1. The graft copolymerization-blending high impact polylactic acid is characterized in that the high impact polylactic acid is a mixture of a hydroxylated rubber-g-polylactic acid graft copolymer and a polylactic acid homopolymer, wherein the mass fraction of the hydroxylated rubber-g-polylactic acid graft copolymer is 5-30%, and the balance is the polylactic acid homopolymer; g represents grafting.

2. The graft copolymerization-blended high impact polylactic acid according to claim 1, wherein the hydroxylated rubber-g-polylactic acid graft copolymer has a comb-like structure, the hydroxylated rubber is a main chain, and the polylactic acid is a branched chain; the molecular weight of the polylactic acid homopolymer is 3-30 ten thousand.

3. The graft copolymerization-blending high impact polylactic acid according to claim 2, wherein the mass fraction of the hydroxylated rubber-g-polylactic acid graft copolymer is 10 to 25 percent, and the molecular weight of the polylactic acid homopolymer is 10 to 20 ten thousand.

4. A preparation method of graft copolymerization-blending high impact polylactic acid is characterized by mainly comprising the following steps:

s1, synthetic hydroxylated rubber: the hydroxylated rubber is a hydroxylated product of rubber and is synthesized by adopting a traditional in-situ peroxyformic acid method;

s2, synthesizing high impact polylactic acid: firstly, adding the hydroxylated rubber and the monomer lactide prepared in the last step into an anhydrous oxygen-free reaction kettle with mechanical stirring, wherein the mass ratio of the hydroxylated rubber to the lactide is 1: 3-19, heating to the polymerization temperature of 100-140 ℃, completely dissolving the hydroxylated rubber in the lactide under mechanical stirring at 40-200r/min, and then adding a small-molecule initiator and a catalyst for reaction for 2-10 h.

5. The preparation method of the graft copolymerization-blending high impact polylactic acid according to claim 4, wherein the amount of the small molecule initiator is 0.002-0.2 times of the amount of the lactide substance.

6. The method for preparing graft copolymerization-blended high impact polylactic acid according to claim 4, wherein: the rubber is at least one of homopolymer, copolymer or blend of rubber containing C-C bond, the molecular weight of the rubber is 2-20 ten thousand, the hydroxylation degree of the hydroxylated rubber is 3-30%, and the glass transition temperature is-30 to-115 ℃.

7. The method for preparing graft copolymerization-blended high impact polylactic acid according to claim 6, wherein: the molecular weight of the homopolymer, copolymer or blend of the rubber is 2-20 ten thousand, the hydroxylation degree of the hydroxylated rubber is 5-15%, and the glass transition temperature is-65 to-95 ℃; the dosage of the small molecular initiator is 0.02-0.15 times of that of the lactide substance.

8. The preparation method of the graft copolymerization-blending high impact polylactic acid according to any one of claims 4 to 7, characterized in that: the rubber is selected from at least one of polybutadiene, polyisoprene and polylaurene; the small molecular initiator is selected from at least one of benzyl alcohol, pentaerythritol and cyclodextrin; the catalyst is at least one of stannous octoate and stannic chloride.

9. The method for preparing graft copolymerization-blended high impact polylactic acid according to claim 8, wherein: the mass ratio of the hydroxylated rubber to the lactide is 1: 7-15, preferably 1: 10; the polymerization temperature is 110-120 ℃; the reaction time is 4-8 or 9-10 hours.

10. The method for preparing graft copolymerization-blended high impact polylactic acid according to claim 8, wherein: the stirring speed is 80-150r/min, and the reaction time is 9-10 hours.

Background

Global supply of petroleum resources is becoming more and more intense, and under the condition that environmental problems caused by synthetic polymers using petroleum as raw materials are becoming more and more prominent, the demand of ecological environment polymers is rapidly increasing. Under the large background of 'carbon peak reaching and carbon neutralization' provided by China, the development of ecological environment macromolecules meets important opportunities and challenges under the requirement of national construction of 'resource-saving and environment-friendly society'. Polylactic acid (PLA) is a novel degradable polymer material, is an important member in ecological environment polymer materials, and can play a positive role in coping with global energy shortage, environmental pollution, climate warming and other crises. At present, the application of PLA is expanded from the fields of biomedicine, food packaging and the like to the fields of automobiles, electronics, aviation and the like, and higher and more comprehensive requirements are put forward on the performance of materials. PLA has strong rigidity, but has poor toughness and ductility, the notch impact strength is only-30J/m, the application range of the PLA is severely limited, and the improvement of the toughness of the PLA material is one of the important research points in the field of PLA modification. The research and development of high-performance polylactic acid materials and key preparation technologies have great value and practical significance to the development of ecological environment macromolecules.

In the prior art, PLA modification usually improves the toughness of PLA by introducing a flexible component such as rubber into the PLA through a copolymerization or blending method. The copolymerization modification is easy to regulate and control the composition and microstructure of the copolymer, but the polymerization process is relatively complex. Compared with copolymerization modification, blending modification is simpler and more direct, but is slightly insufficient in microstructure regulation. Most rubbers are poorly compatible with PLA, and a third component compatibilization is required to improve the compatibility of the rubber with PLA. However, the phase structure of the polymer blend is influenced by multiple factors such as thermodynamics, kinetics, preparation method and process conditions, and the blending method can only regulate and control the size and the rule degree of the dispersed phase particles within a certain range, and can not change the 'sea-island' phase structure. In addition, in order to make the material achieve brittle-tough transition, the addition amount of the rubber is larger, so that the rigidity of the impact-resistant polylactic acid is greatly reduced, and the development and the application of the impact-resistant polylactic acid are adversely affected.

Therefore, if a polylactic acid which is simple in preparation process and can remarkably improve the impact resistance can be developed, the application prospect of the polylactic acid can be greatly expanded.

Disclosure of Invention

In order to solve the problem of application limitation caused by weak impact resistance of polylactic acid in the prior art, the invention provides graft copolymerization-blending high impact polylactic acid and a preparation method thereof,

mainly uses hydroxylated rubber and micromolecular initiator to initiate lactide ring-opening polymerization together, and the prepared high impact polylactic acid is a mixture of hydroxylated rubber-g-polylactic acid graft copolymer and polylactic acid homopolymer. The method is a bulk polymerization method, does not contain solvent, does not have the problems of solvent recovery and solvent residue, and has pure product; the prepared high impact polylactic acid has the characteristics of high molecular weight, high impact resistance and high strength, is a degradable high polymer material, and has the characteristics of simple reaction system and suitability for industrial production.

In order to realize the purpose of the invention, the technical scheme of the invention is as follows:

in a first aspect, the invention provides a graft copolymerization-blending high impact polylactic acid, which is a mixture of a hydroxylated rubber-g-polylactic acid graft copolymer and a polylactic acid homopolymer, wherein the mass fraction of the hydroxylated rubber-g-polylactic acid graft copolymer is 5% -30%, and the balance is the polylactic acid homopolymer; g represents grafting.

Further, the hydroxylated rubber-g-polylactic acid graft copolymer has a comb-shaped structure, the hydroxylated rubber is a main chain, and the polylactic acid is a branched chain.

Further, the molecular weight of the polylactic acid homopolymer is 3 to 30 ten thousand.

Further, the mass fraction of the hydroxylated rubber-g-polylactic acid graft copolymer is 10-25%, and the molecular weight of the polylactic acid homopolymer is 10-20 ten thousand.

On the other hand, the invention provides a simple and efficient preparation method of the graft copolymerization-blending high-impact polylactic acid, which mainly adopts a graft copolymerization-blending method and comprises two parts of the synthesis of hydroxylated rubber and the synthesis of the high-impact polylactic acid.

A preparation method of graft copolymerization-blending high impact polylactic acid mainly comprises the following steps:

s1, synthetic hydroxylated rubber: the hydroxylated rubber is a hydroxylated product of rubber and is synthesized by adopting a traditional in-situ peroxyformic acid method;

s2, synthesizing high impact polylactic acid: firstly, adding the hydroxylated rubber and the monomer lactide prepared in the last step into an anhydrous oxygen-free reaction kettle with mechanical stirring, wherein the mass ratio of the hydroxylated rubber to the lactide is 1: 3-19, heating to the polymerization temperature of 100-.

Further, the dosage of the small molecule initiator is 0.002-0.2 times of the amount of the lactide substance.

Further, the rubber is selected from homopolymers, copolymers or blends of rubbers containing C ═ C bonds, the molecular weight is 2 to 20 ten thousand, the degree of hydroxylation of the hydroxylated rubber is 3 to 30%, and the glass transition temperature is-30 to-115 ℃.

Furthermore, the molecular weight of the homopolymer, the copolymer or the blend of the rubber is 2-20 ten thousand, the hydroxylation degree of the hydroxylated rubber is 5-15%, and the glass transition temperature is-65 ℃ to-95 ℃.

Further, the amount of the small molecule initiator is 0.02-0.15 times of the amount of the lactide substance.

Further, the rubber is selected from at least one of polybutadiene, polyisoprene and polylaurene.

Further, the small molecule initiator is selected from at least one of benzyl alcohol, pentaerythritol and cyclodextrin.

Further, the catalyst is at least one of stannous octoate and stannic chloride.

Further, the mass ratio of the hydroxylated rubber to the lactide is 1: 7-15, and the polymerization temperature is 110-120 ℃; the reaction time is 4-8.

Further, the mass ratio of the hydroxylated rubber to the lactide is 1: 10.

further, the stirring speed is 80-150r/min, and the reaction time is 9-10 hours.

The raw materials or reagents involved in the invention are all common commercial products, and the operations involved are all routine operations in the field unless otherwise specified.

The above-described preferred conditions may be combined with each other to obtain a specific embodiment, in accordance with common knowledge in the art.

The invention has the beneficial effects that:

the invention discloses graft copolymerization-blending high impact polylactic acid and a preparation method thereof based on a graft copolymerization-blending method.

The invention adopts graft copolymerization-blending method to prepare the ultra-high impact polylactic acid. Graft co-blending is a very advanced process for the preparation of multicomponent polymers which usually have a "cellular" phase structure, also known as a "sausage" phase structure, due to the phase inversion that occurs during the polymerization process. The formation of the graft copolymer improves the compatibility between the multicomponent polymers and enhances the force between the rubber phase and the resin phase. In addition, the rubber phase particles contain a large amount of resin inclusions, which not only increases the volume fraction of the rubber phase at the same rubber content, but also reinforces the rubber particles. When the material is impacted, rubber particles containing a large amount of resin inclusions are elongated under the action of external force, the resin inclusions in the particles are basically not deformed due to high modulus, the rubber is partially subjected to microfibrillation, and harmful cavities cannot be generated due to the obstruction of the contained resin particles. Therefore, the special structure gives better toughening effect to the rubber particles. Research shows that when the same impact strength is achieved, the amount of rubber required by the graft copolymerization-blending method is far lower than that of the traditional physical blending method, and meanwhile, the tensile strength and tensile modulus of the material are maintained to a higher degree.

Drawings

FIG. 1 is a schematic diagram of a preparation process for preparing high impact polylactic acid by graft copolymerization-blending.

Detailed Description

In order that the above objects, features and advantages of the present invention may be more clearly understood, a solution of the present invention will be further described below. It should be noted that the embodiments of the present invention and features of the embodiments may be combined with each other without conflict.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those described herein; it is to be understood that the embodiments described in this specification are only some embodiments of the invention, and not all embodiments.

Preferred embodiments of the present invention will be described in detail with reference to the following examples. It is to be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the present invention. Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the spirit and scope of this invention.

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

In the embodiment of the invention, a nuclear magnetic resonance spectrometer, a Gel Permeation Chromatograph (GPC) and a Differential Scanning Calorimeter (DSC) are respectively adopted for detecting the hydroxylation degree, the molecular weight and the glass transition temperature.

The specific test method can refer to academic papers (Wang Yan color, research on epoxidized elastomer/thermoplastic resin toughened polylactic acid, university of great design, 2017; research on high-definition, linear/star amphiphilic double-grafted polymer, university of great design, 2013.)

Examples

The preparation of the graft copolymerization-blending high impact polylactic acid comprises two parts of the synthesis of hydroxylated rubber and the synthesis of the high impact polylactic acid. The first step is as follows: and (3) synthesizing hydroxylated rubber. Synthetic references for hydroxylated rubbers (high definition, study of linear/star amphiphilic double graft polymers, university of great graduate, 2013), all made by the laboratory, the type and main structural parameters of the hydroxylated rubbers are shown in table 1 below.

TABLE 1 hydroxylated rubber Main structural parameters Table

And secondly, synthesizing the high impact polylactic acid. The synthesis of the high impact polylactic acid is carried out in a small anhydrous and oxygen-free reaction kettle with mechanical stirring. Firstly, adding hydroxylated rubber and monomer lactide into a reaction kettle, heating to a polymerization temperature, completely dissolving the hydroxylated rubber in the lactide under mechanical stirring, and then adding a small-molecule initiator and a catalyst to react until the lactide is completely converted. The raw material ratios and process parameters are shown in Table 2, and the product properties are shown in Table 3. It can be seen that the high impact polylactic acid prepared by the method of the present application has impact strength increased by more than 6 times, elongation at break increased by more than 10 times, and significantly improved performance.

TABLE 2 comparison table of graft copolymer-blend high impact polylactic acid synthesized under different raw material parameters and process conditions

TABLE 3 comparison table of properties of graft copolymerization-blending high impact polylactic acid

High impact polylactic acid	Impact strength J/m	Tensile strength/MPa	Elongation at break
				Polylactic acid	30	70	<10％
Example 1	432	61	190％
				Example 2	535	52	255％
Example 3	586	51	320％
				Example 4	191	63	108％
Example 5	397	62	165％

The foregoing are merely exemplary embodiments of the present invention, which enable those skilled in the art to understand or practice the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.