Fluorine-containing chain extender, composition for preparing PLA foaming material, PLA foaming material and preparation method thereof

Abstract

The invention discloses a fluorine-containing chain extender, a composition for preparing a PLA (polylactic acid) foaming material, the PLA foaming material and a preparation method of the PLA foaming material. The fluorine-containing chain extender is prepared by a solution polymerization method, and prepared monomers comprise methyl methacrylate, glycidyl methacrylate and dodecafluoroheptyl acrylate in a molar ratio of (3-6): (0.1-2): (0.1-2). The composition for preparing the PLA foaming material comprises pure PLA and a fluorine-containing chain extender, wherein the mass of the fluorine-containing chain extender is 4-8wt% of the mass of the pure PLA. The PLA foaming material is prepared from the composition for preparing the PLA foaming material. The PLA foaming material prepared by the invention has relatively high expansion rate and cell density.

Description

Technical Field

[0001] The invention belongs to the technical field of PLA foaming, and relates to a fluorine-containing chain extender, a composition for preparing a PLA foaming material, a PLA foaming material and a preparation method thereof. Background Art

[0002] In recent years, biodegradable polymers have attracted increasing attention as green materials due to the increasing resource crisis and environmental pollution caused by traditional non-degradable polymers. As an aliphatic semi-crystalline polyester based on renewable resources, polylactic acid (PLA) can be biodegraded and composted under favorable conditions. As a thermoplastic with properties comparable to some commodity polymers, it is seen as a viable alternative to petroleum-derived plastics. As part of the promotion of renewable energy-based products, thermoplastic foams made of PLA have attracted considerable attention in the fields of packaging, cushioning, and thermal and sound insulation. However, as a biodegradable aliphatic thermoplastic polyester, PLA exhibits defects such as linear molecular structure, low molecular weight, weak crystallization ability, and low melt strength, which hinder its application in the foaming field. Therefore, in order to obtain PLA foam with better foaming properties, it is urgent to modify and foam PLA.

[0003] Wang X. et al. (X. Wang, J. Mi, J. Wang, H. Zhou and X. Wang, RSC Adv., 2018, 8, 34418-34427). The melt strength of polylactic acid (PLA) was improved by chain extension effect by grafting poly(ethylene octene) with glycidyl methacrylate (POE-g-GMA). Although high melt strength helps to limit the agglomeration and rupture of the cells during the cell growth stage, resulting in smaller cells, it also leads to a significant reduction in the volume expansion ratio. At the same time, for PLA materials with high melt strength, a higher saturation temperature is required during the foaming process, and the foaming window becomes narrower.

[0004] At the same time, Li et al. (Li, Y.; Yin, D.; Liu, W.; Zhou, H.; Zhang, Y.; Wang, X. Fabrication of biodegradable poly (lactic acid) / carbon nanotube nanocomposite foams: Significant improvement on rheological property and foamability. Int. J. Biol. Macromol. 2020, 163, 1175–1186.) studied the foaming properties of PLA / CNTS composites using carbon nanotubes (CNTS). The addition of CO2 nucleating agent CNTS has limited effect on the improvement of the pore size of the material, and the pore density is still low. In addition, during the processing, the dispersibility of CNTS in PLA is poor, and it is easy to agglomerate, resulting in uneven pore size of the foaming material and rupture. Summary of the invention

[0005] In order to overcome the problems of low expansion ratio of PLA foaming material when PLA has high melt strength, low cell density and irregular cells when a nucleating agent is added, the present invention provides a fluorine-containing chain extender that can improve melt strength and serve as a nucleating agent, a composition for preparing PLA foaming material, a PLA foaming material and a preparation method thereof. The PLA foaming material prepared by the present invention has high expansion ratio and cell density.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a fluorine-containing chain extender, which is prepared by a solution polymerization method. The preparation monomers include methyl methacrylate (MMA), glycidyl methacrylate (GMA) and dodecafluoroheptyl acrylate, and the molar ratio thereof is 3-6:0.1-2:0.1-2.

[0008] When the monomers for preparing the chain extender of the present invention are methyl methacrylate (I), glycidyl methacrylate (II) and dodecafluoroheptyl acrylate (III), the reaction formula of the copolymerization reaction is as follows:

[0009]

[0010] Preferably, the preparation monomer also includes other monomers, and the other monomers are selected from at least one of butyl acrylate, methyl acrylate, and butyl methacrylate AIBN. The molar ratio of methyl methacrylate, glycidyl methacrylate, dodecafluoroheptyl acrylate, and other monomers is 3-6:0.1-2:0.1-2:0.2-2, and more preferably 4-5:0.2-1:0.2-1:0.2-2.

[0011] Preferably, the preparation monomers are composed of methyl methacrylate, glycidyl methacrylate and dodecafluoroheptyl acrylate, and the molar ratio of the three is 4-5:0.2-1:0.2-1, more preferably 4-4.6:0.5-1:0.5-1.

[0012] Preferably, the solution polymerization method is implemented as follows: dissolving the prepared monomer in a solvent, adding an initiator, heating to 65-80° C. and stirring for 6-10 hours to perform copolymerization, and after the reaction, removing the solvent, washing, and drying to obtain a fluorine-containing chain extender.

[0013] As further preferred, the solvent is a polar solvent, and more preferably the solvent is selected from one or more of tetrahydrofuran (THF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0014] As further preferred, the initiator is selected from at least one of AIBN, ABVN, AIBME, AHCN, and V-601.

[0015] As a further preference, the mass of the solvent is 1.5-2.5 times the mass of the monomers to be prepared, and the mass of the initiator is 0.5-3% of the mass of the monomers to be prepared.

[0016] As further preferred, the washing reagent is methanol, water or ethanol.

[0017] As a further preference, the drying condition is: vacuum drying at 40-80° C. for 6-10 hours.

[0018] In a second aspect, the present invention provides a composition for preparing a PLA foam material, comprising pure PLA and the fluorine-containing chain extender described in the first aspect, wherein the mass of the fluorine-containing chain extender is 4-8wt% of the mass of the pure PLA.

[0019] Preferably, the composition for preparing the PLA foaming material consists of pure PLA and a fluorine-containing chain extender.

[0020] In a third aspect, the present invention provides a PLA foam material, which is prepared from the composition for preparing a PLA foam material according to the second aspect.

[0021] In a fourth aspect, the present invention provides a method for preparing the PLA foam material according to the third aspect, comprising the following steps:

[0022] (1) melt-blending the fluorinated chain extender and pure PLA particles by a torque rheometer to obtain a melt-blended sample;

[0023] (2) hot pressing the melt blended sample obtained in step (1) using a flat vulcanizer to obtain a sheet with a thickness of 1 to 3 mm;

[0024] (3) placing the sheet obtained in step (2) in a supercritical autoclave foaming machine, selecting supercritical CO2 as the supercritical gas for foaming molding, and obtaining a PLA foamed material.

[0025] Preferably, in step (1), the melt blending conditions are: a rotation speed of 60 to 100 r / min, a temperature of 180 to 200° C., and a melt blending time of 5 to 10 min.

[0026] Preferably, the hot pressing forming conditions are as follows: the hot pressing forming temperature is 180-200° C., the pressure is 8.0-11.0 MPa, and the hot pressing time is 10-15 min.

[0027] Preferably, in step (3), the foaming molding conditions are as follows: the saturation temperature is set at 150-170° C., after the reactor is closed, supercritical gas is introduced at a pressure of 10.8-13.8 MPa, the pressure is maintained for 1-2 hours, and then the temperature is lowered to 90-110° C. After saturation for 5-15 minutes, the pressure is quickly released for 0.5-1 second. After the pressure in the reactor is completely released, the reactor is opened to obtain the PLA foaming material.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention copolymerizes glycidyl methacrylate (GMA) and dodecafluoroheptyl acrylate, so that the fluorinated chain extender can react slightly with PLA to improve the melt strength, and increase the CO2 affinity and the solubility of the foaming agent CO2, and provide heterogeneous nucleation sites, so that the PLA foamed sample can have a larger cell density while maintaining a high expansion ratio.

[0030] 2. The synthesis method of the fluorinated chain extender is consistent with the traditional chain extender synthesis method, with high conversion rate, high utilization rate of fluorinated monomers, and easy to carry out large-scale preparation.

[0031] 3. The melt blending and foaming process adopted by the present invention is simple and efficient, and the process conditions are controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The cross-sectional SEM images and expansion ratio statistical graphs of the foamed materials prepared in Example 1 and Comparative Examples 2 and 4 of the present invention are shown. DETAILED DESCRIPTION

[0033] The present invention is further described below by means of specific embodiments in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited thereto.

[0034] Embodiment 1:

[0035] The present embodiment provides a fluorinated chain extender modified PLA foam material, which is prepared by the following steps:

[0036] S1, methyl methacrylate (MMA), glycidyl methacrylate (GMA), and dodecafluoroheptyl acrylate in a molar ratio of 4:1:1, with a total mass of 6.9 g, were dissolved in 13.8 g (200 wt%) of tetrahydrofuran (THF), and 0.1 g (1.5 wt%) of azobisisobutyronitrile (AIBN) initiator was added, heated in a water bath at 70°C, and reacted for 8 h with magnetic stirring;

[0037] S2. After the reaction is completed, the obtained viscous solution is transferred to a rotary evaporator to remove the solvent THF;

[0038] S3, after washing with methanol three times, the product of reduced pressure distillation was placed in a vacuum oven at 50°C for 10 hours to obtain the final product;

[0039] S4, adding 4 wt% of the fluorine chain extender obtained in S3 to pure PLA particles, and melt blending for 10 min at a speed of 60 rad / min using a HAAKE torque rheometer;

[0040] S5, hot pressing the sample after melt blending in S4 using a flat vulcanizer to obtain a sheet with a thickness of 1 mm;

[0041] S6. Select ScCO2 as the supercritical gas, place the 1 mm thick PLA sheet prepared in S5 in a supercritical autoclave pressure foaming machine, raise the temperature of the autoclave pressure foaming machine to 160°C in advance, put in the sample, close the mold and introduce ScCO2, set the pressure to 13.8 MPa and maintain for 1 hour, then cool to 100°C and maintain for 10 minutes, then quickly release the pressure within 1 second, open the mold after the pressure in the reactor is completely released, and obtain the PLA foaming material.

[0042] Embodiment 2:

[0043] The only difference between this embodiment and embodiment 1 is that the molar ratio of methyl methacrylate (MMA), glycidyl methacrylate (GMA), dodecafluoroheptyl acrylate and butyl acrylate is 4:1:0.6:1.2, and the epoxy group content of the fluorinated chain extender added to the pure PLA particles is the same as that in embodiment 1, and the reduced dodecafluoroheptyl acrylate is replaced by butyl acrylate with a longer molecular chain.

[0044] Example 3

[0045] The only difference between this embodiment and embodiment 1 is that the molar ratio of methyl methacrylate (MMA), glycidyl methacrylate (GMA), and dodecafluoroheptyl acrylate is 4.6:0.6:1, and the fluorine content of the fluorine-containing chain extender added to the pure PLA particles is the same as that in embodiment 1, and the reduced GMA is replaced by MMA with similar reaction activity.

[0046] Example 4

[0047] The only difference between this embodiment and embodiment 1 is that the molar ratio of methyl methacrylate (MMA), glycidyl methacrylate (GMA), and dodecafluoroheptyl acrylate is 4:0.6:0.6, and the fluorine content and epoxy group content of the fluorine-containing chain extender added to the pure PLA particles are reduced.

[0048] Comparative Example 1

[0049] The difference between this comparative example and Example 1 is that the molar ratio of methyl methacrylate (MMA), glycidyl methacrylate (GMA) and dodecafluoroheptyl acrylate is 5.1:0.2:1, and the fluorine content of the fluorine-containing chain extender added to the pure PLA particles is the same as that in Example 1, and the reduced GMA is replaced by MMA with similar reaction activity.

[0050] Comparative Example 2

[0051] The only difference between this comparative example and Example 1 is that the molar ratio of methyl methacrylate (MMA), glycidyl methacrylate (GMA) and butyl acrylate is 4:1:1.

[0052] Comparative Example 3

[0053] The difference between this comparative example and Example 1 is that the molar ratio of methyl methacrylate (MMA), glycidyl methacrylate (GMA) and dodecafluoroheptyl acrylate is 4:0.1:1.

[0054] Comparative Example 4

[0055] The difference between this comparative example and Example 1 is that no chain extender is added and pure PLA is foamed.

[0056] Table 1 Performance data of PLA foam materials in Examples and Comparative Examples

[0057]

[0058]

[0059] As can be seen from Table 1, Comparative Example 2 uses a fluorine-free epoxy chain extender to assist PLA foaming. It can be seen that the epoxy chain extender makes the PLA foam material have a higher cell density, but the expansion ratio is greatly reduced.

[0060] Comparative Example 3 uses a fluorine nucleating agent without epoxy groups. It can be seen that the expansion ratio of the PLA foam material with the addition of the fluorine nucleating agent is still relatively high, but the pore density is significantly lower than that of the foam material with the addition of the chain extender.

[0061] Comparison 4 is the foaming of pure PLA without adding chain extender. It can be seen that although the expansion ratio of the PLA foaming material without adding chain extender is higher, the pore density is greatly reduced compared with the foaming material with adding chain extender.

[0062] In various embodiments of the present invention, the fluorine-containing chain extender has a significant improvement in the expansion ratio and cell density of the PLA foam material. The fluorine-containing chain extender improves the rheological properties, thermodynamic properties, mechanical properties and foaming behavior of polylactic acid (PLA) through the chain extension effect, so that a PLA foam material with a more regular cell morphology can be prepared. Since PLA is foamed in a molten state, its melt strength is the main factor controlling the cell size. High melt strength helps to limit the cell agglomeration and rupture during the cell growth stage, thereby resulting in a smaller cell size and an increased cell density. The fluorine in the fluorine-containing chain extender has a strong affinity for CO2, and can adsorb a large amount of CO2 during the foaming process, which plays a role in heterogeneous nucleation of bubbles and increases the expansion ratio. Because when the PLA melt strength is high, the crystallinity is high when foaming in the molten state, the amorphous area that absorbs CO2 is reduced, resulting in insufficient CO2 to promote bubble nucleation during the foaming process. The CO2 adsorbed by the nucleating agent fluorine makes up for this defect, so that the expansion ratio and bubble density of the PLA foam material with the addition of fluorine chain extender are higher.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A fluorinated chain extender, characterized in that: The fluorine-containing chain extender is prepared by solution polymerization, and the preparation monomers include methyl methacrylate, glycidyl methacrylate and dodecafluoroheptyl acrylate, and the molar ratio thereof is 3-6:0.1-2:0.1-2.

2. The fluorinated chain extender according to claim 1, characterized in that: The preparation monomer also includes other monomers, and the other monomers are selected from at least one of butyl acrylate, methyl acrylate, and butyl methacrylate AIBN. The molar ratio of methyl methacrylate, glycidyl methacrylate, dodecafluoroheptyl acrylate, and other monomers is 3-6:0.1-2:0.1-2:0.2-2, and more preferably 4-5:0.2-1:0.2-1:0.2-2.

3. The fluorinated chain extender according to claim 1, characterized in that: The preparation monomers are composed of methyl methacrylate, glycidyl methacrylate and dodecafluoroheptyl acrylate, and the molar ratio of the three is 4-5:0.2-1:0.2-1, and more preferably 4-4.6:0.5-1:0.5-1.

4. The fluorinated chain extender according to any one of claims 1 to 3, characterized in that: The solution polymerization method is implemented as follows: dissolving the prepared monomer in a solvent, adding an initiator, heating to 65-80° C. and stirring for 6-10 hours to perform a copolymerization reaction, and after the reaction is completed, removing the solvent, washing, and drying to obtain a fluorine-containing chain extender.

5. The fluorinated chain extender according to claim 4, characterized in that: The solvent is a polar solvent, and more preferably the solvent is selected from one or more of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

6. The fluorinated chain extender according to claim 4, characterized in that: The initiator is selected from at least one of AIBN, ABVN, AIBME, AHCN and V-601.

7. A composition for preparing a PLA foam material, characterized in that: The composition for preparing PLA foaming material comprises pure PLA and the fluorine-containing chain extender according to any one of claims 1 to 6, wherein the mass of the fluorine-containing chain extender is 4 to 8 wt % of the mass of the pure PLA.

8. The composition for preparing a PLA foam material as claimed in claim 7, characterized in that: The composition for preparing the PLA foaming material consists of pure PLA and a fluorine-containing chain extender.

9. A PLA foam material, prepared from the composition for preparing a PLA foam material according to claim 7 or 8.

10. A method for preparing the PLA foam material according to claim 9, characterized in that: The preparation method comprises the following steps: (1) melt-blending the fluorinated chain extender and pure PLA particles by a torque rheometer to obtain a melt-blended sample; (2) hot pressing the melt blended sample obtained in step (1) using a flat vulcanizer to obtain a sheet with a thickness of 1 to 3 mm; (3) placing the sheet obtained in step (2) in a supercritical autoclave foaming machine, selecting supercritical CO2 as the supercritical gas for foaming molding, and obtaining a PLA foamed material.

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