A high molecular weight PP composite plastic for packaging box and preparation method thereof

Abstract

The present invention discloses a polymer PP composite plastic for packaging boxes, the raw materials of which include: coated polypropylene, low-density polyethylene, copolymerized polypropylene, nucleating agent, and other additives; the mass ratio of coated polypropylene, low-density polyethylene, copolymerized polypropylene, nucleating agent, and other additives is 100:20-30:10-18:1-2:1-2; wherein the coated polypropylene is obtained by freezing and crushing polypropylene, coordinating with hexagonal boron nitride and graphene oxide, dispersing in water with the aid of polyvinyl pyrrolidone, and then curing with ethylenediamine. The present invention discloses a method for preparing the polymer PP composite plastic for packaging boxes. The present invention improves the raw materials to achieve the packaging box having both heat-conducting and anti-freezing properties, excellent cold resistance, improving the impact strength of polypropylene at room temperature and low temperature, improving the toughening effect of polypropylene, reducing food contamination, and extending the shelf life of food.

Description

Technical Field

[0001] The invention relates to the technical field of materials for packaging boxes, and in particular to a high-molecular PP composite plastic for packaging boxes and a preparation method thereof. Background Art

[0002] With the improvement of my country's economic level, the food packaging industry has developed rapidly. Food packaging is a general term for containers, materials and auxiliary materials used to protect products, facilitate storage and transportation, and promote sales during the circulation of food. Food packaging can protect the appearance quality and quality of food. Choosing appropriate food packaging materials can extend the shelf life of food and prevent food from being contaminated by microorganisms.

[0003] As the name implies, packaging boxes are used to package products. Plastic packaging boxes are mainly made of PP (polypropylene), PVC (polyvinyl chloride), and PET (polyethylene terephthalate). Among the five general-purpose plastics, PP has the best heat resistance. PP plastic products can work for a long time at 100°C, and when there is no external force, PP plastic products will not deform when heated to 150°C. After using nucleating agents to improve the crystallization state of PP, its heat resistance can be further improved. It can be used to make utensils for heating food in microwave ovens. The thickness of PP material packaging boxes can reach 0.75mm. Compared with traditional paper boxes and other packaging, PP packaging boxes have the advantages of being environmentally friendly, non-toxic, highly transparent, and more intuitively displaying the packaged products.

[0004] At present, PP packaging boxes have low impact strength in low temperature environments and are prone to cracking when impacted, which can easily cause damage to items. At the same time, PP packaging boxes have poor thermal conductivity, especially for foods that need to be refrigerated. The poor thermal conductivity of the packaging boxes will greatly reduce work efficiency. Direct refrigeration at high temperatures will cause the PP packaging boxes to be used for a short time, limiting their scope of application and requiring an urgent solution. Summary of the invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes a polymer PP composite plastic for a packaging box and a preparation method thereof.

[0006] A high molecular weight PP composite plastic for a packaging box, the raw materials of which include: coated polypropylene, low-density polyethylene, copolymerized polypropylene, a nucleating agent, and other additives; the mass ratio of the coated polypropylene, low-density polyethylene, copolymerized polypropylene, a nucleating agent, and other additives is 100:20-30:10-18:1-2:1-2; wherein the coated polypropylene is prepared by freezing and then crushing polypropylene, coordinating with hexagonal boron nitride and graphene oxide, dispersing it in water with the aid of polyvinyl pyrrolidone, and then curing it with ethylenediamine.

[0007] Preferably, the coated polypropylene is a core-shell structure, with polypropylene as the core, and hexagonal boron nitride and graphene oxide overlapped on the outside of the polypropylene and then cured with ethylenediamine to form a thermally conductive network shell layer.

[0008] Preferably, the coated polypropylene is prepared by the following specific steps: freezing the polypropylene with liquid nitrogen, crushing and sieving, adding hexagonal boron nitride, graphene oxide, polyvinyl pyrrolidone, and deionized water, stirring under pressure at 160-164° C. for 1-2 hours, controlling the pressure to 2-6 MPa during stirring, reducing the pressure, adding ethylenediamine, ultrasonically treating, filtering, washing, and drying to obtain the coated polypropylene.

[0009] Preferably, the particle size of the hexagonal boron nitride is 1-5 μm.

[0010] Preferably, the mass ratio of polypropylene, hexagonal boron nitride, graphene oxide, polyvinyl pyrrolidone and ethylenediamine is 5-15:2-10:1-3:1-2:1-2.

[0011] Preferably, the ultrasonic treatment time is 1-2 h, and the ultrasonic frequency is 10-20 kHz.

[0012] Preferably, the nucleating agent is TMC-300 or TMC-306.

[0013] Preferably, the other auxiliary agent is food grade paraffin.

[0014] The method for preparing the polymer PP composite plastic for the packaging box comprises the following steps: stirring the coated polypropylene, low-density polyethylene and copolymerized polypropylene for 1-2 hours at a stirring speed of 1000-2000 r / min, adding a nucleating agent and other additives; extruding in a screw extruder, and obtaining the polymer PP composite plastic for the packaging box by vacuum forming and cutting.

[0015] Beneficial effects:

[0016] (1) The present invention freezes and crushes polypropylene, and then mixes it with hexagonal boron nitride and graphene oxide, disperses it in water with the help of PVP, and forms an emulsion system through melting treatment. Hexagonal boron nitride and graphene oxide are uniformly and orderly adsorbed on the surface of polypropylene particles, and solidified with ethylenediamine, so that the polypropylene is embedded in the core, and the outer layers overlap each other to form a connected heat conduction network; the orientation of the filler is controlled in the case of low filler, forming a uniform and continuous three-dimensional heat conduction path, and at the same time, the interaction between the filler and the matrix is ​​enhanced, and the gap at the interface is improved, which not only further improves the heat transfer efficiency, but also makes the product have good low-temperature impact strength and excellent mechanical properties.

[0017] (2) After pretreatment, the polypropylene of the present invention can absorb part of the impact energy and act as a stress concentrator to induce and inhibit crack growth, so that the product changes from brittle fracture to ductile fracture, greatly improving its impact strength, effectively improving the toughness of the product, and improving the easy cracking characteristics of the entire packaging box material in a low temperature environment.

[0018] (3) The present invention improves the raw materials to achieve a packaging box with both thermal conductivity and anti-freezing properties, excellent cold resistance, increased impact strength of polypropylene at room temperature and low temperature, improved toughening effect of polypropylene, reduced food contamination, and extended shelf life of food. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a comparison chart of the mechanical properties of the PP composite plastics obtained in Example 5 and Comparative Examples 1-2.

[0020] Figure 2 It is a comparison chart of thermal conductivity of PP composite plastics obtained in Example 5 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is described in detail below through specific embodiments.

[0022] Example 1

[0023] A high molecular weight PP composite plastic for a packaging box, the raw materials of which include: 100 kg of coated polypropylene, 20 kg of low-density polyethylene, 10 kg of copolymerized polypropylene, 1 kg of nucleating agent TMC-300, and 1 kg of food-grade paraffin.

[0024] The coated polypropylene is prepared by the following specific steps: 5 kg of polypropylene is frozen with liquid nitrogen, crushed into powder, passed through a 100-mesh sieve, added into a high-temperature and high-pressure reactor, 2 kg of hexagonal boron nitride with a particle size of 1-5 μm, 1 kg of graphene oxide, 1 kg of polyvinyl pyrrolidone, and 10 kg of deionized water are added, and the mixture is stirred under pressure at 160° C. for 1 hour at a stirring speed of 1000 r / min. During the stirring process, the pressure is controlled to be 2 MPa, the pressure is reduced, 1 kg of ethylenediamine is added, ultrasonic treatment is performed for 1 hour at an ultrasonic frequency of 10 kHz, filtration is performed, washing is performed with deionized water, and drying is performed to obtain the coated polypropylene.

[0025] The method for preparing the polymer PP composite plastic for the packaging box comprises the following steps: putting the coated polypropylene, low-density polyethylene and copolymerized polypropylene into a stirring device for mixing and stirring for 1 hour at a stirring speed of 1000 r / min, adding nucleating agent TMC-300 and food-grade paraffin; extruding in a screw extruder, and obtaining the polymer PP composite plastic for the packaging box through vacuum forming and cutting.

[0026] Example 2

[0027] A high molecular weight PP composite plastic for a packaging box, the raw materials of which include: 100 kg of coated polypropylene, 30 kg of low-density polyethylene, 18 kg of copolymerized polypropylene, 2 kg of nucleating agent TMC-300, and 2 kg of food-grade paraffin.

[0028] The coated polypropylene is prepared by the following specific steps: 15 kg of polypropylene is frozen with liquid nitrogen, crushed into powder, passed through a 100-mesh sieve, added into a high-temperature and high-pressure reactor, 10 kg of hexagonal boron nitride with a particle size of 1-5 μm, 3 kg of graphene oxide, 2 kg of polyvinyl pyrrolidone, and 30 kg of deionized water are added, and the mixture is stirred under pressure at 164° C. for 2 h at a stirring speed of 2000 r / min. During the stirring process, the pressure is controlled to be 6 MPa, the pressure is reduced, 2 kg of ethylenediamine is added, ultrasonic treatment is performed for 2 h at an ultrasonic frequency of 20 kHz, filtration is performed, washing is performed with deionized water, and drying is performed to obtain the coated polypropylene.

[0029] The method for preparing the polymer PP composite plastic for the packaging box comprises the following steps: putting the coated polypropylene, low-density polyethylene and copolymerized polypropylene into a stirring device for mixing and stirring for 2 hours at a stirring speed of 2000 r / min, adding nucleating agent TMC-300 and food-grade paraffin; extruding in a screw extruder, and obtaining the polymer PP composite plastic for the packaging box through vacuum forming and cutting.

[0030] Example 3

[0031] A high molecular weight PP composite plastic for a packaging box, the raw materials of which include: 100 kg of coated polypropylene, 22 kg of low-density polyethylene, 16 kg of copolymerized polypropylene, 1.3 kg of nucleating agent TMC-306, and 1.8 kg of food-grade paraffin.

[0032] The coated polypropylene is prepared by the following specific steps: 8 kg of polypropylene is frozen with liquid nitrogen, crushed into powder, passed through a 100-mesh sieve, added into a high-temperature and high-pressure reactor, 8 kg of hexagonal boron nitride with a particle size of 1-5 μm, 1.5 kg of graphene oxide, 1.7 kg of polyvinyl pyrrolidone, and 15 kg of deionized water are added, and the mixture is stirred under pressure at 163° C. for 80 min at a stirring speed of 1700 r / min. During the stirring process, the pressure is controlled to be 3 MPa, the pressure is reduced, 1.8 kg of ethylenediamine is added, ultrasonic treatment is performed for 80 min at an ultrasonic frequency of 18 kHz, filtration is performed, washing is performed with deionized water, and drying is performed to obtain the coated polypropylene.

[0033] The method for preparing the polymer PP composite plastic for the packaging box comprises the following steps: putting the coated polypropylene, low-density polyethylene and copolymerized polypropylene into a stirring device for mixing and stirring for 80 minutes at a stirring speed of 1700 r / min, adding nucleating agent TMC-306 and food-grade paraffin; extruding in a screw extruder, and obtaining the polymer PP composite plastic for the packaging box through vacuum forming and cutting.

[0034] Example 4

[0035] A high molecular weight PP composite plastic for a packaging box, the raw materials of which include: 100 kg of coated polypropylene, 28 kg of low-density polyethylene, 12 kg of copolymerized polypropylene, 1.7 kg of nucleating agent TMC-306, and 1.2 kg of food-grade paraffin.

[0036] The coated polypropylene is prepared by the following specific steps: 12 kg of polypropylene is frozen with liquid nitrogen, crushed into powder, passed through a 100-mesh sieve, added into a high-temperature and high-pressure reactor, 4 kg of hexagonal boron nitride with a particle size of 1-5 μm, 2.5 kg of graphene oxide, 1.3 kg of polyvinyl pyrrolidone, and 25 kg of deionized water are added, and the mixture is stirred under pressure at 161° C. for 100 min at a stirring speed of 1300 r / min. During the stirring process, the pressure is controlled to be 5 MPa, the pressure is reduced, 1.2 kg of ethylenediamine is added, ultrasonic treatment is performed for 100 min at an ultrasonic frequency of 12 kHz, filtration is performed, washing is performed with deionized water, and drying is performed to obtain the coated polypropylene.

[0037] The method for preparing the polymer PP composite plastic for the packaging box comprises the following steps: putting the coated polypropylene, low-density polyethylene and copolymerized polypropylene into a stirring device and mixing and stirring for 100 minutes at a stirring speed of 1300 r / min, adding nucleating agent TMC-306 and food-grade paraffin; extruding in a screw extruder, and obtaining the polymer PP composite plastic for the packaging box through vacuum forming and cutting.

[0038] Example 5

[0039] A high molecular weight PP composite plastic for packaging boxes, the raw materials of which include: 100 kg of coated polypropylene, 25 kg of low-density polyethylene, 14 kg of copolymerized polypropylene, 1.5 kg of nucleating agent TMC-306, and 1.5 kg of food-grade paraffin.

[0040] The coated polypropylene is prepared by the following specific steps: 10 kg of polypropylene is frozen with liquid nitrogen, crushed into powder, passed through a 100-mesh sieve, added into a high-temperature and high-pressure reactor, 6 kg of hexagonal boron nitride with a particle size of 1-5 μm, 2 kg of graphene oxide, 1.5 kg of polyvinyl pyrrolidone, and 20 kg of deionized water are added, and the mixture is stirred under pressure at 162° C. for 90 minutes at a stirring speed of 1500 r / min. During the stirring process, the pressure is controlled to be 4 MPa, the pressure is reduced, 1.5 kg of ethylenediamine is added, ultrasonic treatment is performed for 90 minutes at an ultrasonic frequency of 15 kHz, filtration is performed, washing is performed with deionized water, and drying is performed to obtain the coated polypropylene.

[0041] The method for preparing the polymer PP composite plastic for the packaging box comprises the following steps: putting the coated polypropylene, low-density polyethylene and copolymerized polypropylene into a stirring device and mixing and stirring for 90 minutes at a stirring speed of 1800 r / min, adding nucleating agent TMC-306 and food-grade paraffin; extruding in a screw extruder, and obtaining the polymer PP composite plastic for the packaging box through vacuum forming and cutting.

[0042] Comparative Example 1

[0043] A high molecular weight PP composite plastic for a packaging box, the raw materials of which include: 100 kg of polypropylene, 25 kg of low-density polyethylene, 14 kg of copolymerized polypropylene, 1.5 kg of nucleating agent TMC-306, and 1.5 kg of food-grade paraffin.

[0044] The method for preparing the polymer PP composite plastic for packaging boxes comprises the following steps: putting polypropylene, low-density polyethylene and copolymerized polypropylene into a stirring device and mixing and stirring for 90 minutes at a stirring speed of 1800 r / min, adding nucleating agent TMC-306 and food-grade paraffin; extruding in a screw extruder, and obtaining the polymer PP composite plastic for packaging boxes through vacuum forming and cutting.

[0045] Comparative Example 2

[0046] A high molecular weight PP composite plastic for packaging boxes, the raw materials of which include: 100 kg of pretreated polypropylene, 25 kg of low-density polyethylene, 14 kg of copolymerized polypropylene, 1.5 kg of nucleating agent TMC-306, and 1.5 kg of food-grade paraffin.

[0047] The pretreated polypropylene is prepared by the following specific steps: 10 kg of polypropylene, 6 kg of hexagonal boron nitride with a particle size of 1-5 μm, and 2 kg of graphene oxide are mixed evenly.

[0048] The method for preparing the polymer PP composite plastic for packaging boxes comprises the following steps: putting pretreated polypropylene, low-density polyethylene and copolymerized polypropylene into a stirring device and mixing and stirring for 90 minutes at a stirring speed of 1800 r / min, adding nucleating agent TMC-306 and food-grade paraffin; extruding in a screw extruder, and obtaining the polymer PP composite plastic for packaging boxes through vacuum forming and cutting.

[0049] The tensile strength of the PP composite plastics obtained in Example 5 and Comparative Examples 1-2 was measured with reference to GB / T 1040.2-2006 "Determination of tensile properties of plastics Part 2: Test conditions for molded and extruded plastics"; the flexural strength of the PP composite plastics obtained in Example 5 and Comparative Examples 1-2 was measured with reference to GB / T 9341-2008 "Determination of flexural properties of plastics"; the notched impact strength of the PP composite plastics obtained in Example 5 and Comparative Examples 1-2 was measured with reference to GB / T 1043.1-2008 "Determination of impact properties of simply supported beams of plastics Part 1: Non-instrumented impact test", and the notched impact strength was measured at 0-4°C.

[0050] like Figure 1 As shown, the tensile strength, flexural strength and notched impact strength of the PP composite plastic obtained in Example 5 are better than those in the comparative example.

[0051] The thermal conductivity of the PP composite plastic obtained in Example 5 and Comparative Examples 1-2 was tested. A sample with a thickness of 1 mm and a length and width of 10 mm was taken and the thermal diffusion coefficient (α) and specific heat capacity (Cp) of the sample were tested by LFA467 laser thermal conductivity meter. The thermal conductivity (κ) of the sample was calculated by the following formula:

[0052] κ = α × Cp × ρ (2-1)

[0053] The unit of α is: mm 2 / s, the unit of Cp is J / (kg·℃), the unit of κ is W / (m·K), and ρ is the density of the sample, the unit is kg / m 3 .

[0054] like Figure 2 As shown, the thermal conductivity of the PP composite plastic obtained in Example 5 is even better.

[0055] The applicant believes that this is because the present invention freezes and crushes polypropylene, and then mixes it with hexagonal boron nitride and graphene oxide, disperses it in water with the cooperation of PVP, and forms an emulsion system after melting treatment. Hexagonal boron nitride and graphene oxide will be uniformly and orderly adsorbed on the surface of polypropylene particles, and ethylenediamine is added for curing, so that polypropylene is embedded in the core, and the outer layers overlap each other to form a connected heat conduction network; the orientation control of the filler is achieved in the case of low filler, forming a uniform and continuous three-dimensional heat conduction path, while enhancing the interaction between the filler and the matrix, improving the gap at the interface, further improving the heat transfer efficiency, and making the product have good low-temperature impact strength and excellent mechanical properties. The present invention can absorb part of the impact energy after pretreatment of polypropylene, and act as a stress concentrator to induce and inhibit crack growth, so that the product changes from brittle fracture to ductile fracture, greatly improves its impact strength, effectively improves the toughness of the product, and improves the cracking characteristics of the entire packaging box material in a low-temperature environment.

[0056] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A high molecular weight PP composite plastic for packaging boxes, characterized in that: The raw materials include: coated polypropylene, low-density polyethylene, copolymerized polypropylene, nucleating agent, and other additives; the mass ratio of coated polypropylene, low-density polyethylene, copolymerized polypropylene, nucleating agent, and other additives is 100:20-30:10-18:1-2:1-2; The coated polypropylene is prepared by freezing and crushing polypropylene, mixing it with hexagonal boron nitride and graphene oxide, dispersing it in water with the aid of polyvinyl pyrrolidone, and then curing it with ethylenediamine. The coated polypropylene has a core-shell structure, with polypropylene as the core, and hexagonal boron nitride and graphene oxide are overlapped on the outside of the polypropylene and then cured with ethylenediamine to form a thermal conductive network shell layer.

2. The polymer PP composite plastic for packaging box according to claim 1, characterized in that: The coated polypropylene is prepared by the following specific steps: freezing the polypropylene with liquid nitrogen, crushing and sieving, adding hexagonal boron nitride, graphene oxide, polyvinyl pyrrolidone, and deionized water, stirring under pressure at 160-164° C. for 1-2 hours, controlling the pressure to be 2-6 MPa during the stirring process, reducing the pressure, adding ethylenediamine, ultrasonically treating, filtering, washing, and drying to obtain the coated polypropylene.

3. The polymer PP composite plastic for packaging box according to claim 1 or 2, characterized in that: The particle size of hexagonal boron nitride is 1-5 μm.

4. The polymer PP composite plastic for packaging box according to claim 2, characterized in that: The mass ratio of polypropylene, hexagonal boron nitride, graphene oxide, polyvinyl pyrrolidone and ethylenediamine is 5-15:2-10:1-3:1-2:1-2.

5. The polymer PP composite plastic for packaging box according to claim 2, characterized in that: The ultrasonic treatment time is 1-2h, and the ultrasonic frequency is 10-20kHz.

6. The polymer PP composite plastic for packaging box according to claim 1, characterized in that: The nucleating agent is TMC-300 or TMC-306.

7. The polymer PP composite plastic for packaging box according to claim 1, characterized in that: Other additives are food grade paraffin.

8. A method for preparing a polymer PP composite plastic for a packaging box as claimed in any one of claims 1 to 7, characterized in that: The method comprises the following steps: stirring coated polypropylene, low-density polyethylene and copolymerized polypropylene for 1-2 hours at a stirring speed of 1000-2000 r / min, adding a nucleating agent and other auxiliary agents; extruding in a screw extruder, and obtaining a high-molecular PP composite plastic for packaging boxes through vacuum forming and cutting.

Images