An anti-hydrolysis and anti-freeze-thaw vinyl succinic anhydride sizing agent emulsion and its preparation method

Abstract

The present invention provides a preparation method of an alkenyl succinic anhydride sizing agent emulsion: Mix nanocellulose and 4-benzoylbenzoic acid in DMF, then add DCC as a catalyst, centrifuge and wash and dry the precipitate after the reaction to obtain CNF / 4-BBA nanoparticles; Disperse it in water as the aqueous phase; Mix ASA with the aqueous phase, emulsify, then add acrylamide and methacrylic acid and mix, and emulsify again under ultraviolet light irradiation to obtain the product. This preparation method is simple, without complex chemical modification and addition of high-cost auxiliaries; In addition, the ultraviolet light-induced cross-linking polymerization technology has the advantages of environmental friendliness, fast reaction rate, etc.; At the same time, the prepared ASA sizing agent emulsion has a long freeze shelf life.

Description

Technical Field

[0001] The present invention belongs to the technical field of material chemistry, and particularly relates to a hydrolysis- and freeze-thaw-resistant vinyl succinic anhydride papermaking sizing agent emulsion and a preparation method thereof. Background Art

[0002] In recent years, ultraviolet (UV) light-induced crosslinking polymerization technology has received extensive attention in the field of polymer material preparation. Through the action of a UV initiator, rapid crosslinking and curing of polymer materials can be achieved, which has the advantages of simple operation, fast reaction rate, and environmental friendliness. However, traditional UV initiators may lead to unstable emulsions during the preparation of vinyl succinic anhydride sizing agents, thereby affecting the performance of the products. Therefore, it is of great significance to develop a UV initiator suitable for the preparation of vinyl succinic anhydride sizing agents.

[0003] Nanocrystalline cellulose (CNF), as a bio-based polymer material, has excellent mechanical properties, biocompatibility, and biodegradability. It has received extensive attention in the field of polymer materials. Combining nanocrystalline cellulose with other functional materials can give play to its advantages in various fields. Especially in the design of UV initiators, the excellent initiation effect can be achieved by combining the characteristics of nanocrystalline cellulose. Summary of the Invention

[0004] Aiming at the problem that the current UV initiator causes instability of vinyl succinic anhydride sizing agents, the present invention provides a preparation method of a vinyl succinic anhydride (ASA) sizing agent emulsion. Using CNF / 4-BBA as an initiator, on the basis of emulsifying and stabilizing the ASA emulsion, monomer molecules are polymerized under ultraviolet light to obtain a hydrolysis- and freeze-thaw-resistant ASA sizing agent emulsion.

[0005] The present invention also provides an ASA sizing agent emulsion prepared by the above method, which has good freeze- and hydrolysis-resistant properties.

[0006] To achieve the above object, the present invention adopts the following technical solutions.

[0007] A preparation method of a vinyl succinic anhydride sizing agent emulsion includes the following steps:

[0008] (1) Mix nanocrystalline cellulose (CNF) and 4-benzoylbenzoic acid (4-BBA) in an N,N'-dimethylformamide (DMF) solvent, then add N,N'-dicyclohexylcarbodiimide (DCC) as a catalyst. After the reaction, centrifuge, wash the precipitate, and dry it to obtain CNF / 4-BBA nanoparticles;

[0009] (2) Disperse the CNF / 4-BBA nanoparticles in water to form an aqueous phase; mix the vinyl succinic anhydride (ASA) with the aqueous phase and emulsify to obtain emulsion A;

[0010] (3) Acrylamide (AAm) and methacrylic acid (MAAc) are added to Emulsion A to obtain a mixed solution, which is emulsified again under ultraviolet light irradiation to obtain Emulsion B, namely the sizing agent emulsion of alkenyl succinic anhydride with freeze-thaw and hydrolysis resistance.

[0011] In step (1), the mass ratio of CNF to 4-BBA is 10:1 - 10, and more preferably 5:2.

[0012] In step (1), the mass ratio of DMF to CNF is 100:1 - 20, and more preferably 100:9.

[0013] In step (1), the mass ratio of DCC to CNF is 1:1 - 15, and more preferably 1:5.

[0014] In step (2), the mass fraction of CNF / 4-BBA in the aqueous phase is 0.1 - 5%wt, and more preferably 1.2%wt.

[0015] In step (2), the mass ratio of ASA to the aqueous phase is 4:1 - 1:10; more preferably 2:3.

[0016] In step (3), the mass ratio of AAm to MAAc is 1:1 - 1:5, and more preferably 1:2.

[0017] In step (3), the mass fraction of AAm in the mixed solution is 1%wt - 10wt%, and more preferably 3%wt.

[0018] An alkenyl succinic anhydride sizing agent emulsion obtained by the above preparation method.

[0019] The above alkenyl succinic anhydride sizing agent emulsion can withstand freezing at least at -20 °C, and the average droplet diameter of the dispersed phase is not greater than 6 μm.

[0020] The mechanism of the present invention is as follows:

[0021] 4-Benzoylbenzoic acid (4-BBA), as an aromatic ketone photoinitiator, has carbonyl and carboxyl functional groups, and can undergo an esterification reaction with nanocellulose to form a covalent bond. Using CNF / 4-BBA as a photoinitiator under ultraviolet light, it initiates the cross-linking polymerization of AAm (acrylamide) and MAAc (methacrylic acid) to emulsify and stabilize the ASA emulsion.

[0022] First, 4-benzoylbenzoic acid (4-BBA) is an aromatic ketone photoinitiator with both carbonyl and carboxyl functional groups. The carboxyl group forms a covalent bond with the hydroxyl groups on the surface of CNF through esterification, while the carbonyl group participates in the photoinitiation process. The first step involves an esterification reaction between the hydroxyl groups on the surface of CNF and the carboxyl group of 4-BBA. To achieve this, CNF and 4-BBA can be mixed in a solvent, and a catalyst such as DCC (N,N'-dicyclohexylcarbodiimide) can be added to promote the esterification reaction. After the reaction, 4-BBA molecules will be grafted onto CNF through ester bonds.

[0023] Second, after exposure to ultraviolet (UV) light, the carbonyl group in CNF / 4-BBA absorbs the UV energy and forms an excited singlet state. This excited state can undergo intersystem crossing to form a reactive triplet state. The triplet state can extract hydrogen atoms from a suitable hydrogen donor to form free radicals. Then, the generated free radicals initiate the polymerization of AAm and MAAc by attacking the double bonds of the monomers. The free radicals continue to propagate, causing the monomers to link together and form a polymer network. Crosslinking occurs when the polymer chains interact through secondary interactions such as hydrogen bonds or hydrophobic interactions.

[0024] In the present invention, 4-BBA can be used to prepare a bifunctional photoinitiator, where the carboxyl group allows covalent connection with CNF to form CNF / 4-BBA nanoparticles with emulsifying stable ASA; when AAm and MAAc aggregate around the CNF / 4-BBA nanoparticles at the oil-water interface and are irradiated with ultraviolet light, the carbonyl group initiates the polymerization of AAm and MAAc when exposed to ultraviolet light, forming a gel layer with freeze-thaw and water molecule penetration resistance, which further prevents water molecules from crossing the interfacial particles into the oil phase at low temperatures, thereby producing the ASA hydrolysis-resistant property.

[0025] The present invention has the following advantages:

[0026] In the present invention, CNF / 4-BBA is prepared as an emulsifier for ASA emulsion and at the same time as a UV photoinitiator to form an AAm / MAAc hydrogel layer at the oil-water interface, which can effectively improve the hydrolysis resistance and freeze-thaw resistance of the alkenyl succinic anhydride sizing agent; the preparation method is simple, without complex chemical modification and addition of high-cost additives; in addition, the UV photoinitiated crosslinking polymerization technology has the advantages of environmental friendliness and fast reaction rate; at the same time, the prepared ASA sizing agent emulsion has a long frozen shelf life. Description of the Drawings

[0027] Figure 1 is the atomic force microscopy image of CNF / 4-BBA;

[0028] Figure 2 is the microscopic picture of the hydrolysis-resistant and freeze-thaw-resistant ASA emulsion;

[0029] Figure 3 It is a comparison picture of the state of the hydrolysis- and freeze-thaw-resistant ASA emulsion before and after freeze-thaw cycles. Detailed implementation manners

[0030] The present invention will be further described below in conjunction with the embodiments and the drawings, but the present invention is not limited by the following embodiments.

[0031] Example 1 Preparation of ASA sizing agent emulsion

[0032] (1) Preparation of CNF / 4-BBA: 10 parts by mass of CNF and 1 part by mass of 4-BBA were mixed in 1000 parts by mass of DMF solvent, then 10 parts by mass of DCC was added as a catalyst, and the mixture was stirred at room temperature for 24 hours. After centrifugation, it was washed with DMF and dried to obtain CNF / 4-BBA nanoparticles;

[0033] The infrared spectrum of CNF / 4-BBA shows that at 3400 - 3500 cm⁻¹: the bending vibration of hydroxyl (OH), indicating the presence of nanocellulose; 2920 - 2980 cm -1 : the stretching vibration of alkyl (C-H), indicating the presence of nanocellulose; 1710 - 1720 cm -1 : the stretching vibration of amide (C=O), indicating the presence of 4-benzoylbenzoic acid; 1630 - 1640 cm -1 : the stretching vibration of carboxylic acid (C=O), indicating the presence of 4-benzoylbenzoic acid; 1600 - 1620 cm -1 : the stretching vibration of aromatic ring (C=C), indicating the presence of 4-benzoylbenzoic acid; 1300 - 1310 cm -1 : the stretching vibration of ester group (C-O), indicating the formation of an ester bond between nanocellulose and 4-benzoylbenzoic acid; the above infrared spectral characteristic peaks can confirm the successful reaction of nanocellulose and 4-benzoylbenzoic acid to obtain an ester;

[0034] Its atomic force microscopy image is as Figure 1 shown, and the CNF / 4-BBA composite nanofibers present a rod-like structure with a large aspect ratio;

[0035] (2) The CNF / 4-BBA nanoparticles were dispersed in water to form an aqueous dispersion with a mass fraction of 0.1%wt, stirred evenly, and used as the aqueous phase; 100 parts by mass of the aqueous phase was mixed with 400 parts by mass of ASA, and the first emulsification was carried out to obtain a homogeneous emulsion; then 1 part by mass of AAm and 1 part by mass of MAAc were added respectively, and the second emulsification was continued under ultraviolet light irradiation to obtain a freeze-thaw- and hydrolysis-resistant alkenyl succinic anhydride sizing emulsion, as Figure 2 shown;

[0036] The particle size statistics software provided by the optical microscope was used to count the diameters of 100 emulsion droplets observed under the microscope, and the average value was taken to obtain an average particle size of 5 μm.

[0037] The prepared emulsion was frozen at -20°C and then thawed at 80-100°C. Figure 3 As shown, the state before and after has not changed, indicating that the emulsion has good stability.

[0038] Example 2 Preparation of ASA sizing agent emulsion

[0039] (1) Preparation of CNF / 4-BBA: 100 parts by weight of CNF and 40 parts by weight of 4-BBA were mixed in 800 parts by weight of DMF solvent, and then 9 parts by weight of DCC was added as a catalyst. The mixture was stirred at room temperature for 24 hours, centrifuged, washed with DMF, and dried to obtain CNF / 4-BBA nanoparticles.

[0040] (2) Dispersing CNF / 4-BBA nanoparticles in water to form an aqueous dispersion with a mass fraction of 1.2%wt, stirring evenly, as the aqueous phase; taking 200 parts by mass of the aqueous phase and mixing it with 300 parts by mass of ASA, after the first emulsification to obtain a uniform emulsion, adding 6 parts by mass of AAm and 12 parts by mass of MAAc respectively, and continuing the second emulsification under ultraviolet light to obtain a freeze-thaw and hydrolysis-resistant alkenyl succinic anhydride sizing emulsion, the average particle size of the emulsion is 4.2 μm;

[0041] The emulsion was frozen at -20°C and its state did not change after thawing at 80-100°C, indicating good stability.

[0042] Example 3 Preparation of ASA sizing agent emulsion

[0043] (1) Preparation of CNF / 4-BBA: 100 parts by mass of CNF and 100 parts by mass of 4-BBA were mixed in 500 parts by mass of DMF solvent, and then 7 parts by mass of DCC was added as a catalyst. The mixture was stirred at room temperature for 24 hours, centrifuged, washed with DMF, and dried to obtain CNF / 4-BBA nanoparticles.

[0044] (2) Dispersing CNF / 4-BBA nanoparticles in water to form a 5%wt aqueous dispersion, stirring evenly, as the aqueous phase; taking 100 parts by weight of the aqueous phase and mixing it with 1000 parts by weight of ASA, after the first emulsification to obtain a uniform emulsion, adding 10 parts by weight of AAm and 50 parts by weight of MAAc respectively, and continuing the second emulsification under ultraviolet light to obtain a freeze-thaw and hydrolysis-resistant alkenyl succinic anhydride sizing emulsion, the average particle size of the emulsion is 5.7 μm;

[0045] The emulsion was frozen at -20°C and its state remained unchanged after thawing at 80 - 100°C, indicating good stability.

[0046] Application Example 1: Application of ASA sizing agent emulsion in paper making

[0047] Sizing was carried out by internal sizing method. Before sizing, the AKD / ASA composite papermaking sizing agent emulsion was diluted to 0.5%, the pulp concentration was adjusted to 1%, and 1% aluminum sulfate (mass percentage relative to oven-dry pulp) was first added to the pulp at a stirring rate of 1000 rpm. Then, the pH value of the pulp was adjusted to 7 - 8.5 with 1 mol / L sodium hydroxide solution. Subsequently, the diluted ASA sizing agent emulsion (dosage: 0.15%, total mass percentage of ASA relative to the total mass of oven-dry pulp), and 0.03% (mass percentage relative to oven-dry pulp) of cationic polyacrylamide were added in sequence. Then, the mixture was stirred for 2 minutes at a shear rate of 1000 rpm with a stirrer, allowed to stand for 30 seconds, and then a hand sheet was made using a PTI sheet former (model: RK3AKWT, origin: Austria). The basis weight of the hand sheet was 60 g / m 2 (T205 om-88, TAPPI). The sheet forming system selected the Kajaani manual sheet forming mode for papermaking according to the standards of ISO5289 / 2 and DIN54358. The made hand sheet was dried at 105°C and then the moisture of the paper was equilibrated at room temperature for 24 h with an environmental humidity of 50%. The sizing performance was evaluated by measuring the sizing degree of the made paper (GB / T5405 - 2002). Before measurement, the paper was cut into 30×30 mm square pieces and equilibrated for moisture in an environment of 25°C and 50% humidity for 24 hours. The four sides of the paper piece were folded up to form a boat-shaped structure with a bottom area of about 20×20 mm, and then it was floated in a 2% ammonium thiocyanate dilute solution. A 0.5 μL drop of 1% ferric chloride solution by mass concentration was dropped on the upper part of the boat-shaped paper piece with a dropper, and a stopwatch was used to time. When a red spot appeared in the middle of the ferric chloride droplet, the timing ended, and the time was the sizing degree of the paper sample. Each side of the test sample was measured 10 times, and the average value was taken.

[0048] Table 1 Performance of different sizing agents

[0049]

[0050] According to the data in Table 1, it can be seen that the average droplet size of the ASA emulsion prepared by the present invention is relatively small. After the emulsion is placed at -20°C for 30 days, no phase separation occurs and no demulsification phenomenon is observed, indicating that the ASA emulsion prepared by the present invention has good stability. When the dosage is 0.15% (mass ratio of ASA to absolutely dry pulp), the sizing degree of the paper sized with the emulsion in the pulp is 353 - 421 seconds, indicating that the sizing performance of the emulsion is excellent. Moreover, when the emulsion is used after being stored for 30 days, the sizing degree of the sized paper is still very high, indicating that the emulsion has good anti-hydrolysis performance. During low-temperature freezing storage, due to the protection of the Amm / MAAc antifreeze gel layer, the emulsion has obvious freeze-thaw and anti-hydrolysis performance. However, the ASA emulsion emulsified by pure CNF or pure 4-BBA is unstable. After being placed for 1 hour, all sizing performance is lost, and it also does not have low-temperature stability. The emulsion will demulsify after freeze-thawing.

Claims

1. A preparation method of an alkenyl succinic anhydride sizing agent emulsion, characterized in that It includes the following steps: (1) Mix nanocellulose and 4-benzoylbenzoic acid in a DMF solvent, then add N,N'-dicyclohexylcarbodiimide as a catalyst. After the reaction, centrifuge, wash and dry the precipitate to obtain CNF / 4-BBA nanoparticles; (2) Disperse the CNF / 4-BBA nanoparticles in water as the aqueous phase; mix the alkenyl succinic anhydride with the aqueous phase and emulsify to obtain emulsion A; (3) Add acrylamide and methacrylic acid to emulsion A to obtain a mixture, and emulsify again under ultraviolet light irradiation to obtain emulsion B, namely the alkenyl succinic anhydride sizing agent emulsion with freeze-thaw and hydrolysis resistance.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of nanocellulose to 4-benzoylbenzoic acid is 10:1 - 10; In step (1), the mass ratio of DMF to nanocellulose is 100:1 - 20; In step (1), the mass ratio of N,N'-dicyclohexylcarbodiimide to nanocellulose is 1:1 - 15; In step (2), the mass fraction of CNF / 4-BBA in the aqueous phase is 0.1 - 5%wt; In step (2), the mass ratio of alkenyl succinic anhydride to the aqueous phase is 4:1 - 1:10; In step (3), the mass ratio of acrylamide to methacrylic acid is 1:1 - 1:5; In step (3), the mass fraction of acrylamide in the mixture is 1%wt - 10wt%.

3. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of nanocellulose to 4-benzoylbenzoic acid is 5:2; In step (1), the mass ratio of DMF to nanocellulose is 100:9; In step (1), the mass ratio of N,N'-dicyclohexylcarbodiimide to nanocellulose is 1:5; In step (2), the mass fraction of CNF / 4-BBA in the aqueous phase is 1.2%wt; In step (2), the mass ratio of alkenyl succinic anhydride to the aqueous phase is 2:3; In step (3), the mass ratio of acrylamide to methacrylic acid is 1:2; In step (3), the mass fraction of acrylamide in the mixture is 3%wt.

4. An alkenyl succinic anhydride sizing agent emulsion obtained by the preparation method according to any one of claims 1 - 3.

5. The alkenyl succinic anhydride sizing agent emulsion according to claim 4, wherein The alkenyl succinic anhydride sizing agent emulsion is resistant to freezing at least at -20 °C, and the average droplet diameter of the dispersed phase is not greater than 6 μm.

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