Lignin reversible cross-linked PE (polyethylene) plastic as well as preparation method and application thereof

Abstract

The invention discloses a lignin reversible cross-linked PE (polyethylene) plastic as well as a preparation method and application thereof, and relates to the field of modified plastics. The lignin reversible cross-linked PE plastic is prepared from the following components in parts by mass: 8 to 12 parts of maleimide functionalized lignin, 2.5 to 15 parts of furan functionalized maleic anhydride grafted polyethylene oligomer and 100 parts of polyethylene. Wherein the maleimide functionalized lignin is obtained through a reaction of alkali lignin and a maleimide compound containing a siloxane group; the furan functionalized maleic anhydride grafted polyethylene oligomer is obtained by reacting a maleic anhydride grafted polyethylene polymer with a furan derivative containing amino groups. By modifying the lignin and introducing a DA bond, the compatibility of the lignin and polyethylene is increased, and reversible crosslinking of the PE plastic is realized, so that the PE plastic has good mechanical properties, ultraviolet resistance and repeatable processability.

Description

Technical Field

[0001] The invention relates to the field of modified plastics, and in particular to a lignin reversibly cross-linked PE plastic and a preparation method and application thereof. Background Art

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

[0003] At present, 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. As a by-product of the papermaking industry, it has the advantages of low cost and large output. However, most plastic polymers belong to non-polar and weakly polar long-chain alkyl polymers. Because of their low surface energy, and the polar groups on the surface of lignin, the two have low compatibility. When direct lignin is applied to plastic polymer systems, the low dispersion of lignin and the low compatibility of components will lead to a decrease in the mechanical properties of the composite material, which is not conducive to practical applications.

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

[0005] CN 117986726 A discloses a lignin composite nano-microsphere modified PE plastic and its preparation method and application. First, lignin and nano-TiO2 are self-assembled to form lignin composite nano-microspheres, and then POE (maleic anhydride grafted ethylene-octene copolymer) is used as a compatibilizer, and polythioic acid is used to regulate the interface properties of different substances in the system, thereby improving the compatibility of nano-TiO2, lignin and PE, and greatly improving the anti-ultraviolet ability of the modified PE plastic. However, the prior art does not focus on the reproducibility of PE plastics. Summary of the invention

[0006] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a lignin reversibly cross-linked PE plastic.

[0007] Another object of the present invention is to provide a method for preparing lignin reversibly cross-linked PE plastic.

[0008] Another object of the present invention is to provide an application of lignin reversibly cross-linked PE plastic.

[0009] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0010] A lignin reversibly cross-linked plastic comprising the following components in parts by weight:

[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 with a maleimide compound containing a siloxane group, and the mass ratio of the alkali lignin to 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 with a furan derivative containing an amino group, and the mass ratio of the furan derivative containing an amino group to the maleic anhydride grafted polyethylene polymer is (0.8-1.2):10.

[0013] The invention introduces DA bonds through maleic anhydride and furan derivatives containing amino groups, thereby realizing reversible cross-linking of PE plastics and improving the compatibility of lignin and PE plastics.

[0014] The present invention adopts the reaction of alkali lignin and maleimide compound containing siloxane group, and introduces maleic anhydride group by modifying lignin, thereby reducing polar groups on the surface of lignin and increasing the compatibility of lignin with polyethylene.

[0015] The invention adopts maleic anhydride grafted polyethylene polymer to react with furan derivatives containing amino groups, grafts the furan derivatives containing amino groups on the maleic anhydride grafted polyethylene polymer, and introduces furan groups. The maleic anhydride grafted polyethylene polymer can be used as a compatibilizer to improve the compatibility between the polar polymer lignin and the non-polar polymer polyethylene, increase the bonding force 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 furan-functionalized maleic anhydride grafted polyethylene oligomer and the carbon-carbon double bond on the molecular structure of maleimide-functionalized lignin undergo DA reaction when heated, thereby improving the compatibility of lignin with PE plastics.

[0017] The present invention introduces maleimide groups on the surface of lignin and grafts amino-containing furan derivatives on maleic anhydride grafted polyethylene polymers, and synthesizes a DA bond polymer matrix with low viscosity characteristics through low molecular weight polymers to increase the compatibility of lignin with the matrix. The DA bond is a regulatable chemical bond. Under high temperature processing conditions, the polymer matrix cross-linked by the DA bond undergoes a retro-DA reaction to dissociate and cross-link, releasing low molecular weight polymers, thereby greatly reducing the melt viscosity, so that the lignin reversibly cross-linked PE plastic still maintains the ability to be injection molded. When the PE plastic is cooled, the cross-linked structure will be formed again, so that the material can be secondary molded. Through the application of the DA bond cross-linked network, the DA bonds in the PE plastic give it excellent recycling and processing capabilities, thereby extending the service life of the PE plastic.

[0018] Through reversible cross-linking technology, polyethylene maintains its thermoplastic properties, allowing the material to be processed and molded multiple times.

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

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

[0021] Specifically, the maleimide compound containing a siloxane group 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] The structural formula of 1-[3-(triethoxysilyl)undecyl]-1H-pyrrole-2,5-dione is:

[0029]

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

[0031] Specifically, the furan derivative containing an amino group is one of 2-aminofuran, 2-furylmethylamine, 2-furylethylamine, and 3-(2-furyl)-1-propylamine.

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

[0033] It should be noted that the maleimide compound containing siloxane groups described in the present invention may include the series of compounds described in patent CN105131027A, and the preparation method thereof may also refer to the patent. In the preparation method disclosed in the patent, the triethoxysilane may be replaced by trimethoxysilane.

[0034] More specifically, the amino group-containing organic silane is one of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 4-aminobutyltriethoxysilane and 11-aminoundecyltriethoxysilane.

[0035] It should be noted that the maleic anhydride of the present invention can also be replaced by 2-methylmaleic anhydride or dimethylmaleic anhydride.

[0036] Maleic anhydride is often used as a raw material for introducing DA bonds. In order to graft maleic anhydride onto lignin, amino-containing organosilanes can be used as coupling agents to assist in grafting maleic anhydride onto lignin. Amino-containing organosilanes can react with both the hydroxyl groups on lignin and 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 Fig. 9 is one example of the synthesis method of the present invention, Figure 8 This is an example of the reaction between alkali lignin and a maleimide compound containing a siloxane group. Fig. 9 This is one example of the reaction of a maleic anhydride grafted polyethylene polymer with an amino group-containing furan derivative.

[0038] In the specific implementation of the present invention, 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 the reaction of maleic anhydride and KH550 can be: dissolving maleic anhydride in solvent A under N2 purging and a temperature of 15 to 45° C., adding KH550 for reaction, adding a catalyst and solvent B after the reaction, adding a desiccant after heating, and obtaining a surface modifier 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione after the reaction.

[0040] It should be noted that the role of N2 purging is to remove water from the air, and the role of the desiccant is to absorb the water produced by the reaction and the water in the air. The purpose is to prevent KH500 from hydrolyzing and polymerizing and ensure that the surface-modified 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione can be grafted onto lignin.

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

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

[0043] More specifically, the reaction time after adding the desiccant is 3 to 5 hours.

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

[0045] After the reaction of maleic anhydride and KH550, the five-membered ring of maleic anhydride will be opened. Zinc chloride is used as a Lewis acid catalyst to achieve the ring-forming reaction.

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

[0047] More specifically, the temperature after heating is 70-90°C.

[0048] Since the boiling point of dichloromethane is 39.6°C and it is easy to vaporize after heating, toluene needs to be added to ensure the reaction.

[0049] More specifically, the desiccant 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 into a solvent for reaction.

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

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

[0053] More specifically, the concentration of the toluene solution of the furan derivative containing an amino group is 0.3 to 0.5 mol / L.

[0054] Specifically, the reaction of maleic anhydride grafted polyethylene polymer and amino-containing furan derivatives 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 reaction temperature during reflux is 75-85°C.

[0057] More specifically, the reflux time is 4 to 6 hours.

[0058] Preferably, the lignin reversibly cross-linked PE plastic further comprises polylipoic acid.

[0059] The addition of polylipoic acid can further improve the UV resistance of PE plastics.

[0060] At the same time, polylipoic acid can also play an interface regulation role, reduce the agglomeration of lignin in polyethylene, increase the dispersion of lignin in polyethylene, and thus improve the mechanical properties of PE plastics.

[0061] More preferably, the lignin reversibly cross-linked PE plastic comprises the following components in parts by mass: 8 to 12 parts of maleimide functionalized lignin, 2.5 to 15 parts of furan functionalized maleic anhydride grafted polyethylene oligomer, 5 to 15 parts of polylipoic acid, and 100 parts of polyethylene.

[0062] More preferably, the lignin reversibly cross-linked PE plastic comprises the following components in parts by mass: 10 parts of maleimide functionalized lignin, 10 parts of furan functionalized maleic anhydride grafted polyethylene oligomer, 5-15 parts of polylipoic acid, and 100 parts of polyethylene.

[0063] More preferably, the lignin reversibly cross-linked PE plastic comprises the following components in parts by mass: 10 parts of maleimide functionalized lignin, 10 parts of furan functionalized maleic anhydride grafted polyethylene oligomer, 10 parts of polylipoic acid, and 100 parts of polyethylene.

[0064] A method for preparing lignin reversibly cross-linked PE plastic comprises the following steps:

[0065] Maleimide functionalized lignin powder, furan functionalized maleic anhydride grafted polyethylene oligomer and polyethylene are blended to obtain lignin reversibly cross-linked PE plastic.

[0066] Specifically, maleimide functionalized lignin powder, furan functionalized maleic anhydride grafted polyethylene oligomer, polylipoic acid and polyethylene are blended to obtain lignin reversibly cross-linked PE plastic added with polylipoic acid.

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

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

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

[0070] More specifically, maleimide functionalized lignin powder and furan functionalized maleic anhydride grafted polyethylene oligomer are first blended, and then polylipoic acid and polyethylene are added and blended again to obtain the polylipoic acid-added lignin reversibly cross-linked PE plastic.

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

[0072] The present invention also protects the use of the above-mentioned lignin reversibly cross-linked PE plastic in the preparation of PE packaging films, PE pipes, modified asphalt, and wires and cables.

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

[0074] (1) By constructing DA bonds to achieve reversible cross-linking of PE plastics, polyethylene maintains its thermoplastic properties, thereby making lignin reversibly cross-linked PE plastics have good reproducibility.

[0075] (2) By modifying lignin and constructing DA bonds, the compatibility of lignin and polyethylene is increased, thereby enhancing the mechanical properties of lignin reversibly cross-linked PE plastics.

[0076] (3) By introducing lignin, the lignin reversibly cross-linked PE plastic has a certain UV resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 This is the synthesis flow chart of lignin reversibly cross-linked PE plastic.

[0078] Figure 2 It is a schematic diagram of dumbbell-shaped splines prepared from PE plastics obtained in the examples and comparative examples.

[0079] Figure 3It is the stress-strain diagram of the PE plastics obtained in Examples 1 to 9 and Comparative Examples 1 to 4.

[0080] Figure 4 It is the stress-strain diagram of the PE plastics obtained in Examples 4 and 8 and Comparative Examples 1 and 3 before and after ultraviolet irradiation.

[0081] Figure 5 It is the UV-vis absorption spectra of the PE plastics obtained in Examples 4 and 8 and Comparative Examples 1 to 3.

[0082] Figure 6 This is the stress-strain diagram of the PE plastic obtained in Example 4 after repeated processing for 4 times.

[0083] Figure 7 This is the stress-strain diagram of the PE plastic obtained in Example 8 after repeated processing for 4 times.

[0084] Figure 8 Schematic diagram of the reaction of step S1 and step S2 in the embodiment.

[0085] Fig. 9 Schematic diagram of the reaction process in step S3 of the embodiment. DETAILED DESCRIPTION

[0086] The present invention is further described below in conjunction with examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples that do not specify specific conditions are usually carried out according to conventional conditions in the art or according to the conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets. Any non-substantial changes and substitutions made by those skilled in the art on the basis of the present invention belong to the scope of protection claimed by the present invention.

[0087] Examples 1 to 6

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

[0089] S1: Under N2 purging, 7.82 g of maleic anhydride was dissolved in 100 mL of dichloromethane at 30 °C, and 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. The mixture was filtered and washed with ethanol solvent. The filtrate was the surface modifier 1-[3-(triethoxysilyl)propyl]-1H-pyrrole-2,5-dione.

[0090] S2: Prepare an acetic acid aqueous solution with a pH of 3, mix it with acetone at a mass ratio of 1:7 to obtain a solvent that can dissolve lignin and a surface modifier, add alkali lignin and a surface modifier to the solvent at a mass ratio of 1.5:1, stir at 50°C for 1 hour, completely hydrolyze the surface modifier, and mix it evenly with the lignin. Cool down to generate a precipitate, let it stand for 2 hours to enrich the solid, remove the supernatant, wash the precipitate repeatedly with ethanol several times, and vacuum dry to obtain maleimide functionalized lignin powder.

[0091] S3: Add 2 g of maleic anhydride grafted polyethylene polymer (grafting rate 1%) to 50 mL of toluene, heat under reflux at 80°C with stirring until the polymer is completely dissolved, add 5 mL of 2-furanmethylamine (furfurylamine) toluene solution (concentration 0.4 mol / L), reflux at 80°C for 5 hours, then cool to room temperature, and then add a large amount of methanol, collect the product, wash, and dry to obtain furan functionalized maleic anhydride grafted polyethylene polymer (the mass ratio of 2-furanmethylamine to maleic anhydride grafted polyethylene polymer is 0.97:10).

[0092] S4: Add maleimide functionalized lignin and furan functionalized maleic anhydride grafted polyethylene oligomer into an open mill and blend for 10 minutes. The mixing speed is 10 rpm and the reaction temperature is 135°C. After the mixture is evenly mixed, polyethylene (PE) is added and blending is continued for 15 minutes at the same reaction temperature. The lignin reversibly cross-linked PE plastic is obtained after the mixture is taken out.

[0093] Table 1. Mass fractions of each component in step S4 in preparing lignin reversibly cross-linked PE plastics in Examples 1 to 6

[0094]

[0095] Embodiments 7 to 9

[0096] A method for preparing lignin reversibly cross-linked PE plastic, which is different from Example 4 in that:

[0097] When polyethylene is added in step S4, polylipoic acid is added and blended simultaneously.

[0098] Table 2. Mass fractions of each component in step S4 in preparing lignin reversibly cross-linked PE plastics in Examples 7 to 9

[0099]

[0100] Comparative Example 1

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

[0102] In step S4, only polyethylene (PE) is added, and the mixture is blended at a temperature of 135° C. for 15 min at a rotation speed of 10 rpm to obtain PE plastic.

[0103] Comparative Example 2

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

[0105] In step S4, no furan functionalized maleic anhydride grafted polyethylene oligomer is added.

[0106] Comparative Example 3

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

[0108] No maleimide functionalized lignin powder is added in step S4.

[0109] Comparative Example 4

[0110] A method for preparing 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 furan methylamine, 10 parts of maleic anhydride grafted polyethylene and 100 parts of PE were added into an open mill according to the above mass parts, and blended at a temperature of 135° C. to obtain PE plastic. The mixing speed was 10 rpm and the blending time was 30 minutes.

[0112] Performance Testing

[0113] Test sample preparation method: The examples and comparative examples were cut into particles, placed in a dumbbell-shaped flat plate template with a thickness of 1 mm, and hot pressed on a flat plate vulcanizer. The temperature was set to 150°C and the hot pressing time was 15 minutes. After cooling to room temperature, 1 mm thick dumbbell-shaped specimens were obtained for sample preparation and testing.

[0114] Testing equipment: Tensile testing machine (UTM 6103, 1kN sensor)

[0115] Test method: The dumbbell-shaped specimens were tested according to the national standard (GB / T 1040.1-2006 / ISO 527-1:1993). The tensile strength and elongation at break of the dumbbell-shaped specimens before and after UV treatment were tested using a tensile testing machine (UTM 6103, 1kN sensor). The distance between the clamps was set to 20mm, and the rising rate of the clamps was 100mm min. -1 . The tests were performed at least three times, and the average data for each sample were obtained.

[0116] Tensile strength test: In the tensile test, the maximum tensile stress to which the specimen is subjected until it breaks, measured in MPa.

[0117] Elongation at Break Test: In a tensile test, the increase in the original gauge length of a specimen strip when it breaks.

[0118] The UV-visible absorption spectrum was obtained by a UV-visible spectrophotometer (UV2450, Shimadzu, Japan). Wavelength range: 200-800 nm. Experimental material preparation method: A 50×10×4 (mm) sample was placed in a flat vulcanizer and rolled into a film with a thickness of 10 μm at 150°C and 15 MPa.

[0119] Repeatability test: After completing the tensile test, the PE plastic was cut into small pieces and re-hot-pressed into dumbbell-shaped specimens at 150°C for a second tensile test; the specimens were cut and hot-pressed three times, for a total of four tensile tests.

[0120] The results of the elongation at break test and tensile strength test of the embodiments and comparative examples are shown in Table 3 and Figure 3 As shown:

[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] It can be seen from Table 3 above that the elongation at break of the lignin reversibly cross-linked PE plastic prepared by the preparation method of the present invention can reach 1240% to 1675%. Preferably, the elongation at break of the lignin reversibly cross-linked PE plastic can reach 1304% to 1675%, and the tensile strength can reach 17.62 MPa to 22.05 MPa.

[0124] As can be seen from Examples 1 to 6, lignin is a macromolecule with a rigid benzene ring. Compared with pure PE, adding polar lignin to polyethylene will cause the mechanical properties of PE plastics to decrease. When the content of maleic anhydride grafted polyethylene oligomer is low, the DA bond content of PE plastics is limited. Since furan functionalized maleic anhydride grafted polyethylene oligomers contain polar functional groups such as furan, the flexibility is far less than that of PE plastics. The influence of maleic anhydride grafted polyethylene oligomers on the tensile strength of the composite material is dominant. Therefore, with the increase of the content of maleic anhydride grafted polyethylene oligomers, the toughness of the plastic matrix deteriorates and the tensile strength of PE plastics decreases. However, when the content of maleic anhydride grafted polyethylene oligomers is large, the interfacial compatibility of lignin and PE plastics increases with the increase of DA bond content. When this influencing factor is stronger than the influence of maleic anhydride grafted polyethylene oligomers on PE plastics, the DA bond influence occupies a dominant position, so the tensile strength of PE plastics increases with the increase of maleic anhydride grafted polyethylene oligomer content. Therefore, the tensile strength of the modified lignin reversibly cross-linked PE plastic first decreases and then increases with the increase of the content of maleic anhydride grafted polyethylene oligomers. Finally, the DA bond content is saturated, and the tensile strength of the modified lignin PE plastic decreases with the increase of the content of maleic anhydride grafted polyethylene oligomers.

[0125] Embodiments 7 to 9 are lignin reversibly cross-linked PE plastics with added polylipoic acid. The blending of lignin and polylipoic acid not only improves the disadvantage of uneven dispersion of lignin in polyethylene, but also forms a strong hydrogen bond with lignin to form a tighter 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 polylipoic acid is 10 parts, and the mass fraction of PE is 100 parts, the tensile strength is increased to 22.05MPa, and the strain is increased to 1675%.

[0126] Figure 1 This is the synthesis flow chart of lignin reversibly cross-linked PE plastic.

[0127] Figure 2 It is a schematic diagram of dumbbell-shaped splines prepared from PE plastics obtained in the embodiments of the present invention and the comparative examples.

[0128] Figure 3 : is the stress-strain diagram of the PE plastic obtained in the embodiment of the present invention and the comparative example. Figure 3 It can be seen that the lignin reversibly cross-linked PE plastic provided by the present invention has mechanical properties similar to those of pure PE.

[0129] Figure 4The stress-strain diagrams of the PE plastics obtained in Examples 4 and 8 of the present invention and Comparative Examples 1 and 3 before and after UV aging are shown in FIG. The degree of mechanical property degradation of the modified PE plastics obtained in Examples 4 and 8 of the present invention after UV irradiation is reduced, but is still better than Comparative Examples 1 and 3.

[0130] Figure 5 The UV-vis absorption spectra of the PE plastics obtained in Examples 4 and 8 of the present invention and Comparative Examples 1 to 3 are shown in the figure. As shown in the figure, since Comparative Examples 1 and 3 do not add lignin, their anti-ultraviolet performance is poor. However, since Example 4 and Comparative Example 2 add the same mass fraction of maleimide functionalized lignin powder, their anti-ultraviolet performance is similar when the wavelength is 200 to 400nm. The ultraviolet transmittance of Example 8 almost reaches 0.01%. This shows that the lignin reversibly cross-linked PE plastic provided by the present invention has excellent anti-ultraviolet performance.

[0131] Figure 6 and Figure 7 The stress-strain diagrams of the PE plastics obtained in Example 4 and Example 8 of the present invention after repeated processing for 4 times are shown in Table 4. 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 4-times of repeated processing

[0133]

[0134] Depend on Figure 6 As shown in Table 4, after 4 processings, the mechanical properties of Example 4 remain stable, the elongation at break remains above 1300%, and the tensile strength remains above 19MPa. This shows that after 4 repeated processings, Example 4 still maintains good mechanical properties. This further illustrates that the reversible cross-linking structure based on DA bonds can enable PE plastics to maintain good and stable mechanical properties during repeated processing, and also proves that the reversible cross-linking network can occur repeatedly during repeated processing of cross-linked polymers. Figure 7 As shown in Table 4, after 4 processing, the mechanical properties of Example 8 slightly decreased, but its elongation at break remained above 1400%, and its tensile strength remained above 17MPa. The decrease in mechanical properties is due to the presence of polylipoic acid in Example 8. During repeated processing, part of the polylipoic acid may be degraded, and the dispersibility of polylipoic acid on lignin is weakened, which leads to the decrease in the mechanical properties of PE plastic. Since no furan-functionalized maleic anhydride-grafted polyethylene oligomer or maleimide-functionalized lignin powder was added to Comparative Examples 2 and 3, after repeated processing, its mechanical properties were inferior to those of Examples 4 and 8. The repeated processing performance of the remaining examples showed a consistent change trend with that of Examples 4 and 8, reflecting that after repeated processing 4 times, good mechanical properties were still maintained.

[0135] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A lignin reversibly cross-linked PE plastic, characterized in that: The invention comprises the following components in parts by weight: 8 to 12 parts of maleimide functionalized lignin, 2.5 to 15 parts of furan functionalized maleic anhydride grafted polyethylene oligomer, and 100 parts of polyethylene; The maleimide functionalized lignin is obtained by reacting alkali lignin with a maleimide compound containing a siloxane group, and the mass ratio of the alkali lignin to 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 with a furan derivative containing an amino group, and the mass ratio of the furan derivative containing an amino group to the maleic anhydride grafted polyethylene polymer is (0.8-1.2):

10.

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

1.

3. The lignin reversibly cross-linked PE plastic according to claim 1, characterized in that: The maleimide compound containing a siloxane group 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 cross-linked PE plastic according to claim 1, characterized in that: The furan derivative containing an amino group is one of 2-aminofuran, 2-furylmethylamine, 2-furylethylamine and 3-(2-furyl)-1-propylamine.

5. The lignin reversibly cross-linked PE plastic according to claim 1, characterized in that: The lignin reversibly cross-linked PE plastic also includes polylipoic acid.

6. The lignin reversibly cross-linked PE plastic according to claim 5, characterized in that: The invention comprises the following components in parts by weight: 8-12 parts of maleimide functionalized lignin, 2.5-15 parts of furan functionalized maleic anhydride grafted polyethylene oligomer, 5-15 parts of polylipoic acid and 100 parts of polyethylene.

7. The lignin reversibly cross-linked PE plastic according to claim 6, characterized in that: The invention comprises the following components in parts by weight: 10 parts of maleimide functionalized lignin, 10 parts of furan functionalized maleic anhydride grafted polyethylene oligomer, 5-15 parts of polylipoic acid and 100 parts of polyethylene.

8. A method for preparing a lignin reversibly cross-linked PE plastic according to any one of claims 1 to 7, characterized in that: The steps include: The maleimide functionalized lignin powder, furan functionalized maleic anhydride grafted polyethylene oligomer and polyethylene are blended to obtain the lignin reversibly cross-linked PE plastic according to any one of claims 1 to 4.

9. The method for preparing lignin reversibly cross-linked PE plastic according to claim 8, characterized in that: The steps include: Maleimide functionalized lignin powder, furan functionalized maleic anhydride grafted polyethylene oligomer, polylipoic acid and polyethylene are blended to obtain the lignin reversibly cross-linked PE plastic according to any one of claims 5 to 7.

10. Use of the lignin reversibly cross-linked PE plastic according to any one of claims 1 to 7 in the preparation of PE packaging films, PE pipes, modified asphalt, and wires and cables.

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