Resin microsphere-modified polylactic acid oligomer and polylactic acid composite material

Abstract

The present invention discloses a polylactic acid oligomer modified with resin microspheres and a polylactic acid composite material. Lactide monomer is used as a starting material, resin microspheres are used as an initiator, and under the action of a specific catalyst, a ring-opening polymerization reaction is triggered to generate a branched structure of dehydrated lactic acid repeating units. The alcoholic hydroxyl groups at different positions in the resin microsphere initiator provide chain growth centers, thereby realizing the synthesis of the polylactic acid oligomer modified with resin microspheres. The polylactic acid composite material is prepared by blending 1-15% by mass of the polylactic acid oligomer modified with resin microspheres and 85-99% by mass of commercial polylactic acid. The excellent heterogeneous nucleation ability of the polylactic acid oligomer modified with resin microspheres can promote the crystallization of commercial polylactic acid and achieve reinforcement. This achieves the simultaneous reinforcement and toughening of commercial polylactic acid with a single component without adding additional components such as compatibilizers.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, in particular to a polylactic acid oligomer modified with resin microspheres and a polylactic acid composite material. Background Art

[0002] Biomass-based polylactic acid (PLA), a thermoplastic polyester made from renewable resources, has been widely used in disposable tableware and packaging due to its excellent biodegradability and non-toxicity. Furthermore, due to its excellent mechanical strength, PLA is also widely used to develop durable structural products in engineering applications. However, PLA's brittleness and low impact strength severely limit its widespread use as a durable material.

[0003] Currently, chemical modification and physical blending are the main methods for improving the toughness of polylactic acid (PLA). Chemical modification involves incorporating flexible molecular chains into PLA through copolymerization or grafting reactions to achieve toughening. However, the modification process is typically complex, expensive, and time-consuming. In contrast, physical blending is a more direct and accessible method, increasing the toughness of PLA by introducing plasticizers, rigid fillers, flexible polymers or rubbers, and multibranched homogeneous polymers. However, physical blending also has certain limitations. For example, plasticizers can migrate to the surface of PLA products over long-term use, causing embrittlement. While rigid fillers, flexible polymers, or rubbers cannot migrate, their compatibility with the PLA matrix is ​​poor, resulting in reduced mechanical strength and modulus of PLA products. Homogeneously branched polymers composed of dehydrated lactic acid units exhibit good compatibility with the PLA matrix, and their large free volume facilitates the migration of PLA chains, achieving toughening. However, these methods inevitably sacrifice mechanical strength to some extent. Therefore, simultaneous strengthening and toughening of PLA remains a challenge. Summary of the Invention

[0004] The object of the present invention is to provide a polylactic acid oligomer modified with resin microspheres and a polylactic acid composite material, which solves the problem that when existing polymers containing dehydrated lactic acid units are used for PLA modification, the toughness increases but the strength decreases as the addition amount increases.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A polylactic acid oligomer modified with resin microspheres, and a preparation method thereof is as follows:

[0007] a) taking lactide monomer, resin microsphere initiator and catalyst and melting them at 100-120° C. to obtain a mixture, wherein the molar ratio of alcoholic hydroxyl group in the resin microsphere initiator to lactide monomer is 1-15:100;

[0008] b) reacting the mixture obtained in step a) at 115-130° C. under an inert gas atmosphere with stirring to obtain a crude product;

[0009] c) cooling, purifying, and drying the crude product obtained in step b) to obtain a resin microsphere-modified polylactic acid oligomer;

[0010] The resin microspheres are phenolic resin microspheres containing multiple alcoholic hydroxyl initiating groups.

[0011] The preparation method of a resin microsphere-modified polylactic acid oligomer uses lactide monomer as the starting material. Under the action of an initiator and catalyst, the monomer triggers a ring-opening polymerization mechanism to generate a branched structure of dehydrated lactic acid repeating units. Alcoholic hydroxyl groups at different positions in the resin microsphere initiator provide branch growth centers, thereby achieving the synthesis of the resin microsphere-modified polylactic acid oligomer. During the process, the degree of polymerization of the dehydrated lactic acid repeating units is adjusted by adjusting the molar ratio of the alcoholic hydroxyl groups to the lactide monomer in the resin microsphere initiator. The structure of the resin microsphere-modified polylactic acid oligomer is adjusted by selecting resin microspheres with different structures, achieving diversified adjustment. The degree of polymerization of the branched polylactic acid oligomer of the resin microsphere-modified polylactic acid oligomer is 63-91, corresponding to a single-arm number-average molecular weight of 1,000-10,000 g / mol. Preferably, the degree of polymerization is 55-90, and the single-arm number-average molecular weight is 4,000-6,500 g / mol. The ring-opening polymerization reaction of the present invention belongs to the coordination-insertion polymerization mechanism, the reaction system is mild and efficient, with few side reactions, and the relative molecular weight distribution of the obtained resin microsphere-modified polylactic acid oligomer is narrow, which can realize the controllable polymerization of polylactic acid with a specific structure.

[0012] Specifically, step b) is carried out at 115-130° C. for 12-48 hours.

[0013] Specifically, in step c), the crude product obtained in step b) is cooled, dissolved in dichloromethane, purified by precipitation with icy methanol, and vacuum dried at 40-50° C. for 24-48 hours.

[0014] The resin microspheres are phenolic resin microspheres containing multiple alcoholic hydroxyl initiating groups synthesized by a hydrothermal reaction of a phenolic compound and formaldehyde (or hexamethylenetetramine) at 80-170°C. They are prepared using a publicly available method. The phenolic compound is an organic substance containing phenolic hydroxyl groups, including but not limited to one or more of phenol, catechol, resorcinol, xylenol, catechin, and gallic acid. The phenolic resin microspheres include but are not limited to one or more of xylenol-formaldehyde resin microspheres, catechin-formaldehyde resin microspheres, gallic acid-formaldehyde resin microspheres, phenol-formaldehyde resin microspheres, catechol-formaldehyde resin microspheres, and resorcinol-formaldehyde resin microspheres.

[0015] The specific preparation method of formaldehyde-phenol resin microspheres is to prepare PFM through a simple one-step hydrothermal method. Phenol and hexamethylenetetramine are dissolved in deionized water (400mL) containing the surfactant polyethylene glycol (0.02g) at a molar ratio of 2:1, and magnetic stirring is carried out at room temperature for 20 minutes. The prepared solution is poured into a hydrothermal reactor and sealed, and the reaction is carried out at 160°C for 6 hours. After cooling to room temperature, the reaction product is collected to obtain phenolic resin microspheres. Among them, hexamethylenetetramine decomposes into formaldehyde and ammonia when heated, which is conducive to the phenolic reaction.

[0016] The lactide monomer is any one of L-lactide, D-lactide and meso-lactide.

[0017] The catalyst is 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), any one of stannous octoate, stannous chloride, cycloalkoxytin, lithium chloride, and aluminum isopropoxide. The molar ratio of the catalyst to the lactide monomer is 1-5:1000. The catalyst used in the present invention has high catalytic activity, mild reaction conditions, short reaction time, high conversion rate, low catalyst dosage, no organic solvent is used in the synthesis process, no yield and cost loss caused by solvent volatilization, good economic benefit, high controllability, convenient production and adjustment, good applicability to different conventional commercial polylactic acids, and can effectively promote the development and application of polylactic acid in the field of engineering materials.

[0018] A polylactic acid composite material is prepared by blending 1-15% by mass of a polylactic acid oligomer modified with resin microspheres and 85-99% by mass of commercial polylactic acid.

[0019] It should be noted that the resin microsphere-modified polylactic acid oligomer and commercial polylactic acid are vacuum-dried at 70-90° C. for 12-24 hours before blending to remove moisture and prevent moisture from affecting subsequent processing.

[0020] It should be noted that the blending process includes but is not limited to one or more of casting, injection molding, foaming, and phase separation.

[0021] Preferably, the number average molecular weight of the commercial polylactic acid is 8-15×10 4 The commercial polylactic acid of the present invention is conventional linear polylactic acid, which is cheap, has many sources, is easily available, and is convenient for application.

[0022] The beneficial effects of the present invention are as follows: resin microspheres with abundant alcohol hydroxyl initiation sites are used as initiators to react with lactide monomers to synthesize resin microsphere-modified polylactic acid oligomers; during blending and modification, the branched structure of the resin microsphere-modified polylactic acid oligomer can destroy the chain entanglement structure of linear polylactic acid; its unique topological structure can generate a larger free volume to promote the movement of linear polylactic acid molecular chains, achieve plasticization, and thus improve the toughness of commercial polylactic acid; on the other hand, due to its excellent heterogeneous nucleation ability, it can promote the crystallization of commercial polylactic acid and achieve reinforcement, thereby achieving the simultaneous reinforcement and toughening of commercial polylactic acid without adding additional components such as compatibilizers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the reaction equation for preparing the resin microsphere-modified polylactic acid oligomer in Example 1.

[0024] Figure 2 This is the reaction equation for preparing the resin microsphere-modified polylactic acid oligomer in Example 2.

[0025] Figure 3 This is the reaction equation for preparing the resin microsphere-modified polylactic acid oligomer in Example 3.

[0026] Figure 4 These are the elongation at break and yield strength of the reinforced and toughened polylactic acid composite material prepared in Example 1.

[0027] Figure 5 The toughness work and Young's modulus of the reinforced and toughened polylactic acid composite material prepared in Example 1.

[0028] Figure 6 The notched impact strength and unnotched impact strength of the reinforced and toughened polylactic acid composite material prepared in Example 1 are shown.

[0029] Figure 7 This is a physical picture of the polylactic acid oligomer initiated by catechol-formaldehyde resin microspheres prepared in Example 2.

[0030] Figure 8 This is the H-NMR spectrum of the resin microsphere-modified polylactic acid oligomer PFM-OLLA prepared in Example 1.

[0031] Figure 9 The polymerization degree of PFM-OLLA prepared at different molar ratios of alcoholic hydroxyl group and lactide monomer in Example 1 is shown.

[0032] Figure 10 This is a physical picture of the polylactic acid oligomer modified with xylenol-formaldehyde resin microspheres prepared in Example 4. DETAILED DESCRIPTION

[0033] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] Example 1

[0035] The present embodiment relates to a method for preparing a reinforced and toughened polylactic acid, comprising the following steps:

[0036] S1 Preparation of polylactic acid oligomer modified with resin microspheres

[0037] a) melt-mixing a monomer (L-lactide), an initiator (phenol-formaldehyde resin microspheres), and a catalyst (stannous octoate) at 120° C. to obtain a mixed system, wherein the molar ratio of the alcoholic hydroxyl group in the initiator to the lactide monomer is 2.5:100, and the molar ratio of the stannous octoate to the lactide monomer is approximately 1:1000;

[0038] The specific preparation method of formaldehyde-phenol resin microspheres is to prepare PFM through a simple one-step hydrothermal method. Phenol and hexamethylenetetramine are dissolved in deionized water (400mL) containing the surfactant polyethylene glycol (0.02g) at a molar ratio of 2:1, and magnetic stirring is carried out at room temperature for 20 minutes. The prepared solution is poured into a hydrothermal reactor and sealed, and the reaction is carried out at 160°C for 6 hours. After cooling to room temperature, the reaction product is collected to obtain phenolic resin microspheres. Among them, hexamethylenetetramine decomposes into formaldehyde and ammonia when heated, which is conducive to the phenolic reaction.

[0039] b) subjecting the mixed system obtained in step a) to a vacuum-nitrogen filling treatment for three cycles, and then reacting in an oil bath at 120° C. under a nitrogen atmosphere and magnetic stirring for 36 hours to obtain a crude product;

[0040] c) The crude product obtained in step b) was cooled, dissolved in dichloromethane, purified by precipitation with icy methanol, and vacuum dried at 40° C. for 24 h to obtain a polylactic acid oligomer PFM modified with resin microspheres. 2.5 -OLLA;

[0041] S2: Polylactic acid oligomer PFM modified with resin microspheres obtained in step S1 2.5 -OLLA mass percentages are 0%, 2%, 4%, 6% and 8% respectively, and the rest is commercial polylactic acid weighed as raw material;

[0042] S3 takes the resin microsphere modified polylactic acid oligomer and commercial polylactic acid weighed in S2, vacuum-dries them at 80°C for 18 hours, mixes and stirs them evenly, and adds them to a preheated torque rheometer for melt mixing at a mixing temperature of 180°C, a mixing speed of 40 r / min, and a mixing time of 10 minutes. Cool and pelletize to obtain modified polylactic acid masterbatch;

[0043] S4: The polylactic acid masterbatch obtained in step S3 is processed in an injection molding machine at a melting temperature of 190° C. to obtain a polylactic acid composite material.

[0044] During the experiment, under the same other conditions, the molar ratio of the alcohol hydroxyl group to the lactide monomer in the initiator was adjusted to 1:100, 2.5:100, 5:100 and 15:100, respectively, and resin microsphere-modified polylactic acid oligomers with good performance were obtained.

[0045] Figure 4-5 The elongation at break, yield strength, toughness work and Young's modulus of the reinforced and toughened polylactic acid obtained under different contents of polylactic acid oligomer modified with resin microspheres prepared in Example 1. It can be seen that the yield strength of pure PLA is 27.9MPa, and the addition of PFM 2.5 -After OLLA, PFM 2.5 -The yield strength of OLLA / PLA composites has been effectively improved. Due to the inherent brittleness of pure PLA, its elongation at break is only 15.2%, while PFM 2.5 -The elongation at break of OLLA / PLA composite materials is above 60.0%. 2.5 -The addition of OLLA enhances the toughness of PLA while increasing its strength. 2.5 -The Young's modulus of OLLA / PLA composites is higher than that of pure PLA (~688.0MPa). 2.5 The strengthening and toughening mechanism of -OLLA in composites may be due to its rigid PFM component increasing the overall stiffness of the composite, its heterogeneous nucleation ability increasing the nucleation density and reducing the spherulite size, and its multi-arm structure with a large free volume enhancing the chain mobility and promoting the growth of spherulites, thereby improving the crystallization properties of the composite and achieving both strengthening and toughening.

[0046] Figure 6 The notched impact strength and unnotched impact strength of the toughened PLA obtained at different contents of PLA oligomer modified with resin microspheres prepared in Example 1. It can be seen that the unnotched and notched impact strengths of pure PLA are only 10.4 and 3.0 kJ / m respectively. 2 PFM 2.5The addition of -OLLA significantly improves the unnotched and notched impact strength of the composites. This result confirms that PFM 2.5 -OLLA toughening effect on PLA matrix.

[0047] Figure 7 This is the H NMR spectrum of the polylactic acid oligomer PFM-OLLA modified with resin microspheres prepared in Example 1. Utilizing the polyhydroxy characteristics of the resin microspheres PFM, the synthesized PFM-OLLA exhibits a multi-arm structure. The average degree of polymerization (DP) of L-lactide L-LA on each arm was obtained based on the integrated area (I) of the methyl proton peak at 5.20 ppm (Ia) and 4.3 ppm (Ia'), and the single-arm number average molecular weight was further calculated based on the DP.

[0048] Example 2

[0049] The present embodiment relates to a method for preparing a reinforced and toughened polylactic acid, comprising the following steps:

[0050] S1 Preparation of polylactic acid oligomer modified with resin microspheres

[0051] a) melt-mixing a monomer (L-lactide), an initiator (catechol-formaldehyde resin microspheres), and a catalyst (stannous chloride) at 120° C. to obtain a mixed system, wherein the molar ratio of the alcoholic hydroxyl group in the initiator to the lactide monomer is 1:100, and the molar ratio of stannous octoate to the lactide monomer is approximately 1:1000;

[0052] b) subjecting the mixed system obtained in step a) to a vacuum-nitrogen filling treatment for three cycles, and then reacting in an oil bath at 120° C. under a nitrogen atmosphere and magnetic stirring for 36 hours to obtain a crude product;

[0053] c) cooling the crude product obtained in step b), dissolving it in dichloromethane, purifying it by precipitation with icy methanol, and vacuum drying it at 40° C. for 24 hours to obtain a polylactic acid oligomer modified with resin microspheres;

[0054] S2 weighs the raw materials according to the following weight percentages: 4% of the polylactic acid oligomer modified with the resin microspheres obtained in step S1 and 96% of commercial polylactic acid;

[0055] S3 takes the resin microsphere-modified polylactic acid oligomer and commercial polylactic acid weighed in S2, and vacuum-dries them at 80°C for 18 hours, mixes them, stirs them evenly, dissolves them in dichloromethane, and after mixing them evenly, casts them into a glass mold, and evaporates them in vacuum at 40°C for 24 hours to obtain a polylactic acid composite material.

[0056] Example 3

[0057] The present embodiment relates to a method for preparing a reinforced and toughened polylactic acid, comprising the following steps:

[0058] S1 Preparation of polylactic acid oligomer modified with resin microspheres

[0059] a) melt-mixing a monomer (meso-lactide), an initiator (resorcinol-formaldehyde resin microspheres), and a catalyst (tin cycloalkoxide) at 120° C. to obtain a mixed system, wherein the molar ratio of the alcoholic hydroxyl group in the initiator to the lactide monomer is 1:100, and the molar ratio of stannous octoate to the lactide monomer is approximately 1:1000;

[0060] b) subjecting the mixed system obtained in step a) to a vacuum-nitrogen filling treatment for three cycles, and then reacting in an oil bath at 120° C. under a nitrogen atmosphere and magnetic stirring for 36 hours to obtain a crude product;

[0061] c) cooling the crude product obtained in step b), dissolving it in dichloromethane, purifying it by precipitation with icy methanol, and vacuum drying it at 40° C. for 24 hours to obtain a polylactic acid oligomer modified with resin microspheres;

[0062] S2 weighs the raw materials according to the following weight percentages: 15% of the polylactic acid oligomer modified with the resin microspheres obtained in step S1 and 85% of commercial polylactic acid;

[0063] S3 takes the resin microsphere-modified polylactic acid oligomer and commercial polylactic acid weighed in S2, and vacuum-dries them at 80°C for 18 hours, mixes them, stirs them evenly, dissolves them in dichloromethane, and after mixing them evenly, casts them into a glass mold, and evaporates them in vacuum at 40°C for 24 hours to obtain a polylactic acid composite material.

[0064] Example 4

[0065] The present embodiment relates to a method for preparing a reinforced and toughened polylactic acid, comprising the following steps:

[0066] S1 Preparation of polylactic acid oligomer modified with resin microspheres

[0067] a) melt-mixing a monomer (L-lactide), an initiator (xylenol-formaldehyde resin microspheres), and a catalyst (stannous octoate) at 100° C. to obtain a mixed system, wherein the molar ratio of the alcoholic hydroxyl group in the initiator to the lactide monomer is 5:100, and the molar ratio of the stannous octoate to the lactide monomer is approximately 3:1000;

[0068] b) subjecting the mixed system obtained in step a) to a vacuum-nitrogen filling treatment for three cycles, and then reacting in an oil bath at 115° C. under a nitrogen atmosphere and magnetic stirring for 36 hours to obtain a crude product;

[0069] c) cooling the crude product obtained in step b), dissolving it in dichloromethane, purifying it by precipitation with icy methanol, and vacuum drying it at 40° C. for 48 hours to obtain a polylactic acid oligomer modified with resin microspheres;

[0070] S2 weighs the raw materials according to the following weight percentages: 15% of the polylactic acid oligomer modified with the resin microspheres obtained in step S1 and 85% of commercial polylactic acid;

[0071] S3 takes the resin microsphere modified polylactic acid oligomer and commercial polylactic acid weighed in S2, vacuum-dries them at 80°C for 18 hours, mixes and stirs them evenly, and adds them to a preheated torque rheometer for melt mixing at a mixing temperature of 180°C, a mixing speed of 40 r / min, and a mixing time of 10 minutes. Cool and pelletize to obtain modified polylactic acid masterbatch;

[0072] S4: The polylactic acid masterbatch obtained in step S3 is processed in an injection molding machine at a melting temperature of 190° C. to obtain a polylactic acid composite material.

[0073] Example 5

[0074] The present embodiment relates to a method for preparing a reinforced and toughened polylactic acid, comprising the following steps:

[0075] S1 Preparation of polylactic acid oligomer modified with resin microspheres

[0076] a) melt-mixing a monomer (L-lactide), an initiator (catechin-formaldehyde resin microspheres), and a catalyst (stannous octoate) at 110° C. to obtain a mixed system, wherein the molar ratio of the alcoholic hydroxyl group in the initiator to the lactide monomer is 5:100, and the molar ratio of the stannous octoate to the lactide monomer is approximately 3:1000;

[0077] b) subjecting the mixed system obtained in step a) to a vacuum-and-nitrogen treatment cycle three times, and then reacting in an oil bath at 130° C. under a nitrogen atmosphere and magnetic stirring for 12 hours to obtain a crude product;

[0078] c) cooling the crude product obtained in step b), dissolving it in dichloromethane, purifying it by precipitation with icy methanol, and vacuum drying it at 50° C. for 24 hours to obtain a polylactic acid oligomer modified with resin microspheres;

[0079] S2 weighs the raw materials according to the following weight percentages: 15% of the polylactic acid oligomer modified with the resin microspheres obtained in step S1 and 85% of commercial polylactic acid;

[0080] S3 takes the resin microsphere-modified polylactic acid oligomer and commercial polylactic acid weighed in S2, and vacuum-dries them at 80°C for 18 hours, mixes them, stirs them evenly, dissolves them in dichloromethane, and after mixing them evenly, casts them into a glass mold, and evaporates them in vacuum at 40°C for 24 hours to obtain a polylactic acid composite material.

[0081] Example 6

[0082] The present embodiment relates to a method for preparing a reinforced and toughened polylactic acid, comprising the following steps:

[0083] S1 Preparation of polylactic acid oligomer modified with resin microspheres

[0084] a) melt-mixing a monomer (dextrose-lactide), an initiator (gallic acid-formaldehyde resin microspheres), and a catalyst (stannous octoate) at 120° C. to obtain a mixed system, wherein the molar ratio of the alcoholic hydroxyl group in the initiator to the lactide monomer is 1:100, and the molar ratio of the stannous octoate to the lactide monomer is approximately 3:1000;

[0085] b) subjecting the mixed system obtained in step a) to a vacuum-nitrogen filling treatment for three cycles, and then reacting in an oil bath at 120° C. under a nitrogen atmosphere and magnetic stirring for 36 hours to obtain a crude product;

[0086] c) cooling the crude product obtained in step b), dissolving it in dichloromethane, purifying it by precipitation with icy methanol, and vacuum drying it at 40° C. for 24 hours to obtain a polylactic acid oligomer modified with resin microspheres;

[0087] S2 weighs the raw materials according to the following weight percentages: 15% of the polylactic acid oligomer modified with the resin microspheres obtained in step S1 and 85% of commercial polylactic acid;

[0088] S3 takes the resin microsphere-modified polylactic acid oligomer and commercial polylactic acid weighed in S2, and vacuum-dries them at 80°C for 18 hours, mixes them, stirs them evenly, dissolves them in dichloromethane, and after mixing them evenly, casts them into a glass mold, and evaporates them in vacuum at 40°C for 24 hours to obtain a polylactic acid composite material.

Claims

1. A polylactic acid oligomer modified with resin microspheres, characterized in that: The preparation method is: a) taking lactide monomer, resin microsphere initiator and catalyst and melting them at 100-120°C to obtain a mixture, wherein the molar ratio of alcoholic hydroxyl group in the resin microsphere initiator to lactide monomer is 1-15:100; b) reacting the mixture obtained in step a) at 115-130° C. under an inert gas atmosphere with stirring to obtain a crude product; c) cooling, purifying, and drying the crude product obtained in step b) to obtain a polylactic acid oligomer modified with resin microspheres; The resin microspheres are phenolic resin microspheres containing multiple alcohol hydroxyl initiating groups; The degree of polymerization in the polylactic acid oligomer side chain is 63-91, and the corresponding polylactic acid oligomer single arm number average molecular weight is 1000-10000 g / mol; The resin microspheres are one or more of xylenol-formaldehyde resin microspheres, catechin-formaldehyde resin microspheres, gallic acid-formaldehyde resin microspheres, phenol-formaldehyde resin microspheres, catechol-formaldehyde resin microspheres and resorcinol-formaldehyde resin microspheres.

2. The resin microsphere-modified polylactic acid oligomer according to claim 1, characterized in that: Step b), reacting at 115-130° C. for 12-48 h.

3. The resin microsphere-modified polylactic acid oligomer according to claim 1, characterized in that: Step c), the crude product obtained in step b) is cooled, dissolved in dichloromethane, purified by precipitation with icy methanol, and dried under vacuum at 40-50° C. for 24-48 h.

4. The resin microsphere-modified polylactic acid oligomer according to claim 1, characterized in that: The resin microspheres are phenolic resin microspheres synthesized by a phenolic compound and formaldehyde or hexamethylenetetramine through a phenolic reaction.

5. The resin microsphere-modified polylactic acid oligomer according to claim 1, characterized in that: The lactide monomer is any one of L-lactide, D-lactide and meso-lactide.

6. The resin microsphere-modified polylactic acid oligomer according to claim 1, characterized in that: The catalyst is any one of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, stannous octoate, stannous chloride, cycloalkoxytin, lithium chloride, and aluminum isopropoxide, and the molar ratio of the catalyst to the lactide monomer is 1-5:1000.

7. A polylactic acid composite material, characterized in that: The invention is prepared by blending 1-15% by mass of the polylactic acid oligomer modified with the resin microspheres according to any one of claims 1 to 6 and 85-99% by mass of commercial polylactic acid.

8. The polylactic acid composite material according to claim 7, characterized in that The number average molecular weight of the commercial polylactic acid is 8-15×10 4 g / mol.

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