A flexible flame-retardant composite pipe

Abstract

The present invention relates to a flexible flame-retardant composite pipe, which is applied to the technical field of composite pipes. The pipe is composed of an outer layer, an intermediate layer and an inner layer, wherein the outer layer is composed of PVC resin, modified PVA, a plasticizer and a filler. The modified PVA is prepared by grafting polyvinyl alcohol (PVA) with flame retardant trichloroethyl phosphate (TCEP). The preparation method of the present invention comprises dissolving PVA in a solvent, adding a modifier TCEP, a base and a catalyst potassium iodide, purifying after heating and refluxing to obtain the modified PVA, and then mixing with the PVC resin, the plasticizer and the filler, and extruding to obtain the pipe.

Description

Technical Field

[0001] The invention relates to the technical field of composite pipes, and in particular to a flexible flame-retardant composite pipe and a preparation method thereof. Background Art

[0002] Organophosphorus flame retardants are an important type of flame retardant materials. They have the advantages of low smoke, non-toxicity, low halogen, and halogen-free, which are in line with the development direction of flame retardants. Commonly used organophosphorus flame retardants: Phosphate esters: Tris(α-chloroethyl) phosphate (TCEP): The molecular formula is C6H 12 O4Cl3P is a colorless transparent liquid, insoluble in aliphatic hydrocarbons, slightly soluble in water. TCEP has excellent flame retardancy, excellent low temperature resistance and UV resistance. It is used as an auxiliary plasticizer flame retardant in soft PVC.

[0003] The mechanism of action of organophosphorus flame retardants is mainly to produce cross-linked solid substances or carbonized layers with more stable structures when heated, preventing the polymer from further pyrolysis and preventing the thermal decomposition products inside from entering the gas phase to participate in the combustion process. They play a flame retardant role in the condensed phase and gas phase, and catalyze the endothermic dehydration and carbonization reaction of hydroxyl compounds by forming phosphoric acid or polyphosphoric acid to generate water and coke, thereby forming a graphite-like coke layer on the surface, isolating oxygen and heat, and suffocating combustion. These organophosphorus flame retardants are increasingly widely used in plastic products such as PVC pipes due to their environmental protection and high efficiency, and are an important substitute for halogen flame retardants.

[0004] Organophosphorus flame retardants mainly work in the condensed phase. The flame retardant mechanism includes: forming phosphoric acid as a dehydrating agent, promoting carbonization, and reducing heat conduction from the flame to the condensed phase. Phosphoric acid can absorb heat because it prevents CO from oxidizing to CO2, reducing the heating process. It forms a thin glassy or liquid protective layer on the condensed phase, reducing oxygen diffusion and heat and mass transfer between the gas phase and the solid phase, inhibiting the carbon oxidation process. The released water vapor absorbs a large amount of heat, causing the flame retardant on the polymer surface to decompose under heat to release volatile phosphides, capture H·, that is, PO·+H·=HPO, and reduce the generation of combustible gases.

[0005] Most organophosphorus flame retardants are liquid and highly volatile, which affects their flame retardant effect and flame retardant durability. Since organophosphorus flame retardants are usually added to polymer materials by physical mixing rather than chemical bonding, they are easily released into the surrounding environment through volatilization, leaching, abrasion and dissolution. This high volatility means that over time, the loss of flame retardants from the material may cause the flame retardant properties to gradually decrease, thus affecting the flame retardant performance of the product.

[0006] When PVA and PVC are blended to prepare flexible flame-retardant pipes, common flame retardants include: halogen flame retardants, phosphorus flame retardants, nitrogen flame retardants, inorganic flame retardants, etc.

[0007] In the PVC-PVA blend system, hydrogen bonds and dipole interactions can be formed between macromolecules, and this interaction improves the mechanical toughness of the material. Although PVC has good physical and chemical properties, its hydrophilicity and film-forming properties are poor, which limits its application in certain fields. By blending with PVA, the hydrophilicity of PVC film materials can be improved, thereby improving its film-forming properties and processing performance.

[0008] Phosphorus-based flame retardants are highly volatile, which may cause them to migrate from the material during the processing or use of PVC-PVA blends, which not only reduces the effective flame retardant components in the material, but may also affect other properties of the material, such as mechanical properties and appearance. Summary of the invention

[0009] In view of the problem of high volatility of phosphorus-based flame retardants in PVC-PVA blends mentioned in the above background technology, the present invention grafts TCEP onto PVA to obtain a flame retardant material with low volatility, and then blends the flame retardant material with PVC to prepare a flexible flame retardant pipe.

[0010] The invention also provides a TCEP grafted to PVA flame retardant and a preparation method thereof.

[0011] The technical solution adopted by the present invention to solve the technical problem is:

[0012] A flexible flame-retardant composite pipe, which consists of an outer layer, a middle layer and an inner layer; the outer layer consists of PVC resin, modified PVA, a plasticizer and a filler, the modified PVA is prepared by grafting the flame retardant trichloroethyl phosphate, and the specific preparation method is as follows: PVA is dissolved in a solvent, the modifier trichloroethyl phosphate, a base, and a catalyst potassium iodide are added, heated to reflux, and then purified to obtain the modified PVA.

[0013] The outer layer is prepared by weighing PVC resin, modified PVA, plasticizer and filler, mixing them evenly, heating and stirring, and extruding them.

[0014] The flexible flame-retardant composite pipe is characterized in that the inner layer is prepared from polyethylene, cross-linked polyethylene, polyvinylidene fluoride, nylon, polypropylene, polyphenylene sulfide, polyimide, and polyetheretherketone.

[0015] The flexible flame-retardant composite pipe is characterized in that the middle layer is selected from steel wire, aramid, polyester, ultra-high molecular polyethylene fiber, and glass fiber.

[0016] The flexible flame-retardant composite pipe is characterized in that the plasticizer is selected from dioctyl phthalate (DOP), diisooctyl phthalate, tricresyl phosphate, triphenyl phosphate, epoxy soybean oil, and epoxy fatty acid octyl ester.

[0017] The flexible flame-retardant composite pipe is characterized in that the filler is selected from calcium carbonate, carbon black, barium sulfate, calcium sulfate, lithopone, aluminum oxide, iron oxide, manganese oxide, zinc oxide, antimony oxide, magnesium oxide, kaolin, and talc.

[0018] The flexible flame-retardant composite pipe is characterized in that the alkali is selected from sodium hydroxide and potassium hydroxide.

[0019] A flame retardant material, characterized in that the preparation method of the trichloroethyl phosphate modified PVA is to dissolve PVA in a solvent, add a modifier trichloroethyl phosphate, a base, and a catalyst potassium iodide, heat and reflux, and then purify.

[0020] The flame retardant material is characterized in that the alkali is selected from sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate.

[0021] The flame retardant material is characterized in that the solvent is selected from toluene, THF, and xylene.

[0022] The flame retardant material is used for preparing pipes.

[0023] The preparation method of the modified PVA is specifically as follows: 5-15 parts by weight of polyvinyl alcohol is dissolved in a certain amount of organic solvent, alkali, catalyst potassium iodide and 30-90 parts by weight of trichloroethyl phosphate are added, heated to reflux, and purified to obtain trichloroethyl phosphate-modified polyvinyl alcohol.

[0024] The preferred molar ratio of hydroxyl group in polyvinyl alcohol to trichloroethyl phosphate is 5:1-1:10.

[0025] Preferably, the molar ratio of the hydroxyl group in the polyvinyl alcohol to the trichloroethyl phosphate is 1:1-1:3.

[0026] The preferred molar ratio of hydroxyl group in polyvinyl alcohol to trichloroethyl phosphate is 1:1.

[0027] A method for preparing an outer tube of a flexible flame-retardant composite pipe, characterized in that it comprises the following steps, measured in parts by weight: Step 1: 40-50 parts of PVC resin, 10-20 parts of modified PVA, 1-3 parts of plasticizer, and 5-10 parts of filler are stirred and mixed uniformly, heated to 100-150°C, stirring is stopped, cooling is performed, and the material is discharged for standby use; Step 2: The final discharge obtained in step 1 is extruded and molded to obtain a PVC pipe; the processing temperature range of the twin-screw extruder is 150-190°C.

[0028] Beneficial effects of the present invention:

[0029] The present invention grafts TCEP onto PVA and connects it to PVA via covalent bonds, thereby effectively reducing the volatility of TCEP and improving the flame retardant effect. At the same time, the present invention blends the modified PVA with PVC to prepare the outer layer of the flexible flame retardant composite pipe, which can effectively improve the flame retardant effect and physical properties.

[0030] The present invention reduces the migration and volatilization of traditional flame retardants in materials by using the method of grafting TCEP onto PVA, thereby reducing the potential risks to the environment and human health. This modification method not only improves the flame retardant properties of the material, but also meets the current demand for environmentally friendly flame retardant materials.

[0031] Due to the hydrogen bonding and dipole interaction between PVA and PVC, the mechanical properties of the flexible flame-retardant composite pipe prepared by the present invention are enhanced. In particular, in terms of tensile and impact resistance, the addition of modified PVA provides the pipe with better toughness and strength.

[0032] The phosphorus and chlorine elements in the modified PVA not only provide excellent flame retardant effects, but also enhance the material's heat resistance. Under high temperature conditions, TCEP modified PVA can form a stable carbon layer to protect the pipe from high temperature, thereby improving the pipe's heat resistance and temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 : The reaction mechanism of the technical solution of this application. DETAILED DESCRIPTION

[0034] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0035] The actual sources and parameters of the materials in the examples are as follows:

[0036] Polyvinyl alcohol: alcoholysis degree: 87.0-89.0 mol%, viscosity: 3.2-3.6 mPa.s, purchased from Aladdin Reagent.

[0037] Trichloroethyl phosphate, CAS: 115-96-8, purity 93.0%, was purchased from J&K Reagents.

[0038] PVC resin, with an average degree of polymerization of 2000, was purchased from Dongguan Suguang Plastic Raw Materials Co., Ltd.

[0039] Calcium carbonate: Heavy calcium carbonate, particle size 2000 mesh.

[0040] Dioctyl phthalate, CAS: 117-81-7, was purchased from Aladdin Reagents.

[0041] THF, KI, etc. are commercially available.

[0042] Example 1 10 g of polyvinyl alcohol (hydroxyl content is about 0.1997 mol) was dissolved in 100 ml of THF, and 12 g of potassium hydroxide, 1 g of potassium iodide and 57.05 g of trichloroethyl phosphate were added. The mixture was heated to reflux and reacted for 3 h. Then, 100 ml of deionized water was added and the mixture was shaken repeatedly to obtain the organic layer. The mixture was distilled under reduced pressure to obtain 50.76 g of trichloroethyl phosphate-modified polyvinyl alcohol.

[0043] Example 2: Dissolve 10 g of polyvinyl alcohol (hydroxyl content is about 0.1997 mol) in 100 ml of THF, add 8 g of sodium hydroxide, 1 g of potassium iodide and 57.05 g of trichloroethyl phosphate, heat to reflux, react for 3 hours, add 100 ml of deionized water, shake repeatedly, take the organic layer, and distill under reduced pressure to obtain 49.63 g of trichloroethyl phosphate-modified polyvinyl alcohol.

[0044] Example 3: Dissolve 20 g of polyvinyl alcohol (hydroxyl content is about 0.3994 mol) in 100 ml of THF, add 24 g of potassium hydroxide, 2 g of potassium iodide and 57.05 g of trichloroethyl phosphate, heat to reflux, react for 4 hours, add 100 ml of deionized water, shake repeatedly, take the organic layer, and distill under reduced pressure to obtain 54.45 g of trichloroethyl phosphate-modified polyvinyl alcohol.

[0045] Example 4 15 g of polyvinyl alcohol (hydroxyl content is about 0.2996 mol) was dissolved in 100 ml of THF, and 20 g of potassium hydroxide, 2 g of potassium iodide and 57.05 g of trichloroethyl phosphate were added. The mixture was heated to reflux and reacted for 4 h. Then, 100 ml of deionized water was added and the mixture was shaken repeatedly to obtain the organic layer. The mixture was distilled under reduced pressure to obtain 51.41 g of trichloroethyl phosphate-modified polyvinyl alcohol.

[0046] Comparative Example 1: 10 g of polyvinyl alcohol (hydroxyl content is about 0.1997 mol) was dissolved in 100 ml of THF, 12 g of potassium hydroxide and 57.05 g of trichloroethyl phosphate were added, and the mixture was heated to reflux. After reacting for 3 h, 100 ml of deionized water was added, and the mixture was shaken repeatedly to obtain the organic layer, and distilled under reduced pressure to obtain 30.57 g of trichloroethyl phosphate-modified polyvinyl alcohol.

[0047] Comparative Example 2 10 g of polyvinyl alcohol (with a hydroxyl content of about 0.1997 mol) was dissolved in 100 ml of THF, and heated and blended with 57.05 g of trichloroethyl phosphate to prepare a mixed flame retardant material.

[0048] In the process of preparing TCEP-modified PVA of the present invention, adding catalyst KI can effectively improve the yield.

[0049] The present invention measures the thermal degradation performance of the modified PVA by thermogravimetric analysis.

[0050] Thermogravimetric analysis (TGA): The thermal degradation properties of the mixture of PVA and TCEP and TCEP-modified PVA were tested using the STA6000 thermogravimetric analyzer from PerkinElmer, USA. The sample weight was about 20 mg, and the temperature was increased at a rate of 20°C / min in the N2 atmosphere of 20 mL / min, with a temperature range of 0°C to 400°C.

[0051] Table 1 Thermal degradation performance data

[0052]

[0053] The present invention grafts TCEP onto polyvinyl alcohol, and the modified polyvinyl alcohol can reduce the volatility of TCEP when used as a flame retardant, because the grafted TCEP forms a covalent bond with the polyvinyl alcohol and is not easy to volatilize from the material. TCEP contains three chloroethyl groups in its structure, which can react with three hydroxyl groups to form ether. The present invention adjusts the molar ratio of PVA and TCEP to obtain different flame retardants, and the volatility of TCEP is also different. The larger the molar amount of PVA, the worse the volatility of TCEP. The chlorine element in the TCEP molecule makes an important contribution to the flame retardant performance. The chlorine element can release chlorine free radicals during the combustion process. These free radicals can capture highly active hydrogen free radicals (H·) and oxygen free radicals (O·) in the combustion chain reaction to form HCl and Cl2, thereby inhibiting the combustion chain reaction. When the amount of PVA increases, if the amount of TCEP remains unchanged, the content of chlorine in the overall material is reduced, which will reduce the flame retardant effect of the material.

[0054] Polyvinyl alcohol modified with trichloroethyl phosphate was used to prepare PVC pipes, and its flame retardant properties were tested.

[0055] Preparation Example 1

[0056] Step 1: 50 parts of PVC resin, 15 parts of TCEP-modified PVA prepared in Example 1, 2 parts of dioctyl phthalate (DOP), and 7 parts of filler calcium carbonate are stirred and mixed uniformly, and the mixture is heated to 120° C., stirring is stopped, the mixture is cooled, and the mixture is discharged for standby use;

[0057] Step 2: Extruding the final output obtained in step 1 to obtain a PVC pipe; the processing temperature range of the twin-screw extruder is 170°C.

[0058] Preparation Example 2

[0059] Step 1: 50 parts of PVC resin, 15 parts of TCEP-modified PVA prepared in Example 3, 2 parts of dioctyl phthalate (DOP), and 7 parts of filler calcium carbonate are stirred and mixed uniformly, heated to 120° C., stirred, cooled, and discharged for standby use;

[0060] Step 2: Extruding the final output obtained in step 1 to obtain a PVC pipe; the processing temperature range of the twin-screw extruder is 170°C.

[0061] Preparation Example 3

[0062] Step 1: 50 parts of PVC resin, 15 parts of TCEP-modified PVA prepared in Example 4, 2 parts of dioctyl phthalate (DOP), and 7 parts of filler calcium carbonate are stirred and mixed uniformly, heated to 120° C., stirred, cooled, and discharged for standby use;

[0063] Step 2: Extruding the final output obtained in step 1 to obtain a PVC pipe; the processing temperature range of the twin-screw extruder is 170°C.

[0064] Comparative Preparation Example

[0065] Step 1: 50 parts of PVC resin, 15 parts of TCEP modified PVA prepared in Comparative Example 2, 2 parts of dioctyl phthalate (DOP), and 7 parts of filler calcium carbonate were stirred and mixed evenly, heated to 120° C., stopped stirring, cooled, and discharged for standby use;

[0066] Step 2: Extruding the final output obtained in step 1 to obtain a PVC pipe; the processing temperature range of the twin-screw extruder is 170°C.

[0067] Vertical combustion (UL-94): According to the national standard GB / T2408-2008 "Horizontal and vertical methods for the determination of combustion performance of plastics", the vertical combustion level of composite materials is determined by using the CZF-2 vertical combustion tester produced by Nanjing Jiangning County Analytical Instrument Factory.

[0068] Table 2 Flame retardant effect data

[0069]

[0070] The modified polyvinyl alcohol may have better flame retardant effect because the phosphorus and chlorine elements of TCEP can improve the flame retardant properties of the material. At the same time, the modified polymer may have better thermal stability and mechanical properties.

[0071] The phosphorus and chlorine elements in the modified PVA not only provide excellent flame retardant effects, but also enhance the material's heat resistance. Under high temperature conditions, TCEP modified PVA can form a stable carbon layer to protect the pipe from high temperature, thereby improving the pipe's heat resistance and temperature range.

[0072] In this specification, the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the embodiments described later, the description is relatively simple, and the relevant parts can be referred to the partial description of the previous embodiments.

[0073] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A flexible flame-retardant composite pipe, characterized in that: The composite pipe is composed of an outer layer, a middle layer and an inner layer; The outer layer is composed of PVC resin, modified PVA, plasticizer and filler. The modified PVA is prepared by grafting with flame retardant trichloroethyl phosphate. The specific preparation method is as follows: PVA is dissolved in a solvent, and a modifier trichloroethyl phosphate, a base and a catalyst potassium iodide are added, heated to reflux, and then purified; the molar ratio of the hydroxyl group in PVA to the trichloroethyl phosphate is 5:1-1:10; The outer layer is prepared by weighing PVC resin, modified PVA, plasticizer and filler, mixing them evenly, heating and stirring, and extruding them.

2. The flexible flame-retardant composite pipe according to claim 1, characterized in that: The inner layer is selected from polyethylene, cross-linked polyethylene, polyvinylidene fluoride, nylon, polypropylene, polyphenylene sulfide, polyimide, and polyetheretherketone.

3. The flexible flame-retardant composite pipe according to claim 1, characterized in that: The middle layer is selected from steel wire, steel plate mesh, aramid, polyester, ultra-high molecular polyethylene fiber, and glass fiber.

4. The flexible flame-retardant composite pipe according to claim 1, characterized in that: The plasticizer is selected from dioctyl phthalate, diisooctyl phthalate, tricresyl phosphate, triphenyl phosphate, epoxy soybean oil, and epoxy fatty acid octyl ester.

5. The flexible flame-retardant composite pipe according to claim 1, characterized in that: The filler is selected from calcium carbonate, carbon black, barium sulfate, calcium sulfate, lithopone, aluminum oxide, iron oxide, manganese oxide, zinc oxide, antimony oxide, magnesium oxide, kaolin, and talc.

6. The flexible flame-retardant composite pipe according to claim 1, characterized in that: The alkali is selected from sodium hydroxide and potassium hydroxide.

7. A flame retardant material, characterized in that: The invention contains trichloroethyl phosphate modified PVA. The preparation method of the trichloroethyl phosphate modified PVA comprises: dissolving PVA in a solvent, adding a modifier trichloroethyl phosphate, a base and a catalyst potassium iodide, heating and refluxing, and then purifying; the molar ratio of the hydroxyl group in the PVA to the trichloroethyl phosphate is 5:1-1:

10.

8. The flame retardant material according to claim 7, characterized in that: The alkali is selected from sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate.

9. The flame retardant material according to claim 7, characterized in that: The solvent is selected from toluene, THF, and xylene.

10. The flame retardant material according to claim 7 is used for preparing pipes.

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