Yellowing-resistant polyurethane and preparation method thereof

Abstract

According to the yellowing-resistant polyurethane and the preparation method thereof, a three-dimensional cross-linked network structure is constructed by adopting polyol, and reaction activity and yellowing resistance are balanced by an isocyanate system; an adopted compound catalytic system has the effects of concerted catalysis and optimization of the mechanical property of the material; the chain extender used by compounding utilizes the coordination effect of orthoacid, so that the yellowing resistance of the material is improved to a certain extent; the functional filler of the modified heterostructure zinc oxide is added and cooperates with the light stabilizer to achieve the effect of improving the yellowing resistance and aging resistance of the polyurethane. In addition, a pre-polymerization-chain extension-final polymerization three-step method is used, microscopic phase separation is accurately controlled through gradient temperature rise, and compared with a traditional process, the reaction time is shortened by 50%, and the energy consumption is reduced by 40%.

Description

Technical Field

[0001] The invention relates to the technical field of polymer material synthesis, and in particular to yellowing-resistant polyurethane and a preparation method thereof. Background Art

[0002] Polyurethane, with its designable molecular structure, has become one of the most widely used polymer materials in modern industry. Alicyclic polyurethanes, among others, offer excellent wear resistance, high elasticity, good oil resistance, and chemical stability, making them particularly attractive for a wide range of applications. They combine the stiffness of aromatics with the weatherability of aliphatics, particularly exhibiting a color difference of ΔE <3 (1000h, UVA 340, 0.76W / m²) in yellowing resistance testing. They also exhibit excellent hydrolysis resistance (water absorption <0.3wt%) and mechanical strength (tensile strength >70MPa), making them crucial for applications such as outdoor composite materials, optical device packaging, and outdoor coatings.

[0003] However, in the process of modifying and / or preparing alicyclic polyurethane, the prior art still has the following technical bottlenecks:

[0004] 1) Low synthesis efficiency

[0005] Traditional processes require multiple chain extension reactions, resulting in reaction times as long as 8-12 hours. These processes also require strict water control, typically keeping the moisture content below 0.01%. For example, patent CN 119569990B discloses a flame-retardant waterborne polyurethane emulsion, its preparation method, and its application. Alkyl siloxanes are formed on the surface of MXene through in-situ condensation to form polyalkylsiloxanes. These are then capped with a silane coupling agent containing active groups (amino or epoxy groups) to enhance the reactivity of the modified MXene. Finally, the resulting modified MXene nanosheets are incorporated into the polyurethane molecular chain through copolymerization, improving the emulsion's storage stability and flame retardancy. This preparation process involves multiple chain extension reactions, resulting in a long reaction time.

[0006] 2) Limited performance

[0007] Existing indicators show that the color difference value in the yellowing resistance test must meet the following requirements: ΔE>3 (500h, UVA 340, 0.76W / m²). However, most commercially available products currently do not meet these yellowing resistance requirements, and there is also the issue of finding a balance between mechanical strength and toughness (elongation at break <300%).

[0008] 3) High cost

[0009] It needs to be further explained that in order to maximize the excellent performance and functions of alicyclic polyurethane, some researchers use special isocyanates such as hydrogenated MDI for preparation. This will result in higher raw material costs than ordinary systems, and the cost will be probably more than 40% higher.

[0010] To address the above issues, the present invention attempts to develop a cost-effective solution for the modification and synthesis of alicyclic polyurethanes through molecular structure optimization and process innovation. In view of this, we disclose a yellowing-resistant polyurethane and its preparation method. Summary of the Invention

[0011] In view of the deficiencies in the prior art, the present invention aims to provide a yellowing-resistant polyurethane and a preparation method thereof.

[0012] To achieve the above objectives, the present invention proposes the following technical solutions:

[0013] A yellowing-resistant polyurethane, comprising the following raw materials in parts by weight:

[0014] 100 parts of polyol;

[0015] 40-55 parts of two-component isocyanate;

[0016] Composite catalyst 0.05-0.18 parts;

[0017] 0.5-2.5 parts of functional filler;

[0018] 6-15 parts of chain extender;

[0019] 0.3-0.7 parts of wetting and leveling agent;

[0020] Light stabilizer 0.2-0.5 parts.

[0021] On the basis of the above solution and as a preferred solution of the above solution, the polyol is tetrafunctional polyneopentyl adipate, and the OH value of the polyol is 56-60 mgKOH / g and the molecular weight is 1800-2200.

[0022] On the basis of the above scheme and as a preferred scheme of the above scheme, the two-component isocyanate includes IPDI and HDI, and the mass ratio of the two is (3-4):(1-2).

[0023] On the basis of the above solution and as a preferred solution of the above solution, the functional filler is modified heterostructured zinc oxide.

[0024] On the basis of the above scheme and as a preferred scheme of the above scheme, the composite catalyst is composed of dibutyltin dilaurate and 1,4-diazabicyclo[2.2.2]octane, and the ratio of the two is 1:(1-4).

[0025] On the basis of the above solution and as a preferred solution of the above solution, the chain extender is a mixed chain extender of a borate-based diol chain extender and an amine chain extender.

[0026] On the basis of the above scheme and as a preferred scheme of the above scheme, the wetting and leveling agent is one or more of BYK-161, BYK-333, EFKA-4061, and FS-161; the light stabilizer is one or more of Chimassorb 81, Tinuvin 770, and Tinuvin 622.

[0027] On the basis of the above scheme and as a preferred scheme of the above scheme, the preparation method of the yellowing-resistant polyurethane comprises the following steps:

[0028] S1. Raw material pretreatment

[0029] Dehydrate the polyol under vacuum at 100-120°C for 2-3 hours until the moisture content is ≤0.05%; at the same time, dry the functional filler under forced air at 120°C for 2 hours for later use;

[0030] S2. Prepolymer Synthesis

[0031] Under dry nitrogen protection, add the dehydrated polyol to the reactor and cool to 50-60°C; slowly add two-component isocyanate at a NCO:OH molar ratio of (1.5-2.0):1, add a composite catalyst, raise the temperature to 60-65°C, and react for 2-3 hours to obtain an isocyanate-terminated prepolymer;

[0032] S3, chain extension reaction

[0033] Mix the chain extender and the wetting and leveling agent, preheat to 40-50°C, then add the light stabilizer and stir evenly to obtain a chain extender mixture; cool the isocyanate-terminated prepolymer to 60°C, slowly add the chain extender mixture, and stir evenly at a stirring speed of 1000-1500 rpm. Control the exothermic reaction temperature to be less than 90°C. After reacting for 30-60 minutes, take a sample and measure the NCO content (di-n-butylamine titration method) until the measured value is close to the designed value to obtain a chain extension product;

[0034] S4, final polymerization reaction

[0035] Add the functional filler to the chain extension product and stir uniformly at a stirring speed of 1000-1500 rpm for 5-10 minutes, then add the remaining isocyanate and the remaining composite catalyst, continue stirring and vacuum degassing until the system viscosity reaches 5000-10000 mPa·s to obtain the final polymer;

[0036] S5, molding and curing

[0037] The final polymer is injected into a mold and cured at 130-150°C for 2-3 hours to obtain a yellowing-resistant polyurethane product.

[0038] On the basis of the above scheme and as a preferred scheme of the above scheme, the functional filler in step S4 is added to the chain extension product in at least three times, and the moisture content of the functional filler is lower than 0.02%.

[0039] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0040] The present invention discloses a yellowing-resistant polyurethane and a preparation method thereof. The polyol used constructs a three-dimensional cross-linked network structure, and the isocyanate system balances reactivity and yellowing resistance. The composite catalytic system used has the effect of synergistic catalysis and optimizes the mechanical properties of the material. The composite chain extender utilizes the coordination effect of the original acid, which improves the yellowing resistance of the material to a certain extent. The functional filler of modified heterostructured zinc oxide is added, and the addition of the light stabilizer synergistically improves the yellowing resistance and aging resistance of the polyurethane. In addition, the three-step "prepolymerization-chain extension-final polymerization" method used in the present invention accurately controls microphase separation through gradient temperature increase, shortening the reaction time by 50% and reducing energy consumption by 40% compared with traditional processes.

[0041] It should be appreciated that all combinations of the foregoing concepts, as well as additional concepts described in greater detail below, to the extent such concepts are not mutually inconsistent, can be considered part of the present subject disclosure.

[0042] The foregoing and other aspects, embodiments and features of the present invention will be more fully understood from the following description. Other additional aspects of the present invention, such as the features and / or beneficial effects of the exemplary embodiments, will become apparent from the following description or will be learned from the practice of the specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0044] Figure 1 It is a process flow chart of the present invention;

[0045] Figure 2 This is a schematic diagram of the synthesis principle of the chain extender of the present invention. DETAILED DESCRIPTION

[0046] In order to enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples, but this should not be construed as limiting this patent.

[0047] Unless otherwise specified, the experimental methods or test methods described in the following examples / comparative examples are conventional methods; the reagents and materials described are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0048] In the present invention, the functional filler is a modified heterostructured zinc oxide, which includes three parts: preparation of composite material A, composite material B, and in-situ polymerization. The preparation method is as follows:

[0049] A1. Preparation of composite material A

[0050] First, graphite oxide was prepared using the Hummers method. After determining the solid content, the graphite oxide was dispersed in deionized water and subjected to ultrasonic exfoliation to obtain a 0.2 M graphene oxide aqueous solution. The graphene oxide aqueous solution was placed in a beaker and stirred at 1500 rpm. Zinc acetate dihydrate was prepared into a 0.1 M aqueous solution. An equal volume of the zinc acetate dihydrate aqueous solution was then added dropwise at a rate of 0.02 mL / min. After mixing, a 0.1 M NaOH solution was added. The molar ratio of zinc acetate dihydrate to NaOH was 1:2. The reaction was carried out at 60°C for 2 hours under magnetic stirring. After completion of the reaction, the reaction product was allowed to settle naturally and washed three times with deionized water to obtain Composite Material A.

[0051] A2. Preparation of composite material B

[0052] A 0.3M LiF / HCl solution was prepared and 70 mL of the solution was placed in a beaker. A predetermined mass of multilayered clay-like MXene powder was then added, followed by 30 mL of deionized water. After ultrasonic treatment (1000 W) for 30 minutes, a 10 wt% layered MXene dispersion was obtained. Zinc acetate dihydrate was then added to the MXene dispersion, and ultrasonic treatment was continued for 20 minutes. Finally, the MXene mixture was placed in a 60°C water bath and 0.1 M NaOH solution was added. The reaction was carried out at 60°C for 2 hours under magnetic stirring. After completion of the reaction, the product was centrifuged and washed three times with deionized water to obtain Composite Material A. The molar ratio of zinc acetate dihydrate to MXene was 1:1, and the molar ratio of zinc acetate dihydrate to NaOH was 1:2.

[0053] A3. In-situ polymerization

[0054] The prepared composite material A and composite material B were placed in 50 mL of deionized water at a mass ratio of 1:1, and further dispersed by ultrasonication (1000 W) to obtain a mixed dispersion. Then, magnetic stirring was performed at a stirring speed of 500 rpm for 5 minutes, and 10 mL of an equimolar concentration (60×10 -3 A ZnO growth solution was prepared by adding zinc nitrate hexahydrate (200 μM) and hexamethylenetetramine to the mixed dispersion and stirring for 10 minutes. The mixture was then poured into a 100 mL reactor and hydrothermally reacted at 95°C for 6 hours. After the reaction was completed, the solution was naturally cooled to room temperature and filtered through a 0.22 μM filter to obtain the modified heterostructured zinc oxide product.

[0055] During the preparation of the modified heterostructured zinc oxide, ZnO seed crystals are deposited on the surfaces of MXene and graphene oxide via in-situ polymerization, forming a "MXene-ZnO-graphene oxide" heterostructure. The negatively charged carboxyl and hydroxyl groups on the graphene oxide surface facilitate uniform dispersion of the MXene-ZnO composite material A within the 3D network. This heterostructure facilitates multiple refraction and reflection of light, facilitating the absorption of light energy, helping to prevent photoaging and improve the product's yellowing resistance. During illumination, the uniformly dispersed 3D network heterostructure increases the number of refraction and reflection paths for light, lengthening the light's propagation path and dissipating the light's energy. This, combined with the use of a light stabilizer, synergistically enhances the material's yellowing resistance. Finally, ZnO particles are synthesized on the surfaces of the MXene and graphene oxide through a second hydrothermal treatment. The presence of ZnO effectively bonds the MXene and graphene oxide to form a heterostructure, thereby enhancing the stability of the material. The ZnO particles themselves also exhibit excellent UV resistance, further contributing to the product's yellowing resistance.

[0056] Furthermore, the chain extender of the present invention is a mixed chain extender of a borate-based diol chain extender and an amine chain extender, and the molar ratio of the two is (1-2):1. Specifically, the amine chain extender is N,N-dimethyl-N,N'-di(2-hydroxypropyl)-1,3-propylenediamine. Further, the mixed chain extender is a borate-based diol chain extender and an amine chain extender N,N-dimethyl-N,N'-di(2-hydroxypropyl)-1,3-propylenediamine in a molar ratio of 1:2. Further, the borate-based diol chain extender is 2,2'-(1,4-phenyl-2,5-dimethyl)-bis[4-(4-hydroxybutyl)-1,3,2-dioxaborinane], and its laboratory synthesis method is as follows:

[0057] First, THF (Runjie Chemical) was added with calcium hydride (CaH2, 98.5%, Aladdin) before use, refluxed for 6-8 hours, and then evaporated for later use; then 2,5-dimethyl-1,4-diphenylboronic acid and 1,2,6-hexanetriol were mixed in a molar ratio of 5:11 as raw materials, and the raw materials were dissolved in the refluxed THF, wherein the amount of THF used was 10 times the volume of the raw materials; then anhydrous magnesium sulfate (98%, Sinopharm Reagent) of the same mass as the raw materials was added, and the reaction was stirred at room temperature for 24 hours; finally, the magnesium sulfate was removed by filtration to obtain a filtrate, and the filtrate was precipitated with n-hexane (Qiangsheng) as a precipitant. After drying, the precipitate was obtained to obtain the product, i.e., the borate ester-based diol chain extender 2,2'-(1,4-phenyl-2,5-dimethyl)-bis[4-(4-hydroxybutyl)-1,3,2-dioxaborinane] of the present invention. After calculation, its yield was 91.25%, and the synthetic route is as follows: Figure 2 shown.

[0058] The present invention synthesizes a diol chain extender containing a borate structural unit, which can form a BN coordination effect with the N element on N,N-dimethyl-N,N'-di(2-hydroxypropyl)-1,3-propylenediamine. The BN coordination bond reduces the electron deficiency of the boron atom and the acidity of phenylboronic acid, and the external energy support can further stabilize the system. Therefore, during external irradiation or heating, it is beneficial to further enhance the stability of the system. In other words, the use of a diol chain extender with a borate structural unit is beneficial to enhancing the heat resistance and yellowing resistance of polyurethane. When not irradiated or heated, the existing polyurethane structure has a soft segment-hard segment structure, which not only has a three-dimensional stable spatial structure, but also can well "freeze" the molecular chain, which can well prevent the instability problem caused by chain segment movement.

[0059] Furthermore, the composite catalyst used is composed of dibutyltin dilaurate and 1,4-diazabicyclo[2.2.2]octane. Through the metal-amine synergistic effect, precise control of the gelation and foaming reactions in polyurethane synthesis is achieved. Compared with existing technologies, the following optimizations can be achieved:

[0060] (1) Reaction balance control

[0061] Balance between gelation and foaming: Dibutyltin dilaurate accelerates molecular chain growth (gelation), and 1,4-diazabicyclo[2.2.2]octane regulates the foaming rate. The two work together to ensure that the foam material completes bubble stabilization at an appropriate viscosity to avoid bubble collapse or closed cells.

[0062] (2) Reaction rate matching

[0063] The compound catalyst enables the chain growth gel reaction and the gas generated foaming reaction to proceed synchronously, avoiding structural defects such as delamination and cracking caused by rate mismatch.

[0064] (3) Improve material properties

[0065] Foam structure uniformity: 1,4-diazabicyclo[2.2.2]octane ensures uniform bubble distribution, and dibutyltin dilaurate ensures polymer backbone strength.

[0066] Therefore, the use of compound catalysts can balance the hardness, elastic modulus and resilience of the material by adjusting the ratio, thereby optimizing the mechanical properties of the material.

[0067] Performance Testing

[0068] Mechanical properties testing

[0069] Mechanical property tests include tensile strength and elongation at break. The tensile strength is tested according to the standard ASTM D412. According to relevant test requirements and regulations, the sample size is unified and the test is carried out at a test speed of 50 mm / min. Furthermore, the elongation at break is tested according to the standard ASTM D638, and the tensile test speed is 50 mm / min.

[0070] Yellowing resistance

[0071] According to the requirements of ASTM D 1148, the sample was placed in an aging box equipped with a UVA-340 lamp at 0.76W / m 2 Irradiation intensity: continuous exposure at 60℃ for 1000h. After aging, observe the yellowing of the product and use a colorimeter to measure the ΔE value to quantify the degree of yellowing.

[0072] Photoaging resistance

[0073] In accordance with GB / T 23987-2009, UV light weathering tests were conducted at a wavelength of 340nm, a temperature of 60°C, and an irradiation time of 240 hours. Samples were then taken for aging resistance testing. The light aging test and yellowing resistance test use the same irradiation wavelength and temperature, so the retention of tensile strength and elongation at break of the aged samples can be tested at 240 hours.

[0074] Thermal stability

[0075] The thermal stability of the samples was tested using a TGA550 thermogravimetric analyzer. In order to eliminate the influence of a small amount of water in the sample on the test results, the sample was first heated at 10°C / min. -1 The temperature was raised to 100℃ at a speed of 100℃ and kept at 100℃ for 5min to remove moisture; then the temperature was raised to 100℃ min -1 The temperature was lowered to 40℃ at a rate of 10℃·min -1 The temperature was raised to 700°C at a rate of 100°C. A nitrogen atmosphere was maintained during the test, and the decomposition temperatures T at which the sample mass loss was 10% and 50% were calculated. 10% (initial decomposition temperature), T 50% (half-decomposition temperature) to evaluate its thermal stability.

[0076] Examples 1-3

[0077] A yellowing-resistant polyurethane is prepared by weighing the components shown in Table 1 by weight percentage: polyol, two-component isocyanate, composite catalyst, functional filler, chain extender, wetting and leveling agent, and light stabilizer. The preparation method of the yellowing-resistant polyurethane is as follows:

[0078] S1. Raw material processing

[0079] Dehydrate the polyol under vacuum at 100-120°C for 2-3 hours until the moisture content is ≤0.05%; at the same time, dry the functional filler under forced air at 120°C for 2 hours for later use;

[0080] S2. Prepolymer Synthesis

[0081] Under dry nitrogen protection, add the dehydrated polyol to the reactor and cool to 50-60°C; slowly add two-component isocyanate at a NCO:OH molar ratio of (1.5-2.0):1, add a composite catalyst, raise the temperature to 60-65°C, and react for 2-3 hours to obtain an isocyanate-terminated prepolymer;

[0082] S3, chain extension reaction

[0083] Mix the chain extender and the wetting and leveling agent, preheat to 40-50°C, then add the light stabilizer and stir evenly to obtain a chain extender mixture; cool the isocyanate-terminated prepolymer to 60°C, slowly add the chain extender mixture, and stir evenly at a stirring speed of 1000-1500 rpm. Control the exothermic reaction temperature to be less than 90°C. After reacting for 30-60 minutes, take a sample and measure the NCO content (di-n-butylamine titration method) until the measured value is close to the designed value to obtain a chain extension product;

[0084] S4, final polymerization reaction

[0085] Add the functional filler to the chain extension product and stir uniformly at a stirring speed of 1000-1500 rpm for 5-10 minutes, then add the remaining isocyanate and the remaining composite catalyst, continue stirring and vacuum degassing until the system viscosity reaches 5000-10000 mPa·s to obtain the final polymer;

[0086] S5, molding and curing

[0087] The final polymer is injected into a mold and cured at 130-150°C for 2-3 hours to obtain a yellowing-resistant polyurethane product.

[0088] Wherein, the functional filler in step S4 is added to the chain extension product in at least three times, and the moisture content of the functional filler is lower than 0.02%.

[0089] Table 1 Material ratio and test results analysis table

[0090] Comparative Example 1

[0091] The difference from Example 1 is that the functional filler is replaced with MXene of equal mass, and the rest is the same as Example 1, and the preparation steps are the same as Example 1.

[0092] Comparative Example 2

[0093] The difference from Example 1 is that the functional filler is replaced with nano ZnO of the same mass. The rest is the same as Example 1, and the preparation steps are the same as Example 1.

[0094] Comparative Example 3

[0095] The difference from Example 1 is that the functional filler is replaced by graphene oxide of equal mass, and the rest is the same as Example 1, and the preparation steps are the same as Example 1.

[0096] Comparative Example 4

[0097] The difference from Example 1 is that the composite catalyst is replaced by an equal mass of dibutyltin dilaurate, and the rest is the same as Example 1, and the preparation steps are the same as Example 1.

[0098] Comparative Example 5

[0099] The difference from Example 1 is that the composite catalyst is replaced by an equal mass of 1,4-diazabicyclo[2.2.2]octane, and the rest is the same as Example 1, and the preparation steps are the same as Example 1.

[0100] Comparative Example 6

[0101] The difference from Example 1 is that the chain extender is replaced by an equal mass of borate-based diol chain extender, and the rest is the same as Example 1, and the preparation steps are the same as Example 1.

[0102] Comparative Example 7

[0103] The difference from Example 1 is that the chain extender is replaced by an amine chain extender of equal mass, N,N-dimethyl-N,N'-di(2-hydroxypropyl)-1,3-propylenediamine. The rest is the same as Example 1, and the preparation steps are the same as Example 1.

[0104] Comparative Example 8

[0105] The difference from Example 1 is that the chain extender is replaced by ethylene glycol of equal mass, and the rest is the same as Example 1, and the preparation steps are the same as Example 1.

[0106] Standard samples of Examples 1 to 3 and Comparative Examples 1 to 8 were prepared according to relevant performance test standards and subjected to performance tests. Five samples were taken for each test and the average value was taken. The relevant test comparison is shown in Table 2.

[0107] Table 2 Test results analysis table

[0108] From the comparative results in Table 1 above, it can be seen that the polyurethane prepared by the present invention has excellent properties such as yellowing resistance and aging resistance, which provides ideas for the application of alicyclic polyurethane in outdoor composite materials, optical device packaging, outdoor coatings and other scenarios.

[0109] The single-element fillers used in Comparative Examples 1-3 do not achieve the functional effects of the modified heterostructured zinc oxide of equal mass. The modified heterostructured zinc oxide uses graphene oxide as a substrate and MXene as an auxiliary material. Using in-situ polymerization, nano-zinc oxide is synthesized and uniformly dispersed in the graphene oxide and MXene. Furthermore, ZnO seeds are deposited on the surfaces of the MXene and graphene oxide through in-situ polymerization to form a "MXene-ZnO-graphene oxide" heterostructure. This not only utilizes the interface between the active functional groups of graphene oxide and the polymer substrate, but also, during illumination, the uniformly dispersed 3D network heterostructure increases the refraction or reflection paths for light, lengthening the light transmission path and consuming the light's energy. Furthermore, the hydrogen bonds between the active functional groups on the graphene oxide surface and the substrate molecules absorb harmful ultraviolet radiation and convert it into heat, protecting the material from damage by ultraviolet radiation, thereby improving the aging resistance of the polyurethane. Furthermore, the light stabilizer in the system absorbs and releases energy without undergoing significant chemical changes, and can absorb ultraviolet radiation for a long time; the two work together to improve the yellowing and aging resistance of polyurethane.

[0110] Furthermore, in compounded chain extenders, diol chain extenders containing borate structural moieties can form BN coordination with the nitrogen element of N,N-dimethyl-N,N'-di(2-hydroxypropyl)-1,3-propylenediamine. Within a certain range, the higher energy can further enhance the structural stability of the structure, thereby making the material more durable. Furthermore, the formation of BN coordination bonds leads to a longer BO bond length. Intramolecular voids have a similar effect on the refraction or reflection of light, which improves the material's yellowing resistance to a certain extent, but the yellowing resistance is not as significant as the impact of functional fillers on the material. Furthermore, the use of compounded catalysts can balance the material's hardness, elastic modulus, and rebound resilience by adjusting the ratio, thereby optimizing the material's mechanical properties. It should be noted that in terms of the impact on the material's mechanical properties, the compounded chain extender has a greater impact on mechanical properties than the functional material and compounded catalyst due to the combined amount of the compounded catalyst.

[0111] While the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Persons skilled in the art will readily appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A yellowing-resistant polyurethane, characterized in that: Calculated by weight, it includes the following raw materials: 100 parts of polyol; 40-55 parts of two-component isocyanate; Composite catalyst 0.05-0.18 parts; 0.5-2.5 parts of functional filler; 6-15 parts of chain extender; 0.3-0.7 parts of wetting and leveling agent; Light stabilizer 0.2-0.5 parts.

2. The yellowing-resistant polyurethane according to claim 1, characterized in that: The polyol is tetrafunctional polyneopentyl adipate, and the OH value of the polyol is 56-60 mgKOH / g and the molecular weight is 1800-2200.

3. The yellowing-resistant polyurethane according to claim 1, characterized in that: The two-component isocyanate includes IPDI and HDI, and the mass ratio of the two is (3-4):(1-2).

4. The yellowing-resistant polyurethane according to claim 1, characterized in that: The functional filler is modified heterostructure zinc oxide.

5. The yellowing-resistant polyurethane according to claim 1, characterized in that: The composite catalyst consists of dibutyltin dilaurate and 1,4-diazabicyclo[2.2.2]octane, and the ratio of the two is 1:(1-4).

6. The yellowing-resistant polyurethane according to claim 1, characterized in that: The chain extender is a mixed chain extender of a borate-based diol chain extender and an amine chain extender.

7. The yellowing-resistant polyurethane according to claim 5, characterized in that: The wetting and leveling agent is one or more of BYK-161, BYK-333, EFKA-4061, and FS-161; the light stabilizer is one or more of Chimassorb 81, Tinuvin 770, and Tinuvin 622.

8. A method for preparing the yellowing-resistant polyurethane according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Raw material pretreatment Dehydrate the polyol under vacuum at 100-120°C for 2-3 hours until the moisture content is ≤0.05%; at the same time, dry the functional filler under forced air at 120°C for 2 hours for later use; S2. Prepolymer Synthesis Under dry nitrogen protection, add the dehydrated polyol to the reactor and cool to 50-60°C; slowly add two-component isocyanate at a NCO:OH molar ratio of (1.5-2.0):1, add a composite catalyst, raise the temperature to 60-65°C, and react for 2-3 hours to obtain an isocyanate-terminated prepolymer; S3, chain extension reaction The chain extender and the wetting and leveling agent are mixed, preheated to 40-50°C, and then the light stabilizer is added and stirred evenly to obtain a chain extender mixture; the isocyanate-terminated prepolymer is cooled to 60°C, and the chain extender mixture is slowly added and stirred evenly at a stirring speed of 1000-1500 rpm. The exothermic reaction temperature is controlled to be less than 90°C. After reacting for 30-60 minutes, a sample is taken to measure the NCO content until the measured value is close to the designed value to obtain a chain extension product; S4, final polymerization reaction Add the functional filler to the chain extension product and stir uniformly at a stirring speed of 1000-1500 rpm for 5-10 minutes, then add the remaining isocyanate and the remaining composite catalyst, continue stirring and vacuum degassing until the system viscosity reaches 5000-10000 mPa·s to obtain the final polymer; S5, molding and curing The final polymer is injected into a mold and cured at 130-150°C for 2-3 hours to obtain a yellowing-resistant polyurethane product.

9. The method for preparing yellowing-resistant polyurethane according to claim 8, wherein: In step S4, the functional filler is added to the chain-extended product in at least three times, and the moisture content of the functional filler is lower than 0.02%.

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