Preparation method of toughened polylactic acid composite material based on interfacial compatibilization effect

Abstract

The invention relates to a preparation method of a toughened polylactic acid composite material based on an interfacial compatibilization effect, which is characterized in that an in-situ compatibilizer is prepared through molecular structure design based on chemical interaction between an active functional group of a grafting agent and a double bond on an ethylene propylene rubber molecular chain; the in-situ compatibilizer is used for improving the binding power between the polylactic acid and the ethylene propylene diene monomer, so that the two-phase interface compatibility is improved; a unique stereocomplex crystal structure of polylactic acid is further introduced into the system, and the two-phase dispersion state is improved by virtue of regulation and control and crystallization induction effects of stereomicrocrystals on a two-phase interface, so that the toughened polylactic acid composite material is prepared; by optimizing the content of an in-situ compatibilizer and a stereocrystal, a processing technology and other methods, formation of composite materials with different phase morphologies is induced, different modification and toughening effects are achieved, and the high-toughness polylactic acid composite material is prepared.

Description

Technical Field

[0001] The invention relates to a preparation method of a toughened polylactic acid composite material based on an interface volume expansion effect, and belongs to the field of biodegradable materials and polymer processing. Background Art

[0002] While traditional polymer materials bring great convenience to people's lives, they also put heavy pressure on the ecological environment, such as the serious "white pollution" problem. In view of this, it is urgent to accelerate the research and development of degradable bio-based polymer materials. Among them, polylactic acid (PLA), as a typical representative of bio-based polyester, has become the most promising bio-based material in recent years due to its excellent mechanical strength, biocompatibility, transparency and barrier properties. It is regarded as an ideal choice to replace petroleum-based plastic products.

[0003] However, the defects of PLA itself, such as high brittleness and poor impact resistance, have greatly limited its application in a wider range of fields. Ethylene propylene diene monomer (EPDM) is a terpolymer composed of ethylene, propylene and non-conjugated dienes. It has good impact resistance and heat resistance, which happens to complement the performance of PLA, so it has become a high-quality candidate material for PLA toughening. However, due to the strong polarity of polylactic acid and the weak polarity of EPDM, there is a serious interface incompatibility problem between the two, which makes it difficult for the rubber phase to be evenly dispersed in the polylactic acid matrix in the blending system, resulting in phase separation. Not only can it not effectively transfer stress, but it will become a stress concentration point, weakening the overall mechanical properties of the material, and the toughening effect is not ideal. Therefore, exploring a simple and efficient way to improve the compatibility of the two, and then improve the comprehensive performance of the composite, has become a key issue that needs to be solved urgently.

[0004] Chinese invention patent CN117511155A discloses a method for preparing a reaction blended toughened polylactic acid starch composite, which strengthens the mechanical properties of the polylactic acid starch composite by introducing lignin-modified silica; Chinese invention patent CN116218172A discloses a method for preparing a blended polylactic acid biodegradable toughened composite material, which introduces a grafting monomer to participate in the copolymerization reaction during the preparation of the graft copolymer, significantly improves the grafting rate of the grafting monomer on the macromolecule, effectively improves the compatibility of the two materials, and finally improves the mechanical properties of the blend; Chinese invention patent CN117209986A discloses a toughened and modified polylactic acid material, preparation method and application, which obtains supermolecular weight polylactide by a series of polymerization operations, and melt-mixes with polylactic acid to obtain a toughened polylactic acid composite material. Although the methods mentioned in the above patents have achieved certain results in improving the toughness of polylactic acid-based composite materials, there are inevitably some shortcomings, such as unsatisfactory compatibility, high raw material costs, and adverse effects on degradation rate. Therefore, the development of a toughened polylactic acid-based composite material that can simply and efficiently improve the compatibility between polylactic acid and EPDM rubber while ensuring that other properties except mechanical properties are basically unaffected has extremely important scientific significance and application value.

[0005] With the development of materials science, modification methods based on the interfacial compatibilization effect have gradually attracted attention. By introducing an interfacial compatibilizer between polylactic acid and the toughening phase, the interaction between the two is enhanced, and the interfacial adhesion is improved, which is expected to overcome the shortcomings of traditional toughening methods. For example, some graft copolymers can be used as interfacial compatibilizers, one end of which has good compatibility with the polylactic acid matrix, and the other end can interact with the toughening phase, thereby promoting the uniform dispersion of the toughening phase in polylactic acid, forming a stable microstructure, and achieving effective toughening of polylactic acid. However, at present, further in-depth research and development of polylactic acid toughening systems and preparation methods based on the interfacial compatibilization effect that are efficient, low-cost and easy to industrialize are still needed in this regard.

[0006] In summary, it is of great practical significance to develop a toughened polylactic acid composite material based on the interface volume expansion effect, which can significantly improve the toughness of polylactic acid, has good interface compatibility and a simple and feasible preparation process, and its preparation method, which will lay a solid foundation for the application of polylactic acid materials in a wider range of fields and promote the development of the bio-based degradable materials industry. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing a toughened polylactic acid composite material based on an interface volume-increasing effect in view of the deficiencies in the prior art. The method is characterized in that, based on the chemical interaction between a grafting agent and a rubber molecular chain, an in-situ volume-increasing agent is prepared by molecular design, and the adhesion between polylactic acid and ethylene propylene diene monomer rubber is improved by the in-situ volume-increasing agent, thereby improving the compatibility of the two-phase interface; further, a unique stereocomposite crystal structure of polylactic acid is introduced into the system, and the regulation and crystallization induction effect of stereocrystals on the two-phase interface is utilized to improve the dispersion state of the two phases, and a toughened polylactic acid composite material is prepared through the interface synergistic effect of the in-situ volume-increasing agent and the stereocrystals; and the formation of composite materials with different phase morphologies is induced by optimizing the content of the in-situ volume-increasing agent and the stereocrystals and the processing technology, etc., so as to achieve different modification and toughening effects and prepare a high-toughness polylactic acid composite material.

[0008] The technical solution of the present invention is a method for preparing a toughened polylactic acid composite material based on the interfacial compatibilization effect, which is specifically implemented according to the following steps: (1) Preparation of in-situ compatibilizer; (2) Preparation of in situ compatibilized polylactic acid / ethylene propylene diene monomer rubber blends; (3) Preparation of in situ compatibilized stereocomposite polylactic acid / ethylene propylene diene rubber composites.

[0009] Furthermore, step (1) comprises: based on the chemical interaction between the active functional groups of the grafting agent and the double bonds on the ethylene-propylene rubber molecular chain, preliminarily mixing the EPDM rubber, the grafting agent and the co-grafting agent according to a certain mass ratio, then adding the blended material into a torque rheometer at a certain temperature and speed for internal mixing, and taking out the sample after a certain period of time, thereby obtaining the in-situ compatibilizer.

[0010] Preferably, in step (1), the grafting agent is one of maleic anhydride and glycidyl methacrylate, the auxiliary grafting agent is one or two of triallyl isocyanurate, dicumyl peroxide and benzoyl peroxide, and the mass ratio of EPDM rubber, grafting agent and auxiliary grafting agent is 90:7:3, the mixing temperature is 150-200 °C, the mixing time is 3-10 min, and the rotation speed is 20-70 rpm.

[0011] Furthermore, in step (2), poly(L-lactic acid), in-situ compatibilizer and EPDM rubber are placed in an electric blast drying oven and dried for 6 hours at a drying temperature of 80°C. Subsequently, the three are mechanically blended in a certain proportion and added to a torque rheometer for internal mixing at a temperature of 150-200°C, a time of 3-10 min, and a rotation speed of 20-70 rpm to obtain an in-situ compatibilized poly(lactic acid) / EPDM rubber blend.

[0012] Preferably, the mass ratio of the L-polylactic acid to the EPDM rubber is (70-90):(10-30), and the content of the in-situ compatibilizer is 0-5 parts of the total amount of the blend.

[0013] Furthermore, in step (3), poly(d-lactic acid) and in-situ compatibilized poly(lactic acid) / ethylene propylene diene monomer rubber blend are blended in a mass ratio of (5-15):(85-95), and then added to a torque rheometer for internal kneading at a temperature of 150-200°C, a time of 3-10 min, and a rotation speed of 20-70 rpm to obtain an in-situ compatibilized stereocomposite poly(lactic acid) / ethylene propylene diene monomer rubber blend, and further the in-situ compatibilized stereocomposite poly(lactic acid) / ethylene propylene diene monomer rubber composite material is prepared by hot pressing.

[0014] Preferably, the in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber blend obtained by banburying is placed on a hot pressing molding machine for molding, and the hot pressing temperature is 170-200 ° C, the hot pressing time is 5-10 min, and the pressure is 5-10 MPa. After the hot pressing is completed, the pressure is kept constant, the temperature is quickly lowered to room temperature, and cold pressed for 3-10 min to obtain an in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber composite material.

[0015] The invention provides a method for preparing a toughened polylactic acid composite material based on an interface compatibilization effect.

[0016] The present invention uses biodegradable polylactic acid as a matrix and ethylene propylene diene monomer rubber as a toughening phase, designs an in-situ compatibilizer through chemical grafting, and subject the three to reactive melt processing to prepare an in-situ compatibilized polylactic acid / ethylene propylene diene monomer rubber blend. The unique stereocomposite crystals of polylactic acid are further introduced into the system. The compatibilization effect of the in-situ compatibilizer on the two-phase interface and the refinement and crystallization induction effect of the stereocomposite crystals on the phase domain are utilized to synergistically regulate the compatibility of the two-phase interface, induce the formation of composite materials with different phase morphologies, achieve different modified toughening effects, and prepare a high-toughness polylactic acid composite material.

[0017] Compared with the prior art, the advantages of the present invention are as follows: 1. The present invention introduces high-elastic EPDM rubber to toughen polylactic acid, thereby effectively overcoming the problems of severe brittleness and poor impact resistance of polylactic acid itself. The toughness of the composite material is significantly improved, making it less likely to suffer brittle fracture when subjected to external impact or bending deformation, thereby expanding its application range.

[0018] 2. The composite material prepared by the present invention not only has greatly improved toughness, but also maintains a good performance level in terms of tensile strength and bending strength due to the synergistic effect of the in-situ compatibilizer and stereocomposite crystals. The drawback of traditional toughening methods that often sacrifice other mechanical properties to improve toughness is avoided, and the comprehensive balance optimization of the mechanical properties of the material is achieved.

[0019] 3. The present invention prepares an in-situ compatibilizer based on the chemical interaction between the grafting agent and the EPDM molecular chain, and the special effect of the stereocomplex crystal at the interface between polylactic acid and EPDM, which greatly improves the compatibility between the two. The phase separation phenomenon caused by poor compatibility is reduced, so that the EPDM can be more evenly dispersed in the polylactic acid matrix, thereby better exerting its toughening effect, and the bonding force of the interface is significantly enhanced, effectively transmitting stress, and further improving the overall performance of the composite material.

[0020] 4. The good compatibility between the two phases of the toughened polylactic acid composite material of the present invention and the presence of stereocomposite crystals make the phase interface structure more stable. During the material processing and long-term use, it can resist the damage to the phase interface caused by external environmental factors such as temperature changes and humidity changes, maintain the stability and reliability of material performance, extend the service life of the material, and reduce the risk of material performance degradation and failure caused by phase interface problems.

[0021] 5. The whole preparation process of the present invention is mainly completed by steps such as banburying in a torque rheometer and hot pressing molding, and the operation is relatively simple. The ratio of each raw material, banburying temperature, time, rotation speed and hot pressing conditions have clear ranges and parameter settings, which are easy to control and realize industrial production. Complex equipment and harsh process conditions are not required, which reduces production costs and production difficulties, and is conducive to the promotion and application of the invention in actual production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Comparison of infrared spectra of in-situ toughening agent and pure EPDM rubber.

[0023] Figure 2 This is the phase interface diagram of polylactic acid / ethylene propylene diene monomer rubber before and after toughening. DETAILED DESCRIPTION

[0024] The present invention is further described below by means of specific examples. It should be noted that the examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make non-essential improvements and adjustments to the present invention based on the contents of the present invention described above. Example 1

[0025] A method for preparing a toughened polylactic acid composite material based on an interfacial compatibilization effect, comprising the following steps: (1) Preparation of in-situ compatibilizer: EPDM rubber, maleic anhydride and triallyl isocyanurate were preliminarily mixed in a mechanical mixer at a mass ratio of 90:7:3. The mixture was then added to a torque rheometer preheated to 180°C and rotating at 50 rpm for internal mixing. The sample was taken out after 5 minutes to obtain the in-situ compatibilizer.

[0026] (2) Preparation of in-situ compatibilized polylactic acid / ethylene propylene diene rubber blends: Poly-L-lactic acid, in-situ compatibilizer and EPDM rubber were placed in an electric blast drying oven and dried for 6 hours at a drying temperature of 80°C. The three were then mechanically blended in a mass ratio of 80:5:15 and added to a torque rheometer for internal mixing at a temperature of 180°C, a mixing time of 3 min and a rotation speed of 50 rpm to obtain an in-situ compatibilized polylactic acid / ethylene propylene diene rubber blend.

[0027] (3) Preparation of in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber composite material: After poly (dextral lactic acid) and in-situ compatibilized polylactic acid / ethylene propylene rubber blend were blended at a mass ratio of 10:90, they were added to a torque rheometer at a mixing temperature of 180°C and a rotation speed of 50 rpm for 3 min to obtain an in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber blend. The in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber blend obtained by mixing was further placed on a hot pressing molding machine for molding at a hot pressing temperature of 200°C, a hot pressing time of 5 min, and a pressure of 8 MPa. After the hot pressing was completed, the pressure was kept constant, the temperature was quickly lowered to room temperature, and cold pressed for 5 min to obtain an in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber composite material. The tensile strength of the composite material is 39.27 MPa, the flexural strength is 44.81 MPa, and the impact strength is 3.62 KJ / m 2 Increased to 17.88 KJ / m 2 . Example 2

[0028] A method for preparing a toughened polylactic acid composite material based on an interfacial compatibilization effect, comprising the following steps: (1) Preparation of in-situ compatibilizer: EPDM rubber, glycidyl methacrylate and benzoyl peroxide were preliminarily mixed in a mechanical mixer at a mass ratio of 90:7:3. The mixture was then added to a torque rheometer preheated to 190°C and rotated at 60 rpm for internal mixing. The sample was taken out after 5 minutes to obtain the in-situ compatibilizer.

[0029] (2) Preparation of in-situ compatibilized polylactic acid / ethylene propylene rubber blends: Poly-L-lactic acid, in-situ compatibilizer and EPDM rubber were placed in an electric blast drying oven and dried for 6 hours at a drying temperature of 80°C. The three were then mechanically blended in a mass ratio of 85:3:12 and added to a torque rheometer for internal mixing at a temperature of 190°C, a mixing time of 5 min and a rotation speed of 60 rpm to obtain an in-situ compatibilized polylactic acid / ethylene propylene rubber blend.

[0030] (3) Preparation of in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber composite material: After poly (dextral lactic acid) and in-situ compatibilized polylactic acid / ethylene propylene rubber blend were blended at a mass ratio of 15:85, they were added to a torque rheometer at a mixing temperature of 190°C and a rotation speed of 60 rpm for 5 min to obtain an in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber blend. The in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber blend obtained by mixing was further placed on a hot pressing molding machine for molding at a hot pressing temperature of 190°C, a hot pressing time of 8 min, and a pressure of 10 MPa. After the hot pressing was completed, the pressure was kept constant, the temperature was quickly lowered to room temperature, and cold pressed for 6 min to obtain an in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber composite material. The tensile strength of the composite material is 48.71 MPa, the flexural strength is 49.26 MPa, and the impact strength is 3.62 KJ / m 2 Increased to 15.97 KJ / m 2 . Example 3

[0031] A method for preparing a toughened polylactic acid composite material based on an interfacial compatibilization effect, comprising the following steps: (1) Preparation of in-situ compatibilizer: EPDM rubber, maleic anhydride, triallyl isocyanurate and benzoyl peroxide were preliminarily mixed in a mechanical mixer at a mass ratio of 90:7:3. The mixture was then added to a torque rheometer preheated to 190°C and rotated at 50 rpm for internal mixing. The sample was taken out after 7 minutes to obtain the in-situ compatibilizer.

[0032] (2) Preparation of in-situ compatibilized polylactic acid / ethylene propylene diene rubber blends: Poly-L-lactic acid, in-situ compatibilizer and EPDM rubber were placed in an electric blast drying oven and dried for 6 hours at a drying temperature of 80°C. The three were then mechanically blended in a mass ratio of 80:5:15 and added to a torque rheometer for internal mixing at a temperature of 190°C, a mixing time of 5 min and a rotation speed of 50 rpm to obtain an in-situ compatibilized polylactic acid / ethylene propylene diene rubber blend.

[0033] (3) Preparation of in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber composite material: After poly (dextral lactic acid) and in-situ compatibilized polylactic acid / ethylene propylene rubber blend were blended at a mass ratio of 15:85, they were added to a torque rheometer at a mixing temperature of 190°C and a rotation speed of 50 rpm for 5 min to obtain an in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber blend. The in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber blend obtained by mixing was further placed on a hot pressing molding machine for molding at a hot pressing temperature of 200°C, a hot pressing time of 5 min, and a pressure of 10 MPa. After the hot pressing was completed, the pressure was kept constant, the temperature was quickly lowered to room temperature, and cold pressed for 5 min to obtain an in-situ compatibilized stereocomposite polylactic acid / ethylene propylene rubber composite material. The tensile strength of the composite material is 42.72 MPa, the flexural strength is 47.17 MPa, and the impact strength is 3.62 KJ / m 2 Increased to 19.37 KJ / m 2 .

[0034] The invention discloses a method for preparing a toughened polylactic acid composite material based on an interface compatibilization effect, wherein biodegradable polylactic acid is used as a matrix, ethylene propylene diene monomer rubber is used as a toughening phase, an in-situ compatibilizer is synthesized by chemical grafting, an in-situ compatibilized polylactic acid / ethylene propylene diene monomer rubber blend is prepared by a reactive melt processing technology, stereocomposite crystals are further introduced into the system, and the compatibilization effect of the in-situ compatibilizer on the two-phase interface and the refinement and crystallization induction effect of the stereocomposite crystals on the phase domain are utilized to coordinately regulate the compatibility of the two-phase interface, induce the formation of composite materials with different phase morphologies, achieve different modified toughening effects, and prepare a high-toughness polylactic acid composite material. The toughened polylactic acid composite material has a simple and feasible preparation process and has wide practicality and promotion value.

[0035] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0036] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for preparing a toughened polylactic acid composite material based on an interfacial compatibilization effect, characterized in that: The preparation of the composite material mainly includes the following steps: (1) Preparation of in-situ compatibilizer; (2) Preparation of in-situ compatibilized polylactic acid / ethylene propylene diene monomer rubber blends; (3) Preparation of in situ compatibilized stereocomposite polylactic acid / ethylene propylene diene rubber composites.

2. The method for preparing a toughened polylactic acid composite material based on the interfacial compatibilization effect according to claim 1, characterized in that: Step (1) comprises: preliminarily mixing EPDM rubber, grafting agent and co-grafting agent according to a certain mass ratio based on the chemical interaction between the active functional groups of the grafting agent and the double bonds on the EPDM rubber molecular chain, then adding the blended material into a torque rheometer at a certain temperature and speed for internal kneading, and taking out the sample after a certain period of time, thereby obtaining an in-situ compatibilizer.

3. The method for preparing a toughened polylactic acid composite material based on the interfacial compatibilization effect according to claim 2, characterized in that: In step (1), the grafting agent is one of maleic anhydride and glycidyl methacrylate, the auxiliary grafting agent is one or two of triallyl isocyanurate, dicumyl peroxide and benzoyl peroxide, and the mass ratio of EPDM rubber, grafting agent and auxiliary grafting agent is 90:7:3, the mixing temperature is 150-200 °C, the mixing time is 3-10 min, and the rotating speed is 20-70 rpm.

4. The method for preparing a toughened polylactic acid composite material based on the interfacial compatibilization effect according to claim 1, characterized in that: In step (2), poly(L-lactic acid), in-situ compatibilizer and EPDM rubber are placed in an electric blast drying oven for 6 hours at a drying temperature of 80°C. The three are then mechanically blended in a certain proportion and added to a torque rheometer for internal kneading at a temperature of 150-200°C, a time of 3-10 min, and a rotation speed of 20-70 rpm to obtain an in-situ compatibilized poly(lactic acid) / EPDM rubber blend.

5. The method for preparing a toughened polylactic acid composite material based on the interfacial compatibilization effect according to claim 4, characterized in that: In step (2), the mass ratio of L-polylactic acid to EPDM is (70-90):(10-30), and the content of the in-situ compatibilizer is 0-5 parts of the total amount of the blend.

6. The method for preparing a toughened polylactic acid composite material based on the interfacial compatibilization effect according to claim 1, characterized in that: In step (3), poly (dextral) lactic acid and in-situ compatibilized poly (lactic acid) / ethylene propylene diene monomer rubber are blended in a mass ratio of (5-15):(85-95), and then added to a torque rheometer for internal kneading at a temperature of 150-200 °C, a time of 3-10 min, and a rotation speed of 20-70 rpm to obtain an in-situ compatibilized stereocomposite poly (lactic acid) / ethylene propylene diene monomer rubber blend, and further prepared by hot pressing a composite material of in-situ compatibilized stereocomposite poly (lactic acid) / ethylene propylene diene monomer rubber.

7. The method for preparing a toughened polylactic acid composite material based on the interfacial compatibilization effect according to claim 6, characterized in that: Step (3) comprises: placing the in-situ expanded stereocomposite polylactic acid / ethylene propylene diene monomer rubber blend obtained by internal mixing on a hot pressing molding machine for molding, the hot pressing temperature is 170-200°C, the hot pressing time is 5-10 min, and the pressure is 5-10 MPa; after the hot pressing is completed, the pressure is kept constant, the temperature is quickly lowered to room temperature, and cold pressing is performed for 3-10 min to obtain the in-situ expanded stereocomposite polylactic acid / ethylene propylene diene monomer rubber composite material.

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