High-filling type II anhydrite / polyethylene composite packaging material and preparation method thereof

Abstract

The invention discloses a high-filling type II anhydrite polyethylene composite packaging material and a preparation method thereof, and belongs to the technical field of plastic packaging materials. The composite material comprises modified gypsum which is coated by nano SiO2 and is synergistically modified by double coupling agents, and polyethylene serving as a base material, wherein the addition amount of the modified gypsum is 60%; a gradient temperature control twin-screw extruder is adopted for processing, during extrusion processing, the front-section temperature is 155-165 DEG C, the middle-section temperature is 185-195 DEG C, the rear-section temperature is 205-215 DEG C, and a gradient filler distribution material is formed after extrusion; the problems that under the condition of 60% high doping, II type anhydrite is difficult to disperse in a polyethylene base material, and under the condition of high doping, the material surface is rough are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic packaging materials, in particular to a highly filled II type anhydrous gypsum / polyethylene composite packaging material and a preparation method thereof. Background Art

[0002] Plastic packaging materials, with their advantages of lightweight, high transparency, moisture and humidity resistance, and excellent chemical stability, are widely used in the food, pharmaceutical, and chemical industries. Common plastic packaging materials include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and polyethylene terephthalate (PET). These materials are widely used due to their excellent physical and mechanical properties, corrosion resistance, insulation, and processability.

[0003] Currently, single plastic packaging materials are no longer able to meet the needs of actual use. Therefore, functional fillers are generally added to single base materials to form composite materials to improve the performance of packaging materials.

[0004] As a byproduct of chemical production, increasing the utilization of chemical gypsum is key to energy conservation and environmental protection. Using Type II anhydrous gypsum as a filler, leveraging its biodegradability, can significantly reduce environmental pollution caused by plastic packaging materials. Polyethylene packaging materials modified with Type II anhydrous gypsum not only improve strength and durability but also possess properties such as water resistance, moisture resistance, and insect resistance, making them highly effective in practical applications.

[0005] With a certain amount of filler doping, the mechanical properties of composite packaging materials can be significantly improved as the filler doping level increases. However, generally speaking, the doping level of Type II anhydrous gypsum should not exceed 55%. If the filler doping level is too high, it will cause an increase in the interfacial area, hindering the attraction between the resin matrix and the filler, resulting in poor interfacial bonding. Moreover, excessive filler doping is prone to cause filler agglomeration, affecting overall performance. This impact is particularly pronounced when Type II anhydrous gypsum is added as an inorganic filler to a polymer matrix. Summary of the Invention

[0006] One of the objectives of the present invention is to provide a highly filled type II anhydrous gypsum / polyethylene composite packaging material to solve the problem that type II anhydrous gypsum is difficult to disperse in a polyethylene substrate under a high doping level of 60% and that the material surface is rough under high doping levels.

[0007] In order to solve the above problems, the present invention adopts the following technical means: A highly filled type II anhydrous gypsum / polyethylene composite packaging material, comprising modified gypsum coated with nano-SiO2 / synergistically modified with a double coupling agent, and polyethylene as a base material, wherein the modified gypsum is added in an amount of 60%; Among them, a double coupling agent is used in conjunction with nano-SiO2 coating to modify type II anhydrous gypsum. Firstly, the chemical bonding of the double coupling agent is used to enhance the interfacial bonding between the filler and the polyethylene matrix, thereby solving the problems of agglomeration and uneven dispersion caused by high filling; secondly, the coated nano-SiO2 is used to enhance the heat resistance of the filler and reduce the oil absorption value, thereby improving the processing fluidity of type II anhydrous gypsum under high doping conditions.

[0008] In addition, the coating of nano-SiO2 can also prevent the expansion of silver streaks in the composite material and improve its durability.

[0009] A gradient temperature-controlled twin-screw extruder is used for processing. During extrusion processing, the temperature of the front section is 155~165℃, the temperature of the middle section is 185~195℃, and the temperature of the back section is 205~215℃. After extrusion, a gradient filler distribution material is formed.

[0010] During extrusion, the screw temperature is controlled in zones to achieve a gradient filler distribution along the extrusion direction: 50% filler in the surface layer and 60% in the core layer. The low filler content in the surface layer improves surface smoothness, while the high filler content in the core layer enhances overall strength. This not only ensures that the composite material possesses the mechanical properties of high filler content, such as tensile strength, but also avoids the surface roughness that can occur under high filler content, affecting the composite's aesthetics.

[0011] Preferably, the modified gypsum has a core-shell structure, with type II anhydrous gypsum particles as the core, and a nano-SiO2 layer as the shell is covered on the surface of the type II anhydrous gypsum particles by a sol / gel method.

[0012] In this way, a nano-SiO2 layer is in situ loaded on the surface of the type II anhydrous gypsum particles. The SiO2 layer can, on the one hand, block the contact between moisture and the type II anhydrous gypsum particles, thereby preventing the filler from absorbing moisture and agglomerating; on the other hand, it can also play a self-lubricating role, reduce the surface energy of the filler, and reduce the van der Waals force between the particles; moreover, it can also increase the thermal deformation temperature of the composite material.

[0013] Furthermore, the double coupling agent used for synergistic modification consists of KH-550 and NDZ-101.

[0014] Among them, KH-550 and NDZ-101 are used to form gradient grafting on type II anhydrous gypsum particles coated with SiO2, forming an "inorganic-organic" gradient cross-section, thereby improving the interface bonding strength of the filler and greatly improving the interface shear strength between the filler and the body.

[0015] Furthermore, during the extrusion process, the pitch of the front-stage screw is greater than the pitch of the middle-stage screw, and the modified gypsum is added in the front-stage.

[0016] In this way, when gradient temperature control is used to form a gradient filler distribution, during the front section operation, a larger pitch is used to force the filler to migrate to the core layer; during the middle section operation, the pitch is smaller than the front section, thereby enhancing shear dispersion during the middle section reaction; and during the back section operation, the filler reflux is further slowed down.

[0017] Furthermore, for the packaging material involved in this application, when a large amount of filler is added, the dual effects of the double coupling agent combined with the nano-coating are utilized to avoid the agglomeration of the filler in the matrix when a large amount of filler is added, enhance the interfacial bonding strength between the filler and the polyethylene matrix, improve the heat resistance of the filler, and reduce the oil absorption value. Even when a large amount of filler is added, the packaging material can still have good processing fluidity and is easy to process.

[0018] At the same time, gradient temperature control processing is adopted to form a gradient filler distribution, so that the filler is gradiently distributed along the extrusion direction, with the filler content of the surface layer being 50% and the core layer being 60%, balancing the mechanical properties and processing stability.

[0019] Furthermore, the present application also provides a method for preparing the aforementioned packaging material, comprising preparing modified gypsum and using the modified gypsum as a filler to prepare the material using a dynamic extrusion process; The modified gypsum is prepared in the following manner: A1. Type II anhydrous gypsum with a particle size of 50μm was mixed with 0.5% calcium stearate dispersant in a high-speed mixer and then vacuum-dried at 80°C to obtain a dispersed mixture; Calcium stearate is used as a dispersant, and its calcium carboxylate group has a strong adsorption effect on the hydroxyl groups on the surface of type II anhydrous gypsum, thereby reducing the agglomeration of the filler in the pre-dispersion stage and avoiding competitive adsorption with the surface of gypsum particles during subsequent modification using a double coupling agent.

[0020] A2. The dispersed mixture was mixed with a 5% KH-550 / ethanol mixed solution and ultrasonically in a water bath at 60°C for 30 min to obtain a gypsum / KH-550 complex; A3. The gypsum / KH-550 complex was mixed with a 3% NDZ-101 / toluene mixed solution under nitrogen protection and reacted in a vacuum environment at 80 ° C for 2h to obtain a gypsum / double coupling agent composite; This results in the formation of gypsum particles with a gradient modification of the double coupling agent, which significantly increases the hydrophobicity of the filler, strengthens the interfacial bonding between the filler and the polyethylene, prevents glass formation at the interface between the filler and the substrate, and improves tensile strength. KH-550 and NDZ-101 form a "chemical bond + physical entanglement" dual interface, enhancing the compatibility of the filler with the polyethylene substrate.

[0021] A4. 0.3% of ethyl orthosilicate was dissolved in an ethanol / water mixed solvent, mixed with the gypsum / double coupling agent composite, and stirred at 50 ° C for 6h to obtain the modified gypsum; In this way, after the SiO2 layer is in situ coated on the outside of the double coupling agent-modified gypsum filler, electrostatic repulsion is used to prevent filler agglomeration. In addition, the coated SiO2 layer can also form a physical barrier to limit the contact distance between filler particles. By reducing the aspect ratio of the filler, the melt flow shear rate is increased, thereby improving processing fluidity.

[0022] After forming the core-shell structure, the SiO2 layer can also block the penetration of moisture and polymer molecular chains, thereby improving heat resistance.

[0023] The dynamic extrusion process includes using polyethylene as the base material, setting the front section temperature of the twin-screw extruder to 155~65°C, the middle section temperature to 185~195°C, and the rear section temperature to 205~215°C, adding polyethylene base material and modified gypsum to the front section, adding an in-situ nucleating agent to the middle section, using high temperature to promote crystallization induction, adding self-repairing microcapsules to the rear section, and the pitch of the front section screw is greater than the pitch of the middle section screw.

[0024] In this way, by controlling the screw temperature in different zones and taking advantage of the temperature-dependent viscosity of polyethylene melt, the highly filled gypsum particles are distributed in a gradient along the extrusion direction. In the surface layer near the die, the filler content is 50%, reducing melt flow resistance and improving surface finish. In the core layer, away from the die, the filler content is 60%, enhancing the overall mechanical properties of the material.

[0025] Among them, in the front section of the process, the polyethylene melt has a high viscosity and poor fluidity. The filler is more likely to settle at the bottom of the screw groove due to gravity, and the filler content in the front section close to the die head is low (50% on the surface); in the middle section of the process, the polyethylene melt viscosity decreases and the fluidity increases. The filler is evenly dispersed under the action of shear force and is fully mixed with the PE matrix (60% on the core layer); in the back section of the process, the polyethylene melt viscosity is further reduced. By reducing the screw speed, the screw shear force is weakened, the filler migration rate is reduced, and the low filler structure on the surface is fixed.

[0026] Furthermore, the in-situ nucleating agent is prepared by compounding calcium stearate and zinc oxide in a ratio of 2:1.

[0027] Furthermore, in order to reach the processing temperature, calcium stearate and zinc oxide are used as heterogeneous nucleating agents to reduce the crystallization activation energy of polyethylene; moreover, calcium stearate and zinc oxide are compounded in a mass ratio of 2:1, and the hydroxyl groups on the surface of zinc oxide form a hydrogen bond network with the carboxylate groups of calcium stearate, which slows down the growth rate of the crystal nucleus, refines the grain size, reduces stress concentration, and can also serve as a functional optimizer to improve the tensile strength of the composite material.

[0028] Furthermore, the self-repairing microcapsules are polyurethane prepolymer microcapsules with urea-formaldehyde resin as the capsule wall and isocyanate monomer wrapped inside.

[0029] The technical solution involved in this application has the following beneficial effects: Through the synergistic modification of nano-coating / double coupling agent, the addition effect of 60% of type II anhydrous gypsum filler can be achieved, which increases the filler utilization rate, reduces the cost of composite materials, and ensures the performance of the composite materials. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0031] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0032] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0033] A highly filled type II anhydrous gypsum / polyethylene composite packaging material, comprising modified gypsum coated with nano-SiO2 / synergistically modified with a double coupling agent, and polyethylene as a base material, wherein the modified gypsum is added in an amount of 60%; A gradient temperature-controlled twin-screw extruder is used for processing. During extrusion processing, the temperature of the front section is 155~165℃, the temperature of the middle section is 185~195℃, and the temperature of the back section is 205~215℃. After extrusion, a gradient filler distribution material is formed.

[0034] Preferably, the modified gypsum has a core-shell structure, with type II anhydrous gypsum particles as the core, and a nano-SiO2 layer as the shell is covered on the surface of the type II anhydrous gypsum particles by a sol / gel method.

[0035] Furthermore, the double coupling agent used for synergistic modification consists of KH-550 and NDZ-101.

[0036] Furthermore, during the extrusion process, the pitch of the front-stage screw is greater than the pitch of the middle-stage screw, and the modified gypsum is added in the front-stage.

[0037] Furthermore, the present application also provides a method for preparing the aforementioned packaging material, comprising preparing modified gypsum and using the modified gypsum as a filler to prepare the material using a dynamic extrusion process; The modified gypsum is prepared in the following manner: A1. Type II anhydrous gypsum with a particle size of 50μm was mixed with 0.5% calcium stearate dispersant in a high-speed mixer and then vacuum-dried at 80°C to obtain a dispersed mixture; A2. The dispersed mixture was mixed with a 5% KH-550 / ethanol mixed solution and ultrasonically in a water bath at 60°C for 30 min to obtain a gypsum / KH-550 complex; A3. The gypsum / KH-550 complex was mixed with a 3% NDZ-101 / toluene mixed solution under nitrogen protection and reacted in a vacuum environment at 80 ° C for 2h to obtain a gypsum / double coupling agent composite; A4. 0.3% of ethyl orthosilicate was dissolved in an ethanol / water mixed solvent, mixed with the gypsum / double coupling agent composite, and stirred at 50 ° C for 6h to obtain the modified gypsum; The dynamic extrusion process includes using polyethylene as the base material, setting the front section temperature of the twin-screw extruder to 155~65°C, the middle section temperature to 185~195°C, and the rear section temperature to 205~215°C, adding polyethylene base material and modified gypsum to the front section, adding an in-situ nucleating agent to the middle section, using high temperature to promote crystallization induction, adding self-repairing microcapsules to the rear section, and the pitch of the front section screw is greater than the pitch of the middle section screw.

[0038] Furthermore, the in-situ nucleating agent is prepared by compounding calcium stearate and zinc oxide in a ratio of 2:1.

[0039] Furthermore, the self-repairing microcapsules are polyurethane prepolymer microcapsules with urea-formaldehyde resin as the capsule wall and isocyanate monomer wrapped inside. Example

[0040] Material ratio: Modified type II anhydrous gypsum (core-shell structure, SiO2 coating thickness 50nm): 60wt%; Polyethylene (PE): 40wt%; Additives: calcium stearate (dispersant) 0.5wt%, in-situ nucleating agent (calcium stearate: zinc oxide = 2:1) 0.3wt%, self-healing microcapsules (urea-formaldehyde resin capsule wall / isocyanate monomer) 0.2wt% Preparation process: Prepare according to steps A1-A4, Twin-screw extrusion process parameters: Front section temperature: 155℃ (pitch 60mm); Middle section temperature: 190℃ (pitch 40mm); Rear section temperature: 210℃ (pitch 20mm); Adding order: add polyethylene + modified gypsum in the front section, add nucleating agent in the middle section, and add microcapsules in the back section.

[0041] Material ratio: Type II anhydrous gypsum (untreated): 60wt%; Polyethylene: 40wt% Additives: same as in Example 1; Preparation process: The twin-screw extrusion temperature is uniformly set at 180°C; Add the filler evenly.

[0042] Modification process: The NDZ-101 treatment step was omitted (only KH-550 was used for modification), and other conditions were the same as in Example 1.

[0043] Process parameters: The extrusion temperature was 200° C. throughout the entire process, and other conditions were the same as those in Example 1.

[0044] Step A4 was omitted, and other conditions were the same as those in Example 1.

[0045] Corresponding test items and data comparison: A. Filler dispersion and interface bonding:

[0046]

[0047] B. Processing performance:

[0048] C. Mechanical properties

[0049]

[0050] D. Heat resistance and dimensional stability:

[0051] E. Surface quality and functionality:

[0052]

[0053] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A highly filled type II anhydrous gypsum / polyethylene composite packaging material, characterized in that: The invention comprises modified gypsum synergistically modified by nano-SiO2 coating and double coupling agent, and polyethylene as a base material, wherein the addition amount of the modified gypsum is 60%; A gradient temperature-controlled twin-screw extruder is used for processing. During extrusion processing, the temperature of the front section is 155~165℃, the temperature of the middle section is 185~195℃, and the temperature of the back section is 205~215℃. After extrusion, a gradient filler distribution material is formed.

2. A highly filled type II anhydrous gypsum / polyethylene composite packaging material according to claim 1, characterized in that: The modified gypsum has a core-shell structure, with type II anhydrous gypsum particles as the core, and a nano-SiO2 layer as the shell is covered on the surface of the type II anhydrous gypsum particles by a sol / gel method.

3. A highly filled type II anhydrous gypsum / polyethylene composite packaging material according to claim 1 or 2, characterized in that: The double coupling agent used for synergistic modification consists of KH-550 and NDZ-101.

4. The highly filled type II anhydrous gypsum / polyethylene composite packaging material according to claim 1, characterized in that: During the extrusion process, the pitch of the front-stage screw is greater than the pitch of the middle-stage screw, and the modified gypsum is added in the front-stage.

5. A method for preparing the highly filled type II anhydrous gypsum / polyethylene composite packaging material according to any one of claims 1 to 4, characterized in that: The method comprises preparing modified gypsum and using the modified gypsum as filler by adopting a dynamic extrusion process; The modified gypsum is prepared in the following manner: A1. Type II anhydrous gypsum with a particle size of 50μm was mixed with 0.5% calcium stearate dispersant in a high-speed mixer and then vacuum-dried at 80°C to obtain a dispersed mixture; A2. The dispersed mixture was mixed with a 5% KH-550 / ethanol mixed solution and ultrasonically in a water bath at 60°C for 30 min to obtain a gypsum / KH-550 complex; A3. The gypsum / KH-550 complex was mixed with a 3% NDZ-101 / toluene mixed solution under nitrogen protection and reacted in a vacuum environment at 80 ° C for 2h to obtain a gypsum / double coupling agent composite; A4. 0.3% of ethyl orthosilicate was dissolved in an ethanol / water mixed solvent, mixed with the gypsum / double coupling agent composite, and stirred at 50 ° C for 6h to obtain the modified gypsum; The dynamic extrusion process includes using polyethylene as the base material, setting the front section temperature of the twin-screw extruder to 155-65°C, the middle section temperature to 185-195°C, and the rear section temperature to 205-215°C, adding the polyethylene base material and modified gypsum to the front section, adding the in-situ nucleating agent to the middle section, and adding self-repairing microcapsules to the rear section, and the pitch of the front section screw is greater than the pitch of the middle section screw.

6. The preparation method according to claim 5, characterized in that The in-situ nucleating agent is prepared by mixing calcium stearate and zinc oxide in a ratio of 2:

1.

7. The preparation method according to claim 5, characterized in that The self-repairing microcapsules are polyurethane prepolymer microcapsules with urea-formaldehyde resin as the capsule wall and isocyanate monomer wrapped inside.

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