and the flame retardant performance is rated V-0.

[0072] Comparing Example 3 with Comparative Examples 1-3, it can be seen that when magnesium hydroxide flame retardant is used alone, its flame retardant efficiency is relatively low, requiring a very high addition amount to achieve similar levels of flameless smoke density and flame retardant performance. However, excessive addition will damage the mechanical properties. Although the addition of aluminum borate whiskers or strontium carbonate can improve smoke suppression and flame retardancy to some extent, the improvement in smoke suppression and flame retardancy is extremely limited, and it significantly damages the tensile strength and elongation at break of the material. Surprisingly, it was found that by combining aluminum borate whiskers and strontium carbonate, the smoke density of polyethylene material can be significantly reduced and the flame retardant performance can be improved, and the loss of tensile strength and elongation at break can be greatly reduced.

[0073] Comparing Examples 3 and 9 with Comparative Example 4, it can be seen that when the total amount of aluminum borate whiskers and strontium carbonate is excessive, the compatibility of the system is destroyed, resulting in a significant decrease in the tensile strength, elongation at break, smoke suppression performance and flame retardant performance of the material.

[0074] Comparing Example 3 and Comparative Examples 5-6, it can be seen that when aluminum borate whiskers were replaced with calcium carbonate whiskers, or strontium carbonate was replaced with zinc borate carbonizing agent, the smoke suppression performance failed to meet expectations, proving that there is a synergistic effect between aluminum borate whiskers and strontium carbonate in this invention.

[0075] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A low smoke density, flame retardant polyethylene material characterized in that, The low-smoke density flame-retardant polyethylene material comprises the following components by mass fraction: polyethylene 30-40 parts, compatibility agent 5-15 parts, hydroxide flame retardant 30-40 parts, borate whisker 1-10 parts, strontium carbonate 1-10 parts; the mass ratio of the borate whisker and the strontium carbonate is (1-6) : 1; the borate whisker is aluminum borate whisker and / or magnesium borate whisker.

2. The low smoke density, flame retardant polyethylene material of claim 1, wherein, the polyethylene is metallocene linear low-density polyethylene.

3. The low smoke density, flame retardant polyethylene material of claim 2, wherein, the mass ratio of the borate whisker and the strontium carbonate is (2-4) :

1.

4. The low smoke density, flame retardant polyethylene material of claim 1, wherein, the total amount of the borate whisker agent and the strontium carbonate accounts for 5-16% of the mass fraction of the polyethylene material.

5. The low smoke density, flame retardant polyethylene material of claim 1, wherein, the average length of the borate whisker is 5-40 μm, and the diameter is 0.5-5 μm.

6. The low smoke density, flame retardant polyethylene material of claim 1, wherein, the particle size D90 of the strontium carbonate is ≤ 20 μm.

7. The low smoke density, flame retardant polyethylene material of claim 1, wherein, the hydroxide flame retardant is a compound hydroxide flame retardant with a magnesium hydroxide content of not less than 50 wt%.

8. A process for the preparation of a low smoke density, flame retardant polyethylene material according to any one of claims 1 to 7, characterized in that, The low-smoke density flame-retardant polyethylene material comprises the following steps: mixing and stirring the components uniformly, and then densifying and extruding to obtain the low-smoke density flame-retardant polyethylene material.

9. Use of the low-smoke density flame-retardant polyethylene material according to any one of claims 1-7 in the preparation of a cable sheath.

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