A time-dependent composite crystal form control agent and an ADC foaming agent particle size control method and its application

Abstract

This application provides a time-dependent composite crystal form control agent for particle size control of ADC blowing agents, comprising: melamine-formaldehyde prepolymer microspheres with a particle size of 20-50 nm, used at an amount of 0.2-0.4 wt% of the theoretical ADC yield; a gemini surfactant containing phosphate ester groups, used at an amount of 0.3-0.6 wt% of the theoretical ADC yield; and carboxylated β-cyclodextrin, used at an amount of 0.4-0.8 wt% of the theoretical ADC yield. The particle size control method for the ADC blowing agent of this application involves adding the above composite crystal form control agent in the following sequence: Step 1: 10 min before the start of the biuret oxidation reaction, add the melamine-formaldehyde prepolymer microspheres and stir until homogeneous. Step 2: 30 min after the start of the reaction, add the gemini surfactant containing phosphate ester groups. Step 3: 60 min after the start of the reaction, add the carboxylated β-cyclodextrin. Through the temporal synergistic effect of the three types of components, the particle size of the ADC can be controlled within the range of 2 to 20 μm, and the particle size distribution range can be stabilized between 0.6 and 0.9.

Description

Technical Field

[0001] This application relates to the field of ADC foaming agent preparation, and in particular to a time-dependent composite crystal form control agent and a method for controlling the particle size of ADC foaming agents and their applications. Background Technology

[0002] ADC (azodicarbonamide) is currently the most widely used organic foaming agent, boasting advantages such as high gas evolution, suitable decomposition temperature, and low cost, and is extensively used in insulation boards, packaging materials, and automotive interiors. However, traditionally industrially produced ADC foaming agents generally suffer from problems such as wide particle size distribution, irregular particle morphology, and poor powder dispersibility. Agglomeration easily occurs during processing, leading to defects such as uneven cell size, a mixture of large and small pores, and low closed-cell rate in the foamed material. This limits the insulation performance of the foamed material, making it difficult to meet the demands of high-end applications.

[0003] In recent years, with the rapid development of industries such as building energy conservation and cold chain logistics, the market demand for high-insulation foam materials has continued to grow. The performance shortcomings of traditional ADC foaming agents have become a major bottleneck restricting the large-scale application of high-insulation foam materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a time-dependent composite crystal form control agent. Through the cascade synergistic effect of three types of components and the time-sequential regulation of stepwise addition, it improves the powder dispersibility of ADC foaming agent, realizes the regulation of ADC particle size and directional crystal growth, and improves the thermal insulation performance of foamed materials.

[0005] A time-dependent complex crystal form control agent includes: Melamine-formaldehyde prepolymer microspheres with a particle size of 20–50 nm were used at an amount of 0.2–0.4 wt% of the theoretical yield of ADC. The melamine-formaldehyde prepolymer microspheres were used to induce the formation of ADC crystal nuclei. When used alone, they had no crystal form regulation effect and easily led to a decrease in the thermal stability of ADC.

[0006] Gemini surfactants containing phosphate ester groups are used at a rate of 0.3–0.6 wt% of the theoretical yield of ADC. When used alone, gemini surfactants have a weaker dispersing effect than conventional sodium dodecylbenzene sulfonate and are more likely to cause a decrease in foaming ratio.

[0007] Carboxylated β-cyclodextrin is used at an amount of 0.4–0.8 wt% of the theoretical yield of ADC. β-cyclodextrin is used to restrict and induce the directional growth of ADC crystals. When used alone, it has no crystal form regulation effect and is prone to residue, which leads to a decrease in foaming porosity.

[0008] The ADC foaming agent particle size control method of this application involves adding the above-mentioned composite crystal form control agent in the following sequence: Step 1: 10 minutes before the start of the biurea oxidation reaction, add melamine-formaldehyde prepolymer microspheres and stir evenly. The imino groups on the surface of the microspheres form hydrogen bonds with the carbonyl groups on the biurea urea groups, providing heterogeneous nucleation sites and increasing the crystal nucleus generation rate and the number of initial crystal nuclei.

[0009] Step 2: 30 minutes after the reaction begins, add a gemini surfactant containing phosphate ester groups. The phosphate ester groups specifically coordinate with the amino groups on the surface of the melamine-formaldehyde prepolymer microspheres, and the hydrophobic chains combine with the hydrophobic crystal surface of the ADC crystal nucleus to construct a microsphere-surfactant bilayer interface, which reduces the surface energy of the crystal nucleus and inhibits crystal nucleus aggregation.

[0010] Step 3: 60 min after the reaction begins, add carboxylated β-cyclodextrin. The hydrophobic cavity of β-cyclodextrin encapsulates the exposed hydrophobic chains of the gemini surfactant, and the outer carboxyl groups provide strong electrostatic repulsion, forming a three-layer shell structure of microsphere-surfactant-cyclodextrin, which restricts the lateral growth of crystals and induces the directional growth of crystals.

[0011] If the above order of addition is reversed, the three-shell structure cannot be formed, and the crystal form regulation effect is completely lost.

[0012] The ADC foaming agent prepared in this application can be used in thermal insulation polyurethane foam materials, which can improve the uniformity of foam cells and thus improve the thermal insulation performance of the foam material.

[0013] The technical advantages of this application are as follows: Through the temporal synergistic effect of the three types of components, the particle size of the ADC can be controlled within the range of 2 to 20 μm, and the particle size distribution range is stabilized at 0.6 to 0.9, which is much lower than the conventional 1.5 or more.

[0014] It enables ADC crystals to grow in a directional manner, resulting in a higher uniformity of decomposition rate during foaming.

[0015] The total addition amount is ≤1.8wt%, and the three components are completely degraded at the ADC thermal decomposition temperature with no residue, and do not affect the mechanical properties and thermal stability of the foamed product.

[0016] This time-series coordinated regulation mechanism can be extended to other hydrothermal synthesis organic crystal particle size regulation scenarios, and has universality. Detailed Implementation

[0017] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0018] Time-dependent complex crystal form control agents include: Melamine-formaldehyde prepolymer microspheres with a particle size of 20–50 nm were used at an amount of 0.2–0.4 wt% of the theoretical yield of ADC. The melamine-formaldehyde prepolymer microspheres were used to induce the formation of ADC crystal nuclei. When used alone, they had no crystal form regulation effect and easily led to a decrease in the thermal stability of ADC.

[0019] Melamine-formaldehyde prepolymer microspheres are monodisperse polymer microspheres prepared using a specific process as a matrix, formed by the condensation of melamine and formaldehyde under alkaline conditions. In a preferred embodiment, the melamine-formaldehyde prepolymer microspheres are prepared by soap-free emulsion polymerization, with the specific steps as follows: Melamine and 37% formaldehyde solution are mixed at a molar ratio of 1:2.5 to 1:3. The pH is adjusted to 8.0 to 8.5 with triethanolamine. The mixture is stirred at 70°C for 20 to 30 minutes until the solution is completely clear to obtain a prepolymer solution with a solid content of 10% to 12%.

[0020] The prepolymer solution was cooled to 40°C, and citric acid equivalent to 0.5%–1% of the prepolymer mass was added as a curing catalyst. The reaction was carried out at high speed of 800–1000 rpm for 1–1.5 h. During the process, the particle size was monitored by dynamic light scattering. When the particle size reached the range of 20–50 nm, the pH was immediately adjusted to 9.0 with sodium hydroxide to terminate the reaction.

[0021] Unreacted monomers and small molecule impurities were removed by dialysis of the reaction solution, and then freeze-dried to obtain powdered microspheres with a dispersibility index (PDI) ≤ 0.12 and a surface amino content of 1.2–1.5 mmol / g.

[0022] The microspheres prepared by the above method do not require additional surface modification and have abundant imino active sites, which can directly form hydrogen bonds with ADC synthesis raw materials to induce nucleation.

[0023] The theoretical yield of ADC described in this application refers to the maximum calculated yield when all the raw materials are converted into the target product ADC under ideal reaction conditions.

[0024] Gemini surfactants containing phosphate ester groups are used at a rate of 0.3–0.6 wt% of the theoretical yield of ADC. When used alone, gemini surfactants have a weaker dispersing effect than conventional sodium dodecylbenzene sulfonate and are more likely to cause a decrease in foaming ratio.

[0025] In a preferred embodiment, the phosphate ester-containing gemini surfactant of this application is prepared by a two-step method of diol bridging and phosphate esterification. The product has a structure of hydrophilic diphosphate ester groups and double hydrophobic long chains. The phosphate ester groups can form specific coordination with amino groups. The specific preparation steps are as follows: 1 mol of dodecyl alcohol and 0.5 mol of epichlorohydrin were reacted at 80 °C for 4 h under the action of tetrabutylammonium bromide phase transfer catalyst to obtain dodecyl glycidyl ether; then 2 mol of this product was reacted with 0.5 mol of ethylene glycol under alkaline conditions at 120 °C for 6 h to obtain a bi-long-chain alkyl intermediate with hydroxyl groups at both ends and an ethoxy group in the middle.

[0026] The above intermediate was mixed with phosphorus pentoxide at a molar ratio of 3:1 and stirred at 60°C for 5 hours under nitrogen protection. During the process, phosphorus pentoxide was added in batches to avoid local overheating. After the reaction was completed, a small amount of polyphosphate ester generated by water hydrolysis was added to obtain crude gemini surfactant containing diphosphate ester groups.

[0027] The crude Gemini surfactant was dissolved in hot ethanol, filtered to remove insoluble matter, and then distilled under reduced pressure to remove ethanol. It was then neutralized with 30% sodium hydroxide solution to pH 7.0–7.5 to obtain an aqueous product with a solid content of 30%. After freeze-drying, powdered Gemini surfactant was obtained.

[0028] In a preferred embodiment, the hydrophobic chain length of the gemini surfactant is C. 12 ~C 18 The linking group between the two hydrophilic groups of the Gemini surfactant is an ethoxy group. Experiments have shown that this length of hydrophobic chain has a suitable binding energy with the hydrophobic surface of the ADC crystal; it avoids insufficient adsorption strength due to excessively short chains leading to easy desorption, and also avoids interchain entanglement and crystal aggregation due to excessively long chains. Furthermore, this length of hydrophobic chain can be completely degraded and volatilized at the ADC thermal decomposition temperature, leaving no residue that would affect the mechanical properties of the foamed product.

[0029] Carboxylated β-cyclodextrin is used at an amount of 0.4–0.8 wt% of the theoretical yield of ADC. β-cyclodextrin is used to restrict and induce the directional growth of ADC crystals. When used alone, it has no crystal form regulation effect and is prone to residue, which leads to a decrease in foaming porosity.

[0030] Carboxylated β-cyclodextrin can be prepared by chloroacetic acid etherification, a mature process with controllable carboxyl substitution degree, which meets the requirements of embedding hydrophobic chains and providing electrostatic repulsion in this scheme. In a preferred embodiment, the specific preparation steps are as follows: 1 mol of β-cyclodextrin was dissolved in a 20% sodium hydroxide aqueous solution, with the solid content controlled at 25%–30%. The solution was stirred and activated at 40°C for 1 h to fully activate the hydroxyl groups on the cyclodextrin molecules into oxygen anions, providing active sites for the subsequent etherification reaction.

[0031] Add 3-5 mol of chloroacetic acid slowly in batches to the above alkaline solution, control the reaction temperature at 60℃, and stir the reaction for 4-6 hours; the degree of carboxyl substitution can be controlled by adjusting the chloroacetic acid feed ratio.

[0032] After the reaction was completed, the pH was adjusted to neutral with dilute hydrochloric acid. The reaction solution was then poured into 8 times its volume of anhydrous ethanol to precipitate the product. The crude product was obtained by filtration. The product was then washed three times with anhydrous ethanol to remove unreacted chloroacetic acid and sodium chloride impurities. After freeze-drying, a white powdery carboxylated β-cyclodextrin was obtained with a carboxyl content of 1.0–1.8 mmol / g.

[0033] In a preferred embodiment, the degree of carboxyl substitution of the β-cyclodextrin is 3 to 6, more preferably 4. That is, on average, 3 to 6 hydroxyl groups on each β-cyclodextrin molecule are replaced with carboxymethyl groups (-CH2COOH). Experiments have shown that when the degree of substitution is less than 3: the number of carboxyl groups on the outer side of the β-cyclodextrin is insufficient, the electrostatic repulsion effect is weak, a stable shell-confined structure cannot be formed, and crystal aggregation is easily caused. When the degree of substitution is greater than 6: excessive carboxyl groups will change the cavity polarity of the β-cyclodextrin, resulting in a significant decrease in hydrophobic embedding ability and an inability to effectively anchor the hydrophobic end of the surfactant.

[0034] The ADC foaming agent particle size control method of this application involves adding the above-mentioned composite crystal form control agent in the following sequence: Step 1: 10 minutes before the start of the biurea oxidation reaction, add melamine-formaldehyde prepolymer microspheres and stir evenly. The imino groups on the surface of the microspheres form hydrogen bonds with the carbonyl groups on the biurea urea groups, providing heterogeneous nucleation sites and increasing the crystal nucleus generation rate and the number of initial crystal nuclei.

[0035] Step 2: 30 minutes after the reaction begins, in the early stage of crystal nucleus growth, a gemini surfactant containing phosphate ester groups is added. The phosphate ester groups undergo specific coordination with the amino groups on the surface of the melamine-formaldehyde prepolymer microspheres, and the hydrophobic chains combine with the hydrophobic crystal surface of the ADC crystal nucleus, thereby constructing a microsphere-surfactant bilayer interface, which can reduce the surface energy of the crystal nucleus and inhibit crystal nucleus aggregation.

[0036] Step 3: 60 min after the reaction begins, add carboxylated β-cyclodextrin. The hydrophobic cavity of β-cyclodextrin encapsulates the exposed hydrophobic chains of the gemini surfactant, and the outer carboxyl groups provide strong electrostatic repulsion, forming a three-layer shell structure of microsphere-surfactant-cyclodextrin, which restricts the lateral growth of crystals and induces the directional growth of crystals.

[0037] Directionally grown ADC crystals exhibit a regular short rod / needle morphology, resulting in a higher specific surface area compared to random aggregates and more uniform heat transfer efficiency during thermal decomposition. Furthermore, the N2 and CO2 gases released during the decomposition of directionally grown crystals can escape in an orderly manner along the crystal orientation, forming a uniform closed-pore structure. Simultaneously, the good dispersibility of directionally grown crystals enhances the mixing uniformity in foamed materials.

[0038] If the above order of addition is reversed, the three-shell structure cannot be formed, and the crystal form regulation effect is completely lost.

[0039] The ADC foaming agent prepared in this application can be used in thermal insulation polyurethane foam materials, which can improve the uniformity of foam cells and thus improve the thermal insulation performance of the foam material.

[0040] The following are embodiments and comparative examples of this application.

[0041] Example 1 The composite crystal form control agent in this embodiment consists of: 0.3 wt% 30 nm melamine-formaldehyde prepolymer microspheres, C 14 Phosphate ester type gemini surfactant 0.4wt, β-cyclodextrin with a carboxyl substitution degree of 4 0.6wt.

[0042] Add biuret to the reactor, add water to adjust the solid content to 12%, and adjust the initial pH to 1.2 with hydrochloric acid. Control the reaction temperature at 20±1℃, and introduce chlorine gas at a uniform rate of 0.8 m / s. 3 The reaction time was approximately 150 minutes, with a reaction rate of 1 h. After the reaction was completed, chlorination was stopped, and the product was filtered, washed with deionized water until the filtrate was neutral, and then vacuum dried at 60°C for 12 hours to obtain the ADC foaming agent product.

[0043] In this process, melamine-formaldehyde prepolymer microspheres were added 10 minutes before the start of the biuret oxidation reaction, and the mixture was stirred at 350 rpm. After 30 minutes of reaction, C14 phosphate ester type gemini surfactant was added, and the stirring speed was adjusted to 250 rpm. After 60 minutes of reaction, β-cyclodextrin with a carboxyl substitution degree of 4 was added, and the stirring speed was adjusted to 180 rpm until the reaction was completed.

[0044] Comparative Example 1 The component dosages were the same as in Example 1, but the order of addition was adjusted to melamine-formaldehyde prepolymer microspheres → β-cyclodextrin → gemini surfactant. The rest of the process was the same as in Example 1.

[0045] Comparative Example 2 The component dosages were the same as in Example 1, but the order of addition was adjusted to Gemini surfactant → melamine-formaldehyde prepolymer microspheres → β-cyclodextrin. The rest of the process was the same as in Example 1.

[0046] Comparative Example 3 The component dosages were the same as in Example 1, but the order of addition was adjusted to Gemini surfactant → β-cyclodextrin → melamine-formaldehyde prepolymer microspheres. The rest of the process was the same as in Example 1.

[0047] Comparative Example 4 The component dosages were the same as in Example 1, but the order of addition was adjusted to β-cyclodextrin → gemini surfactant → melamine-formaldehyde prepolymer microspheres. The rest of the process was the same as in Example 1.

[0048] Comparative Example 5 The component dosages were the same as in Example 1, but the order of addition was adjusted to β-cyclodextrin → melamine-formaldehyde prepolymer microspheres → Gemini surfactant. The rest of the process was the same as in Example 1.

[0049] Comparative Example 6 The component lacks β-cyclodextrin, and the rest of the process is the same as in Example 1.

[0050] Comparative Example 7 The component lacks the gemini surfactant, and the rest of the process is the same as in Example 1.

[0051] Comparative Example 8 The melamine-formaldehyde prepolymer microspheres were missing from the sample, but the rest of the process was the same as in Example 1.

[0052] Comparative Example 9 Only 1.3 wt% of conventional sodium dodecylbenzenesulfonate was added as a dispersant, and the rest of the process remained the same.

[0053] The ADC foaming agents prepared in the above embodiments and comparative examples were sampled and tested. The test results are shown in Table 1. Table 1: In the table, the aspect ratio of the crystal is obtained by taking microscopic images of the ADC crystal with SEM, measuring the ratio of the axial length to the radial diameter of a single crystal, and statistically analyzing the average value of the crystals, which is the average aspect ratio of the sample.

[0054] The closed-cell rate was tested in accordance with GB / T 10799-2008 "Determination of Open and Closed Cell Volume Percentage of Rigid Foamed Plastics".

[0055] The thermal conductivity of the foamed material was tested in accordance with GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Insulation Materials - Protective Hot Plate Method".

[0056] Particle size distribution span (SPAN) is calculated using the formula SPAN = (D 90 -D 10 ) / D 50 Calculate, where D 10 D 50 D 90 These are the particle size values ​​corresponding to 10%, 50%, and 90% on the cumulative distribution curve, respectively.

[0057] The results in the table show that the average aspect ratio of the crystals in all comparative examples (1-5) with different addition order is less than 3:1, which is much smaller than the aspect ratio of 4.3:1 in Example 1. This indicates that the timing addition strategy of this application is a prerequisite for achieving directional crystal growth. An incorrect order will cause the Gemini surfactant to fail to form effective adsorption sites on the crystal nucleus surface and the β-cyclodextrin to fail to directionally encapsulate the crystal nucleus, thereby losing the ability to directionally control the growth.

[0058] The performance of the comparative examples (6-8) lacking any one component was significantly worse than that of Example 1: when cyclodextrin was missing, there was no growth confinement effect, and the crystals were prone to agglomeration; when the gemini surfactant was missing, there was no molecular bridging effect, and the confinement agent could not bind to the crystal nucleus; when the microspheres were missing, there were no uniform nucleation sites, and the crystals grew randomly. This shows that the three components form a three-level synergistic structure of "crystal nucleus induction-interface anchoring-growth confinement", and none of them can be missing, achieving a regulatory effect of 1+1+1>3.

[0059] Compared with Comparative Example 9, which added a conventional dispersant, Example 1 showed a three-fold increase in crystal aspect ratio, a 24% increase in closed-pore rate, and a 90% reduction in storage agglomeration rate, matching the beneficial effects described in this patent.

[0060] When ADC foaming agent is used in thermal insulation polyurethane foam materials, the uniformity of the foam cells after foaming is ≥95%, the coefficient of variation of the foam cell size is ≤5%, and the thermal conductivity of the material is ≤0.022W / (m·K).

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A time-dependent composite crystal form control agent for particle size regulation of ADC blowing agents, characterized in that, It includes the following three types of components: Melamine-formaldehyde prepolymer microspheres with a particle size of 20–50 nm were used at an amount of 0.2–0.4 wt% of the theoretical yield of ADC. Gemini surfactants containing phosphate ester groups are used at an amount of 0.3–0.6 wt% of the theoretical yield of ADC; Carboxylated β-cyclodextrin was used at an amount of 0.4–0.8 wt% of the theoretical yield of ADC. The three components are added in the following order: melamine-formaldehyde prepolymer microspheres are added 10 minutes before the start of the biuret oxidation reaction; the Gemini surfactant is added 30 minutes after the start of the reaction; and the β-cyclodextrin is added 60 minutes after the start of the reaction.

2. The time-dependent complex crystal form control agent as described in claim 1, characterized in that, The hydrophobic chain length of the gemini surfactant is C. 12 ~C 18 In Gemini surfactants, the linking group between the two hydrophilic groups is an ethoxy group.

3. The time-dependent complex crystal form control agent as described in claim 1, characterized in that, The degree of carboxyl substitution of the β-cyclodextrin is 3 to 6.

4. A method for controlling the particle size of an ADC foaming agent using any one of the time-dependent composite crystal form control agents according to claims 1 to 3, characterized in that, Add the control agent according to the following timing sequence: 10 minutes before the start of the biurea oxidation reaction, add melamine-formaldehyde prepolymer microspheres and stir until homogeneous. 30 minutes after the reaction begins, add the Gemini surfactant and stir until homogeneous. 60 minutes after the reaction begins, add β-cyclodextrin and stir until the reaction is complete.

5. The method as described in claim 4, characterized in that, After adding melamine-formaldehyde prepolymer microspheres, the stirring speed was 300-400 rpm; after adding Gemini surfactant, the stirring speed was 200-300 rpm; and after adding β-cyclodextrin, the stirring speed was 150-200 rpm.

6. The method as described in claim 4, characterized in that, The prepared ADC foaming agent crystals have an aspect ratio ≥3.

7. The application of an ADC blowing agent prepared by any one of claims 4 to 6 in thermal insulation polyurethane foam materials.

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