Hydrophobic and oleophobic packaging paper bag and preparation method thereof

Abstract

The invention discloses a hydrophobic and oleophobic packaging paper bag and a preparation method thereof, and belongs to the technical field of packaging processing.The hydrophobic and oleophobic packaging paper bag is prepared by adding hydrophobic modified nano silicon dioxide into a polymethyl methacrylate polymerization system, adding paraffin after polymerization is completed and mixing to form a coating solution; and coating the surface of the paper bag body with the mixture, and drying to form a film to obtain the hydrophobic and oleophobic packaging paper bag. According to the invention, the roughness of a coating layer is increased by using nano silicon dioxide with a small particle size, grafting hydrophobic modification is carried out by using polydimethylsiloxane, and a hydrophobic long chain on the surface of the modified nano silicon dioxide is wound with a gradually growing polymethyl methacrylate molecular chain in a monomer polymerization process; the paraffin is gathered on the periphery of the hydrophobic nano silicon dioxide through hydrophobic induction, the paraffin migrated to the surface after being dried to form a film exists in peripheral gaps of the hydrophobic modified nano silicon dioxide, the effect of making up hydrophobic defects between particles is achieved, and the packaging paper bag has excellent hydrophobic and oleophobic performance under the condition that fluorine-containing materials are not used.

Description

Technical Field

[0001] This invention belongs to the field of packaging processing technology, specifically relating to a hydrophobic and oleophobic packaging paper bag and its preparation method. Background Technology

[0002] Paper and paperboard materials have advantages such as a long history of use, abundant raw material sources, light weight, and ease of processing, and are widely used for packaging and protecting consumer goods such as food. Due to the environmental pollution risks associated with plastic materials, paper bags have become widely used in recent years.

[0003] Compared to plastic packaging materials, paper bags have the advantage of being environmentally friendly, but they are easily affected by moisture and damage, and have poor waterproof and moisture-proof performance. They are not suitable for long-term storage or storing goods with high humidity. When used to package oily foods, it is necessary to prevent oil penetration to protect the food from contamination and avoid contaminating other items. Natural paper materials have poor resistance to liquids, stability and chemical migration, and must be treated to be waterproof and oil-proof.

[0004] Current methods for waterproofing and oil-repellentizing paper bags primarily employ protective coatings, often using fluorinated materials, including perfluorinated or polyfluoroalkyl compounds. These materials exhibit typical hydrophobic and oleophobic structures and contain C-F bonds, resulting in high chemical stability. Consequently, they exhibit slow biodegradation and bioaccumulation, making them a persistent pollutant of significant global concern. While adding fluorinated materials can effectively improve the hydrophobic, oleophobic, and heat-resistant properties of food-contact paper, the contact between treated paper products and food may pose potential human health risks. With increasingly stringent food safety requirements, traditional fluorinated materials are gradually being regulated. Therefore, using fluorine-free materials to replace fluorinated materials for waterproofing and oil-repellent treatment is currently a hot research topic. Summary of the Invention

[0005] This invention provides a hydrophobic and oleophobic packaging paper bag and its preparation method, which can solve the problem of poor hydrophobic and oleophobic properties of packaging paper bags in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions: This invention provides a method for preparing hydrophobic and oleophobic packaging paper bags, comprising the following steps: Step 1: Disperse nano-silica in toluene, add phenyl diisocyanate under anhydrous and oxygen-free conditions, stir and heat under reflux for 4-6 hours, add monohydroxy-terminated polydimethylsiloxane, continue reflux for 5-8 hours, centrifuge and wash the precipitate with toluene, and dry to obtain hydrophobic modified silica. Step 2: Add methyl methacrylate to a beaker, add initiator, stir evenly, add hydrophobic modified silica, stir and heat to polymerize, and after the reaction is complete, mix with paraffin to obtain coating liquid; Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0007] In step one, phenyl diisocyanate is used as a linker. The highly reactive isocyanate groups on phenyl diisocyanate react with the silanol groups on the surface of nano silica. Another less reactive unreacted isocyanate group reacts with monohydroxy-terminated polydimethylsiloxane, which grafts the monohydroxy-terminated polydimethylsiloxane onto the surface of nano silica. The hydrophobic long chain of polydimethylsiloxane changes its surface from hydrophilic to hydrophobic, and its surface energy is significantly reduced.

[0008] Among coating film-forming materials, polytetrafluoroethylene (PTFE) exhibits the best hydrophobic and oleophobic properties, but due to its high fluorine content, it poses a significant environmental pollution risk. Polymethyl methacrylate (PMMA) itself possesses good chemical stability, weather resistance, and recyclability, with relatively low environmental pollution hazards. Furthermore, it has high light transmittance, so as a coating material, it does not obstruct the patterns on packaging paper bags and does not affect their appearance. While PMMA possesses some hydrophobicity due to the presence of hydrophobic hydrocarbon chains in its molecules, its hydrophobicity is limited, and its oleophobic properties are even worse. Adding siloxanes with low surface energy can improve the hydrophobic and oleophobic properties of the material, but PMMA and polydimethylsiloxane have poor compatibility, and phase separation occurs under direct blending conditions, failing to achieve the goal of uniformly improving hydrophobic and oleophobic properties. In step two of this invention, hydrophobically modified silica is added to the polymerization system of methyl methacrylate monomers. During the polymerization process, the polymer formed by the methyl methacrylate monomers and the hydrophobic long chains grafted onto the surface of the modified silica intertwine and interweave, resulting in a uniformly mixed composite material.

[0009] Furthermore, the particle size of the nano-silica is 10-50 nm, and the concentration of silica in toluene is 10-20 g / L. The smaller particle size of silica can increase the roughness of the formed coating layer, reduce the surface energy of the coating layer, and enhance the hydrophobic and oleophobic properties.

[0010] The hydrophobic and oleophobic properties of a material are determined by the relationship between the surface energy of the solid material and the surface energy of the liquid in contact with it. Oil generally has a lower surface energy than water, and solid materials generally have a higher surface energy than water. Therefore, oleophobic materials are usually hydrophobic, but hydrophobic materials are not necessarily oleophobic. Furthermore, simply reducing surface energy is insufficient to achieve oleophobicity; the surface roughness of the material needs to be increased simultaneously. This increases the actual contact area while keeping the projected area of ​​the solid-liquid interface constant, thereby increasing the energy required for the liquid to completely wet the solid surface and improving the material's liquid-repellent ability. In this invention, hydrophobically modified nano-silica is used to increase the roughness of the paper bag coating layer, further reducing the surface energy.

[0011] Further, the phenyl diisocyanate is one of toluene diisocyanate and diphenylmethane diisocyanate, and the molar ratio of phenyl diisocyanate to nano-silica is 1-2:5. In the molecular structure of isocyanate, electron-withdrawing groups increase the positive charge of carbon atoms in the isocyanate, increasing reactivity, while electron-donating groups decrease the reactivity of the isocyanate. Due to steric hindrance and inductive effects, the two -NCO groups in the phenyl diisocyanate molecule have different reactivity. The more reactive -NCO group will participate in the reaction first, reacting with the silanol groups on the surface of nano-silica.

[0012] Furthermore, the reflux reaction temperature is 110-120°C.

[0013] Furthermore, the molar ratio of the monohydroxy-terminated polydimethylsiloxane to phenyl diisocyanate is 1:5-10. After the addition of the monohydroxy-terminated polydimethylsiloxane, the unreacted -NCO groups in the phenyl diisocyanate react with the terminal hydroxyl groups of the monohydroxy-terminated polydimethylsiloxane, grafting hydrophobic long chains onto the surface of nano-silica. By adjusting the molar amount of the monohydroxy-terminated polydimethylsiloxane, a layer of polymer molecular chains is ensured to coat the silica surface, effectively reducing surface energy and improving its hydrophobic properties.

[0014] Furthermore, the initiator is one of azobisisobutyronitrile and benzoyl peroxide.

[0015] Furthermore, the mass of the initiator is 3-5% of the mass of methyl methacrylate.

[0016] Furthermore, the mass ratio of the hydrophobically modified silica to methyl methacrylate is 4-10:1.

[0017] When hydrophobically modified silica is simply blended into polymerized polymethyl methacrylate (PMMA), uneven dispersion can occur due to the incompatibility between polydimethylsiloxane and PMMA. However, when hydrophobically modified silica and PMMA monomers are combined to form a polymerization reaction system, the long-chain entanglement of the hydrophobically modified silica during the stirring reaction results in uniform dispersion in the coating solution. This entanglement also ensures tight bonding with other materials. As the polymerization reaction proceeds, the viscosity gradually increases, and the hydrophobically modified silica is evenly and stably distributed in the coating solution, resulting in a uniform surface roughness of the coated packaging paper bag with no significant difference in surface hydrophobic and oleophobic properties.

[0018] Furthermore, the temperature of the stirring and heating polymerization reaction is 90-110℃, and the reaction time is 60-90 min.

[0019] Furthermore, the paraffin wax accounts for 5-10% of the mass of the coating liquid. Paraffin wax is a mineral wax composed of hydrocarbons, the main component of which is straight-chain alkanes, giving it good hydrophobic and oleophobic properties. However, the oleophobic properties of pure paraffin wax still need to be further improved. In the polymethyl methacrylate (PMMA) system, paraffin wax, being a nonpolar molecule, primarily interacts with PMMA through van der Waals forces, a relatively weak intermolecular force. Additionally, the polar groups of PMMA may weakly interact with paraffin molecules via dipole-dipole interactions, but these interactions remain weak. Consequently, the mixture exhibits poor stability. However, in the presence of hydrophobically modified silica, the hydrophobicity induces paraffin wax to aggregate around it, thus improving the system's stability. During the coating drying and curing process, the paraffin wax around the hydrophobically modified silica migrates to the coating surface. The uniformly distributed hydrophobically modified silica forms an uneven, rough structure on the resulting coating, and the migrating paraffin wax forms a hydrophobic and oleophobic layer around it, compensating for the hydrophobic defects between adjacent hydrophobically modified silica particles. Simultaneously, the synergistic reduction of surface energy by polydimethylsiloxane and paraffin wax, coupled with the rough surface constructed by nano-silica, further enhances the liquid-repellent properties, achieving both hydrophobicity and oleophobicity.

[0020] The present invention also provides a hydrophobic and oleophobic packaging paper bag, which is prepared by the above-described preparation method.

[0021] The beneficial effects of this invention are: (1) This invention utilizes small-particle-size nano-silica to increase the roughness of the coating layer and grafts it with polydimethylsiloxane to achieve hydrophobic modification of nano-silica. Unlike the conventional method of blending hydrophobic modified nano-silica with film-forming materials, this invention adds hydrophobic modified nano-silica to the polymerization monomer reaction system of polymethyl methacrylate. The hydrophobic long chains on the surface of the modified nano-silica are entangled with the gradually growing polymethyl methacrylate molecular chains during the monomer polymerization process. The hydrophobic modified nano-silica is evenly dispersed, and its hydrophobic properties reduce the surface energy of the material. The increased roughness further reduces the surface energy, achieving oleophobic properties.

[0022] (2) In this invention, paraffin is added to the coating liquid. On the one hand, paraffin itself has good hydrophobic and oleophobic properties. On the other hand, conventional coating liquids with added hydrophobic modified nanoparticles will have insufficient hydrophobicity due to agglomeration. In this invention, the modified nano-silica can be dispersed through the long chain entanglement during the polymerization of polymethyl methacrylate. However, there are gaps between the dispersed hydrophobic nano-silica, and the hydrophobic properties of the polymethyl methacrylate material in the gaps are limited. During the preparation process, paraffin is agglomerated around the hydrophobic nano-silica through hydrophobic induction. After drying and forming a film, the paraffin that migrates to the surface exists in the gaps around the hydrophobic modified nano-silica, thus compensating for the hydrophobic defects between particles.

[0023] (3) Polymethyl methacrylate itself is brittle. Although it has high light transmittance and does not affect the appearance of the packaging paper bag, it is prone to cracking. In this invention, hydrophobic modified nano-silica is doped in the polymerization of polymethyl methacrylate. A stable bond is formed through the long chain winding effect, which inhibits the crack propagation caused by stress concentration and improves the impact resistance of the coating layer. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 10-20nm, place it in a flask, add 1L of toluene, ultrasonically disperse for 30min until uniformly dispersed, replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for reaction, after 6h of reaction, add 536.3g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), continue reflux reaction for 8h, centrifuge and wash the precipitate 3 times with toluene, dry at 80℃ to obtain hydrophobic modified silica; Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 2000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 132.37g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0026] Example 2 The only difference from Example 1 is that the particle size of the nano-silica is 20-30 nm.

[0027] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 20-30nm, place it in a flask, add 1L of toluene, and ultrasonically disperse for 30min until uniformly dispersed. Replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for reaction. After reacting for 6h, add 536.3g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), and continue reflux for 8h. After centrifugation, wash the precipitate three times with toluene, and dry at 80℃ to obtain hydrophobic modified silica. Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 2000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 132.37g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0028] Example 3 The only difference from Example 1 is that the particle size of the nano-silica is 40-50 nm.

[0029] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 40-50nm, place it in a flask, add 1L of toluene, ultrasonically disperse for 30min until uniformly dispersed, replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for reaction, after 6h of reaction, add 536.3g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), continue reflux reaction for 8h, centrifuge and wash the precipitate 3 times with toluene, dry at 80℃ to obtain hydrophobic modified silica; Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 2000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 132.37g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0030] Example 4 The only difference from Example 2 is that the amount of toluene diisocyanate added was adjusted from 200g to 232g, and the mass of monohydroxy-terminated polydimethylsiloxane was adjusted accordingly to 622.11g.

[0031] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 20-30nm, place it in a flask, add 1L of toluene, ultrasonically disperse for 30min until uniformly dispersed, replace the air with nitrogen, add 232g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for reaction, after 6h of reaction, add 622.11g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), continue reflux reaction for 8h, centrifuge, wash the precipitate 3 times with toluene, dry at 80℃ to obtain hydrophobic modified silica; Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 2000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 132.37g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0032] Example 5 The only difference from Example 2 is that the amount of toluene diisocyanate added was adjusted from 200g to 117g, and the mass of monohydroxy-terminated polydimethylsiloxane was adjusted accordingly to 4667.55g.

[0033] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 20-30nm, place it in a flask, add 1L of toluene, and ultrasonically disperse for 30min until uniformly dispersed. Replace the air with nitrogen, add 117g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for reaction. After reacting for 6h, add 313.74g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), and continue reflux for 8h. After centrifugation, wash the precipitate three times with toluene, and dry at 80℃ to obtain hydrophobic modified silica. Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 2000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 132.37g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0034] Example 6 The only difference from Example 2 is that the mass of the monohydroxy-terminated polydimethylsiloxane was adjusted to 1608.90 g.

[0035] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 20-30nm, place it in a flask, add 1L of toluene, and ultrasonically disperse for 30min until uniformly dispersed. Replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for 6h. After reaction, add 1608.90g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), and continue reflux for 8h. After centrifugation, wash the precipitate three times with toluene, and dry at 80℃ to obtain hydrophobic modified silica. Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 2000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 132.37g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0036] Example 7 The only difference from Example 2 is that the mass of the monohydroxy-terminated polydimethylsiloxane was adjusted to 2681.5g.

[0037] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 20-30nm, place it in a flask, add 1L of toluene, ultrasonically disperse for 30min until uniformly dispersed, replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for reaction, after 6h of reaction, add 2681.5g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), continue reflux reaction for 8h, centrifuge and wash the precipitate 3 times with toluene, dry at 80℃ to obtain hydrophobic modified silica; Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 2000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 132.37g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0038] Example 8 The only difference from Example 6 is that in step two, the mass of hydrophobically modified silica is adjusted from 2000g to 3000g, and the mass of paraffin is adjusted to 185g accordingly.

[0039] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 20-30nm, place it in a flask, add 1L of toluene, and ultrasonically disperse for 30min until uniformly dispersed. Replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for 6h. After reaction, add 1608.90g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), and continue reflux for 8h. After centrifugation, wash the precipitate three times with toluene, and dry at 80℃ to obtain hydrophobic modified silica. Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 3000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 185g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0040] Example 9 The only difference from Example 6 is that in step two, the mass of hydrophobically modified silica is adjusted from 2000g to 5000g, and the mass of paraffin is adjusted accordingly to 290.26g.

[0041] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 20-30nm, place it in a flask, add 1L of toluene, and ultrasonically disperse for 30min until uniformly dispersed. Replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for 6h. After reaction, add 1608.90g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), and continue reflux for 8h. After centrifugation, wash the precipitate three times with toluene, and dry at 80℃ to obtain hydrophobic modified silica. Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 5000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 290.26g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0042] Example 10 The only difference from Example 8 is that in step two, the amount of paraffin added is adjusted from 185g to 305.65g.

[0043] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 20-30nm, place it in a flask, add 1L of toluene, and ultrasonically disperse for 30min until uniformly dispersed. Replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for 6h. After reaction, add 1608.90g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), and continue reflux for 8h. After centrifugation, wash the precipitate three times with toluene, and dry at 80℃ to obtain hydrophobic modified silica. Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 3000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 305.65g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0044] Example 11 The only difference from Example 8 is that in step two, the amount of paraffin added is adjusted from 185g to 390.56g.

[0045] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 20-30nm, place it in a flask, add 1L of toluene, and ultrasonically disperse for 30min until uniformly dispersed. Replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for 6h. After reaction, add 1608.90g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), and continue reflux for 8h. After centrifugation, wash the precipitate three times with toluene, and dry at 80℃ to obtain hydrophobic modified silica. Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 3000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 390.56g of paraffin wax and mix to obtain the coating liquid. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

[0046] Comparative Example 1 The only difference from Example 1 is that hydrophobic modified silica is not prepared, and no hydrophobic modified silica is added when preparing the coating liquid.

[0047] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 500g of methyl methacrylate and put it into a beaker. Add 15g of azobisisobutyronitrile as an initiator, turn on the stirrer, and heat to 90℃ for polymerization reaction. After the reaction is completed, add 390.56g of paraffin wax and mix to obtain the coating liquid. Step 2: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain the packaging paper bag.

[0048] Comparative Example 2 The only difference from Example 1 is that hydrophobically modified silica is not prepared, and monohydroxy-terminated polydimethylsiloxane is directly added when preparing the coating liquid.

[0049] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 2000g of monohydroxy-terminated polydimethylsiloxane, turn on the stirrer, heat to 90℃ for polymerization reaction, and after the reaction is completed, add 390.56g of paraffin wax and mix to obtain the coating liquid. Step 2: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain the packaging paper bag.

[0050] Comparative Example 3 The only difference from Example 1 is that hydrophobically modified silica is directly added to the polymethyl methacrylate solution.

[0051] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 10-20nm, place it in a flask, add 1L of toluene, ultrasonically disperse for 30min until uniformly dispersed, replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for reaction, after 6h of reaction, add 536.3g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), continue reflux reaction for 8h, centrifuge and wash the precipitate 3 times with toluene, dry at 80℃ to obtain hydrophobic modified silica; Step 2: Weigh 500g of polymethyl methacrylate and put it into a beaker. Add 500g of acetone and stir to dissolve. Add 2000g of hydrophobic modified silica and stir to mix evenly. Add 390.56g of paraffin wax and mix evenly to obtain the coating solution. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain the packaging paper bag.

[0052] Comparative Example 4 The only difference from Example 1 is that no paraffin is added when preparing the coating liquid.

[0053] Preparation of hydrophobic and oleophobic packaging paper bags: Step 1: Weigh 200g of nano-silica with a particle size of 10-20nm, place it in a flask, add 1L of toluene, ultrasonically disperse for 30min until uniformly dispersed, replace the air with nitrogen, add 200g of toluene diisocyanate, start stirring, heat to 110℃ and reflux for reaction, after 6h of reaction, add 536.3g of monohydroxy-terminated polydimethylsiloxane (Mn=4670), continue reflux reaction for 8h, centrifuge and wash the precipitate 3 times with toluene, dry at 80℃ to obtain hydrophobic modified silica; Step 2: Weigh 500g of methyl methacrylate into a beaker, add 15g of azobisisobutyronitrile as an initiator, stir evenly, add 2000g of hydrophobic modified silica prepared according to Step 1, turn on the stirrer, heat to 90℃ for polymerization reaction, and obtain the coating liquid after the reaction is completed. Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain the packaging paper bag.

[0054] The packaging paper bags prepared in Examples 1-11 and Comparative Examples 1-4 were subjected to performance tests, and the results are shown in Table 1.

[0055] Hydrophobicity test: 10 μL of water was dropped onto the coated surface of the paper bag, and the water contact angle value was measured using a contact angle meter.

[0056] Oleophobic properties: 10 μL of hexadecane was dropped onto the coated surface of the paper bag, and the oil contact angle value was measured using a contact angle meter.

[0057] Anti-cracking and anti-detachment performance: Place the packaging paper bag at a low temperature (4℃) for 30 minutes and fold it back and forth 3 times to observe the cracking of the surface coating layer.

[0058] Table 1

[0059] As shown in Table 1, under normal conditions, reducing the particle size of nano-silica can maximize surface roughness and improve hydrophobic and oleophobic properties to increase hydrophobicity. However, in Examples 1-3 of the invention, Example 1, with the smallest particle size, exhibits weaker hydrophobic and oleophobic properties than Example 2. Under excessively small particle size conditions, on the one hand, the strong van der Waals and electrostatic forces between particles during hydrophobic modification easily lead to agglomeration, resulting in incomplete hydrophobic modification of silica. On the other hand, the modified particles with excessively small particle sizes move faster during the polymerization reaction, which is not conducive to long-chain entanglement. In Example 4, increasing the amount of toluene diisocyanate gradually improves the degree of surface hydrophobic modification of nano-silica and reduces the amount of hydroxyl groups on the surface. However, at this point, the fully hydrophobically modified nano-silica leads to poor film-forming properties of the coating, and the hydrophobic properties actually decrease. In Example 6, appropriately adding a single-hydroxyl-terminated polydimethylsiloxane ensures sufficient reaction and grafting with toluene diisocyanate, improving hydrophobic and oleophobic properties. In Examples 8 and 9, the proportion of hydrophobic modified silica in the coating liquid was increased. Example 8 showed the best hydrophobic and oleophobic properties. In Example 9, excessive hydrophobic modified silica caused stacking, resulting in surface defects and spots, thus affecting the hydrophobic and oleophobic properties. In Example 10, the water / oil contact angle increased with the addition of paraffin wax. In Example 11, further addition of paraffin wax did not significantly enhance the hydrophobic and oleophobic properties. In Comparative Example 1, without the addition of hydrophobic modified silica, the paper bag lacked oleophobic properties, with an oil contact angle below 70°, and significant stress cracking at low temperatures. Comparative Examples 2 and 3 showed inferior hydrophobic and oleophobic properties compared to Example 1. Due to the lack of stress relief from nano-silica, the coating surface of Comparative Example 2 was more prone to brittle cracking. Although hydrophobic modified silica was added in Comparative Example 3, its direct addition to the polymer was not conducive to compatibility, resulting in poor material uniformity and stress concentration leading to crack propagation.

[0060] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0061] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a hydrophobic and oleophobic packaging paper bag, characterized in that, Includes the following steps: Step 1: Disperse nano-silica in toluene, add phenyl diisocyanate under anhydrous and oxygen-free conditions, stir and heat under reflux for 4-6 hours, add monohydroxy-terminated polydimethylsiloxane, continue reflux for 5-8 hours, centrifuge and wash the precipitate with toluene, and dry to obtain hydrophobic modified silica. Step 2: Add methyl methacrylate to a beaker, add initiator, stir evenly, add hydrophobic modified silica, stir and heat to polymerize, and after the reaction is complete, mix with paraffin to obtain coating liquid; Step 3: Apply the coating liquid to the surface of the paper bag body and dry it to form a film to obtain a hydrophobic and oleophobic packaging paper bag.

2. The method for preparing a hydrophobic and oleophobic packaging paper bag according to claim 1, characterized in that, The nano-silica has a particle size of 10-50 nm and a silica concentration of 10-20 g / L in toluene.

3. The method for preparing a hydrophobic and oleophobic packaging paper bag according to claim 1, characterized in that, The phenyl diisocyanate is one of toluene diisocyanate and diphenylmethane diisocyanate, and the molar ratio of phenyl diisocyanate to nano silica is 1-2:

5.

4. The method for preparing a hydrophobic and oleophobic packaging paper bag according to claim 1, characterized in that, The molar ratio of the monohydroxy-terminated polydimethylsiloxane to phenyl diisocyanate is 1:5-10.

5. The method for preparing a hydrophobic and oleophobic packaging paper bag according to claim 1, characterized in that, The initiator is one of azobisisobutyronitrile and benzoyl peroxide.

6. The method for preparing a hydrophobic and oleophobic packaging paper bag according to claim 1, characterized in that, The mass of the initiator is 3-5% of the mass of methyl methacrylate.

7. The method for preparing a hydrophobic and oleophobic packaging paper bag according to claim 1, characterized in that, The mass ratio of the hydrophobically modified silica to methyl methacrylate is 4-10:

1.

8. The method for preparing a hydrophobic and oleophobic packaging paper bag according to claim 1, characterized in that, The stirring and heating polymerization reaction is carried out at a temperature of 90-110℃ for a reaction time of 60-90 min.

9. The method for preparing a hydrophobic and oleophobic packaging paper bag according to claim 1, characterized in that, The paraffin wax accounts for 5-10% of the mass of the coating solution.

10. A hydrophobic and oleophobic packaging paper bag, characterized in that, The hydrophobic and oleophobic packaging paper bag is prepared by the preparation method described in any one of claims 1-9.

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