Novel ionic liquid / waterborne polyurethane composite sizing agent and preparation method thereof

Abstract

The invention provides a novel ionic liquid / waterborne polyurethane composite sizing agent and a preparation method thereof, and belongs to the field of carbon fiber sizing agents. The ionic liquid in the composite sizing agent is composed of L-malic acid and triethylamine and is partially similar to synthetic raw materials of waterborne polyurethane, and the ionic liquid can be tightly combined with the waterborne polyurethane according to the principle of'similar miscibility '. The unique molecular structure of the L-malic acid brings an-OH functional group for the IL, and-OH in the IL participates in the curing ring-opening reaction of the epoxy resin in the heating curing process of the epoxy resin, so that not only is the crosslinking density of the epoxy resin increased, but also a specific molecular chain of the L-malic acid and the triethylamine is connected into a molecular chain of the epoxy resin.

Description

Technical Field

[0001] The invention belongs to the field of carbon fiber sizing agents, and particularly relates to a novel ionic liquid / aqueous polyurethane composite sizing agent and a preparation method thereof. Background Art

[0002] Bio-based waterborne polyurethane (WPU) sizing agents are considered an important alternative to traditional solvent-based sizing agents due to their environmental friendliness, flexible molecular chain structure, and wetting protection for carbon fibers. However, the polarity difference between the hydrophilic groups in the WPU backbone and the epoxy resin matrix limits interpenetration between the two molecular segments, making it difficult to form close intermolecular forces at the interface, severely restricting the performance and long-term serviceability of the composite material.

[0003] To address the bottleneck of composite interfacial compatibility, existing technologies often employ strategies such as carbon fiber surface etching (e.g., amino modification), plasma processing, or electropolymerization. However, these methods involve high-temperature treatment or cause physical damage to the carbon fiber surface. In recent years, ionic liquids (ILs) have been widely used in materials science due to their tunable molecular structure and low volatility. Recently, they have been studied as potential plasticizers to modify resin properties, but ILs have not been introduced into the sizing process to evaluate their impact on the interface. Furthermore, most commercial ILs used do not meet the concepts of sustainability and green chemistry. Summary of the Invention

[0004] The purpose of the present invention is to provide a novel ionic liquid / aqueous polyurethane composite sizing agent and a preparation method thereof. The sizing agent is used to enhance the interfacial bonding strength of carbon fiber / epoxy resin composite materials.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The invention first provides a novel ionic liquid / aqueous polyurethane composite sizing agent. The novel ionic liquid / aqueous polyurethane composite sizing agent comprises, by weight of raw materials, 20.1135 parts of L-malic acid, 40 parts of triethylamine, 100 parts of methanol, 8.52 parts of poly (L-malic acid polyethylene glycol ester) polyol, 8.89 parts of L-lysine diisocyanate, 0.6468 parts of tartaric acid as a hydrophilic chain extender, 0.0132 parts of tartaric acid-zinc oxide as a chain extender, 0.01 parts of dibutyltin dilaurate as a catalyst, 0.89 parts of triethylamine as a neutralizer, 15 parts of gamma-valerolactone, and 50 parts of deionized water.

[0007] The present invention also provides a method for preparing a novel ionic liquid / aqueous polyurethane composite sizing agent, comprising:

[0008] Step 1: Preparation of ionic liquid

[0009] Under nitrogen protection, L-malic acid, triethylamine and solvent methanol are added to a reaction vessel for reaction to obtain an ionic liquid;

[0010] Step 2: Preparation of waterborne polyurethane

[0011] L-lysine diisocyanate, poly (L-malic acid polyethylene glycol ester) polyol, tartaric acid, and tartaric acid-zinc oxide are added to a reaction vessel, and a solvent, γ-valerolactone, is added to react. The reaction system is then cooled, and triethylamine is added to neutralize the reaction. Finally, the obtained prepolymer is dispersed in water to obtain a waterborne polyurethane.

[0012] Step 3: Preparation of composite sizing agent

[0013] The waterborne polyurethane obtained in step 2 is diluted with deionized water to form an emulsion, and the ionic liquid obtained in step 1 is added and stirred to obtain a novel ionic liquid / waterborne polyurethane composite sizing agent.

[0014] Preferably, the reaction temperature in step 1 is 30-40° C., and the reaction time is 45-50 h.

[0015] Preferably, the reaction temperature in step 2 is 60-70° C., and the reaction time is 3.5-4 h.

[0016] Preferably, in step 2, the reaction system is cooled to 35-40° C., and the neutralization reaction time is 20-40 min.

[0017] Preferably, the solid content of the emulsion in step 3 is 2 wt %.

[0018] Preferably, the mass ratio of the ionic liquid and the aqueous polyurethane in step three is (0.5-1):1.

[0019] Preferably, the stirring temperature in step 3 is 30-40° C., and the stirring time is 30-40 min.

[0020] Beneficial effects of the present invention

[0021] The present invention proposes a novel ionic liquid / aqueous polyurethane composite sizing agent. The ionic liquid in the composite sizing agent is composed of L-malic acid and triethylamine, which is similar to the synthetic raw materials of aqueous polyurethane. According to the principle of "like dissolves like," the ionic liquid can tightly bind to the aqueous polyurethane. The unique molecular structure of L-malic acid provides an -OH functional group to the IL. During the epoxy resin temperature curing process, the -OH in the IL participates in the epoxy resin's curing ring-opening reaction, not only increasing the epoxy resin's crosslinking density but also allowing the specific molecular chains of L-malic acid and triethylamine to be incorporated into the epoxy resin's molecular chain. This greatly enhances the compatibility of the epoxy resin with the aqueous polyurethane. This method optimizes the carbon fiber surface wettability and interfacial energy while chemically bonding the active groups in the ionic liquid to the epoxy resin. This significantly improves the interfacial bonding strength of the composite material while ensuring the integrity of the carbon fiber's bulk properties, providing a new approach for the preparation of carbon fiber sizing agents. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the appearance of the ionic liquid and composite sizing agent prepared by the present invention;

[0023] Figure 2 The stress-strain curves and bending strength diagrams of the composite materials prepared in Comparative Examples 1-2 and Examples 1-3 of the present invention;

[0024] Figure 3 The load-deflection curves and ILSS strengths of the composite materials prepared in Comparative Examples 1-2 and Examples 1-3 of the present invention are shown;

[0025] Figure 4 These are SEM images of the fracture morphologies of the composite materials prepared in Comparative Example 1 and Examples 1-3 of the present invention. DETAILED DESCRIPTION

[0026] The present invention first provides a novel ionic liquid / aqueous polyurethane composite sizing agent.

[0027] Calculated by weight of the raw materials, the mixture includes 20.1135 parts of L-malic acid, 40 parts of triethylamine, 100 parts of methanol, 8.52 parts of poly (L-malic acid polyethylene glycol ester) polyol, 8.89 parts of L-lysine diisocyanate, 0.6468 parts of tartaric acid as a hydrophilic chain extender, 0.0132 parts of tartaric acid-zinc oxide as a chain extender, 0.01 parts of dibutyltin dilaurate as a catalyst, 0.89 parts of triethylamine as a neutralizer, 15 parts of γ-valerolactone, and 50 parts of deionized water.

[0028] The present invention also provides a method for preparing a novel ionic liquid / aqueous polyurethane composite sizing agent, comprising:

[0029] Step 1: Preparation of ionic liquid

[0030] Under nitrogen protection, L-malic acid, triethylamine and solvent methanol are added to the reaction vessel for reaction. The reaction temperature is preferably 30-40°C, and the reaction time is preferably 45-50h.

[0031] Obtaining an ionic liquid; the mass ratio of the L-malic acid and triethylamine is preferably 1:2;

[0032] Step 2: Preparation of waterborne polyurethane

[0033] L-lysine diisocyanate, poly (L-malic acid polyethylene glycol ester) polyol, tartaric acid, and tartaric acid-zinc oxide are added to a reaction vessel, and γ-valerolactone is added as a solvent to react to reduce viscosity and prevent gelation of the system. The reaction temperature is preferably 60-70° C., and the reaction time is preferably 3.5-4 hours. The reaction system is then cooled, preferably to 35-40° C., and triethylamine is added for neutralization reaction. The reaction time is preferably 20-40 minutes. Finally, the obtained prepolymer is dispersed in water to obtain a waterborne polyurethane.

[0034] Step 3: Preparation of composite sizing agent

[0035] The aqueous polyurethane obtained in step 2 is diluted with deionized water to form an emulsion, wherein the solid content of the emulsion is preferably 2 wt %, and the ionic liquid obtained in step 1 is added and stirred. The stirring temperature is preferably 30-40° C. and the stirring time is preferably 30-40 minutes to obtain a novel ionic liquid / aqueous polyurethane composite sizing agent. The mass ratio of the ionic liquid to the aqueous polyurethane is preferably (0.5-1):1.

[0036] According to the present invention, the preparation method of the poly (L-malic acid polyethylene glycol) ester polyol preferably comprises:

[0037] L-malic acid, PEG, and dibutyltin dilaurate were added to a four-necked flask equipped with a mechanical stirrer, a water separator, and a thermometer and heated to 130°C under a nitrogen atmosphere. Throughout the esterification reaction, the acid value of the mixture was monitored to track the reaction progress until the reaction was completed. Finally, the reaction mixture was cooled to 60°C. The product was a light yellow transparent liquid and then dried in a vacuum oven for 12 hours. The mass ratio of L-malic acid, PEG, and dibutyltin dilaurate was preferably 1:2.2:0.08;

[0038] The preparation method of tartaric acid-zinc oxide preferably comprises:

[0039] Zinc oxide and tartaric acid were added to a three-necked flask containing isopropyl alcohol. The mixture was heated to 80°C under nitrogen and stirred continuously for 12 hours. After the reaction was complete, the mixture was washed five times with ethanol to remove excess tartaric acid, and the tartaric acid-zinc oxide product was recovered by centrifugation. The mass ratio of zinc oxide to tartaric acid was preferably 1:4.4.

[0040] The present invention will be further described in detail below with reference to specific embodiments.

[0041] Comparative Example 1

[0042] Preparation of carbon fiber / epoxy resin composite materials:

[0043] Before preparing carbon fiber / epoxy resin composites, the original sizing agent of commercial carbon fibers was first desized using acetone as a solvent via Soxhlet extraction. The resulting fibers are referred to as untreated carbon fibers (UCF). The CF / EP composites were prepared using vacuum-assisted resin infusion (VARI) technology. Six layers of UCF were placed in a mold and infused with epoxy resin and the curing agent diethylenetriamine (mass ratio of 100:10.8) under vacuum conditions. The composite was cured by gradually increasing the temperature from 90°C for 2 hours, 120°C for 2 hours, and 150°C for 2 hours. The resulting product is named UCF / EP. The three-point bending and interlaminar shear properties of UCF / EP are 1140 and 47 MPa, respectively.

[0044] Comparative Example 2

[0045] The preparation method of poly (L-malic acid polyethylene glycol) ester polyol comprises:

[0046] 33.5225g of L-malic acid, 75g of PEG, and dibutyltin dilaurate were added to a four-necked flask equipped with a mechanical stirrer, a water separator, and a thermometer. The mixture was heated to 130°C under a nitrogen atmosphere. The acid value of the mixture was monitored throughout the esterification reaction to track its progress until completion. Finally, the reaction mixture was cooled to 60°C, resulting in a light yellow, transparent liquid. The product was then dried in a vacuum oven for 12 hours.

[0047] Preparation method of tartaric acid-zinc oxide:

[0048] 0.82 g of zinc oxide and 3.6 g of tartaric acid were added to a three-necked flask containing isopropanol, heated to 80°C under nitrogen, and stirred continuously for 12 hours. After the reaction was complete, the mixture was washed five times with ethanol to remove excess tartaric acid, and the tartaric acid-zinc oxide product was subsequently recovered by centrifugation.

[0049] Preparation of bio-based waterborne polyurethane:

[0050] In a four-necked flask equipped with a reflux condenser, stirrer, thermometer, and nitrogen inlet, 8.89 g of L-lysine diisocyanate, 8.52 g of poly (L-malic acid polyethylene glycol ester) polyol, 0.6468 g of tartaric acid, 0.0132 g of tartaric acid-zinc oxide, and 0.01 g of dibutyltin dilaurate catalyst were added in sequence. The reaction was continued at 60°C for 4 hours. During the reaction, 15 ml of γ-valerolactone was added to reduce viscosity and prevent gelation. The reaction temperature was then lowered to 35°C, and 0.89 g of triethylamine was added to neutralize the polymer system. The reaction continued for 30 minutes. The resulting prepolymer was then dispersed in 50 g of deionized water at 35°C and 1200 rpm for approximately 20 minutes, yielding a WPU waterborne polyurethane dispersion with a solids content of 30%.

[0051] Preparation of sizing agent:

[0052] 10 g of WPU emulsion was diluted into an emulsion with a solid content of 2 wt % by introducing 140 g of deionized water to obtain a WPU sizing agent.

[0053] Preparation of carbon fiber / epoxy resin composite materials:

[0054] Before preparing the carbon fiber / epoxy resin composite, the original sizing agent of the commercial carbon fiber was first desized using acetone as a solvent via Soxhlet extraction. The carbon fiber was then sizing with the sizing agent WPU. The resulting carbon fiber is called WCF. The CF / EP composite was prepared using vacuum-assisted resin infusion (VARI) technology. Six layers of WCF were placed in a mold and infused with epoxy resin and the curing agent diethylenetriamine (mass ratio of 100:10.8) under vacuum conditions. The composite was cured by gradually increasing the temperature from 90°C for 2 hours, 120°C for 2 hours, and 150°C for 2 hours. The resulting product is named WCF / EP. The three-point bending and interlaminar shear properties of WCF / EP are 1740 and 73 MPa respectively.

[0055] Example 1

[0056] The preparation method of poly (L-malic acid polyethylene glycol) ester polyol comprises:

[0057] 33.5225g of L-malic acid, 75g of PEG, and dibutyltin dilaurate were added to a four-necked flask equipped with a mechanical stirrer, a water separator, and a thermometer. The mixture was heated to 130°C under a nitrogen atmosphere. The acid value of the mixture was monitored throughout the esterification reaction to track its progress until completion. Finally, the reaction mixture was cooled to 60°C, resulting in a light yellow, transparent liquid. The product was then dried in a vacuum oven for 12 hours.

[0058] Preparation method of tartaric acid-zinc oxide:

[0059] 0.82 g of zinc oxide and 3.6 g of tartaric acid were added to a three-necked flask containing isopropanol, heated to 80°C under nitrogen, and stirred continuously for 12 hours. After the reaction was complete, the mixture was washed five times with ethanol to remove excess tartaric acid, and the tartaric acid-zinc oxide product was subsequently recovered by centrifugation.

[0060] Preparation of ionic liquids:

[0061] 20.1135g of L-malic acid, 40g of triethylamine, and 100ml of methanol were placed in a three-necked flask under nitrogen and uniformly dispersed at 200 rpm. The reaction was continued in a 30°C oil bath for 48 hours. After the reaction, the sample was removed from the excess triethylamine and methanol solvents using a rotary evaporator at 80°C, yielding a clear, viscous liquid product.

[0062] Preparation of bio-based waterborne polyurethane:

[0063] In a four-necked flask equipped with a reflux condenser, stirrer, thermometer, and nitrogen inlet, 8.89 g of L-lysine diisocyanate, 8.52 g of poly (L-malic acid polyethylene glycol ester) polyol, 0.6468 g of tartaric acid, 0.0132 g of tartaric acid-zinc oxide, and 0.01 g of dibutyltin dilaurate catalyst were added in sequence. The reaction was continued at 60°C for 4 hours. During the reaction, 15 ml of γ-valerolactone was added to reduce viscosity and prevent gelation. The reaction temperature was then lowered to 35°C, and 0.89 g of triethylamine was added to neutralize the polymer system. The reaction continued for 30 minutes. The resulting prepolymer was then dispersed in 50 g of deionized water at 35°C and 1200 rpm for approximately 20 minutes, yielding a WPU waterborne polyurethane dispersion with a solids content of 30%.

[0064] Preparation of sizing agent:

[0065] 10 g of WPU emulsion was diluted to an emulsion with a solid content of 2 wt % by introducing 140 g of deionized water to obtain a WPU sizing agent, and 75 g of IL with a concentration of 2 wt % was introduced dropwise with stirring to obtain a WPU-IL0.5 sizing agent.

[0066] Preparation of carbon fiber / epoxy resin composite materials:

[0067] Before preparing the carbon fiber / epoxy resin composite, the original sizing agent of the commercial carbon fiber was first desized using acetone as a solvent using the Soxhlet extraction method. The carbon fiber was then sizing with the sizing agent WPU-IL0.5. The resulting carbon fiber is called CF1. The CF / EP composite is prepared using vacuum-assisted resin infusion (VARI) technology. Six layers of CF1 are placed in a mold and infused with epoxy resin and the curing agent diethylenetriamine (mass ratio of 100:10.8) under vacuum conditions. The composite is cured by gradually increasing the temperature from 90°C for 2 hours, 120°C for 2 hours, and 150°C for 2 hours. The resulting product is named CF1 / EP. The three-point bending and interlaminar shear properties of CF1 / EP are 1780 and 77 MPa respectively.

[0068] Example 2

[0069] The preparation method and reaction conditions were the same as those in Example 1, except that, during the preparation of the sizing agent, 112.5 g of IL with a concentration of 2 wt % was introduced dropwise with stirring to obtain a WPU-IL0.75 sizing agent.

[0070] Preparation of carbon fiber / epoxy resin composite materials:

[0071] Before preparing the carbon fiber / epoxy resin composite, the original sizing agent of the commercial carbon fiber was first desized using acetone as a solvent via Soxhlet extraction. The carbon fiber was then sizing with the sizing agent WPU-IL0.75. The resulting carbon fiber is called CF2. The CF / EP composite was prepared using vacuum-assisted resin infusion (VARI) technology. Six layers of CF2 were placed in a mold and infused with epoxy resin and the curing agent diethylenetriamine (mass ratio of 100:10.8) under vacuum conditions. The composite was cured by gradually increasing the temperature from 90°C for 2 hours, 120°C for 2 hours, and 150°C for 2 hours. The resulting product is named CF2 / EP. The three-point bending and interlaminar shear properties of CF2 / EP are 1810 and 86 MPa, respectively.

[0072] Example 3

[0073] The preparation method and reaction conditions were the same as those in Example 1, except that, during the preparation of the sizing agent, 150 g of IL with a concentration of 2 wt % was introduced dropwise with stirring to obtain the WPU-IL1 sizing agent.

[0074] Preparation of carbon fiber / epoxy resin composite materials:

[0075] Before preparing the carbon fiber / epoxy resin composite, the original sizing agent of the commercial carbon fiber was first desized using acetone as a solvent via Soxhlet extraction. The carbon fiber was then sizing with the sizing agent WPU-IL1. The resulting carbon fiber is called CF3. The CF / EP composite was prepared using vacuum-assisted resin infusion (VARI) technology. Six layers of CF3 were placed in a mold and infused with epoxy resin and the curing agent diethylenetriamine (mass ratio of 100:10.8) under vacuum conditions. The composite was cured by gradually increasing the temperature from 90°C for 2 hours, 120°C for 2 hours, and 150°C for 2 hours. The resulting product is named CF3 / EP. The three-point bending and interlaminar shear properties of CF3 / EP are 1550 and 68 MPa, respectively.

[0076] Figure 1 This is the appearance of the ionic liquid and composite sizing agent prepared by the present invention, wherein: Figure 1 a is the appearance of ionic liquid, Figure 1 b is the appearance of the composite sizing agent.

[0077] Figure 2 The stress-strain curves and bending strength diagrams of the composite materials prepared in Comparative Examples 1-2 and Examples 1-3 of the present invention are shown in FIG. Figure 2 a is the stress-strain curve, Figure 2 b is the flexural strength. The results show that when the ratio of WPU to IL is 1:0.75, the flexural properties of CF2 / EP reach 1810 MPa, which is an increase of 58.77% compared with the unsizing UCF / EP.

[0078] Figure 3 The load-deflection curves and ILSS strengths of the composite materials prepared in Comparative Examples 1-2 and Examples 1-3 of the present invention are shown. Figure 3 a represents the load-deflection curve, Figure 3 b represents ILSS strength. The results show that the ILSS value of the composite material increased from 47.73MPa to 86.02MPa, an increase of 80.22%. The results show that with an appropriate ratio of IL to WPU, the composite material exhibits good interlaminar shear performance. Figure 3 Typical load-deflection curves show that the unsized UCF / EP composite experiences rapid crack growth and failure, resulting in a lower load. However, the sized composite exhibits a jagged curve, which is attributed to the strong physical and chemical interactions at the composite interface, effectively transferring stress.

[0079] Figure 4 The SEM images of the fracture morphology of the composite materials prepared in Comparative Example 1 and Examples 1-3 of the present invention are as follows. Figure 4As shown in a, there are many cracks and pores at the interface between carbon fiber and epoxy resin, indicating that the bonding between fiber and matrix is ​​poor. However, after the sizing agent treatment, the composite material, especially CF2 / EP (see Figure 4 c), no fiber pull-out, cracks and pores were observed, and the resin and fiber were tightly bonded. Figure 4 d) Obvious pores appeared on the fracture surface of the composite material. This is because excessive ILs will affect the viscosity of the sizing agent, resulting in uneven coating during carbon fiber impregnation and poor resin wettability between fiber bundles, which will have an adverse effect on the mechanical properties of the composite material. This is consistent with the previous mechanical properties test results.

Claims

1. A novel ionic liquid / aqueous polyurethane composite sizing agent, characterized in that: Calculated by weight of the raw materials, the mixture includes 20.1135 parts of L-malic acid, 40 parts of triethylamine, 100 parts of methanol, 8.52 parts of poly (L-malic acid polyethylene glycol ester) polyol, 8.89 parts of L-lysine diisocyanate, 0.6468 parts of tartaric acid as a hydrophilic chain extender, 0.0132 parts of tartaric acid-zinc oxide as a chain extender, 0.01 parts of dibutyltin dilaurate as a catalyst, 0.89 parts of triethylamine as a neutralizer, 15 parts of γ-valerolactone, and 50 parts of deionized water.

2. The method for preparing a novel ionic liquid / aqueous polyurethane composite sizing agent according to claim 1, characterized in that: include: Step 1: Preparation of ionic liquid Under nitrogen protection, L-malic acid, triethylamine and solvent methanol are added to a reaction vessel for reaction to obtain an ionic liquid; Step 2: Preparation of waterborne polyurethane L-lysine diisocyanate, poly (L-malic acid polyethylene glycol ester) polyol, tartaric acid, and tartaric acid-zinc oxide are added to a reaction vessel, and a solvent, γ-valerolactone, is added to react. The reaction system is then cooled, and triethylamine is added to neutralize the reaction. Finally, the obtained prepolymer is dispersed in water to obtain a waterborne polyurethane. Step 3: Preparation of composite sizing agent The waterborne polyurethane obtained in step 2 is diluted with deionized water to form an emulsion, and the ionic liquid obtained in step 1 is added and stirred to obtain a novel ionic liquid / waterborne polyurethane composite sizing agent.

3. The method for preparing a novel ionic liquid / aqueous polyurethane composite sizing agent according to claim 2, wherein: The reaction temperature in step 1 is 30-40° C., and the reaction time is 45-50 h.

4. The method for preparing a novel ionic liquid / aqueous polyurethane composite sizing agent according to claim 1, wherein: The reaction temperature in step 2 is 60-70° C., and the reaction time is 3.5-4 h.

5. The method for preparing a novel ionic liquid / aqueous polyurethane composite sizing agent according to claim 1, characterized in that: In step 2, the reaction system is cooled to 35-40° C., and the neutralization reaction time is 20-40 minutes.

6. The method for preparing a novel ionic liquid / aqueous polyurethane composite sizing agent according to claim 1, characterized in that: The solid content of the emulsion in step 3 is 2 wt %.

7. The method for preparing a novel ionic liquid / aqueous polyurethane composite sizing agent according to claim 1, characterized in that: The mass ratio of the ionic liquid and the aqueous polyurethane in step three is (0.5-1):

1.

8. The method for preparing a novel ionic liquid / aqueous polyurethane composite sizing agent according to claim 1, characterized in that: The stirring temperature in step 3 is 30-40° C., and the stirring time is 30-40 min.

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