Environment-friendly flame-retardant PVC (polyvinyl chloride) plastic and preparation method thereof

Abstract

The invention discloses environment-friendly flame-retardant PVC (polyvinyl chloride) plastic and a preparation method thereof, and belongs to the technical field of flame-retardant materials. The preparation method of the environment-friendly flame-retardant PVC plastic comprises the following steps: fully blending 80-100 parts by weight of PVC matrix resin, 10-20 parts by weight of a phosphorus-containing composite flame retardant, 20-30 parts by weight of a vegetable oil modified plasticizer and 1-5 parts by weight of a lubricant to form a mixture, and mixing the mixture in an internal mixer at 180-190 DEG C for 10-15 minutes to obtain the environment-friendly flame-retardant PVC plastic. And the phosphorus-containing composite flame retardant and the vegetable oil modified plasticizer are combined for use, so that the PVC plastic has good flame retardance, and meanwhile, the mechanical property is also guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant materials, and in particular relates to an environmentally friendly flame retardant PVC plastic and a preparation method thereof. Background Art

[0002] Polyvinyl chloride (PVC) is an important plastic product. It is known as the world's five major general-purpose resins together with polyethylene, ABS resin, polypropylene and polystyrene. PVC is the earliest synthetic resin to achieve industrialization and its annual output is second only to polyethylene. Due to its low price and cost, it has many excellent properties, such as good insulation performance, high cost performance, wide sources, inherent flame retardancy, long service life, and easy processing. It is widely used in textiles, food, pipe consumables, construction packaging and other fields. However, although the plasticizers in traditional PVC plastics (such as commonly used dioctyl phthalate, oxalic acid esters, chlorinated paraffin and phosphate esters) have a good improvement on the mechanical properties of PVC materials, due to the poor thermal stability and high flammability of the plasticizers, the flame retardancy of PVC materials will be reduced, and PVC materials are prone to produce toxic and harmful gases under high temperature or fire, posing a threat to the environment and human health.

[0003] In the prior art, adding flame retardants can improve the flame retardant properties of PVC, but commonly used halogen-containing flame retardants will release harmful substances such as dioxins, affecting environmental safety. Inorganic flame retardants have been widely used in PVC flame retardant materials due to their advantages such as high stability, low toxicity and low cost. However, due to the generally low flame retardant efficiency of inorganic flame retardants, a large amount of addition is required to meet the flame retardant requirements. In addition, inorganic materials have poor compatibility with PVC materials and inorganic materials themselves are easy to agglomerate, making it difficult to disperse when used in large quantities. As a result, although PVC has good flame retardant properties, its mechanical properties are poor.

[0004] Patent CN110204843B discloses a flame-retardant PVC material. The invention calcines kaolin, and then treats it with sulfuric acid, ethanol and water to obtain calcined kaolin treated with a subcritical ethanol-water-sulfuric acid system. Nickel nitrate, ammonium hydrogen phosphate and urea are then added to the calcined kaolin treated with the subcritical ethanol-water-sulfuric acid system for reaction to obtain a calcined kaolin-loaded nanotube structured nickel phosphate flame retardant, so that the flame retardant forms a nanostructure, thereby improving the compatibility of the flame retardant with the PVC matrix resin. When the flame retardant is used within a certain range, the PVC material can maintain good flame retardant properties while maintaining good tensile properties.

[0005] Therefore, it is of great significance to develop an environmentally friendly flame-retardant PVC plastic while maintaining the good mechanical properties of PVC plastic. Summary of the invention

[0006] In view of the deficiencies of the prior art, the present invention uses polyhydroxy sugar as a carbon source, covalently bonds the acid source phosphoric acid to the carbon source through an esterification reaction, and then indirectly solidifies and connects the nitrogen-containing compound that produces ammonia by thermal decomposition to the carbon source through electrostatic adsorption with phosphoric acid, thereby forming a phosphorus-containing composite flame retardant with good compatibility with PVC resin to achieve a flame retardant effect; the vegetable oil-modified plasticizer obtained by modifying the vegetable oil has the advantage of low toxicity compared to phthalate plasticizers, and the coordinated use of the phosphorus-containing composite flame retardant and the vegetable oil-modified plasticizer ensures that the mechanical properties of PVC plastics are guaranteed while having good flame retardant properties, thereby solving the technical problems raised in the background technology. Specifically, the technical solution of the present invention includes the following contents:

[0007] An environmentally friendly flame-retardant PVC plastic, characterized in that the environmentally friendly flame-retardant PVC plastic comprises the following raw materials in parts by weight:

[0008] 80-100 parts of PVC base resin, 10-20 parts of phosphorus-containing composite flame retardant, 20-30 parts of vegetable oil modified plasticizer and 1-5 parts of lubricant.

[0009] Furthermore, the preparation method of the phosphorus-containing composite flame retardant comprises the following steps:

[0010] Mixing polyhydroxy sugar, phosphoric acid and a water-absorbing solvent to form a reaction solution, heating the reaction solution to 90-110° C. and subjecting the reaction solution to reflux reaction for 4-8 hours to obtain polyhydroxy sugar phosphate;

[0011] The polyhydroxy sugar phosphate and the nitrogen-containing compound are mixed and dissolved in a methanol solution, and then the temperature is raised to 140° C. to 160° C. and refluxed for 3 to 4 hours to obtain the phosphorus-containing composite flame retardant.

[0012] Furthermore, the polyhydroxy sugar includes glucose, fructose or sucrose. Sugars with high molecular weight may have poor fluidity due to high viscosity, thereby deteriorating the flame retardant effect and mechanical properties of the material.

[0013] Furthermore, the molar ratio of the polyhydroxy sugar to the phosphoric acid is 1:2-5.

[0014] Furthermore, the water-absorbing solvent includes dimethyl sulfoxide.

[0015] Furthermore, the nitrogen-containing compound includes urea or melamine, and the nitrogen-containing compound is selected to be able to decompose ammonia at high temperature.

[0016] Furthermore, the mass ratio of the polyhydroxy sugar phosphate ester to the nitrogen-containing compound is 2 to 3:1.

[0017] Furthermore, the preparation method of the vegetable oil modified plasticizer comprises the following steps:

[0018] After castor oil and epichlorohydrin are mixed, Lewis acid is added and the mixture is heated to 50-70° C. for reaction for 4-8 hours. After the reaction is completed, an inorganic strong base is added, and then the reaction temperature is controlled to be 25-35° C. for reaction for 2-3 hours to obtain the vegetable oil modified plasticizer;

[0019] The castor oil has a hydroxyl group, and epichlorohydrin can form an oxonium ion after being treated with a Lewis acid, thereby causing the epoxy group to open the ring to form a carbon cation. The castor oil acts as a nucleophilic reagent to attack the carbon cation to condense into an ether, and then the epoxy group after the ring opening condenses under an alkaline environment to remove the chloride ion and re-cyclize to form an epoxy group. The vegetable oil modified plasticizer can not only improve the mechanical properties of PVC plastics, but also the epoxy group on the vegetable oil modified plasticizer has high reactivity and can accept hydrogen chloride generated by PVC at high temperature to prevent the overflow of harmful gases.

[0020] Furthermore, the castor oil may also be other vegetable oils having carboxylic acid esters which are modified to obtain a vegetable oil having a carboxylic acid structure, and then condensed with epichlorohydrin.

[0021] Furthermore, the molar ratio of the castor oil to the epichlorohydrin is 1:3-5.

[0022] Furthermore, the lubricant includes magnesium stearate or calcium stearate.

[0023] A method for preparing environmentally friendly flame-retardant PVC plastic, the preparation method comprising the following steps:

[0024] 80 to 100 parts by weight of the PVC matrix resin, 10 to 20 parts by weight of the phosphorus-containing composite flame retardant, 20 to 30 parts by weight of the vegetable oil-modified plasticizer and 1 to 5 parts by weight of the lubricant are fully blended to form a mixture, and then the mixture is placed in an internal mixer at 180 to 190° C. and kneaded for 10 to 15 minutes to obtain the environmentally friendly flame-retardant PVC plastic.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention combines phosphoric acid with polyhydroxy sugar through an esterification reaction, and the amino group of the nitrogen-containing compound receives hydrogen ions generated by the phosphoric acid to be protonated to form amino cations with positive charges, and the amino cations on the nitrogen-containing compound are solidified to the polyhydroxy sugar through electrostatic adsorption with the negatively charged phosphoric acid, thereby obtaining an organic phosphorus-containing composite flame retardant with good compatibility with PVC resin; and then, by using environmentally friendly vegetable oil as a plasticizer matrix, an epoxy group is introduced into the side chain of the vegetable oil, and the high reactivity of the epoxy group can be used to combine with hydrogen chloride, a harmful gas released by PVC due to high temperature. The phosphorus-containing composite flame retardant and the vegetable oil modified plasticizer are used in combination, and the reduced mechanical properties of PVC caused by the poor compatibility caused by the use of inorganic flame retardants and the environmental pollution caused by the use of highly toxic phthalate plasticizers are synergistically improved. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below through the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0028] Unless otherwise specified, the raw materials and reagents used in the present invention are commercially available or can be prepared by known methods.

[0029] PVC resin is purchased from Qingdao Haijing Chemical.

[0030] Preparation Example 1:

[0031] The preparation method of the phosphorus-containing composite flame retardant specifically comprises the following steps:

[0032] Dissolve 1 mol of glucose in 600 ml of dimethyl sulfoxide, add 2 mol of phosphoric acid and mix and stir, then heat the reaction solution to 90°C, reflux for 4 hours, remove dimethyl sulfoxide by vacuum distillation to obtain glucose phosphate; take 0.5 mol of glucose phosphate and dissolve it in an equal volume of methanol solution, then add 0.25 mol of urea and glucose phosphate and mix and stir, raise the temperature of the mixed solution composed of the two to 140°C and reflux for 3 hours, and after the reaction is completed, vacuum dry at 50°C for 15 hours to obtain a phosphorus-containing composite flame retardant.

[0033] Preparation Example 2:

[0034] The preparation method of the phosphorus-containing composite flame retardant specifically comprises the following steps:

[0035] Dissolve 1 mol of fructose in 600 ml of dimethyl sulfoxide, add 3 mol of phosphoric acid and mix, then heat the reaction solution to 100°C, reflux for 6 hours, remove dimethyl sulfoxide by vacuum distillation to obtain fructose phosphate; take 0.6 mol of fructose phosphate and dissolve it in an equal volume of methanol solution, then add 0.24 mol of urea and fructose phosphate and mix, raise the temperature of the mixed solution of the two to 150°C and reflux for 3 hours, and after the reaction is completed, vacuum dry at 50°C for 15 hours to obtain a phosphorus-containing composite flame retardant.

[0036] Preparation Example 3:

[0037] The preparation method of the phosphorus-containing composite flame retardant specifically comprises the following steps:

[0038] Dissolve 1 mol of sucrose in 1000 ml of dimethyl sulfoxide, add 4 mol of phosphoric acid and mix and stir, then heat the reaction solution to 110°C, reflux for 8 hours, remove dimethyl sulfoxide by vacuum distillation to obtain sucrose phosphate; take 0.6 mol of sucrose phosphate and dissolve it in an equal volume of methanol solution, then add 0.2 mol of melamine and sucrose phosphate and mix and stir, raise the temperature of the mixed solution composed of the two to 160°C and reflux for 4 hours, and after the reaction is completed, vacuum dry at 50°C for 15 hours to obtain a phosphorus-containing composite flame retardant.

[0039] Preparation Example 4:

[0040] The preparation method of the phosphorus-containing composite flame retardant specifically comprises the following steps:

[0041] Dissolve 1 mol of glucose in 600 ml of dimethyl sulfoxide, add 5 mol of phosphoric acid and mix and stir, then heat the reaction solution to 110°C, reflux for 8 hours, remove dimethyl sulfoxide by vacuum distillation to obtain glucose phosphate; take 0.6 mol of glucose phosphate and dissolve it in an equal volume of methanol solution, then add 0.2 mol of melamine and glucose phosphate and mix and stir, raise the temperature of the mixed solution composed of the two to 160°C and reflux for 4 hours, and after the reaction is completed, vacuum dry at 50°C for 15 hours to obtain a phosphorus-containing composite flame retardant.

[0042] Preparation Example 5:

[0043] The preparation method of the vegetable oil modified plasticizer specifically comprises the following steps:

[0044] Dissolve 1 mol of castor oil in 2000 ml of chloroform solution, then add 3 mol of epichlorohydrin and mix with the castor oil, then add 0.5 L of 1 mol / L ferric chloride solution and mix well, heat the mixed system to 50°C and react for 4 hours, add an equal volume of deionized water after the reaction, stir, mix and separate to obtain an organic phase, add 3 mol of sodium hydroxide to the organic phase, stir and place in a water bath at 25°C for a timed reaction of 2 hours, after the reaction, rinse repeatedly with deionized water for 3 to 4 times, and then dry in an oven at 50°C for 18 hours to obtain a vegetable oil modified plasticizer.

[0045] Preparation Example 6:

[0046] The preparation method of the vegetable oil modified plasticizer specifically comprises the following steps:

[0047] Dissolve 1 mol of castor oil in 2000 ml of chloroform solution, then add 4 mol of epichlorohydrin and mix with the castor oil, then add 0.5 L of 1 mol / L aluminum chloride solution and mix well, heat the mixed system to 60°C and react for 6 hours, add an equal volume of deionized water after the reaction, stir, mix and separate to obtain an organic phase, add 4 mol of sodium hydroxide to the organic phase, stir and place in a 30°C water bath environment to react for 2 hours, after the reaction, rinse repeatedly with deionized water 3 to 4 times, and then dry in an oven at 50°C for 18 hours to obtain a vegetable oil modified plasticizer.

[0048] Preparation Example 7:

[0049] The preparation method of the vegetable oil modified plasticizer specifically comprises the following steps:

[0050] Dissolve 1 mol of castor oil in 2000 ml of chloroform solution, then add 5 mol of epichlorohydrin and mix with the castor oil, then add 0.6 L of 1 mol / L zinc chloride solution and mix well, heat the mixed system to 70°C and react for 8 hours, add an equal volume of deionized water after the reaction, stir, mix and separate to obtain an organic phase, add 5 mol of sodium hydroxide to the organic phase, stir and place in a 35°C water bath environment for a timed reaction of 3 hours, after the reaction is completed, rinse repeatedly with deionized water 3 to 4 times, and then dry in an oven at 50°C for 18 hours to obtain a vegetable oil modified plasticizer.

[0051] Preparation Example 8:

[0052] The preparation method of the vegetable oil modified plasticizer specifically comprises the following steps:

[0053] Dissolve 1 mol of castor oil in 2000 ml of chloroform solution, then add 5 mol of epichlorohydrin and mix with the castor oil, then add 0.6 L of 1 mol / L copper chloride solution and mix well, heat the mixed system to 70°C and react for 8 hours, add an equal volume of deionized water after the reaction, stir, mix and separate to obtain an organic phase, add 5 mol of sodium hydroxide to the organic phase, stir and place in a 35°C water bath environment to react for 3 hours, after the reaction, rinse repeatedly with deionized water 3 to 4 times, and then dry in an oven at 50°C for 18 hours to obtain a vegetable oil modified plasticizer.

[0054] Embodiment 1:

[0055] A method for preparing environmentally friendly flame-retardant PVC plastics, specifically comprising the following processes:

[0056] 80 parts by weight of PVC matrix resin, 10 parts by weight of the phosphorus-containing composite flame retardant of Preparation Example 1, 20 parts by weight of the vegetable oil-modified plasticizer of Preparation Example 5 and 1 part by weight of magnesium stearate were blended by physical stirring, and then the mixture was put into an internal mixer, the temperature of the internal mixer was controlled to be 180°C, and mixing was started for 10 minutes to obtain an environmentally friendly flame-retardant PVC plastic, which was put into a flat mold while hot for hot pressing and cold pressing to obtain a test specimen.

[0057] Embodiment 2:

[0058] A method for preparing environmentally friendly flame-retardant PVC plastics, specifically comprising the following processes:

[0059] 85 parts by weight of PVC matrix resin, 15 parts by weight of the phosphorus-containing composite flame retardant of Preparation Example 1, 25 parts by weight of the vegetable oil-modified plasticizer of Preparation Example 5 and 2 parts by weight of magnesium stearate were blended by physical stirring, and then the mixture was put into an internal mixer, the temperature of the internal mixer was controlled to be 180°C, and mixing was started for 10 minutes to obtain an environmentally friendly flame-retardant PVC plastic, which was put into a flat mold while hot for hot pressing and cold pressing to obtain a test specimen.

[0060] Embodiment 3:

[0061] A method for preparing environmentally friendly flame-retardant PVC plastics, specifically comprising the following processes:

[0062] 90 parts by weight of PVC matrix resin, 20 parts by weight of the phosphorus-containing composite flame retardant of Preparation Example 2, 25 parts by weight of the vegetable oil-modified plasticizer of Preparation Example 6 and 3 parts by weight of magnesium stearate are blended by physical stirring, and then the mixture is put into an internal mixer, the temperature of the internal mixer is controlled to be 185°C, and mixing is started for 15 minutes to obtain an environmentally friendly flame-retardant PVC plastic, which is put into a flat mold while hot for hot pressing and cold pressing to obtain a test specimen.

[0063] Embodiment 4:

[0064] A method for preparing environmentally friendly flame-retardant PVC plastics, specifically comprising the following processes:

[0065] 95 parts by weight of PVC matrix resin, 20 parts by weight of the phosphorus-containing composite flame retardant of Preparation Example 3, 30 parts by weight of the vegetable oil-modified plasticizer of Preparation Example 7 and 4 parts by weight of calcium stearate were blended by physical stirring, and then the mixture was put into an internal mixer, the temperature of the internal mixer was controlled at 185°C, and mixing was started for 15 minutes to obtain an environmentally friendly flame-retardant PVC plastic, which was put into a flat mold while hot for hot pressing and cold pressing to obtain a test specimen.

[0066] Embodiment 5:

[0067] A method for preparing environmentally friendly flame-retardant PVC plastics, specifically comprising the following processes:

[0068] 100 parts by weight of PVC matrix resin, 20 parts by weight of the phosphorus-containing composite flame retardant of Preparation Example 4, 30 parts by weight of the vegetable oil-modified plasticizer of Preparation Example 8 and 5 parts by weight of calcium stearate are blended by physical stirring, and then the mixture is put into an internal mixer, the temperature of the internal mixer is controlled to be 190°C, and mixing is started for 15 minutes to obtain an environmentally friendly flame-retardant PVC plastic, which is put into a flat mold while hot for hot pressing and cold pressing to obtain a test specimen.

[0069] Comparative Example 1:

[0070] A method for preparing environmentally friendly flame-retardant PVC plastics, specifically comprising the following processes:

[0071] Preparation of phosphorus-containing composite flame retardant:

[0072] 100 g of glucan is added to 600 ml of deionized water, heated to 50°C and stirred until the glucan is completely dissolved, then 100 g of phosphoric acid is added and mixed and stirred, and then the reaction solution is heated to 110°C and refluxed for 8 hours to obtain glucan phosphate; 50 g of glucan phosphate is dissolved in an equal volume of acetone solution, and then 50 g of melamine and glucan phosphate are added and mixed and stirred, and the temperature of the mixed solution composed of the two is raised to 160°C and refluxed for 4 hours. After the reaction is completed, it is vacuum dried at 50°C for 15 hours to obtain a phosphorus-containing composite flame retardant.

[0073] Preparation of environmentally friendly flame-retardant PVC plastics:

[0074] 100 parts by weight of PVC matrix resin, 20 parts by weight of the phosphorus-containing composite flame retardant of this comparative example, 30 parts by weight of the vegetable oil-modified plasticizer of Preparation Example 8 and 5 parts by weight of calcium stearate are blended by physical stirring, and then the mixture is put into an internal mixer, the temperature of the internal mixer is controlled to be 190°C, and mixing is started for 15 minutes to obtain an environmentally friendly flame-retardant PVC plastic, which is put into a flat mold while hot for hot pressing and cold pressing to obtain a test specimen.

[0075] Comparative Example 2:

[0076] A method for preparing environmentally friendly flame-retardant PVC plastics, specifically comprising the following processes:

[0077] 100 parts by weight of PVC matrix resin, 20 parts by weight of the phosphorus-containing composite flame retardant of Preparation Example 4 and 5 parts by weight of calcium stearate were blended by physical stirring without adding a vegetable oil-modified plasticizer. The mixture was then put into an internal mixer, the temperature of the internal mixer was controlled to be 190°C, and mixing was started for 15 minutes to obtain an environmentally friendly flame-retardant PVC plastic. The plastic was put into a flat mold while hot for hot pressing and cold pressing to obtain a test specimen.

[0078] Comparative Example 3:

[0079] A method for preparing environmentally friendly flame-retardant PVC plastics, specifically comprising the following processes:

[0080] 100 parts by weight of PVC matrix resin, 30 parts by weight of the vegetable oil modified plasticizer of Preparation Example 8 and 5 parts by weight of calcium stearate are blended by physical stirring without adding a phosphorus-containing composite flame retardant. The mixture is then put into an internal mixer, the temperature of the internal mixer is controlled to be 190°C, and mixing is started for 15 minutes to obtain an environmentally friendly flame-retardant PVC plastic. While hot, it is put into a flat mold for hot pressing and cold pressing to obtain a test specimen.

[0081] The environmentally friendly flame-retardant PVC plastic test specimens obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to mechanical property tests, and the test results are as follows:

[0082] Sources Tensile strength(MPa) Tear strength (kN / m) Elongation at break (%) Example 1 9.87 45.27 154.02 Example 2 11.08 47.15 187.14 Example 3 15.12 48.03 221.84 Example 4 16.42 51.74 242.41 Example 5 16.58 49.68 235.53 Comparative Example 1 5.51 19.62 101.41 Comparative Example 2 10.47 31.74 168.16 Comparative Example 3 11.09 35.31 202.45

[0083] The limiting oxygen index of the environmentally friendly flame-retardant PVC plastic test specimens obtained in Examples 1 to 5 and Comparative Examples 1 to 3 was tested using a limiting oxygen index instrument, and the test results are as follows:

[0084]

[0085]

[0086] The above-described embodiments provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected.

Claims

1. An environmentally friendly flame-retardant PVC plastic, characterized in that: The environmentally friendly flame-retardant PVC plastic comprises the following raw materials in parts by weight: 80-100 parts of PVC base resin, 10-20 parts of phosphorus-containing composite flame retardant, 20-30 parts of vegetable oil modified plasticizer and 1-5 parts of lubricant.

2. The environmentally friendly flame-retardant PVC plastic according to claim 1, characterized in that: The preparation method of the phosphorus-containing composite flame retardant comprises the following steps: Mixing polyhydroxy sugar, phosphoric acid and a water-absorbing solvent to form a reaction solution, heating the reaction solution to 90-110° C. and subjecting the reaction solution to reflux reaction for 4-8 hours to obtain polyhydroxy sugar phosphate; The polyhydroxy sugar phosphate and the nitrogen-containing compound are mixed and dissolved in a methanol solution, and then the temperature is raised to 140° C. to 160° C. and refluxed for 3 to 4 hours to obtain the phosphorus-containing composite flame retardant.

3. The environmentally friendly flame-retardant PVC plastic according to claim 2, characterized in that: The polyhydroxy sugar includes glucose, fructose or sucrose.

4. The environmentally friendly flame-retardant PVC plastic according to claim 2, characterized in that: The molar ratio of the polyhydroxy sugar to the phosphoric acid is 1:2-5.

5. The environmentally friendly flame-retardant PVC plastic according to claim 2, characterized in that: The nitrogen-containing compound includes urea or melamine.

6. The environmentally friendly flame-retardant PVC plastic according to claim 2, characterized in that: The mass ratio of the polyhydroxy sugar phosphate ester to the nitrogen-containing compound is 2 to 3:

1.

7. The environmentally friendly flame-retardant PVC plastic according to claim 1, characterized in that: The preparation method of the vegetable oil modified plasticizer comprises the following steps: After castor oil and epichlorohydrin are mixed, Lewis acid is added and the mixture is heated to 50-70° C. for reaction for 4-8 hours. After the reaction is completed, an inorganic strong base is added, and then the reaction temperature is controlled to be 25-35° C. for reaction for 2-3 hours to obtain the vegetable oil modified plasticizer.

8. The environmentally friendly flame-retardant PVC plastic according to claim 7, characterized in that: The molar ratio of the castor oil to the epichlorohydrin is 1:3-5.

9. The environmentally friendly flame-retardant PVC plastic according to claim 1, characterized in that: The lubricant includes magnesium stearate or calcium stearate.

10. A method for preparing an environmentally friendly flame-retardant PVC plastic as claimed in any one of claims 1 to 9, characterized in that: The preparation method comprises the following steps: 80 to 100 parts by weight of the PVC matrix resin, 10 to 20 parts by weight of the phosphorus-containing composite flame retardant, 20 to 30 parts by weight of the vegetable oil-modified plasticizer and 1 to 5 parts by weight of the lubricant are fully blended to form a mixture, and then the mixture is placed in an internal mixer at 180 to 190° C. and kneaded for 10 to 15 minutes to obtain the environmentally friendly flame-retardant PVC plastic.

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