Polyurethane foam with low density, high flame retardance and strong mechanical property and preparation method thereof

Abstract

The invention belongs to the technical field of polyurethane foam, and particularly relates to polyurethane foam with low density, high flame retardance and strong mechanical property and a preparation method of the polyurethane foam. According to the polyurethane foam with low density, high flame retardance and strong mechanical property provided by the invention, only the chitosan grafted ammonium polyphosphate is adopted as the bio-based flame retardant, and the grafting rate of the chitosan is regulated and controlled, so that the flame retardance of the polyurethane foam can be remarkably improved under the conditions of reducing the dosage of the flame retardant and ensuring the low density of the polyurethane foam. Meanwhile, the bio-based flame retardant can also cooperate with components such as isocyanate, so that the binding force between the flame retardant and a polyurethane matrix is improved, the polarity difference between ammonium polyphosphate and the polyurethane matrix is relieved, precipitation, agglomeration and the like of the flame retardant are avoided, and the mechanical property of the polyurethane foam is improved; the polyurethane foam with low density, high flame retardant property and strong mechanical property can be prepared.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyurethane foam, more specifically, relates to a low-density high-flame-retardant high-performance polyurethane foam and a preparation method thereof. BACKGROUND

[0002] Polyurethane foam is widely used in furniture, new energy battery packaging, automotive interior and other fields due to its light weight and high resilience, but polyurethane itself is a flammable material, which not only drips during combustion, but also produces a large amount of harmful gas, which causes great harm to the human body and the environment during combustion. In order to meet the demand for flame retardant performance of materials in the above fields, a large amount of flame retardant is usually added to the formula to improve the flame retardant performance of polyurethane foam, slow down the burning speed and reduce the harmful gas produced during combustion.

[0003] Traditional flame retardants are usually divided into inorganic flame retardants and organic flame retardants, among which inorganic flame retardants mainly include magnesium hydroxide, aluminum hydroxide, basic magnesium carbonate, expanded graphite, etc. Due to the poor flame-retardant effect of such flame retardants, a large amount of addition is required to achieve the expected flame-retardant performance, but excessive addition will significantly increase the density of polyurethane foam and destroy the cell structure, resulting in a decrease in mechanical properties. Organic flame retardants are mainly divided into halogen-containing organic flame retardants and halogen-free organic flame retardants. Halogen-containing organic flame retardants are usually used in combination with antimony trioxide, but a large amount of toxic gas is released during combustion, which is harmful to the environment. Halogen-free organic flame retardants mainly include ammonium polyphosphate, melamine phosphate, and melamine polyphosphate nitrogen-phosphorus flame retardants, which are usually compounded with expandable graphite to form a carbon-nitrogen-phosphorus ternary flame-retardant system. However, a high amount of addition is still required to achieve good flame-retardant effect, which significantly affects the density and mechanical properties of polyurethane foam.

[0004] In recent years, bio-based flame retardants have gradually become the choice of carbon source to replace expandable graphite in the flame retardant system due to their environmental protection and renewable characteristics. Among them, chitosan (CS) based flame retardants can provide carbon and nitrogen sources in the flame retardant system due to their unique chemical structure and properties, and are often used in combination with nitrogen-phosphorus flame retardants to better play the flame-retardant effect. However, the compatibility of chitosan-based flame retardants with nitrogen-phosphorus flame retardants is poor, which leads to easy agglomeration during blending and seriously affects the structural uniformity of polyurethane foam. In addition, a large amount of such flame retardants is often required to achieve good flame-retardant performance, and a large amount of powder will significantly increase the density and brittleness of polyurethane foam, affecting its lightness and limiting its application scenarios. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a low-density high-flame-retardant strong mechanical property polyurethane foam and a preparation method thereof, aiming to solve the problems that the amount of flame retardant in the existing flame-retardant polyurethane foam is too large, the foam density is large, the brittleness is high, the flame-retardant effect needs to be improved, and it is difficult to balance low density, high flame-retardant performance and strong mechanical performance while reducing the amount of flame retardant.

[0006] To achieve the above-mentioned purpose, in a first aspect, the present application provides a low-density high-flame-retardant strong mechanical property polyurethane foam, which is obtained by foaming a mixture of polyether polyol, foam stabilizer, foaming agent, chain extender, catalyst, bio-based flame retardant and isocyanate. The above-mentioned bio-based flame retardant is chitosan grafted ammonium polyphosphate, wherein the grafting rate of chitosan is 20% or more.

[0007] Preferably, the grafting rate of chitosan in the above-mentioned chitosan grafted ammonium polyphosphate is 20% to 60%.

[0008] Preferably, the addition amount of the above-mentioned chitosan grafted ammonium polyphosphate is 3wt% to 10wt% of the total mass of all raw materials of the above-mentioned polyurethane foam.

[0009] Preferably, the preparation method of the above-mentioned chitosan grafted ammonium polyphosphate comprises the following steps: Mixing chitosan and ammonium polyphosphate in a solvent, heating and grafting under the action of a crosslinking agent to graft the above-mentioned ammonium polyphosphate onto the above-mentioned chitosan, and then centrifuging, washing and drying to obtain the above-mentioned chitosan grafted ammonium polyphosphate.

[0010] Preferably, the above-mentioned solvent is selected from one or more of water, acetic acid, N,N-dimethylformamide, 1-methyl-2-pyrrolidone and dimethyl sulfoxide.

[0011] Preferably, the above-mentioned crosslinking agent is selected from one or more of glutaraldehyde, glyoxal, epichlorohydrin, ethylene glycol diglycidyl ether and epichlorohydrin.

[0012] Preferably, the temperature of the above-mentioned grafting reaction is 60°C to 80°C, and the time of the grafting reaction is 4h to 6h.

[0013] Preferably, the mass ratio of the above-mentioned ammonium polyphosphate to the above-mentioned chitosan is (2-6):1.

[0014] Preferably, the amount of the above-mentioned crosslinking agent is 1wt% to 5wt% of the mass of the above-mentioned ammonium polyphosphate.

[0015] Preferably, the above-mentioned polyether polyol is selected from one or more of polyether polyols with a hydroxyl value of 25mg KOH / g to 60mg KOH / g.

[0016] Preferably, the above-mentioned foam stabilizer is selected from one or more of bis-hydroxypropyl silicone oil, Y-10366 and gelatin.

[0017] Preferably, the above-mentioned foaming agent is water.

[0018] Preferably, the above-mentioned chain extender is selected from one or more of ethylene glycol, 1,3-propanediol and 1,4-butanediol.

[0019] Preferably, the above-mentioned catalyst is selected from one or more of amine catalysts and / or organometallic catalysts.

[0020] Preferably, the above-mentioned isocyanate is selected from one or more of isocyanates with an isocyanate content of 28% to 40%.

[0021] Further preferably, the above-mentioned isocyanate is selected from one or more of phenylene diisocyanate, diphenylmethane diisocyanate and hexamethylene diisocyanate.

[0022] Preferably, in the above-mentioned polyurethane foam, the mass ratio of polyether polyol, foam stabilizer, foaming agent, chain extender, catalyst, bio-based flame retardant and isocyanate is 100:(0.5 to 2.5):(2 to 3):(1 to 2.5):(0.2 to 0.4):(5 to 15):(35 to 50).

[0023] In a second aspect, the present application provides a preparation method of the above-mentioned polyurethane foam, comprising the following steps: After the above-mentioned polyether polyol, foam stabilizer, foaming agent, chain extender, catalyst and bio-based flame retardant are uniformly mixed according to the ratio, the isocyanate is added and uniformly mixed, and the uniformly mixed material is applied to the surface of the substrate for foaming to obtain the above-mentioned polyurethane foam.

[0024] Preferably, the foaming temperature is 80°C to 100°C, and the foaming time is 10 min to 20 min.

[0025] In a third aspect, the present application provides a lightweight flame-retardant material comprising the above-mentioned polyurethane foam.

[0026] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages: (1) The low-density high-flame-retardant strong mechanical property polyurethane foam provided by the present application only uses chitosan grafted ammonium polyphosphate as a new bio-based flame retardant, and controls the grafting rate of chitosan, which can realize molecular-level cooperation of phosphorus-nitrogen-carbon elements and form a stronger synergistic flame-retardant effect. Compared with the prior art, the present application can significantly improve the flame-retardant performance of the polyurethane foam while reducing the amount of flame retardant and ensuring the low density of the polyurethane foam.

[0027] (2) The bio-based flame retardant chitosan grafted ammonium polyphosphate in the polyurethane foam provided by the application can cooperate with isocyanate and other components to improve the bonding force between the bio-based flame retardant and the polyurethane matrix, avoid precipitation of the bio-based flame retardant, and improve the mechanical properties of the polyurethane foam. In addition, the bio-based flame retardant and the polyurethane matrix have good compatibility, can alleviate the polarity difference between ammonium polyphosphate and the polyurethane matrix, reduce the influence of the flame retardant on the foaming process of the foam, avoid agglomeration of the flame retardant, improve the uniformity of the polyurethane foam, and comprehensively make the polyurethane foam have stable flame retardant properties and mechanical properties, and be suitable for use as a lightweight flame retardant material.

[0028] (3) The bio-based flame retardant chitosan grafted ammonium polyphosphate used in the application has good biocompatibility and biodegradability, and the preparation and use process of the bio-based flame retardant has less harm to the human body and the environment, and is suitable for medical, furniture and other fields. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the application and not to limit the application.

[0030] In the description of the application, it should be understood that the term "and / or" is a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In this paper, the symbol " / " represents the relationship of or, for example, A / B represents A or B.

[0031] In the description of the embodiments of the application, the words "exemplary" or "for example" are used to mean serving as an example, instance, or illustration. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of the application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the use of "exemplary" or "for example" is intended to present the relevant concept in a specific manner.

[0032] In the description of the embodiments of the application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0033] Unless otherwise indicated, all numerical values ​​expressing the amount of components, reaction conditions, etc. used in the specification and claims are understood to be modified by the term "about". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximate values ​​that can vary according to the desired performance required. Numerical ranges represented by endpoints include all numbers within the range and any range within the range, for example, 3wt% to 10wt% include 3wt%, 3.4wt%, 5.2wt%, 6.3wt%, 7.3wt%, 8.9wt%, 9wt% and 10wt%, etc.

[0034] The term "grafting rate" refers to the ratio of the mass of the branched polymer grafted onto the main polymer to the mass of the main polymer, usually expressed as a percentage, and is used to evaluate the efficiency of the grafting reaction. In this application, the "grafting rate of chitosan" in chitosan-grafted ammonium polyphosphate refers to the ratio of the mass of ammonium polyphosphate grafted onto the chitosan backbone to the initial mass of chitosan, reflecting the efficiency of the successful grafting of ammonium polyphosphate onto chitosan. The specific calculation formula is as follows: Grafting rate of chitosan (%) = ((mtotal mass of the product obtained by the grafting reaction - minitial mass of chitosan) / minitial mass of chitosan) × 100%.

[0035] In order to improve the flame retardant properties of polyurethane foam, this application initially attempted to use chitosan and ammonium polyphosphate as flame retardants, which were added to the polyurethane foam after physical mixing. However, chitosan and ammonium polyphosphate are very easy to agglomerate during the mixing process, resulting in poor uniformity of the polyurethane foam, and the flame retardant effect of the foam cannot be effectively improved, and the flame retardant grade does not meet the standards. Further increasing the amount of flame retardant, although the flame retardant properties of the foam are improved to V0 level, the density of the foam increases and the brittleness is too large to be used normally. In addition, the ammonium polyphosphate flame retardant has poor compatibility with the polyurethane matrix and is prone to agglomeration, migration or precipitation, which will further affect the flame retardant properties of the foam. How to reduce the amount of flame retardant while ensuring the low density of the polyurethane foam, significantly improve the flame retardant properties and mechanical properties of the polyurethane foam, and achieve a balance between low density, high flame retardant properties and strong mechanical properties is the technical problem that this application actually aims to solve.

[0036] Based on this, the present application provides a low-density, highly flame-retardant, and strong mechanical property polyurethane foam, which is obtained by foaming a mixture of polyether polyol, foam stabilizer, foaming agent, chain extender, catalyst, bio-based flame retardant, and isocyanate; The above-mentioned bio-based flame retardant is chitosan grafted ammonium polyphosphate, wherein the grafting rate of chitosan is 20% or more.

[0037] The inventors of the present application accidentally discovered during experiments that only using chitosan grafted ammonium polyphosphate (CS-g-APP) as a novel bio-based flame retardant, by grafting ammonium polyphosphate (APP) onto chitosan (CS) chains and controlling the grafting rate of chitosan to be within a suitable range, the molecular level synergy of phosphorus-nitrogen-carbon elements can be achieved, and a stronger synergistic flame retardant effect can be formed, that is, the flame retardant performance can be significantly improved under the conditions of reducing the amount of flame retardant and ensuring the low density of polyurethane foam. Specifically, the chitosan molecular chains in chitosan grafted ammonium polyphosphate provide carbon and nitrogen sources, and can form a dense carbon layer on the surface of polyurethane foam at high temperatures to insulate heat and oxygen, and release carbon dioxide and water vapor to dilute combustible gases; the ammonium polyphosphate grafted on the chitosan chains provides phosphorus and nitrogen sources, and can decompose to generate phosphoric acid at high temperatures to promote carbon formation, greatly improve the speed and thickness of the carbon layer formed by chitosan at high temperatures, and enhance its flame retardant ability, while APP releases NH3 at high temperatures, which together with the carbon dioxide and water vapor released by CS at high temperatures, dilutes the combustible gases and inhibits the combustion chain reaction, thereby achieving high flame retardant performance through the synergistic effect between components.

[0038] In addition, the amino and hydroxyl groups on the chitosan molecular chain can react with the isocyanate groups in the isocyanate to form covalent bonds such as urethane bonds and urea bonds, thereby chemically bonding CS-g-APP to the polyurethane backbone, improving the bonding force between the flame retardant and the polyurethane matrix, avoiding the precipitation of the flame retardant, and at the same time improving the mechanical properties of the polyurethane foam. At the same time, the amino groups on the chitosan molecular chain can also form hydrogen bonds between the urethane groups in the polyurethane segments, enhancing the intermolecular forces, improving the cell wall strength of the foam, avoiding the collapse of the foam under low density, and enhancing the compressive strength of the foam. In addition, the natural high molecular segment on the chitosan has good compatibility with the polyurethane matrix, which can act as an interface bridge to alleviate the polarity difference between ammonium polyphosphate and the polyurethane matrix, reduce the interfacial energy, reduce the influence of flame retardant filler on the foaming process, avoid the agglomeration of flame retardant, improve the uniformity of polyurethane foam, and ensure that the polyurethane foam has stable flame retardant performance and mechanical properties.

[0039] The inventors found during experiments that when the grafting rate of chitosan is too low, the flame retardant performance and mechanical properties of the polyurethane foam cannot be effectively improved; when the grafting rate of chitosan in the above chitosan grafted ammonium polyphosphate is 20% to 60%, the flame retardant performance and mechanical properties of the polyurethane foam can be effectively improved; when the grafting rate of chitosan continues to increase, the flame retardant performance and mechanical properties of the polyurethane foam decrease instead, which may be because the chitosan molecules self-crosslink, causing the bio-based flame retardant to agglomerate in the polyurethane matrix, thereby affecting the flame retardant performance and mechanical properties of the polyurethane foam.

[0040] In some embodiments, the amount of the chitosan grafted ammonium polyphosphate added is 3wt% to 10wt% of the total mass of all raw materials of the polyurethane foam. Compared with the prior art, the application can significantly improve the flame retardant performance and mechanical properties of the polyurethane foam while reducing the amount of the flame retardant, and ensure the low density of the polyurethane foam, achieving a balance of low density, high flame retardant performance and strong mechanical properties.

[0041] In some embodiments, the preparation method of the chitosan grafted ammonium polyphosphate comprises the following steps: Chitosan (CS) and ammonium polyphosphate (APP) are mixed in a solvent, and a grafting reaction is carried out under the action of a crosslinking agent by heating, so that the ammonium polyphosphate is grafted onto the chitosan, and then centrifugation, washing and drying are performed to obtain the chitosan grafted ammonium polyphosphate (abbreviated as CS-g-APP).

[0042] The solvent in the application can dissolve chitosan and ammonium polyphosphate and uniformly disperse in the reaction system, and the type of the solvent is not limited, and any solvent capable of dissolving chitosan and ammonium polyphosphate disclosed in the prior art can be used in the application. In some embodiments, the solvent is selected from one or more of water, acetic acid, N,N-dimethylformamide (DMF), 1-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO). The amount of the solvent is not particularly limited in the application, as long as the grafting reaction can proceed, which is within the scope of the application.

[0043] In some embodiments, the mass ratio of the ammonium polyphosphate to the chitosan is (2 to 6):1, which can ensure that the grafting reaction proceeds sufficiently and improve the grafting rate of the chitosan.

[0044] In some embodiments, the crosslinking agent is selected from one or more of glutaraldehyde (GA), glyoxal, epichlorohydrin (ECH), ethylene glycol diglycidyl ether (EGDE), and epichlorohydrin. In some embodiments, the amount of the crosslinking agent is 1wt% to 5wt% of the mass of the ammonium polyphosphate.

[0045] In some embodiments, the temperature of the grafting reaction is 60°C to 80°C, and the time of the grafting reaction is 4h to 6h.

[0046] In some embodiments, the polyether polyol is selected from one or more of polyether polyols with a hydroxyl value of 25mg KOH / g to 60mg KOH / g. When the hydroxyl value of the polyether polyol is too high, the polyurethane foam prepared from the chitosan grafted ammonium polyphosphate, the polyether polyol and other raw materials has greater brittleness, poor flexibility and is prone to breakage, which cannot be used normally.

[0047] In some embodiments, the foam stabilizer is selected from one or more of bis-hydroxypropyl dimethicone, Y-10366, and gelatin.

[0048] In some embodiments, the foaming agent is water.

[0049] In some embodiments, the chain extender is selected from one or more of ethylene glycol, 1,3-propanediol, and 1,4-butanediol.

[0050] In some embodiments, the catalyst is selected from one or more of an amine catalyst and / or an organometallic catalyst. The amine catalyst includes, but is not limited to, one or more of triethylenediamine, triethylamine, triethylenediamine, pentamethyldipropylenetriamine, dimethylethanolamine, triethanolamine, and N,N-dimethylcyclohexylamine. The organometallic catalyst includes an organozinc compound, an organotin compound, and an organobismuth compound, wherein the organotin compound includes, but is not limited to, one or more of stannous octoate, dibutyltin dilaurate, dibutyltin bis(laurylthio)borate, and dibutyltin diacetate.

[0051] In some embodiments, the isocyanate is selected from one or more of isocyanates with an isocyanate content of 28% to 40%, which can be compounded with other components to prepare the polyurethane foam. The type of the isocyanate is not particularly limited in the present application. In some embodiments, the isocyanate includes, but is not limited to, one or more of phenylene diisocyanate, diphenylmethane diisocyanate, and hexamethylene diisocyanate.

[0052] In some embodiments, the mass ratio of the polyether polyol, the foam stabilizer, the foaming agent, the chain extender, the catalyst, the bio-based flame retardant, and the isocyanate in the polyurethane foam provided by the present application is 100:(0.5-2.5):(2-3):(1-2.5):(0.2-0.4):(5-15):(35-50).

[0053] In another aspect, the present application also provides a method for preparing the polyurethane foam described above, which comprises the following steps: After the polyether polyol, the foam stabilizer, the foaming agent, the chain extender, the catalyst, and the bio-based flame retardant are uniformly mixed according to the ratio, the isocyanate is added and uniformly mixed, and the uniformly mixed material is applied to the surface of the substrate for foaming to obtain the polyurethane foam described above.

[0054] In some embodiments, the foaming temperature is 80°C to 100°C, and the foaming time is 10 minutes to 20 minutes.

[0055] The density of the polyurethane foam provided by the present application is 40 Kg / m 3 to 60 Kg / m 3, the compressive strength is 13 KPa~26 KPa, and the elongation at break is 110%~135%; the UL94 vertical burning test of the polyurethane foam is performed, the flame-retardant performance reaches V0 level, and the polyurethane foam is suitable for use as a lightweight flame-retardant material. Based on this, the application further provides a lightweight flame-retardant material, which comprises the polyurethane foam.

[0056] It should be understood that materials identical or similar to the types, models, qualities, properties or functions of the reagents and instruments used in the following examples can be used to implement the present application. The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents and the like used in the following examples can be obtained from commercial channels unless otherwise specified.

[0057] The following are examples and comparative examples: Example 1 The preparation method of the low-density high-flame-retardant high-mechanical-property polyurethane foam provided in this embodiment comprises the following steps: According to weight parts, 5 parts of a bio-based flame retardant (chitosan grafted ammonium polyphosphate powder, the grafting rate of chitosan is 23%), 100 parts of polyether polyol (Shandong Lanshengdong POP36 / 28, the hydroxyl value is 25~29 mg KOH / g), 0.5 parts of a foam stabilizer (double-end hydroxypropyl silicone oil), 2 parts of a foaming agent (water), 1 part of a chain extender (1,4-butanediol), and 0.2 parts of an amine catalyst (triethylenediamine) are uniformly mixed, then 37 parts of diphenylmethane diisocyanate is added and uniformly stirred, and the mixture is coated on a PET film, foamed at 80°C for 20 min, to obtain a low-density high-flame-retardant high-mechanical-property polyurethane foam.

[0058] The preparation method of the chitosan grafted ammonium polyphosphate powder (abbreviated as CS-g-APP powder) is as follows: a. According to weight parts, 1 part of chitosan is dissolved in 100 parts of acetic acid solution, stirred until transparent, to obtain a chitosan acetic acid solution; b. 2 parts of ammonium polyphosphate and 0.02 parts of glutaraldehyde are added to the chitosan acetic acid solution, reacted at 60°C for 6 h, to obtain a preliminary product; c. After centrifugation, the preliminary product is washed with acetic acid solution to remove unreacted raw materials, then washed with ethanol to remove the acetic acid solution, and dried to obtain the CS-g-APP powder.

[0059] The grafting rate of chitosan in the CS-g-APP powder is calculated according to the following formula: CS grafting rate (%) = ((W2-W1) / W1)×100%, wherein W1 is the mass of the reaction raw material chitosan, and W2 is the mass of the CS-g-APP powder.

[0060] Example 2 The preparation method of the low-density high-flame-retardant high-mechanical-property polyurethane foam provided by the embodiment comprises the following steps: According to the weight parts, 8 parts of bio-based flame retardant (CS-g-APP powder, the grafting rate of chitosan is 29%), 100 parts of polyether polyol (Dow Chemical Company VORANOL4000LM, the hydroxyl value is 28 mg KOH / g), 1 part of foam stabilizer (double-end hydroxypropyl silicone oil), 2.3 parts of foaming agent (water), 1.8 parts of chain extender (1,4-butanediol), and 0.25 parts of amine catalyst (triethylenediamine) are uniformly mixed, then 40 parts of diphenyl methane diisocyanate is added and uniformly stirred, the mixture is coated on a PET film, foamed at 85℃ for 18 min, and a low-density high-flame-retardant high-mechanical-property polyurethane foam is obtained.

[0061] The preparation method of the CS-g-APP powder is as follows: a. According to the weight parts, 2 parts of chitosan are dissolved in 100 parts of acetic acid solution, and stirred until transparent to obtain a chitosan acetic acid solution; b. 6 parts of ammonium polyphosphate and 0.12 parts of glutaraldehyde are added to the chitosan acetic acid solution, and reacted at 65℃ for 5.5 h to obtain a preliminary product; c. The preliminary product is centrifuged, washed with acetic acid solution to remove unreacted raw materials, then washed with ethanol to remove the acetic acid solution, and dried to obtain the CS-g-APP powder.

[0062] Example 3 The preparation method of the low-density high-flame-retardant high-mechanical-property polyurethane foam provided by the embodiment comprises the following steps: According to the weight parts, 10 parts of bio-based flame retardant (CS-g-APP powder, the grafting rate of chitosan is 37%), 100 parts of polyether polyol (Shandong Lanshengdongda EP-3600, the hydroxyl value is 26-30 mg KOH / g), 1.5 parts of foam stabilizer (double-end hydroxypropyl silicone oil), 2.5 parts of foaming agent (water), 2 parts of chain extender (1,4-butanediol), and 0.3 parts of amine catalyst (triethylenediamine) are uniformly mixed, then 42 parts of diphenyl methane diisocyanate is added and uniformly stirred, the mixture is coated on a PET film, foamed at 90℃ for 15 min, and a low-density high-flame-retardant high-mechanical-property polyurethane foam is obtained.

[0063] The preparation method of the CS-g-APP powder is as follows: a. According to the weight parts, 3 parts of chitosan are dissolved in 100 parts of acetic acid solution, and stirred until transparent to obtain a chitosan acetic acid solution; b. 12 parts of ammonium polyphosphate and 0.36 parts of glutaraldehyde were added to the above chitosan acetic acid solution, and reacted at 70°C for 5h to obtain a preliminary product; c. After centrifugation of the preliminary product, acetic acid solution was used for washing to remove unreacted raw materials, and then ethanol was used for washing to remove the acetic acid solution, and after drying, a CS-g-APP powder was obtained.

[0064] Example 4 The preparation method of the low-density high-flame-retardant high-mechanical-property polyurethane foam provided in this example includes the following steps: According to weight parts, 12 parts of bio-based flame retardant (CS-g-APP powder, grafting rate of chitosan is 49%), 100 parts of polyether polyol (Shandong Lansen East Star EP-330N, hydroxyl value is 32-36 mg KOH / g), 2 parts of foam stabilizer (double-end hydroxypropyl silicone oil), 2.7 parts of foaming agent (water), 2.3 parts of chain extender (1,4-butanediol), and 0.35 parts of amine catalyst (triethylenediamine) were uniformly mixed, then 44 parts of diphenylmethane diisocyanate was added and stirred uniformly, the mixture was coated on a PET film, and foamed at 95°C for 12 min to obtain a low-density high-flame-retardant high-mechanical-property polyurethane foam.

[0065] The preparation method of the CS-g-APP powder is as follows: a. According to weight parts, 4 parts of chitosan were dissolved in 100 parts of acetic acid solution, and stirred until transparent to obtain a chitosan acetic acid solution; b. 20 parts of ammonium polyphosphate and 0.8 parts of glutaraldehyde were added to the above chitosan acetic acid solution, and reacted at 75°C for 4.5h to obtain a preliminary product; c. After centrifugation of the preliminary product, acetic acid solution was used for washing to remove unreacted raw materials, and then ethanol was used for washing to remove the acetic acid solution, and after drying, a CS-g-APP powder was obtained.

[0066] Example 5 The preparation method of the low-density high-flame-retardant high-mechanical-property polyurethane foam provided in this example includes the following steps: According to weight parts, 15 parts of bio-based flame retardant (CS-g-APP powder, grafting rate of chitosan is 55%), 100 parts of polyether polyol (Shandong Lansen East Star DL-2000D, hydroxyl value is 54-58 mg KOH / g), 2.5 parts of foam stabilizer (double-end hydroxypropyl silicone oil), 3 parts of foaming agent (water), 2.5 parts of chain extender (1,4-butanediol), and 0.4 parts of amine catalyst (triethylenediamine) were uniformly mixed, then 46 parts of diphenylmethane diisocyanate was added and stirred uniformly, the mixture was coated on a PET film, and foamed at 100°C for 10 min to obtain a low-density high-flame-retardant high-mechanical-property polyurethane foam.

[0067] The preparation method of the CS-g-APP powder is as follows: a. 5 parts of chitosan were dissolved in 100 parts of acetic acid solution by weight fraction, and stirred until transparent to obtain a chitosan acetic acid solution; b. 30 parts of ammonium polyphosphate and 1.5 parts of glutaraldehyde were added to the chitosan acetic acid solution, and reacted at 80°C for 4h to obtain a preliminary product; c. The preliminary product was centrifuged and washed with acetic acid solution to remove unreacted raw materials, and then washed with ethanol to remove the acetic acid solution, and dried to obtain the CS-g-APP powder.

[0068] Comparative Example 1 The preparation method of the polyurethane foam provided by the present comparative example comprises the following steps: According to weight fraction, 100 parts of polyether polyol (Shandong Lansheng Dongda DL-2000D, hydroxyl value of 54-58 mg KOH / g), 2.5 parts of foam stabilizer (double-end hydroxypropyl silicone oil), 3 parts of foaming agent (water), 2.5 parts of chain extender (1,4-butanediol) and 0.4 parts of amine catalyst (triethylenediamine) were mixed uniformly, then 38 parts of diphenyl methane diisocyanate was added and stirred uniformly, the mixture was coated on a PET film, foamed at 100°C for 10 min to obtain a polyurethane foam.

[0069] Comparative Example 2 The preparation method of the polyurethane foam provided by the present comparative example comprises the following steps: According to weight fraction, 15 parts of chitosan, 100 parts of polyether polyol (Shandong Lansheng Dongda DL-2000D, hydroxyl value of 54-58 mg KOH / g), 2.5 parts of foam stabilizer (double-end hydroxypropyl silicone oil), 3 parts of foaming agent (water), 2.5 parts of chain extender (1,4-butanediol) and 0.4 parts of amine catalyst (triethylenediamine) were mixed uniformly, then 46 parts of diphenyl methane diisocyanate was added and stirred uniformly, the mixture was coated on a PET film, foamed at 100°C for 10 min to obtain a polyurethane foam.

[0070] Comparative Example 3 The preparation method of the polyurethane foam provided by the present comparative example comprises the following steps: According to the weight fraction, 15 parts of ammonium polyphosphate, 100 parts of polyether polyol (Shandong Lansheng Dongda DL-2000D, hydroxyl value of 54-58 mg KOH / g), 2.5 parts of foam stabilizer (double-end hydroxypropyl silicone oil), 3 parts of foaming agent (water), 2.5 parts of chain extender (1,4-butanediol) and 0.4 parts of amine catalyst (triethylenediamine) are uniformly mixed, then 46 parts of diphenyl methane diisocyanate is added and stirred uniformly, the mixture is coated on the PET film, foamed at 100℃ for 10 min, and the polyurethane foam is obtained.

[0071] Comparative Example 4 The preparation method of the polyurethane foam provided by the present comparative example comprises the following steps: According to the weight fraction, 15 parts of ammonium polyphosphate, 100 parts of polyether polyol (Shandong Lansheng Dongda DL-2000D, hydroxyl value of 54-58 mg KOH / g), 2.5 parts of foam stabilizer (double-end hydroxypropyl silicone oil), 3 parts of foaming agent (water), 2.5 parts of chain extender (1,4-butanediol) and 0.4 parts of amine catalyst (triethylenediamine) are uniformly mixed, then 46 parts of diphenyl methane diisocyanate is added and stirred uniformly, the mixture is coated on the PET film, foamed at 100℃ for 10 min, and the polyurethane foam is obtained.

[0072] Comparative Example 5 The preparation method of the polyurethane foam provided by the present comparative example comprises the following steps: According to the weight fraction, 15 parts of bio-based flame retardant (CS-g-APP powder, grafting rate of chitosan is 49%, same as Example 5), 100 parts of polyether polyol (Shandong Lansheng Dongda DL-1000D, hydroxyl value of 109-115 mg KOH / g), 2.5 parts of foam stabilizer (double-end hydroxypropyl silicone oil), 3 parts of foaming agent (water), 2.5 parts of chain extender (1,4-butanediol) and 0.4 parts of amine catalyst (triethylenediamine) are uniformly mixed, then 62 parts of diphenyl methane diisocyanate is added and stirred uniformly, the mixture is coated on the PET film, foamed at 100℃ for 10 min, and the polyurethane foam is obtained.

[0073] Comparative Example 6 The preparation method of the polyurethane foam provided by the present comparative example comprises the following steps: According to the weight fraction, 15 parts of bio-based flame retardant (CS-g-APP powder, grafting rate of chitosan is 11%), 100 parts of polyether polyol (Shandong Lanshengdongda DL-2000D, hydroxyl value is 54-58 mg KOH / g), 2.5 parts of foam stabilizer (double-end hydroxypropyl silicone oil), 3 parts of foaming agent (water), 2.5 parts of chain extender (1,4-butanediol) and 0.4 parts of amine catalyst (triethylenediamine) are uniformly mixed, then 46 parts of diphenyl methane diisocyanate is added and stirred uniformly, the mixture is coated on the PET film, foamed at 100℃ for 10 min, and polyurethane foam is obtained.

[0074] The preparation method of the CS-g-APP powder is as follows: a. According to the weight fraction, 5 parts of chitosan is dissolved in 100 parts of acetic acid solution, and stirred until transparent to obtain a chitosan acetic acid solution; b. 30 parts of ammonium polyphosphate and 1.5 parts of glutaraldehyde are added to the chitosan acetic acid solution, and reacted at 60℃ for 2h to obtain a preliminary product; c. The preliminary product is centrifuged, washed with acetic acid solution to remove unreacted raw materials, then washed with ethanol to remove the acetic acid solution, and dried to obtain the CS-g-APP powder.

[0075] Comparative Example 7 The preparation method of the polyurethane foam provided in this comparative example includes the following steps: According to the weight fraction, 5 parts of bio-based flame retardant (CS-g-APP powder, grafting rate of chitosan is 68%), 100 parts of polyether polyol (Shandong Lanshengdongda POP36 / 28, hydroxyl value is 25-29 mg KOH / g), 0.5 parts of foam stabilizer (double-end hydroxypropyl silicone oil), 2 parts of foaming agent (water), 1 part of chain extender (1,4-butanediol) and 0.2 parts of amine catalyst (triethylenediamine) are uniformly mixed, then 37 parts of diphenyl methane diisocyanate is added and stirred uniformly, the mixture is coated on the PET film, foamed at 80℃ for 20 min, and polyurethane foam is obtained.

[0076] The preparation method of the CS-g-APP powder is as follows: a. According to the weight fraction, 5 parts of chitosan is dissolved in 100 parts of acetic acid solution, and stirred until transparent to obtain a chitosan acetic acid solution; b. 30 parts of ammonium polyphosphate and 1.5 parts of glutaraldehyde are added to the chitosan acetic acid solution, and reacted at 80℃ for 6h to obtain a preliminary product; c. The preliminary product is centrifuged, washed with acetic acid solution to remove unreacted raw materials, then washed with ethanol to remove the acetic acid solution, and dried to obtain the CS-g-APP powder.

[0077] The density, compressive strength, elongation at break and flame retardant performance of the polyurethane foam prepared in Examples 1-5 and Comparative Examples 1-7 were tested, and the test methods are as follows, and the test results are shown in Table 1.

[0078] (1) Density: reference ASTM3574-2017 Test A, measured by using a balance and a thickness gauge.

[0079] (2) Compressive strength: reference ASTM3574-2017 Test C, measured by using a universal testing machine, compression rate 5 mm / min, and recording the stress of the polyurethane foam at 40% compression strain.

[0080] (3) Elongation at break: reference ASTM3574-2017 Test E, measured by using a universal testing machine, test speed 500 mm / min, and testing the elongation at break of the polyurethane foam.

[0081] (4) Flame retardant performance: reference UL94-2016, vertical flame retardant test was performed by using a combustion test box, and the flame retardant grade of the sample was determined.

[0082] Table 1 Performance of polyurethane foam prepared in examples and comparative examples

[0083] Comparative Example 1 did not add a flame retardant, Comparative Example 2 only added 15 parts of chitosan (CS) as a flame retardant, Comparative Example 3 only added 15 parts of ammonium polyphosphate (APP) as a flame retardant, and Comparative Example 4 used 15 parts of a physical mixture of chitosan and ammonium polyphosphate (CS / APP mixture) as a flame retardant. As can be seen from Table 1, the flame retardant grade of the polyurethane foam prepared in Comparative Examples 2-4 can only reach V1 level, and cannot effectively improve the flame retardant performance of the polyurethane foam. However, the flame retardant performance of the polyurethane foam prepared in Example 1 can reach V0 level by only adding 3 parts of CS-g-APP powder as a flame retardant, indicating that the flame retardant effect of CS-g-APP is better than that of CS, APP and CS / APP mixture, and even better than the simple addition of technical effects. By comparing various performance indicators, it can be seen that compared with Comparative Examples 1-4, the present application can significantly improve the flame retardant performance and mechanical properties of the polyurethane foam while reducing the amount of flame retardant, and ensure the low density of the polyurethane foam, achieving a balance of low density, high flame retardant performance and strong mechanical properties.

[0084] The elongation at break of the polyurethane foam prepared in Comparative Example 5 using a high-hydroxyl-value polyol as a raw material was low, only 51.2%, and the foam was too brittle, the foam structure was damaged during the test of the compressive strength, and the mechanical properties could not be normally tested, marked as "-".

[0085] Comparative Example 6 uses 15 parts of CS-g-APP powder with a grafting rate of 11% as a flame retardant, which cannot effectively improve the flame retardant performance and mechanical properties of the polyurethane foam. Comparative Example 7 uses 3 parts of CS-g-APP powder with a grafting rate of 68% as a flame retardant, and the polyurethane foam prepared has poorer compressive strength, lower elongation at break, and flame retardant performance only reaches V1 level, which does not meet the requirements. The reason is that when the chitosan grafting rate of the bio-based flame retardant CS-g-APP powder is too high, excessive crosslinking causes self-crosslinking of chitosan, leading to agglomeration of CS-g-APP powder in the polyurethane foam, thereby reducing the flame retardant performance and mechanical properties.

[0086] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A low-density, highly flame-retardant, and strong mechanical property polyurethane foam, characterized in that: The polyurethane foam is obtained by mixing polyether polyol, foam stabilizer, foaming agent, chain extender, catalyst, bio-based flame retardant and isocyanate and foaming; The bio-based flame retardant is chitosan grafted ammonium polyphosphate, wherein the grafting rate of chitosan is 20% or more.

2. The polyurethane foam according to claim 1, characterized in that The addition amount of the chitosan grafted ammonium polyphosphate is 3wt% to 10wt% of the total mass of all raw materials of the polyurethane foam; Preferably, the grafting rate of chitosan in the chitosan-grafted ammonium polyphosphate is 20% to 60%.

3. The polyurethane foam according to claim 1 or 2, characterized in that The preparation method of the chitosan-grafted ammonium polyphosphate comprises the following steps: Chitosan and ammonium polyphosphate are mixed in a solvent, and heated under the action of a cross-linking agent to carry out a grafting reaction so that the ammonium polyphosphate is grafted onto the chitosan. The mixture is then centrifuged, washed, and dried to obtain the chitosan-grafted ammonium polyphosphate.

4. The polyurethane foam according to claim 3, characterized in that The solvent is selected from one or more of water, acetic acid, N,N-dimethylformamide, 1-methyl-2-pyrrolidone, and dimethyl sulfoxide; and / or The cross-linking agent is selected from one or more of glutaraldehyde, glyoxal, epichlorohydrin, ethylene glycol diglycidyl ether, and epichlorohydrin; and / or, The temperature of the grafting reaction is 60° C. to 80° C., and the time of the grafting reaction is 4 h to 6 h.

5. The polyurethane foam according to claim 3 or 4, characterized in that The mass ratio of the ammonium polyphosphate to the chitosan is (2-6):1; and / or, The amount of the cross-linking agent is 1 wt% to 5 wt% of the ammonium polyphosphate.

6. The polyurethane foam according to claim 1, wherein The polyether polyol is selected from one or more polyether polyols having a hydroxyl value of 25 mgKOH / g to 60 mgKOH / g; and / or The foam stabilizer is selected from one or more of bihydroxypropyl silicone oil, Y-10366 and gelatin; and / or, The foaming agent is water; and / or, The chain extender is selected from one or more of ethylene glycol, 1,3-propylene glycol, and 1,4-butanediol; and / or, The catalyst is selected from one or more of an amine catalyst and / or an organometallic catalyst; and / or, The isocyanate is selected from one or more isocyanates having an isocyanate content of 28% to 40%; optionally, the isocyanate is selected from one or more of phenylene diisocyanate, diphenylmethane diisocyanate and hexamethylene diisocyanate.

7. The polyurethane foam according to claim 1, characterized in that The mass ratio of the polyether polyol, foam stabilizer, foaming agent, chain extender, catalyst, bio-based flame retardant and isocyanate is 100:(0.5~2.5):(2~3):(1~2.5):(0.2~0.4):(5~15):(35~50).

8. A method for preparing the polyurethane foam according to any one of claims 1 to 7, characterized in that: The steps include: The polyether polyol, foam stabilizer, blowing agent, chain extender, catalyst and bio-based flame retardant are mixed according to a proportion, and then isocyanate is added and mixed. The mixed material is applied to the surface of the substrate for foaming to obtain the polyurethane foam.

9. The preparation method according to claim 8, characterized in that The foaming temperature is 80° C. to 100° C., and the foaming time is 10 min to 20 min.

10. A lightweight flame retardant material, characterized in that: The polyurethane foam comprises the polyurethane foam according to any one of claims 1 to 7.

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