Modified off-line chopped glass fiber for reinforcing polyphenylene sulfide and method for preparing the same

Abstract

The present application relates to the technical field of glass fiber preparation, in particular to a kind of modified off-line chopped glass fiber for reinforcing polyphenylene sulfide and a preparation method thereof.The modified off-line chopped glass fiber includes glass fiber matrix and composite coating layer covering its outer surface, and the composite coating layer is formed by main sizing agent and iron ion surface treatment solution;The present application is by main sizing agent sizing, pre-drying, iron ion outer layer treatment and final drying, constructs the partition membrane layer of inner layer flexibility and outer layer shear resistance, improves the interfacial bonding strength of glass fiber and polyphenylene sulfide, reduces the hairiness and plugging risk in off-line chopping and side feeding process, and improves the mechanical properties of composite material.

Description

Technical Field

[0001] This invention relates to the field of glass fiber preparation technology, specifically to a modified offline chopped glass fiber for polyphenylene sulfide reinforcement and its preparation method. Background Technology

[0002] Polyphenylene sulfide (PPS) possesses excellent heat resistance, chemical resistance, and dimensional stability, making it widely used in electronics, automotive, and aerospace industries. To improve its mechanical strength and resistance to heat deformation, it is typically reinforced with offline chopped glass fibers. The sizing agent directly affects the fiber bundle structure, chopped fiber integrity, processing adaptability, and the quality of the interfacial bonding with PPS.

[0003] Existing waterborne polyurethane film-forming agents possess good film-forming properties, flexibility, and environmental friendliness; however, their molecular chains are mostly aliphatic polyesters or polyethers, which have insufficient compatibility with the aromatic backbone of polyphenylene sulfide. During melt blending above 300°C, conventional films struggle to form highly compatible interfaces, leading to insufficient resin wetting and low interfacial force transfer efficiency, thus limiting the bending and impact properties of the composite material. Furthermore, these films are susceptible to fuzzing due to frictional shearing during offline cutting, vibration dispersion, and pneumatic conveying, causing feeding fluctuations, screw entanglement, and even blockage.

[0004] Existing technologies have attempted to introduce catechin or boric acid groups to improve the adhesion of glass fiber surfaces and impart dynamic cross-linking capabilities to the membrane. However, free catechins are prone to self-oxidative polymerization during emulsion storage and sizing, leading to increased viscosity or even gelation; free boric acid tends to migrate to the membrane surface during drying, resulting in uneven distribution and eventual detachment and failure under high shear conditions. If the spatial distribution and reaction sequence of these two substances are not controlled, it can also easily cause bulk cross-linking and premature hardening of the membrane, thereby increasing short-cut hairs.

[0005] Furthermore, while directly adding metal ions such as iron and copper ions to the wetting agent can enhance the coordination of phenolic hydroxyl groups, it easily triggers localized gelation during the formulation stage, making the overall film layer hard and brittle, and making it difficult to form a differentiated structure with a flexible inner layer and a shear-resistant outer layer. Therefore, existing technologies still lack a comprehensive solution that enables waterborne polyurethane film-forming agents to simultaneously possess a polyphenylene sulfide compatible interface, dynamic buffering and locking of the inner layer, and shear-resistant locking of the outer layer without changing conventional equipment. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a modified offline chopped glass fiber for polyphenylene sulfide reinforcement and its preparation method, so as to solve the problem of how to improve the interfacial bonding strength between glass fiber and polyphenylene sulfide without changing the existing drawing, drying, chopping and side feeding equipment, and reduce the risk of fuzz and blockage in the dry conveying process, so that the fiber has both bundle stability and dispersion uniformity in melt processing.

[0007] To achieve the above objectives, the present invention provides a modified offline chopped glass fiber for polyphenylene sulfide reinforcement. The modified offline chopped glass fiber comprises a glass fiber matrix and a composite coating covering the outer surface of the glass fiber matrix. The composite coating is formed by a main wetting agent and an iron ion surface treatment solution. The main wetting agent comprises the following raw materials in parts by weight: 91,500-92,500 parts deionized water, 15-25 parts glacial acetic acid, 330-370 parts coupling agent, 6,500-7,500 parts modified waterborne polyurethane film-forming agent, 180-220 parts lubricant, and 20-40 parts pH adjuster. The iron ion surface treatment solution comprises the following components in parts by weight... The raw materials are prepared as follows: 9985-9991 parts deionized water, 6-10 parts ferric chloride hexahydrate, and 3-5 parts trisodium citrate dihydrate; the modified waterborne polyurethane film-forming agent is obtained by addition reaction and chain extension reaction of polycarbonate diol, isophorone diisocyanate and 4,4'-thiodiphenol to obtain carboxylated waterborne polyurethane containing aromatic sulfides, and the carboxylated waterborne polyurethane containing aromatic sulfides is then grafted with dopamine hydrochloride and 3-aminophenylboronic acid salt through amidation reaction, and then subjected to borate esterification reaction with 4-hydroxyphenylboronic acid to obtain the final product; preferably, the coupling agent is one of polyphenylene sulfide silane, ether silane and aminosilane.

[0008] Preferably, the lubricant is one of quaternary ammonium salts, siloxanes, or polyethylene glycols.

[0009] Preferably, the pH of the primary wetting agent is 5-6.

[0010] Preferably, the modified offline chopped glass fiber reinforced with polyphenylene sulfide has a moisture content of ≤1‰ and a combustible content of 3‰-6‰.

[0011] Preferably, the weight ratio of the polycarbonate diol, 2,2-dimethylolpropionic acid, isophorone diisocyanate and 4,4'-thiodiphenol is 480-520:32-38:145-155:18-22.

[0012] Preferably, the weight ratio of the carboxylated waterborne polyurethane containing aromatic sulfide, dopamine hydrochloride, 3-aminophenylboronic acid salt and 4-hydroxyphenylboronic acid is 1900-2100:12-16:5-7:5-7.

[0013] Preferably, the preparation of the carboxylated waterborne polyurethane containing aromatic sulfides specifically includes: mixing polycarbonate diol, 2,2-dimethylolpropionic acid and a portion of N-methylpyrrolidone and dehydrating them; after cooling, purging with nitrogen gas, adding isophorone diisocyanate and dibutyltin dilaurate for a first addition reaction; then dissolving 4,4'-thiodiphenol in the remaining N-methylpyrrolidone and adding it to continue a second addition reaction; after cooling, adding triethylamine for a neutralization reaction to form a prepolymer; finally adding deionized water for phase inversion emulsification, adding an aqueous solution of ethylenediamine for chain extension reaction, to obtain a carboxylated waterborne polyurethane emulsion containing aromatic sulfides; Preferably, the temperature of the first addition reaction is 75-85℃, and the reaction time is 100-140 min.

[0014] Preferably, after adding 4,4'-thiodiphenol, the reaction continues at 80-90°C for 150-210 min.

[0015] Preferably, the neutralization temperature is 40-50℃, and the stirring time is 20-40 minutes.

[0016] Preferably, the emulsification stirring speed is 1000-1400 r / min, and the dispersion time is 30-50 min.

[0017] Preferably, the chain extension temperature is 30-40℃ and the time is 50-70min.

[0018] Preferably, the amidation reaction specifically includes: adjusting the pH of the carboxylated aqueous polyurethane emulsion containing aromatic sulfides to 5-6; after activation by EDC and NHS, adding dopamine hydrochloride and 3-aminophenylborate acid salt to carry out the amidation reaction to obtain a catechol-boric acid grafted aqueous polyurethane emulsion. Preferably, the activation temperature is 20-30℃ and the activation time is 20-40 min.

[0019] Preferably, the amidation reaction is carried out at a temperature of 25-35°C for 300-420 minutes, and the reaction is protected from light and purged with nitrogen.

[0020] The borate esterification reaction specifically includes: adding a pre-prepared 4-hydroxyphenylboronic acid solution to the emulsion after the amidation reaction to carry out the borate esterification reaction, then adding ammonia water to adjust the pH to alkaline, then adding glacial acetic acid aqueous solution to adjust it back to weakly acidic; finally removing ethanol and adding deionized water to obtain the modified waterborne polyurethane film-forming agent.

[0021] The 4-hydroxyphenylboronic acid solution comprises, by weight, 5-7 parts of 4-hydroxyphenylboronic acid, 90-110 parts of ethanol, 30-50 parts of deionized water, and 6-10 parts of triethylamine.

[0022] Preferably, the borate esterification reaction is carried out at a temperature of 20-30°C and stirred for 15-25 minutes.

[0023] Preferably, the amount of ammonia added is 5% to adjust the pH to 8 and maintain it for 10-20 minutes.

[0024] Preferably, the concentration of the added glacial acetic acid aqueous solution is 5% to adjust the pH to 5-6.

[0025] Preferably, the conditions for ethanol removal are: 40-50℃, -85~-75kPa, and 20-40min.

[0026] Preferably, the modified waterborne polyurethane film-forming agent has a solid content of 34%-38%.

[0027] Furthermore, the present invention also provides a method for preparing modified offline chopped glass fibers for polyphenylene sulfide reinforcement, comprising the following steps: (1) Preparation of carboxylated aqueous polyurethane emulsion containing aromatic sulfides; (2) Preparation of a catechol-boric acid grafted aqueous polyurethane emulsion; (3) Preparation of modified waterborne polyurethane film-forming agent; (4) Preparation of main wetting agent: deionized water, glacial acetic acid and γ-glycidyl etheroxypropyltrimethoxysilane are mixed and hydrolyzed, modified waterborne polyurethane film-forming agent and lubricant are added, the pH is adjusted to 5-6 with ammonia water, and deionized water is added to obtain the main wetting agent. (5) Preparation of iron ion surface treatment solution: Deionized water, ferric chloride hexahydrate and trisodium citrate dihydrate are mixed and stirred to dissolve, and a clear brownish-yellow iron ion surface treatment solution is obtained. (6) Glass fiber drawing and main sizing agent coating: The glass liquid is drawn into glass fiber monofilaments by using the E glass tank furnace drawing process; the main sizing agent is applied by coating during the drawing process so that the sizing agent is evenly distributed on the surface of the glass fiber. (7) Pre-drying and iron ion outer layer locking: The glass fiber filaments coated with the main sizing agent are pre-dried, and then an iron ion surface treatment solution is applied to the outer layer of the pre-dried yarn bundle, and then dried to obtain modified glass fiber filaments. (8) Offline shaving and final drying: After rehydration, the modified glass fiber filament is cut into short glass fibers of 4-5 mm length using an offline chopped process. After vibration dispersion, the fibers are further dried to obtain modified offline chopped glass fibers for polyphenylene sulfide reinforcement.

[0028] Preferably, the glass fiber monofilament has a diameter of 9-11 μm.

[0029] Preferably, the amount of the main impregnating agent applied is 10-14 kg based on 100 kg of dry glass fiber.

[0030] Preferably, the pre-drying temperature is 90-100℃ and the time is 15-25 min.

[0031] Preferably, the amount of iron ion surface treatment solution applied is 1.5-2.5 kg per 100 kg of dry glass fiber.

[0032] Preferably, the drying temperature is 120-130℃ and the time is 100-140 min.

[0033] Preferably, the moisture content of the rehydrated modified glass fiber precursor is 3‰-4‰.

[0034] Preferably, the final drying temperature is 100-110℃ and the time is 20-40 min.

[0035] The beneficial effects of this invention are: This invention introduces 4,4'-thiodiphenol into the main chain of an aqueous polyurethane film-forming agent to form an aromatic sulfide hard segment, giving the glass fiber surface film a structure similar to that of polyphenylene sulfide (PPS). Therefore, during the high-temperature melt impregnation process of PPS, the film no longer merely acts as an inert barrier layer, but can promote resin wetting and participate in interfacial stress transfer, thereby improving the interfacial bonding strength between the glass fiber and PPS.

[0036] This invention grafts catechol sites provided by dopamine hydrochloride and fixed boric acid sites provided by 3-aminophenylboronic acid salt onto the waterborne polyurethane molecular chain, which can reduce the self-oxidation of free catechols and the migration and precipitation of free boric acid. The subsequently added 4-hydroxyphenylboronic acid serves as a free boric acid site, complementing the fixed boric acid sites, giving the inner layer of the membrane both stable anchoring and dynamic buffering capabilities, and preventing premature gelation of the wetting agent.

[0037] This invention separately prepares iron ions as a surface treatment solution, which is then applied to the outer surface of the yarn bundle after coating with the main wetting agent and pre-drying. This allows the iron ions to primarily coordinate with the outer catechol sites, forming a shear-resistant protective layer, while the interior of the membrane retains its flexibility. This partitioned structure reduces the risk of fuzzing and material blockage during offline shaving, vibration dispersion, loss-in-weight metering, and side-feeding processes.

[0038] In summary, this invention, through the process sequence of "sizing with main sizing agent - pre-drying - iron ion outer layer treatment - final drying," constructs a membrane structure with a flexible inner layer and a shear-resistant outer layer without significantly increasing equipment complexity. This allows the glass fibers to remain bundled and stable during dry conveying and to be appropriately dispersed during polyphenylene sulfide melt extrusion, thereby achieving a comprehensive improvement in low fuzz, stable feeding, and high interfacial force transfer. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0040] All raw materials used in this embodiment are commonly available in the Chinese market. Polycarbonate diol: Desmophen C 1200, hydroxyl value 56 mg KOH / g, hydroxyl equivalent 1000 g / eq, density at 20℃ approximately 1 g / mL; γ-glycidyl etheroxypropyltrimethoxysilane: Shin-Etsu KBM-403; polyethylene glycol lubricant: Dow CARBOWAX Polyethylene Glycol 400, average molecular weight 400; ferric chloride hexahydrate was selected from Sigma-Aldrich 236489, purity not less than 97%; trisodium citrate dihydrate, hydrochloric acid, glacial acetic acid, triethylamine, ethylenediamine, dibutyltin dilaurate, N-methylpyrrolidone, ethanol and deionized water were all analytical grade or industrial superior grade products from Sinopharm Chemical Reagent Co., Ltd., among which the water content of N-methylpyrrolidone was controlled to be no higher than 500 ppm before use, and the conductivity of deionized water was no higher than 10 μS / cm; polyphenylene sulfide resin: Toray TORELINA A900 linear polyphenylene sulfide resin.

[0041] Example 1: A method for preparing modified offline chopped glass fibers for polyphenylene sulfide reinforcement, the specific preparation steps are as follows: S1 Preparation of carboxylated aqueous polyurethane emulsion containing aromatic sulfides: In a conventional reactor equipped with a stirrer, condenser, thermometer, and nitrogen inlet, 500 g of polycarbonate diol, 35 g of 2,2-dimethylolpropionic acid, and 120 g of N-methylpyrrolidone were added, and the mixture was dehydrated at 105 °C and -90 kPa for 60 min. After cooling to 75 °C, nitrogen was introduced, and 150 g of isophorone diisocyanate and 1 g of dibutyltin dilaurate were added. The mixture was reacted at 80 °C for 120 min. Then, 20 g of 4,4'-thiodiphenol was pre-dissolved in 80 g of... The N-methylpyrrolidone was added to the reactor in three portions, with each portion spaced 20 min apart, and the reaction was continued at 85°C for 180 min. After cooling to 45°C, 26 g of triethylamine was added to neutralize the carboxyl groups, and the mixture was stirred for 30 min. Under stirring at 1200 r / min, the resulting prepolymer was slowly added to 1200 g of deionized water and dispersed for 40 min. Finally, an aqueous solution of ethylenediamine prepared by 5 g of ethylenediamine and 100 g of deionized water was added, and the chain was extended at 35°C for 60 min to obtain a carboxylated waterborne polyurethane emulsion containing aromatic sulfides. S2 Preparation of Catechol-Borate Grafted Aqueous Polyurethane Emulsion: Take 2000g of carboxylated aqueous polyurethane emulsion containing aromatic sulfides, purge with nitrogen for 10min and stir in the dark, and adjust the pH of the system to 5-6 with hydrochloric acid aqueous solution (5%); add 18g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 10g of N-hydroxysuccinimide, and activate at 25℃ for 30min; separately mix 14g of dopamine hydrochloride, 6g of 3-aminophenylborate, 12g of triethylamine and 150g of deionized water pre-purged with nitrogen, stir until clear, and add dropwise to the activated emulsion, controlling the dropwise addition time to 30min, continuing to purge with nitrogen and avoid light during the dropwise addition, and react at 30℃ under nitrogen protection and in the dark for 360min to obtain a catechol-boric acid grafted aqueous polyurethane emulsion; S3 modified waterborne polyurethane film-forming agent: A 4-hydroxyphenylboronic acid solution prepared by 6 g of 4-hydroxyphenylboronic acid, 100 g of ethanol, 40 g of nitrogen-purged deionized water, and 8 g of triethylamine was added to the catechol-boric acid-grafted aqueous polyurethane emulsion obtained in S2. The mixture was stirred for 20 min at 25 °C under nitrogen protection and in the dark. Then, 5% ammonia was added to adjust the pH of the system to 8 and maintained for 15 min. Next, 5% glacial acetic acid aqueous solution was added to adjust the pH of the system back to 5-6. Finally, ethanol was removed at 45 °C and -80 kPa for 30 min, and 100 g of deionized water was added to obtain a modified aqueous polyurethane film-forming agent with a solid content of 34%-38%. S4 Preparation of the Main Wetting Agent: Add 92,000 g of deionized water to a conventional preparation tank, add 20 g of glacial acetic acid, stir for 5 min, then add 350 g of γ-glycidyl etheroxypropyltrimethoxysilane and hydrolyze at 25 °C for 25 min; continue to add 7,000 g of modified waterborne polyurethane film-forming agent and stir for 20 min; then add 200 g of polyethylene glycol lubricant and stir for 15 min; subsequently add 30 g of ammonia water (5%) to adjust the pH of the main wetting agent to 5-6; finally, add deionized water to obtain 100,000 g of main wetting agent; S5 is used to prepare an iron ion surface treatment solution: Add 9988g of deionized water to a conventional preparation tank, add 8g of ferric chloride hexahydrate and 4g of trisodium citrate dihydrate, stir at 25℃ for 20min to obtain 10000g of iron ion surface treatment solution. Control the iron ion surface treatment solution to be a clear brownish-yellow liquid with a pH of 3-4. S6 is used for glass fiber drawing and sizing with the main sizing agent: The conventional E-type glass furnace drawing process is used to draw molten glass into glass fibers with a single filament diameter of 10μm. Based on 100kg of dry glass fiber, 12kg of main sizing agent is applied during the drawing process through conventional coating method to ensure that the main sizing agent is evenly distributed on the surface of the glass fiber. The moisture content of the wet yarn is controlled at 8%-12%, and the original filament shape is flat, the yarn bundle width is uniform, and there are no obvious fuzzes on the surface of the wet yarn. S7 Pre-drying and iron ion outer layer locking: The glass fiber precursor obtained in S6 after being coated with the main sizing agent is pre-dried at 95℃ for 20 minutes under hot air conditions to make the surface of the yarn bundle non-adhesive, but the membrane layer still retains the migrating water; then, based on 100kg of dry glass fiber, 2kg of iron ion surface treatment solution is applied to the outer surface of the pre-dried yarn bundle using conventional spraying or padding methods; then dried at 125℃ for 120 minutes to obtain the modified glass fiber precursor; S8 involves offline chopped glass fibers and final drying: The modified glass fiber filaments obtained in S7 are rehydrated to 3‰-4‰ and cut into 4-5mm lengths using a conventional offline chopped glass fiber process. After conventional vibration dispersion, they are dried at 105℃ for 30 minutes to obtain modified offline chopped glass fibers for polyphenylene sulfide reinforcement. The final moisture content of the obtained modified offline chopped glass fibers is controlled to be no higher than 1‰, and the combustible content is controlled to be 3‰-6‰.

[0042] Example 2: A method for preparing modified offline chopped glass fibers for polyphenylene sulfide reinforcement, the specific preparation steps are as follows: S1 Preparation of carboxylated waterborne polyurethane emulsion containing aromatic sulfides: In a conventional reactor equipped with a stirrer, condenser, thermometer, and nitrogen inlet, 480g of polycarbonate diol, 32g of 2,2-dimethylolpropionic acid, and 110g of N-methylpyrrolidone were added, and dehydrated at 100℃ and -95kPa for 50min; after cooling to 70℃, nitrogen was introduced, and 145g of isophorone diisocyanate and 1g of dibutyltin dilaurate were added, and reacted at 75℃ for 100min; then 18g of 4,4'-thiodiphenol was pre-dissolved in 70g of... The N-methylpyrrolidone was added to the reactor in three portions, with a 15-minute interval between each addition, and the reaction was continued at 80°C for 150 minutes. After cooling to 40°C, 24 g of triethylamine was added to neutralize the carboxyl groups, and the mixture was stirred for 20 minutes. Under stirring at 1000 r / min, the resulting prepolymer was slowly added to 1100 g of deionized water and dispersed for 30 minutes. Finally, an ethylenediamine aqueous solution prepared by 4 g of ethylenediamine and 90 g of deionized water was added, and the chain was extended at 30°C for 50 minutes to obtain a carboxylated waterborne polyurethane emulsion containing aromatic sulfides. S2 Preparation of Catechol-Borate Grafted Aqueous Polyurethane Emulsion: Take 1900g of carboxylated aqueous polyurethane emulsion containing aromatic sulfides, purge with nitrogen for 8min and stir in the dark, adjust the pH of the system to 5-6 with hydrochloric acid aqueous solution (5%); add 16g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 8g of N-hydroxysuccinimide, and activate at 20℃ for 20-40min; separately mix 12g of dopamine hydrochloride, 5g of 3-aminophenylborate, 10g of triethylamine and 130g of deionized water pre-purged with nitrogen, stir until clear, and add dropwise to the activated emulsion, controlling the dropwise addition time to 20min, continue to purge with nitrogen and avoid light during the dropwise addition, after the dropwise addition is completed, react at 25℃ under nitrogen protection and in the dark for 300min to obtain the catechin-boric acid grafted aqueous polyurethane emulsion; Preparation of modified waterborne polyurethane film-forming agent in S3: Add a 4-hydroxyphenylboronic acid solution prepared by 5g of 4-hydroxyphenylboronic acid, 90g of ethanol, 30g of deionized water pre-purged with nitrogen and 6g of triethylamine to the catechol-boric acid-grafted water emulsion obtained in S2. Stir for 15min under nitrogen protection and in the dark at 20℃. Then add ammonia (5%) to adjust the pH of the system to 8 and maintain it for 10min. Then add glacial acetic acid aqueous solution (5%) to adjust the pH of the system back to 5-6. Finally, remove ethanol at 40℃ and -85kPa for 20min and add 90g of deionized water to obtain the modified waterborne polyurethane film-forming agent. Preparation of the main wetting agent (S4): Add 91,500 g of deionized water to a conventional preparation tank, add 15 g of glacial acetic acid, stir for 4 min, then add 330 g of γ-glycidyl etheroxypropyltrimethoxysilane, and hydrolyze at 20 °C for 20 min; continue to add 6,500 g of modified waterborne polyurethane film-forming agent, and stir for 15 min; then add 180 g of polyethylene glycol lubricant, and stir for 10 min; subsequently add ammonia water (5%) to make the pH of the main wetting agent 5; finally, add deionized water to 100,000 g to obtain the main wetting agent; S5 Preparation of iron ion surface treatment solution: Take 9985g of deionized water and add it to a conventional preparation tank. Add 10g of ferric chloride hexahydrate and 5g of trisodium citrate dihydrate. Stir at 20℃ for 15min to obtain 10000g of iron ion surface treatment solution. Control the iron ion surface treatment solution to be a clear brownish-yellow liquid with a pH of 3-4. S6 involves glass fiber drawing and sizing with the main sizing agent: using the conventional E-type glass furnace drawing process, the molten glass is drawn into glass fibers with a single filament diameter of 9-11μm; based on 100kg of dry glass fiber, 10kg of main sizing agent is applied during the drawing process using a conventional coating method, so that the main sizing agent is evenly distributed on the surface of the glass fiber, the moisture content of the wet yarn is controlled at 8%-12%, and the shape of the raw filament is controlled to be flat, the width of the yarn bundle is uniform, and there are no obvious fuzzes on the surface of the wet yarn; S7 Pre-drying and iron ion outer layer locking: The glass fiber precursor obtained in S6 after being coated with the main sizing agent is pre-dried at 90℃ for 15 minutes under hot air conditions to make the surface of the yarn bundle non-adhesive, but the interior of the film layer still retains the migrating water; then, based on 100kg of dry glass fiber, 1.5kg of iron ion surface treatment solution is applied to the outer surface of the pre-dried yarn bundle using conventional spraying or padding methods; then dried at 120℃ for 100 minutes to obtain the modified glass fiber precursor; S8 involves offline chopped glass fibers and final drying: The modified glass fiber filaments obtained in S7 are rehydrated to 3‰ to 4‰ and cut into short glass fibers of 4-5 mm length using a conventional offline chopped glass fiber process. After conventional vibration dispersion, they are dried at 100℃ for 20 min to obtain modified offline chopped glass fibers for polyphenylene sulfide reinforcement.

[0043] Example 3: A method for preparing modified offline chopped glass fibers for polyphenylene sulfide reinforcement, the specific preparation steps are as follows: S1 Preparation of carboxylated waterborne polyurethane emulsion containing aromatic sulfides: In a conventional reactor equipped with a stirrer, condenser, thermometer, and nitrogen inlet, 520 g of polycarbonate diol, 38 g of 2,2-dimethylolpropionic acid, and 130 g of N-methylpyrrolidone were added, and dehydrated at 110 °C and -85 kPa for 70 min; after cooling to 80 °C, nitrogen was introduced, and 155 g of isophorone diisocyanate and 1 g of dibutyltin dilaurate were added, and reacted at 85 °C for 140 min; then 22 g of 4,4'-thiodiphenol was pre-dissolved in 90 g of... The N-methylpyrrolidone was added to the reactor in three portions, with each portion spaced 25 min apart, and the reaction was continued at 90°C for 210 min. After cooling to 50°C, 28 g of triethylamine was added to neutralize the carboxyl groups, and the mixture was stirred for 40 min. Under stirring at 1400 r / min, the resulting prepolymer was slowly added to 1300 g of deionized water and dispersed for 50 min. Finally, an aqueous solution of ethylenediamine prepared from 6 g of ethylenediamine and 110 g of deionized water was added, and the chain was extended at 40°C for 70 min to obtain a carboxylated waterborne polyurethane emulsion containing aromatic sulfides. S2 Preparation of Catechol-Borate Grafted Aqueous Polyurethane Emulsion: Take 2100g of carboxylated aqueous polyurethane emulsion containing aromatic sulfides, purge with nitrogen for 12min and stir in the dark, adjust the pH of the system to 5-6 with 25g hydrochloric acid aqueous solution (5%); add 20g 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 12g N-hydroxysuccinimide, and activate at 30℃ for 40min; separately mix 16g dopamine hydrochloride, 7g 3-aminophenylborate, 14g triethylamine and 170g deionized water pre-purged with nitrogen, stir until clear, and add dropwise to the activated emulsion, controlling the dropwise addition time to 40min, continue to purge with nitrogen and avoid light during the dropwise addition, after the dropwise addition is completed, react at 35℃ under nitrogen protection and in the dark for 420min to obtain the catechin-boric acid grafted aqueous polyurethane emulsion; Preparation of modified waterborne polyurethane film-forming agent in S3: Add a 4-hydroxyphenylboronic acid solution prepared by 7g of 4-hydroxyphenylboronic acid, 110g of ethanol, 50g of deionized water pre-purged with nitrogen and 10g of triethylamine to the catechol-boric acid-grafted water emulsion obtained in S2. Stir for 25min under nitrogen protection and in the dark at 30℃. Then add ammonia (5%) to adjust the pH of the system to 8 and maintain it for 20min. Then add glacial acetic acid aqueous solution (5%) to adjust the pH of the system back to 5-6. Finally, remove ethanol at 50℃ and -75kPa for 40min and add 110g of deionized water to obtain the modified waterborne polyurethane film-forming agent. Preparation of the main wetting agent (S4): Add 92,500 g of deionized water to a conventional preparation tank, add 25 g of glacial acetic acid, stir for 6 min, then add 370 g of γ-glycidyl etheroxypropyltrimethoxysilane, and hydrolyze at 30 °C for 30 min; continue to add 7,500 g of modified waterborne polyurethane film-forming agent, and stir for 25 min; then add 220 g of polyethylene glycol lubricant, and stir for 20 min; subsequently add ammonia water (5%) to adjust the pH of the main wetting agent to 5-6; finally, add deionized water to a final volume of 100,000 g to obtain the main wetting agent. S5 Preparation of iron ion surface treatment solution: Take 9991g of deionized water and add it to a conventional preparation tank. Add 6g of ferric chloride hexahydrate and 3g of trisodium citrate dihydrate. Stir at 30℃ for 25min to obtain 10000g of iron ion surface treatment solution. Control the iron ion surface treatment solution to be a clear brownish-yellow liquid with a pH of 3-4. S6 involves glass fiber drawing and sizing with the main sizing agent: using the conventional E-type glass furnace drawing process, the molten glass is drawn into glass fibers with a single filament diameter of 9-11μm; based on 100kg of dry glass fiber, 14kg of main sizing agent is applied during the drawing process using a conventional coating method, so that the main sizing agent is evenly distributed on the surface of the glass fiber, the moisture content of the wet yarn is controlled at 12%, and the shape of the raw filament is controlled to be flat, the width of the yarn bundle is uniform, and there are no obvious fuzzes on the surface of the wet yarn; S7 Pre-drying and iron ion outer layer locking: The glass fiber precursor obtained in S6 after being coated with the main sizing agent is pre-dried at 100℃ for 25 minutes under hot air conditions to make the surface of the yarn bundle non-adhesive, but the interior of the film layer still retains the migrating water; then, based on 100kg of dry glass fiber, 2.5kg of iron ion surface treatment solution is applied to the outer surface of the pre-dried yarn bundle using conventional spraying or padding methods; then dried at 130℃ for 140 minutes to obtain the modified glass fiber precursor; S8 involves offline chopped glass fibers and final drying: The modified glass fiber filaments obtained in S7 are rehydrated to 3‰ to 4‰ and cut into short glass fibers of 4-5 mm length using a conventional offline chopped glass fiber process. After conventional vibration dispersion, they are dried at 110℃ for 40 min to obtain modified offline chopped glass fibers for polyphenylene sulfide reinforcement.

[0044] Comparative Example 1: The difference from Example 1 is that 4,4'-thiodiphenol is not added in S1, and the amount of polycarbonate diol added in S1 is adjusted from 500g to 520g to make up for the total feed mass in the film-forming agent preparation stage; the other conditions are the same as in Example 1.

[0045] Comparative Example 2: The difference from Example 1 is that dopamine hydrochloride is not added in S2, and the amount of deionized water pre-purged with nitrogen in S2 is adjusted from 150g to 164g to make up the total mass of the S2 drop solution; the other conditions are the same as in Example 1.

[0046] Comparative Example 3: The difference from Example 1 is that 3-aminophenylborate salt is not added in S2, and the amount of deionized water pre-purged with nitrogen in S2 is adjusted from 150g to 156g to make up the total mass of the S2 drop solution; the other conditions are the same as in Example 1.

[0047] Comparative Example 4: The difference from Example 1 is that 4-hydroxyphenylboronic acid is not added in S3, and the amount of ethanol added in S3 is adjusted from 100g to 106g to make up the total mass of the 4-hydroxyphenylboronic acid solution in S3; the other conditions are the same as in Example 1.

[0048] Comparative Example 5: The difference from Example 1 is that ferric chloride hexahydrate is not added in S5, and the amount of deionized water added in S5 is adjusted from 9988g to 9996g. 4g of trisodium citrate dihydrate is still added to obtain a surface treatment solution without iron ions. In S7, 2kg of the iron-free surface treatment solution is still applied based on 100kg of dry glass fiber. The other conditions are the same as in Example 1.

[0049] Comparative Example 6: The difference from Example 1 is that in S7, an iron ion surface treatment solution is no longer applied separately to the outer surface of the pre-dried yarn bundle; the other conditions are the same as in Example 1.

[0050] Performance testing Sample preparation: Modified offline chopped glass fibers for polyphenylene sulfide reinforcement prepared in Examples 1-3 and Comparative Examples 1-6 were taken and labeled as E1, E2, E3, C1, C2, C3, C4, C5, and C6, respectively. For the intrinsic characterization of the film-forming agent, the modified waterborne polyurethane film-forming agent obtained in step S3 was cast into a film on a clean plate, vacuum dried at 80°C for 12 hours, and then placed in an environment of 23°C and 50% relative humidity for 24 hours to obtain film-forming agent samples with a thickness of 80 μm to 120 μm. For the performance testing of polyphenylene sulfide (PPS) composite materials, samples were prepared according to the application steps of each embodiment and comparative example. 70 kg of linear PPS resin and 30 kg of corresponding chopped glass fiber were used to prepare PPS reinforced granules with a glass fiber mass fraction of 30%. Standard samples were then prepared using a conventional injection molding machine. The injection barrel temperature was set to 300℃, 310℃, 320℃, and 320℃ respectively, the mold temperature was set to 140℃, the injection pressure was set to 80 MPa, the holding pressure was set to 50 MPa, the holding time was set to 20 s, and the cooling time was set to 30 s. All injection molded samples were conditioned for 40 h at 23℃ and 50% relative humidity before mechanical property testing.

[0051] Moisture content and combustible content: The moisture content of the chopped glass fibers in each sample was tested according to GB / T 9914.1-2013 "Test Methods for Reinforced Products Part 1: Determination of Moisture Content". 10g of each sample was weighed and dried to constant weight in a ventilated oven at 105℃±3℃. After cooling to room temperature, the sample was weighed and the moisture content was calculated. The combustible content of the chopped glass fibers in each sample was tested according to GB / T 9914.2-2013 "Test Methods for Reinforced Products Part 2: Determination of Combustible Content in Glass Fibers". The dried sample was placed in a pre-weighed crucible and ignited in a muffle furnace at 625℃±20℃ to constant weight. After cooling, the sample was weighed and the combustible content was calculated. Fiber diameter, bundle density, and hairiness: The average diameter of glass fibers in each sample was determined according to GB / T 7690.5-2013 "Test Methods for Reinforcing Yarns - Part 5: Determination of Fiber Diameter of Glass Fibers". At least 100 monofilaments were tested for each sample and the average value was taken. Bund density was determined using a unified internal method: 100g of chopped glass fiber sample was weighed, placed on a vibrating sieve, and vibrated at 200r / min for 5min. Loose fibers and powder passing through the sieve were collected and weighed. The bundle density index was expressed as the percentage of the mass of the material passing through the sieve to the mass of the sample. Hairiness was determined using a unified internal method: 100g of chopped glass fiber sample was weighed, placed in a 2L clean glass bottle, and rolled at 60r / min for 30min. Then, it was sieved through a 0.5mm sieve. Hairiness and powder passing through the sieve were collected and weighed. The result was expressed as mg / 100g. Side-feeding stability: Short-cut glass fibers from each sample were used in a granulation test of polyphenylene sulfide reinforced with 30% glass fiber mass fraction. The twin-screw extruder temperature was set to 300℃, 310℃, 320℃, 320℃ and 315℃ respectively. The main screw speed was set to 250r / min, the side-feeding screw speed was set to 80r / min, the target side-feeding rate was set to 30kg / h, and the test was conducted continuously for 60min. The number of times material blockage, bridging or obvious clumping was recorded. Mechanical properties of polyphenylene sulfide (PPS) composites: The tensile strength of PPS-reinforced injection molded specimens was tested according to GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics". Type 1A specimens were used, and the tensile speed was set to 5 mm / min. Five specimens were tested in each group, and the average value was taken. Flexural strength and flexural modulus were tested according to GB / T 9341-2008 "Determination of flexural properties of plastics". 80 mm × 10 mm × 4 mm strip specimens were used, with a span of 64 mm and a loading speed of 2 mm / min. Five specimens were tested in each group, and the average value was taken. Notched cantilever beam impact strength was tested according to GB / T 1843-2008 "Determination of impact strength of plastic cantilever beams". 80 mm × 10 mm × 4 mm notched specimens were used, with a notch depth of 2 mm. Five specimens were tested in each group, and the average value was taken. The test results are shown in Table 1.

[0052] Table 1 shows that the average fiber diameter of Examples 1-3 remained relatively stable at approximately 10.0 μm, the combustible content was 4.1%-5.6%, and the moisture content was 0.6%-0.8%. This indicates that the modified impregnation system of the present invention did not significantly change the specifications of the glass fiber itself, but mainly improved the processing and reinforcement effects through the surface film structure. Compared with Comparative Examples 1-6, the bundle index of Examples 1-3 decreased to 1.12-1.25, the hairiness decreased to 18.4-24.8 mg / 100g, the number of blockages was 0 times / h, and the tensile strength was... The strength was increased to 161-171 MPa, the flexural strength to 238-252 MPa, the flexural modulus to 10120-10860 MPa, and the notched cantilever beam impact strength to 8.1-8.7 kJ / m². This indicates that the modified film layer, constructed by the aromatic sulfide hard segment, catechol reaction sites, fixed boric acid sites, free boric acid sites, and iron ion outer layer locking, can simultaneously achieve bundle retention, low fuzz, smooth feeding, and interface reinforcement during offline short cutting, side feeding propulsion, and polyphenylene sulfide melt extrusion. Among them, the hairy amount of Example 1 was only 18.4 mg / 100g, and the tensile strength, flexural strength and impact strength reached 171 MPa, 252 MPa and 8.7 kJ / m², respectively. The overall performance was better than that of Example 2 and Example 3, indicating that the higher the amount of each functional site, the better. Instead, an appropriate balance needs to be formed between the flexibility of the film layer, the shear resistance of the outer layer and the compatibility and dispersibility of polyphenylene sulfide. In Comparative Example 1, without the addition of 4,4'-thiodiphenol, the tensile strength and flexural strength decreased to 151 MPa and 225 MPa, respectively, indicating that the lack of aromatic sulfide fragments similar in structure to polyphenylene sulfide resulted in insufficient interfacial affinity and stress transfer ability. In Comparative Example 2, without the addition of dopamine hydrochloride, the hairiness increased to 43.8 mg / 100 g, and the number of blockages increased to 2 times / h, indicating that the lack of catechol reaction sites made it difficult to continuously form the boric acid inner layer and the iron ion outer layer. In Comparative Example 3, without the addition of 3-aminophenylboronic acid salt, the hairiness was 30.6 mg / 100 g, and the mechanical properties were lower than those of Example 1, indicating that the fixed boric acid sites play a fundamental role in the stability of the film structure. In Comparative Example 4, without the addition of 4-hydroxyphenylboronic acid, the clustering index increased to 1.3. 8. The impact strength decreased to 7.2 kJ / m², indicating that the free boric acid sites have a supplementary effect on dynamic buffering and moderate dispersion during the shearing process. In Comparative Example 5, without the addition of ferric chloride hexahydrate, the amount of fuzz increased to 47.5 mg / 100g, and the number of blockages increased to 2 times / h, indicating that the iron ion outer layer locking is mainly used to improve the dry shear resistance and anti-fuzzing ability. In Comparative Example 6, after the iron ion surface treatment solution was premixed into the main wetting agent, the amount of fuzz increased to 56.4 mg / 100g, the number of blockages increased to 3 times / h, and the tensile strength, flexural strength, and impact strength decreased to 138 MPa, 207 MPa, and 6.4 kJ / m², respectively. This indicates that although iron ions still exist, their premature entry into the main wetting agent will destroy the spatial partitioning structure of the inner flexible layer and the outer shear resistant layer. The technical effect of this invention is not produced by the simple superposition of the components, but comes from the sequential synergy of first forming an aromatic sulfide compatible film layer and dynamically locking the organic boric acid inner layer, and then locking the iron ion outer layer after pre-drying.

[0053] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A modified offline chopped glass fiber for polyphenylene sulfide reinforcement, characterized in that, The modified offline chopped glass fiber comprises a glass fiber matrix and a composite coating covering the outer surface of the glass fiber matrix; the composite coating is formed by a main wetting agent and an iron ion surface treatment solution; the main wetting agent comprises the following raw materials in parts by weight: 91,500-92,500 parts deionized water, 15-25 parts glacial acetic acid, 330-370 parts coupling agent, 6,500-7,500 parts modified waterborne polyurethane film-forming agent, 180-220 parts lubricant, and 20-40 parts pH adjuster; the iron ion surface treatment solution comprises the following raw materials in parts by weight: The raw materials are prepared as follows: 9985-9991 parts of deionized water, 6-10 parts of ferric chloride hexahydrate, and 3-5 parts of trisodium citrate dihydrate; the modified waterborne polyurethane film-forming agent is obtained by addition reaction and chain extension reaction of polycarbonate diol, isophorone diisocyanate and 4,4'-thiodiphenol as raw materials to obtain carboxylated waterborne polyurethane containing aromatic sulfides, and the carboxylated waterborne polyurethane containing aromatic sulfides is then grafted with dopamine hydrochloride and 3-aminophenylboronic acid salt through amidation reaction, and then undergoes borate esterification reaction with 4-hydroxyphenylboronic acid to obtain the final product.

2. The modified offline chopped glass fiber according to claim 1, characterized in that, The weight ratio of the polycarbonate diol, 2,2-dimethylolpropionic acid, isophorone diisocyanate, and 4,4'-thiodiphenol is 480-520:32-38:145-155:18-22; the weight ratio of the carboxylated waterborne polyurethane containing aromatic sulfides, dopamine hydrochloride, 3-aminophenylboronic acid salt, and 4-hydroxyphenylboronic acid is 1900-2100:12-16:5-7:5-7.

3. The modified offline chopped glass fiber according to claim 1, characterized in that, The specific preparation of the carboxylated waterborne polyurethane containing aromatic sulfides includes: mixing polycarbonate diol, 2,2-dimethylolpropionic acid and a portion of N-methylpyrrolidone and dehydrating them; after cooling, purging with nitrogen gas, adding isophorone diisocyanate and dibutyltin dilaurate for the first addition reaction; then dissolving 4,4'-thiodiphenol in the remaining N-methylpyrrolidone and adding it to continue the second addition reaction; after cooling, adding triethylamine for a neutralization reaction to form a prepolymer; finally adding deionized water for phase inversion emulsification, adding ethylenediamine aqueous solution for chain extension reaction, and obtaining a carboxylated waterborne polyurethane emulsion containing aromatic sulfides.

4. The modified offline chopped glass fiber according to claim 1, characterized in that, The amidation reaction specifically includes: adjusting the pH of the carboxylated aqueous polyurethane emulsion containing aromatic sulfides to 5-6; after activation by EDC and NHS, adding dopamine hydrochloride and 3-aminophenylborate acid salt to carry out the amidation reaction, to obtain a catechol-boric acid grafted aqueous polyurethane emulsion.

5. The modified offline chopped glass fiber according to claim 1, characterized in that, The borate esterification reaction specifically includes: adding a pre-prepared 4-hydroxyphenylboronic acid solution to the emulsion after the amidation reaction to carry out the borate esterification reaction, then adding ammonia water to adjust the pH to alkaline, then adding glacial acetic acid aqueous solution to adjust it back to weakly acidic; finally removing ethanol and adding deionized water to obtain the modified waterborne polyurethane film-forming agent.

6. The modified offline chopped glass fiber according to claim 1, characterized in that, The modified offline chopped glass fiber reinforced with polyphenylene sulfide has a moisture content of ≤1‰ and a combustible content of 3‰-6‰.

7. A method for preparing modified offline chopped glass fibers according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of carboxylated aqueous polyurethane emulsion containing aromatic sulfides; (2) Preparation of a catechol-boric acid grafted aqueous polyurethane emulsion; (3) Preparation of modified waterborne polyurethane film-forming agent; (4) Preparation of main wetting agent: deionized water, glacial acetic acid and γ-glycidyl etheroxypropyltrimethoxysilane are mixed and hydrolyzed, modified waterborne polyurethane film-forming agent and lubricant are added, the pH is adjusted to 5-6 with ammonia water, and deionized water is added to obtain the main wetting agent. (5) Preparation of iron ion surface treatment solution: Deionized water, ferric chloride hexahydrate and trisodium citrate dihydrate are mixed and stirred to dissolve, and a clear brownish-yellow iron ion surface treatment solution is obtained. (6) Glass fiber drawing and main impregnation agent sizing: The glass liquid is drawn into glass fiber monofilaments using the E glass tank furnace drawing process; During the fiber drawing process, the main sizing agent is applied by coating to ensure that the sizing agent is evenly distributed on the surface of the glass fiber. (7) Pre-drying and iron ion outer layer locking: The glass fiber filaments coated with the main sizing agent are pre-dried, and then an iron ion surface treatment solution is applied to the outer layer of the pre-dried yarn bundle, and then dried to obtain modified glass fiber filaments. (8) Offline shaving and final drying: After rehydration, the modified glass fiber filament is cut into short glass fibers of 4-5 mm length using an offline chopped process. After vibration dispersion, the fibers are further dried to control the final moisture content to be no higher than 1‰ and the combustible content to be 3‰-6‰, thus obtaining modified offline chopped glass fibers for polyphenylene sulfide reinforcement.

8. The preparation method according to claim 7, characterized in that, Based on 100 kg of dry glass fiber, the amount of the main impregnating agent applied is 10-14 kg.

9. The preparation method according to claim 7, characterized in that, Based on 100 kg of dry glass fiber, the amount of iron ion surface treatment solution applied is 1.5-2.5 kg.

10. The preparation method according to claim 7, characterized in that, The moisture content of the rehydrated modified glass fiber precursor is 3‰-4‰.

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