Polyethylene cast film and preparation method thereof

Abstract

The present application relates to the technical field of cast film, and specifically discloses a polyethylene cast film and a preparation method thereof. The polyethylene cast film comprises the following raw materials in parts by weight: 15-25 parts of low-density polyethylene; 50-60 parts of high-density polyethylene; 20-30 parts of linear low-density polyethylene; 40-50 parts of recycled polyethylene; 120-130 parts of filler; 5-10 parts of polypropylene; 35-60 parts of pentaerythritol tetraacetate; and 1-2 parts of cross-linking agent. The polyethylene cast film of the present application can be used for cast film production, and has the advantages of good mechanical properties, environmental protection, degradability, and good tearing performance.

Description

Technical Field

[0001] The present application relates to the technical field of cast films, and more specifically, to a polyethylene cast film and a preparation method thereof. Background Art

[0002] Cast film is a non-stretched, non-directional flat extruded film produced by melt casting and quenching. Polyethylene film produced by casting is widely used in sanitary packaging of products such as baby diapers and adult hygiene products. Since polyethylene film has the characteristics of stable structure and is not easily degraded, with the large-scale use of cast film, environmental pollution problems have gradually become prominent.

[0003] At present, the amount of polyethylene added in the existing polyethylene film is reduced by adding easily degradable fillers to reduce the environmental problems caused by polyethylene. However, when the amount of fillers added increases, the mechanical properties of the polyethylene film will be reduced, which is not conducive to the actual use of the polyethylene film. Summary of the invention

[0004] In order to ensure the mechanical properties of polyethylene films while reducing the environmental problems caused by polyethylene films, the present application provides a polyethylene cast film and a preparation method thereof.

[0005] In a first aspect, the present application provides a polyethylene cast film, which adopts the following technical solution:

[0006] A polyethylene cast film comprises the following raw materials in parts by weight:

[0007] 15-25 parts of low density polyethylene;

[0008] 50-60 parts of high density polyethylene;

[0009] 20-30 parts of linear low density polyethylene;

[0010] 40-50 parts of recycled polyethylene;

[0011] 120-130 parts of filler;

[0012] Polypropylene 5-10 parts;

[0013] Pentaerythritol tetraacetate 35-60 parts;

[0014] 1-2 parts of crosslinking agent.

[0015] By adopting the above technical solution, in order to ensure the mechanical properties of the existing polyethylene film, usually only a small amount of filler can be added. The present application reduces the amount of polyethylene added by increasing the amount of filler added, and further adds recycled polyethylene in the present application to achieve the recycling of recycled polyethylene, while ensuring the mechanical properties of the polyethylene film, thereby reducing the problem of environmental pollution caused by the inconvenient degradation of polyethylene, and adding pentaerythritol tetraacetate to carry out graft cross-linking with polyethylene to ensure the mechanical properties of the polyethylene film;

[0016] Pentaerythritol tetraacetate has good biodegradability, which is conducive to the subsequent degradation of polyethylene film; polyethylene is a linear flexible chain, and the network polymer obtained after cross-linking is usually an irregular network structure. Although the polyethylene film formed after cross-linking has good mechanical properties, it is easy to cause the polyethylene film to be difficult to tear when used as a packaging film for sanitary products. The pentaerythritol tetraacetate used in the present application can form a neatly arranged network structure after graft cross-linking with polyethylene, which not only ensures the mechanical properties of the polyethylene film, but also can maintain a straight fracture when the polyethylene film is torn, thereby improving the performance of the polyethylene film;

[0017] Under the action of the cross-linking agent, pentaerythritol tetraacetate is grafted onto polyethylene or polypropylene by melt grafting; pentaerythritol tetraacetate contains 4 unsaturated carbon-oxygen double bonds, which can quickly react with macromolecular free radicals, which is beneficial to the rapid grafting of pentaerythritol tetraacetate and polyethylene, reduces the self-polymerization of polyethylene during the grafting process, and ensures that the polyethylene film formed after cross-linking polymerization has a neatly arranged network structure, thereby achieving the improvement of the mechanical properties of the polyethylene film while maintaining a straight fracture when the polyethylene film is torn.

[0018] During the cross-linking process of pentaerythritol tetraacetate with polyethylene or polypropylene, the filler can be embedded in the cross-linking structure of polyethylene, so that it can ensure the mechanical properties of the polyethylene film. The amount of filler added within the dosage range of this application can ensure the mechanical properties and degradation properties of the polyethylene film, which has the effect of saving costs and being environmentally friendly.

[0019] Preferably, the filler is rice husk powder, and the particle size of the rice husk powder is 20-35 nm.

[0020] By adopting the above technical scheme, the rice husk powder is rich in lignin fiber, cellulose, and hemicellulose and has good biodegradability, and the rice husk powder within the particle size range of the present application can make the polyethylene film exhibit good mechanical properties.

[0021] Preferably, the rice husk powder is silane-modified rice husk powder, and the preparation steps of the silane-modified rice husk powder are as follows:

[0022] The unmodified rice husk powder and nitric acid are mixed in a weight ratio of 1: (1-1.3) to activate, and then glycidyloxypropyltrimethoxysilane is added and stirred. The weight ratio of rice husk powder to glycidyloxypropyltrimethoxysilane is 10: (2-3). After filtering, washing and drying, silane-modified rice husk powder is obtained.

[0023] By adopting the above technical solution, the silane-modified rice husk powder can further enhance the compatibility between the rice husk powder and polyethylene or polypropylene, reduce the agglomeration of the rice husk powder, and thus ensure the mechanical properties of the polyethylene film.

[0024] Preferably, 20-30 parts of polybutylene succinate are also included.

[0025] By adopting the above technical scheme, polybutylene succinate has good biodegradability, and polybutylene succinate is a semi-crystalline polymer. With the increase of melting temperature, the molecular chain mobility of polybutylene succinate is enhanced, and the crystallization is gradually improved. Rice husk powder plays a role of heterogeneous nucleation in the crystallization process of polybutylene succinate. The action of rice husk powder on polybutylene succinate can reduce the nucleation activation energy, which is beneficial to improve the strength of the polyethylene film.

[0026] Polybutylene succinate is conducive to the uniform dispersion of rice husk powder in the polyethylene film, so that the rice husk powder is in a directional arrangement in the polyethylene film, and there is also a strong interfacial adhesion between the rice husk powder and polyethylene or polypropylene, which ensures the mechanical properties of the polyethylene film and the performance of being easy to tear.

[0027] Preferably, it also includes 0.3-0.5 parts of an opening agent, and the opening agent is olein.

[0028] By adopting the above technical scheme, oleic acid glyceryl is used as an opening agent, which can significantly reduce the adhesion between polyethylene films, make the surface of the produced polyethylene film smoother, and improve the surface finish of the polyethylene film; the addition of oleic acid glyceryl can improve the temperature resistance of the polyethylene film, and improve the stability of the polyethylene film when used under different temperature conditions; oleic acid glyceryl has good biodegradability. Since the glyceride group is easily hydrolyzed, the unsaturated double bonds in the ester chain are easily oxidized under the attack of microorganisms, which is conducive to the subsequent degradation of the polyethylene film and reduces the pollution of the polyethylene film to the environment during the degradation process.

[0029] In addition, oleylglycerol is a non-ionic surfactant, which has the effects of emulsification and defoaming, and reduces the rupture of polyethylene film due to the presence of bubbles.

[0030] Preferably, the cross-linking agent is dicumyl peroxide.

[0031] By adopting the above technical scheme, dicumyl peroxide is used as a cross-linking agent to initiate pentaerythritol tetraacetate and polyethylene or polypropylene. When the temperature reaches the melting point of polyethylene, dicumyl peroxide generates primary free radicals to capture hydrogen atoms on the hydrocarbon chain, generating macromolecular free radicals to initiate polymerization reactions, so that the final polyethylene film has a neatly arranged network structure, and the rice husk powder is evenly dispersed in the network structure, thereby improving the mechanical properties and tear properties of the polyethylene film.

[0032] Preferably, 2-5 parts of masterbatch are also included.

[0033] By adopting the above technical solution, adding masterbatch can make the polyethylene cast film have good glossiness, meeting the use requirements of the polyethylene film when it is applied to packaging.

[0034] In a second aspect, the present application provides a method for preparing a polyethylene cast film, using the following technical solution:

[0035] A method for preparing a polyethylene cast film comprises the following steps:

[0036] Plasticizing and extruding: feed the raw materials of polyethylene cast film according to the weight proportion, melt blend and extrude at 130-160°C, adjust the extrusion temperature to 165-185°C, and plasticize and extrude;

[0037] Casting: The casting temperature is 200-230℃. After flowing out, it is squeezed and cooled by a cooling roller at 15-20℃ to obtain a cast film.

[0038] By adopting the above technical scheme, during the melt blending process, pentaerythritol tetraacetate and polyethylene or polypropylene are grafted and cross-linked under the action of a cross-linking agent, and the filler is tightly combined with polyethylene or polypropylene during the cross-linking process. Due to the special structure of pentaerythritol tetraacetate, a neatly arranged three-dimensional network structure is generated after cross-linking. Even if the amount of filler added is increased, a polyethylene film with excellent mechanical properties can still be obtained, and it is ensured that the cast film can be neatly torn when in use, which is convenient for people to use. In addition, the cast film prepared in this application has good biodegradability, which helps to reduce the pollution of the polyethylene film to the environment.

[0039] In summary, this application has the following beneficial effects:

[0040] 1. Since the present application adopts pentaerythritol tetraacetate and utilizes the grafting and cross-linking process of pentaerythritol tetraacetate and polyethylene or polypropylene, the polyethylene film can still have strong mechanical properties after a high amount of filler is added to the polyethylene film raw material.

[0041] 2. In the present application, rice husk powder is preferably used as the filler. The rice husk powder can be evenly dispersed in the polyethylene film under the action of polybutylene succinate, ensuring that the polyethylene film has strong mechanical properties and tear properties.

[0042] 3. The rice husk powder, pentaerythritol tetraacetate, polybutylene succinate, oleyl glycerol, etc. used in this application as raw materials for polyethylene film have good biodegradability, are beneficial to the later degradation of polyethylene film, and have the advantages of being green and environmentally friendly.

[0043] 4. The method of the present application produces a cast film through processes such as melt blending, extrusion, casting, cooling and shaping. The temperature environment of melt blending provides reaction conditions for the grafting and cross-linking of polyethylene and polypropylene. The raw materials have good dispersibility and compatibility, thereby obtaining a polyethylene cast film with good mechanical properties, good tear properties, and environmental protection and degradability. DETAILED DESCRIPTION

[0044] The present application is further described in detail below with reference to the embodiments.

[0045] All raw materials in the examples of this application can be obtained commercially.

[0046] Among them, the molecular weight of low-density polyethylene (LDPE) is 100,000-500,000, the molecular weight of high-density polyethylene (HDPE) is 200,000-500,000, and the molecular weight of linear low-density polyethylene (LLDPE) is 25,000-50,000;

[0047] Polypropylene CAS number: 90003-07-0;

[0048] Pentaerythritol tetraacetate CAS number: 597-71-7;

[0049] Pentaerythritol octanoate CAS No.: 68441-68-9;

[0050] Dicumyl peroxide CAS number: 80-43-3;

[0051] Polybutylene succinate CAS number: 25777-14-4;

[0052] Polybutylene succinate-adipate CAS No.: 67423-06-7;

[0053] Oleic acid glyceride CAS number: 111-03-5;

[0054] Oleamide CAS number: 301-02-0;

[0055] Methylcellulose CAS No.: 9004-67-5; Molecular weight: 658.73;

[0056] Gelatin CAS number: 9000-70-8.

[0057] Example

[0058] Examples 1.1-1.3

[0059] A polyethylene cast film comprises the following raw materials by weight:

[0060] Low density polyethylene 15-25kg;

[0061] High-density polyethylene 50-60kg;

[0062] Linear low-density polyethylene 20-30kg;

[0063] Recycled polyethylene 40-50kg;

[0064] Filling material 120-130kg;

[0065] Polypropylene 5-10kg;

[0066] Pentaerythritol tetraacetate 35-60kg;

[0067] Cross-linking agent 1-2 kg;

[0068] Masterbatch 2-5kg;

[0069] The filler is rice husk powder, the particle size of the rice husk powder is 20nm, and the cross-linking agent is diisopropylbenzene peroxide;

[0070] The method for preparing the polyethylene cast film comprises the following steps:

[0071] S1, plasticizing and extruding: feeding the raw materials of polyethylene cast film into the cast extruder according to the weight, melt blending at 155°C, melting time 30min, extruding, adjusting the extrusion temperature to 185°C, and plasticizing and extruding;

[0072] S2. Casting: The casting temperature is 220°C. After flowing out, the film is squeezed and cooled by a cooling roller at 18°C ​​to obtain a cast film.

[0073] The raw material dosage of the polyethylene cast film of Examples 1.1-1.3 is shown in Table 1.

[0074] Table 1 Raw material dosage of polyethylene cast film of Examples 1.1-1.3 (unit: kg)

[0075] Example 1.1 Example 1.2 Example 1.3 Low density polyethylene 15 22 25 High-density polyethylene 50 53 60 Linear low density polyethylene 20 26 30 Recycled Polyethylene 40 42 50 Filling 120 126 130 Polypropylene 5 8 10 Pentaerythritol tetraacetate 35 45 60 Crosslinking agent 1 1.2 2 Masterbatch 2 3.6 5

[0076] Example 2

[0077] A polyethylene cast film, which is different from Example 1.1 in that the unmodified rice husk powder is replaced with an equal amount of silane-modified rice husk powder;

[0078] The method for preparing silane-modified rice husk powder comprises the following steps:

[0079] Rice husk powder and nitric acid are mixed in a weight ratio of 1:1 to activate the surface of the rice husk powder, and then glycidyloxypropyltrimethoxysilane is added and stirred. The weight ratio of rice husk powder to glycidyloxypropyltrimethoxysilane is 10:2. After filtering, washing, and drying at 80°C for 2h, silane-modified rice husk powder is obtained.

[0080] Examples 3.1-3.3

[0081] A polyethylene cast film, which is different from Example 2 in that 20-30 kg of polybutylene succinate is further added, wherein the amount of polybutylene succinate added in Example 3.1 is 20 kg,

[0082] The amount of polybutylene succinate added in Example 3.2 is 24 kg.

[0083] The amount of polybutylene succinate added in Example 3.3 is 30 kg.

[0084] Example 4

[0085] A polyethylene cast film, which is different from Example 3.1 in that an equal amount of polybutylene succinate-adipate is used to replace polybutylene succinate.

[0086] Examples 5.1-5.3

[0087] A polyethylene cast film, which is different from Example 3.1 in that 0.3-0.5 kg of an opening agent is further added, and the opening agent is oleic acid glyceride.

[0088] The amount of the opening agent added in Example 5.1 is 0.3 kg;

[0089] The amount of the opening agent added in Example 5.2 is 0.4 kg;

[0090] The amount of the opening agent added in Example 5.3 is 0.5 kg;

[0091] Example 6

[0092] A polyethylene cast film, which differs from Example 5.1 in that oleyl glyceride is replaced by an equal amount of oleamide.

[0093] Comparative Example 1

[0094] A polyethylene cast film, which is different from Example 1.1 in that the amount of pentaerythritol tetraacetate used is 0 kg.

[0095] Comparative Example 2

[0096] A polyethylene cast film, which is different from Example 1.1 in that pentaerythritol tetraacetate is replaced with an equal amount of pentaerythritol tetraoctanoate.

[0097] Comparative Example 3

[0098] A polyethylene cast film, which is different from Example 3.1 in that the rice husk powder is replaced by an equal amount of gelatin.

[0099] Comparative Example 4

[0100] A polyethylene cast film is different from Example 1.1 in that, compared with a commercially available polyethylene cast film, the filler in the commercially available cast film is calcium carbonate, and the amount of calcium carbonate added accounts for 30% of the polyethylene cast film.

[0101] Comparative Example 5

[0102] A polyethylene cast film, which is different from Example 1.1 in that the amount of filler used is 80 kg, wherein the filler is rice husk powder.

[0103] Comparative Example 6

[0104] A polyethylene cast film, which is different from Example 1.1 in that the amount of filler used is 150 kg, wherein the filler is rice husk powder.

[0105] Comparative Example 7

[0106] A polyethylene cast film, which is different from Example 1.1 in that the filler is methyl cellulose.

[0107] Performance testing

[0108] The tests include:

[0109] 1. Tensile performance test

[0110] The tensile properties test was carried out in accordance with GB / T1040.3-2006 "Determination of tensile properties of plastics Part 3: Experimental conditions for films and sheets"; the higher the tensile strength, the better the mechanical properties of the polyethylene film.

[0111] 2. Tear resistance test

[0112] The tear resistance is tested according to GB / T 16578.1-2008 "Determination of tear resistance of plastic films and sheets". The higher the tear strength, the worse the tear resistance of the polyethylene film.

[0113] 3. Biodegradability test

[0114] With reference to GB / T19277.1-2011, the composting degradation test was carried out on the materials. The sample materials were mixed with compost inoculants and placed in a composting container. A full composting test was carried out under the conditions of oxygen content of 21%, temperature (58±2℃) and humidity (50-55%). In this experiment, the ratio of the carbon dioxide release after 6 months of material degradation to the theoretical value was set to calculate the biodegradation rate.

[0115] The polyethylene cast film was subjected to a tensile property test and a tear resistance test, and the sample size was: 7 cm in length, 3 cm in width, and 0.03±0.01 mm in thickness.

[0116] The test results are shown in Table 2.

[0117] Table 2 Test results of Examples 1-7 and Comparative Examples 1-6

[0118]

[0119]

[0120] It can be seen from Examples 1.1-1.3 and Comparative Examples 1-2 and Table 2 that even when recycled polyethylene is added, the polyethylene film obtained after cross-linking still has good mechanical properties, which is beneficial to reducing costs; the present application preferably uses pentaerythritol tetraacetate, which utilizes the highly symmetrical structure of pentaerythritol tetraacetate, and can ensure the mechanical properties of the polyethylene film while maintaining a straight fracture when the polyethylene film is torn, thereby ensuring the tearability of the polyethylene film; when pentaerythritol tetraoctanoate is used to replace pentaerythritol tetraacetate, although the graft cross-linking between pentaerythritol tetraoctanoate and polyethylene can be achieved due to the longer chain length of pentaerythritol tetraoctanoate, the increase in chain length is prone to curling, which makes it difficult to form a neatly arranged network structure, affecting the tearing performance of the polyethylene film.

[0121] Combining Examples 1.1-1.3 and Comparative Examples 1 and 4 with Table 2, it can be seen that, under the premise of increasing the amount of filler, the use of pentaerythritol tetraacetate and polyethylene or polypropylene for graft cross-linking can improve the mechanical properties of the polyethylene film while ensuring that the polyethylene film has a straight tear seam for easy tearing; although the commercially available polyethylene film has good mechanical properties, it has the disadvantage of being inconvenient to tear and is not conducive to the subsequent degradation of the polyethylene film;

[0122] It can be seen from Example 1.1 and Comparative Examples 5-6 and Table 2 that when the amount of rice husk powder added is not within the scope of the present application, although a small amount of rice husk powder added allows the polyethylene film to have better mechanical properties, it is not conducive to the tearing of the polyethylene film; when the amount of rice husk powder added is too much, it is not conducive to the film formation of the polyethylene film, and the brittleness of the polyethylene film is increased, and some rice husk powder agglomerates can be seen at the tear seam fracture of the polyethylene film, resulting in the tear seam of the polyethylene film being unable to maintain a smooth and straight state.

[0123] From Example 1.1 and Comparative Example 3 and Comparative Example 7 combined with Table 2, it can be seen that when the filler is methyl cellulose, the methyl cellulose is not easy to disperse evenly during the casting process. Although the mechanical properties of the polyethylene film can be guaranteed to a certain extent, it cannot ensure that the polyethylene film maintains a straight tear when it is torn; when the filler is gelatin, although gelatin is more beneficial to the film-forming properties of the polyethylene film than rice husk powder, the film hardness is too hard compared to rice husk powder, resulting in the polyethylene film being difficult to tear during use.

[0124] Combining Example 1.1 and Example 2 with Table 2, it can be seen that the use of silane-modified rice husk powder can further enhance the compatibility between rice husk powder and polyethylene and enhance the mechanical properties of the polyethylene film.

[0125] Combining Example 2 and Examples 3.1-3.3 and Example 4 and Table 2, it can be seen that the addition of polybutylene succinate can play a synergistic role with rice husk powder, which is beneficial to the neat arrangement and distribution of rice husk powder in the polyethylene film, and improves the mechanical properties and tear properties of the polyethylene film.

[0126] It can be seen from Example 3.1, Example 5.1-5.3 and Example 6 and Table 2 that the use of oleyl glycerol as an opening agent is beneficial to improving the gloss of the polyethylene film, reducing the generation of bubbles during melt blending, which causes the cast film with bubbles to easily rupture, and is beneficial to improving the stability of the polyethylene cast film.

[0127] The polyethylene cast films prepared in Examples 1-6 and Comparative Examples 1-7 were tested for biodegradability.

[0128] The test results are shown in Table 3.

[0129] Table 3 Degradation performance test results

[0130]

[0131]

[0132] It can be seen from Examples 1-6 and Comparative Examples 1-7 and Tables 2-3 that the biodegradation rate of the polyethylene film of the present application is above 80%, and has good biodegradability; the change in the particle size of the rice husk powder and the introduction of the modified rice husk powder have no significant effect on the degradation performance of the polyethylene film; polybutylene succinate itself has good biodegradability, and its addition is beneficial to improving the biodegradability of the polyethylene film; when oleic acid glyceride is used as an opening agent, in addition to being beneficial to improving the opening performance of the polyethylene film, it can also ensure that the degradability of the polyethylene film is not affected.

[0133] When pentaerythritol tetraacetate is not added, it has no significant effect on the degradation performance, but it will obviously affect the mechanical properties of the film; when pentaerythritol tetraoctanoate is used to replace pentaerythritol tetraacetate, it will be unfavorable for the degradation of polyethylene film due to the larger molecular weight of pentaerythritol tetraoctanoate; when corn starch and gelatin are used to replace rice husk powder, there will be no significant effect on the biodegradability, but it will affect the mechanical properties and tearability of the polyethylene film;

[0134] When the amount of filler added is not within the scope of this application, it will have an adverse effect on the performance of the polyethylene film. When the amount of filler added is too low, although it is beneficial to the improvement of the mechanical properties of the polyethylene film, it is not conducive to the later degradation of the polyethylene film. When the amount of filler added is too much, although it is beneficial to the degradation of the film, the mechanical properties of the polyethylene film will be significantly reduced.

[0135] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A polyethylene cast film, characterized in that The invention comprises the following raw materials in parts by weight: 15-25 parts of low density polyethylene; 50-60 parts of high density polyethylene; 20-30 parts of linear low density polyethylene; 40-50 parts of recycled polyethylene; 120-130 parts of filler; Polypropylene 5-10 parts; Pentaerythritol tetraacetate 35-60 parts; 1-2 parts of cross-linking agent; 20-30 parts of polybutylene succinate; The filler is rice husk powder, and the particle size of the rice husk powder is 20-35nm; The rice husk powder is silane-modified rice husk powder, and the preparation steps of the silane-modified rice husk powder are as follows: The unmodified rice husk powder and nitric acid are mixed in a weight ratio of 1: (1-1.3) to activate, and then glycidyloxypropyltrimethoxysilane is added and stirred. The weight ratio of rice husk powder to glycidyloxypropyltrimethoxysilane is 10: (2-3). After filtering, washing and drying, silane-modified rice husk powder is obtained.

2. A polyethylene cast film according to claim 1, characterized in that: The invention also comprises 0.3-0.5 parts of an opening agent, wherein the opening agent is olein.

3. A polyethylene cast film according to claim 1, characterized in that: The cross-linking agent is dicumyl peroxide.

4. A polyethylene cast film according to claim 1, characterized in that: Also includes 2-5 parts of masterbatch.

5. A method for preparing a polyethylene cast film according to any one of claims 1 to 4, characterized in that: The following steps are involved: Plasticizing and extruding: feed the raw materials of polyethylene cast film according to the weight proportion, melt blend and extrude at 130-160°C, adjust the extrusion temperature to 165-185°C, and plasticize and extrude; Casting: The casting temperature is 200-230℃. After flowing out, it is squeezed and cooled by a cooling roller at 15-20℃ to obtain a cast film.

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