Multi-melting-point wax synergistic fluorine-free gradient oil-proofing agent and preparation method thereof

Abstract

The invention discloses a multi-melting-point wax synergistic fluorine-free gradient oil-proofing agent and a preparation method thereof, and the multi-melting-point wax synergistic fluorine-free gradient oil-proofing agent comprises the following components in parts by mass: 30-75 parts of deionized water, 0.5-8 parts of a cationic emulsifier, 4-10 parts of a starch emulsifier, 8-20 parts of a multi-melting-point wax composition, 15-50 parts of a flaky functional material, 2-6 parts of low-temperature wax with a melting point of 30-50 DEG C, and 2-8 parts of medium-temperature wax with a melting point of 55-85 DEG C, the low-temperature wax and the medium-temperature wax are used, the high-temperature wax and the low-temperature wax can effectively permeate into fiber pores in a molten state, oil substance permeation channels are blocked through physical filling, the medium-temperature wax forms a transition layer, the high-temperature wax constructs a heat-resistant barrier, and a gradient oil-proof structure is formed.

Description

Technical Field

[0001] The present invention relates to the technical field of pulp molding food packaging, and particularly relates to a fluorine-free gradient oil-proof agent based on the synergistic effect of a cationic emulsifier and multi-melting-point waxes and a preparation method thereof. Background Art

[0002] In the field of pulp molding oil-proof agents, in recent years, some developed countries in Europe and America have started to issue some bans on the use of fluorine-containing compounds. For example, the European Chemicals Agency (ECHA) announced a restriction proposal on its official website in April, proposing to ban the production and use of per- and polyfluoroalkyl compounds.

[0003] Traditional fluorine-containing oil-proof agents have been restricted due to environmental toxicity, while fluorine-free oil-proof agents mostly rely on single components (such as acrylate or starch) to achieve the oil-proof effect, and there are problems such as a narrow temperature resistance range and insufficient long-term effectiveness. In addition, most of the wax additives in the prior art have a single melting point and are difficult to simultaneously adapt to extreme conditions from low-temperature food packaging to high temperature (-30°C - 90°C).

[0004] The melting point of wax directly affects its physical state in a low-temperature environment. When the ambient temperature is lower than the melting point, the wax remains solid and can form a physical barrier by filling the fiber pores to block the oil penetration channel. Although high-melting-point wax can maintain a solid state at low temperatures, its hardness may be too high, resulting in brittle fracture. Under temperature stress and external forces during use, it is easy to cause the separation of the wax from the fiber, leading to a decrease in the oil-proof ability and the pore closing ability. If the ambient temperature is close to or exceeds the melting point of the wax, its solid structure may undergo plastic deformation or even partial melting, which will also cause the separation of the wax from the fiber, leading to a decrease in the oil-proof ability and the pore closing ability. Summary of the Invention

[0005] In order to solve the above problems, the purpose of the present invention is to provide an environmentally friendly hydrogen peroxide stabilizer for chemical mechanical pulp bleaching and a preparation method thereof, which have a wide temperature resistance range and better long-term effectiveness.

[0006] To achieve the above effects, the present invention provides a fluorine-free gradient oil-proof agent with synergistic effect of multi-melting-point waxes, which is composed of the following components in parts by mass: 30 - 75 parts of deionized water, 0.5 - 8 parts of cationic emulsifier, 4 - 10 parts of starch emulsifier, 8 - 20 parts of multi-melting-point wax composition, 15 - 50 parts of flaky functional material, 2 - 6 parts of low-temperature wax with a melting point of 30 - 50°C, 2 - 8 parts of medium-temperature wax with a melting point of 55 - 85°C, and 4 - 12 parts of high-temperature wax with a melting point of 90 - 130°C.

[0007] In one embodiment of the present invention, the cationic emulsifier is at least one of polydimethyldiallylammonium chloride (PDADMAc), cetyltrimethylammonium chloride (CTA), polyamide polyamine epichlorohydrin (PAE), and poly(methacryloyloxyethyltrimethylammonium chloride) (PDMC), and the cationic charge density is 2 - 6 meq / g.

[0008] In one embodiment of the present invention, the starch emulsifier is at least one of hydroxypropyl starch, starch octenyl succinate, and acetylated oxidized starch, or other starch emulsifiers with a degree of substitution of 0.05 - 0.2 and a gelatinization temperature of 60 - 85°C.

[0009] In one embodiment of the present invention, the low-temperature wax is selected from beeswax, paraffin wax, or rice bran wax, the medium-temperature wax is selected from palm wax, candelilla wax, or montan wax, and the high-temperature wax is selected from microcrystalline wax, lignite wax, or Fischer-Tropsch wax.

[0010] In one embodiment of the present invention, the sheet-shaped functional material is bentonite or kaolin modified with a silane coupling agent, with a particle size of 0.5 - 20 μm and a specific surface area ≥ 50 m 2 / g.

[0011] The present invention also provides a preparation method of a fluorine-free gradient oil-proof agent with synergistic effect of multi-melting-point waxes, comprising the following steps: (1) Mix the cationic emulsifier with part of deionized water, and perform high-speed shear emulsification at 50 - 70°C (8000 - 12000 rpm, 20 - 40 min) to form emulsion A; (2) Mix the starch emulsifier with the remaining deionized water, gelatinize at 80 - 95°C and then cool down to 50°C, add the low-temperature wax, medium-temperature wax, and high-temperature wax, and perform homogenization treatment with a homogenizer to obtain emulsion B; (3) Mix emulsion A and emulsion B, add the sheet-shaped functional material, and perform mechanical stirring (30 - 60 min) and ultrasonic dispersion (40 KHz, 15 - 30 min) in sequence to prepare the fluorine-free gradient oil-proof agent with synergistic effect of multi-melting-point waxes.

[0012] In one embodiment of the present invention, the pressure of the homogenizer is controlled at a low pressure of 5 - 15 Mpa and a high pressure of 20 - 50 Mpa, and the cycle is 2 - 6 times.

[0013] In one embodiment of the present invention, in step (2), the gelatinization time is 10 - 40 min, the viscosity after gelatinization is 100 - 800 mPa·s, and the particle size distribution D90 of emulsion B ≤ 10 μm.

[0014] In one embodiment of the present invention, the fluorine-free gradient oil-proof agent with synergistic effect of multi-melting-point waxes is applicable to pulp molding products, degradable films, and textile coatings.

[0015] The present invention solves the above problems through the following technical solutions:

[0016] (1) The cationic emulsifier (such as PDADMAc) is compounded with the starch emulsifier. The former enhances the binding force between the fiber and the wax through electrostatic interaction, and the latter, as a biodegradable carrier, improves the emulsion stability. In the wet-end chemistry system, the cationic additive can be preferentially adsorbed on the surface of the fiber and fines to form a charge compensation layer, enhancing the spreading property and uniform adhesion of the wax on the fiber surface. The starch forms a micelle structure through the hydroxyl groups and hydrophobic regions of the molecular chain, coating the wax particles, inhibiting emulsion stratification or demulsification, and improving the long-term stability of the system. As a biodegradable carrier, after being compounded with the cationic emulsifier, the starch can reduce the dosage of traditional petroleum-based emulsifiers, meeting the environmental protection requirements of pulp molding products for recyclability and repulpability. The electrostatic adsorption of the cationic emulsifier and the steric hindrance of the starch are complementary, constructing a "charge-space" double-stabilization mechanism, reducing the interfacial free energy of the wax emulsion, and achieving the long-term storage stability of the high-solid-content emulsion. The compounding of the cationic emulsifier and the starch emulsifier optimizes the fluidity of medium-temperature wax and high-temperature wax, achieving coating uniformity. At the same time, the binding force between the wax and the fiber is enhanced through electrostatic interaction, reducing the risk of coating peeling in low-temperature environments.

[0017] (2) Low-temperature wax, medium-temperature wax, and high-temperature wax are used. The low-temperature wax can effectively penetrate into the fiber pores in the molten state, blocking the penetration channels of oily substances through physical filling. The medium-temperature wax forms a transition layer, and the high-temperature wax constructs a heat-resistant barrier, forming a gradient oil-proof structure. The medium-temperature wax forms a continuous coverage on the surface of the low-temperature wax layer, alleviating the interlayer peeling caused by temperature fluctuations or mechanical stress through its viscoelastic properties. The high-temperature wax layer can maintain the structural stability, avoiding the sticking problem caused by the softening of traditional paraffin wax at high temperatures. When the temperature changes, the phase transitions of each wax layer coordinately regulate the oil-proof performance (low-temperature barrier, medium-temperature buffering, high-temperature anti-permeation). The low-temperature wax and medium-temperature wax melt and flow during local heating to repair microcracks. The gradient structure combines the solid filling and molten self-healing characteristics of the wax, maintaining the oil-proof stability in the range of -30°C to 90°C and avoiding the low-temperature brittleness or high-temperature softening problems of single-melting-point materials.

[0018] (3) The sheet-like functional material (such as modified kaolin) acts through the synergistic effect of physical barrier and chemical adsorption. The sheet-like functional material can well fill the fiber gaps and adsorb wax and starch particles, further extending the oil-water penetration path.

[0019] (4) In this application, a cationic emulsifier is mixed with a part of deionized water and subjected to high-speed shear emulsification at 50 - 70 °C to form emulsion A; a starch emulsifier is mixed with the remaining deionized water, gelatinized at 80 - 95 °C, and then cooled to 50 °C to avoid charge inactivation caused by high temperature, while ensuring that the emulsifier molecules are fully dispersed in water. Low-temperature wax, medium-temperature wax, and high-temperature wax are added. When the temperature is cooled to 50 °C after the starch is gelatinized, multi-melting-point wax is added. The wax particles are wrapped by the starch three-dimensional network to prevent premature melting of the wax phase caused by high temperature. After homogenization treatment by a homogenizer, multi-scale dispersion of the wax phase is achieved. The particle size of the low-temperature wax is controlled at 1 - 5 μm, and the particle size of the high-temperature wax is ≤10 μm, forming a continuous gradient distribution to obtain emulsion B; emulsion A and emulsion B are mixed, and sheet-shaped functional materials are added. Mechanical stirring (30 - 60 min) and ultrasonic dispersion (40 KHz, 15 - 30 min) are carried out in sequence to precisely control the dispersion degree of the sheet-shaped functional materials and avoid uneven oil-proof performance caused by agglomeration, thus preparing a fluorine-free gradient oil-proof agent with synergistic effect of multi-melting-point wax.

[0020] (5) The compounding ratio of emulsifiers (such as cationic emulsifier and starch emulsifier) is adjustable to adapt to the coating process requirements of different viscosities and curing rates. The actual dosage of deionized water needs to be determined according to the actual solid content of the product. Too little is likely to cause demulsification, and too much will affect the subsequent processing performance. Brief Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the oil-proof mechanism of the oil-proof agent of the present invention.

[0022] Figure 2 It is the thermogravimetric analysis (TGA) curve of Example 1 and Comparative Example 1, showing that the thermal stability of the multi-melting-point wax combination is significantly better than that of a single wax.

[0023] Figure 3 It is a comparison diagram after 48 h of stability test for Example 1 and Comparative Example 4, proving the stability of this emulsification system. Detailed Embodiments

[0024] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] The melting point of each wax in this application is the starting melting temperature.

[0026] Beeswax 48 °C

[0027] Paraffin wax 55 °C (low melting point grade)

[0028] Rice bran wax 75 °C

[0029] Note: Although the melting point is slightly higher, it is still classified as a low-temperature wax due to its soft texture and good low-temperature fluidity.

[0030] Carnauba wax 85°C

[0031] Candelilla wax 68°C

[0032] Montan wax 82°C

[0033] Microcrystalline wax 60 - 95°C (the high melting point grade can reach above 90°C)

[0034] Lignite wax 95°C (the refined product can reach 100°C)

[0035] Fischer-Tropsch synthetic wax 90 - 120°C (higher melting points can be customized)

[0036] Example 1

[0037] Formula: 60 parts of deionized water, 3 parts of PDADMAC, 5 parts of hydroxypropyl starch, 4 parts of beeswax (melting point 48°C), 6 parts of carnauba wax (melting point 72°C), 8 parts of microcrystalline wax (melting point 98°C), 30 parts of silane-modified kaolin.

[0038] Preparation:

[0039] (1) Emulsify PDADMAC with 20 parts of water at 60°C under high-speed shearing (10,000 rpm, 30 min) to obtain emulsion A;

[0040] (2) Gelatinize hydroxypropyl starch with 40 parts of water at 90°C for 20 min, cool down to 50°C, then add beeswax, carnauba wax, and microcrystalline wax, and homogenize 4 times to obtain emulsion B. The pressure of the homogenizer is controlled at 10 Mpa for low pressure and 25 Mpa for high pressure;

[0041] (3) Mix emulsion A and B, add silane-modified kaolin, and mechanically stir for 40 min and then ultrasonically disperse for 20 min.

[0042] Example 2

[0043] Formula: 50 parts of deionized water, 5 parts of PAE, 8 parts of octenyl succinic anhydride starch ester (substitution degree 0.15), 4 parts of paraffin wax (melting point 42°C), 4 parts of candelilla wax (melting point 68°C), 24 parts of lignite wax (melting point 115°C), modified bentonite with a mass ratio of 1:1:6, 40 parts.

[0044] The preparation steps are the same as those in Example 1, and the pressure of the homogenizer is controlled at 10 Mpa for low pressure and 25 Mpa for high pressure.

[0045] Example 3

[0046] Formula: 50 parts of deionized water, 5 parts of PAE, 8 parts of octenyl succinic anhydride starch ester (substitution degree 0.15), 4.6 parts of paraffin wax (melting point 42°C), 18.3 parts of candelilla wax (melting point 68°C), 9.1 parts of montan wax (melting point 115°C), and 40 parts of modified bentonite with a mass ratio of 1:4:2.

[0047] The preparation steps are the same as those in Example 1, and the pressure of the homogenizer is controlled at a low pressure of 10 Mpa and a high pressure of 25 Mpa.

[0048] Example 4

[0049] Formula: 50 parts of deionized water, 5 parts of PAE, 8 parts of octenyl succinic anhydride starch ester (substitution degree 0.15), 16 parts of paraffin wax (melting point 42°C), 10.6 parts of candelilla wax (melting point 68°C), 5.3 parts of montan wax (melting point 115°C), and 40 parts of modified bentonite with a mass ratio of 3:1:2.

[0050] The preparation steps are the same as those in Example 1, and the pressure of the homogenizer is controlled at a low pressure of 10 Mpa and a high pressure of 25 Mpa.

[0051] Example 5

[0052] Formula: 60 parts of deionized water, 3 parts of PDADMAC, 5 parts of hydroxypropyl starch, 6 parts of beeswax (melting point 48°C), 9 parts of palm wax (melting point 72°C), 12 parts of microcrystalline wax (melting point 98°C), and 30 parts of silane-modified kaolin.

[0053] Preparation:

[0054] (1) Emulsify PDADMAC with 20 parts of water at 60°C by high-speed shearing (10000 rpm, 30 min) to obtain emulsion A;

[0055] (2) Gelatinize hydroxypropyl starch with 40 parts of water at 90°C for 20 min, cool to 50°C, then add beeswax, palm wax, and microcrystalline wax, and homogenize 4 times to obtain emulsion B. The pressure of the homogenizer is controlled at a low pressure of 10 Mpa and a high pressure of 25 Mpa;

[0056] (3) Mix emulsion A and B, add silane-modified kaolin, and mechanically stir for 40 min and then ultrasonically disperse for 20 min.

[0057] Comparative Example 1

[0058] Replace the multi-melting-point wax in Example 1 with a single-melting-point beeswax (48°C), and keep the other conditions unchanged.

[0059] Comparative Example 2

[0060] 0.5 part of cationic emulsifier PDADMAC and 10 parts of starch emulsifier, and the rest is the same as in Example 1.

[0061] Comparative Example 3

[0062] 8 parts of cationic emulsifier PDADMAC and 4 parts of starch emulsifier, and the rest is the same as in Example 1.

[0063] Comparative Example 4

[0064] Omit the cationic emulsifier PDADMAC and only use the starch emulsifier, and the rest is the same as in Example 1.

[0065] Performance Test and Result Analysis

[0066] (1) Test the pulp molded paper bowls obtained in Examples 1, 2, 3, 4, 5 and Comparative Examples 1, 3, 4. The test method is for reference. The test results are shown in Table 1: The grammage of the paper bowl is 15 g, the thickness at the thinnest part is 5 mm, and the dosage of the oil-proof agent is 5% of the paper weight.

[0067] Oil-proof property: Refer to GB / T 36787-2018. Since it is necessary to verify the oil-proof performance at different temperatures, soak it in edible oil at -30°C, 20°C, 50°C, and 90°C, and place the paper bowl on a vibration table (vibration frequency 1 hz), and observe the penetration time. The selected edible oil is Jinlongyu soybean oil, and the dosage is 50% of the paper bowl capacity.

[0068] Compressive performance: Refer to GB / T 36787-2018. Place the model paper bowl in an environment that meets the GB / T 10739 standard for at least 4 hours, and then conduct a compression test under the same conditions. When testing, place the specimen in the middle position of the lower platen of the compression tester, start the instrument until the specimen is crushed, record the pressure value, accurate to 1 Newton.

[0069] Table 1

[0070]

[0071] (2) Result Analysis

[0072] By comparing the test data of Examples 1-4 with Comparative Examples 1, 3, 4, and combining the results of oil-proof property and compressive performance, the following conclusions are obtained:

[0073] 1. The multi-melting point wax combination significantly improves the oil-proof performance.

[0074] In Example 1 (a mixture of beeswax, palm wax, and microcrystalline wax), the oil-proof time in each temperature range is qualified.

[0075] In Example 5 (a mixture of beeswax, palm wax, and microcrystalline wax), the oil-proof time at 20°C is the longest (105 min), and it performs stably at high temperatures (50 - 90°C) (68 min). However, the wax dosage is 1.5 times that of Example 1, and the oil-proof performance has no obvious improvement. Therefore, Example 1 is preferred.

[0076] Comparative Example 1 (using only single-melting-point beeswax) showed that the oil-proof time dropped sharply to 9 minutes at high temperature (90 °C), indicating that the synergistic effect of multi-melting-point waxes can broaden the temperature adaptation range and enhance high-temperature stability.

[0077] Example 4 (paraffin wax, candelilla wax, and montan wax mixed in a ratio of 3:1:2) had the best oil-proof performance (106 minutes) at 20 °C, but its performance decreased significantly at high temperature (90 °C), suggesting that the melting point distribution of the wax needs to balance low-temperature and high-temperature requirements.

[0078] 2. The ratio of emulsifiers affects the compressive performance

[0079] Comparison between Example 1 (3 parts of PDADMAC) and Comparative Example 3 (8 parts of PDADMAC) showed that an excessive amount of cationic emulsifier (Comparative Example 3) would cause a significant reduction in compressive strength (308 N) and deterioration of oil-proof performance, indicating that an excessive amount of emulsifier may damage the material structure.

[0080] Comparative Example 4 (without PDADMAC) had the lowest compressive strength (324 N), and its oil-proof performance was also significantly inferior to that of the examples, confirming that cationic emulsifiers are indispensable for enhancing interfacial bonding force and stability.

[0081] 3. Comparison with blank samples to verify the effectiveness of the formula

[0082] The oil-proof time of the blank sample was extremely short (≤10 seconds), and its compressive strength was 445 N. However, the compressive performance (522 - 578 N) and oil-proof performance of all examples were significantly better than those of the blank sample, proving that the oil-proof agent formula effectively improves the comprehensive performance.

[0083] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

[0084] Industrial Application

[0085] This product can be widely applied to pulp molding packaging such as frozen food trays (-30 °C), microwave meal boxes (100 °C), and hot drink cups (120 °C). By adjusting the wax ratio and emulsifier type, customized oil-proof solutions can be achieved. After testing, the pulp molding products added with this oil-proof agent still maintain excellent oil-proof performance in extreme environments and meet the FDA food contact material standards.

Claims

1. A fluorine-free gradient oil-proofing agent with synergistic effects of multi-melting point waxes, characterized in that: The invention is composed of the following components in parts by mass: 30-75 parts of deionized water, 0.5-8 parts of cationic emulsifier, 4-10 parts of starch emulsifier, 8-20 parts of multi-melting point wax composition, 15-50 parts of flaky functional material, 2-6 parts of low-temperature wax with a melting point of 30-50°C, 2-8 parts of medium-temperature wax with a melting point of 55-85°C, and 4-12 parts of high-temperature wax with a melting point of 90-130°C.

2. The fluorine-free gradient oil-proofing agent with multi-melting point wax synergistic effect according to claim 1, characterized in that: The cationic emulsifier is at least one of polydimethyldiallyl ammonium chloride (PDADMAc), hexadecyltrimethylammonium chloride (CTA), polyamide polyamine epichlorohydrin (PAE), and polymethacryloyloxyethyltrimethylammonium chloride (PDMC), and the cationic charge density is 2-6 meq / g.

3. The fluorine-free gradient oil-proofing agent with multi-melting point wax synergistic effect according to claim 1, characterized in that: The starch emulsifier is at least one of hydroxypropyl starch, octenyl succinate starch ester, acetylated oxidized starch, or other starch emulsifiers with a degree of substitution of 0.05-0.2 and a gelatinization temperature of 60-85°C.

4. The fluorine-free gradient oil-proofing agent with multi-melting point wax synergistic effect according to claim 1, characterized in that: The low-temperature wax is selected from beeswax, paraffin or rice bran wax, the medium-temperature wax is selected from palm wax, candelilla wax or montan wax, and the high-temperature wax is selected from microcrystalline wax, montan wax or Fischer-Tropsch wax.

5. The fluorine-free gradient oil-proofing agent with multi-melting point wax synergistic effect according to claim 1, characterized in that: The sheet-like functional material is bentonite or kaolin modified by a silane coupling agent, with a particle size of 0.5-20 μm and a specific surface area of ​​≥50 m² / g.

6. A method for preparing the fluorine-free gradient oil-proofing agent with synergistic effects of multi-melting point waxes according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Mix the cationic emulsifier with part of the deionized water, and perform high-speed shear emulsification at 50-70°C and 8000-12000 rpm for 20-40 minutes to form emulsion A; (2) Mix the starch emulsifier with the remaining deionized water, gelatinize at 80-95°C, cool to 50°C, add low-temperature wax, medium-temperature wax, and high-temperature wax, and homogenize with a homogenizer to obtain emulsion B; (3) Emulsion A and emulsion B are mixed, and the flaky functional material is added, followed by mechanical stirring for 30-60 min and 35-45 kHz ultrasonic dispersion for 15-30 min, to obtain a fluorine-free gradient oil repellent with synergistic effects of multi-melting point waxes.

7. The method for preparing the fluorine-free gradient oil-proofing agent with synergistic effects of multi-melting point waxes according to claim 7, characterized in that: The homogenizer pressure is controlled at low pressure 5-15Mpa, high pressure 20-50Mpa, and cycled 2-6 times.

8. The method for preparing the fluorine-free gradient oil-proofing agent with synergistic effects of multi-melting point waxes according to claim 7, characterized in that: In step (2), the gelatinization time is 10-40 min, the viscosity after gelatinization is 100-800 mPa·s, and the particle size distribution D90 of emulsion B is ≤10 μm.

9. The method for preparing the fluorine-free gradient oil-proofing agent with synergistic effects of multi-melting point waxes according to claim 9, characterized in that: The fluorine-free gradient oil-proofing agent with synergistic effects of multi-melting point waxes is suitable for pulp molding products, degradable films, and textile coatings.

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