Maleic anhydride modified lignosulfonic acid metal salt compatilizer as well as preparation method and application thereof

Abstract

The invention provides a maleic anhydride modified lignosulfonic acid metal salt compatilizer and a preparation method and application thereof.The maleic anhydride modified lignosulfonic acid metal salt compatilizer is prepared by the steps that lignosulfonate and maleic anhydride are subjected to graft modification in the presence of an initiator, then zinc salt is added for continuous reaction, and the maleic anhydride modified lignosulfonic acid metal salt compatilizer is obtained. And after the reaction is completed, salting out and precipitating a reaction product, and then separating, washing and drying to obtain the maleic anhydride modified lignosulfonic acid metal salt. After the prepared maleic anhydride modified lignosulfonic acid metal salt compatilizer is utilized, the interface action and dispersion uniformity of two phases of PBAT and PLA are improved, so that a PLA / PBAT sea-island structure is converted into a bicontinuous structure, and the mechanical properties such as tensile strength, puncture strength and elongation at break of a PBAT / PLA composite film product are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of compatibilizers for polyester-based composite films, and relates to a maleic anhydride-modified metal lignosulfonate compatibilizer, its preparation method and application. Specifically, it relates to a method for synergistically modifying lignosulfonate with maleic anhydride and zinc salt, and using it to compatibilize PBAT / PLA composite films. Background Art

[0002] In the National General Terms for Packaging (GB4122—83), the definition of flexible packaging is: Flexible packaging refers to packaging whose container shape can change after filling or removing the contents. Generally, plastic sheets with a thickness of less than 0.25 mm are called films. Plastic packaging films are an important guarantee for the transportation and storage of goods. At present, most of the widely used plastic packaging films are disposable products and are non-degradable. Biodegradable plastics are an environmentally friendly material, which can be finally degraded by microorganisms such as algae, fungi and bacteria existing in nature into water, carbon dioxide and mineral salts, etc. Replacing traditional disposable non-degradable plastic packaging with biodegradable plastic packaging is one of the important ways to solve "white pollution".

[0003] Among many biodegradable plastics, poly(butylene adipate-co-terephthalate) (PBAT) belongs to thermoplastic biodegradable high-flexibility copolyesters, which have both the biodegradability of aliphatic main-chain polymers and the mechanical properties of aromatic main-chain polymers. Polylactic acid (PLA) is a biodegradable aliphatic polyester obtained by polymerizing lactic acid. It has brittleness, high tensile strength but poor toughness. Generally, it needs to be blended with other plastics to improve its own toughness. PLA itself can also be a good blend component to improve the strength of tough materials. In theory, alloying PBAT and PLA is expected to maximize the toughness of the former and the strength of the latter. However, due to the large difference in their molecular structures, the interfacial adhesion of the blend is weak, and the phase separation problem affects the mechanical properties of the material. In order to obtain high-performance biodegradable packaging films, it is necessary to introduce a compatibilizer into the blend to improve the interfacial interaction and dispersion uniformity of the two phases of PBAT and PLA, transform the sea-island structure of PLA / PBAT into a bicontinuous structure, improve the mixing effect and enhance the mechanical properties of the film products.

[0004] Generally, the compatibilization modification of polymer alloys usually chooses to add compatibilizers to improve the compatibility of two-phase / multiphase systems. Compatibilizers mainly include reactive compatibilizers such as cyclic anhydrides, carboxylic acids, epoxies, isocyanates, oxazolines, etc. However, the preparation processes of most reactive compatibilizers are complex, the costs are high, and they are not biodegradable. Therefore, it is of great research value to develop renewable, environmentally friendly and low-cost reactive compatibilizers. Summary of the Invention

[0005] In order to solve the problems in the above-mentioned prior art, the present invention provides a maleic anhydride-modified lignosulfonate metal salt compatibilizer, its preparation method and application. This compatibilizer uses maleic anhydride and zinc salt to synergistically modify lignosulfonate. After using the prepared maleic anhydride-modified lignosulfonate metal salt compatibilizer, the interfacial interaction and dispersion uniformity between the PBAT and PLA phases are improved, enabling the sea-island structure of PLA / PBAT to transform into a bicontinuous structure, and significantly improving the mechanical properties such as tensile strength, puncture strength and elongation at break of PBAT / PLA composite film products.

[0006] To achieve the above object, the present invention is realized by a technical solution composed of the following technical measures.

[0007] The present invention provides a preparation method of a maleic anhydride-modified lignosulfonate metal salt compatibilizer, which mainly includes the following steps:

[0008] Graft-modify lignosulfonate with maleic anhydride at 35-60 °C for at least 4 h under the condition of having an initiator, and then add zinc salt and continue to react for at least 2 h. After the time is up, salt out and precipitate the reaction product, then separate, wash and dry to obtain maleic anhydride-modified lignosulfonate metal salt; wherein, the mass ratio of the lignosulfonate to maleic anhydride is 1:(0.6-1.4), and the addition amount of the zinc salt is 20-100 wt% of the mass percentage of the lignosulfonate.

[0009] In this article, the lignosulfonate is a class of compounds formed by the reaction of lignin with sulfite, usually a by-product of sulfite pulping of wood pulp. Based on the demand for low cost, conventional commercially available raw materials such as sodium lignosulfonate, calcium lignosulfonate, magnesium lignosulfonate, potassium lignosulfonate and ammonium lignosulfonate can be selected.

[0010] In this article, graft-modifying lignosulfonate with maleic anhydride at 35-60 °C for at least 4 h under the condition of having an initiator. The selected initiator promotes the graft reaction between maleic anhydride and lignosulfonate. Therefore, those skilled in the art can select a suitable initiator according to chemical common sense, especially the initiators commonly used in the prior art for maleic anhydride graft modification reactions.

[0011] In one of the technical solutions, the initiator is selected from any one of ammonium persulfate (APS), potassium persulfate (PPS), sodium persulfate (SPS), ammonium persulfate hydrogen (AMBN); the addition amount of the initiator is 0.5-6 wt% of the mass of maleic anhydride.

[0012] In this text, the lignosulfonate is graft-modified with maleic anhydride in the presence of an initiator at 35 - 60 °C for at least 4 h. For the specific graft-modification steps / conditions, those skilled in the art can adapt them according to the actual reaction scale and on-site conditions. It should be noted that maleic anhydride graft-modification is a conventional modification method in the prior art, and those skilled in the art can directly know the specific graft-modification steps / conditions based on the common general knowledge in the art.

[0013] To better illustrate the present invention and provide a reference technical solution, the graft-modification of lignosulfonate with maleic anhydride in the presence of an initiator at 35 - 60 °C for at least 4 h is specifically as follows: The lignosulfonate and maleic anhydride are respectively dissolved in deionized water to obtain an aqueous lignosulfonate solution and an aqueous maleic anhydride solution with a mass concentration of 0.05 - 0.2 g / mL. An initiator is added to the aqueous lignosulfonate solution, and then the aqueous maleic anhydride solution is added dropwise at a dropping rate of 20 - 50 drops / min with stirring at 35 - 60 °C, and the stirring reaction continues for at least 4 h. It should be emphasized that although this technical solution is adopted in the following examples, this does not mean that this is the only / limiting process for maleic anhydride graft-modifying lignosulfonate. Those skilled in the art should fully realize that they can adapt and adjust according to the reaction scale and on-site conditions and based on the common general knowledge in the art.

[0014] In one technical solution, the zinc salt is selected from at least one of zinc chloride, zinc sulfate, zinc acetate, and zinc nitrate.

[0015] In one technical solution, in order to make the maleic anhydride-modified lignosulfonate metal salt disperse better in the polyester matrix as a compatibilizer, the particle size of the maleic anhydride-modified lignosulfonate metal salt is preferably not higher than 100 μm. It can be obtained by routinely grinding and sieving the dried product.

[0016] To better illustrate the technical effects of the present invention and characterize the technical effects of the prepared maleic anhydride-modified lignosulfonate metal salt compatibilizer, the present invention also provides a preparation method for compatibilizing a PBAT / PLA composite film using the maleic anhydride-modified lignosulfonate metal salt compatibilizer, which mainly includes the following steps:

[0017] (1) By weight, the raw materials mainly including the following components are mixed and prepared as a mixture:

[0018] PBAT 50 - 90 parts,

[0019] Polylactic acid 10 - 50 parts,

[0020] Maleic anhydride-modified lignosulfonate metal salt 0.1 - 5 parts,

[0021] Among them, the total amount of PBAT and polylactic acid is 100 parts;

[0022] (2) The mixture obtained in step (1) is subjected to melt blending and film forming to prepare a PBAT / PLA composite film.

[0023] In this article, the polylactic acid (PLA) described in step (1) is a selection of conventional polylactic acid industrial raw materials, and further preferably a selection of the conventional polylactic acid raw material models in the polylactic acid-based film products described in the prior art. Those skilled in the art can select a suitable polylactic acid grade according to specific needs and process requirements.

[0024] In one technical solution, the PLA selection in step (1) includes any one or more of PLA110 / PLA290 of Changchun Institute of Applied Chemistry, NatureWorks4032D / 4060D, Fengyuan FY802, Haizheng Biology REVODE110, and Total L175.

[0025] In this article, the PBAT described in step (1) is a selection of conventional industrial raw materials, and further preferably a selection of the PBAT raw material models suitable as packaging materials described in the prior art. Those skilled in the art can select a suitable PBAT grade according to specific needs and process requirements.

[0026] In one technical solution, in order to make the maleic anhydride-modified lignosulfonate metal salt disperse better in the matrix, the particle size of the maleic anhydride-modified lignosulfonate metal salt in step (1) is preferably not higher than 100 μm. It can be obtained by routinely grinding and sieving the dried product.

[0027] In one technical solution, before the mixture in step (2) is subjected to melt blending, it can be optionally pre-treated by heat drying to remove moisture and ash in the mixture. Specifically, the mixture is dried at a temperature of 50-80 °C for 6-12 h.

[0028] In one of the technical solutions, additives commonly used in the processing and molding of polylactic acid / PBAT can also be added to the mixture in step (1) to achieve further functional expansion / process assistance for the product. For the specific selection of additives, those skilled in the art can refer to the prior art or existing literature, such as processing additives / functional additives like antioxidants, lubricants, flame retardants, anti-aging agents, heat stabilizers, plasticizers, antibacterial agents, etc. It should be noted that the mixture in step (1) may or may not include the additives commonly used in the processing and molding of polylactic acid / PBAT. In the following preferred technical solutions and specific embodiments, in order to minimize the influencing factors in the comparative experiments, no additives are added to the mixture, but this does not mean that appropriate additives cannot be added to the mixture. However, it should be emphasized that the selection and addition of the above additives should not affect the dispersion effect of maleic anhydride-modified lignosulfonate metal salt in the matrix.

[0029] In this article, the mixture in step (2) is subjected to melt blending and film formation to prepare a PBAT / PLA composite film. Among them, melt blending is a conventional polyester-based composite material process method using polyester as the matrix raw material, such as melt kneading, melt extrusion, etc. The specific process steps / parameters can be directly referred to the prior art records / existing process methods of polylactic acid / PBAT during melt blending.

[0030] In one of the technical solutions, the mixture in step (2) is subjected to melt blending and film formation. Among them, melt blending is carried out using a screw extruder, and the specific process parameters are: the temperatures of each zone are 130 - 180 °C respectively, and the screw speed is 180 - 200 rpm.

[0031] In this article, the mixture in step (2) is subjected to melt blending and film formation to prepare a PBAT / PLA composite film. Among them, film formation is a conventional polyester-based film preparation process method, such as hot pressing film formation, blow molding film formation. The specific process steps / parameters can be directly referred to the prior art records / existing process methods of polylactic acid / PBAT during film formation.

[0032] In one of the technical solutions, the mixture in step (2) is subjected to melt blending and film formation. Among them, film formation is carried out by blow molding using a blow molding machine, and the specific process parameters are: the temperatures of each zone are 150 - 180 °C respectively, and the screw speed is 30 - 50 rpm.

[0033] It should be noted that during the research on the relevant topics of the technical solution of the present invention, the inventor retrieved that lignin is a highly potential reinforcing filler. Lignin is an amorphous polymer formed by connecting three kinds of phenylpropane units through carbon-carbon bonds and ether bonds. Its molecular structure is rich in active functional groups such as benzene rings, aliphatic hydroxyl groups and phenolic hydroxyl groups, and its structure can be modified by various means. Lignin mainly comes from the by-products of the pulp and paper making and biorefining industries. It is the second largest biomass resource in the plant kingdom after cellulose in terms of reserves. Most of it is used as fuel, and only 5% of industrial lignin is used to manufacture high-value-added products such as additives, dispersants, and surfactants, which not only causes waste of resources but also leads to secondary pollution due to combustion. However, when lignin is used as a filler in polymers, due to its highly variable and complex molecular structure, it is easy to form aggregates in the polymer matrix, which reduces the toughness and transparency of the polymer to a certain extent.

[0034] Based on this, the inventor carried out chemical modification on lignin in order to solve the above problems. During the experimental exploration process, in order to endow the composite film with good antibacterial properties at the same time, in the experiment of preparing maleic anhydride and zinc chloride modified lignosulfonate by hydrothermal method, on the one hand, it was unexpectedly found that the reaction product could be quickly crystallized out by weak base salting-out, and on the other hand, it was pleasantly discovered that through the synergistic modification of maleic anhydride and zinc chloride, the compatibility of PBAT / PLA composites could be significantly improved, and the mechanical properties of the composite film could be improved. In the prior art, when maleic anhydride modified lignosulfonate is used to precipitate the reaction product, organic solvents are usually selected to precipitate the reaction product or strong acids are selected to precipitate the reaction product, or other more complex methods are used to precipitate the product. There is no record in any existing literature that its precipitation preparation is carried out based on the principle of salting-out. Introducing maleic anhydride can improve the flexibility of the modified lignin molecular chain and reduce the color of lignin itself. Introducing zinc can improve the thermal stability of the modified lignin and play a synergistic antibacterial and antioxidant role. At the same time, combining the synergistic modification of maleic anhydride and zinc salt on lignosulfonate greatly improves the mechanical properties of the composite film, and can also act as a lubricant and chain extender for PBAT / PLA composites, improving the processability of PBAT / PLA composites.

[0035] Based on the above invention points, in one of the technical solutions, the reaction product is precipitated by salting-out, specifically by adding a weak base to carry out salting-out precipitation of the reaction product. For example, any one of sodium percarbonate, sodium bicarbonate, sodium sulfite and ammonia water, which are conventional weak bases for salting-out, is added for neutralization precipitation of the reaction product.

[0036] In one of the preferred technical solutions, the reaction product is salted out by adding a weak base, specifically, the reaction product is salted out by adding a weak base until the pH of the reaction solution is 1.5 to 7; more preferably, a weak base is added until the pH of the reaction solution is 2.5 to 3.

[0037] In one of the preferred technical solutions, the reaction product is salted out by preparing the weak base into a saturated aqueous solution of the weak base and salting out the reaction product by adding the saturated aqueous solution of the weak base.

[0038] In this article, the mixing, separation, washing, and drying all follow the conventional principles in chemical engineering processes, and those skilled in the art can perform specific operations according to common knowledge.

[0039] The present invention has the following beneficial effects:

[0040] 1. The present invention provides a preparation method of a maleic anhydride-modified lignosulfonate metal salt compatibilizer. This compatibilizer uses maleic anhydride and zinc salt to synergistically modify lignosulfonate, increase the carboxyl group content of lignin, and introduce zinc ions at the terminal carboxyl group. The overall molecular structure of the maleic anhydride-modified lignosulfonate metal salt compatibilizer bridges lignin and zinc ions with a long fatty chain. The zinc ions further bridge the long fatty chain and lignin to form a larger network structure, increasing the molecular flexibility of the reaction product and reducing the color of lignin itself. As a compatibilizer, it can significantly improve the compatibility between polylactic acid and PBAT in the composite film and the toughness of the prepared composite film.

[0041] 2. The maleic anhydride-modified lignosulfonate metal salt compatibilizer provided by the present invention has good antibacterial and antioxidant properties. By structurally modifying lignosulfonate and introducing zinc ions onto the macromolecular chain of maleic anhydride-modified lignin, the antibacterial and antioxidant properties of the composite film are improved when used as a compatibilizer.

[0042] 3. The preparation process of the present invention is simple, the conditions are mild, it is easy to operate, and it can be mass-produced. The raw materials used are all environmentally degradable raw materials or low-toxic raw materials. The raw materials in the reaction process consume less, can be recycled and reused, and no toxic by-products are generated, belonging to an environmentally friendly method. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a physical diagram of the sodium lignosulfonate, the prepared maleic anhydride-modified sodium lignosulfonate, and the maleic anhydride-modified lignosulfonate metal salt used as raw materials in Synthesis Example 1 and Synthesis Comparative Example 1 of the present invention. Among them, SL is sodium lignosulfonate, ML is the maleic anhydride-modified sodium lignosulfonate prepared in Synthesis Comparative Example 1, and MLZn is the maleic anhydride-modified lignosulfonate metal salt prepared in Synthesis Example 1.

[0044] Figure 2 This is the infrared absorption spectrogram of the raw materials in Synthesis Example 1 of the present invention and the metal salt of maleic anhydride-modified lignosulfonic acid obtained. Among them, SL is sodium lignosulfonate, MA is maleic anhydride, and MLZn is the metal salt of maleic anhydride-modified lignosulfonic acid obtained in Synthesis Example 1.

[0045] Figure 3 This is the comparison chart of the mechanical properties of the PBAT / PLA composite films prepared in Comparative Examples 1-3 and Examples 1-3 of the present invention.

[0046] Figure 4 This is the comparison chart of the puncture performance of the PBAT / PLA composite films prepared in Comparative Examples 1-3 and Examples 1-3 of the present invention.

[0047] Figure 5 This is the brittle fracture surface morphology diagram of the PBAT / PLA composite films prepared in Comparative Examples 1-2 and Example 1 of the present invention. Among them, Figure (a) refers to the PBAT / PLA composite film prepared in Comparative Example 1, Figure (b) refers to the PBAT / PLA composite film prepared in Comparative Example 2, and Figure (c) refers to the PBAT / PLA composite film prepared in Example 1; Figures (a1), (b1), and (c1) are the enlarged views of (a), (b), and (c), respectively. Detailed implementation manners

[0048] To further understand the present invention, the preferred implementation manners of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention. Those skilled in the art can draw on the content of this article and appropriately modify the process parameters to achieve. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the present invention. The methods and applications of the present invention have been described through preferred examples, and those skilled in the art can obviously make changes or appropriate modifications and combinations to the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention. Although it is believed that those of ordinary skill in the art are fully familiar with the following terms, the following definitions are still stated to help illustrate the subject matter disclosed by the present invention.

[0049] The present invention provides a preparation method of a compatibilizer for a metal salt of maleic anhydride-modified lignosulfonic acid, which mainly includes the following steps:

[0050] The lignosulfonate is graft-modified with maleic anhydride at 35-60 °C for at least 4 h in the presence of an initiator, and then a zinc salt is added and the reaction continues for at least 2 h. After the time is up, the reaction product is precipitated by salting out, separated, washed, and dried to obtain the metal salt of maleic anhydride-modified lignosulfonic acid; wherein, the mass ratio of the lignosulfonate to maleic anhydride is 1:(0.6-1.4), and the addition amount of the zinc salt is 20-100 wt% of the mass percentage of the lignosulfonate.

[0051] In this article, the lignosulfonate is a class of compounds formed by the reaction of lignin with sulfite, usually a by-product of sulfite pulping. Based on the demand for low cost, in one embodiment, conventional commercially available raw materials such as sodium lignosulfonate, calcium lignosulfonate, magnesium lignosulfonate, potassium lignosulfonate, and ammonium lignosulfonate can be selected.

[0052] In this article, the lignosulfonate is graft-modified with maleic anhydride at 35-60 °C for at least 4 h in the presence of an initiator. The selected initiator promotes the graft reaction between maleic anhydride and lignosulfonate. Therefore, those skilled in the art can select a suitable initiator according to chemical common sense, especially the initiators commonly used in the graft modification reaction of maleic anhydride in the prior art.

[0053] In one embodiment, the initiator is selected from any one of ammonium persulfate (APS), potassium persulfate (PPS), sodium persulfate (SPS), and ammonium bisulfate (AMBN); the addition amount of the initiator is 0.5-6 wt% of the mass of maleic anhydride.

[0054] In this article, the lignosulfonate is graft-modified with maleic anhydride at 35-60 °C for at least 4 h in the presence of an initiator. For the specific graft modification steps / conditions, those skilled in the art can adapt them according to the actual reaction scale and on-site conditions. It should be noted that the graft modification of maleic anhydride is a conventional modification method in the prior art, and those skilled in the art can directly know the specific graft modification steps / conditions according to the common general knowledge in the art.

[0055] To better illustrate the present invention and provide a reference implementation, the lignosulfonate is graft-modified with maleic anhydride at 35-60 °C for at least 4 h in the presence of an initiator. Specifically, the lignosulfonate and maleic anhydride are respectively dissolved in deionized water to obtain an aqueous lignosulfonate solution and an aqueous maleic anhydride solution with a mass concentration of 0.05-0.2 g / mL. An initiator is added to the aqueous lignosulfonate solution, and then the aqueous maleic anhydride solution is added dropwise at a dropping rate of 20-50 drops / min with stirring at 35-60 °C, and the stirring reaction continues for at least 4 h. It should be emphasized that although this technical solution is adopted in the following examples, this does not mean that this is the only / limiting process for graft-modifying lignosulfonate with maleic anhydride. Those skilled in the art should fully realize that it can be adapted and adjusted according to the reaction scale and on-site conditions based on the common general knowledge in the art.

[0056] In one of the embodiments, the zinc salt is selected from at least one of zinc chloride, zinc sulfate, zinc acetate, and zinc nitrate.

[0057] In one of the embodiments, in order to make the maleic anhydride-modified lignosulfonate metal salt disperse better in the polyester matrix as a compatibilizer, the particle size of the maleic anhydride-modified lignosulfonate metal salt is preferably not higher than 100 μm. It can be obtained by routinely grinding and sieving the dried product.

[0058] In one of the embodiments, the mass ratio of the lignosulfonate to maleic anhydride is 1:(0.6-1.4), such as 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, or any range or point value between them.

[0059] In one of the embodiments, the addition amount of the zinc salt is 20-100 wt% of the mass percentage of the lignosulfonate, such as 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, 100 wt%, or any range or point value between them.

[0060] To better illustrate the technical effects of the present invention and characterize the technical effects of the prepared maleic anhydride-modified lignosulfonate metal salt compatibilizer, the present invention also provides a preparation method for compatibilizing a PBAT / PLA composite film with the maleic anhydride-modified lignosulfonate metal salt compatibilizer, which mainly includes the following steps:

[0061] (1) Mix and prepare raw materials mainly including the following components by weight parts to obtain a mixed material:

[0062] 50 - 90 parts of PBAT,

[0063] 10 - 50 parts of polylactic acid,

[0064] 0.1 - 5 parts of maleic anhydride modified lignosulfonic acid metal salt,

[0065] wherein, the total of PBAT and polylactic acid is 100 parts;

[0066] (2) Prepare a PBAT / PLA composite film by subjecting the mixed material obtained in step (1) to melt blending and film forming.

[0067] In this article, the polylactic acid (PLA) described in step (1) is a conventional polylactic acid industrial raw material selection, and is further preferably a selection of conventional polylactic acid raw material models in the polylactic acid - based film products recorded in the prior art. Those skilled in the art can select a suitable polylactic acid grade according to specific needs and process requirements.

[0068] In one embodiment, the PLA described in step (1) is selected from any one or more of PLA110 / PLA290 of Changchun Institute of Applied Chemistry, NatureWorks4032D / 4060D, Fengyuan FY802, Haizheng Biology REVODE110, and Total L175.

[0069] In this article, the PBAT described in step (1) is a conventional industrial raw material selection, and is further preferably a selection of PBAT raw material models suitable as packaging materials recorded in the prior art. Those skilled in the art can select a suitable PBAT grade according to specific needs and process requirements.

[0070] In one embodiment, in order to better disperse the maleic anhydride modified lignosulfonic acid metal salt in the matrix, the particle size of the maleic anhydride modified lignosulfonic acid metal salt described in step (1) is preferably not higher than 100 μm. It can be obtained by routinely grinding and sieving the dried product.

[0071] In one embodiment, the maleic anhydride modified lignosulfonic acid metal salt described in step (1) is 0.1 - 5 parts, such as 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part, 1.0 part, 1.1 part, 1.2 part, 1.3 part, 1.4 part, 1.5 part, 1.6 part, 1.7 part, 1.8 part, 1.9 part, 2.0 part, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts or any range or point value between them.

[0072] In one embodiment, the polylactic acid in step (1) is 10 to 50 parts, such as 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 parts, 49 parts, 50 parts or any range or point value therebetween.

[0073] In one embodiment, before the mixture in step (2) undergoes melt blending, it can be optionally pre-treated by heat drying to remove moisture and ash in the mixture. Specifically, the mixture is dried at a temperature of 50 to 80 °C for 6 to 12 h.

[0074] In one embodiment, additives commonly used in the processing and molding of polylactic acid / PBAT can also be added to the mixture in step (1) to achieve further functional expansion / process assistance for the product. For the specific selection of additives, those skilled in the art can refer to the existing technology or existing literature, such as processing additives / functional additives like antioxidants, lubricants, flame retardants, anti-aging agents, heat stabilizers, plasticizers, antibacterial agents, etc. It should be noted that the mixture in step (1) may or may not include the additives commonly used in the processing and molding of polylactic acid / PBAT; in the following preferred technical solutions and specific embodiments, in order to minimize the influencing factors in the comparative experiments, no additives are added to the mixture, but this does not mean that appropriate additives cannot be added to the mixture. However, it should be emphasized that the selection and addition of the above additives should not affect the dispersion effect of maleic anhydride-modified lignosulfonate metal salt in the matrix.

[0075] In this article, the mixture in step (2) undergoes melt blending and film formation to prepare a PBAT / PLA composite film. Among them, melt blending is a conventional polyester-based composite material process method using polyester as the matrix raw material, such as melt kneading, melt extrusion, etc. The specific process steps / process parameters can directly refer to the existing technical records / existing process methods of polylactic acid / PBAT during melt blending.

[0076] In one embodiment, the mixture in step (2) undergoes melt blending and film formation. Among them, melt blending is carried out using a screw extruder, and the specific process parameters are: the temperatures of each zone are 130 to 180 °C respectively, and the screw speed is 180 to 200 rpm.

[0077] In this article, the mixture described in step (2) is prepared into a PBAT / PLA composite film through melt blending and film forming. The film forming is a preparation process method for conventional polyester-based films, such as hot pressing film forming and blow molding film forming. The specific process steps / process parameters can directly refer to the existing technical records / existing process methods when preparing and forming polylactic acid / PBAT.

[0078] In one of the embodiments, the mixture described in step (2) is subjected to melt blending and film forming, where the film forming is carried out by blow molding using a blow molding machine. The specific process parameters are: the temperatures of each zone are 150 - 180 °C respectively, and the screw speed is 30 - 50 rpm.

[0079] It should be noted that during the research on the relevant topics of the technical solution of the present invention, the inventor retrieved that lignin is a highly potential reinforcing filler. Lignin is an amorphous polymer formed by connecting three kinds of phenylpropane units through carbon-carbon bonds and ether bonds. Its molecular structure is rich in active functional groups such as benzene rings, aliphatic hydroxyl groups, and phenolic hydroxyl groups, and its structure can be modified by various means. Lignin mainly comes from the by-products of the pulp and paper making and biorefining industries. It is the second largest biomass resource in the plant kingdom after cellulose in terms of reserves. Most of it is used as fuel, and only 5% of industrial lignin is used to manufacture high-value-added products such as additives, dispersants, and surfactants, which not only causes waste of resources but also leads to secondary pollution due to combustion. However, when lignin is used as a filler in polymers, due to its highly variable and complex molecular structure, it is easy to form aggregates in the polymer matrix, reducing the toughness and transparency of the polymer to a certain extent.

[0080] Based on this, the inventors carried out chemical modification on lignin in order to solve the above problems. During the experimental exploration process, in order to endow the composite film with good antibacterial properties at the same time, during the experiment of preparing maleic anhydride and zinc chloride modified lignosulfonate by hydrothermal method, on the one hand, it was unexpectedly found that the reaction product could be quickly crystallized and precipitated by weak base salting-out, and on the other hand, it was pleasantly discovered that through the synergistic modification of maleic anhydride and zinc chloride, the compatibility of PBAT / PLA composites could be significantly improved, and the mechanical properties of the composite film could be improved. In the prior art, when maleic anhydride modified lignosulfonate is used, organic solvents are usually selected to precipitate the reaction product, or strong acids are selected to precipitate the reaction product, or other more complex methods are used to precipitate the product. There is no record in any existing literature that its precipitation preparation is carried out based on the principle of salting-out. Introducing maleic anhydride can improve the flexibility of the modified lignin molecular chain and reduce the color of lignin itself. Introducing zinc can improve the thermal stability of the modified lignin and play a synergistic antibacterial and antioxidant role. At the same time, combining the synergistic modification of maleic anhydride and zinc salt on lignosulfonate greatly improves the mechanical properties of the composite film, and can also act as a lubricant and chain extender for PBAT / PLA composites, improving the processability of PBAT / PLA composites.

[0081] Based on the above invention points, in one of the embodiments, the reaction product is precipitated by salting-out, specifically by adding a weak base to precipitate the reaction product by salting-out. For example, any one of sodium percarbonate, sodium bicarbonate, sodium sulfite and ammonia water, which are conventional weak bases for salting-out, is added to neutralize and precipitate the reaction product.

[0082] In one of the preferred embodiments, the reaction product is precipitated by salting-out, specifically by adding a weak base to precipitate the reaction product by salting-out, and the weak base is added until the pH of the reaction solution is 1.5 - 7; more preferably, the weak base is added until the pH of the reaction solution is 2.5 - 3.

[0083] In one of the preferred embodiments, the reaction product is precipitated by salting-out, and the weak base is configured as a saturated aqueous solution of the weak base, and the reaction product is neutralized and precipitated by adding the saturated aqueous solution of the weak base.

[0084] In this article, the mixing, separation, washing, and drying all follow the conventional principles in chemical engineering, and those skilled in the art can perform specific operations according to common knowledge.

[0085] The following will further explain the present application with reference to the embodiments. However, those skilled in the art should understand that these embodiments are provided for illustrative purposes only and are not intended to limit the present application.

[0086] Examples

[0087] The implementation scheme of the present application will be described in detail below in combination with embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase. The present application should not be construed as being limited to the specific embodiments described.

[0088] 1. Raw materials

[0089] Poly(butylene adipate-co-terephthalate) (PBAT), grade A400, Zhuhai Jinfa Biomaterials Co., Ltd.;

[0090] Polylactic acid (PLA), grade PLA110, density 1.2 - 1.3 g / cm 3 , Changchun Institute of Applied Chemistry, Chinese Academy of Sciences;

[0091] Lignosulfonate (SL), Hefei BASF Biotechnology Co., Ltd.;

[0092] Maleic anhydride (MA), Shanghai Titan Scientific Co., Ltd.;

[0093] Zinc chloride (ZnCl2), Chengdu Kelong Chemical Co., Ltd.;

[0094] Ammonium persulfate, Chengdu Kelong Chemical Co., Ltd.;

[0095] Anhydrous sodium carbonate (Na2CO3), Chengdu Kelong Chemical Co., Ltd.

[0096] 2. Test methods

[0097] Mechanical properties: The mechanical properties and puncture resistance of the composite film were tested according to the standards ISO 527 and GB / T 37841-2019 respectively under a load-bearing capacity of 1 kN using an Instron 5567 universal material testing machine at a tensile rate of 50 mm / min and a puncture needle falling speed of 50 mm / min.

[0098] Synthesis example 1

[0099] Dissolve 6 g of sodium lignosulfonate and 6 g of maleic anhydride in deionized water respectively to obtain an aqueous solution of sodium lignosulfonate and an aqueous solution of maleic anhydride with a mass concentration of 0.2 g / mL. Add 0.24 g of initiator ammonium persulfate to the aqueous solution of sodium lignosulfonate, and then add the aqueous solution of maleic anhydride dropwise at a dropping rate of 30 drops / min with stirring at 40 °C. Continue stirring and reacting for 4 h, then add 2 g of zinc chloride and continue stirring and reacting for 2 h. After the time is up, salt out and precipitate the reaction product with saturated sodium carbonate aqueous solution, then separate, wash and dry. The dried product is ground and sieved to a particle size not higher than 100 μm to obtain maleic anhydride-modified lignosulfonate metal salt, denoted as MLZn.

[0100] Synthesis Comparative Example 1

[0101] Dissolve 6 g of sodium lignosulfonate and 6 g of maleic anhydride in deionized water respectively to obtain an aqueous solution of sodium lignosulfonate and an aqueous solution of maleic anhydride with a mass concentration of 0.2 g / mL. Add 0.24 g of initiator ammonium persulfate to the aqueous solution of sodium lignosulfonate, and then add the aqueous solution of maleic anhydride dropwise at a dropping rate of 30 drops / min with stirring at 40 °C. Continue stirring and reacting for 4 h. After the time is up, salt out and precipitate the reaction product with saturated sodium carbonate aqueous solution, then separate, wash and dry. The dried product is ground and sieved to a particle size not higher than 100 μm to obtain maleic anhydride-modified sodium lignosulfonate, denoted as ML.

[0102] Example 1

[0103] Example 1 is a preparation method of using the maleic anhydride-modified lignosulfonate metal salt prepared in Synthesis Example 1 as a compatibilizer to compatibilize the PBAT / PLA composite film, which mainly includes the following steps:

[0104] (1) By weight, mix the raw materials mainly including the following components as a mixed material:

[0105] 80 parts of PBAT,

[0106] 20 parts of polylactic acid,

[0107] 0.3 part of maleic anhydride-modified lignosulfonate metal salt;

[0108] (2) Extrude and blow the mixed material obtained in step (1) through melting in sequence to prepare a PBAT / PLA composite film, denoted as P8P2MLZn0.3;

[0109] Among them, the melt extrusion is carried out by using a screw extruder for extrusion granulation, and the specific process parameters are as follows: the temperatures of each zone are 130°C, 130°C, 150°C, 170°C, 180°C, 180°C, 180°C, 180°C, 180°C, 180°C, 180°C, 170°C respectively, and the screw speed is 200 rpm;

[0110] The extrusion blow molding is carried out by using a blow molding machine, and the specific process parameters are as follows: the temperatures of each zone are 150°C, 170°C, 180°C, 175°C, 160°C respectively, and the screw speed is 30 rpm.

[0111] After testing, the PBAT / PLA composite film prepared in this example has a tensile strength of 25.65 MPa, an elongation at break of 1033.61%, and a puncture strength of 66.74 N / mm.

[0112] Example 2

[0113] Example 2 is a preparation method of a PBAT / PLA composite film using the maleic anhydride-modified lignosulfonate metal salt prepared in Synthesis Example 1 as a compatibilizer, which mainly includes the following steps:

[0114] (1) By weight, the raw materials mainly including the following components are mixed and prepared as a mixture:

[0115] 80 parts of PBAT,

[0116] 20 parts of polylactic acid,

[0117] 0.5 part of maleic anhydride-modified lignosulfonate metal salt;

[0118] (2) The mixture obtained in step (1) is successively subjected to melt extrusion and extrusion blow molding to prepare a PBAT / PLA composite film, denoted as P8P2MLZn0.5;

[0119] Among them, the melt extrusion is carried out by using a screw extruder for extrusion granulation, and the specific process parameters are as follows: the temperatures of each zone are 130°C, 130°C, 150°C, 170°C, 180°C, 180°C, 180°C, 180°C, 180°C, 180°C, 180°C, 170°C respectively, and the screw speed is 200 rpm;

[0120] The extrusion blow molding is carried out by using a blow molding machine, and the specific process parameters are as follows: the temperatures of each zone are 150°C, 170°C, 180°C, 175°C, 160°C respectively, and the screw speed is 30 rpm.

[0121] After testing, the PBAT / PLA composite film prepared in this example has a tensile strength of 24.76 MPa, an elongation at break of 1002.19%, and a puncture strength of 65.85 N / mm.

[0122] Example 3

[0123] Example 3 is a preparation method of compatibilizing PBAT / PLA composite film by using the maleic anhydride modified lignosulfonate metal salt prepared in Synthesis Example 1 as a compatibilizer, which mainly includes the following steps:

[0124] (1) By weight, mix the raw materials mainly including the following components as a mixture:

[0125] 80 parts of PBAT,

[0126] 20 parts of polylactic acid,

[0127] 1 part of maleic anhydride modified lignosulfonate metal salt;

[0128] (2) Extrude and blow the mixture obtained in step (1) successively through melt extrusion and extrusion blow molding to prepare a PBAT / PLA composite film, denoted as P8P2MLZn1;

[0129] Among them, the melt extrusion is carried out by using a screw extruder for pelletizing, and the specific process parameters are: the temperatures of each zone are 130°C, 130°C, 150°C, 170°C, 180°C, 180°C, 180°C, 180°C, 180°C, 180°C, 180°C, 170°C respectively, and the screw speed is 200 rpm;

[0130] The extrusion blow molding is carried out by using a blow molding machine, and the specific process parameters are: the temperatures of each zone are 150°C, 170°C, 180°C, 175°C, 160°C respectively, and the screw speed is 30 rpm.

[0131] After testing, the PBAT / PLA composite film prepared in this example has a tensile strength of 20.89 MPa, an elongation at break of 840.22%, and a puncture strength of 58.46 N / mm.

[0132] Comparative Example 1

[0133] This Comparative Example 1 is for comparison without adding maleic anhydride modified lignosulfonate metal salt, and mainly includes the following steps:

[0134] (1) By weight, mix the raw materials mainly including the following components as a mixture:

[0135] 80 parts of PBAT,

[0136] 20 parts of polylactic acid;

[0137] (2) Extrude and blow the mixture obtained in step (1) successively through melt extrusion and extrusion blow molding to prepare a PBAT / PLA composite film, denoted as P8P2;

[0138] Among them, the melt extrusion is carried out by using a screw extruder for extrusion granulation, and the specific process parameters are as follows: the temperatures of each zone are 130 °C, 130 °C, 150 °C, 170 °C, 180 °C, 180 °C, 180 °C, 180 °C, 180 °C, 180 °C, 180 °C, 170 °C respectively, and the screw speed is 200 rpm;

[0139] The extrusion blow molding is carried out by using a blow molding machine, and the specific process parameters are as follows: the temperatures of each zone are 150 °C, 170 °C, 180 °C, 175 °C, 160 °C respectively, and the screw speed is 30 rpm.

[0140] After testing, the PBAT / PLA composite film prepared in this comparative example has a tensile strength of 22.52 MPa, an elongation at break of 788.62%, and a puncture strength of 60.23 N / mm.

[0141] Comparative Example 2

[0142] In this Comparative Example 2, the maleic anhydride-modified lignosulfonate metal salt is replaced by sodium lignosulfonate for comparison, which mainly includes the following steps:

[0143] (1) By weight, the raw materials mainly including the following components are mixed and prepared as a mixture:

[0144] 80 parts of PBAT,

[0145] 20 parts of polylactic acid,

[0146] 0.3 part of sodium lignosulfonate;

[0147] (2) The mixture obtained in step (1) is successively subjected to melt extrusion and extrusion blow molding to prepare a PBAT / PLA composite film, denoted as P8P2SL0.3;

[0148] Among them, the melt extrusion is carried out by using a screw extruder for extrusion granulation, and the specific process parameters are as follows: the temperatures of each zone are 130 °C, 130 °C, 150 °C, 170 °C, 180 °C, 180 °C, 180 °C, 180 °C, 180 °C, 180 °C, 180 °C, 170 °C respectively, and the screw speed is 200 rpm;

[0149] The extrusion blow molding is carried out by using a blow molding machine, and the specific process parameters are as follows: the temperatures of each zone are 150 °C, 170 °C, 180 °C, 175 °C, 160 °C respectively, and the screw speed is 30 rpm.

[0150] After testing, the PBAT / PLA composite film prepared in this comparative example has a tensile strength of 21.57 MPa, an elongation at break of 737.38%, and a puncture strength of 58.96 N / mm.

[0151] Comparative Example 3

[0152] In Comparative Example 3, maleic anhydride-modified lignosulfonate metal salt was replaced with sodium lignosulfonate for comparison, which mainly included the following steps:

[0153] (1) By weight, the raw materials mainly including the following components were mixed and prepared as a mixture:

[0154] 80 parts of PBAT,

[0155] 20 parts of polylactic acid,

[0156] 1 part of sodium lignosulfonate;

[0157] (2) The mixture obtained in step (1) was successively subjected to melt extrusion and extrusion blow molding to prepare a PBAT / PLA composite film, denoted as P8P2SL1;

[0158] Among them, the melt extrusion was carried out by using a screw extruder for pelletizing, and the specific process parameters were: the temperatures of each zone were 130°C, 130°C, 150°C, 170°C, 180°C, 180°C, 180°C, 180°C, 180°C, 180°C, 180°C, 170°C respectively, and the screw speed was 200 rpm;

[0159] The extrusion blow molding was carried out by using a blow molding machine, and the specific process parameters were: the temperatures of each zone were 150°C, 170°C, 180°C, 175°C, 160°C respectively, and the screw speed was 30 rpm.

[0160] After testing, the PBAT / PLA composite film prepared in this comparative example had a tensile strength of 17.63 MPa, an elongation at break of 578.25%, and a puncture strength of 55.45 N / mm.

[0161] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a maleic anhydride modified lignosulfonate metal salt compatibilizer, characterized in that It mainly includes the following steps: Graft-modify lignosulfonate with maleic anhydride at 35-60 °C for at least 4 h in the presence of an initiator, then add zinc salt and continue to react for at least 2 h. After the time is up, salt out and precipitate the reaction product, then separate, wash and dry it to obtain the metal salt of maleic anhydride-modified lignosulfonic acid; wherein, the mass ratio of the lignosulfonate to maleic anhydride is 1:(0.6-1.4), and the addition amount of the zinc salt is 20-100 wt% of the mass percentage of the lignosulfonate.

2. The preparation method according to claim 1, characterized in that: The initiator includes any one of ammonium persulfate, potassium persulfate, sodium persulfate, and ammonium bisulfate; the addition amount of the initiator is 0.5-6 wt% of the mass of maleic anhydride.

3. The preparation method according to claim 1, wherein: The step of graft-modifying lignosulfonate with maleic anhydride at 35-60 °C for at least 4 h in the presence of an initiator is specifically to dissolve the lignosulfonate and maleic anhydride in deionized water respectively, and prepare an aqueous solution of lignosulfonic acid with a mass concentration of 0.05-0.2 g / mL and an aqueous solution of maleic anhydride respectively. Add the initiator to the aqueous solution of lignosulfonic acid, and then add the aqueous solution of maleic anhydride at a dropping rate of 20-50 drops / min with stirring at 35-60 °C, and continue to stir and react for at least 4 h.

4. The preparation method according to claim 1, characterized in that: The zinc salt includes at least one of zinc chloride, zinc sulfate, zinc acetate, and zinc nitrate.

5. The preparation method according to claim 1, wherein: The step of salting out and precipitating the reaction product is specifically to salt out and precipitate the reaction product by adding a weak base, and add the weak base until the pH of the reaction solution is 1.5-7.

6. The metal salt of maleic anhydride-modified lignosulfonic acid prepared by the preparation method of the compatibilizer for the metal salt of maleic anhydride-modified lignosulfonic acid according to claim 1.

7. The application of the metal salt of maleic anhydride-modified lignosulfonic acid as a compatibilizer according to claim 6.

8. A preparation method for compatibilizing PBAT / PLA composite films using the maleic anhydride-modified lignosulfonate metal salt described in claim 6, characterized in that It mainly includes the following steps: (1) By weight, mix the raw materials mainly including the following components as a mixture: 50-90 parts of PBAT, 10-50 parts of polylactic acid, 0.1-5 parts of the metal salt of maleic anhydride-modified lignosulfonic acid, wherein, PBAT and polylactic acid total 100 parts; (2) Melt-blend and film the mixture obtained in step (1) to prepare a PBAT / PLA composite film.

9. The preparation method according to claim 8, characterized in that: In step (2), the mixture is melt-blended and formed into a film. The melt blending is carried out by using a screw extruder, and the specific process parameters are: the temperatures of each zone are 130-180 °C respectively, and the screw speed is 180-200 rpm.

10. According to the preparation method described in claim 8, characterized in that: In step (2), the mixture is melt-blended and formed into a film. The film forming is carried out by blow molding with a blow molding machine, and the specific process parameters are: the temperatures of each zone are 150-180 °C respectively, and the screw speed is 30-50 rpm.

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