Polylactic acid composite material and preparation method thereof

Abstract

The invention provides a polylactic acid composite material and a preparation method thereof. The polylactic acid composite material is prepared from the following components in parts by weight: 70 to 90 parts of polylactic acid, 10 to 30 parts of elastomer, 5 to 6 parts of gas-phase nano filler and 0.1 to 0.5 part of antioxidant, wherein the specific surface area of the gas-phase nano filler is 200-380m < 2 > / g, and the number of surface hydroxyl groups is 2.02-3.37 / nm < 2 >. According to the invention, the gas-phase nanofiller with a specific specific surface area range and a specific number of hydroxyl groups is selected, and the characteristic that the gas-phase nanofiller spontaneously aggregates in a polymer melt to form a network is utilized to drive elastomer droplets to agglomerate in a polylactic acid matrix to form a special'bicontinuous-like structure '; the toughness is greatly improved while the rigidity of the composite material is ensured, so that the rigidity-toughness balance of the composite material is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biodegradable composite materials, in particular to a polylactic acid composite material and a preparation method thereof. BACKGROUND

[0002] The synthesis of traditional high molecular materials is highly dependent on non-renewable petrochemical resources, and its products are difficult to degrade quickly in the natural environment after being discarded. With the increasing shortage of petrochemical resources and the increasing problem of white pollution worldwide, developing a new generation of high molecular materials with renewable resources as raw materials and biodegradable properties has become an inevitable trend to replace traditional petroleum-based plastics. Among the many biobased biodegradable high molecular materials, polylactic acid (PLA) is one of the green plastics with the most development potential. It can be synthesized from natural resources such as corn, grains, and food, and after use, it can be quickly degraded through simple composting, realizing complete carbon cycle. In addition, PLA has the advantages of excellent biocompatibility, mechanical strength and processing performance, and shows broad application prospects in replacing traditional high molecular materials in the fields of food packaging, automobile industry, electronics and electrical appliances. However, the inherent brittleness of PLA, such as tensile elongation at break <5%, notched impact toughness <3kJ / m 2 , greatly limits its wide application as a general-purpose plastic and engineering plastic.

[0003] The most effective method to improve the brittleness of PLA at present is elastomer toughening - blending thermoplastic polyurethane (Polymer, 2014, 55, 1593-1600), polyamide elastomer (Polymer, 2009, 50, 1311-1315), polycaprolactone (Frontiers in Materials, 2019, 6, 206), ethylene-vinyl acetate copolymer (European Polymer Journal, 2012, 48, 146-154) with PLA. When the content of elastomer is low, it is uniformly distributed in the PLA matrix in the form of spherical or near-spherical, showing a typical sea-island phase structure, at this time the strength and modulus can be well maintained, but the toughening efficiency is low; when the content of elastomer is high, the elastomer phase is connected from "island" to "sea", showing a typical double continuous structure, the toughness of PLA is greatly improved, but the strength and modulus also decrease significantly. Therefore, how to realize the precise regulation of the phase structure of PLA / elastomer blend is still a challenging task.

[0004] A kind of poly lactic acid composite material and its preparation method of Chinese invention patent CN103113730A, it includes poly lactic acid, polycaprolactone, nano silicon dioxide, antioxidant and compatible agent, it is although also the mechanical property of composite material is promoted, but its introduction compatible agent Ag80, E44, TGIC, not only has toxicity but also can influence the degradation process of poly lactic acid.Therefore, it is imminent to develop a kind of simple, efficient method for preparing rigid and tough balanced PLA material or product. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a kind of poly lactic acid composite material and its preparation method, solve the problems raised in the above background art.

[0006] To achieve the above object, the present application is realized by the following technical solutions: According to the first aspect of the application, a kind of poly lactic acid composite material includes the following components by weight fraction: 70~90 parts of poly lactic acid, 10~30 parts of elastomer, 5~6 parts of fumed nano filler, 0.1~0.5 parts of antioxidant;Wherein, the specific surface area of the fumed nano filler is 200~380m 2 / g, the number of surface hydroxyl group is 2.02~3.37 per nm 2 .

[0007] Due to the weak interaction between fumed nano filler and elastomer, the present application selects fumed nano filler with specific hydroxyl group number and specific surface area range, uses the characteristics of fumed nano filler in polymer melt to form network spontaneously, drives elastomer droplets to agglomerate in poly lactic acid matrix to form a special "similar double continuous structure", while ensuring the rigidity of the composite material, the strength and toughness are improved.

[0008] Preferably, the fumed nano filler is selected from at least one of fumed silica, fumed alumina, fumed titanium dioxide or fumed zirconium dioxide.

[0009] Preferably, the poly lactic acid is selected from linear poly lactic acid, and the weight average molecular weight of the linear poly lactic acid is 1×10 4 ~4×10 5 g / mol.

[0010] Preferably, the elastomer is selected from at least one of thermoplastic polyurethane, polyamide, polycaprolactone, ethylene-glycidyl methacrylate.

[0011] Preferably, the antioxidant is selected from at least one of antioxidant 168, antioxidant 1010, antioxidant 1076.

[0012] The polylactic acid composite provided by the application has a yield strength of 50.3-55.5 MPa, a Young's modulus of 2.21-2.56 MPa, an elongation at break of 248-337%, and a notched impact strength of 60.3-85.3 kJ / m 2 According to a second aspect of the application, a preparation method of a polylactic acid composite is provided, comprising the following steps: Step 1, mechanically mixing polylactic acid and gas-phase nano-filler to obtain a premix; Step 2, melt blending the premix with an elastomer and an antioxidant, and injection molding to obtain the polylactic acid composite.

[0013] Preferably, the mechanical mixing is performed by using a high-speed mixer, and the stirring rate of the mechanical mixing is 500-2000 rpm / min, and the stirring time is 3-5 min.

[0014] Preferably, the melt blending is performed by using an extruder or an internal mixer, and the temperature of the melt blending is 170-200 DEG C, and the time is 5-15 min.

[0015] The application provides a polylactic acid composite and a preparation method thereof. Traditional elastomer toughened PLA has two main structures of sea-island structure and double-continuous structure, the sea-island structure has low toughening effect, and the double-continuous structure can greatly reduce the strength and modulus, and it is difficult to achieve the balance of rigidity and toughness; the compatibility agents Ag80, E44 and TGIC introduced in the existing patent CN103113730A not only have toxicity but also damage the excellent biodegradability of PLA, and the addition of the compatibility agents increases the cost, and in addition, the compatibility agents need to be distributed at the phase interface of PLA and polycaprolactone or nano-silicon dioxide to play a role, which brings difficulties to the stable preparation of the composite material; however, the polylactic acid composite provided by the application can drive the elastomer droplets to agglomerate in the polylactic acid matrix to form a special "double-continuous structure" by adjusting the specific surface area and the number of hydroxyl groups of the gas-phase nano-filler and using the characteristics of the gas-phase nano-filler in the polymer melt to form a network, so that the toughness of the polylactic acid composite is improved while the rigidity is ensured, and a better balance of rigidity and toughness is achieved.

[0016] The polylactic acid composite provided by the application reduces the amount of antioxidant used, and improves the mechanical properties of the polylactic acid composite while avoiding the use of toxic compatibility agents.

[0017] The preparation method of the polylactic acid composite provided by the application has the advantages of less material, low equipment investment, reduced process steps, high production efficiency and easy industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The structure schematic diagram of the polylactic acid composite material with "bicontinuous structure" provided by the application, wherein (a) is a scanning electron microscope image, and (b) is a transmission electron microscope image. DETAILED DESCRIPTION

[0019] In order to more clearly explain the application, more clearly understand the technical features, objects and beneficial effects of the application, the technical solutions in the embodiments of the application will be clearly and completely described below in combination with the drawings in the embodiments. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, any other embodiments obtained by those skilled in the art without creative work fall within the scope of the application.

[0020] In order to better illustrate the content of the application, the specific embodiments will be described below.

[0021] Embodiment 1

[0022] 85 parts of linear polylactic acid with a weight average molecular weight of 207000 g / mol and 5 parts of fumed nanosilica were added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica was 200 m 2 / g, and the number of surface hydroxyl groups was 2.37 per nm 2 ; the premix was melt blended with 15 parts of ethylene-glycidyl methacrylate and 0.1 part of antioxidant 1010 in an extruder for 5 min at 175 ℃, and then injection molded to obtain a composite material product, the scanning electron microscope image and the transmission electron microscope image of which are shown in Figure 1 .

[0023] Embodiment 2

[0024] The preparation method of this embodiment was the same as that of Embodiment 1, except that 85 parts of polylactic acid and 5 parts of fumed nanosilica were added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica was 200 m 2 / g, and the number of surface hydroxyl groups was 2.02 per nm 2 .

[0025] Embodiment 3

[0026] The preparation method of this embodiment was the same as that of Embodiment 1, except that 85 parts of polylactic acid and 5 parts of fumed nanosilica were added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica was 200 m 2 / g, the number of surface hydroxyl groups is 2.83 per nm 2 .

[0027] Example 4

[0028] The preparation method of this example is the same as that of Example 1, except that 85 parts of polylactic acid and 5 parts of fumed nanosilica are added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica is 200 m 2 / g, the number of surface hydroxyl groups is 3.37 per nm 2 .

[0029] Example 5

[0030] The preparation method of this example is the same as that of Example 1, except that 85 parts of polylactic acid and 5 parts of fumed nanosilica are added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica is 380 m 2 / g, the number of surface hydroxyl groups is 2.37 per nm 2 .

[0031] Example 6

[0032] The preparation method of this example is the same as that of Example 1, except that 85 parts of polylactic acid and 6 parts of fumed nanosilica are added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica is 200 m 2 / g, the number of surface hydroxyl groups is 2.37 per nm 2 .

[0033] Example 7

[0034] The preparation method of this example is the same as that of Example 1, except that 90 parts of polylactic acid and 5 parts of fumed nanosilica are added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica is 200 m 2 / g, the number of surface hydroxyl groups is 2.37 per nm 2 ; and then the premix is added into an extruder to melt blend with 10 parts of ethylene-glycidyl methacrylate and 0.1 part of antioxidant 1010.

[0035] Example 8

[0036] The preparation method of this example is the same as that of Example 1, except that 85 parts of polylactic acid and 5 parts of fumed nanosilica are added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica is 200 m 2 / g, and the number of surface hydroxyl groups is 2.37 per nm 2 ; and then the premix is added into an extruder to melt blend with 15 parts of polyamide elastomer and 0.1 part of antioxidant 1010.

[0037] Comparative Example 1 85 parts of polylactic acid and 15 parts of ethylene-glycidyl methacrylate are added into an extruder to melt blend, and after mixing at 175°C for 5 min, injection molding is performed to obtain a composite product.

[0038] Comparative Example 2 The preparation method of this comparative example is the same as that of Example 1, except that 85 parts of polylactic acid and 5 parts of fumed nanosilica are added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica is 200 m 2 / g, and the number of surface hydroxyl groups is 1 per nm 2 .

[0039] Comparative Example 3 The preparation method of this comparative example is the same as that of Example 1, except that 85 parts of polylactic acid and 5 parts of fumed nanosilica are added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica is 200 m 2 / g, and the number of surface hydroxyl groups is 4.13 per nm 2 .

[0040] Comparative Example 4 The preparation method of this comparative example is the same as that of Example 1, except that 85 parts of polylactic acid and 5 parts of fumed nanosilica are added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica is 50 m 2 / g, and the number of surface hydroxyl groups is 2.37 per nm 2 .

[0041] Comparative Example 5 The preparation method of this comparative example is the same as that of Example 1, except that 85 parts of polylactic acid and 1 part of fumed nanosilica are added into a high-speed blender to stir at 1000 rpm / min for 3 min to obtain a premix, wherein the specific surface area of the fumed nanosilica is 200 m 2 / g, and the number of surface hydroxyl groups is 2.37 per nm2 .

[0042] Comparative Example 6 The preparation method of the present comparative example is the same as that of Example 1, except that 85 parts of polylactic acid and 7 parts of fumed nano-silica with a specific surface area of 200 m 2 / g and a surface hydroxyl group number of 2.37 g / nm are added into a high-speed mixer and stirred at 1000 rpm / min for 3 min to obtain a premix. 2 .

[0043] Comparative Example 7 85 parts of polylactic acid, 15 parts of ethylene-glycidyl methacrylate and 0.1 part of antioxidant 1010 are added into a high-speed mixer and stirred for 3 min to obtain a premix; the mixture is put into the hopper of a twin-screw extruder for melt blending, 5 parts of fumed nano-silica with a specific surface area of 200 m 2 / g and a surface hydroxyl group number of 2.37 g / nm are added through a side feeding mode, and then extruded and injection molded to obtain a composite product. 2 .

[0044] Performance Test A universal testing machine is used to perform a tensile test on the composite product to measure the yield strength, Young's modulus and elongation at break at 25°C; A notched impact test is performed on the composite product using an impact testing machine to measure the notched impact strength at 25°C. The test data of the yield strength, Young's modulus, elongation at break and notched impact strength of the composite product are shown in Table 1.

[0045] Table 1

[0046] As can be seen from the data in Table 1, the yield strength of the composite product of the present application is 50.3-55.5 MPa, the Young's modulus is 2.21-2.56 MPa, the elongation at break is 248-337%, and the notched impact strength is 60.3-85.3 kJ / m 2 . Compared with the comparative examples, the technical solution of the present application can significantly improve the ductility and toughness of the composite material while ensuring comparable strength and stiffness.

[0047] Compared with the prior art, the present application can achieve comparable strength and toughness in the prior art by adjusting the specific surface area and surface hydroxyl group number of the fumed nano-filler and the amount of the fumed nano-filler while reducing the types and amounts of additives, thereby improving the environmental friendliness and safety of the composite material.

[0048] From the comparison of Examples 1-4 and Comparative Examples 2-3, it can be seen that the number of surface hydroxyl groups of the fumed nano-filler needs to be 2.02-3.37 / nm 2 If the number of surface hydroxyl groups is too low, the interaction between the fumed nano-filler and the elastomer is weak, which is not enough to induce the elastomer to spontaneously aggregate into a network to form a "pseudo-bicontinuous structure". If the number of surface hydroxyl groups is too high, the interaction between the fumed nano-filler is too strong, which is easy to form agglomerates rather than a network structure, and cannot induce the elastomer to form a "pseudo-bicontinuous structure". As shown in Table 1, the number of surface hydroxyl groups of the fumed nano-filler is 2.37 / nm 2 which is optimal.

[0049] From the comparison of Examples 1, 5 and Comparative Example 4, it can be seen that the specific surface area of the fumed nano-filler needs to be 200-300 g / nm 2 If the specific surface area is too low, the interaction area between the fumed nano-filler and the elastomer is too small, which results in weak interaction between them, which is not enough to induce the elastomer to spontaneously aggregate into a network to form a "pseudo-bicontinuous structure". As shown in Table 1, the specific surface area of the fumed nano-filler is 200 g / nm 2 which is optimal.

[0050] From the comparison of Examples 1, 7 and Comparative Examples 5-6, it can be seen that the amount of the fumed nano-filler needs to be 5-6 parts. If the amount is too low, the fumed nano-filler is not enough to form a network structure. If the amount is too high, the fumed nano-filler is easy to form agglomerates, which cannot induce the elastomer to form a "pseudo-bicontinuous structure". As shown in Table 1, the optimal amount of the fumed nano-filler is 5 parts.

[0051] From the comparison of Examples 1 and Comparative Example 7, it can be seen that the fumed nano-filler is first mixed with polylactic acid, so that the fumed nano-filler is uniformly wrapped on the surface of the polylactic acid. In the subsequent mixing process with the elastomer, since the interaction force between the fumed nano-filler and the elastomer is greater than the interaction force between the fumed nano-filler and PLA, the fumed nano-filler will gradually migrate from the interface to the inside of the elastomer, so as to induce the elastomer to form a special "pseudo-bicontinuous structure" in the process of aggregation into a network structure.

[0052] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A polylactic acid composite, characterized by: By weight parts, including the following components: 70~90 parts of polylactic acid, 10~30 parts of elastomer, 5~6 parts of fumed nano filler, 0.1~0.5 parts of antioxidant; wherein, the specific surface area of the fumed nano filler is 200~380 m 2 / g, the number of surface hydroxyl groups is 2.02~3.37 per nm 2 .

2. The polylactic acid composite of claim 1, wherein: The fumed nanofiller is selected from at least one of fumed silica, fumed alumina, fumed titania or fumed zirconia.

3. The polylactic acid composite of claim 1, wherein: The polylactic acid is selected from linear polylactic acid having a weight average molecular weight of 1 x 10 4 4 x 10 5 g / mol.

4. The polylactic acid composite of claim 1, wherein: The elastomer is selected from at least one of thermoplastic polyurethane, polyamide, polycaprolactone, ethylene-glycidyl methacrylate.

5. The polylactic acid composite of claim 1, wherein: The antioxidant is selected from at least one of antioxidant 168, antioxidant 1010, antioxidant 1076.

6. The polylactic acid composite of any one of claims 1 to 5, characterized in that: The polylactic acid composite has a yield strength of 50.3-55.5 MPa, a Young's modulus of 2.21-2.56 MPa, an elongation at break of 248-337%, and a notched impact strength of 60.3-85.3 kJ / m 2 .

7. A method of producing the polylactic acid composite material according to any one of claims 1 to 6, characterized by: The method comprises the following steps: Step 1, mechanically primary mixing polylactic acid and fumed nanofiller to obtain a premix; Step 2, melt blending the premix with elastomer and antioxidant, and injection molding to obtain the polylactic acid composite material.

8. The method for preparing a polylactic acid composite material according to claim 7, characterized in that: In step 1, the stirring rate of the mechanical primary mixing is 500-2000 rpm / min, and the stirring time is 3-5 min.

9. The method for preparing a polylactic acid composite material according to claim 7, characterized in that: The temperature of the melt blending is 170-200℃, and the time is 5-15 min.

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