Foaming-promoting composite heat stabilizer and preparation method thereof

Abstract

The invention belongs to the technical field of chemical stabilizers, and particularly relates to a foaming-promoting type composite heat stabilizer, a preparation method of the foaming-promoting type composite heat stabilizer and application of the foaming-promoting type composite heat stabilizer in a PVC foaming material. The preparation method comprises the following steps: esterifying citric acid by using phthalic anhydride to synthesize citric anhydride, and then synthesizing the citric anhydride and a metal compound to prepare a main heat stabilizer zinc / calcium citrate; secondly, modifying o-cresol formaldehyde epoxy resin through nano zinc oxide to prepare modified o-cresol formaldehyde epoxy resin; citrate zinc / calcium and modified o-cresol formaldehyde epoxy resin are compounded to prepare the foaming-promoting type composite heat stabilizer, and the foaming-promoting type composite heat stabilizer is applied to PVC foaming materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical stabilizers, and particularly relates to a foam-promoting composite heat stabilizer and a preparation method thereof. Background Art

[0002] Polyvinyl chloride (PVC) is a thermoplastic polymer with low price and excellent properties, and is one of the five major general-purpose plastics in the world. PVC foam materials use PVC as the main material, supplemented with other additives, including heat stabilizers, lubricants, plasticizers, fillers, modifiers and other auxiliaries for blending, and then plasticized. They have the advantages of light weight, high strength, strong corrosion resistance, good wear resistance, etc., and are widely used in the fields of energy conservation and insulation, sound reduction and noise reduction, and buffering and vibration reduction.

[0003] The processing temperature of PVC is generally 150 - 230 °C. However, due to the presence of active chlorine atoms (tertiary carbon position chlorine atoms and allyl chlorine atoms) in the PVC structure, PVC begins to decompose at about 90 °C during the processing temperature. The generated hydrogen chloride (HCl) is easily removed from the PVC structure, thereby further catalyzing its degradation, resulting in the product turning from white to black and affecting the service life of the product. Therefore, it is necessary to use a heat stabilizer to inhibit the heat loss caused by high temperature during the PVC processing. Heat stabilizers are generally divided into four categories, including lead salt heat stabilizers, organotin heat stabilizers, metal salt heat stabilizers, and rare earth heat stabilizers, which mainly delay the degradation of PVC in four ways: (1) absorbing HCl generated during the thermal degradation of PVC to prevent the destruction of the polymer chain by HCl; (2) replacing the active chlorine atoms on the PVC polymer chain to prevent the dehydrochlorination reaction; (3) undergoing a D-A addition reaction with conjugated polyenes to form a saturated single bond structure and improve the thermal stability; (4) neutralizing free radicals to prevent the chain reaction initiated by free radicals and slow down the degradation process of PVC.

[0004] Among them, calcium-zinc heat stabilizers are the most used and studied metal salt heat stabilizers. Calcium-zinc heat stabilizers are not only non-toxic and environmentally friendly, but also have a relatively simple synthesis process and good thermal stability performance. However, calcium-zinc heat stabilizers also have some problems, such as poor transparency, poor self-thermal stability, etc., and zinc heat stabilizers will generate a Lewis acid, zinc chloride ( ZnCl2 ), during the action process. This substance will catalyze the formation of HCl, causing "zinc burning" and accelerating the degradation of PVC. In addition, currently widely used calcium-zinc heat stabilizers, such as zinc stearate and calcium stearate heat stabilizers, have poor compatibility with the PVC matrix, which affects the application and promotion of calcium-zinc heat stabilizers. Summary of the Invention

[0005] The purpose of the present invention is to overcome the technical problems of insufficient thermal stability and poor compatibility with the matrix of existing calcium-zinc stabilizers, and to propose a foam-promoting composite heat stabilizer and a preparation method thereof.

[0006] To achieve the above technical objectives, the technical solution provided by the present invention is as follows: A preparation method of a foaming-promoting composite heat stabilizer, comprising the following steps: S1. Using a 15wt% acetic acid solution as a medium, preparing a citric anhydride mixed solution with citric acid and acid anhydride as raw materials, and back-dropping the obtained citric anhydride mixed solution into chloroform, stirring for 30 min until a large amount of white crystals appear in the solution, and obtaining citric anhydride powder after suction filtration, washing, and drying; S2. Mixing the citric anhydride powder with alcohol, stirring and reacting at an oil bath temperature of 85°C for 1.5 h, adding petroleum ether, stirring and reacting for 45 min, centrifuging and drying to obtain modified citric acid powder; S3. Adding a saturated calcium hydroxide solution dropwise to the modified citric acid powder until the pH of the system solution is 10.5. At this time, a large amount of white crystals appear in the system, and after filtration, washing, suction filtration, and drying, calcium citrate is obtained; S4. Using deionized water as a medium, mixing the modified citric acid powder with zinc oxide powder, adding acetic acid dropwise to keep the pH of the solution at 3-4, and stirring and reacting at a water bath temperature of 65°C for 56 h; after the reaction is completed, liquid-solid separation and drying are carried out to obtain zinc citrate; S5. Mixing nano-zinc oxide and silane evenly, adding an o-cresol novolac epoxy resin mixed solution, and stirring and reacting at 110-125°C for 2-4 h; after the reaction is completed, ultrasonic dispersion is carried out on the mixed system at a power of 600 W. After the dispersion is completed, it is cooled to room temperature, and after evaporation, washing, and drying, modified o-cresol novolac epoxy resin is obtained; S6. Mixing zinc citrate, calcium citrate, and modified o-cresol novolac epoxy resin in a mass ratio of 2:3:5 to obtain a foaming-promoting composite heat stabilizer.

[0007] Preferably, in step S1, the acid anhydride is phthalic anhydride, the molar ratio of citric acid to acid anhydride is 1:1.5, and the volume ratio of the citric anhydride mixed solution to chloroform is 1:2.

[0008] Preferably, in step S1, the preparation method of the citric anhydride mixed solution is: mixing citric acid and phthalic anhydride in a molar ratio of 1:1.5, heating and stirring the mixed system in a water bath at 45°C for 24 h, and stopping the reaction until the solution is clear and transparent and there is no color change to obtain the citric anhydride mixed solution.

[0009] Preferably, in step S2, the alcohol organic matter is cetyl alcohol, the mass ratio of citric anhydride powder to cetyl alcohol is 1:10, and the mass ratio of citric anhydride powder to petroleum ether is 1:3.

[0010] Preferably, in step S4, the molar ratio of the modified citric acid powder to the zinc oxide powder is 1-2:1.05.

[0011] Preferably, in step S5, the mass of the nano-zinc oxide is 25%-40% of the mass of the o-cresol novolac epoxy resin mixture; the mass ratio of the silane to the nano-zinc oxide is 1:1.

[0012] Preferably, the preparation method of the o-cresol novolac epoxy resin mixture described in step S5 is as follows: Mix o-cresol and paraformaldehyde evenly and stir, add p-toluenesulfonic acid dropwise to keep the pH of the system at 5-6, heat in a water bath at 85-110 °C under nitrogen protection for 2-4 h. After the reaction, carry out vacuum dehydration and filtration at 0.08 MPa to obtain linear o-cresol novolac resin; mix the o-cresol novolac resin with epichlorohydrin and trioctylmethylammonium chloride, stir and react at a constant temperature of 90 °C for 6 h, and then cool to room temperature; add 15 wt% NaOH solution, place the system in a water bath at 75 °C and react for 2 h. After the reaction is completed, wash with deionized water and carry out vacuum desolvation at 0.05 MPa to obtain the o-cresol novolac epoxy resin mixture.

[0013] Preferably, the molar ratio of the o-cresol to the paraformaldehyde is 1:1.2.

[0014] Preferably, the mass ratio of the o-cresol novolac resin to the epichlorohydrin and the 15 wt% NaOH solution is 1:2:300, and the addition amount of the trioctylmethylammonium chloride is 4% of the mass of the reaction system.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) Phthalic anhydride is used to modify citric acid, the citric anhydride is esterified by cetyl alcohol, and then a zinc / calcium citrate stabilizer is synthesized with metal ions. This avoids the problems that citric acid is difficult to directly synthesize with alcohol organic substances and the reaction products are difficult to control, promotes the synthesis of zinc / calcium citrate diester, and enables the -COO- in calcium citrate diester to more effectively fill the vacancies generated due to the removal of Cl atoms during the aging process of PVC, preventing the generation of double bonds on the PVC chain, thereby slowing down the thermal degradation of the PVC foaming material; (2) The molecular structure of citric acid contains three carboxyl groups and one hydroxyl group. Compared with stearic acid derivatives, it has better compatibility with PVC materials. Therefore, it can form a strong cross-linking effect with the atomic groups in PVC, restricting the thermal movement of the polymer molecular chain and stabilizing the foam cells generated in the PVC material; (3) The hydroxyl group introduced by the phenolic resin in the modified o-cresol novolac epoxy resin combines with epichlorohydrin, which can exhibit excellent high-temperature resistance. After the chlorine radicals in the PVC polymer chain react with the epoxy groups in the epoxy resin, more stable o-chlorohydrin can be generated, playing a better thermal stabilization role; (4)The o-cresol novolac epoxy resin modified by nano-ZnO. Part of the Zn can produce a conjugation effect with the benzene ring connected to the epoxy group, making the o-cresol novolac epoxy resin form a more robust cross-linked network, thus stabilizing the cell structure. On the other hand, the modified o-cresol novolac epoxy resin can provide more bubble nucleation sites, thereby increasing the foaming rate of the PVC foamed plastics and improving the foaming performance. Description of the Drawings

[0016] Figure 1 are the test results of the apparent density of the samples of different embodiments. Detailed Embodiments

[0017] The technical solutions of the present invention will be clearly and completely described below in conjunction with the detailed embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0018] Example 1 A preparation method of a foam-promoting composite heat stabilizer: 1. Preparation of zinc / calcium citrate ester (1) Using 15 wt% acetic acid solution as the medium, citric acid and phthalic anhydride are mixed according to a molar ratio of 1:1.5. The mixed system is stirred and reacted in a water bath at 45 °C for 24 h. After the solution becomes clear and transparent and there is no color change, the reaction is stopped to obtain a mixed solution of citric anhydride. (2) According to the volume ratio of the citric anhydride mixed solution: chloroform of 1:2, the citric anhydride mixed solution is added dropwise to chloroform and stirred for 30 min until a large amount of white crystals appear in the solution. After filtering the obtained crystals with a vacuum filter for 45 min, they are washed with chloroform and then dried in a vacuum drying oven at 45 °C for 4 h to obtain citric anhydride powder. (3) According to a mass ratio of 1:10, the citric anhydride powder and cetyl alcohol are mixed and stirred in an oil bath at 85 °C for 1.5 h until the system becomes a colorless, clear and transparent oily liquid. According to the mass ratio of citric anhydride: petroleum ether of 1:3, petroleum ether is added and stirred for 45 min until a large amount of white crystals are formed. The white crystals are centrifuged for 30 min at a centrifugal speed of 400 rpm. Finally, they are dried in a vacuum drying oven at 65 °C for 12 h to obtain modified citric acid powder. (4 ） Dropwise add saturated A solution was added until the pH of the system solution reached 10.5. At this time, a large amount of white crystals appeared in the system. The white crystals were filtered out using filter paper, washed with deionized water, then filtered by a vacuum filter for 20 min, and sent to an oven to be dried at 50 °C for 2 h to obtain calcium citrate ester; (5)Mix the modified citric acid powder and ZnO powder evenly according to a molar ratio of 1:1.05. Use deionized water to disperse the powder, and add acetic acid to keep the pH of the solution at 3. Stir and react at 65 °C in a water bath for 56 h; After the reaction is completed, perform liquid-solid separation and drying to obtain zinc citrate ester A; 2. Preparation of modified o-cresol novolac epoxy resin (1)Mix o-cresol and paraformaldehyde evenly according to a molar ratio of 1:1.2, add p-toluenesulfonic acid dropwise to keep the pH of the system at 5, and react in a water bath at 85 °C for 2 h under nitrogen protection. After the reaction is completed, perform vacuum dehydration and filtration at 0.08 MPa to obtain linear o-cresol novolac resin; (2)According to the mass ratio of o-cresol novolac resin, epichlorohydrin, and 15 wt% NaOH solution being 1:2:300, and the addition amount of trioctylmethylammonium chloride being 4% of the mass of the reactants, mix o-cresol novolac resin, epichlorohydrin, and trioctylmethylammonium chloride, stir and react at a constant temperature of 90 °C for 6 h, and then cool to room temperature; Add 15 wt% NaOH solution, place the system in a water bath at 75 °C to react for 2 h, cool after the reaction is completed, wash with deionized water, and perform vacuum desolvation at 0.05 MPa to obtain a mixed solution of o-cresol novolac epoxy resin; (3)By weight, take 25 parts of nano-ZnO, 25 parts of silane, and 100 parts of the mixed solution of o-cresol novolac epoxy resin. Mix nano-ZnO and silane evenly, add the mixed solution of o-cresol novolac epoxy resin, and stir and react at 120 °C for 3 h; After stirring, use an ultrasonic disperser to disperse the mixed system at a power of 600 W for 2 h to obtain a mixed solution of modified o-cresol novolac epoxy resin; Evaporate for 40 min using an evaporator to remove excess epichlorohydrin; Wash away the excess impurities with absolute ethanol and deionized water, and obtain modified o-cresol novolac epoxy resin B after drying; 3. By weight, 20 parts of zinc citrate ester A, 30 parts of calcium citrate ester, and 50 parts of modified o-cresol novolac epoxy resin B are compounded to obtain a foaming-promoting composite heat stabilizer C.

[0019] 4. Apply the prepared foaming-promoting composite heat stabilizer to a PVC foaming board: Raw materials: PVC resin: 120 parts, white carbon black: 15 parts, AC: 0.9 part, sodium bicarbonate: 0.4 part, DCP: 9 parts, composite heat stabilizer C: 7 parts, DOP: 10 parts.

[0020] Mix the above raw materials, stir at 80 °C for 2 h in a high-speed mixer, cool, heat and melt at 180 °C through a screw extruder, extrude through a die orifice, cool and shape, and cut to obtain a PVC foam board. Test the heat resistance and foaming properties of the obtained PVC foam board.

[0021] Example 2. A preparation method of a foaming-promoting composite heat stabilizer: The difference from Example 1 is as follows: Change the raw material ratio in process (5) of step 1, and the other steps and conditions are the same as those in Example 1, specifically as follows: In step 1, mix the modified citric acid powder and ZnO powder evenly according to a molar ratio of 2:1.05, disperse the powder with deionized water, add acetic acid dropwise to keep the pH of the solution at 3, and stir and react at 65 °C in a water bath for 56 h; after the reaction, perform liquid-solid separation and drying to obtain zinc citrate ester D; In step 3, according to the parts by weight, 20 parts of zinc citrate D, 30 parts of calcium citrate ester, and 50 parts of modified o-cresol novolac epoxy resin B are compounded to obtain a foaming-promoting composite heat stabilizer E. In step 4, apply the prepared foaming-promoting composite heat stabilizer to the PVC foam board: Raw materials: 120 parts of PVC resin, 15 parts of white carbon black, 0.9 part of AC, 0.4 part of sodium bicarbonate, 9 parts of DCP, 7 parts of composite heat stabilizer C, 10 parts of DOP.

[0022] Mix the above raw materials, stir at 80 °C for 2 h in a high-speed mixer, cool, heat and melt at 180 °C through a screw extruder, extrude through a die orifice, cool and shape, and cut to obtain a PVC foam board. Test the heat resistance and foaming properties of the obtained PVC foam board.

[0023] Example 3. A preparation method of a foaming-promoting composite heat stabilizer: The difference from Example 1 is as follows: Change the raw material ratio in process (3) of step 2, and the other steps and conditions are the same as those in Example 1, specifically as follows: In step 2, according to the parts by weight, take 40 parts of nano-ZnO, 40 parts of silane, and 100 parts of o-cresol novolac epoxy resin mixture. Mix the nano-ZnO and silane evenly, add the o-cresol novolac epoxy resin mixture, and stir and react at 120 °C for 3 h; after stirring, use an ultrasonic disperser to disperse the mixed system at a power of 600 W for 2 h to obtain a modified o-cresol novolac epoxy resin mixture; evaporate for 40 min using an evaporator to remove the excess epichlorohydrin; wash away the excess impurities with absolute ethanol and deionized water, and dry to obtain modified o-cresol novolac epoxy resin F; In Step 3, by weight, 20 parts of zinc citrate A, 30 parts of calcium citrate, and 50 parts of modified o-cresol novolac epoxy resin F are compounded to obtain a foaming-promoting composite heat stabilizer G.

[0024] In Step 4, the prepared foaming-promoting composite heat stabilizer is applied to a PVC foamed board: Raw materials: 120 parts of PVC resin, 15 parts of silica white, 0.9 part of AC, 0.4 part of sodium bicarbonate, 9 parts of DCP, 7 parts of composite heat stabilizer C, and 10 parts of DOP.

[0025] The above raw materials are mixed and stirred in a high-speed mixer at 80 °C for 2 h. After cooling, they are heated and melted at 180 °C by a screw extruder, extruded through a die orifice, cooled and shaped, and cut to obtain a PVC foamed board. The heat resistance and foaming properties of the obtained PVC foamed board are tested.

[0026] Comparative Example 1 A preparation method of a foaming-promoting composite heat stabilizer: The difference from Example 1 is as follows: The raw material ratio in Process (3) of Step 2 is changed, and the mass parts of each component in Step 3 are changed. Other steps and conditions are the same as those in Example 1. Specifically as follows: In Step 2, by weight, 40 parts of nano-ZnO, 40 parts of silane, and 100 parts of o-cresol novolac epoxy resin mixture are taken. The nano-ZnO and silane are mixed evenly, the o-cresol novolac epoxy resin mixture is added, and the mixture is stirred and reacted at 120 °C for 3 h; after stirring, an ultrasonic disperser is used to disperse the mixed system at a power of 600 W for 2 h to obtain a modified o-cresol novolac epoxy resin mixture; the excessive epichlorohydrin is removed by evaporation for 40 min using an evaporator; the excess impurities are washed away with anhydrous ethanol and deionized water, and after drying, modified o-cresol novolac epoxy resin F is obtained; In Step 3, by weight, 0 part of zinc citrate A, 50 parts of calcium citrate, and 50 parts of modified o-cresol novolac epoxy resin F are compounded to obtain a foaming-promoting composite heat stabilizer H.

[0027] In Step 4, the prepared foaming-promoting composite heat stabilizer is applied to a PVC foamed board: Raw materials: 120 parts of PVC resin, 15 parts of silica white, 0.9 part of AC, 0.4 part of sodium bicarbonate, 9 parts of DCP, 7 parts of composite heat stabilizer C, and 10 parts of DOP.

[0028] Mix the above raw materials, stir them at 80 °C for 2 h in a high-speed mixer, cool them, heat and melt them at 180 °C through a screw extruder, extrude them through a die orifice, cool and shape them, and cut them to obtain a PVC foamed board. Test the heat resistance and foaming properties of the obtained PVC foamed board.

[0029] Comparative Example 2 A preparation method of a foam-promoting composite heat stabilizer: The difference from Example 1 is that: The raw material ratio in process (3) of step 2 is changed, and the mass numbers of each component in step 3 are changed. Other steps and conditions are the same as those in Example 1. Specifically as follows: In step 2, according to parts by weight, take 40 parts of nano-ZnO, 40 parts of silane, and 100 parts of o-cresol novolac epoxy resin mixture. Mix nano-ZnO and silane evenly, add the o-cresol novolac epoxy resin mixture, and stir and react at 120 °C for 3 h; after stirring, use an ultrasonic disperser to disperse the mixed system at a power of 600 W for 2 h to obtain a modified o-cresol novolac epoxy resin mixture; evaporate for 40 min using an evaporator to remove excess epichlorohydrin; wash away the excess impurities with absolute ethanol and deionized water, and dry to obtain modified o-cresol novolac epoxy resin F; In step 3, according to parts by weight, 50 parts of zinc citrate A, 0 parts of calcium citrate, and 50 parts of modified o-cresol novolac epoxy resin F are compounded to obtain a foam-promoting composite heat stabilizer I.

[0030] In step 4, apply the prepared foam-promoting composite heat stabilizer to the PVC foamed board: Raw materials: 120 parts of PVC resin, 15 parts of white carbon black, 0.9 part of AC, 0.4 part of sodium bicarbonate, 9 parts of DCP, 7 parts of composite heat stabilizer C, 10 parts of DOP.

[0031] Mix the above raw materials, stir them at 80 °C for 2 h in a high-speed mixer, cool them, heat and melt them at 180 °C through a screw extruder, extrude them through a die orifice, cool and shape them, and cut them to obtain a PVC foamed board. Test the heat resistance and foaming properties of the obtained PVC foamed board.

[0032] Comparative Example 3 A preparation method of a foam-promoting composite heat stabilizer: The difference from Example 1 is that: The raw material ratio in process (3) of step 2 is changed, and the mass numbers of each component in step 3 are changed. Other steps and conditions are the same as those in Example 1. Specifically as follows: In Step 2, 40 parts by weight of nano-ZnO, 40 parts by weight of silane, and 100 parts by weight of o-cresol novolac epoxy resin mixture are taken. The nano-ZnO and silane are mixed evenly, and then the o-cresol novolac epoxy resin mixture is added. The mixture is stirred and reacted at 120 °C for 3 h. After stirring, an ultrasonic disperser is used to disperse the mixed system at a power of 600 W for 2 h to obtain a modified o-cresol novolac epoxy resin mixture. Then, it is evaporated for 40 min using an evaporator to remove the excessive epichlorohydrin. Excess impurities are washed away with absolute ethanol and deionized water, and after drying, modified o-cresol novolac epoxy resin F is obtained. In Step 3, 50 parts by weight of zinc citrate A, 50 parts by weight of calcium citrate, and 0 parts by weight of the modified o-cresol novolac epoxy resin are compounded to obtain a foaming-promoting composite heat stabilizer J.

[0033] In Step 4, the prepared foaming-promoting composite heat stabilizer is applied to a PVC foamed board: Raw materials: 120 parts by weight of PVC resin, 15 parts by weight of white carbon black, 0.9 part of AC, 0.4 part of sodium bicarbonate, 9 parts of DCP, 7 parts of composite heat stabilizer C, and 10 parts of DOP.

[0034] The above raw materials are mixed and stirred in a high-speed mixer at 80 °C for 2 h. After cooling, they are heated and melted at 180 °C through a screw extruder, extruded through a die orifice, cooled and shaped, and cut to obtain a PVC foamed board. The heat resistance and foaming properties of the obtained PVC foamed board are tested.

[0035] Comparative Example 4 A preparation method of a foaming-promoting composite heat stabilizer: The difference from Example 1 is as follows: Process (3) in Step 2 is removed, that is, the modification step of o-cresol novolac epoxy resin is removed; other steps and conditions are the same as those in Example 1. Specifically as follows: In Step 2, the preparation of modified o-cresol novolac epoxy resin: (1) o-Cresol and paraformaldehyde are mixed and stirred evenly according to a molar ratio of 1:1.2, and p-toluenesulfonic acid is added dropwise to adjust the pH of the system to 6. The mixture is heated in a water bath at 110 °C for 4 h under nitrogen protection. After the reaction, vacuum dehydration and filtration are carried out at 0.08 MPa to obtain a linear o-cresol novolac resin. (2) According to the mass ratio of o-cresol novolac resin, epichlorohydrin, and 15 wt% NaOH solution being 1:2:300, and the addition amount of trioctylmethylammonium chloride being 4% of the mass of the reactants, mix o-cresol novolac resin, epichlorohydrin, and trioctylmethylammonium chloride. After stirring and reacting at a constant temperature of 90 °C for 6 h, cool to room temperature, add 15 wt% NaOH solution, place the system in a water bath at 75 °C and react for 2 h. After the reaction is completed, wash with deionized water, carry out vacuum desolvation at 0.05 MPa, and obtain an o-cresol novolac epoxy resin mixture. Evaporate for 40 min using an evaporator to remove the excess epichlorohydrin, and obtain o-cresol novolac epoxy resin L after drying; In step 3, according to the weight parts, 20 parts of zinc citrate A, 30 parts of calcium citrate, and 50 parts of o-cresol novolac epoxy resin L are compounded to obtain a foaming-promoting composite heat stabilizer M.

[0036] In step 4, apply the prepared foaming-promoting composite heat stabilizer to a PVC foamed board: Raw materials: 120 parts of PVC resin, 15 parts of white carbon black, 0.9 part of AC, 0.4 part of sodium bicarbonate, 9 parts of DCP, 7 parts of composite heat stabilizer C, 10 parts of DOP.

[0037] Mix the above raw materials, stir at 80 °C in a high-speed mixer for 2 h, cool, heat and melt at 180 °C through a screw extruder, extrude through a die orifice, cool and shape, and cut to obtain a PVC foamed board. Test the heat resistance and foaming properties of the obtained PVC foamed board.

[0038] (1) Static heat stability test: Conduct the test according to the Congo red method of GB / T 2917-2002, record the time when the Congo red test paper starts to turn blue, which is the static heat stability time, and take the average value after parallel determination 3 times. The test results are shown in Table 1:

[0039] According to the test results in Table 1, the foaming-promoting composite heat stabilizer prepared in this example has good heat resistance. The synergistic effect between zinc citrate, calcium citrate, and the modified o-cresol novolac epoxy resin can effectively inhibit the thermal degradation process of PVC foaming materials and improve the long-term stability of the product.

[0040] In Comparative Example 1, no zinc citrate heat stabilizer is added, and the activity of calcium citrate as the main stabilizer is not high enough. The modified o-cresol epoxy resin as an auxiliary heat stabilizer cannot play a complexing role on the unstable components in the PVC polymer chain, so the thermal stability of the PVC foam material is reduced; in Comparative Example 2, no calcium citrate stabilizer is added. During the reaction of the zinc citrate heat stabilizer, zinc combines with unstable chlorine in the polymer chain to generate zinc chloride, which is a Lewis acid. When its concentration reaches a certain level, it further accelerates the dehydrochlorination and the degradation process; after calcium citrate is added, calcium citrate can undergo a substitution reaction with zinc chloride to inhibit the catalytic degradation of the polymer chain; in Comparative Examples 3 and 4, no modified o-cresol epoxy resin is added and unmodified o-cresol epoxy resin is added, respectively, and their thermal stability also decreases to a certain extent.

[0041] (2) Foaming performance test The prepared PVC foam board was pressed into a plastic film with a length of 2 cm, a width of 2 cm, and a thickness of 2 mm using a sheet press. The film was placed in an oven at 200°C and baked for 100 seconds. After cooling, it was taken out. The cross-sectional area was cut and the number of cells in the cross-sectional area was counted (rounded off), and the average area of ​​a single cell and the average radius of the cell were calculated. The results are shown in Table 2. The apparent density of the sample was tested, and the results are shown in Table 2. Figure 1 shown.

[0042]

[0043] Combination Figure 1 As shown in Table 2, in Comparative Examples 1-4, the number of cells decreases, the cell diameter increases significantly, and the apparent density of the material increases. It is shown that the foaming-promoting heat stabilizer requires the coordination of each component, and the prepared PVC foam material can have better performance. And the foaming performance test results of Comparative Example 2 and Comparative Example 4 show that the number of bubbles in the sample of Example 2 is more, the pore radius is significantly reduced, and the apparent density is significantly reduced. After the nano ZnO is compounded with the o-cresol epoxy resin, the o-cresol epoxy resin loaded with nano ZnO has a significant foaming-promoting effect on the PVC foam material. Citric acid, as a bio-based polycarboxylic acid, contains three carboxyl groups and one hydroxyl group in each molecular structure, can form a strong cross-linking effect with the atomic groups in PVC, and has a limiting effect on the thermal motion of the polymer molecular chain, thereby stabilizing the generated pores, increasing the amount of bubbles in the PVC foam material, and reducing the apparent density of the material, so that the material obtains better functionality.

[0044] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a foaming-promoting composite thermal stabilizer, characterized in that: The following steps are involved: S1, using 15wt% acetic acid solution as a medium, citric acid and anhydride as raw materials to prepare a citric anhydride mixed solution, back-titrifying the obtained citric anhydride mixed solution into chloroform, stirring for 30 minutes until a large amount of white crystals appear in the solution, and obtaining citric anhydride powder after suction filtration, washing and drying; S2, mixing citric anhydride powder with alcohol, stirring and reacting in an oil bath at 85°C for 1.5 hours, adding petroleum ether, stirring and reacting for 45 minutes, centrifuging and drying to obtain modified citric acid powder; S3, adding saturated calcium hydroxide solution to the modified citric acid powder until the pH of the system solution is 10.5, at which time a large amount of white crystals appear in the system, and after filtering, washing, suction filtration and drying, calcium citrate is obtained; S4, using deionized water as a medium, mixing the modified citric acid powder and the zinc oxide powder, adding acetic acid dropwise to keep the pH of the solution at 3-4, and stirring the reaction in a 65°C water bath for 56 hours; after the reaction is completed, liquid-solid separation and drying are performed to obtain zinc citrate; S5, mixing nano zinc oxide and silane evenly, adding the o-cresol epoxy resin mixed solution, stirring and reacting at 110-125° C. for 2-4 hours; after the reaction is completed, ultrasonically dispersing the mixed system, cooling to room temperature after the dispersion is completed, evaporating, washing, and drying to obtain a modified o-cresol epoxy resin; S6. Mix zinc citrate, calcium citrate and modified o-cresol epoxy resin in a mass ratio of 2:3:5 to obtain a foaming-promoting composite thermal stabilizer.

2. The method for preparing the foaming-promoting composite thermal stabilizer according to claim 1, characterized in that: In step S1, the acid anhydride is phthalic anhydride, the molar ratio of citric acid to acid anhydride is 1:1.5, and the volume ratio of the citric anhydride mixed solution to chloroform is 1:

2.

3. The method for preparing the foaming-promoting composite thermal stabilizer according to claim 1, characterized in that: In step S1, the preparation method of the citric anhydride mixed solution is: citric acid and phthalic anhydride are mixed in a molar ratio of 1:1.5, the mixed system is heated in a water bath at 45°C with stirring for 24 hours, and the reaction is stopped when the solution is clear and transparent without color change, to obtain a citric anhydride mixed solution.

4. The method for preparing the foaming-promoting composite thermal stabilizer according to claim 1, characterized in that: In step S2, the alcohol organic substance is hexadecanol, the mass ratio of citric anhydride powder to hexadecanol is 1:10, and the mass ratio of citric anhydride powder to petroleum ether is 1:

3.

5. The method for preparing the foaming-promoting composite thermal stabilizer according to claim 1, characterized in that: In step S4, the molar ratio of the modified citric acid powder to the zinc oxide powder is 1-2:1.

05.

6. The method for preparing the foaming-promoting composite thermal stabilizer according to claim 1, characterized in that: In step S5, the mass of the nano zinc oxide is 25%-40% of the mass of the o-cresol epoxy resin mixed solution; and the mass ratio of silane to the nano zinc oxide is 1:

1.

7. The method for preparing the foaming-promoting composite thermal stabilizer according to claim 1, characterized in that: The preparation method of the o-cresol-formaldehyde epoxy resin mixed solution described in step S5 is as follows: o-cresol and paraformaldehyde are mixed and stirred evenly, toluenesulfonic acid is added dropwise to keep the pH of the system at 5-6, and the reaction is heated in a water bath at 85-110°C under nitrogen protection for 2-4 hours. After the reaction is completed, dehydration and suction filtration are performed under reduced pressure at 0.08MPa to obtain a linear o-cresol-formaldehyde resin; o-cresol-formaldehyde resin is mixed with epichlorohydrin and trioctylmethylammonium chloride, stirred at a constant temperature of 90°C for 6 hours, and then cooled to room temperature; 15wt% NaOH solution is added, and the system is placed in a water bath at 75°C for reaction for 2 hours. After the reaction is completed, it is washed with deionized water, and desolventized at 0.05MPa to obtain an o-cresol-formaldehyde epoxy resin mixed solution.

8. The method for preparing the foaming-promoting composite thermal stabilizer according to claim 7, characterized in that: The molar ratio of o-cresol to paraformaldehyde is 1:1.

2.

9. The method for preparing the foaming-promoting composite thermal stabilizer according to claim 7, characterized in that: The mass ratio of the o-cresol-formaldehyde resin to epichlorohydrin and 15 wt % NaOH solution is 1:2:300, and the added amount of trioctylmethylammonium chloride is 4% of the mass of the reaction system.

10. The foaming-promoting composite thermal stabilizer prepared by the preparation method of the foaming-promoting composite thermal stabilizer according to claim 1.

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