Dolomite compounded active silica filler for engineering plastics and preparation method thereof

Abstract

The application discloses dolomite compounded active silica filler for engineering plastics and a preparation method thereof, and belongs to the technical field of plastics. The method is characterized by the following steps: modifying dolomite powder with chitosan and modifying silica powder with epoxy, and reacting the modified dolomite powder and the modified silica powder in boron trifluoride ether. The epoxy modified silica powder can be deposited between the layers and on the surface of the chitosan modified dolomite, so that the mechanical strength of the dolomite can be improved. The surface deposition of the silica can improve the surface roughness of the dolomite, increase the direct physical contact area with the engineering plastics, avoid the flat crystal cleavage plane of the dolomite particles from being unfavorable to the combination of the matrix and the particle surface, and avoid the micro internal stress concentration formed in the micro area where the sharp edges and corners of the dolomite particles contact with the engineering plastics, so that the micro cracks and macro cracks caused by stress concentration when the material is subjected to macro stress can be avoided.

Description

Technical Field

[0001] This invention belongs to the field of plastics technology, specifically to a dolomite-based active silica filler for engineering plastics and its preparation method. Background Technology

[0002] Engineering plastics can be divided into two categories: general-purpose engineering plastics and special-purpose engineering plastics. The former mainly includes five major general-purpose engineering plastics: polyamide, polycarbonate, polyoxymethylene, modified polyphenylene ether, and thermoplastic polyester. The latter mainly refers to engineering plastics with heat resistance up to 150℃ or higher, including polyimide, polyphenylene sulfide, polysulfone, aromatic polyamide, polyarylate, polyphenylene ester, polyaryletherketone, liquid crystal polymers, and fluoropolymers. However, single-component polyamide engineering plastics often have the disadvantages of insufficient strength or poor wear resistance.

[0003] Dolomite is a calcium carbonate ore containing about 15% magnesium oxide. Dolomite powder has been widely used in the plastics, rubber and other chemical industries to reduce the cost of rubber and plastic products and improve some of their properties. However, during the mechanical processing and crushing of dolomite ore, dolomite undergoes crystal dissociation, resulting in sharp edges and smooth crystals on the surface of the dolomite particles. This reduces its physical properties, such as bulk density and sphericity, and increases porosity and volume when packed. On the other hand, when dolomite powder is used as a filler, the flat crystal cleavage planes of its particles are not conducive to the bonding between the matrix and the particle surface. Moreover, the sharp edges of the dolomite particles are very likely to form micro-stress concentrations in the micro-area of ​​the composite material when in contact with the resin. When the material is subjected to macro-stress, micro-cracks, macro-cracks and even fracture failure may occur due to stress concentration, thus affecting the use of the composite material. Summary of the Invention

[0004] The purpose of this invention is to provide a dolomite-modified active silica filler for engineering plastics and its preparation method. By reacting chitosan-modified dolomite powder and epoxy-modified silica powder in boron trifluoride ether, the epoxy-modified silica powder can be deposited into the interlayer and surface of the chitosan-modified dolomite. This improves the mechanical strength of the dolomite, and the surface deposition of silica increases the surface roughness of the dolomite, increasing the physical contact area with the engineering plastics. This avoids the flat crystal cleavage planes of the dolomite particles hindering the bonding between the matrix and the particle surface, and prevents micro-stress concentration in the micro-regions where the sharp edges of the dolomite particles contact the engineering plastics. Therefore, it avoids micro-cracks and macro-cracks caused by stress concentration when the material is subjected to macro-stress.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] The preparation method of dolomite-compounded active silica filler for engineering plastics includes the following steps:

[0007] Step 1: Graft lipoic acid onto chitosan through a dehydration condensation reaction between the amino groups on chitosan and the carboxyl groups on lipoic acid, resulting in a modified chitosan solution containing disulfide bonds.

[0008] Step 2: After grinding and sieving the dolomite powder, pretreated dolomite powder is obtained. This powder is then mixed with a modified chitosan solution and precipitated to prepare chitosan-modified dolomite powder.

[0009] Step 3: Treat the nano-silica powder with γ-glycidyl etheroxypropyltrimethoxysilane to obtain epoxy-modified silica powder; then, through the ring-opening combination of the hydroxyl groups on the surface of the chitosan-modified dolomite powder and the epoxy groups on the surface of the epoxy-modified silica powder under the action of boron trifluoride ether, a dolomite-based active silica filler is obtained.

[0010] Furthermore, the specific preparation steps of the modified chitosan solution are as follows:

[0011] Chitosan and deionized water are added to a reaction vessel and stirred for 10-12 minutes at 60-70℃ and 500-600 rpm. Then, acetic acid with a concentration of 1 mol / L is added to adjust the pH to 3-4 to obtain a chitosan solution. The chitosan solution, thioctic acid, and sodium hydroxide are added to the reaction vessel and stirred for 30-40 minutes at 20-25℃ and 500-600 rpm. Then, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide are added and stirred for another 20-30 minutes. Anhydrous ethanol is then added as a desiccant and the reaction is continued for 16-17 hours to obtain a modified chitosan solution containing disulfide bonds.

[0012] Furthermore, the ratio of chitosan, deionized water, and acetic acid is 5-6g: 200-240mL: 1-2mL.

[0013] Furthermore, the ratio of chitosan solution, thioctic acid, sodium hydroxide, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride, N-hydroxysuccinimide, and anhydrous ethanol is 200-250 mL: 1-1.2 g: 1-2 g: 1.2-1.8 g: 1.4-1.6 g: 75-80 mL.

[0014] Furthermore, the specific preparation steps for chitosan-modified dolomite powder are as follows:

[0015] Dolomite powder was ground and passed through an 800-1200 mesh sieve to obtain pretreated dolomite powder. Potassium dihydrogen phosphate, modified chitosan solution and pretreated dolomite powder were added to a reaction vessel and stirred for 1-2 hours at 30-40℃ and 500-600 r / min. After centrifugation at 5000-6000 r / min for 4-5 minutes, the mixture was filtered, the precipitate was collected, and the filter cake was washed 2-3 times with deionized water and anhydrous ethanol, respectively. The mixture was then vacuum dried at 60-70℃ for 1-2 hours to obtain chitosan-modified dolomite powder.

[0016] Furthermore, the ratio of potassium dihydrogen phosphate, modified chitosan solution, and pretreated dolomite powder is 5-6g: 200-300mL: 30-40g.

[0017] Furthermore, the specific preparation steps for epoxy-modified silica powder are as follows:

[0018] Deionized water, anhydrous ethanol, and γ-glycidyl etheroxypropyltrimethoxysilane were added to a reaction vessel and stirred for 40-50 min at 20-25℃ and 500-600 r / min to obtain a mixed solution. 180-200 g of nano-silica powder with a particle size of 50-60 nm, 120-200 mL of deionized water, and 160-180 mL of anhydrous ethanol were added to the reaction vessel and stirred for 10-12 min at 20-25℃ and 500-600 r / min. Then, 600-800 mL of the mixed solution was added, and stirring was continued for 2-3 h. After the reaction was completed, the product was vacuum filtered using a circulating water multi-purpose vacuum pump. The filter cake was washed 2-3 times with deionized water and anhydrous ethanol and vacuum dried at 60-70℃ for 1-2 h to obtain epoxy-modified silica powder.

[0019] Furthermore, the ratio of deionized water, anhydrous ethanol, and γ-glycidoxypropyltrimethoxysilane is 100-120 mL: 800-900 mL: 9-10 mL.

[0020] Furthermore, the specific preparation steps for dolomite-compounded activated silica filler are as follows:

[0021] Chitosan-modified dolomite powder, epoxy-modified silica powder, and N,N-methylformamide were added to a polytetrafluoroethylene reactor and stirred for 40-50 minutes at 20-25℃ and 500-600 rpm. Then, boron trifluoride diethyl ether was added as a catalyst, and the mixture was heated to 65-70℃ and reacted for another 2-3 hours. A 25-30% sodium hydroxide solution was then added, and the reaction was continued for another 2-3 hours. The mixture was centrifuged at 5000-6000 rpm for 4-5 minutes, filtered, and the precipitate was collected. The filter cake was washed 2-3 times with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 60-70℃ for 1-2 hours to obtain the dolomite-composite active silica filler.

[0022] Furthermore, the ratio of chitosan-modified dolomite powder, epoxy-modified silica powder, N,N-methylformamide, boron trifluoride ether, and sodium hydroxide solution is 40-50g: 50-60g: 500-600mL: 1-2g: 30-40mL.

[0023] The beneficial effects of this invention are:

[0024] 1. The dolomite-based active silica filler prepared by this invention, when applied to engineering plastics, can significantly improve the tensile and flexural strength of engineering plastics and reduce wear.

[0025] 2. The dolomite-modified active silica filler of the present invention, through the reaction of chitosan-modified dolomite powder and epoxy-modified silica powder in boron trifluoride ether, allows the epoxy-modified silica powder to be deposited into the interlayer and surface of the chitosan-modified dolomite, thereby improving the mechanical strength of the dolomite. The surface deposition of silica can improve the surface roughness of the dolomite, increase the physical contact area with the engineering plastic, avoid the flat crystal cleavage planes of the dolomite particles being unfavorable to the bonding between the matrix and the particle surface, and avoid the micro-stress concentration formed in the micro-regions where the sharp edges of the dolomite particles contact the engineering plastic, thus preventing the material from developing micro-cracks and macro-cracks due to stress concentration when subjected to macro-stress.

[0026] 3. The dolomite compounded active silica filler of the present invention contains chitosan on its surface. Chitosan has a certain swelling effect. During the mechanical processing and crushing of dolomite, the dolomite will undergo crystal dissociation, thereby forming sharp edges and smooth crystals on the surface of the dolomite particles. This reduces its physical properties such as loose density and sphericity, increases porosity and volume when packed, and the swelling effect of chitosan can help fill the pores between the dolomite particles.

[0027] 4. In the chitosan-modified dolomite powder of the present invention, a dehydration condensation reaction is carried out between the amino groups on chitosan and the carboxyl groups on lipoic acid to obtain chitosan containing disulfide bonds, which coats the dolomite powder. The presence of disulfide bonds can endow the dolomite compounded with active silica filler with self-healing properties. During the process of chitosan coating the dolomite powder, the calcium and magnesium ions carried on the surface of the dolomite powder itself will coordinate with some of the hydroxyl groups in chitosan, promoting the coating of chitosan. Furthermore, the presence of calcium ions can promote the cross-linking of chitosan. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1: A method for preparing dolomite-compounded activated silica filler for engineering plastics, comprising the following steps:

[0030] S1: Add 6g of chitosan and 240mL of deionized water to a reaction vessel and stir for 12min at 70℃ and 600r / min. Then add 2mL of 1mol / L acetic acid and adjust the pH to 4 to obtain a chitosan solution. Add 250mL of chitosan solution, 1.2g of lipoic acid and 2g of sodium hydroxide to a reaction vessel and stir for 40min at 25℃ and 600r / min. Then add 1.8g of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and 1.6g of N-hydroxysuccinimide and continue stirring for 30min. Then add 80mL of anhydrous ethanol as a desiccant and continue stirring for 17h to obtain a modified chitosan solution containing disulfide bonds.

[0031] S2: Grind dolomite powder through a 1200-mesh sieve to obtain pretreated dolomite powder; add 6g potassium dihydrogen phosphate, 300mL modified chitosan solution and 40g pretreated dolomite powder to a reaction vessel, stir for 2h at 40℃ and 600r / min, centrifuge at 6000r / min for 5min, filter, collect the precipitate, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and vacuum dry at 70℃ for 2h to obtain chitosan modified dolomite powder.

[0032] S3: Add 120 mL of deionized water, 900 mL of anhydrous ethanol and 10 mL of γ-glycidoxypropyltrimethoxysilane (KH-550) to the reaction vessel and stir for 50 min at 25 °C and 600 r / min to obtain a mixed solution; add 200 g of 60 nm nano-silica powder, 200 mL of deionized water and 180 mL of anhydrous ethanol to the reaction vessel and stir for 12 min at 25 °C and 600 r / min, then add 800 mL of the mixed solution and continue stirring for 3 h. After the reaction is completed, vacuum filter the product using a circulating water multi-purpose vacuum pump, wash the filter cake three times with deionized water and anhydrous ethanol, and vacuum dry at 70 °C for 2 h to obtain epoxy-modified silica powder.

[0033] S4: Add 50g of chitosan-modified dolomite powder, 60g of epoxy-modified silica powder, and 600mL of N,N-methylformamide to a polytetrafluoroethylene reactor. Stir for 50min at 25℃ and 600r / min. Then add 2g of boron trifluoride diethyl ether as a catalyst, heat to 70℃, and continue the reaction for 3h. Then add 40mL of 30% sodium hydroxide solution and continue the reaction for 3h. Centrifuge at 6000r / min for 5min, filter, collect the precipitate, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and vacuum dry at 70℃ for 2h to obtain dolomite-composite active silica filler.

[0034] Example 2: This example provides a method for preparing dolomite-compounded active silica filler for engineering plastics. The difference from Example 1 is that in step S1, the ratio of chitosan solution, thioctic acid, sodium hydroxide, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride, N-hydroxysuccinimide and anhydrous ethanol is 220mL:1.1g:1.2g:1.6g:1.5g:78mL.

[0035] Example 3: This example provides a method for preparing dolomite-compounded active silica filler for engineering plastics. The difference from Example 1 is that the ratio of potassium dihydrogen phosphate, modified chitosan solution and pretreated dolomite powder in step S2 is 5.6g:250mL:35g.

[0036] Example 4: This example provides a method for preparing dolomite-compounded active silica filler for engineering plastics. The difference from Example 1 is that the ratio of deionized water, anhydrous ethanol and γ-glycidoxypropyltrimethoxysilane in step S3 is 110mL:820mL:9.5mL.

[0037] Example 5: This example provides a method for preparing dolomite-modified active silica filler for engineering plastics. The difference from Example 1 is that in step S4, the ratio of chitosan-modified dolomite powder, epoxy-modified silica powder, N,N-methylformamide, boron trifluoride ether, and sodium hydroxide solution is 45g:55g:550mL:1.2g:35mL.

[0038] Comparative Example 1: Based on Example 3, the modified chitosan solution in step S2 was replaced with the chitosan solution in step S1, while the other steps remained unchanged, to prepare a dolomite-composite active silica filler.

[0039] Comparative Example 2: Based on Example 3, the chitosan-modified dolomite powder in step S4 was replaced with the pretreated dolomite powder in step S2, while the other steps remained unchanged, to prepare a dolomite-composite active silica filler.

[0040] Comparative Example 3: Based on Example 3, the epoxy-modified silica powder in step S4 was replaced with the nano silica powder in step S3, while the other steps remained unchanged, to prepare a dolomite-composite active silica filler.

[0041] The performance of the dolomite-based activated silica fillers prepared in Examples 1-5 and Comparative Examples 1-3 was tested. Polyamide, epoxidized soybean oil, and the dolomite-based activated silica filler were mixed at a mass ratio of 26:1.2:2.5 and placed in a plasticizer. The mixture was plasticized at 130°C for 4 minutes, then extruded and granulated using an injection molding machine to obtain engineering plastics. Tensile strength was tested according to ASTM D638, flexural strength according to ASTM D790A, and abrasion resistance according to ASTM G99. The results are shown in Table 1.

[0042] Table 1. Test Results of Engineering Plastics

[0043]

[0044] As can be seen from Table 1, the dolomite-composite active silica fillers prepared in Examples 1-5 and Comparative Examples 1-3 can significantly improve the tensile strength and flexural strength of engineering plastics and reduce wear when applied to engineering plastics.

[0045] In Comparative Example 1, the modified chitosan solution was replaced with a chitosan solution. The coordination between the unmodified chitosan and dolomite was weak, and the coating layer was easy to fall off. In addition, the interfacial bonding with epoxy-modified silica was insufficient, which made the interface easy to peel off under stress. Due to the poor swelling properties of unmodified chitosan, it could not effectively fill the pores of dolomite particles, and the friction between particles increased. At the same time, the surface roughness was insufficient, the contact with the plastic matrix was not tight, the sliding resistance increased, and the lack of disulfide bonds caused microcracks to fail to heal. Engineering plastics are prone to microcracks under cyclic stress.

[0046] In Comparative Example 2, chitosan-modified dolomite powder was replaced with pretreated dolomite powder. Because the dolomite surface was not coated with chitosan, the reaction sites with epoxy-modified silica were missing, and silica could not be effectively deposited into the interlayer and surface. This resulted in weak interfacial bonding between dolomite and silica, making it prone to particle debonding under stress. The sharp edges and smooth cleavage surfaces of the original dolomite surface were not modified, which easily caused severe abrasive wear when in contact with the plastic matrix, leading to increased wear. The sharp edges of the uncoated dolomite particles formed high stress concentration in the micro-regions where they bonded with the plastic matrix, making it easy for cracks to initiate from the edges when the material was subjected to external forces, which macroscopically manifested as brittle fracture.

[0047] In Comparative Example 3, epoxy-modified silica powder was replaced with nano-silica powder. Because the surface of unmodified silica lacks epoxy groups, it cannot form covalent bonds with the hydroxyl groups of chitosan and can only rely on physical adsorption deposition. This results in weak bonding force between silica and dolomite surfaces / layers, making it easy to fall off under stress and unable to play a reinforcing role. The surface of unmodified silica is highly polar and has poor compatibility with the hydrophobic plastic matrix, leading to uneven dispersion and the formation of local agglomerates. During sliding, the agglomerates increase frictional resistance, resulting in increased wear.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing dolomite-compounded activated silica filler for engineering plastics, characterized in that, Includes the following steps: Step 1: By the dehydration condensation reaction between the amino groups on chitosan and the carboxyl groups on lipoic acid, lipoic acid is grafted onto chitosan to obtain a modified chitosan solution containing disulfide bonds. Step 2: After grinding and sieving the dolomite powder, pretreated dolomite powder is obtained. This powder is then mixed with a modified chitosan solution and precipitated to prepare chitosan-modified dolomite powder. Step 3: Treat the nano silica powder with γ-glycidyl etheroxypropyltrimethoxysilane to obtain epoxy-modified silica powder; then, through the ring-opening combination of the hydroxyl groups on the surface of the chitosan-modified dolomite powder and the epoxy groups on the surface of the epoxy-modified silica powder under the action of boron trifluoride ether, dolomite composite active silica filler is obtained. The specific preparation steps of the modified chitosan solution are as follows: Chitosan and deionized water are added to a reaction vessel and stirred for 10-12 minutes at 60-70℃ and 500-600 rpm. Then, 1 mol / L acetic acid is added to adjust the pH to 3-4 to obtain a chitosan solution. The chitosan solution, thioctic acid, and sodium hydroxide are added to the reaction vessel and stirred for 30-40 minutes at 20-25℃ and 500-600 rpm. Then, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide are added and stirred for another 20-30 minutes. Finally, anhydrous ethanol is added as a desiccant and the reaction is continued for 16-17 hours to obtain a modified chitosan solution. The specific preparation steps for the chitosan-modified dolomite powder are as follows: Dolomite powder was ground and passed through an 800-1200 mesh sieve to obtain pretreated dolomite powder. Potassium dihydrogen phosphate, modified chitosan solution and pretreated dolomite powder were added to a reaction vessel and stirred for 1-2 hours at 30-40℃ and 500-600 r / min. After centrifugation at 5000-6000 r / min for 4-5 minutes, the mixture was filtered, the precipitate was collected, and the filter cake was washed 2-3 times with deionized water and anhydrous ethanol, respectively. The mixture was then vacuum dried at 60-70℃ for 1-2 hours to obtain chitosan-modified dolomite powder. The specific preparation steps for the dolomite-compounded active silica filler are as follows: Chitosan-modified dolomite powder, epoxy-modified silica powder, and N,N-methylformamide were added to a polytetrafluoroethylene reactor and stirred for 40-50 minutes at 20-25℃ and 500-600 rpm. Then, boron trifluoride ether was added, and the mixture was heated to 65-70℃ and reacted for another 2-3 hours. Next, a 25-30% sodium hydroxide solution was added, and the reaction was continued for another 2-3 hours. The mixture was then centrifuged at 5000-6000 rpm for 4-5 minutes, filtered, and the precipitate was collected. The filter cake was washed 2-3 times with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 60-70℃ for 1-2 hours to obtain the dolomite-composite active silica filler.

2. The method for preparing dolomite-compounded activated silica filler for engineering plastics according to claim 1, characterized in that, The ratio of chitosan, deionized water, and acetic acid is 5-6g: 200-240mL: 1-2mL; the ratio of chitosan solution, lipoic acid, sodium hydroxide, N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride, N-hydroxysuccinimide, and anhydrous ethanol is 200-250mL: 1-1.2g: 1-2g: 1.2-1.8g: 1.4-1.6g: 75-80mL.

3. The method for preparing dolomite-compounded active silica filler for engineering plastics according to claim 1, characterized in that, The ratio of potassium dihydrogen phosphate, modified chitosan solution, and pretreated dolomite powder is 5-6g: 200-300mL: 30-40g.

4. The method for preparing dolomite-compounded active silica filler for engineering plastics according to claim 1, characterized in that, The specific preparation steps for the epoxy-modified silica powder are as follows: Deionized water, anhydrous ethanol, and γ-glycidyl etheroxypropyltrimethoxysilane were added to a reaction vessel and stirred for 40-50 min at 20-25℃ and 500-600 r / min to obtain a mixed solution. 180-200 g of nano-silica powder with a particle size of 50-60 nm, 120-200 mL of deionized water, and 160-180 mL of anhydrous ethanol were added to the reaction vessel and stirred for 10-12 min at 20-25℃ and 500-600 r / min. Then, 600-800 mL of the mixed solution was added, and stirring was continued for 2-3 h. After the reaction was completed, the product was vacuum filtered using a circulating water multi-purpose vacuum pump. The filter cake was washed 2-3 times with deionized water and anhydrous ethanol and vacuum dried at 60-70℃ for 1-2 h to obtain epoxy-modified silica powder.

5. The method for preparing dolomite-compounded active silica filler for engineering plastics according to claim 4, characterized in that, The ratio of deionized water, anhydrous ethanol, and γ-glycidoxypropyltrimethoxysilane is 100-120 mL: 800-900 mL: 9-10 mL.

6. The method for preparing dolomite-compounded activated silica filler for engineering plastics according to claim 1, characterized in that, The ratio of chitosan-modified dolomite powder, epoxy-modified silica powder, N,N-methylformamide, boron trifluoride ether, and sodium hydroxide solution is 40-50g: 50-60g: 500-600mL: 1-2g: 30-40mL.

7. A dolomite-compounded activated silica filler for engineering plastics, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

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