A high-toughness waterproof paper-plastic composite bag and a preparation method thereof

Abstract

The application relates to the technical field of paper-plastic composite bags, in particular to a high-toughness waterproof paper-plastic composite bag and a preparation method thereof. The application specifically comprises the following steps: step one, preparing a modified cellulose, introducing a benzyl group, an ester group and a double bond; then, melt grafting the modified cellulose and polypropylene to obtain modified polypropylene; step two, modifying two fillers by compounding and using a mixed silane coupling agent to obtain modified fillers; step three, grafting ethylene-octene block copolymer and itaconic anhydride to further promote compatibility to obtain an elastomer; step four, uniformly mixing all component raw materials to extrude a plastic layer; the plastic layer is adhered to both surfaces of a paper layer through an adhesive, and the composite paper is obtained after drying; finally, the composite paper is processed into a high-toughness waterproof paper-plastic composite bag.

Description

Technical Field

[0001] This invention relates to the field of paper-plastic composite bag technology, specifically to a high-toughness waterproof paper-plastic composite bag and its preparation method. Background Technology

[0002] Paper-plastic composite bags consist of a plastic film and a paper layer. The plastic film is typically made of polyolefin woven fabric with a polyolefin base material, while the paper layer is made of kraft paper. The two are bonded together through a molten plastic heat-sealing process. Paper-plastic composite bags are widely used for packaging various items such as food, grains, minerals, and fertilizers. They are environmentally friendly, easy to carry lightweight materials, and a convenient packaging material. However, these bags also have some drawbacks. When exposed to water, the composite bag softens, causing the packaged material to become damp and affecting its performance. For example, moisture-sensitive pharmaceutical powders cannot be packaged in paper-plastic composite bags. Secondly, paper-plastic composite bags need a certain degree of toughness to prevent damage during transportation and spillage of the packaged material.

[0003] To address the above problems, this invention provides a high-toughness waterproof paper-plastic composite bag and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a high-toughness waterproof paper-plastic composite bag and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A high-toughness waterproof paper-plastic composite bag includes a paper layer and a plastic layer adhered to both sides of the paper layer.

[0007] More preferably, the plastic layer comprises the following raw materials in parts by weight: 90-120 parts polypropylene, 20-30 parts modified polypropylene, 15-25 parts high-density polyethylene, 15-25 parts modified filler, 15-25 parts elastomer, 5-10 parts dioctyl phthalate, 1-5 parts β-nucleating agent, and 1-2 parts antioxidant.

[0008] A more optimized method for preparing the high-toughness waterproof paper-plastic composite bag includes the following steps:

[0009] Step 1: Melt graft modified cellulose onto polypropylene to obtain modified polypropylene;

[0010] Step 2: Modify the packing material with a mixed silane coupling agent to obtain the modified packing material;

[0011] Step 3: Mix polypropylene, modified polypropylene, high-density polyethylene, modified filler, elastomer, dioctyl phthalate, β-nucleating agent, and antioxidant evenly, and extrude at 180-230℃ to obtain a plastic layer.

[0012] Step 4: The plastic layer is bonded to both sides of the paper layer with adhesive, and after drying, a composite paper is obtained; finally, the composite paper is processed into a high-toughness waterproof paper-plastic composite bag.

[0013] In a more optimized manner, the preparation method of the modified cellulose is as follows: (1) 10 parts of cellulose are added to 10-20 parts of ethyl acetate to prepare a homogeneous cellulose suspension, and then 1-4 parts of ethylenediamine are added dropwise under stirring. The mixture is stirred at 30-60°C for 1-3 hours to obtain the reaction solution A; (2) 2-4 parts of modifier are added dropwise to the reaction solution A. The mixture is stirred at 30-60°C for 1-3 hours, and then a large amount of anhydrous ethanol is added. After standing for 3-6 hours, the mixture is filtered and dried to obtain the modified cellulose.

[0014] Ideally, the cellulose includes, but is not limited to, lignocellulose.

[0015] More preferably, the modifier includes, but is not limited to, any one of N-benzylacrylamide and N,N-dibenzylacrylamide.

[0016] A more optimized method for preparing the modified polypropylene is as follows: 10 parts of polypropylene, 1-2 parts of itaconic anhydride, and 0.3-0.5 parts of benzoyl peroxide are added to a mixer in a certain proportion. After mixing at 170-190°C for 5-10 minutes, 2-5 parts of modified cellulose are added to the mixer. After mixing for 5-8 minutes, the mixture is melt-blended using a twin-screw extruder and extruded at 160-175°C and a speed of 120-210 rpm to obtain the modified polypropylene.

[0017] Cellulose is widely available and its addition to polymers can toughen them and significantly improve the strength of polymer materials. However, its compatibility with resins is poor, and cellulose has a certain degree of hydrophilicity. Therefore, this solution modifies cellulose by esterification, introducing ester groups, benzyl groups, and double bonds. The introduction of ester and benzyl groups enhances the hydrophobicity of cellulose, and the modification treatment also improves its compatibility with resins. Furthermore, the modified cellulose is grafted onto polypropylene. Before grafting, the polypropylene is first grafted with itaconic anhydride to further enhance the compatibility between polypropylene and modified cellulose, allowing the modified cellulose to be uniformly dispersed in the polypropylene.

[0018] A more optimized method for preparing the modified filler is as follows: the filler is added to an ethanol solution containing a mixed silane coupling agent, and ultrasonically treated at 40–60°C for 60–120 min, followed by filtration and drying to obtain the modified filler.

[0019] Ideally, the mass ratio of the filler and the mixed silane coupling agent is 50:1.

[0020] In a more optimized manner, the filler is obtained by uniformly mixing potassium hexatitanate whiskers and nano-calcium carbonate at a mass ratio of 1:(0.5~1).

[0021] More optimally, the mixed silane coupling agent is obtained by mixing an epoxy silane coupling agent and an itaconic anhydride-grafted mercapto silane coupling agent at a mass ratio of 2:1.

[0022] More preferably, the epoxy silane coupling agent includes, but is not limited to, WD-60 and WD-62.

[0023] In a more optimized manner, the preparation method of the itaconic anhydride-grafted mercaptosilane coupling agent is as follows: 0.5-1 parts itaconic anhydride, 0.01-0.05 parts photoinitiator, and 3-5 parts mercaptosilane coupling agent are dispersed in anhydrous ethanol to form a homogeneous solution. The solution is then irradiated with 365 nm ultraviolet light for 30-60 min, and then heated to 75-80 °C until the ethanol evaporates and is removed, thereby obtaining the itaconic anhydride-grafted mercaptosilane coupling agent.

[0024] More preferably, the mercapto-based silane coupling agents include, but are not limited to, WD-80 and WD-81.

[0025] Calcium carbonate readily forms smaller crystal structures in polypropylene, improving its toughness but reducing tensile strength. Excessive calcium carbonate addition can cause particles to occupy space within the polypropylene molecular structure, increasing steric hindrance and decreasing toughness. Furthermore, calcium carbonate has poor compatibility in polypropylene and is prone to agglomeration. Therefore, this design uses a blend of calcium carbonate and potassium hexatitanate whiskers. Potassium hexatitanate whiskers have good compatibility with polypropylene, forming a cross-woven structure that improves the strength and toughness of the polypropylene material. To further enhance filler compatibility, itaconic anhydride and mercapto-based silane coupling agents are used as auxiliary silane coupling agents. Modification of the filler with these mixed silane coupling agents significantly improves its compatibility in polypropylene, ensuring uniform dispersion and synergistic reinforcement, thus greatly improving the strength and toughness of the polypropylene material. The addition of fillers also improves the wear resistance of the polypropylene. Ultimately, this results in a significantly improved toughness and increased durability of the composite bag.

[0026] Ideally, the mass ratio of polypropylene to high-density polyethylene is 5:1.

[0027] More preferably, the elastomer is obtained by mixing a polymer of ethylene-octene block copolymer and ethylene-octene block copolymer grafted with itaconic anhydride in a mass ratio of 1:1.

[0028] In a more optimized manner, the preparation method of the ethylene-octene block copolymer grafted itaconic anhydride polymer is as follows: 0.1 to 0.3 parts of itaconic anhydride, 5 parts of ethylene-octene block copolymer, and 0.01 to 0.03 parts of benzoyl peroxide are added to a mixer, melt-blended using a twin-screw extruder, and extruded at 170 to 220°C and a speed of 120 to 210 rpm to obtain the ethylene-octene block copolymer grafted itaconic anhydride polymer.

[0029] Ideally, the grafting rate of the ethylene-octene block copolymer grafted with itaconic anhydride is between 1 and 5 wt%.

[0030] Ethylene-octene block copolymers are elastomers with good compatibility with polypropylene and can significantly improve the impact resistance, abrasion resistance, and heat resistance of polypropylene. Considering that polypropylene is a non-polar material and taking into account the compatibility differences of the components in the scheme, the grafting rate is adjusted by controlling the screw speed and the amount of itaconic anhydride added to prepare a polymer of ethylene-octene block copolymer grafted with itaconic anhydride. This polymer is then mixed with ethylene-octene block copolymer to formulate an elastomer, which serves as a toughening material and also promotes compatibility. Under the synergistic effect of high-density polyethylene, elastomer, β-nucleating agent, modified filler, and dioctyl phthalate, the tensile strength and impact resistance of polypropylene materials are improved. At the same time, the presence of elastomer and modified filler also improves the temperature resistance of polypropylene materials, maintaining high toughness even at low temperatures. Finally, the elastomer, high-density polyethylene, and modified polypropylene provide good waterproof performance.

[0031] Compared with the prior art, the beneficial effects achieved by this invention are as follows: This invention enhances the hydrophobicity of cellulose by introducing benzyl and ester groups through cellulose modification, while improving the compatibility between cellulose and polypropylene, ultimately allowing it to be uniformly dispersed in polypropylene, giving the polypropylene material a toughening and waterproof effect; further, the combination of potassium hexatitanate whiskers and calcium carbonate further improves the compatibility of the filler in polypropylene, effectively enhancing the strength and toughness of the polypropylene material; finally, itaconic anhydride is grafted onto ethylene-octene block copolymer, which acts as both a compatibilizer and a toughening agent, working synergistically with high-density polyethylene, elastomer, β-nucleating agent, modified filler, and dioctyl phthalate to improve the tensile strength and impact resistance of the polypropylene material; finally, it is processed into a paper-plastic composite bag, which has good toughness and waterproof effect. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In this embodiment, it should be noted that there are no special restrictions on the manufacturers of the raw materials involved in this invention. Exemplary examples include: polypropylene melt index 2.2 g / 10 min, item number: S51655 (Shanghai Yuanye Biotechnology Co., Ltd.); high-density polyethylene molecular weight 80000 (Wuhan Rongcan Biotechnology Co., Ltd.); lignocellulose purity 99%, item number: 003 (Hubei Chengfeng Chemical Co., Ltd.); N,N-dibenzylacrylamide purity 97%, item number: HBWS-2023 (Hubei Weideli Chemical Reagent Co., Ltd.); itaconic anhydride purity 99% (Wuhan Jixin Yibang Biotechnology Co., Ltd.); benzoyl peroxide purity 99% (Hubei Xinmingtai Chemical Co., Ltd.); and potassium hexatite whiskers purity 99%. Length 5-100μm (Forsmann Technology (Beijing) Co., Ltd.), Nano calcium carbonate 99% purity (Shanghai Yuanye Biotechnology Co., Ltd.), WD-60 99% purity, item number: SH0462 (Guangzhou Shanghe Chemical Technology Co., Ltd.), Ethylene-octene block copolymer melt index 1g / min, grade: OBC9507, item number: 88888 (Dongguan Bailing New Materials Co., Ltd.), β-nucleating agent model: TMB-5 (Wuhan Penglei Biotechnology Co., Ltd.), Antioxidant 246 99% purity (Hubei Nuona Technology Co., Ltd.).

[0034] Example 1: A method for preparing a high-toughness, waterproof paper-plastic composite bag:

[0035] Step 1: Preparation of modified cellulose: (1) Add 20 parts of lignocellulose to 36 parts of ethyl acetate to prepare a homogeneous cellulose suspension. Then, under stirring, add 6 parts of ethylenediamine dropwise. Stir at 50°C for 2 hours to obtain reaction solution A. (2) Add 7 parts of N,N-dibenzylacrylamide dropwise to reaction solution A. Stir at 50°C for 3 hours. Then, add 50 parts of anhydrous ethanol. After standing for 5 hours, filter and dry to obtain modified cellulose.

[0036] Preparation of modified polypropylene: 30 parts of polypropylene, 6 parts of itaconic anhydride and 1.2 parts of benzoyl peroxide were added to a mixer and stirred at 180°C for 8 minutes. Then, 13 parts of modified cellulose were added to the mixer and stirred for 7 minutes. The mixture was then melt-blended using a twin-screw extruder and extruded at 165°C and 150 rpm to obtain modified polypropylene.

[0037] Step 2: The preparation method of itaconic anhydride-grafted mercaptosilane coupling agent is as follows: 0.6 parts itaconic anhydride, 0.03 parts photoinitiator, and 4 parts WD-80 are dispersed in anhydrous ethanol to form a homogeneous solution. After reacting with 365nm ultraviolet light for 45 minutes, the solution is heated to 78℃ until the ethanol evaporates and is removed, thus obtaining the itaconic anhydride-grafted mercaptosilane coupling agent.

[0038] WD-60 and itaconic anhydride-grafted mercaptosilane coupling agent were mixed at a mass ratio of 2:1 to obtain a mixed silane coupling agent.

[0039] Preparation of modified filler: 20 parts of potassium hexatitanate whiskers and 10 parts of nano calcium carbonate were added to a mixer and mixed evenly. Then, the mixture was added to 30 parts of anhydrous ethanol solution containing 2 wt% mixed silane coupling agent. The mixture was ultrasonically treated at 50°C for 120 min. After filtration and drying, the modified filler was obtained.

[0040] Step 3: Preparation of the polymer grafted with itaconic anhydride from ethylene-octene block copolymer: 0.8 parts of itaconic anhydride, 15 parts of ethylene-octene block copolymer, and 0.08 parts of benzoyl peroxide were added to a mixer and melt-blended using a twin-screw extruder. The mixture was then extruded at 195°C and 150 rpm to obtain the polymer grafted with itaconic anhydride from ethylene-octene block copolymer, with the grafting rate controlled at 3 ± 0.3 wt%.

[0041] The elastomer was obtained by mixing the ethylene-octene block copolymer grafted with itaconic anhydride and the ethylene-octene block copolymer at a mass ratio of 1:1.

[0042] Plastic layer preparation: Polypropylene, modified polypropylene, high-density polyethylene, modified filler, elastomer, dioctyl phthalate, β-nucleating agent, and antioxidant 264 are added to a mixer and mixed evenly. The mixture is then extruded at 220°C to obtain the plastic layer.

[0043] The raw materials of the plastic layer, by weight, are: 100 parts polypropylene, 26 parts modified polypropylene, 20 parts high-density polyethylene, 18 parts modified filler, 23 parts elastomer, 7 parts dioctyl phthalate, 5 parts β-nucleating agent, and 1.5 parts antioxidant.

[0044] Step 4: The plastic layer is bonded to both sides of the paper layer with adhesive, and after drying, a composite paper is obtained; finally, the composite paper is processed into a high-toughness waterproof paper-plastic composite bag.

[0045] Example 2: A method for preparing a high-toughness waterproof paper-plastic composite bag:

[0046] Step 1: Preparation of modified cellulose: (1) Add 20 parts of lignocellulose to 36 parts of ethyl acetate to prepare a homogeneous cellulose suspension. Then, under stirring, add 6 parts of ethylenediamine dropwise. Stir at 50°C for 2 hours to obtain reaction solution A. (2) Add 4 parts of N,N-dibenzylacrylamide dropwise to reaction solution A. Stir at 50°C for 3 hours. Then, add 50 parts of anhydrous ethanol. After standing for 5 hours, filter and dry to obtain modified cellulose.

[0047] Preparation of modified polypropylene: 30 parts of polypropylene, 6 parts of itaconic anhydride and 1.2 parts of benzoyl peroxide were added to a mixer and stirred at 170°C for 5 minutes. Then, 13 parts of modified cellulose were added to the mixer and stirred for 5 minutes. The mixture was then melt-blended using a twin-screw extruder and extruded at 165°C and 120 rpm to obtain modified polypropylene.

[0048] Step 2: The preparation method of itaconic anhydride-grafted mercaptosilane coupling agent is as follows: 0.6 parts itaconic anhydride, 0.03 parts photoinitiator, and 4 parts WD-80 are dispersed in anhydrous ethanol to form a homogeneous solution. After reacting with 365nm ultraviolet light for 45 minutes, the solution is heated to 78℃ until the ethanol evaporates and is removed, thus obtaining the itaconic anhydride-grafted mercaptosilane coupling agent.

[0049] WD-60 and itaconic anhydride-grafted mercaptosilane coupling agent were mixed at a mass ratio of 2:1 to obtain a mixed silane coupling agent.

[0050] Preparation of modified filler: 20 parts of potassium hexatitanate whiskers and 10 parts of nano calcium carbonate were added to a mixer and mixed evenly. Then, the mixture was added to 30 parts of anhydrous ethanol solution containing 2 wt% mixed silane coupling agent. The mixture was ultrasonically treated at 50°C for 120 min. After filtration and drying, the modified filler was obtained.

[0051] Step 3: Preparation of the polymer grafted with itaconic anhydride from ethylene-octene block copolymer: 0.5 parts itaconic anhydride, 15 parts ethylene-octene block copolymer, and 0.08 parts benzoyl peroxide were added to a mixer and melt-blended using a twin-screw extruder. The mixture was then extruded at 170°C and 150 rpm to obtain the polymer grafted with itaconic anhydride from ethylene-octene block copolymer, with the grafting rate controlled at 1.3 ± 0.3 wt%.

[0052] The elastomer was obtained by mixing the ethylene-octene block copolymer grafted with itaconic anhydride and the ethylene-octene block copolymer at a mass ratio of 1:1.

[0053] Preparation of the plastic layer: Polypropylene, modified polypropylene, high-density polyethylene, modified filler, elastomer, dioctyl phthalate, β-nucleating agent, and antioxidant 264 are added to a mixer and mixed evenly. The mixture is then extruded at 220°C to obtain the plastic layer.

[0054] The raw materials of the plastic layer, by weight, are: 100 parts polypropylene, 26 parts modified polypropylene, 20 parts high-density polyethylene, 18 parts modified filler, 23 parts elastomer, 7 parts dioctyl phthalate, 5 parts β-nucleating agent, and 1.5 parts antioxidant.

[0055] Step 4: The plastic layer is bonded to both sides of the paper layer with adhesive, and after drying, a composite paper is obtained; finally, the composite paper is processed into a high-toughness waterproof paper-plastic composite bag.

[0056] Example 3: A method for preparing a high-toughness, waterproof paper-plastic composite bag:

[0057] Step 1: Preparation of modified cellulose: (1) Add 20 parts of lignocellulose to 36 parts of ethyl acetate to prepare a homogeneous cellulose suspension. Then, under stirring, add 6 parts of ethylenediamine dropwise. Stir at 50°C for 2 hours to obtain reaction solution A. (2) Add 8 parts of N,N-dibenzylacrylamide dropwise to reaction solution A. Stir at 50°C for 3 hours. Then, add 50 parts of anhydrous ethanol. After standing for 5 hours, filter and dry to obtain modified cellulose.

[0058] Preparation of modified polypropylene: 30 parts of polypropylene, 6 parts of itaconic anhydride and 1.2 parts of benzoyl peroxide were added to a mixer and stirred at 190°C for 10 min. Then, 13 parts of modified cellulose were added to the mixer and stirred for 8 min. The mixture was then melt-blended using a twin-screw extruder and extruded at 175°C and 210 rpm to obtain modified polypropylene.

[0059] Step 2: The preparation method of itaconic anhydride-grafted mercaptosilane coupling agent is as follows: 0.6 parts itaconic anhydride, 0.03 parts photoinitiator, and 4 parts WD-80 are dispersed in anhydrous ethanol to form a homogeneous solution. After reacting with 365nm ultraviolet light for 45 minutes, the solution is heated to 78℃ until the ethanol evaporates and is removed, thus obtaining the itaconic anhydride-grafted mercaptosilane coupling agent.

[0060] WD-60 and itaconic anhydride-grafted mercaptosilane coupling agent were mixed at a mass ratio of 2:1 to obtain a mixed silane coupling agent.

[0061] Preparation of modified filler: 20 parts of potassium hexatitanate whiskers and 20 parts of nano calcium carbonate were added to a mixer and mixed evenly. Then, they were added to 40 parts of anhydrous ethanol solution containing 2 wt% mixed silane coupling agent. The mixture was ultrasonically treated at 50℃ for 120 min, filtered and dried to obtain the modified filler.

[0062] Step 3: Preparation of the polymer grafted with itaconic anhydride from ethylene-octene block copolymer: 0.8 parts of itaconic anhydride, 15 parts of ethylene-octene block copolymer, and 0.08 parts of benzoyl peroxide were added to a mixer and melt-blended using a twin-screw extruder. The mixture was then extruded at 220°C and 210 rpm to obtain the polymer grafted with itaconic anhydride from ethylene-octene block copolymer, with the grafting rate controlled at 4.7 ± 0.3 wt%.

[0063] The elastomer was obtained by mixing the ethylene-octene block copolymer grafted with itaconic anhydride and the ethylene-octene block copolymer at a mass ratio of 1:1.

[0064] Preparation of the plastic layer: Polypropylene, modified polypropylene, high-density polyethylene, modified filler, elastomer, dioctyl phthalate, β-nucleating agent, and antioxidant 264 are added to a mixer and mixed evenly. The mixture is then extruded at 220°C to obtain the plastic layer.

[0065] The raw materials of the plastic layer, by weight, are: 100 parts polypropylene, 26 parts modified polypropylene, 20 parts high-density polyethylene, 18 parts modified filler, 23 parts elastomer, 7 parts dioctyl phthalate, 5 parts β-nucleating agent, and 1.5 parts antioxidant.

[0066] Step 4: The plastic layer is bonded to both sides of the paper layer with adhesive, and after drying, a composite paper is obtained; finally, the composite paper is processed into a high-toughness waterproof paper-plastic composite bag.

[0067] Comparative Example 1: Compared with Example 1, Comparative Example 1 was adjusted as follows: no modified polypropylene was added; other processes remained unchanged, specifically:

[0068] The raw materials of the plastic layer, by weight, are: 100 parts polypropylene, 20 parts high-density polyethylene, 18 parts modified filler, 23 parts elastomer, 7 parts dioctyl phthalate, 5 parts β-nucleating agent, and 1.5 parts antioxidant.

[0069] Comparative Example 2: Compared with Example 1, Comparative Example 2 was adjusted as follows: Acrylamide was used for cellulose modification, while the other processes remained unchanged. Specifically:

[0070] Preparation of modified cellulose: (1) Add 20 parts of lignocellulose to 36 parts of ethyl acetate to prepare a homogeneous cellulose suspension. Then, under stirring, add 6 parts of ethylenediamine dropwise. Stir at 50°C for 2 hours to obtain reaction solution A. (2) Add 7 parts of acrylamide dropwise to reaction solution A. Stir at 50°C for 3 hours. Then, add 50 parts of anhydrous ethanol. After standing for 5 hours, filter and dry to obtain modified cellulose.

[0071] Comparative Example 3: Compared with Example 1, Comparative Example 3 was adjusted to use only nano-calcium carbonate as a filler, while keeping the other processes unchanged. Specifically:

[0072] Step 2: Preparation of modified filler: Add 30 parts of nano calcium carbonate to a mixer and mix evenly. Then add it to 30 parts of anhydrous ethanol solution containing 2 wt% mixed silane coupling agent. Sonicate at 50°C for 120 min. After filtration and drying, the modified filler is obtained.

[0073] Comparative Example 4: Compared with Example 1, Comparative Example 4 was adjusted to use only WD-60 as a silane coupling agent, while keeping the other processes unchanged. Specifically:

[0074] Preparation of modified filler: 20 parts of potassium hexatitanate whiskers and 10 parts of nano calcium carbonate were added to a mixer and mixed evenly. Then, the mixture was added to 30 parts of 2 wt% anhydrous ethanol solution containing WD-60. The mixture was ultrasonically treated at 50℃ for 120 min, filtered and dried to obtain the modified filler.

[0075] Comparative Example 5: Compared with Example 1, Comparative Example 5 was adjusted to use only ethylene-octene block copolymer as the elastomer, while the rest of the process remained unchanged.

[0076] Comparative Example 6: Compared with Example 1, Comparative Example 6 was adjusted to have a polypropylene to high-density polyethylene mass ratio of 10:1, with the remaining processes unchanged. Specifically:

[0077] The raw materials of the plastic layer, by weight, are: 100 parts polypropylene, 26 parts modified polypropylene, 10 parts high-density polyethylene, 18 parts modified filler, 23 parts elastomer, 7 parts dioctyl phthalate, 5 parts β-nucleating agent, and 1.5 parts antioxidant.

[0078] The high-toughness waterproof paper-plastic composite bags prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests to detect their waterproof performance and toughness.

[0079] Testing Experiment: At room temperature, the composite bags prepared in Examples 1-3 and Comparative Examples 1-6 were immersed in water for 24 hours. After drying, their tensile strength and elongation at break were tested according to GB / T 1040.3-2006 to evaluate their waterproof performance and toughness. Specific data are shown in Table 1.

[0080] Table 1

[0081]

[0082] Conclusion: As can be seen from the data in Table 1 above, the paper-plastic composite bag prepared by the present invention has good waterproofness and toughness. Through the modification of polypropylene, selection of fillers, and synergy of elastomers and other raw materials in the present invention, the performance of the paper-plastic composite bag is greatly improved. Moreover, it can still maintain good performance after water immersion treatment. That is, the present invention has prepared a high-toughness waterproof paper-plastic composite bag.

[0083] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-toughness waterproof paper-plastic composite bag, characterized in that: The plastic layer comprises the following components: 90-120 parts of polypropylene, 20-30 parts of modified polypropylene, 15-25 parts of high-density polyethylene, 15-25 parts of modified filler, 15-25 parts of elastomer, 5-10 parts of dioctyl phthalate, 1-5 parts of β-nucleating agent, and 1-2 parts of antioxidant. ​ The mass ratio of the polypropylene and the high-density polyethylene is 5:

1. The preparation method of the modified polypropylene comprises the following steps: adding 10 parts of polypropylene, 1-2 parts of itaconic anhydride, and 0.3-0.5 parts of dibenzoyl peroxide into a blender, stirring and mixing at 170-190 ℃ for 5-10 min, then adding 2-5 parts of modified cellulose into the blender, stirring and mixing for 5-8 min, and then extruding the mixture through a twin-screw extruder at 160-175 ℃ and at a rotating speed of 120-210 rpm to obtain the modified polypropylene. The preparation method of the modified cellulose comprises the following steps: adding 10 parts of cellulose into 10-20 parts of ethyl acetate to prepare a uniform cellulose suspension, adding 1-4 parts of ethylenediamine dropwise under stirring, stirring at 30-60 ℃ for 1-3 h to obtain a reaction liquid A, adding 2-4 parts of a modifier dropwise into the reaction liquid A, stirring and reacting at 30-60 ℃ for 1-3 h, adding a large amount of anhydrous ethanol, standing for 3-6 h, and then filtering and drying to obtain the modified cellulose. The preparation method of the modified filler comprises the following steps: adding a filler into an ethanol solution containing a mixed silane coupling agent, ultrasonic treating at 40-60 ℃ for 60-120 min, and then filtering and drying to obtain the modified filler. The mass ratio of the filler and the mixed silane coupling agent is 50:

1. The preparation method of the itaconic anhydride grafted mercapto silane coupling agent comprises the following steps: dispersing 0.5-1 parts of itaconic anhydride, 0.01-0.05 parts of a photoinitiator, and 3-5 parts of a mercapto silane coupling agent into anhydrous ethanol to form a uniform solution, irradiating the solution with ultraviolet light of 365 nm for 30-60 min, and then heating to 75-80 ℃ until the anhydrous ethanol is volatilized and removed. The elastomer is a mixture of ethylene-octene block copolymer and ethylene-octene block copolymer grafted itaconic anhydride polymer at a mass ratio of 1:

1. The grafting rate of the ethylene-octene block copolymer grafted itaconic anhydride polymer is 1-5 wt%. ​ ​ ​ ​ The preparation method of the ethylene-octene block copolymer grafted itaconic anhydride polymer is as follows: 0.1-0.3 parts of itaconic anhydride, 5 parts of ethylene-octene block copolymer and 0.01-0.03 parts of dibenzoyl peroxide are added into a blender, melt-blended by a double-screw extruder, extruded at 170-220 DEG C and at a rotating speed of 120-210 rpm to obtain the ethylene-octene block copolymer grafted itaconic anhydride polymer.

2. The method for preparing a high-toughness waterproof paper-plastic composite bag according to claim 1, characterized in that: The method comprises the following steps: Step one: melt grafting the modified cellulose with polypropylene to obtain modified polypropylene; Step two: modifying the filler with a mixed silane coupling agent to obtain modified filler; Step three: mixing polypropylene, modified polypropylene, high-density polyethylene, modified filler, elastomer, dioctyl phthalate, beta-nucleating agent and antioxidant uniformly, and extruding at 180-230 DEG C to obtain a plastic layer; Step four: bonding the plastic layer to both sides of the paper layer by using an adhesive, and drying to obtain a composite paper; and finally processing the composite paper into a high-toughness waterproof paper-plastic composite bag.

Images