Polylactic acid grafted modified zinc oxide nanoparticles and their preparation method

Abstract

This invention relates to the technical field of zinc oxide surface modification, specifically to polylactic acid (PLA) grafted zinc oxide nanoparticles and their preparation method, comprising the following steps: adding zinc oxide nanoparticles to an alkaline solution of a certain pH value for surface modification, followed by drying to obtain surface-treated ZnO powder; reacting the obtained surface-treated ZnO powder with PLA at a certain temperature; after the reaction, cooling the system to room temperature, adding an organic solvent to disperse the powder, centrifuging to obtain a precipitate, and drying to obtain the grafted zinc oxide nanoparticles. In the preparation method of this invention, the grafting reaction can be carried out without a catalyst and solvent. By surface-treating ZnO, its reactivity is improved, thereby increasing the grafting rate. The zinc oxide nanoparticles grafted by the preparation method of this invention can effectively avoid particle agglomeration and can be suspended in solution for a long time, effectively improving their blending effect in PLA.

Description

Technical Field

[0001] This invention relates to the technical field of zinc oxide surface modification, specifically to a polylactic acid grafted modified zinc oxide nanoparticle and its preparation method. Background Technology

[0002] Zinc oxide, a commonly used chemical additive, is applied in semiconductor products such as liquid crystal displays, thin-film transistors, and light-emitting diodes. However, due to the presence of hydroxyl groups on its surface, high hydrophilicity, and surface energy, zinc oxide particles are prone to agglomeration and are difficult to disperse uniformly in a matrix.

[0003] Solution polymerization is often used to graft polylactic acid (PLA) onto particle surfaces. This method involves grafting lactide monomer, catalyst, and modified particles onto the surface to achieve surface modification. However, because lactide monomer is used, the polymerization reaction occurs during the grafting process, making it difficult to control the molecular weight of the grafted PLA. Furthermore, the addition of the catalyst introduces additional organic reagents. Therefore, it is necessary to achieve controllable synthesis of the grafting process. In addition, the preparation process requires the addition of organic reagents, which can cause environmental pollution. Melt grafting is usually difficult to achieve due to its low reactivity.

[0004] To solve this problem, the surface of ZnO is treated to enhance its reactivity, thus enabling grafting reactions to occur without solvents. ZnO is surface-treated in an alkaline solution to increase the activity of hydroxyl groups on the ZnO surface, thereby improving reactivity and allowing grafting reactions to occur without solvents or catalysts. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing polylactic acid grafted modified zinc oxide nanoparticles, which can carry out the grafting reaction without the need for catalysts and solvents, and improves the grafting rate by surface treatment of ZnO to enhance its reactivity.

[0006] The second objective of this invention is to provide polylactic acid grafted modified zinc oxide nanoparticles, which can effectively prevent particle agglomeration and can be suspended in solution for a long time, thus effectively improving their blending effect in polylactic acid.

[0007] One of the solutions adopted to achieve the objective of this invention is: a method for preparing polylactic acid grafted modified zinc oxide nanoparticles, comprising the following steps:

[0008] Step 1: Add zinc oxide nanoparticles to an alkaline solution with a certain pH value for surface modification, and then dry to obtain surface-treated ZnO powder;

[0009] Step 2: React the surface-treated ZnO powder obtained in Step 1 with polylactic acid at a certain temperature;

[0010] Step 3: After the reaction is complete, the system is cooled to room temperature, an organic solvent is added to disperse the powder, centrifugation is performed to obtain a precipitate, and after drying, the grafted modified zinc oxide nanoparticles are obtained.

[0011] Preferably, in step 1, the alkaline solution NaOH is used.

[0012] Preferably, in step 1, the pH value is 12-14.

[0013] Preferably, in step 1, zinc oxide nanoparticles are added to a deionized aqueous solution so that the liquid level is just above the powder, the pH is adjusted to 12-14 with 0.1 mol / L NaOH solution, the reaction is stirred for 2-4 hours, and after drying, surface-treated ZnO powder is obtained.

[0014] Preferably, in step 1, the drying temperature is 60-80℃.

[0015] Preferably, in step 2, the reaction temperature is 160-180℃.

[0016] Preferably, in step 2, the mass ratio of zinc oxide to polylactic acid is 1:1-2.

[0017] Preferably, in step 2, the stirring speed is 350-650 rpm.

[0018] Preferably, in step 3, the organic solvent is at least one of dichloromethane, N,N-dimethylformamide, dimethyl acetal, and hexafluoroisopropanol.

[0019] Preferably, in step 3, the speed is 10000-12000 rpm and the time is 10-20 min.

[0020] The second objective of this invention is achieved by preparing polylactic acid grafted modified zinc oxide nanoparticles using the aforementioned preparation method.

[0021] The present invention has the following advantages and beneficial effects:

[0022] In the preparation method of the present invention, the grafting reaction can be carried out without catalyst and solvent. The grafting rate is improved by surface treatment of ZnO to enhance its reactivity.

[0023] The zinc oxide nanoparticles grafted by the preparation method of the present invention can effectively avoid particle agglomeration and can be suspended in solution for a long time, which can effectively improve their blending effect in polyemulsion.

[0024] The preparation method of this invention is simple and easy to implement, and is easy to promote and apply. Attached Figure Description

[0025] Figure 1: A schematic diagram of the appearance and structure of the polylactic acid surface-grafted modified zinc oxide particles of the present invention;

[0026] Figure 2 X-ray diffraction pattern of the microstructure of polylactic acid surface-grafted modified zinc oxide particles of the present invention;

[0027] Figure 3 Infrared spectroscopy of polylactic acid-grafted modified zinc oxide particles of the present invention;

[0028] Figure 4 Thermogravimetric curves of polylactic acid surface-grafted modified zinc oxide particles of this invention;

[0029] Figure 5 Dynamic light scattering analysis spectrum of polylactic acid surface-grafted modified zinc oxide particles of this invention;

[0030] Figure 6 Scanning electron microscopy morphology analysis of polylactic acid surface-grafted modified zinc oxide particles of the present invention. Detailed Implementation

[0031] To better understand the present invention, the following embodiments are further illustrations of the present invention, but the content of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] A method for preparing polylactic acid grafted modified zinc oxide nanoparticles, the specific preparation method is as follows:

[0034] Step 1: Add zinc oxide particles to a 100ml flask, add deionized water so that the liquid level just covers the powder, adjust the pH value to 12 with 0.1mol / L NaOH solution, react for 2 hours, and then dry to obtain surface-treated ZnO particles.

[0035] Step 2: Add the surface-treated ZnO particles and polylactic acid to a 100ml flask, raise the temperature to 160℃, stir at 350rpm, and react for 2-4 hours.

[0036] Step 3: After sufficient cooling, pour 50 ml of dichloromethane into the flask. After the powder disperses, pour out the solution. Centrifuge the obtained solution and discard the supernatant to obtain the lower layer powder. Dry the powder at 60℃ for 24 h to obtain polylactic acid surface-grafted modified zinc oxide particles. According to the reaction grafting time, they are named g-ZnO-2 (2 hours), g-ZnO-3 (3 hours), and g-ZnO-4 (4 hours).

[0037] More specifically, in step 2 of this embodiment, the mass of zinc oxide particles added is 10g, and in step 3 of this embodiment, the centrifugation rate is 12000rpm / min and the time is 10min.

[0038] The prepared polylactic acid surface-grafted modified zinc oxide particles, such as Figure 1 As shown.

[0039] The samples prepared in the above embodiments were subjected to the following tests:

[0040] 1. X-ray diffraction pattern:

[0041] The X-ray diffraction pattern of the microstructure of polylactic acid surface-grafted zinc oxide particles is shown in the figure. Figure 2 As shown, X-ray diffraction analysis confirmed that the polylactic acid surface-modified zinc oxide particles g-ZnO-2, g-ZnO-3, and g-ZnO-4 have the same pattern as standard zinc oxide, indicating that the polylactic acid surface modification has no effect on the structure of zinc oxide, although the peak intensity will be slightly reduced.

[0042] 2. Infrared Spectroscopy

[0043] Infrared spectroscopy of polylactic acid-grafted zinc oxide particles as follows: Figure 3 As shown, infrared spectroscopy confirms that the surface-modified zinc oxide particles g-ZnO-2, g-ZnO-3, and g-ZnO-4 of polylactic acid exhibit a high spectral density at 3450 cm⁻¹. -1 Absorption peaks appeared near the band, which is attributed to OH stretching, at 1586 cm⁻¹. -1 The absorption peaks appearing in the band are attributed to COO - Antisymmetric stretching, at 1048cm -1 The absorption peaks appearing in the band are attributed to the stretching and contraction of CO, while the unmodified ZnO particles do not exhibit the aforementioned absorption peaks. Combined with infrared spectroscopy analysis, this also confirms the success of the surface modification of the zinc oxide particles.

[0044] 3. Thermogravimetric curve

[0045] The thermogravimetric curve of polylactic acid surface-grafted modified zinc oxide particles is as follows: Figure 4 As shown, zinc oxide particles exhibit high heat resistance; thermogravimetric analysis reveals a mass loss of less than 2% at 600℃. For zinc oxide particles modified with polylactic acid (PLA), the mass loss below 150℃ is primarily due to the evaporation of surface crystal water and adsorbed solvent; at 150℃, surface PLA begins to degrade; and the mass loss in the 150-450℃ range is mainly caused by the decomposition of grafted PLA. The grafting rate of PLA surfaces at different grafting times can be calculated using the following formula:

[0046]

[0047] Among them, L g-ZnO This represents the mass loss of polylactic acid surface-modified zinc oxide particles in the temperature range of 150–600℃; L ZnOThis represents the mass loss of zinc oxide particles in the temperature range of 150–600℃.

[0048] Calculations showed that the grafting rate of g-ZnO-3 was the highest at 31.6% with a reaction time of 3 hours, while the grafting rate of g-ZnO-4 decreased to 28.5% with a reaction time of 4 hours. The grafting rate of g-ZnO-2 was the lowest at 8.7% with a reaction time of 2 hours. This may be because the reaction time of 2 hours is too short, resulting in poor polylactic acid grafting, while the reaction time of 4 hours is too long, causing thermal decomposition of the polylactic acid grafted on the surface, thus reducing the grafting rate. The best grafting effect was observed at 3 hours.

[0049] 4. Dynamic light scattering

[0050] Dynamic light scattering analysis spectrum of polylactic acid surface-grafted modified zinc oxide particles as shown in the figure. Figure 5 As shown, dynamic light scattering confirms that with increasing reaction time, the intensity of the peaks of g-ZnO-2, g-ZnO-3, and g-ZnO-4 in the lower size direction gradually increases, and the width of the peaks gradually decreases with increasing reaction time. This also confirms that the surface grafting modification of polylactic acid can improve the dispersion of zinc oxide particles, making the particle size distribution more uniform and reducing the occurrence of agglomeration.

[0051] 5. Scanning electron microscopy morphology analysis

[0052] Scanning electron microscopy morphology analysis of polylactic acid surface-grafted modified zinc oxide particles as follows: Figure 6 As shown, scanning electron microscopy also confirmed the success of polylactic acid (PLA) surface modification, with no PLA deposition on the unmodified zinc oxide surface. PLA deposition appeared on the surface of the PLA-modified zinc oxide particles. The surface of g-ZnO-2 grafted for 2 hours showed less PLA, while g-ZnO-3 grafted for 3 hours and g-ZnO-4 grafted for 4 hours showed significant PLA deposition.

[0053] The above description is merely a preferred embodiment of the present invention, and should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing polylactic acid grafted modified zinc oxide nanoparticles, characterized in that, Includes the following steps: Step 1: Add zinc oxide nanoparticles to an alkaline solution with a pH of 12-14 for surface modification, and then dry to obtain surface-treated ZnO powder; Step 2: React the surface-treated ZnO powder obtained in Step 1 with polylactic acid at 160-180℃; Step 3: After the reaction is complete, the system is cooled to room temperature, an organic solvent is added to disperse the powder, centrifugation is performed to obtain a precipitate, and after drying, the grafted modified zinc oxide nanoparticles are obtained.

2. The method for preparing polylactic acid grafted modified zinc oxide nanoparticles according to claim 1, characterized in that: In step 1, the alkaline solution used is NaOH solution.

3. The method for preparing polylactic acid grafted modified zinc oxide nanoparticles according to claim 1, characterized in that: In step 1, the drying temperature is 60-80℃.

4. The method for preparing polylactic acid grafted modified zinc oxide nanoparticles according to claim 1, characterized in that: In step 2, the reaction time is 2-4 hours.

5. The method for preparing polylactic acid grafted modified zinc oxide nanoparticles according to claim 1, characterized in that: In step 2, the mass ratio of zinc oxide to polylactic acid is 1:1-2.

6. The method for preparing polylactic acid grafted modified zinc oxide nanoparticles according to claim 1, characterized in that: In step 3, the organic solvent is at least one of dichloromethane, N,N-dimethylformamide, dimethyl acetal, and hexafluoroisopropanol.

7. A polylactic acid grafted modified zinc oxide nanoparticle, characterized in that: It is prepared by any one of claims 1-6.

Images