Preparation method of high-toughness degradable polylactic acid-based plastic

Abstract

The invention belongs to the technical field of preparation methods of polylactic acid-based plastics, and particularly relates to a preparation method of a high-toughness degradable polylactic acid-based plastic, which comprises the following production processes: proportioning corn starch, an iodomethyl ether etherification reagent, a dimethylformamide organic solvent, nano iron oxide, a plasticizer and PBS (Phosphate Buffer Solution), weighing raw materials, adding into a high-speed mixer, uniformly mixing, and granulating to obtain the high-toughness degradable polylactic acid-based plastic. Obtaining a mixture; putting the mixture into a hopper of a double-screw extruder, melting, plasticizing, mixing, extruding, water-cooling, bracing, pelletizing and drying the raw materials through the double-screw extruder to obtain the toughened polylactic acid composite material, and finally, the toughened polylactic acid composite material is used for preparing injection molding products, thin films, plastic products and the like. According to the invention, a dimethylformamide organic solvent and a lactic acid monomer obtained after hydrolysis and metabolism of corn starch are subjected to a copolymerization reaction to generate a lactic acid-amide copolymer, so that the tensile strength of the plastic is improved.

Description

Technical Field

[0001] The invention relates to the technical field of preparation methods of polylactic acid-based plastics, and in particular to a preparation method of high-toughness and degradable polylactic acid-based plastics. Background Art

[0002] Traditional plastics are not biodegradable in the natural environment and have gradually been regarded as one of the main factors of environmental pollution. In this context, the research and development of environmentally friendly plastics as new biodegradable materials is particularly important. This type of material uses the principle of biodegradation and can be decomposed by environmental microorganisms, showing characteristics that are more friendly to the ecological environment.

[0003] However, the industrialization process of environmentally friendly plastics still faces several technical bottlenecks. Specifically, the limitations of existing production processes lead to the common problems of high water solubility, insufficient mechanical strength and unsatisfactory degradation rate in products. High water solubility limits the stable use of materials under wet conditions and reduces the diversity of its application scenarios; low tensile strength affects the durability and load-bearing capacity of the product and weakens its market competitiveness; in addition, the non-optimization of degradation rate may not only lead to ineffective use of resources, but also may fail to meet the demand for rapid degradation to reduce environmental pollution in some cases.

[0004] In view of the above challenges, future research should focus on improving the synthesis path and material design of environmentally friendly plastics, aiming to improve their water resistance, enhance their mechanical properties, and precisely control their degradation kinetics to make them more in line with practical application needs. Such innovations have far-reaching significance for broadening the application scope of environmentally friendly plastics and promoting green and sustainable development;

[0005] Starch is a natural polymer second only to cellulose in production on Earth. It is abundant, renewable, and inexpensive. It can be used to produce starch-based plastics through modification and plasticization. As an important category of bio-based materials, starch-based plastics have been successfully industrialized and applied. Starch-based plastics are a type of plastic product made from starch as the main raw material, which is modified and plasticized and then blended with other polymers. Starch-based materials have different degrees of brittleness, poor mechanical properties, and easy water absorption due to different starch content, which limits their promotion and application in real life. Polylactic acid (PLA) is a biodegradable, renewable, eco-friendly, biocompatible and hydrophobic synthetic polymer. Common starch-based composite degradable plastics are obtained by blending starch with synthetic polymers (such as polyvinyl alcohol PVA, etc.), natural polymers (such as plant fibers, starch particles, bacterial cellulose, chitosan, etc.), other additives (such as clay, graphene, talc, etc.) and plasticizers to obtain starch-based composite degradable plastics. These plastics are fully biodegradable and can be used in a variety of fields such as packaging materials, food containers, disposable tableware, cushioning packaging materials, children's toys, etc.

[0006] Starch / PVA biodegradable plastics are blends of starch / PVA and plasticizers (formamide and urea) in different ratios. As the starch content increases, the fracture surface of the blend presents a rough surface, indicating that the composite has a tough fracture; the equilibrium water absorption decreases, and the tensile strength, elongation at break, and Young's modulus decrease; adding nanomaterials such as kaolin, clay, and talc to starch-based biodegradable materials can improve the hardness and water barrier properties of the material. Adding different corresponding functional materials to starch-based biodegradable materials according to usage requirements can realize its intelligent sensing of changes in the surrounding environment such as temperature, pH, brightness, humidity, and external stimuli; biodegradable plastics prepared by composite blending of starch and a variety of natural polymer compounds can effectively improve the mechanical properties of starch-based materials, and the addition of cellulose materials can improve the hydrophobicity of starch-based biodegradable plastics to a certain extent. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing a high-toughness degradable polylactic acid-based plastic, thereby solving the existing problems.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] Corn starch, iodomethyl ether etherification agent, dimethylformamide organic solvent, nano iron oxide, plasticizer and PBS are weighed according to numerical proportions and added into a high mixer to obtain a mixture; the mixture is put into a hopper of a twin-screw extruder, and the raw materials are melted, plasticized, mixed, extruded, water-cooled, stretched, pelletized and dried by the twin-screw extruder to obtain a toughened polylactic acid composite material; finally, the toughened polylactic acid composite material is used to prepare injection molded products and films.

[0010] Further, the mixture is added into a high-speed mixer, and the mixture is mixed at high speed for 6 minutes to 9 minutes.

[0011] Furthermore, the twin-screw extruder melts the raw materials at a temperature of 130°C to 185°C.

[0012] Furthermore, a connecting pipe is arranged outside the twin-screw extruder, an external thread is opened outside the connecting pipe, a shaping pipe is installed on the thread outside the connecting pipe, and the material diameter of the twin-screw extruder base is the same as the inner diameter of the shaping pipe.

[0013] Furthermore, the extruded material is water-cooled by spraying water, and the water can flow into the filter box after spraying, so that the water can be recycled for multiple times. After water cooling, it can be pelletized by a cutting device, and after pelletizing, the material can be air-dried by a fan.

[0014] Furthermore, the dimethylformamide organic solvent is copolymerized with the lactic acid monomer after hydrolysis and metabolism of corn starch to generate a lactic acid-amide copolymer.

[0015] Furthermore, a toughening agent may be added to the toughened polylactic acid composite material.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) By adding a toughening agent to polylactic acid, the melt strength and toughness of polylactic acid are effectively improved, and the processing properties of polylactic acid are improved;

[0018] (2) The raw material is mainly corn starch, which is safe, environmentally friendly, widely available, and low in cost. The corn starch is etherified by using an iodomethyl ether etherification reagent to introduce the methyl group in the iodomethyl ether into the starch molecule to form an ether bond, thereby producing methyl etherified starch, reducing the formation of hydrogen bonds between starch molecules, enhancing the mechanical strength of plastic products under humid conditions, and reducing their solubility in water;

[0019] (3) Dimethylformamide is used as an organic solvent to copolymerize with lactic acid monomers after hydrolysis and metabolism of corn starch to produce lactic acid-amide copolymers, thereby improving the tensile strength of the plastic. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] A method for preparing a highly tough and biodegradable polylactic acid-based plastic comprises the following steps: mixing corn starch, iodomethyl ether etherification reagent, dimethylformamide organic solvent, nano iron oxide, plasticizer and PBS numerically, weighing raw materials, adding the raw materials into a high-speed mixer, and obtaining a mixture; putting the mixture into a hopper of a twin-screw extruder, and using the twin-screw extruder to melt, plasticize, mix, extrude, water-cool, draw, pelletize and dry the raw materials, and obtaining a toughened polylactic acid composite material; and finally, the toughened polylactic acid composite material is used to prepare injection molded products and films.

[0023] In this embodiment,

[0024] The mixture is added into a high-speed mixer, and the mixture is mixed at high speed for 6 minutes to 9 minutes.

[0025] In this embodiment,

[0026] The twin-screw extruder melts the raw materials at a temperature of 130℃~185℃.

[0027] In this embodiment,

[0028] A connecting pipe is arranged outside the twin-screw extruder, an external thread is opened outside the connecting pipe, a shaping pipe is installed on the thread outside the connecting pipe, and the material diameter of the twin-screw extruder foundation is the same as the inner diameter of the shaping pipe.

[0029] In this embodiment,

[0030] The extruded material is water-cooled by spraying water, and the water can flow into the filter box after spraying, so that the water can be recycled for many times. After the water cooling is completed, it can be pelletized by a cutting device, and after the pelletizing is completed, the material can be air-dried by a fan.

[0031] In this embodiment,

[0032] The dimethylformamide organic solvent copolymerizes with the lactic acid monomer obtained by hydrolysis and metabolism of corn starch to form a lactic acid-amide copolymer.

[0033] In this embodiment,

[0034] A toughening agent may be added to the toughened polylactic acid composite material.

[0035] The implementation principle of one of the embodiments of the present application is: by adding a toughening agent to polylactic acid, the melt strength and toughness of polylactic acid are effectively improved, and the processing performance of polylactic acid is improved; the raw material is mainly corn starch, which is safe, environmentally friendly, widely available, and low in cost; the corn starch is etherified by using an iodomethyl ether etherification reagent, and the methyl group in the iodomethyl ether is introduced into the starch molecule to form an ether bond to produce methyl etherified starch, thereby reducing the formation of hydrogen bonds between starch molecules, enhancing the mechanical strength of plastic products under humid conditions, and reducing its solubility in water; dimethylformamide organic solvent is selected to copolymerize with the lactic acid monomer after hydrolysis and metabolism of corn starch to form a lactic acid-amide copolymer, thereby improving the tensile strength of the plastic.

[0036] The preparation method comprises the following steps: weighing raw materials according to a certain ratio of corn starch, iodomethyl ether etherification agent, dimethylformamide organic solvent, nano iron oxide, plasticizer and PBS, adding the raw materials into a high-speed mixer to obtain a mixture; putting the mixture into a hopper of a twin-screw extruder, melting, plasticizing, mixing, extruding, water-cooling, drawing, pelletizing and drying the raw materials through the twin-screw extruder to obtain a toughened polylactic acid composite material; finally, the toughened polylactic acid composite material is used to prepare injection molded products and films.

[0037] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0038] The above is a detailed introduction to the preparation method of a high-toughness biodegradable polylactic acid-based plastic provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above examples is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a highly tough and degradable polylactic acid-based plastic, characterized in that: Corn starch, iodomethyl ether etherification agent, dimethylformamide organic solvent, nano iron oxide, plasticizer and PBS are weighed according to numerical proportions and added into a high mixer to obtain a mixture; the mixture is put into a hopper of a twin-screw extruder, and the raw materials are melted, plasticized, mixed, extruded, water-cooled, stretched, pelletized and dried by the twin-screw extruder to obtain a toughened polylactic acid composite material; finally, the toughened polylactic acid composite material is used to prepare injection molded products and films.

2. The method for preparing a highly tough and degradable polylactic acid-based plastic according to claim 1, characterized in that: The mixture is added into a high-speed mixer, and the mixture is mixed at high speed for 6 minutes to 9 minutes.

3. The method for preparing a highly tough and degradable polylactic acid-based plastic according to claim 1, characterized in that: The twin-screw extruder melts the raw materials at a temperature of 130°C to 185°C.

4. The method for preparing a highly tough and degradable polylactic acid-based plastic according to claim 1, characterized in that: A connecting pipe is arranged outside the twin-screw extruder, an external thread is opened outside the connecting pipe, a shaping pipe is installed on the thread outside the connecting pipe, and the material diameter of the twin-screw extruder foundation is the same as the inner diameter of the shaping pipe.

5. The method for preparing a highly tough and degradable polylactic acid-based plastic according to claim 1, characterized in that: The extruded material is water-cooled by spraying water, and the water can flow into the filter box after spraying, so that the water can be recycled for multiple times. After the water cooling is completed, it can be pelletized by a cutting device, and after the pelletizing is completed, the material can be air-dried by a fan.

6. The method for preparing a highly tough and degradable polylactic acid-based plastic according to claim 1, characterized in that: The dimethylformamide organic solvent and the lactic acid monomer obtained by hydrolysis and metabolism of corn starch undergo copolymerization reaction to generate a lactic acid-amide copolymer.

7. The method for preparing a highly tough and degradable polylactic acid-based plastic according to claim 1, characterized in that: A toughening agent may be added to the toughened polylactic acid composite material.