A polylactic acid nucleating agent and its preparation method and application

Abstract

The present invention relates to the technical field of environmentally friendly materials, and discloses a polylactic acid nucleating agent and its preparation method and application. First, 5-sulfo dimethyl isophthalate sodium is reacted with hydrazine hydrate to prepare isophthalic acid hydrazide-5-sulfonate sodium, and then isophthalic acid hydrazide-5-sulfonate sodium is reacted with lactic acid, and a capping agent is added after a period of time to continue the reaction to obtain a novel nucleating agent. The present invention prepares a high heat-resistant polylactic acid composition by melt blending a nucleating agent and polylactic acid, and adding a very small amount of nucleating agent can greatly increase the crystallization rate of polylactic acid, and enables polylactic acid products to obtain better heat resistance. This type of nucleating agent preparation method is simple and has good industrial prospects.

Description

Technical Field

[0001] The invention relates to the technical field of environmentally friendly materials, and in particular to a polylactic acid nucleating agent and a preparation method and application thereof. Background Art

[0002] Polylactic acid (PLA) is a biodegradable polymer material made from lactic acid. It is widely used in disposable tableware and food packaging because of its non-toxicity. However, the crystallization rate of polylactic acid itself is slow and its crystallization ability is poor. The products obtained under conventional processing conditions do not have high heat resistance, and the working temperature can only be lower than the glass transition temperature, which greatly limits its application and promotion in the field of disposable food packaging. Therefore, it is necessary to improve the crystallization performance of polylactic acid to achieve high heat resistance of the product. At present, there are many ways to improve the crystallization performance of polylactic acid in industry, but it is generally recognized that the simplest and most efficient way is to use nucleating agents for heterogeneous nucleation. The nucleating agents of polylactic acid can be divided into two categories: inorganic nucleating agents and organic nucleating agents. Inorganic nucleating agents usually include montmorillonite, hydrotalcite, silica, apatite and carbon black. Nucleating agents have one thing in common—poor nucleating effect. When the addition amount is small, the nucleating effect is not obvious. When the content is high, it is easy to agglomerate, which eventually leads to the decrease of mechanical properties of polylactic acid products and affects their use.

[0003] In order to solve this problem, people have turned their attention to organic nucleating agents. Publication No. CN111333910A discloses a rare earth aryl phosphate containing an amino group, which can be used as a nucleating agent for polylactic acid to increase its Vicat softening temperature. Publication No. CN101857715A discloses a method for rapid crystallization of polylactic acid, in which a bisamide compound synthesized from benzoyl hydrazide and alkyl diacyl dichloride is used as a nucleating agent for polylactic acid.

[0004] Publication No. CN113150381A discloses a 1,4-naphthalene dicarboxylic acid dinicotinyl hydrazide polylactic acid nucleating agent, which can improve the crystallinity of polylactic acid and enhance its heat resistance. The nucleating effect of the above-mentioned organic nucleating agents is significant, but these nucleating agents mostly contain aromatic hydrocarbon structures and heavy metal ions, which have potential safety hazards for products used in the food field. Therefore, the development of an efficient and safe polylactic acid nucleating agent is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The invention aims at the problem that the nucleation efficiency of polylactic acid organic nucleating agent is low and provides a polylactic acid nucleating agent, which can greatly accelerate and improve the crystallinity and heat resistance of polylactic acid when used in a trace amount.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a polylactic acid nucleating agent comprises the steps of:

[0008] Step 1, reflux reaction of dimethyl isophthalate-5-sodium sulfonate and hydrazine hydrate in a solvent to obtain isophthalic acid hydrazide-5-sodium sulfonate;

[0009] Step 2, subjecting sodium isophthalic acid hydrazide-5-sulfonate and lactic acid to a polymerization reaction under the action of a catalyst, adding a capping agent after the reaction is completed to continue the reaction, and obtaining the nucleating agent through dehydration.

[0010] The reaction formula is as follows:

[0011] .

[0012] In the present invention, dimethyl isophthalate-5-sodium sulfonate and hydrazine hydrate are used as raw materials to prepare a nucleation precursor containing both hydrazide and sulfonate structures, and the nucleation precursor is polymerized with lactic acid to obtain an oligomer containing hydrazide and sulfonate structures. Since the matrix is ​​lactic acid, the oligomer has good compatibility when mixed with polylactic acid, and does not have problems such as poor dispersibility and easy migration. The reason for preparing the oligomer is to prevent small molecular hydrazide compounds from migrating to the surface of the product and causing toxicity.

[0013] Preferably, the molar ratio of dimethyl isophthalate-5-sodium sulfonate to hydrazine hydrate in step 1 is 1:4-8, so as to promote the full reaction of the dimethyl isophthalate-5-sodium sulfonate raw material.

[0014] Preferably, the solvent in step 1 comprises one or more of methanol, ethanol, isopropanol, and n-butanol;

[0015] Preferably, in step 1, the reaction temperature is 70-100° C. and the reaction time is 0.5-1 h.

[0016] Preferably, in step 2, the molar ratio of sodium 5-sulfonate of phthaloyl dicarboxylic acid hydrazide, lactic acid and the end-capping agent is 1:(5-10):(1-2).

[0017] Preferably, in step 2, the polymerization reaction temperature is 130-200° C., and the reaction time is 12-25 h; after adding the end-capping agent, the reaction is continued for 2-6 h.

[0018] Preferably, the dehydration in step 2 is carried out by vacuum distillation at 130-200° C. and 0.001-0.01 MPa for 1-2 h to remove water and part of the unreacted raw materials.

[0019] Preferably, the end-capping agent comprises one or two of benzoic acid, n-butyric acid and propionic acid.

[0020] Preferably, the catalyst comprises one or more of stannous octoate, stannous chloride, antimony trioxide, and tetrapropyl titanate; the mass of the catalyst is 0.1-3% of the total mass of sodium isophthaloyl hydrazide-5-sulfonate, lactic acid and the capping agent.

[0021] The present invention also provides a nucleating agent prepared according to the preparation method.

[0022] The present invention also provides a highly crystalline polylactic acid, comprising polylactic acid and the nucleating agent; the mass of the nucleating agent is 0.1-3% of the polylactic acid. In the present invention, the amount of the nucleating agent used is extremely small, and a significant nucleating effect can be achieved at an amount of only 0.5%, which greatly improves the crystallization performance of the polylactic acid, has a fast crystallization speed, and a good nucleating effect. And because the amount added is small, the mechanical properties of the matrix are very little affected.

[0023] The present invention also provides a method for preparing the highly crystalline polylactic acid, characterized in that it comprises the steps of: premixing the polylactic acid and the nucleating agent after drying, and then melt-blending, extruding and granulating to obtain the highly crystalline polylactic acid. The melt-blending temperature is 160-190°C.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The nucleating agent prepared by the present invention is a precursor containing hydrazide and sulfonate structures and a polymer of lactic acid, and has good compatibility with a polylactic acid matrix; this type of nucleating agent has the structural characteristics of sulfonate and hydrazide, can accelerate the crystallization of PLA through a unique self-assembly behavior, thereby improving its heat resistance, and can achieve an excellent nucleation crystallization effect when added in a very small amount. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the H NMR spectrum of sodium isophthaloyl hydrazide-5-sulfonate prepared in Example 1.

[0027] Figure 2 This is the Fourier infrared spectrum of sodium isophthaloyl hydrazide-5-sulfonate prepared in Example 1.

[0028] Figure 3 It is the DSC curve diagram of the polylactic acid prepared in the examples and comparative examples when cooled at 10°C / min. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

[0030] The raw materials used in the following specific embodiments are all purchased from the market.

[0031] Example 1

[0032] (1) Preparation of sodium isophthalic acid hydrazide-5-sulfonate: 0.1 mol of sodium 5-sulfoisophthalic acid dimethyl ester, 0.7 mol of hydrazine hydrate (80%) and an excess of anhydrous ethanol solvent were added to a reactor and refluxed at 80°C for 15 h. After the reaction was completed, the mixture was cooled to room temperature, filtered and repeatedly washed with anhydrous ethanol, and dried to obtain sodium isophthalic acid hydrazide-5-sulfonate. Its NMR spectrum is shown in the figure below. Figure 1 As shown, the Fourier infrared spectrum is Figure 2 As shown, the target structure compound can be obtained through analysis.

[0033] (2) 0.1 mol of sodium isophthalic acid hydrazide-5-sulfonate, 0.8 mol of lactic acid and 2.7 g of stannous octoate prepared above were added into a reactor, and the mixture was stirred and reacted in a N2 atmosphere at 150°C for 12 h. Then, 0.1 mol of benzoic acid was added into the N2 atmosphere and the mixture was stirred and reacted for 4 h. After the reaction, the mixture was dehydrated at 160°C and 0.001 MPa to finally obtain a polymer containing a hydrazide and sulfonate structure, which was used as a nucleating agent for polylactic acid.

[0034] (3) 5 g of the above-obtained oligomer was taken, premixed with 1000 g of polylactic acid, and then fed into a twin-screw extruder, and extruded and granulated at 180° C. to obtain highly crystalline polylactic acid pellets.

[0035] The non-isothermal crystallization melting behavior of polylactic acid was studied on a differential scanning calorimeter using the highly crystalline polylactic acid particles. The test temperature program was as follows: 5-10 mg of polylactic acid material was taken, heated to 200°C at 10°C / min, and isothermally heated for 5 minutes to eliminate the thermal history; then cooled to 30°C at 10°C / min; finally heated to 200°C at 10°C / min, and then cooled to 30°C at 10°C / min. The DSC curve is shown in Figure 2. Figure 3 shown.

[0036] The highly crystalline polylactic acid particles were injection molded into 80×10×4 mm rectangular standard specimens at 190°C, and then the heat deformation temperature of the specimens was measured using a heat deformation temperature tester, wherein the test conditions were a load of 0.45 MPa and a heating rate of 120°C / h.

[0037] Example 2

[0038] (1) Preparation of sodium isophthalic acid hydrazide-5-sulfonate: First, 0.1 mol of sodium 5-sulfoisophthalic acid dimethyl ester, 0.7 mol of hydrazine hydrate (80%) and methanol were added into a reactor and refluxed at 70°C for 20 h. After the reaction, the mixture was cooled to room temperature, filtered and repeatedly washed with anhydrous ethanol, and dried to obtain sodium isophthalic acid hydrazide-5-sulfonate.

[0039] (2) 0.1 mol of sodium isophthalic acid hydrazide-5-sulfonate, 1 mol of lactic acid and 3.9 g of tetrapropyl titanate prepared above were added into a reactor, and the mixture was stirred and reacted in a N2 atmosphere at 160°C for 18 h. Then, 0.15 mol of n-butyric acid was added in a N2 atmosphere and the mixture was stirred and reacted for 6 h. After the reaction, the mixture was dehydrated at 170°C and 0.01 MPa to finally obtain a polymer containing hydrazide and sulfonate structures.

[0040] (3) Take 5 g of the above-obtained oligomer, premix it with 1000 g of polylactic acid, and then put it into a twin-screw extruder. Extrusion granulation is performed at 180° C. to obtain highly crystalline polylactic acid particles.

[0041] The non-isothermal crystallization melting behavior of polylactic acid was studied on a differential scanning calorimeter using the highly crystalline polylactic acid particles. The test temperature program was as follows: 5-10 mg of polylactic acid material was taken, heated to 200°C at 10°C / min, and isothermally heated for 5 minutes to eliminate the thermal history; then cooled to 30°C at 10°C / min; finally heated to 200°C at 10°C / min, and then cooled to 30°C at 10°C / min. The DSC curve is shown in Figure 2. Figure 3 shown.

[0042] The highly crystalline polylactic acid particles were injection molded into 80×10×4 mm rectangular standard specimens at 190°C, and then the heat deformation temperature of the specimens was measured using a heat deformation temperature tester, wherein the test conditions were a load of 0.45 MPa and a heating rate of 120°C / h.

[0043] Example 3

[0044] (1) Preparation of sodium isophthalic acid hydrazide-5-sulfonate: First, 0.1 mol of sodium 5-sulfoisophthalic acid dimethyl ester, 0.7 mol of hydrazine hydrate (80%) and anhydrous ethanol were added into a reactor, and refluxed at 80°C for 15 h. After the reaction, the mixture was cooled to room temperature, filtered and repeatedly washed with anhydrous ethanol, and dried to obtain sodium isophthalic acid hydrazide-5-sulfonate.

[0045] (2) 0.1 mol of sodium isophthalic acid hydrazide-5-sulfonate, 1 mol of lactic acid and 3.25 g of antimony trioxide prepared above were added into a reactor, and the mixture was stirred and reacted in a N2 atmosphere at 140°C for 25 h. Then, 0.15 mol of propionic acid was added in a N2 atmosphere and the mixture was stirred and reacted for 6 h. After the reaction, the mixture was dehydrated at 150°C and 0.005 MPa to finally obtain a polymer containing hydrazide and sulfonate structures.

[0046] (3) Take 5 g of the above-obtained oligomer, premix it with 1000 g of polylactic acid, and then put it into a twin-screw extruder. Extrusion granulation is performed at 180° C. to obtain highly crystalline polylactic acid particles.

[0047] The non-isothermal crystallization melting behavior of polylactic acid was studied on a differential scanning calorimeter using the highly crystalline polylactic acid particles. The test temperature program was as follows: 5-10 mg of polylactic acid material was taken, heated to 200°C at 10°C / min, and isothermally heated for 5 minutes to eliminate the thermal history; then cooled to 30°C at 10°C / min; finally heated to 200°C at 10°C / min, and then cooled to 30°C at 10°C / min. The DSC curve is shown in Figure 2. Figure 3 shown.

[0048] The highly crystalline polylactic acid particles were injection molded into 80×10×4 mm rectangular standard specimens at 190°C, and then the heat deformation temperature of the specimens was measured using a heat deformation temperature tester, wherein the test conditions were a load of 0.45 MPa and a heating rate of 120°C / h.

[0049] Comparative Example 1

[0050] The commercial nucleating agent TMC300 and polylactic acid were dried in a vacuum drying oven at 60°C for 24 hours, and then 5g of TMC300 and 1000g of polylactic acid were premixed and evenly put into a twin-screw extruder, and extruded and granulated at 180°C to obtain highly crystalline polylactic acid particles.

[0051] The non-isothermal crystallization melting behavior of polylactic acid was studied on a differential scanning calorimeter using the highly crystalline polylactic acid particles. The test temperature program was as follows: 5-10 mg of polylactic acid material was taken, heated to 200°C at 10°C / min, and isothermally heated for 5 minutes to eliminate the thermal history; then cooled to 30°C at 10°C / min; finally heated to 200°C at 10°C / min, and then cooled to 30°C at 10°C / min. The DSC curve is shown in Figure 2. Figure 3 shown.

[0052] The highly crystalline polylactic acid particles were injection molded into 80×10×4 mm rectangular standard specimens at 190°C, and then the heat deformation temperature of the specimens was measured using a heat deformation temperature tester, wherein the test conditions were a load of 0.45 MPa and a heating rate of 120°C / h.

[0053] Comparative Example 2

[0054] The polylactic acid was dried at 60°C in a vacuum drying oven for 24 h, and then the dried polylactic acid particles were put into a twin-screw extruder and extruded and granulated at 180°C to obtain pure PLA samples.

[0055] The above-mentioned polylactic acid particles were used to study the non-isothermal crystallization melting behavior of polylactic acid on a differential scanning calorimeter. The test temperature program was as follows: 5-10 mg of polylactic acid material was taken, and the temperature was raised to 200°C at 10°C / min, and the temperature was kept isothermally for 5 minutes to eliminate the thermal history; then the temperature was lowered to 30°C at 10°C / min; finally, the temperature was raised to 200°C at 10°C / min, and then the temperature was lowered to 30°C at 10°C / min. The DSC curve is as follows: Figure 3 shown.

[0056] The polylactic acid particles were injection molded into 80×10×4 mm rectangular standard specimens at 190° C., and then the heat deformation temperature of the specimens was measured using a heat deformation temperature tester, wherein the test conditions were a load of 0.45 MPa and a heating rate of 120° C. / h.

[0057] The DSC data of the embodiments and comparative examples are shown in Tables 1 and Figure 3 As shown, it can be seen that pure PLA has basically no crystallinity. The nucleating agents prepared in Examples 1-3 of the present invention can significantly increase the crystallization rate of polylactic acid, and the crystallinity is also significantly improved. In the embodiment, only 0.5% of the nucleating agent is added, and the crystallization temperature of polylactic acid is increased to 130.2°C, 131.1°C and 131.3°C, respectively, and the crystallinity can reach 52.7, 51.1 and 51.5, respectively; the effect is better than the nucleating agent TMC300 in Comparative Example 1 (crystallization temperature is 127.2°C, crystallinity is 50.2%). The amount of this type of nucleating agent is also the amount of conventional nucleating agents, indicating that it is a very efficient new type of hydrazide nucleating agent.

[0058] Table 1 DSC data of examples and comparative examples

[0059] Serial number Crystallization temperature (℃) Crystallinity (%) Crystallization enthalpy (J / g) Example 1 130.2 52.7 49.36 Example 2 131.1 51.1 47.87 Example 3 131.3 51.5 48.27 Comparative Example 1 127.2 50.2 47.04 Comparative Example 2 none none none

[0060] Table 2 Heat deformation temperature data of examples and comparative examples

[0061] Serial number Heat deformation temperature (℃) Example 1 92.4 Example 2 90.9 Example 3 91.2 Comparative Example 1 90.5 Comparative Example 2 54.3 .

[0062] The heat deformation temperature data of the examples and comparative examples are shown in Table 2. The heat deformation temperature of pure PLA is only 54.3°C, which does not have high temperature resistance. The nucleating agents prepared in Examples 1-3 of the present invention can significantly increase the heat deformation temperature of polylactic acid. In the examples, only 0.5% of the nucleating agent is added, and the heat deformation temperature of polylactic acid is increased to 92.4°C, 90.9°C and 91.2°C respectively; slightly higher than the nucleating agent TMC300 in Comparative Example 1 (heat deformation temperature is 90.5°C), and both show good heat resistance.

Claims

1. A method for preparing a polylactic acid nucleating agent, characterized in that: Includes steps: Step 1, reflux reaction of dimethyl isophthalate-5-sodium sulfonate and hydrazine hydrate in a solvent to obtain isophthalic acid hydrazide-5-sodium sulfonate; Step 2, subjecting sodium isophthaloyl hydrazide-5-sulfonate and lactic acid to a polymerization reaction under the action of a catalyst, adding a capping agent after the reaction is completed to continue the reaction, and obtaining the nucleating agent through dehydration; The end-capping agent is one or two of benzoic acid, n-butyric acid and propionic acid; The catalyst is one or more of stannous octoate, stannous chloride, antimony trioxide, and tetrapropyl titanate.

2. The method for preparing a polylactic acid nucleating agent according to claim 1, characterized in that: In step 1, the molar ratio of dimethyl 5-sulfonate sodium isophthalate to hydrazine hydrate is 1:4-8; The solvent in step 1 includes one or more of methanol, ethanol, isopropanol, and n-butanol.

3. The method for preparing a polylactic acid nucleating agent according to claim 1, characterized in that: In step 1, the reaction temperature is 70-100° C. and the reaction time is 0.5-1 h.

4. The method for preparing a polylactic acid nucleating agent according to claim 1, characterized in that: In step 2, the molar ratio of sodium 5-sulfonate of phthaloyl dicarboxylic acid hydrazide, lactic acid and the end-capping agent is 1:(5-10):(1-2).

5. The method for preparing a polylactic acid nucleating agent according to claim 1, characterized in that: In step 2, the polymerization reaction temperature is 130-200° C., and the reaction time is 12-25 hours; after adding the end-capping agent, the reaction is continued for 2-6 hours.

6. The method for preparing a polylactic acid nucleating agent according to claim 1, characterized in that: The mass of the catalyst is 0.1-3% of the total mass of sodium isophthaloyl hydrazide-5-sulfonate, lactic acid and the end-capping agent; In step 2, dehydration is carried out by vacuum distillation at 130-200° C. and 0.001-0.01 MPa for 1-2 h.

7. A nucleating agent obtained according to the preparation method according to any one of claims 1 to 6.

8. A highly crystalline polylactic acid, characterized in that: The invention comprises polylactic acid and the nucleating agent according to claim 7; the mass of the nucleating agent is 0.1-3% of the polylactic acid.

9. The method for preparing highly crystalline polylactic acid according to claim 8, characterized in that: The method comprises the following steps: premixing the polylactic acid and the nucleating agent after drying, and then performing melt blending, extrusion and granulation to obtain the highly crystalline polylactic acid.

10. The method for preparing highly crystalline polylactic acid according to claim 9, characterized in that: The temperature of melt blending is 160-190°C.

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