Flame-retardant toughened polyvinyl alcohol film and preparation method thereof

Abstract

The invention discloses a flame-retardant toughened polyvinyl alcohol film and a preparation method thereof, and belongs to the technical field of flame-retardant materials. According to the method, pentaerythritol, boric acid and an amino methylene phosphonic acid compound are used for synthesizing a phosphorus-nitrogen-boron-based flame-retardant toughening agent with the molecular structure containing phosphorus, nitrogen and boron flame-retardant elements and a methylene phosphonic acid group, and then the flame-retardant toughening agent is prepared by utilizing phosphonic acid esterification reaction and hydrogen bond cross-linking effect of the methylene phosphonic acid group and hydroxyl in polyvinyl alcohol molecules. The flame-retardant toughened polyvinyl alcohol film is prepared. The limit oxygen index of the flame-retardant toughened polyvinyl alcohol film prepared by the invention is greater than 28% under the condition of containing 10-20w% of the phosphorus-nitrogen-boron-based flame-retardant toughening agent, the UL-94 vertical combustion meets the VTM-0 grade, the tensile strength and the elongation at break are remarkably improved, and meanwhile, the process is simple and convenient, the conditions are mild, and the flame-retardant toughened polyvinyl alcohol film is suitable for industrial popularization and application.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant materials, and in particular relates to a flame retardant toughened polyvinyl alcohol film and a preparation method thereof. Background Art

[0002] Polyvinyl alcohol (PVA) is a water-soluble polymer formed by the hydrolysis of polyvinyl acetate, with a carbon chain as the main chain and a large number of hydroxyl groups in the side chain. PVA has good film-forming properties, and the film materials made from it have the characteristics of being non-toxic and odorless, highly transparent, excellent in biocompatibility, high in gas barrier properties, and good in mechanical properties. It is widely used in drug delivery, separation membrane materials, green packaging materials, tissue engineering and other fields. However, polyvinyl alcohol is a flammable substance with a limiting oxygen index of only about 19%. After burning, it will quickly cause the fire to spread, accompanied by a large amount of thick smoke and pungent odor, posing a serious threat to personal and property safety. Therefore, in order to meet the various applications of PVA and reduce its safety hazards, it is of great significance to develop highly flame-retardant PVA.

[0003] Patent CN 115109420B discloses a flame-retardant polyvinyl alcohol modified composition and a preparation method thereof, which is composed of polyvinyl alcohol modified resin, flame retardant methyl octabromoether, triphenyl phosphate, dimethicone, antioxidant 1010, antioxidant 168, erucamide, degradation stabilizer 1,4-dioxane-2,5-hexanedione and ferrocene, but the preparation of polyvinyl alcohol modified resin in this method needs to be carried out under high temperature and organic solvent conditions, and methyl octabromoether is a halogen-containing flame retardant, which does not meet green environmental protection requirements. Patent CN 111040349B discloses a flame-retardant polyvinyl alcohol composite material and a preparation method thereof, which is blended with polyvinyl alcohol, plasticizer and phytate choline flame retardant, but the method uses a large amount of organic solvents in the synthesis process of phytate choline flame retardant. Patent CN 113845678B discloses a method for preparing a transparent flame-retardant polyvinyl alcohol film, which is prepared from a mixed solution of acid-dissolved L-aspartic acid and polyvinyl alcohol, but the tensile strength of the flame-retardant polyvinyl alcohol film prepared by this method is greatly reduced. Therefore, it is still an urgent problem to develop a preparation method with simple process and mild reaction conditions to give polyvinyl alcohol excellent flame retardant and mechanical properties. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a flame retardant toughened polyvinyl alcohol film and a preparation method thereof. The preparation process provided is simple and the reaction conditions are mild, and the polyvinyl alcohol film can be endowed with excellent flame retardant and mechanical properties.

[0005] To achieve the above object, the present invention adopts the following technical solution: A method for preparing a flame retardant toughened polyvinyl alcohol film comprises the following steps: 1) dispersing pentaerythritol and boric acid in toluene, and then performing reflux reaction under heating and stirring conditions, and after the reaction is completed, performing rotary evaporation, washing, and vacuum drying to obtain pentaerythritol diborate; 2) dissolving the aminomethylphosphonic acid compound and the obtained pentaerythritol diborate in deionized water, reacting under heating and stirring conditions, and after the reaction, performing rotary evaporation and vacuum drying to obtain a phosphorus-nitrogen-boron-based flame retardant toughening agent; 3) Adding the prepared phosphorus, nitrogen and boron based flame retardant and toughening agent to the polyvinyl alcohol aqueous solution, mixing and reacting under heating and stirring conditions, and after the reaction is completed, naturally cooling and standing to defoam, pouring the mixed solution evenly into a film-forming plate, and then drying in an oven to obtain the flame retardant and toughened polyvinyl alcohol film.

[0006] In the above technical scheme, the phosphorus-nitrogen-boron based flame retardant toughening agent has good water solubility and thermal stability. Its molecular structure not only contains flame retardant elements phosphorus, nitrogen and boron, but also the methylene phosphonic acid group can react with the hydroxyl group in the polyvinyl alcohol molecule to undergo phosphonate esterification and form hydrogen bond cross-linking, thereby giving the polyvinyl alcohol excellent flame retardant and mechanical properties.

[0007] Furthermore, the molar ratio of pentaerythritol to boric acid used in step 1) is 2:1.

[0008] Furthermore, the temperature of the reflux reaction in step 1) is 110-120° C., and the time is 2-4 hours.

[0009] Furthermore, the amino methylene phosphonic acid compound in step 2) is any one of amino trimethylene phosphonic acid, ethylenediaminetetramethylene phosphonic acid, hexamethylenediaminetetramethylene phosphonic acid or diethylenetriaminepenta methylene phosphonic acid.

[0010] Furthermore, the molar ratio of the aminomethylphosphonic acid compound and pentaerythritol diborate used in step 2) is (1-2):1.

[0011] Furthermore, the reaction temperature in step 2) is 50-90° C. and the reaction time is 2-6 hours.

[0012] Furthermore, the mass concentration of the polyvinyl alcohol aqueous solution in step 3) is 5-10wt%.

[0013] Furthermore, the reaction temperature in step 3) is 20-80°C and the reaction time is 0.5-4h.

[0014] Furthermore, in step 3), the drying temperature is 20-60° C. and the drying time is 12-36 hours.

[0015] In terms of mass percentage, the proportion of polyvinyl alcohol in the obtained flame retardant and toughened polyvinyl alcohol film is 80-90wt%, the proportion of phosphorus, nitrogen and boron based flame retardant and toughening agent is 10-20wt%, and the sum of the mass percentages of the two is 100%.

[0016] The obtained flame retardant toughened polyvinyl alcohol film has a limiting oxygen index greater than 28%, and the UL-94 vertical combustion meets the VTM-0 grade.

[0017] Compared with the prior art, the present invention has the following significant advantages: (1) The phosphorus, nitrogen and boron-based flame retardant and toughening agent and polyvinyl alcohol provided by the present invention have good water solubility. The process for preparing the flame retardant and toughened polyvinyl alcohol film is simple, the reaction conditions are mild, and the energy consumption is low, which is suitable for industrial promotion and application.

[0018] (2) The phosphorus, nitrogen and boron flame retardant toughening agent provided by the present invention contains phosphorus, nitrogen and boron flame retardant elements. The methylene phosphonic acid group in its molecular structure can react with the hydroxyl group in the polyvinyl alcohol molecule to form a phosphonate esterification reaction and form a hydrogen bond cross-linking reaction, thereby chemically bonding the phosphorus, nitrogen and boron flame retardant elements to the side chains of the polyvinyl alcohol (such as Figure 1 ), the polyvinyl alcohol composite film produced not only has excellent flame retardant properties (its limiting oxygen index is greater than 28% under the condition of containing 10-20wt% phosphorus, nitrogen and boron based flame retardant and toughening agent, and UL-94 vertical combustion meets VTM-0 grade), but also effectively solves the problem of poor compatibility and weak bonding between traditional additive flame retardants and polyvinyl alcohol, while improving the tensile strength and elongation at break of polyvinyl alcohol, broadening the application field of polyvinyl alcohol film, and has extremely high industrial production value and prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The figure is a schematic diagram of the preparation of the phosphorus-nitrogen-boron-based flame retardant toughening agent in the present invention and the principle of its phosphonation reaction with polyvinyl alcohol (the reaction formula only takes the reaction of a single methylene phosphonic acid group with a hydroxyl group as an example).

[0020] Figure 2 Infrared spectra of the flame retardant toughened polyvinyl alcohol film prepared in Example 1 and the polyvinyl alcohol film prepared in Comparative Example 1.

[0021] Figure 3 The stress-strain curves of the flame-retardant toughened polyvinyl alcohol films prepared in Examples 1-4 and the polyvinyl alcohol film prepared in Comparative Example 1 are shown.

[0022] Figure 4 It is a diagram of the vertical burning test process of the flame retardant toughened polyvinyl alcohol film prepared in Example 4 and the polyvinyl alcohol film prepared in Comparative Example 1. DETAILED DESCRIPTION

[0023] A flame retardant toughened polyvinyl alcohol film, the preparation method of which comprises the following steps: 1) Pentaerythritol and boric acid are dispersed in toluene in a molar ratio of 2:1, and then refluxed for reaction at 110-120°C with stirring for 2-4 hours. After the reaction, the mixture is subjected to rotary evaporation, washing, and vacuum drying to obtain pentaerythritol diborate; 2) dissolving the aminomethylphosphonic acid compound and the obtained pentaerythritol diborate in deionized water in a molar ratio of (1-2):1, heating and stirring at 50-90°C for 2-6 hours, and after the reaction, performing rotary evaporation and vacuum drying to obtain a phosphorus-nitrogen-boron-based flame retardant toughening agent; 3) Add the prepared phosphorus, nitrogen and boron based flame retardant and toughening agent to a 5-10 wt% aqueous solution of polyvinyl alcohol, and heat and stir at 20-80°C for a mixed reaction for 0.5-4 h. After the reaction is completed, naturally cool and stand to defoam, and then pour the mixed solution evenly into a film-forming plate, and then place it in an oven at 20-60°C for drying for 12-36 h to obtain a flame retardant and toughened polyvinyl alcohol film.

[0024] Mentioning "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The word "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in this application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution. Unless otherwise defined, the technical terms used in this article have the same meaning as that generally understood by technicians in the technical field to which this application belongs; the use of relevant terms in this article is only for describing specific embodiments, and is not intended to limit this application.

[0025] The raw materials used in the following examples of the present invention are described as follows: pentaerythritol, boric acid, aminomethylphosphonic acid compound, and polyvinyl alcohol are all commercially available conventional products. Among them, the polyvinyl alcohol is 1799 type.

[0026] The performance measurement methods involved in the following embodiments of the present invention are described as follows: the limiting oxygen index is tested according to ASTM D 2863, the UL-94 vertical burning grade is tested according to ASTM D 4804, the tensile properties are tested according to GB / T 1040.3-2006, and the thickness is measured using a micrometer thickness gauge.

[0027] Example 1 This embodiment provides a method for preparing a flame retardant toughened polyvinyl alcohol film: (1) 0.2 mol of pentaerythritol and 0.1 mol of boric acid were dispersed in toluene, heated and stirred at 110°C for 3 h under reflux, and after the reaction was completed, the mixture was subjected to rotary evaporation, washing, and vacuum drying to obtain pentaerythritol diborate; (2) dissolving 0.1 mol of aminotri(methylenephosphonic acid) and 0.1 mol of pentaerythritol diborate in deionized water, heating and stirring at 90° C. for 2 h, and after the reaction, performing rotary evaporation and vacuum drying to obtain a phosphorus-nitrogen-boron-based flame retardant and toughening agent; (3) A certain amount of the prepared phosphorus, nitrogen and boron based flame retardant and toughening agent was added to a 5 wt% polyvinyl alcohol aqueous solution, and the mixture was heated and stirred at 60°C for 2 h. After the reaction was completed, the mixture was naturally cooled and allowed to stand for defoaming. The mixture was poured into a film-forming plate and placed in an oven at 60°C for drying for 12 h to obtain a flame retardant and toughened polyvinyl alcohol film containing 15 wt% phosphorus, nitrogen and boron based flame retardant and toughening agent.

[0028] Example 2 This embodiment provides a method for preparing a flame retardant toughened polyvinyl alcohol film: (1) Dispersing 0.2 mol of pentaerythritol and 0.1 mol of boric acid in toluene, heating and stirring under reflux at 120°C for 2 h, and after the reaction, rotary evaporation, washing, and vacuum drying were performed to obtain pentaerythritol diborate; (2) dissolving 0.2 mol of ethylenediaminetetramethylenephosphonic acid and 0.1 mol of pentaerythritol diborate in deionized water, heating and stirring at 50° C. for 6 h, and after the reaction, performing rotary evaporation and vacuum drying to obtain a phosphorus-nitrogen-boron-based flame retardant and toughening agent; (3) A certain amount of the prepared phosphorus, nitrogen and boron based flame retardant and toughening agent was added to a 10 wt% polyvinyl alcohol aqueous solution, and the mixture was heated and stirred at 20°C for 4 h. After the reaction was completed, the mixture was naturally cooled and allowed to stand for defoaming. The mixture was poured into a film-forming plate and placed in an oven at 20°C for drying for 36 h to obtain a flame retardant and toughened polyvinyl alcohol film containing 20 wt% phosphorus, nitrogen and boron based flame retardant and toughening agent.

[0029] Example 3 This embodiment provides a method for preparing a flame retardant toughened polyvinyl alcohol film: (1) 0.2 mol of pentaerythritol and 0.1 mol of boric acid were dispersed in toluene, heated and stirred at 120°C for 3 h under reflux, and after the reaction was completed, the mixture was subjected to rotary evaporation, washing, and vacuum drying to obtain pentaerythritol diborate; (2) dissolving 0.2 mol of hexamethylenediaminetetramethylenephosphonic acid and 0.1 mol of pentaerythritol diborate in deionized water, heating and stirring at 70°C for 5 h, and after the reaction, performing rotary evaporation and vacuum drying to obtain a phosphorus-nitrogen-boron-based flame retardant and toughening agent; (3) A certain amount of the prepared phosphorus, nitrogen and boron based flame retardant and toughening agent was added to an 8 wt % polyvinyl alcohol aqueous solution, and the mixture was heated and stirred at 80 ° C for 0.5 h. After the reaction was completed, it was naturally cooled and allowed to stand for defoaming. The mixed solution was poured into a film-forming plate and placed in an oven at 50 ° C for 24 h to obtain a flame retardant and toughened polyvinyl alcohol film containing 10 wt % phosphorus, nitrogen and boron based flame retardant and toughening agent.

[0030] Example 4 This embodiment provides a method for preparing a flame retardant toughened polyvinyl alcohol film: (1) 0.2 mol of pentaerythritol and 0.1 mol of boric acid were dispersed in toluene, heated and stirred at 110°C for 4 h under reflux, and after the reaction was completed, the mixture was subjected to rotary evaporation, washing, and vacuum drying to obtain pentaerythritol diborate; (2) Dissolving 0.1 mol of diethylenetriamine penta (methylenephosphonic acid) and 0.1 mol of pentaerythritol diborate in deionized water, heating and stirring at 80° C. for 3 h, and after the reaction, performing rotary evaporation and vacuum drying to obtain a phosphorus-nitrogen-boron-based flame retardant and toughening agent; (3) A certain amount of the prepared phosphorus, nitrogen and boron based flame retardant and toughening agent was added to a 5 wt% polyvinyl alcohol aqueous solution, and the mixture was heated and stirred at 40°C for 3 h. After the reaction was completed, the mixture was naturally cooled and allowed to stand for defoaming. The mixture was poured into a film-forming plate and placed in an oven at 40°C for drying for 30 h to obtain a flame retardant and toughened polyvinyl alcohol film containing 12 wt% phosphorus, nitrogen and boron based flame retardant and toughening agent.

[0031] Comparative Example 1 This comparative example provides a method for preparing a polyvinyl alcohol film: The prepared 5 wt % polyvinyl alcohol aqueous solution was naturally cooled, allowed to stand for defoaming, poured into a film-forming plate, and placed in an oven at 40° C. for drying for 30 h to obtain a polyvinyl alcohol film.

[0032] Comparative Example 2 This comparative example provides a method for preparing a flame retardant toughened polyvinyl alcohol film: (1) 0.2 mol of pentaerythritol and 0.1 mol of boric acid were dispersed in toluene, heated and stirred at 110°C for 4 h under reflux, and after the reaction was completed, the mixture was subjected to rotary evaporation, washing, and vacuum drying to obtain pentaerythritol diborate; (2) A certain amount of the prepared pentaerythritol diborate was added to a 5 wt% polyvinyl alcohol aqueous solution, and the mixture was heated and stirred at 40°C for 3 h. After the reaction was completed, the mixture was naturally cooled and allowed to stand for defoaming. The mixture was poured into a film-forming plate and dried in an oven at 40°C for 30 h to obtain a flame-retardant toughened polyvinyl alcohol film containing 12 wt% pentaerythritol diborate.

[0033] Comparative Example 3 This comparative example provides a method for preparing a flame retardant toughened polyvinyl alcohol film A certain amount of hexamethylenediaminetetramethylenephosphonic acid was added to a 5wt% polyvinyl alcohol aqueous solution, and the mixture was heated and stirred at 40°C for 3 hours. After the reaction was completed, it was naturally cooled and allowed to stand for defoaming. The mixed solution was poured into a film-forming plate and dried in an oven at 40°C for 30 hours to obtain a flame-retardant and toughened polyvinyl alcohol film containing 12wt% hexamethylenediaminetetramethylenephosphonic acid.

[0034] Figure 2 The infrared spectra of the flame retardant toughened polyvinyl alcohol film prepared in Example 1 and the polyvinyl alcohol film prepared in Comparative Example 1 are shown in the figure. It can be seen from the figure that after adding the phosphorus, nitrogen and boron based flame retardant toughening agent, in addition to the characteristic absorption peaks of P=O, PO, PC and BO, the C-OH absorption peak in the flame retardant toughened polyvinyl alcohol film is significantly weakened, indicating that the hydroxyl groups in the polyvinyl alcohol molecular chain undergo phosphonate esterification reaction. At the same time, the absorption peaks of 3600~3000cm -1 The -OH absorption peak at the position becomes weaker and red-shifts, indicating that hydrogen bond cross-linking is formed between the hydroxyl groups in the polyvinyl alcohol molecules and the phosphorus, nitrogen and boron based flame retardant and toughening agent.

[0035] Figure 3 The stress-strain curves of the flame-retardant toughened polyvinyl alcohol films prepared in Examples 1-4 and the polyvinyl alcohol film prepared in Comparative Example 1 are shown in the figure. It can be found from the figure that the introduction of phosphorus, nitrogen and boron based flame-retardant toughening agent increases the tensile strength and elongation at break of the polyvinyl alcohol film to varying degrees, and effectively plays a role in strengthening and toughening.

[0036] Figure 4 The vertical combustion test process diagram of the flame retardant toughened polyvinyl alcohol film prepared in Example 4 and the polyvinyl alcohol film prepared in Comparative Example 1. From the comparison in the figure, it can be found that the polyvinyl alcohol film burns rapidly after the first ignition until the sample is burned out, and a large amount of molten droplets are produced, and the limiting oxygen index (LOI) is only 19.3%, which cannot pass the UL-94 vertical combustion test; while the addition of phosphorus, nitrogen and boron based flame retardant toughening agent makes the flame retardant toughened polyvinyl alcohol film self-extinguish within 10s after the fire source is removed twice, and the flame does not spread above the marking line, and no molten droplets are produced, reaching the UL-94 vertical combustion VTM-0 level, and the LOI is greater than 28%.

[0037] Table 1 shows the parameters and performance test results of the flame retardant toughened polyvinyl alcohol films prepared in Examples 1-4 and the polyvinyl alcohol films prepared in Comparative Examples 1-3.

[0038] Table 1 Comparison of parameters and properties of polyvinyl alcohol films prepared in Examples 1-4 and Comparative Examples 1-3

[0039] From the results shown in Table 1, it can be seen that the flame-retardant toughened polyvinyl alcohol film prepared in Examples 1-4 has excellent flame retardant and mechanical properties, and the limiting oxygen index (LOI value) of the polyvinyl alcohol film containing 10-20wt% of phosphorus, nitrogen and boron-based flame retardant toughening agent is greater than 28%, and the UL-94 vertical combustion meets the VTM-0 grade. Compared with the polyvinyl alcohol film using only pentaerythritol diborate or aminomethylphosphonic acid, its flame retardant effect is significantly improved, indicating the synergistic flame retardant effect of the three elements of phosphorus, nitrogen and boron in the phosphorus, nitrogen and boron-based flame retardant toughening agent. At the same time, compared with pure polyvinyl alcohol film and polyvinyl alcohol film using only pentaerythritol diborate or aminomethylphosphonic acid, its tensile strength and elongation at break are significantly improved. Therefore, the preparation method of the flame-retardant toughened polyvinyl alcohol film provided by the present invention is worthy of being widely promoted and applied.

[0040] It should be noted that, although the above embodiments have been described in this article, the patent protection scope of the present invention is not limited thereby. Therefore, based on the innovative concept of the present invention, changes and modifications made to the embodiments described herein, or equivalent structures or equivalent process changes made using the contents of the present invention specification, directly or indirectly applying the above technical solutions to other related technical fields are all included in the patent protection scope of the present invention.

Claims

1. A method for preparing a flame retardant toughened polyvinyl alcohol film, characterized in that: The following steps are involved: 1) dispersing pentaerythritol and boric acid in toluene, and then performing reflux reaction under heating and stirring conditions, and after the reaction is completed, performing rotary evaporation, washing, and vacuum drying to obtain pentaerythritol diborate; 2) dissolving the aminomethylphosphonic acid compound and the obtained pentaerythritol diborate in deionized water, reacting under heating and stirring conditions, and after the reaction, performing rotary evaporation and vacuum drying to obtain a phosphorus-nitrogen-boron-based flame retardant toughening agent; 3) Adding the prepared phosphorus, nitrogen and boron based flame retardant and toughening agent to the polyvinyl alcohol aqueous solution, mixing and reacting under heating and stirring conditions, and after the reaction is completed, naturally cooling and standing to defoam, pouring the mixed solution evenly into a film-forming plate, and then drying in an oven to obtain the flame retardant and toughened polyvinyl alcohol film.

2. The preparation method according to claim 1, characterized in that: The molar ratio of pentaerythritol to boric acid used in step 1) is 2:

1.

3. The preparation method according to claim 1, characterized in that: The temperature of the reflux reaction in step 1) is 110-120° C. and the time is 2-4 hours.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the amino methylene phosphonic acid compound and pentaerythritol diborate used in step 2) is (1-2):1, and the amino methylene phosphonic acid compound is any one of amino tri methylene phosphonic acid, ethylene diamine tetra methylene phosphonic acid, hexamethylene diamine tetra methylene phosphonic acid or diethylene triamine penta methylene phosphonic acid.

5. The preparation method according to claim 1, characterized in that: The reaction temperature in step 2) is 50-90°C and the reaction time is 2-6 hours.

6. The preparation method according to claim 1, characterized in that: The mass concentration of the polyvinyl alcohol aqueous solution in step 3) is 5-10wt%.

7. The preparation method according to claim 1, characterized in that: In step 3), the reaction temperature is 20-80°C and the time is 0.5-4h; the drying temperature is 20-60°C and the time is 12-36h.

8. A flame retardant toughened polyvinyl alcohol film prepared by the method according to any one of claims 1 to 7.

9. The flame retardant toughened polyvinyl alcohol film according to claim 8, characterized in that: In terms of mass percentage, the proportion of polyvinyl alcohol in the flame retardant and toughened polyvinyl alcohol film is 80-90wt%, the proportion of phosphorus, nitrogen and boron based flame retardant and toughening agent is 10-20wt%, and the sum of the mass percentages of the two is 100%.

10. The flame retardant toughened polyvinyl alcohol film according to claim 8, characterized in that: Its limiting oxygen index is greater than 28%, and UL-94 vertical combustion meets VTM-0 grade.

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