Methylenefuran-containing aromatic skeleton diurea nucleating agent, heat-resistant polylactic acid composition and preparation method thereof

Abstract

The application belongs to the technical field of polymer materials, and particularly relates to a kind of methylene furan-containing aromatic skeleton double urea nucleating agent, heat-resistant polylactic acid composition and a preparation method thereof. A series of methylene furan-containing aromatic skeleton double urea polylactic acid nucleating agents are prepared by a green route using non-isocyanate as raw material, and a furfurylamine derived from biomass by a one-pot two-step method. In the polylactic acid composition, the mass content ratio of polylactic acid and nucleating agent is 100:0.1-5. Dry polylactic acid and methylene furan-containing aromatic skeleton double urea nucleating agent are mixed by a double-screw mixer at 150-220 DEG C for 3-15 min. The polylactic acid composition modified by the nucleating agent has a significant improvement in crystallization rate and crystallinity, and the heat resistance is further enhanced, so the composition has a good industrialization prospect.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a class of aromatic skeleton diurea nucleating agents containing methylene furan, heat-resistant polylactic acid compositions, and their preparation methods. Background Technology

[0002] Seeking sustainable alternatives to traditional petroleum-based plastics is an effective way to address the depletion of petroleum resources and reduce environmental pollution. To meet this urgent market demand, biodegradable plastics derived from renewable resources have emerged as a promising solution. Among various biodegradable plastics, polylactic acid (PLLA) stands out due to its excellent overall properties. PLA is derived from renewable resources, possesses good biodegradability and compatibility, and can be widely used in packaging materials and consumer goods.

[0003] However, polylactic acid (PLA) has significant drawbacks in heat resistance (Tg = 50–60℃), primarily due to its relatively low crystallinity. Therefore, improving the crystallinity of PLA is crucial. Modification of its chemical structure and processing techniques (such as biaxial stretching) are two key aspects of enhancing PLA crystallinity. Among various modification methods, adding nucleating agents (NAs) is a simple way to accelerate PLA crystallization. Adding nucleating agents provides nucleation sites, lowers the nucleation energy barrier, promotes rapid crystallization, and increases crystallinity. PLA nucleating agents can be broadly classified into inorganic and organic nucleating agents. Inorganic nucleating agents typically include talc, montmorillonite, carbon black, and apatite, but these agents have poor nucleation effects; small amounts have little effect, and higher concentrations can make the product brittle, affecting its performance.

[0004] Currently, several patents have disclosed nucleating agents for polylactic acid (PLA). For example, Chinese invention patent CN114634617A discloses an organic PLA nucleating agent synthesized from lactide polymerized by hexamethylolmelamine. The molecular chain ends form ester bonds with one carboxyl group of a carboxylate salt, while other carboxyl groups form ionic bonds with metal cations. However, the preparation process of this type of nucleating agent, which requires participation in PLA polymerization, is quite complex, and the raw material melamine suffers from poor solubility, which is clearly detrimental to the industrialization of PLA modifying agents. For instance, Chinese patent CN102634180A discloses a type of PLA nucleating agent containing one or two urea bonds, but it uses isocyanate obtained from phosgene as a raw material, which poses environmental pollution problems. Therefore, how to utilize biomass raw materials to develop a green and environmentally friendly nucleating agent with a simple preparation process and its preparation route, especially a green and environmentally friendly high-efficiency nucleating agent suitable for PLA and its preparation method, is an urgent technical problem to be solved. Summary of the Invention

[0005] To address the environmental pollution issues associated with the preparation of polylactic acid (PLA) nucleating agents in existing technologies, this application provides a type of methylene furan-containing aromatic skeleton biuret nucleating agent, a heat-resistant PLA composition, and a method for preparing the same. The methylene furan-containing aromatic skeleton biuret nucleating agent utilizes a green route using non-isocyanate raw materials, prepared from biomass-derived furfurylamine via a "one-pot two-step" method, which can significantly improve the crystallization temperature, crystallization rate, and heat resistance of PLA.

[0006] In a first aspect, the present invention provides a method for preparing a class of aromatic skeleton diurea nucleating agents containing methylene furan, mainly comprising the following steps:

[0007] S1. Under inert gas protection, furfurylamine, N,N'-carbonyldiimidazole, and ether solvents are added to the reactor and stirred at 20-35°C for 1-4 hours.

[0008] S2. Continue to add aromatic diamines with a benzene ring skeleton, react for 3-8 hours, and obtain the nucleating agent containing methylene furan and its aromatic skeleton diurea after separation and purification.

[0009] Furthermore, the molar ratio of furfurylamine to N,N'-carbonyldiimidazole is 1:1 to 1.2.

[0010] Furthermore, the molar ratio of the aromatic diamine to furfurylamine is 1:2 to 2.2.

[0011] Further, the ether solvent is at least one selected from diethyl ether, dipropyl ether, diisopropyl ether, ethyl butyl ether, dibutyl ether, dipentyl ether, tetrahydrofuran, 3-methylfuran, diisopentyl ether, dioxolane, 1,4-dioxane, 1,4-dichlorohexane, and cyclochloroethane.

[0012] Furthermore, the aromatic diamine is selected from at least one of p-phenylenediamine or m-phenylenediamine.

[0013] Furthermore, the inert gas is nitrogen or argon.

[0014] The specific synthetic route of the above preparation method is shown below:

[0015]

[0016] in, It is p-phenylenediamine or m-phenylenediamine. The specific response is as follows:

[0017]

[0018] Secondly, the present invention provides a class of aromatic skeleton diurea nucleating agents containing methylene furan prepared by the above method, the structural formula of which is shown below:

[0019]

[0020] Thirdly, the present invention provides a type of heat-resistant polylactic acid composition, comprising, by mass parts, 100 parts of polylactic acid and 0.1 to 5 parts of an aromatic skeleton biuret nucleating agent containing methylene furan.

[0021] Furthermore, the heat-resistant polylactic acid composition contains, by mass, 100 parts of polylactic acid and 1-2 parts of an aromatic skeleton biuret nucleating agent containing methylene furan.

[0022] Fourthly, the present invention provides a method for preparing a type of heat-resistant polylactic acid composition, the specific steps of which are as follows:

[0023] (1) Weigh out polylactic acid and a diurea nucleating agent containing methylene furan in proportion and place them in a vacuum oven to dry at 50-80°C for 8-24 hours, then mix them in advance;

[0024] (2) Place the mixture in a mixer, mix at a temperature of 160-220°C for 3-15 minutes, and rotate the rotor at 15-50 rpm to obtain the heat-resistant polylactic acid composition.

[0025] Beneficial effects:

[0026] The methylene furan-containing aromatic skeleton biuret nucleating agent prepared by this invention adopts a green synthesis route using non-isocyanate raw materials and is obtained from biomass-derived furfurylamine in a "one-pot two-step" method. This not only solves the problem of insufficient environmental protection in the synthesis process of nucleating agents in the prior art, but also significantly improves the crystallization temperature, crystallization rate and heat resistance of polylactic acid with the prepared methylene furan-containing aromatic skeleton biuret nucleating agent. Attached Figure Description

[0027] Figure 1 The synthetic route of dimethylene furan-terephthalurea in the examples is shown below;

[0028] Figure 2 The dimethylenefuran-phenylenediurea in Example 1 1 H-NMR spectrum;

[0029] Figure 3 The following are DSC cooling curves for Examples 4 and 1-3. Detailed Implementation

[0030] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0032] The preferred embodiments of the present invention will now be described in detail with reference to specific examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and essence.

[0033] Test instrument models: The nuclear magnetic resonance spectrometer used was a Bruker AVANCEⅢ500 (Bruker, Switzerland), and the differential scanning calorimeter used was a DSC 25 (TA, USA).

[0034] Example 1 (Preparation of a diurea nucleating agent with an aromatic skeleton containing methylene furan, dimethylene furan-terephthalurea)

[0035] The round-bottom reaction flask equipped with a magnetic stir bar was preheated and purged three times with nitrogen. Then, under a nitrogen atmosphere, a tetrahydrofuran solution containing 6.482 g (40 mmol) of N,N'-carbonyldiimidazole and 3.882 g (40 mmol) of furfurylamine were added sequentially. The reaction was carried out at 25°C with vigorous stirring for 2 hours, followed by the addition of 2.16 g (20 mmol) of 1,4-p-phenylenediamine, and the reaction was continued for 6 hours. After the reaction was complete, the mixture was filtered, the filter cake was washed once with tetrahydrofuran, and once with anhydrous ethanol. After drying, 6.94 g of a white powder was obtained, which is the aromatic skeleton biuret nucleating agent containing methylene furan, with a yield of 95.6%. The synthetic route is shown below. Figure 1 .

[0036] The product was characterized by 1H NMR spectroscopy, and the results are shown in the figure. Figure 2 .

[0037] Example 2 (Preparation of nucleating agent used in comparative example: dimethylenepyridine-terephthalurea)

[0038] The round-bottom reaction flask containing the magnetic inlet was preheated and purged three times with nitrogen. Then, under a nitrogen atmosphere, a tetrahydrofuran solution containing 6.482 g (40 mmol) of N,N'-carbonyldiimidazole and 4.33 g (40 mmol) of 2-aminomethylpyridine were added sequentially. After reacting with vigorous stirring at 25 °C for 2 hours, 2.16 g (20 mmol) of 1,4-p-phenylenediamine was added, and the reaction was continued for 6 hours. After the reaction was completed, the mixture was filtered, the filter cake was washed once with tetrahydrofuran, and once with anhydrous ethanol. After drying, 7.25 g of white powder was obtained, which was the nucleating agent, with a yield of 96.4%.

[0039] Example 3 (Preparation of nucleating agent used in comparative example, dibenzyl-terephthalurea)

[0040] The round-bottom reaction flask containing the magnetic inlet was preheated and purged three times with nitrogen. Then, under a nitrogen atmosphere, a tetrahydrofuran solution containing 6.482 g (40 mmol) of N,N'-carbonyldiimidazole and 4.28 g (4.0 mmol) of benzylamine were added sequentially. After reacting with vigorous stirring at 25 °C for 2 hours, 2.16 g (20 mmol) of 1,4-p-phenylenediamine was added, and the reaction was continued for 6 hours. After the reaction was completed, the mixture was filtered, the filter cake was washed once with tetrahydrofuran, and once with anhydrous ethanol. After drying, 7.04 g of white powder was obtained, which was the nucleating agent, with a yield of 92.0%.

[0041] Example 4 (Polylactic acid blend)

[0042] The nucleating agent dimethylene furan terephthalurea and polylactic acid prepared in Example 1 were dried in a vacuum oven at 60°C for 12 hours. 60g of polylactic acid and 0.18g of the nucleating agent were pre-mixed in a self-sealing bag and then placed in a SU-70B type micro mixer for melt mixing. The melt temperature and the three temperature control zones of the mixer were set to 180°C, 179°C, 178°C, and 175°C, respectively, and the rotor speed was set to 15 rpm. DSC non-isothermal crystallization testing showed a crystallization temperature of 105.6°C and a peak enthalpy of 32.7 J / g.

[0043] Example 5 (Polylactic Acid Blend)

[0044] The nucleating agent dimethylene furan terephthalurea and polylactic acid prepared in Example 1 were dried in a vacuum oven at 60°C for 12 hours. 60g of polylactic acid and 0.06g of the nucleating agent were pre-mixed in a self-sealing bag and then placed in a SU-70B type micro mixer for melt mixing. The melt temperature and the three temperature control zones of the mixer were set to 180°C, 179°C, 178°C, and 175°C, respectively, and the rotor speed was set to 15 rpm. DSC non-isothermal crystallization testing showed a crystallization temperature of 98.2°C and a peak enthalpy of 22.7 J / g.

[0045] Comparative Example 1 (Polylactic Acid Blend)

[0046] The comparative nucleating agent dimethylenepyridine terephthalurea prepared in Example 2 and polylactic acid were dried in a vacuum oven at 60°C for 12 hours. 60g of polylactic acid and 0.18g of the nucleating agent were pre-mixed in a self-sealing bag and then placed in a SU-70B micro internal mixer for melt mixing. The melt temperature and the three temperature control zones of the internal mixer were set to 180°C, 179°C, 178°C, and 175°C, respectively, and the rotor speed was set to 15 rpm. DSC non-isothermal crystallization testing showed a crystallization temperature of 99.1°C and a peak enthalpy of 26.4 J / g.

[0047] Comparative Example 2 (Polylactic Acid Blend)

[0048] The comparative nucleating agent dibenzyl terephthalurea and polylactic acid prepared in Example 3 were dried in a vacuum oven at 60°C for 12 hours. 60g of polylactic acid and 0.18g of the nucleating agent were pre-mixed in a self-sealing bag and then placed in a SU-70B micro internal mixer for melt mixing. The melt temperature and the three temperature control zones of the internal mixer were set to 180°C, 179°C, 178°C, and 175°C, respectively, and the rotor speed was set to 15 rpm. DSC non-isothermal crystallization testing showed a crystallization temperature of 96.8°C and a peak enthalpy of 16.3 J / g.

[0049] Comparative Example 3 (Polylactic Acid Intensive Mixture)

[0050] Polylactic acid (PLA) was dried in a vacuum oven at 60°C for 12 hours. 60g of PLA was then placed in a SU-70B mini internal mixer for melt mixing. The melt temperature and the three temperature control zones of the mixer were set to 180°C, 179°C, 178°C, and 175°C, respectively, and the rotor speed was set to 15 rpm. No crystallization peak was observed on the cooling curve using DSC non-isothermal crystallization testing.

[0051] As can be seen from the above embodiments and comparative examples, the 2-methylenefuran-terminated aromatic skeleton diurea nucleating agent of this application has a better nucleation effect on polylactic acid (e.g., Figure 3 Its crystallization temperature and enthalpy have increased significantly compared to before, indicating that the degree of crystallization has been improved.

Claims

1. A type of heat-resistant polylactic acid composition, characterized in that, The product comprises, by weight, 100 parts polylactic acid and 0.1-5 parts an aromatic skeleton biuret nucleating agent containing methylene furan; the structural formula of the aromatic skeleton biuret nucleating agent containing methylene furan is as follows: or 。 2. The heat-resistant polylactic acid composition according to claim 1, characterized in that, It contains 100 parts by weight of polylactic acid and 1-2 parts of an aromatic skeleton biuret nucleating agent containing methylene furan.

3. A method for preparing a heat-resistant polylactic acid composition as described in any one of claims 1 or 2, characterized in that, First, the dried polylactic acid and the aromatic skeleton biuret nucleating agent containing methylene furan are premixed in proportion, and then the mixture is placed in a mixer for internal mixing to obtain the heat-resistant polylactic acid composition.

4. The preparation method according to claim 3, characterized in that, The mixing temperature is 160-220℃, the mixing time is 3-15 minutes, and the rotor speed is 15-50 rpm.

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