Lignin reversibly cross-linked pe plastic and preparation method and application thereof

Abstract

The application discloses a kind of lignin reversible crosslinking PE plastics and its preparation method and application, it is related to the field of modified plastics.Lignin reversible crosslinking PE plastics includes the following components by mass fraction: maleimide functionalized lignin 8~12 parts, furan functionalized maleic anhydride grafted polyethylene oligomer 2.5~15 parts, polyethylene 100 parts.The maleimide functionalized lignin is obtained by reaction of alkali lignin and maleimide compound containing siloxane group;The furan functionalized maleic anhydride grafted polyethylene oligomer is obtained by reaction of maleic anhydride grafted polyethylene polymer and furan derivative containing amino group.By modifying lignin and introducing DA bond, the compatibility of lignin and polyethylene is increased, and the reversible crosslinking of PE plastic is realized, so that the PE plastic has good mechanical properties, ultraviolet resistance and repeatable processability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of modified plastics, in particular to a lignin reversibly crosslinked PE plastic and a preparation method and application thereof. BACKGROUND

[0002] Polyethylene (PE) is one of the five synthetic resins, and is the largest in production capacity and the most imported variety in China. Polyethylene plastic plays an important role in improving the quality of life, but the traditional polyethylene plastic often has the problem of insufficient ultraviolet resistance. Ultraviolet radiation affects the physical properties and mechanical strength of plastics, and may even cause aging of plastics, reducing their service life.

[0003] Currently, the main method to solve this problem is to introduce lignin into polyethylene plastic. Lignin has the characteristics of biodegradability and shielding ultraviolet (UV) radiation, and as a byproduct of the paper industry, it has the advantages of low cost and large output. However, most plastic polymers are non-polar and weakly polar long-chain alkyl polymers, and due to their low surface energy, the compatibility between lignin and plastic polymers is low. Direct application of lignin in plastic polymer systems can result in low dispersion and low compatibility of components, which can reduce the mechanical properties of the composite material and is not conducive to practical application.

[0004] In addition, thermoplastic polymers such as polyethylene do not have a stable crosslinked network like thermosetting polymers, which cannot guarantee the mechanical strength and structural stability of the material. Although it can be reprocessed, its mechanical properties are generally reduced after reprocessing, limiting its practical value and greatly shortening the service life of the plastic. In order to reduce pollution and waste, it is necessary to develop a class of crosslinked polymers with good mechanical properties, ultraviolet resistance and repeatable processability to extend the service life of the material.

[0005] CN 117986726 A discloses a lignin composite nanomicrosphere modified PE plastic and a preparation method and application thereof. First, lignin and nano-TiO2 are self-assembled to form lignin composite nanomicrospheres, then POE (maleic anhydride grafted ethylene-octene copolymer) is used as a compatibilizer, and polysulphated fatty acid is used to regulate the interfacial properties of different substances in the system, which improves the compatibility of nano-TiO2, lignin and PE, and greatly improves the ultraviolet resistance of the modified PE plastic. However, the prior art does not focus on the repeatable processability of the PE plastic. SUMMARY

[0006] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a lignin reversibly crosslinked PE plastic.

[0007] Another purpose of the present application is to provide a preparation method of the lignin reversibly crosslinked PE plastic.

[0008] It is another object of the present application to provide an application of the lignin reversibly crosslinked PE plastic.

[0009] The above objects of the present application are achieved by the following technical solutions.

[0010] A lignin reversibly crosslinked plastic comprises the following components by mass:

[0011] 8-12 parts of maleimide functionalized lignin, 2.5-15 parts of furan functionalized maleic anhydride grafted polyethylene oligomer, and 100 parts of polyethylene.

[0012] The maleimide functionalized lignin is obtained by reacting alkali lignin and a maleimide compound containing a siloxane group, and the mass ratio of the alkali lignin and the maleimide compound containing a siloxane group is (1-2):(1-2); the furan functionalized maleic anhydride grafted polyethylene oligomer is obtained by reacting a maleic anhydride grafted polyethylene polymer and a furan derivative containing an amino group, and the mass ratio of the furan derivative containing an amino group and the maleic anhydride grafted polyethylene polymer is (0.8-1.2):10.

[0013] The present application realizes the reversible crosslinking of PE plastic and improves the compatibility of lignin and PE plastic by introducing DA bonds through maleic anhydride and a furan derivative containing an amino group.

[0014] The present application reacts alkali lignin with a maleimide compound containing a siloxane group, modifies the lignin by introducing maleic anhydride groups, reduces the polar groups on the surface of the lignin, and further increases the compatibility of the lignin and polyethylene.

[0015] The present application reacts a maleic anhydride grafted polyethylene polymer with a furan derivative containing an amino group, grafts the furan derivative containing an amino group on the maleic anhydride grafted polyethylene polymer, and introduces furan groups. The maleic anhydride grafted polyethylene polymer as a compatibilizer can improve the compatibility between the polar polymer lignin and the non-polar polymer polyethylene, increase the adhesion of the two polymers, form a stable structure, and promote the uniformity of the dispersed phase and the continuous phase.

[0016] The conjugated diene on the molecular structure of the furan functionalized maleic anhydride grafted polyethylene oligomer and the carbon-carbon double bond on the molecular structure of the maleimide functionalized lignin undergo DA reaction when heated, and the compatibility of the lignin and PE plastic is further improved.

[0017] The present application introduces maleimide groups on the surface of lignin and grafts furan derivatives containing amino groups on the maleic anhydride grafted polyethylene polymer, synthesizes a DA bond polymer matrix with low viscosity characteristics through a low molecular weight polymer, to increase the compatibility of lignin and the matrix. DA bond is a controllable chemical bond, under high temperature processing conditions, the DA bond crosslinked polymer matrix dissociates crosslinking through retro-DA reaction, releases low molecular weight polymer, thereby greatly reducing the melt viscosity, so that the lignin reversibly crosslinked PE plastic still maintains the ability of injection molding. When the PE plastic cools down, the crosslinking structure will be formed again, so that the material can be secondarily formed. Through the application of DA bond crosslinking network, the DA bond in the PE plastic gives it excellent recycling processing ability, thereby prolonging the service life of the PE plastic.

[0018] Through the reversible crosslinking technology, the polyethylene retains its thermoplastic properties, so that the material can be processed and formed multiple times.

[0019] More specifically, the mass ratio of the alkali lignin and the maleimide compound containing siloxane groups is 1.5:1.

[0020] The maleimide compound containing siloxane groups is used as a surface modifier to modify the alkali lignin through reaction, thereby improving the compatibility of lignin and the matrix.

[0021] Specifically, the maleimide compound containing siloxane groups is one of 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione, 1-[(3-trimethoxysilyl)propyl]-1H-pyrrole-2,5-dione, 1-[3-(triethoxysilyl)butyl]-1H-pyrrole-2,5-dione, and 1-[3-(triethoxysilyl)undecyl]-1H-pyrrole-2,5-dione.

[0022] The structural formula of 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione is:

[0023]

[0024] The structural formula of 1-[(3-trimethoxysilyl)propyl]-1H-pyrrole-2,5-dione is:

[0025]

[0026] The structural formula of 1-[3-(triethoxysilyl)butyl]-1H-pyrrole-2,5-dione is:

[0027]

[0028] 1-[3-(triethoxysilyl)undecyl]-1H-pyrrole-2,5-dione has the structural formula:

[0029]

[0030] Specifically, the grafting rate of the maleic anhydride grafted polyethylene polymer is 0.8% to 1.2%.

[0031] Specifically, the amino-containing furan derivative is one of 2-amino furan, 2-furanmethanamine, 2-furanethanamine, and 3-(2-furan)-1-propanamine.

[0032] More specifically, the siloxane group-containing maleimide compound is prepared by reacting maleic anhydride with an amino-containing organosilane.

[0033] It should be noted that the siloxane group-containing maleimide compound of the present application can include the series of compounds described in the patent CN105131027A, and the preparation method can also refer to the patent. In the preparation method disclosed in the patent, the triethoxysilane can be replaced with trimethoxysilane.

[0034] More specifically, the amino-containing organosilane is one of 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane, 4-aminobutyl triethoxysilane, and 11-aminoundecyl triethoxysilane.

[0035] It should be noted that the maleic anhydride of the present application can also be replaced by 2-methyl maleic anhydride or dimethyl maleic anhydride.

[0036] Maleic anhydride is often used as a raw material for introducing DA bonds. In order to graft maleic anhydride on lignin, amino-containing organosilanes can be used as coupling agents to assist in grafting maleic anhydride on lignin. Amino-containing organosilanes can not only react with the hydroxyl groups on lignin, but also interact with the long-chain molecules in polyethylene, thereby increasing the interaction between the polyethylene molecular chain and lignin, thereby improving the mechanical properties and compatibility of PE plastics.

[0037] Figure 8 and Figure 9 is one of the examples of the synthesis method of the present application, Figure 8 represents one of the examples of the reaction of alkali lignin and the siloxane group-containing maleimide compound, Figure 9 represents one of the examples of the reaction of the maleic anhydride grafted polyethylene polymer and the amino-containing furan derivative.

[0038] In the specific implementation of the present application, 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione is selected as the surface modifier. 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione can be obtained by reacting maleic anhydride with KH550.

[0039] The operation of reacting the maleic anhydride with the KH550 can be: dissolving the maleic anhydride in the solvent A under N2purging at a temperature of 15-45℃, adding the KH550 for reaction, adding the catalyst and the solvent B after the reaction, adding the drying agent after warming, and obtaining the surface modifier 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione after the reaction.

[0040] It should be noted that the role of N2purging is to remove water in the air, and the role of the drying agent is to absorb water produced in the reaction and water in the air, so as to prevent the hydrolysis and polymerization of the KH500 and ensure that the surface modifier 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione can be grafted onto the lignin.

[0041] More specifically, the solvent A is dichloromethane.

[0042] More specifically, the reaction time after adding the KH550 is 0.5-1.5h.

[0043] More specifically, the reaction time after adding the drying agent is 3-5h.

[0044] More specifically, the catalyst is zinc chloride.

[0045] After the reaction of the maleic anhydride with the KH550, the five-membered ring of the maleic anhydride is opened. The zinc chloride acts as a Lewis acid catalyst to achieve the ring-closing reaction.

[0046] More specifically, the solvent B is toluene.

[0047] More specifically, the temperature after warming is 70-90℃.

[0048] Since the boiling point of dichloromethane is 39.6℃, it is easy to vaporize after warming, so toluene needs to be added to ensure the reaction.

[0049] More specifically, the drying agent is hexamethyldisilazane.

[0050] More specifically, the alkali lignin and the surface modifier 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione need to be added to the solvent for reaction.

[0051] More specifically, the solvent is a mixed solution prepared by mixing the pH=3 aqueous acetic acid solution and the acetone at a mass ratio of 1:7.

[0052] Specifically, the amino-containing furan derivative is a toluene solution of the amino-containing furan derivative.

[0053] More specifically, the toluene solution of the amino-containing furan derivative has a concentration of 0.3-0.5 mol / L.

[0054] Specifically, the reaction of the maleic anhydride grafted polyethylene polymer with the amino-containing furan derivative needs to be carried out under reflux conditions, and a large amount of methanol needs to be added after the reaction is cooled.

[0055] The role of methanol is to dilute the solvent and accelerate the precipitation of the product.

[0056] More specifically, the temperature of the reaction under reflux is 75-85℃.

[0057] More specifically, the reflux time is 4-6h.

[0058] Preferably, the lignin reversibly crosslinked PE plastic further comprises polysulfated fatty acid.

[0059] The addition of polysulfated fatty acid can further improve the ultraviolet resistance of the PE plastic.

[0060] At the same time, polysulfated fatty acid can also play an interface regulation role, reducing the agglomeration of lignin in polyethylene and increasing the dispersion degree of lignin in polyethylene, thereby improving the mechanical properties of the PE plastic.

[0061] More preferably, the lignin reversibly crosslinked PE plastic comprises the following components by mass fraction: maleimide functionalized lignin 8-12 parts, furan functionalized maleic anhydride grafted polyethylene oligomer 2.5-15 parts, polysulfated fatty acid 5-15 parts, and polyethylene 100 parts.

[0062] More preferably, the lignin reversibly crosslinked PE plastic comprises the following components by mass fraction: maleimide functionalized lignin 10 parts, furan functionalized maleic anhydride grafted polyethylene oligomer 10 parts, polysulfated fatty acid 5-15 parts, and polyethylene 100 parts.

[0063] More preferably, the lignin reversibly crosslinked PE plastic comprises the following components by mass fraction: maleimide functionalized lignin 10 parts, furan functionalized maleic anhydride grafted polyethylene oligomer 10 parts, polysulfated fatty acid 10 parts, and polyethylene 100 parts.

[0064] A preparation method of a lignin reversibly crosslinked PE plastic, comprising the following steps:

[0065] Blending maleimide functionalized lignin powder, furan functionalized maleic anhydride grafted polyethylene oligomer, and polyethylene to obtain a lignin reversibly crosslinked PE plastic.

[0066] Specifically, the maleimide functionalized lignin powder, furan functionalized maleic anhydride grafted polyethylene oligomer, polysulfated fatty acid and polyethylene are blended to obtain the lignin reversibly crosslinked PE plastic added with polysulfated fatty acid.

[0067] Specifically, the temperature of the blending is 120-150 DEG C.

[0068] Specifically, the preparation method of the lignin reversibly crosslinked PE plastic comprises the following steps:

[0069] The maleimide functionalized lignin powder, furan functionalized maleic anhydride grafted polyethylene oligomer are first blended, and then polyethylene is added again to blend to obtain the lignin reversibly crosslinked PE plastic.

[0070] More specifically, the maleimide functionalized lignin powder, furan functionalized maleic anhydride grafted polyethylene oligomer are first blended, and then polysulfated fatty acid and polyethylene are added again to blend to obtain the lignin reversibly crosslinked PE plastic added with polysulfated fatty acid.

[0071] More specifically, the first blending time is 8-12 min, and the second blending time is 10-20 min.

[0072] The application also protects the application of the above lignin reversibly crosslinked PE plastic in preparing PE packaging film, PE pipe, modified asphalt and electric wire and cable.

[0073] Compared with the prior art, the application has the following technical effects:

[0074] (1) The DA bond is constructed to reversibly crosslink the PE plastic, so that the polyethylene retains its thermoplastic property, thereby making the lignin reversibly crosslinked PE plastic have good repeatable processability.

[0075] (2) The compatibility of the lignin and the polyethylene is increased by modifying the lignin and constructing the DA bond, thereby enhancing the mechanical property of the lignin reversibly crosslinked PE plastic.

[0076] (3) The lignin reversibly crosslinked PE plastic has certain ultraviolet resistance by introducing the lignin. BRIEF DESCRIPTION OF DRAWINGS

[0077] Figure 1 is a synthesis flow chart of the lignin reversibly crosslinked PE plastic.

[0078] Figure 2 is a schematic diagram of a dumbbell-shaped sample prepared from the PE plastic of the examples and comparative examples.

[0079] Figure 3Stress-strain curves of PE plastics obtained from Examples 1-9 and Comparative Examples 1-4.

[0080] Figure 4 Stress-strain curves of PE plastics obtained from Examples 4 and 8 and Comparative Examples 1 and 3 before and after UV irradiation.

[0081] Figure 5 UV-vis absorption spectra of PE plastics obtained from Examples 4 and 8 and Comparative Examples 1-3.

[0082] Figure 6 Stress-strain curves of PE plastics obtained from Example 4 after repeated processing for 4 times.

[0083] Figure 7 Stress-strain curves of PE plastics obtained from Example 8 after repeated processing for 4 times.

[0084] Figure 8 Reaction principle diagram of Step S1 and Step S2 in the example.

[0085] Figure 9 Reaction principle diagram of Step S3 in the example. DETAILED DESCRIPTION

[0086] The application will be further described in conjunction with the examples. These examples are only used to illustrate the application and not used to limit the scope of the application. The experimental methods in the following example are not specified, which are usually according to the conventional conditions in the art or according to the conditions suggested by the manufacturers; the raw materials, reagents and the like used, if not specifically stated, are all raw materials and reagents that can be obtained from the conventional market or commercial channels. Any non-essential changes and substitutions made by the person skilled in the art on the basis of the application all belong to the scope of the application claimed.

[0087] Examples 1-6

[0088] The preparation method of the lignin reversibly crosslinked PE plastic of Examples 1-6 comprises the following steps:

[0089] S1: 7.82 g of maleic anhydride was dissolved in 100 mL of dichloromethane under N2purging at 30°C, 17.71 g of KH550 was added for reaction, after 1 hour of reaction, 10.90 g of zinc chloride and 200 mL of toluene were added, the temperature was raised to 80°C, 12.91 g of hexamethyldisilazane was added, and the reaction was carried out for 4 hours, then filtered, washed with ethanol solvent, and the filtrate was the surface modifier 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione.

[0090] S2: An acetic acid aqueous solution with pH=3 was prepared, mixed with acetone at a mass ratio of 1:7 to obtain a solvent that can dissolve lignin and surface modifier, and the alkali lignin and surface modifier were added into the solvent at a mass ratio of 1.5:1, stirred at 50°C for 1 h to make the surface modifier completely hydrolyzed and uniformly mixed with the lignin. The temperature was lowered to make the precipitate generated, and the solid was enriched by standing for 2 h, the supernatant was removed, and the precipitate was repeatedly washed with ethanol for several times, and vacuum dried to obtain a maleimide functionalized lignin powder.

[0091] S3: 2 g of maleic anhydride grafted polyethylene polymer (grafting rate 1%) was added into 50 mL of toluene, heated and stirred at 80°C until the polymer was completely dissolved, 5 mL of 2-furfurylamine (furfurylamine) toluene solution (concentration 0.4 mol / L) was added, and refluxed at 80°C for 5 hours, and then cooled to room temperature, followed by adding a large amount of methanol, collecting the product, washing, and drying to obtain a furan functionalized maleic anhydride grafted polyethylene polymer (mass ratio of 2-furfurylamine to maleic anhydride grafted polyethylene polymer 0.97:10).

[0092] S4: The maleimide functionalized lignin and furan functionalized maleic anhydride grafted polyethylene oligomer were added into an open mill and blended for 10 min at a mixing speed of 10 rpm and a reaction temperature of 135°C, and then polyethylene (PE) was added and blended for another 15 min at the same reaction temperature, and the lignin reversibly crosslinked PE plastic was obtained.

[0093] Table 1. Mass fraction of each component in step S4 for preparing the lignin reversibly crosslinked PE plastic in examples 1-6

[0094]

[0095] Examples 7-9

[0096] A method for preparing a lignin reversibly crosslinked PE plastic, which is different from example 4 in that:

[0097] Polythioctic acid was added and blended when polyethylene was added in step S4.

[0098] Table 2. Mass fraction of each component in step S4 for preparing the lignin reversibly crosslinked PE plastic in examples 7-9

[0099]

[0100] Comparative example 1

[0101] A method for preparing a PE plastic, which is different from example 4 in that:

[0102] Step S4: 6 parts of unmodified alkali lignin, 4 parts of surface modifier 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione, 0.92 parts of furanmethanamine, 10 parts of maleic anhydride grafted polyethylene and 100 parts of PE were added into the open mill, and PE plastic was obtained by blending at a temperature of 135 °C. The mixing speed was 10 rpm, and the blending time was 30 min.

[0103] Comparative Example 2

[0104] A method for preparing a PE plastic, which is different from Example 4 in that:

[0105] Step S4: No furan-functionalized maleic anhydride grafted polyethylene oligomer was added.

[0106] Comparative Example 3

[0107] A method for preparing a PE plastic, which is different from Example 4 in that:

[0108] Step S4: No maleimide-functionalized lignin powder was added.

[0109] Comparative Example 4

[0110] A method for preparing a PE plastic, which is different from Example 4 in that:

[0111] Step S4: 6 parts of unmodified alkali lignin, 4 parts of surface modifier 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione, 0.92 parts of furanmethanamine, 10 parts of maleic anhydride grafted polyethylene and 100 parts of PE were added into the open mill, and PE plastic was obtained by blending at a temperature of 135 °C. The mixing speed was 10 rpm, and the blending time was 30 min.

[0112] Performance test

[0113] Test sample preparation method: cut the examples and comparative examples into particles, and place them in a dumbbell-shaped flat template with a thickness of 1 mm, and heat press on a flat press vulcanizer, with a temperature setting of 150 °C and a heat pressing time of 15 minutes. After cooling to room temperature, a 1 mm thick dumbbell-shaped sample was obtained for sample preparation testing.

[0114] Test instrument: tensile testing machine (UTM 6103, 1 kN sensor)

[0115] Test method: test the dumbbell-shaped sample according to the national standard (GB / T 1040.1-2006 / ISO 527-1:1993), and test the tensile strength and breaking elongation of the dumbbell-shaped sample before and after UV treatment using a tensile testing machine (UTM 6103, 1 kN sensor), with a clamp distance setting of 20 mm and a clamp rising rate of 100 mm·min -1 . At least three tests were performed, and the average data of each sample were obtained.

[0116] Tensile strength test: the maximum tensile stress, in MPa, experienced by a test strip until it breaks in a tensile test.

[0117] Elongation at break test: the increase in original gauge length of a test strip at the point of break in a tensile test.

[0118] UV-Vis absorption spectra were obtained from a UV-Vis spectrophotometer (UV2450, Shimadzu, Japan). Wavelength range: 200-800 nm. Experimental material preparation method: 50 x 10 x 4 (mm) test samples were placed in a flat plate curing machine and pressed into a 10 μm thick film at 150 °C and 15 MPa.

[0119] Reproducibility test: after the tensile test was completed, the PE plastic was cut into small pieces and re-pressed into dumbbell-shaped test strips at 150 °C, and a second tensile test was performed; the test strips were repeatedly cut and re-pressed three times, for a total of four tensile tests.

[0120] The results of the elongation at break test and the tensile strength test for the examples and the comparative examples are shown in Table 3 and Table 4 below. Figure 3

[0121] Table 3. Elongation at break and tensile strength of examples and comparative examples

[0122] Sample Elongation at break (%) Tensile strength (MPa) Example 1 1384 19.76 Example 2 1304 17.62 Example 3 1208 16.96 Example 4 1353 21.61 Example 5 1440 18.32 Example 6 1288 19.99 Example 7 1339 18.33 Example 8 1675 22.05 Example 9 1240 13.17 Comparative Example 1 1645 22.00 Comparative Example 2 1358 21.56 Comparative Example 3 1417 16.21 Comparative Example 4 1240 10.31

[0123] As can be seen from Table 3 above, the lignin reversibly crosslinked PE plastic prepared using the preparation method of the present application has an elongation at break of 1240% to 1675%, preferably, the lignin reversibly crosslinked PE plastic has an elongation at break of 1304% to 1675%, and a tensile strength of 17.62 MPa to 22.05 MPa.

[0124] ​From examples 1-6, lignin is a macromolecule with rigid benzene ring, compared with pure PE, adding polar lignin into polyethylene will lead to the mechanical properties of PE plastic to decline. When the content of maleic anhydride grafted polyethylene oligomer is low, the content of DA bond of PE plastic is limited, because the furan functionalized maleic anhydride grafted polyethylene oligomer contains polar functional groups such as furan, the flexibility is far less than PE plastic, the influence of maleic anhydride grafted polyethylene oligomer on the tensile strength of the composite is dominant. Therefore, with the increase of the content of maleic anhydride grafted polyethylene oligomer, the toughness of the plastic matrix becomes poor, and the tensile strength of PE plastic decreases. However, when the content of maleic anhydride grafted polyethylene oligomer is large, the interfacial compatibility between lignin and PE plastic increases with the increase of the content of DA bond, when the influence of this factor is stronger than the influence of maleic anhydride grafted polyethylene oligomer on PE plastic, the influence of DA bond is dominant, therefore, the tensile strength of PE plastic increases with the increase of the content of maleic anhydride grafted polyethylene oligomer. Therefore, the tensile strength of the modified lignin reversibly crosslinked PE plastic decreases first and then increases with the increase of the content of maleic anhydride grafted polyethylene oligomer. Finally, the content of DA bond is saturated, and the tensile strength of the modified lignin PE plastic decreases with the increase of the content of maleic anhydride grafted polyethylene oligomer.

[0125] Examples 7-9 are lignin reversibly crosslinked PE plastics added with polysulphuric acid, lignin is blended with polysulphuric acid, which not only improves the uneven dispersion of lignin in polyethylene, but also forms strong hydrogen bond between lignin and polysulphuric acid, and forms a more compact coordination network structure, so that lignin and PE are better combined. When the mass fraction of maleimide functionalized lignin powder is 10 parts, the mass fraction of furan functionalized maleic anhydride grafted polyethylene oligomer is 10 parts, the mass fraction of polysulphuric acid is 10 parts, and the mass fraction of PE is 100 parts, the tensile strength is increased to 22.05 MPa, and the strain is increased to 1675%.

[0126] Figure 1 is a synthesis flow chart of lignin reversibly crosslinked PE plastic.

[0127] Figure 2 is a schematic diagram of the dumbbell-shaped sample prepared from the PE plastic obtained in the examples and comparative examples of the present application.

[0128] Figure 3 is a stress-strain diagram of the PE plastic obtained in the examples and comparative examples of the present application. Figure 3 It can be seen that the lignin reversibly crosslinked PE plastic provided by the present application has similar mechanical properties to pure PE.

[0129] Figure 4are the stress-strain diagrams of the PE plastics obtained in Example 4 and 8 of the present application and Comparative Examples 1 and 3 before and after UV aging. The degree of decline of the mechanical properties of the modified PE plastics obtained in Example 4 and 8 of the present application after UV light irradiation is reduced, but is still superior to that of Comparative Examples 1 and 3.

[0130] Figure 5 are the UV-vis absorption spectra of the PE plastics obtained in Example 4 and 8 of the present application and Comparative Examples 1 to 3. As can be seen from the figures, Comparative Example 1 and Comparative Example 3 have poor UV resistance because no lignin is added. Example 4 and Comparative Example 2 have similar UV resistance at a wavelength of 200 to 400 nm because the same mass fraction of maleimide functionalized lignin powder is added. The UV transmittance of Example 8 is almost 0.01%. This shows that the lignin reversibly crosslinked PE plastic provided by the present application has excellent UV resistance.

[0131] Figure 6 and Figure 7 are the stress-strain diagrams of the PE plastics obtained in Example 4 and Example 8 of the present application after repeated processing for 4 times. The corresponding elongation at break and tensile strength are shown in Table 4.

[0132] Table 4 Elongation at break and tensile strength of Example 4 and Example 8 after repeated processing for 4 times

[0133]

[0134] From Figure 6 and Table 4, it can be seen that the mechanical properties of Example 4 remain stable after 4 times of processing, the elongation at break is still maintained at more than 1300%, and the tensile strength is still maintained at more than 19 MPa. This shows that Example 4 still maintains good mechanical properties after repeated processing for 4 times. This further shows that the reversibly crosslinked structure based on the DA bond can make the PE plastic maintain good and stable mechanical properties during repeated processing, and also proves that the reversibly crosslinked network can repeatedly occur during the repeated processing of the crosslinked polymer. From Figure 7 and Table 4, it can be seen that the mechanical properties of Example 8 slightly decrease after 4 times of processing, but the elongation at break is maintained at more than 1400%, and the tensile strength is maintained at more than 17 MPa. The decline of the mechanical properties is due to the presence of polysulphoscinic acid in Example 8, which may be partially degraded during repeated processing, and the dispersing effect of polysulphoscinic acid on lignin is weakened, thereby leading to the decline of the mechanical properties of the PE plastic. Comparative Examples 2 and 3 have inferior mechanical properties to Example 4 and Example 8 after repeated processing because no furan functionalized maleic anhydride grafted polyethylene oligomer or maleimide functionalized lignin powder is added. The repeated processing of the remaining examples shows consistent change trends with Example 4 and Example 8, which still maintains good mechanical properties after repeated processing for 4 times.

[0135] Obviously, the above-mentioned embodiments of the present application are only examples for clearly illustrating the present application, but not limitation on the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and also impossible to enumerate all the embodiments. Any modification, equivalent replacement and improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A lignin-reversibly crosslinked PE plastic, characterized in that, The composition includes the following components in parts by weight: 10-12 parts maleimide-functionalized lignin, 10 parts furan-functionalized maleic anhydride-grafted polyethylene oligomer, 100 parts polyethylene, and 10 parts polythiooctanoic acid. The maleimide-functionalized lignin is obtained by reacting alkali lignin with a maleimide compound containing siloxane, wherein the mass ratio of the alkali lignin to the maleimide compound containing siloxane is (1~2):(1~2); the furan-functionalized maleic anhydride-grafted polyethylene oligomer is obtained by reacting maleic anhydride-grafted polyethylene polymer with an amino-containing furan derivative, wherein the mass ratio of the amino-containing furan derivative to the maleic anhydride-grafted polyethylene polymer is (0.8~1.2):

10.

2. The lignin-reversibly crosslinked PE plastic according to claim 1, characterized in that, The mass ratio of the alkali lignin to the maleimide compound containing siloxane is 1.5:

1.

3. The lignin-reversibly crosslinked PE plastic according to claim 1, characterized in that, The maleimide compound containing siloxane is one of 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione, 1-[(3-trimethoxysilyl)propyl]-1H-pyrrole-2,5-dione, 1-[3-(triethoxysilyl)butyl]-1H-pyrrole-2,5-dione, and 1-[3-(triethoxysilyl)undecyl]-1H-pyrrole-2,5-dione.

4. The lignin-reversibly crosslinked PE plastic according to claim 1, characterized in that, The amino-containing furan derivative is one of 2-aminofuran, 2-furanmethylamine, 2-furanethylamine, and 3-(2-furan)-1-propylamine.

5. A method for preparing lignin-reversibly crosslinked PE plastic as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Maleimide-functionalized lignin powder, furan-functionalized maleic anhydride-grafted polyethylene oligomer, polythioctic acid, and polyethylene are blended to obtain the lignin reversible crosslinked PE plastic according to any one of claims 1 to 4.

6. The application of the lignin-reversibly crosslinked PE plastic as described in any one of claims 1 to 4 in the preparation of PE packaging films, PE pipes, modified asphalt, and wires and cables.

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