Process for the preparation of phosphorus / silicon synergistic flame-retardant non-ionic waterborne polyurethanes

Abstract

The application discloses a preparation method of phosphorus / silicon synergistic flame-retardant nonionic water-based polyurethane, and adopts PDMS, polypropylene glycol and toluene diisocyanate as main raw materials to prepare polyurethane prepolymer, adopts self-made PHAD and trimethylolpropane as chain extenders, and adopts polyethylene glycol with a molecular weight of 2000 as a hydrophilic chain extender to prepare nonionic water-based polyurethane dispersion with phosphorus / silicon synergistic flame-retardant effect. The introduction of PDMS can effectively improve the thermal stability and flame retardancy of polyurethane adhesive film; when the introduction amount of PDMS accounts for 15% of the prepolymer polyol component, the limiting oxygen index (LOI) of the adhesive film is as high as 28.2%, and the residual ash rate at 600 DEG C reaches 7.46%; the special molecular structure of PHAD can be more effectively integrated into the polyurethane network, the intermolecular interaction force is enhanced in cooperation with PDMS, so that the overall structural strength and toughness of the material are fundamentally consolidated, the brittleness and strength loss phenomenon caused by the traditional silicon-based flame retardant are effectively inhibited, and the perfect balance of flame retardancy and mechanical property improvement is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of functional polymers, in particular to a flame-retardant non-ionic waterborne polyurethane and a preparation method thereof. BACKGROUND

[0002] Waterborne flame-retardant polyurethane is a specially designed environmentally friendly polyurethane material, which has excellent physical properties and flame-retardant properties of polyurethane, and uses water as a dispersion medium. Compared with solvent-based polyurethane, it has the advantages of low toxicity, low volatile organic compounds (VOC) and environmental friendliness. Waterborne flame-retardant polyurethane is widely used in fields such as building, furniture, automobile, electronic and electrical appliances, textiles, etc., such as fireproof coatings, flame-retardant soft and hard foam materials, fabric coatings, etc.

[0003] The preparation of waterborne flame-retardant polyurethane generally involves the synthesis of polyurethane prepolymer, the selection and addition of flame retardants, and the final dispersion process with water as the medium. The limiting oxygen index of ordinary waterborne polyurethane (WPU) material is only 18%, which belongs to flammable materials, which seriously restricts the application of WPU in the field of flame-retardant materials. The preparation of flame-retardant waterborne polyurethane is to introduce flame-retardant components into the waterborne polyurethane system through physical or chemical processes, so as to endow the material with flame-retardant properties and high temperature resistance. According to the main element composition of the added flame retardant, flame-retardant waterborne polyurethane is mainly divided into halogen-based, phosphorus-based, silicon-based and intumescent flame-retardant modified types. By introducing different types of flame-retardant components, the flame-retardant properties and high temperature resistance of the material can be improved to different degrees to meet the needs in different application fields. Among them, phosphorus / silicon synergistic flame-retardant non-ionic waterborne polyurethane shows many advantages. The synergistic effect of phosphorus and silicon elements can significantly improve the flame-retardant properties of the material. Phosphorus element can generate phosphoric acid or phosphate in the combustion process, forming a protective carbon layer to inhibit flame spread; silicon element helps to form a more dense heat insulation layer, reducing the transfer of heat and oxygen. The two work together to more effectively prevent the material from burning and improve the self-extinguishing property of the material.

[0004] However, the introduction of phosphorus and silicon-based flame retardants, especially by grafting them onto the polyurethane main chain or side chain through chemical reactions, can lead to poor compatibility with the original non-ionic waterborne polyurethane segments. Unfavorable compatibility can cause micro-phase separation, forming an island structure that reduces intermolecular forces and continuity, resulting in a decrease in tensile strength and elongation at break of the material. Phosphorus / silicon flame retardants generally have high rigidity, and their addition can increase the rigidity of the entire polyurethane molecular chain, making the material more brittle and hard. The molecular chain that is too rigid is not easy to deform under stress, and thus is prone to breakage at stress concentration points, affecting the tensile performance. The introduction of flame retardants is sometimes accompanied by crosslinking reactions, and an inappropriate degree of crosslinking can change the network structure of the material. Too high or too low crosslinking can adversely affect the mechanical properties of the material. Too high crosslinking causes the material to become brittle and weak in tensile resistance, and too low crosslinking can reduce the strength of the material. SUMMARY

[0005] The present application provides a preparation method of phosphorus / silicon synergistic flame-retardant non-ionic waterborne polyurethane to solve the problem of reduced mechanical properties (tensile strength) of existing phosphorus / silicon synergistic flame-retardant non-ionic waterborne polyurethane.

[0006] The present application adopts the following technical scheme: a preparation method of phosphorus / silicon synergistic flame-retardant non-ionic waterborne polyurethane, at least comprising:

[0007] (1) 56.0 grams of pre-polyol and 29.0 grams of TDI-80 are stirred at room temperature under nitrogen protection for 0.5 h, then heated to 80℃, and reacted for 3 h; the pre-polyol is composed of N210 and PDMS, and the PDMS is within 11.2 g; the PDMS is grafted onto the polyurethane main chain by replacing part of the polyether polyol N210 and participating in the pre-polymerization reaction.

[0008] (2) The temperature is lowered to 70℃, 3.0 grams of TMP and a mixture of 15.0 grams of PHAD and 20 ml of acetone are added, and reacted for 1 h; wherein, the molecular formula of the PHAD is:

[0009]

[0010] (3) The temperature is lowered to 60℃, 20.0 grams of PEG2000 are added, and reacted for 3 h;

[0011] (4) The temperature is lowered to 20℃, a mixed solution of 2.0 grams of EDA and 20 ml of acetone is added dropwise, and reacted for 1 h;

[0012] (5) After dispersing in deionized water for 1 h, the acetone in the system is removed by distillation under reduced pressure to obtain a phosphorus / silicon synergistic flame-retardant non-ionic waterborne polyurethane dispersion.

[0013] Further, the preparation method of PHAD in step 2 comprises:

[0014] Synthesizing 4-((4-hydroxybenzylidene)amino)phenol (PHA) containing C=N double bond from p-hydroxybenzaldehyde and p-aminophenol;

[0015] Further synthesizing DOPO-based aromatic Schiff base derivative PHAD from 4-((4-hydroxybenzylidene)amino)phenol (PHA) and DOPO.

[0016] Further, the synthesis method of 4-((4-hydroxybenzylidene)amino)phenol (PHA) is as follows:

[0017] Mixing p-aminophenol, p-hydroxybenzaldehyde, acetic acid, 4A molecular sieve and anhydrous ethanol uniformly, wherein the molar ratio of p-aminophenol and p-hydroxybenzaldehyde is 1:1; heating to 70 DEG C and keeping at the temperature for 8h, then pouring the reaction into ice water, solid precipitates, vacuum filtration and washing to obtain solid; drying in a vacuum oven at 100 DEG C to constant weight to obtain orange yellow powder PHA.

[0018] Further, the p-aminophenol is 18g (0.15mol), the p-hydroxybenzaldehyde is 18.32g (0.15mol), the acetic acid is 0.45g (0.0075mol), the 4A molecular sieve is 8g, and the anhydrous ethanol is 360mL.

[0019] Further, the synthesis method of DOPO-based aromatic Schiff base derivative PHAD is as follows:

[0020] Mixing DOPO (17.30g, 0.08mol), PHA (17.04g, 0.08mol) and 300mL anhydrous ethanol uniformly; ice water bath reaction, keeping the reaction temperature at 3-5 DEG C, reacting at the temperature for 6h, then pouring the reaction into ice water prepared in advance, solid precipitates, vacuum filtration, washing with water twice to obtain solid; drying in a vacuum oven at 100 DEG C to constant weight to obtain light yellow powder PHA-DOPO.

[0021] The application has the beneficial effects that the application innovatively uses PHAD to replace the traditional chemical small molecule chain extender 1,4-butanediol (BDO), ingeniously solves the problem that the introduction of silicon elements usually causes the mechanical property of polyurethane to decrease, the special molecular structure of PHAD can more effectively enhance the strength of polyurethane network compared with BDO, cooperates with PDMS to enhance the intermolecular interaction force, thereby fundamentally consolidates the overall structural strength and toughness of the material, effectively inhibits the embrittlement and strength loss phenomenon possibly caused by the traditional silicon-based flame retardant, and realizes the perfect balance of flame retardation and mechanical property improvement. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 1H NMR spectra of PHA and PHAD, (a) PHA, (b) PHAD;

[0023] Figure 2 Infrared spectra of PHA and PHAD;

[0024] Figure 3 Synthesis scheme of phosphorus / silicon flame-retardant nonionic waterborne polyurethane dispersion;

[0025] Figure 4 Infrared spectra of PWPU and SiPWPU;

[0026] Figure 5 Particle size distribution of SiPWPU dispersions with different PDMS contents;

[0027] Figure 6 TGA (a) and DTG (b) curves of SiPWPU films with different PDMS contents;

[0028] Figure 7 SEM images of carbon residue of different films and elemental analysis of the corresponding combustion residues. (a) WPU, (b) PWPU, (c) SiPWPU (15%). DETAILED DESCRIPTION

[0029] The present application will be further described in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application.

[0030] The operation methods in the following examples without specific conditions are generally according to the conventional conditions or according to the conditions suggested by the manufacturers.

[0031] In the following examples, the tensile strength is tested according to the standard "Test Method for Tensile Properties of Plastic Films" (GB 13022-91), and a polytetrafluoroethylene mold is customized according to the type II sample specification. Pour the WPU dispersion onto the mold and use a glass rod to scrape off the excess glue. Place the film at room temperature for 24 h, then bake at 160℃ for 8 min to prepare a WPU film with a thickness of about 0.3 mm. The tensile strength (tensile fracture stress, tensile yield stress) of the sample is expressed as σ (MPa) and calculated according to formula (1):

[0032]

[0033] In the formula: F - maximum load, breaking load, yield load, N;

[0034] b - sample width, mm;

[0035] d - sample thickness, mm.

[0036] Example 1

[0037] 1) Para-aminophenol (18 g, 0.15 mol), p-hydroxybenzaldehyde (18.32 g, 0.15 mol), acetic acid (0.45 g, 0.0075 mol), 8 g of 4A molecular sieves and 360 mL of absolute ethanol were placed in a round 500 mL four-necked flask fitted with a nitrogen inlet, condenser, thermometer and mechanical stirrer. The reaction mixture was heated to 70 °C and maintained at this temperature for 8 h, then the reaction was poured into ice water prepared in advance, and a large amount of orange solid was precipitated, which was filtered under vacuum, washed with water twice, and the solid was obtained, dried in a vacuum oven at 100 °C to constant weight to obtain an orange-yellow powder PHA with a yield of 88.46%.

[0038] 2) DOPO (17.30 g, 0.08 mol), product (1) PHA (17.04 g, 0.08 mol) and 300 mL of absolute ethanol were placed in a round 500 mL four-necked flask fitted with a nitrogen inlet, condenser, thermometer and mechanical stirrer. The reaction was carried out in an ice water bath, maintaining the reaction temperature at 3-5 °C, and the reaction was carried out at this temperature for 6 h, then the reaction was poured into ice water prepared in advance, and a large amount of light yellow solid was precipitated, which was filtered under vacuum, washed with water twice, and the solid was obtained, dried in a vacuum oven at 100 °C to constant weight to obtain a light yellow powder PHA-DOPO with a yield of 90.13%.

[0039] The infrared test of PHA and PHA-DOPO obtained in this step is shown in Figure 1 From the Figure 1 FTIR spectrum of PHA, it can be seen that there is an absorption peak at 1586 cm -1 , which is the typical stretching vibration of C=N, confirming the condensation of aldehyde group and amino group to form a Schiff base structure. In contrast, PHAD shows characteristic absorption peaks of DOPO structure at about 1202 cm -1 , 930 cm -1 , 752 cm -1 , which are attributed to P=O, P-O-Ar and P-C stretching vibration, respectively. In addition, a new absorption peak at 1370 cm -1 , which is the stretching vibration of C-N, appears in the spectrum of PHAD, while the typical stretching vibration of C=N at 1651 cm -1 disappears, which further proves the successful addition reaction of P-H of DOPO and C=N in PHA.

[0040] The structure of PHA and PHAD was further confirmed by nuclear magnetic resonance characterization, as shown in Figure 2 1 ​HNMR analysis showed that PHA exhibited a singlet at 8.5 ppm (3) which belonged to the characteristic proton of H-C=N and multiplets at 6.7-7.8 ppm (1, 2, 4, 5) which belonged to the characteristic proton of benzene ring. After the reaction of DOPO with PHA, the obtained PHAD exhibited the characteristic proton of phosphaphenanthrene ring at 7.0-8.2 ppm (6-13). Therefore, the multiplet of the characteristic proton of benzene ring (2, 3, 5, 4) shifted to 6.3-7.2 ppm, which was related to the different chemical environment. Two secondary amino peaks (NH and NH') appeared at 5.5-6.1 ppm and two aliphatic hydrogen peaks (1 and 1') appeared at 4.7-5.3 ppm, which was due to the existence of two diastereoisomers.

[0041] 3) N210, PHAD and PEG were vacuum dehydrated at a temperature of 120°C and a pressure of greater than 0.1 MPa for 6 h, and then were reserved after being reduced to room temperature.

[0042] 4) 56.0 g of prepolymer polyol (N210) and 29.0 g of TDI-80 were added into a dry four-necked flask, nitrogen was introduced for protection, and stirring was carried out at room temperature for 0.5 h, then the temperature was increased to 80°C, and reaction was carried out for 3 h, then the temperature was reduced to 70°C, 3.0 g of TMP and 15.0 g of PHAD mixed with 20 ml of acetone were added, reaction was carried out for 1 h, then the temperature was reduced to 60°C, 20.0 g of PEG was added, reaction was carried out for 3 h, then the temperature was reduced to 20°C, a mixture solution of 2.0 g of EDA and 20 ml of acetone was added dropwise, reaction was carried out for 1 h, then deionized water was added for high-speed dispersion for 1 h, then acetone in the system was removed by distillation under reduced pressure, and a phosphorus / silicon synergistic flame-retardant non-ionic waterborne polyurethane dispersion with a theoretical solid content of 30% was obtained. The synthesis principle is shown in Figure 3 .

[0043] Table 1

[0044] Ingredients N210 PDMS PHAD TDI-80 TMP PEG2000 EDA H2O Mass (g) 56～44.8 0.0～11.2 15 29 3 20 2 125

[0045] Figure 4 The infrared spectra of the phosphorus flame-retardant modified waterborne polyurethane (abbreviated as PWPU) and the phosphorus / silicon synergistic flame-retardant modified waterborne polyurethane (abbreviated as SiPWPU) film. 2260-2280 cm -1 is the absorption peak of -NCO group. Figure 2 It is shown that after the completion of prepolymerization, chain extension and dispersion, the NCO group has completely participated in the reaction. The typical absorption peak of polyurethane structure 1715-1750 cm -1 , 1520-1560 cm -1 appears in both spectra. Compared with the spectrum of the phosphorus flame-retardant modified waterborne polyurethane, there is a new absorption peak at 1285 cm -1 in the spectrum of the phosphorus / silicon synergistic flame-retardant modified waterborne polyurethane, which is the stretching vibration absorption peak of Si-O-Si bond.

[0046] Table 2 is the performance data of SiPWPU dispersion with different PDMS content (mPDMS / m(PDMS+N210)), Figure 5 The particle size distribution of SiPWPU with different PDMS content. From Table 2, with the continuous increase of PDMS addition amount, the appearance of the dispersion gradually changes from light yellow opaque to yellow opaque, and the viscosity of the dispersion also gradually increases with the increase of PDMS content. When the PDMS content is less than 20%, the synthesized dispersion can pass the stability test. From Figure 5 It can be seen that with the increase of PDMS content, the particle size of the dispersion gradually increases.

[0047] Table 2 Effect of PDMS content on the appearance, stability, viscosity and average particle size of SiPWPU dispersion

[0048]

[0049]

[0050] Comparative Example 1

[0051] Prepolymer polyol (N210, PDMS) 56.0 grams and 29.0 grams of TDI-80 were added to a dry four-necked flask, protected by nitrogen, stirred at room temperature for 0.5 h, then heated to 80°C, reacted for 3 h, then cooled to 70°C, added 3.0 grams of TMP and 15.0 grams of 1,4-butanediol (BDO) mixed with 20 ml of acetone, reacted for 1 h, then cooled to 60°C, added 20.0 grams of PEG, reacted for 3 h, then cooled to 20°C. Added a mixture of 2.0 grams of EDA and 20 ml of acetone, reacted for 1 h, then dispersed with deionized water at high speed for 1 h, then removed the acetone in the system by reduced pressure distillation, to obtain a phosphorus / silicon synergistic flame-retardant non-ionic waterborne polyurethane dispersion with a theoretical solid content of 30%.

[0052] Performance test

[0053] The effect of PDMS on the mechanical properties of waterborne polyurethane adhesive film is shown in Table 3. From Table 3, in Example 1, with the increase of PDMS addition amount, the tensile strength and elongation at break of SiPWPU both show a gradually decreasing trend. However, compared with the BDO system of Comparative Example 1, the PHAD system of Example 1 shows significant advantages in mechanical properties.

[0054] When the PDMS addition amount reaches 25% or more, the dispersion is unstable, and a large number of cracks appear on the film surface, and the film cannot be formed. This is because the PDMS used is a siloxane polymer, which has low polarity and very weak intermolecular interaction, and is incompatible with the hard segment of WPU, reducing the crystallinity of the polyurethane hard segment and weakening the intermolecular interaction, thereby causing phase separation. This phase separation can form microscopic silicone rubber phases in the adhesive film, thereby affecting the overall mechanical properties of the adhesive film.

[0055] Table 3 Effect of PDMS content on the mechanical properties of polyurethane adhesive film

[0056]

[0057] Table 4 and Figure 6 Table 4 and Figure 6 are the TGA and DTG curves of polyurethane adhesive films with different PDMS contents in N2 atmosphere. The results show that the addition of PDMS improves the thermal stability of the adhesive film. With the increase of the addition amount of PDMS, the initial decomposition temperature of the adhesive film also increases. When no PDMS is added, the initial decomposition temperature of the adhesive film is 282.6°C. When the PDMS content increases to 15%, the initial decomposition temperature of the adhesive film rises to 291.2°C. The residual ash rate of the WPU adhesive film without adding flame retardant is 0.76%, the residual ash rate of the WPU adhesive film with the addition of phosphorus-containing flame retardant PHAD is 6.6%, and the residual ash rate of the SiPWPU adhesive film with the addition of phosphorus-containing flame retardant PHAD and PDMS rises to 7.4%. This is because PDMS itself has excellent thermal stability and is not easy to decompose at high temperatures. In summary, the introduction of PDMS into WPU can improve the thermal stability of the polymer and improve the heat resistance of the adhesive film.

[0058] Table 4 Thermogravimetric data of SiPWPU adhesive films with different PDMS contents

[0059] PDMS content (%) T5％(℃) Ash content (%) 0 282.6 6.6 5 286.4 6.7 10 288.7 7.0 15 291.2 7.4

[0060] Horizontal burning test and limiting oxygen index test are commonly used to evaluate the flame retardant performance of materials. Table 5 is the results of horizontal burning test and limiting oxygen index test of SiPWPU adhesive films with different contents. From the data in Table 5, the flame retardant grade of all samples reaches HB level. In the horizontal burning test, the PWPU and SiPWPU(5%) samples continue to burn after the fire source leaves the sample. While the SiPWPU(10%) and SiPWPU(15%) samples are naturally extinguished one after another after leaving the fire source, and fail to continue to burn to the 100mm mark line. According to the standard, the burning rate of the sample is 0mm / min, and the flame retardant grade is HB level. With the increase of the content of end PDMS, the LOI value also gradually increases, and the SiPWPU(15%) sample can reach 28.2%, which belongs to difficult-to-burn materials. This is because phosphorus compounds can catalyze the dehydration and carbonization reaction in the combustion area at high temperature, form a carbon layer, and the released phosphoric acid can also capture combustion free radicals to achieve the effect of flame retardant. After adding PDMS, the inorganic silicate layer formed by silicon compounds at high temperature has high thermal stability and chemical stability, and the carbon layer formed by the phosphorus-silicon synergistic system during combustion is more dense and stable than when using phosphorus or silicon flame retardants alone. This carbon layer can effectively isolate heat and oxygen.

[0061] Table 5 results of horizontal burning test and LOI value

[0062]

[0063] The combustion residues of WPU (laboratory self-made) without flame retardant modification, and phosphorus flame retardant modified PWPU and phosphorus / silicon synergistic flame retardant modified SiPWPU(15%) adhesive films were tested by SEM morphology analysis, and the results are shown in Figure 7 The WPU without flame retardant modification shows loose and thin blocky carbon residues with many pores. The phosphorus flame retardant modified PWPU shows a more continuous and dense lamellar accumulation structure with cracks, indicating that the combustion process is inhibited. SiPWPU(15%) shows a more dense carbon residue layer, which is due to the combination of phosphorus and silicon, forming an effective physical barrier and enhancing the flame retardancy of the material.

[0064] In addition, it should be understood that after reading the above description of the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope defined by the claims attached to the present application.

Claims

1. Process for the preparation of phosphorus / silicon synergistic flame-retardant non-ionic aqueous polyurethanes, characterized in that, At least comprising: (1) stirring 56.0 grams of prepolymer polyol and 29.0 grams of TDI-80 at room temperature for 0.5 hours under nitrogen protection, then heating to 80°C and reacting for 3 hours; the prepolymer polyol is composed of N210 and PDMS, and the PDMS is within 11.2g; (2) cooling to 70°C, adding 3.0 grams of TMP and a mixture of 15.0 grams of PHAD and 20ml of acetone, and reacting for 1 hour; wherein the molecular formula of the PHAD is: ； (3) cooling to 60°C, adding 20.0 grams of PEG2000, and reacting for 3 hours; (4) cooling to 20°C, adding a mixed solution of 2.0 grams of EDA and 20ml of acetone dropwise, and reacting for 1 hour; (5) after dispersing in deionized water for 1 hour, removing acetone in the system by reduced pressure distillation to obtain a phosphorus / silicon synergistic flame-retardant non-ionic water-based polyurethane dispersion.

2. The production method according to claim 1, characterized by, The preparation method of PHAD in step (2) comprises: synthesizing 4-((4-hydroxybenzylidene)amino)phenol PHA containing a C=N double bond from p-hydroxybenzaldehyde and p-aminophenol; further synthesizing DOPO-based aromatic Schiff base derivative PHAD from 4-((4-hydroxybenzylidene)amino)phenol PHA and DOPO.

3. The production method according to claim 2, characterized by, The synthesis method of 4-((4-hydroxybenzylidene)amino)phenol PHA is as follows: mixing p-aminophenol, p-hydroxybenzaldehyde, acetic acid, 4A molecular sieve and anhydrous ethanol uniformly, wherein the molar ratio of p-aminophenol to p-hydroxybenzaldehyde is 1:1; heating to 70°C and keeping at this temperature for 8 hours, then pouring the reaction into ice water, solid precipitates, vacuum filtration and washing to obtain a solid; drying in a vacuum oven at 100°C to constant weight to obtain orange yellow powder PHA.

4. The production method according to claim 3, characterized by, The p-aminophenol is 18 g, the p-hydroxybenzaldehyde is 18.32 g, the acetic acid is 0.45 g, the 4A molecular sieve is 8 g, and the anhydrous ethanol is 360 mL.

5. The preparation method according to claim 2, characterized in that The synthesis method of DOPO-based aromatic Schiff base derivative PHAD is as follows: mixing 17.30 g of DOPO, 17.04 g of PHA and 300 mL of anhydrous ethanol uniformly; ice water bath reaction, keeping the reaction temperature at 3-5°C, reacting at this temperature for 6 hours, then pouring the reaction into ice water prepared in advance, solid precipitates, vacuum filtration, washing with water twice to obtain a solid; drying in a vacuum oven at 100°C to constant weight to obtain light yellow powder PHAD.

6. The method of claim 1, wherein, The PDMS accounts for 15% of the total mass of the prepolymer polyol.

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