Green and efficient method for improving miscibility of lignin and PBAT and application

Abstract

The invention belongs to the technical field of composite material preparation, and discloses a green and efficient method for improving miscibility of lignin and PBAT, industrial lignin and an alcohol-based DES solvent are mixed and then subjected to low-temperature heat treatment, DES lignin is obtained after treatment, and the DES lignin and PBAT are subjected to melt blending to prepare a composite material; the composite material is prepared from the following components in parts by weight: 60-90 parts of PBAT and 10-40 parts of DES lignin, and the total part by weight of the DES lignin and PBAT is 100 parts. According to the method, the lignin with specific components is extracted from the industrial lignin by adopting a green and environment-friendly solvent, and the lignin components and the PBAT are subjected to melt blending, so that the miscibility of the industrial lignin and the PBAT is effectively enhanced by adopting a green and environment-friendly reagent, a solubilizer and an auxiliary agent do not need to be added, and the cost is reduced. The obtained lignin / PBAT composite material has higher mechanical strength than the original industrial lignin composite material.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material preparation, and in particular, to a green and efficient method and application for improving the miscibility of lignin and PBAT. Background Art

[0002] In recent years, the large-scale use of disposable plastic products has led to the large-scale accumulation of non-degradable plastics in the natural environment, causing serious environmental pollution problems. With people's yearning for a better life and the enhancement of environmental protection awareness, many biodegradable plastic products have increasingly attracted the attention of the industry and the country. Among them, poly(butylene adipate-co-terephthalate) (PBAT) has gradually become an important substitute for non-degradable plastics in fields such as packaging and agricultural production due to its excellent elongation at break, good flexibility, and mechanical properties. However, the high production cost, poor light stability, and single performance of PBAT limit its practical applications. Therefore, it is of great practical significance to improve the performance of PBAT composites and reduce their costs for high-value utilization. Lignin is a natural polymer that is abundant, inexpensive, and biodegradable in nature. It has various functional properties and thermoplasticity and can be compounded with the biodegradable plastic PBAT to prepare bio-based environmental protection composites. However, industrial lignin has a complex structure, resulting in poor melt miscibility when blended with PBAT, leading to poor interfacial compatibility of the materials, which is not conducive to the development of high-performance composites. Therefore, separating lignin components with a uniform structure from industrial lignin for the preparation of high-performance lignin / PBAT composites is the key and important prerequisite for lignin utilization and the preparation of functional environmental protection composites.

[0003] Deep eutectic solvents (DES) are green and low-cost composite solvents formed by combining two or more hydrogen bond donors (HBD) and hydrogen bond acceptors (HBA) to form a transparent solvent, usually liquid at room temperature. A large number of studies have confirmed that DES has excellent solubility for lignin and can selectively dissolve lignin components in biomass raw materials. For industrial lignin components, the component differences of DES solvents and functional groups such as phenolic hydroxyl groups, aliphatic hydroxyl groups, and carboxyl groups contained in the lignin molecular structure can be used to carry out solvothermal reactions in the molten state, while realizing the modification of lignin molecules, improving the interfacial interaction between lignin and polymer materials, and being conducive to improving the miscibility and compatibility of lignin and PBAT.

[0004] In addition, in the prior art, the preparation of lignin / PBAT composites usually requires complex chemical modification of lignin, with a cumbersome process flow, and may also use toxic organic solvents; the preparation of composites from some organic solvent-fractionated lignin has high costs and a long cycle, and additives such as plasticizers, toughening agents, coupling agents, or chain extenders need to be added to the composites; the lignin addition amount in the composite membrane material is low, and its mechanical strength is difficult to meet the national standard.

[0005] Based on the above research, the present invention uses an alcohol-based DES to treat industrial lignin, and then melt-blends the treated lignin with PBAT. This method significantly enhances the miscibility of industrial lignin and PBAT. The miscibility and compatibility of the treated lignin and PBAT are significantly improved, and the agglomeration of lignin in the matrix is significantly reduced during blending. Further hot pressing can obtain a lignin / PBAT composite membrane material with good mechanical properties, which is suitable for application scenarios such as packaging bags, garbage bags, and mulch films.

[0006] Through retrieval, the following two patent disclosure documents related to the present invention patent application were found:

[0007] 1. A composite material based on in-situ lignin regeneration, its preparation method and application (CN 116554576B). Before the co-melting of corn straw and polyethylene, choline chloride / oxalic acid dihydrate DES is used to pretreat corn straw to dissolve lignin, remove hemicellulose, and regenerate hydrophobic lignin on the surface of cellulose by adding water and stirring, thereby preparing a strong and tough wood-plastic composite material, which can be widely used in structural and load-bearing materials. The formula used is regenerated corn straw and high-density polyethylene, where the lignin-regenerated corn straw is obtained by treating corn straw with DES and is applied in structural and load-bearing materials. It is significantly different from the method and idea of using lignin to prepare composites in this patent.

[0008] 2. A lignin-modified PBAT biodegradable plastic and its preparation method (CN 113637295A). Lignin is dispersed in choline chloride and lactic acid DES for treatment. After solid-liquid separation, the dried lignin is dispersed again in the eutectic waste liquid, and lipase and adipic acid are added for reaction. A polyethylene glycol diglycidyl ether-ethyl acetate solution is added and stirred evenly, and an aqueous sodium hydroxide solution is added dropwise for reaction. PBAT, the lignin mixture, and corn starch are sequentially added to a high-speed mixer for homogenization, kneaded in a kneader, granulated, and injection molded. However, in this treatment method, the lignin modification process is complex, there are many reaction reagents, and the reaction time is long; environmentally unfriendly and expensive organic solvents are used, which does not conform to the principle of green environmental protection.

[0009] By comparison, the present invention patent application is essentially different from the above patent disclosure documents. Summary of the Invention

[0010] The object of the present invention is to overcome the deficiencies in the prior art and provide a green and efficient method and application for improving the miscibility of lignin and PBAT.

[0011] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0012] A green and efficient method for improving the miscibility of lignin and PBAT, which mixes industrial lignin with an alcohol-based DES solvent and then performs low-temperature heat treatment. After treatment, DES lignin is obtained, and it is melt-blended with PBAT to prepare a composite material;

[0013] Among them, by weight, the composite material is prepared from 60-90 parts by weight of PBAT and 10-40 parts by weight of DES lignin, and the total weight of DES lignin and PBAT is 100 parts by weight.

[0014] Furthermore, the tensile strength of the composite material is in the range of 12.20-23.21 MPa, and its elongation at break is in the range of 309.65-849.36%.

[0015] Furthermore, the DES lignin is obtained by subjecting industrial lignin to heat treatment, solid-liquid separation, rotary evaporation and acid precipitation with an alcohol-based DES solvent.

[0016] Furthermore, the specific preparation steps of the DES lignin are as follows:

[0017] 1) Mix a hydrogen bond acceptor and a hydrogen bond donor in a molar ratio of 1:1-5 and stir in a constant temperature water bath. The temperature of the constant temperature water bath is 80-100 °C to prepare a uniform and transparent alcohol-based DES. This alcohol-based DES is a neutral solvent, a non-acidic or non-basic system;

[0018] 2) Mix industrial lignin with the DES obtained in step 1). The mass ratio of industrial lignin to DES is 1:5-10, stir and react in a constant temperature oil bath. The temperature of the oil bath is 80-140 °C, and the reaction time is 1.5-3.0 h;

[0019] 3) Add the reaction mixture obtained in step 2) to a 50% acetone solution by volume, mix and centrifuge for solid-liquid separation. The supernatant is concentrated by rotary evaporation and then dropped into a hydrochloric acid solution with a pH value of 2-4 to precipitate lignin. The lignin is washed and freeze-dried to obtain DES lignin.

[0020] Furthermore, in step 1), the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is any one of ethylene glycol, propylene glycol, glycerol, 1,4-butanediol, and pentanediol.

[0021] Further, in step 2), the industrial lignin is at least one of alkali lignin, kraft lignin, enzymatic hydrolysis residue lignin, and pre-hydrolysis lignin.

[0022] Further, in this method, DES lignin and PBAT are directly melt-mixed without adding any plasticizers and plasticating agents, and the prepared composite material is hot-pressed to obtain a composite film material with significantly improved miscibility.

[0023] Further, during the melt mixing, at least one of an extruder and an open mill is used;

[0024] During the melt mixing, the mixing temperature is 145 - 155 °C, and the mixing time is 15 - 45 min; the hot pressing temperature is 145 - 160 °C, the hot pressing time is 30 - 50 min, the pressure is 6 - 15 T, and the running time is 1 - 5 min.

[0025] Application of the composite material prepared by the method as described above in the preparation of packaging bags, garbage bags, and mulch films.

[0026] The advantages and positive effects achieved by the present invention are as follows:

[0027] 1. The technical problem to be solved by the present invention is to extract a specific component lignin from industrial lignin using a green and environmentally friendly solvent and melt-blend the lignin component with PBAT. This method effectively enhances the miscibility of industrial lignin and PBAT using green and environmentally friendly reagents, without the need to add solubilizers and additives, and the obtained lignin / PBAT composite material has higher mechanical strength than the original industrial lignin composite material.

[0028] 2. The solvent used in the present invention can be recycled, reducing the cost of lignin separation, and the treatment conditions are mild, improving the homogeneity of the obtained lignin component and weakening the agglomeration behavior in the plastic matrix. There is better melt miscibility and compatibility between the lignin and PBAT obtained by this method. By controlling the treatment conditions of lignin, the properties of the lignin / PBAT composite material can be regulated to prepare environmentally friendly composite materials with excellent properties.

[0029] 3. The lignin / PBAT composite film material prepared by the present invention has significant market competitiveness. When the content of the separated lignin is greater than 30 wt.%, the composite material system still has good miscibility. The excellent tensile properties and significantly improved hydrophobicity of the composite material make it suitable for functional packaging, mulch films, etc. This method can significantly promote the directional high-value utilization of industrial lignin, and at the same time, the process is simple and green and environmentally friendly, which is of great significance for the large-scale efficient preparation of environmentally friendly composite materials from industrial lignin.

[0030] 4. The method of the present invention has a high extraction efficiency. The processing time can be as low as 0.5 hours, the lignin component obtained by separation reaches 60-90%, and the purity is above 95%. In the prior art, the time for extracting DES lignin is at least 1 hour, and the lignin yield is between 40-60%. Therefore, the method of the present invention has significant advantages. Description of the Drawings

[0031] Figure 1 It is the effect diagram of melt blending of lignin separated by alcohol-based DES treatment in the present invention and PBAT. Detailed Embodiments

[0032] The following further illustrates the present invention in conjunction with embodiments. The following embodiments are narrative and not restrictive, and the protection scope of the present invention cannot be limited by the following embodiments.

[0033] All kinds of experimental operations involved in the specific embodiments are conventional techniques in the art. For the parts not specifically annotated in this article, those of ordinary skill in the art can refer to various common reference books, scientific and technological literatures, or relevant specifications, manuals, etc. before the application date of the present invention for implementation.

[0034] A green and efficient method for improving the miscibility of lignin and PBAT. In this method, industrial lignin is mixed with an alcohol-based DES solvent and then subjected to low-temperature heat treatment. After treatment, DES lignin is obtained, and it is melt-blended with PBAT to prepare a composite material;

[0035] Among them, by weight, the composite material is prepared from 60-90 parts by weight of PBAT and 10-40 parts by weight of DES lignin, and the total weight of DES lignin and PBAT is 100 parts by weight.

[0036] Preferably, the tensile strength of the composite material is in the range of 12.20-23.21 MPa, and its elongation at break is in the range of 309.65-849.36%.

[0037] Preferably, the DES lignin is obtained by subjecting industrial lignin to heat treatment, solid-liquid separation, and rotary evaporation and acid precipitation with an alcohol-based DES solvent.

[0038] Preferably, the specific preparation steps of the DES lignin are as follows:

[0039] 1) Mix a hydrogen bond acceptor and a hydrogen bond donor in a molar ratio of 1:1-5 and stir in a constant temperature water bath. The temperature of the constant temperature water bath is 80-100 °C to prepare a uniform and transparent alcohol-based DES. This alcohol-based DES is a neutral solvent, a non-acidic or non-basic system;

[0040] 2) Mix the industrial lignin with the DES obtained in step 1), with the mass ratio of industrial lignin to DES being 1:5 - 10, stir and react in a constant-temperature oil bath, the oil bath temperature is 80 - 140 °C, and the reaction time is 1.5 - 3.0 h;

[0041] 3) Add the reaction mixture obtained in step 2) to a 50% (v / v) acetone solution, mix and then centrifuge for solid-liquid separation. The supernatant is concentrated by rotary evaporation and then dropped into a hydrochloric acid solution with a pH value of 2 - 4 to precipitate lignin. The lignin is washed and freeze-dried to obtain DES lignin.

[0042] Preferably, in step 1), the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is any one of ethylene glycol, propylene glycol, glycerol, 1,4-butanediol, and pentanediol.

[0043] Preferably, in step 2), the industrial lignin is at least one of alkali lignin, kraft lignin, enzymatic hydrolysis residue lignin, and pre-hydrolyzed lignin.

[0044] Preferably, in the method, the DES lignin and PBAT are directly melt-kneaded without adding any plasticizers and plasticizing agents, and the prepared composite material is hot-pressed to obtain a composite film material with significantly improved miscibility.

[0045] Preferably, during the melt-kneading, at least one of an extruder and an open mill is used;

[0046] During the melt-kneading, the kneading temperature is 145 - 155 °C, and the kneading time is 15 - 45 min; the hot-pressing temperature is 145 - 160 °C, the hot-pressing time is 30 - 50 min, the pressure is 6 - 15 T, and the running time is 1 - 5 min.

[0047] Application of the composite material prepared by the method as described above in the preparation of packaging bags, garbage bags, and mulch films.

[0048] Specifically, the relevant preparation and detection are as follows:

[0049] Example 1:

[0050] A green and efficient method for improving the miscibility of lignin and PBAT, in which industrial lignin is mixed with alcohol-based DES and then heat-treated at low temperature. After treatment, DES lignin and PBAT are melt-blended to prepare a composite material; the composite material is prepared from 10% DES lignin and 90% PBAT by mass percentage. For example:

[0051] (1) 10 parts by weight of DES lignin

[0052] (2) 90 parts by weight of poly(butylene adipate-co-terephthalate) (PBAT)

[0053] The above-mentioned green and efficient method for improving the miscibility of lignin and PBAT includes the following steps:

[0054] 1) Prepare an industrial lignin sample treated with alcohol-based DES

[0055] Mix choline chloride and ethylene glycol in a molar ratio of 1:4, and then place them in an 80 °C water bath and stir for 30 min to obtain a DES solvent. Mix kraft lignin and the prepared DES solvent evenly at a mass ratio of 1:8, place them in a constant-temperature oil bath at 110 °C and stir for 1.5 - 3.0 h; after the reaction is completed, cool the mixture to room temperature, add an acetone solution with a volume concentration of 50% and mix evenly. After centrifugal solid-liquid separation, the supernatant is rotary evaporated and concentrated, and then dropped into a hydrochloric acid solution with a pH value of 2 - 4 to precipitate lignin. The precipitated lignin is washed and freeze-dried to obtain DES lignin.

[0056] 2) Take 10 parts by weight of DES lignin and 90 parts by weight of PBAT particles and melt-blend them through a two-roll mill to obtain a composite masterbatch. The processing parameters of the two-roll mill are as follows: the heating temperature is set at 145 - 160 °C, the roller speed is set at 10 - 20 r / min, and the mixing time is set at 15 - 45 min.

[0057] 3) Hot-press the composite material particles into a film in a flat vulcanizing machine to obtain a lignin / PBAT composite film material. The processing parameters of the flat vulcanizing machine are as follows: the heating temperature is set at 145 - 160 °C, the pressure is set at 6 - 15 T, the preheating time is set at 30 - 50 min, and the running time is set at 1 - 5 min.

[0058] The results of the tensile strength and elongation at break of the DES lignin / PBAT composite film material in this example are shown in Table 1.

[0059] Example 2:

[0060] A green and efficient method for improving the miscibility of lignin and PBAT, in which industrial lignin is mixed with alcohol-based DES and then heat-treated at low temperature. After treatment, DES lignin and PBAT are melt-blended to prepare a composite material; the composite film material is prepared from 20% DES lignin and 80% PBAT by mass percentage. For example:

[0061] (1) DES lignin 20 parts by weight

[0062] (2) Poly(butylene adipate-co-terephthalate) (PBAT) 80 parts by weight

[0063] The above-mentioned green and efficient method for improving the miscibility of lignin and PBAT includes the following steps:

[0064] Step 1) is the same as in Example 1.

[0065] Step 2) is the same as Example 1, where the mass ratio of DES lignin to PBAT particles is 20:80, that is, 20 parts by weight of DES lignin and 80 parts by weight of PBAT particles are added.

[0066] Step 3) is the same as Example 1.

[0067] The results of the tensile strength and elongation at break of the DES lignin / PBAT composite film material of this example are shown in Table 1.

[0068] Example 3:

[0069] A green and efficient method for improving the miscibility of lignin and PBAT, in which industrial lignin is mixed with alcohol-based DES and then heat-treated at low temperature. After treatment, DES lignin and PBAT are melt-blended to prepare a composite material; the composite film material is prepared from 30% DES lignin and 70% PBAT by mass percentage. For example:

[0070] (1) 30 parts by weight of DES lignin

[0071] (2) Poly(butylene adipate-co-terephthalate) (PBAT) 70 parts by weight

[0072] The above green and efficient method for improving the miscibility of lignin and PBAT includes the following steps:

[0073] Step 1) is the same as Example 1.

[0074] Step 2) is the same as Example 1, where the mass ratio of DES lignin to PBAT particles is 30:70, that is, 30 parts by weight of DES lignin and 70 parts by weight of PBAT particles are added.

[0075] Step 3) is the same as Example 1.

[0076] The results of the tensile strength and elongation at break of the DES lignin / PBAT composite film material of this example are shown in Table 1.

[0077] Example 4:

[0078] A green and efficient method for improving the miscibility of lignin and PBAT, in which industrial lignin is mixed with alcohol-based DES and then heat-treated at low temperature. After treatment, DES lignin and PBAT are melt-blended to prepare a composite material; the composite film material is prepared from 10% DES lignin and 90% PBAT by mass percentage. For example:

[0079] (1) 10 parts by weight of DES lignin

[0080] (2) 90 parts by weight of poly(butylene adipate-co-terephthalate) (PBAT)

[0081] The above-mentioned green and efficient method for improving the miscibility of lignin and PBAT includes the following steps:

[0082] Step 1) The same as Example 1, in which sulfate lignin and the prepared alcohol-based DES are mixed evenly at a mass ratio of 1:4, and placed in a constant-temperature oil bath at 140 °C and stirred for 1.5 - 3.5 h.

[0083] Step 2) The same as Example 1.

[0084] Step 3) The same as Example 1.

[0085] The results of the tensile strength and elongation at break of the DES lignin / PBAT composite film material in this example are shown in Table 1.

[0086] Example 5:

[0087] A green and efficient method for improving the miscibility of lignin and PBAT, in which industrial lignin is mixed with alcohol-based DES and then heat-treated at low temperature. After treatment, DES lignin and PBAT are melt-blended to prepare a composite material; the composite film material is prepared from 20% DES lignin and 80% PBAT by mass percentage. For example:

[0088] (1) 20 parts by weight of DES lignin

[0089] (2) 80 parts by weight of poly(butylene adipate-co-terephthalate) (PBAT)

[0090] The above-mentioned green and efficient method for improving the miscibility of lignin and PBAT includes the following steps:

[0091] Step 1) The same as Example 4.

[0092] Step 2) The same as Example 2.

[0093] Step 3) The same as Example 1.

[0094] The results of the tensile strength and elongation at break of the DES lignin / PBAT composite film material in this example are shown in Table 1.

[0095] Example 6:

[0096] A green and efficient method for improving the miscibility of lignin and PBAT, in which industrial lignin is mixed with alcohol-based DES and then heat-treated at low temperature. After treatment, DES lignin and PBAT are melt-blended to prepare a composite material; the composite film material is prepared from 30% DES lignin and 70% PBAT by mass percentage. For example:

[0097] (1) DES lignin 30 parts by weight

[0098] (2) Polybutylene adipate terephthalate (PBAT) 70 parts by weight

[0099] The above green and efficient method for improving the miscibility of lignin and PBAT includes the following steps:

[0100] Step 1) is the same as Example 4.

[0101] Step 2) is the same as Example 3.

[0102] Step 3) is the same as Example 1.

[0103] The results of the tensile strength and elongation at break of the DES lignin / PBAT composite film material of this example are shown in Table 1.

[0104] Example 7:

[0105] A green and efficient method for improving the miscibility of lignin and PBAT, in which industrial lignin is mixed with alcohol-based DES and then heat-treated at low temperature. After treatment, DES lignin and PBAT are melt-blended to prepare a composite material; the composite film material is prepared from 40% DES lignin and 60% PBAT by mass percentage. For example:

[0106] (1) DES lignin 40 parts by weight

[0107] (2) Polybutylene adipate terephthalate (PBAT) 60 parts by weight

[0108] The above green and efficient method for improving the miscibility of lignin and PBAT includes the following steps:

[0109] Step 1) is the same as Example 4.

[0110] Step 2) is the same as Example 1, where the mass ratio of DES lignin to PBAT particles is 40:60, that is, 40 parts by weight of DES lignin and 60 parts by weight of PBAT particles are added.

[0111] Step 3) is the same as Example 1.

[0112] The results of the tensile strength and elongation at break of the DES lignin / PBAT composite film material of this example are shown in Table 1.

[0113] Comparative Example 1:

[0114] A lignin / PBAT composite film material, the composite film material is prepared from 90% PBAT and 10% kraft lignin by mass percentage. For example:

[0115] (1) Kraft lignin (KL) 10 parts by weight

[0116] (2) Poly(butylene adipate-co-terephthalate) (PBAT) 90 parts by weight

[0117] The preparation method of the above composite film material includes the following steps:

[0118] 1) Take 10 parts by weight of dried kraft lignin and 90 parts by weight of PBAT particles and blend them through a two-roll mill to obtain composite material particles. The processing parameters of the two-roll mill are as follows: the heating temperature is set at 145 - 160 °C, the roller speed is set at 10 - 20 r / min, and the mixing time is set at 15 - 45 min.

[0119] 2) Hot press the composite material particles into a film in a flat vulcanizing machine to obtain a lignin / PBAT composite film material. The processing parameters of the flat vulcanizing machine are as follows: the heating temperature is set at 145 - 160 °C, the pressure is set at 6 - 15 T, the preheating time is set at 30 - 50 min, and the running time is set at 1 - 5 min.

[0120] The results of the tensile strength and elongation at break of the dried kraft lignin / PBAT composite film material of this comparative example are shown in Table 1.

[0121] Comparative Example 2:

[0122] A lignin / PBAT composite film material, calculated by mass percentage, is prepared from 80% of PBAT and 20% of kraft lignin. For example:

[0123] (1) Kraft lignin (KL) 20 parts by weight

[0124] (2) Poly(butylene adipate-co-terephthalate) (PBAT) 80 parts by weight

[0125] The preparation method of the above composite film material includes the following steps:

[0126] Step 1) is the same as that of Comparative Example 1, where the mass ratio of dried kraft lignin to PBAT particles is 20:80, that is, 20 parts by weight of dried kraft lignin and 80 parts by weight of PBAT particles are added.

[0127] Step 2) is the same as that of Comparative Example 1.

[0128] The results of the tensile strength and elongation at break of the dried kraft lignin / PBAT composite film material of this comparative example are shown in Table 1.

[0129] Comparative Example 3:

[0130] A lignin / PBAT composite film material. In terms of mass percentage, the composite film material is prepared from 70% PBAT and 30% sulfate lignin. For example:

[0131] (1) 30 parts by weight of sulfate lignin (KL)

[0132] (2) 70 parts by weight of poly(butylene adipate-co-terephthalate) (PBAT)

[0133] The preparation method of the above composite film material includes the following steps:

[0134] Step 1) The same as Comparative Example 1, where the mass ratio of dry sulfate lignin to PBAT particles is 30:70, that is, 30 parts by weight of dry sulfate lignin and 70 parts by weight of PBAT particles are added.

[0135] Step 2) The same as Comparative Example 1.

[0136] The results of the tensile strength and elongation at break of the dried sulfate lignin / PBAT composite film material of this comparative example are shown in Table 1.

[0137] Performance test method:

[0138] Tensile property detection: According to the national standard "GB / T1040.2-2006 Plastics - Determination of tensile properties - Part 2: Test conditions for moulding and extrusion plastics", the tensile properties of all the above composite film materials are measured. Each sample needs to be measured at least 5 times, and the average value is taken.

[0139] The results of the tensile strength and elongation at break of the lignin / PBAT composite film material of this comparative example are shown in Table 1.

[0140] Sample Name Tensile Strength (MPa) Elongation at Break (%) Pure PBAT 30.50 915.55 Example 1 23.21 849.36 Example 2 18.02 612.56 Example 3 14.21 417.05 Example 4 26.32 860.30 Example 5 19.16 720.12 Example 6 15.12 523.18 Example 7 12.20 309.65 Comparative Example 1 18.62 504.73 Comparative Example 2 11.44 378.37 Comparative Example 3 8.31 100.66

[0141] It can be seen from the test data in Table 1 above that under the same lignin addition amount, the lignin-based composite film material prepared by mixing DES lignin (DL) treated by the method of the present invention with PBAT has better tensile properties than the kraft lignin (KL) / PBAT composite film material. Compared with the KL / PBAT composite film material, when the DL substitution rate is 10%, 20%, and 30%, the elongation at break and tensile strength of the composite film material reach 849%, 612%, 417% and 23 MPa, 18 MPa, 14 MPa respectively. For DL treated at 140 °C under the same lignin substitution rate, the elongation at break and tensile strength of the composite film material are 860%, 720%, 523%, 309% and 26 MPa, 19 MPa, 15 MPa, 12 MPa respectively. In contrast, for untreated KL at substitution rates of 10%, 20%, and 30%, the elongation at break and tensile strength of the composite film material are 504%, 378%, 100% and 18 MPa, 11 MPa, 8 MPa respectively. It can be seen that with the increase of its content, the mechanical properties of the composite film material decrease greatly. In fact, this is because the compatibility between lignin and PBAT increases after treatment with alcohol-based DES, thereby improving the miscibility and overall properties of the two materials. Figure 1 is the effect diagram of the melt blending of DES lignin and PBAT. It can be clearly seen that DL and PBAT have significantly improved miscibility and compatibility.

[0142] In summary, the miscibility and stability of the composite film material system prepared by this method are effectively improved, making the mechanical properties of the composite material significantly higher than those of the untreated industrial lignin / PBAT composite film material, fully demonstrating its operability and superiority.

[0143] There is no report in the prior art on using alcohol-based deep eutectic solvents to treat industrial lignin to prepare lignin / PBAT composite materials. However, this preparation method has simple steps, is green and efficient, and has low process costs. The alcohol-based DES treatment of lignin and PBAT proposed by the present invention has excellent miscibility and compatibility, and the retention rate of its mechanical properties is significantly improved under different lignin addition amounts. Further, at 140 °C, the composite film material prepared by mixing alcohol-based DES-treated industrial lignin with PBAT still has good tensile properties even when the lignin addition amount is as high as 40%. Its tensile strength (12.12 Mpa) and elongation at break (442.04%) are significantly higher than the mechanical properties of the untreated industrial kraft lignin and PBAT composite film material. Moreover, the mechanical strength of the composite film material prepared by this method meets the national standard requirements for this type of material (GB / T 29646-2013 and GB / T 10004-2008: tensile strength ≥ 12 MPa, elongation at break ≥ 200%), and has great practical application value.

[0144] Although embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that: without departing from the spirit and scope of the present invention and the appended claims, various substitutions, changes and modifications are possible. Therefore, the scope of the present invention is not limited to the content disclosed in the embodiments.

Claims

1. A green and efficient method for improving the miscibility of lignin and PBAT, characterized in that: The method comprises mixing industrial lignin with an alcohol-based DES solvent and then performing low-temperature heat treatment to obtain DES lignin, which is then melt-blended with PBAT to prepare a composite material; Wherein, in parts by weight, the composite material is prepared from 60 to 90 parts by weight of PBAT and 10 to 40 parts by weight of DES lignin, and the total weight of DES lignin and PBAT is 100 parts by weight.

2. The green and efficient method according to claim 1, characterized in that: The tensile strength of the composite material is within the range of 12.20 to 23.21 MPa, and the elongation at break is within the range of 309.65 to 849.36%.

3. The green and efficient method according to claim 1, characterized in that: The DES lignin is obtained by subjecting industrial lignin to heat treatment, solid-liquid separation, and rotary distillation and acid precipitation with an alcohol-based DES solvent.

4. The green and efficient method according to claim 3, characterized in that: The specific preparation steps of the DES lignin are as follows: 1) mixing a hydrogen bond acceptor and a hydrogen bond donor in a molar ratio of 1:1 to 5 and stirring in a constant temperature water bath at a temperature of 80 to 100° C. to prepare a uniform and transparent alcohol-based DES, wherein the alcohol-based DES is a neutral solvent and a non-acidic or alkaline system; 2) mixing industrial lignin with the DES obtained in step 1) at a mass ratio of industrial lignin to DES of 1:5-10, stirring and reacting in a constant temperature oil bath at an oil bath temperature of 80-140° C. for a reaction time of 1.5-3.0 h; 3) The reaction mixture obtained in step 2) is added with a 50% acetone solution and mixed, and then centrifuged to separate the solid and liquid. The supernatant is concentrated by rotary evaporation and then added dropwise to a hydrochloric acid solution with a pH value of 2 to 4 to precipitate lignin. The lignin is washed and freeze-dried to obtain DES lignin.

5. The green and efficient method according to claim 4, characterized in that: In step 1), the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is any one of ethylene glycol, propylene glycol, glycerol, 1,4-butanediol, and pentanediol.

6. The green and efficient method according to claim 4, characterized in that: In step 2), the industrial lignin is at least one of alkali lignin, kraft lignin, enzymatic residue lignin and pre-hydrolyzed lignin.

7. The green and efficient method according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: directly melting and kneading DES lignin and PBAT without adding any plasticizer or plasticizer, and the prepared composite material is subjected to hot pressing to obtain a composite film material with significantly improved miscibility.

8. Use of the composite material obtained by the method according to any one of claims 1 to 7 in the preparation of packaging bags, garbage bags and ground films.

Images