Polylactic acid graft modified zinc oxide nanoparticles and preparation method thereof

Abstract

The invention relates to the technical field of zinc oxide surface modification, in particular to polylactic acid graft modified zinc oxide nanoparticles and a preparation method thereof.The preparation method comprises the following steps that the zinc oxide nanoparticles are added into an alkali solution with a certain pH value for surface modification, drying is conducted after surface modification is completed, and ZnO powder with the surface treated is obtained; reacting the obtained ZnO powder subjected to surface treatment with polylactic acid at a certain temperature; and after the reaction is finished, fully cooling the system to room temperature, adding an organic solvent to disperse the powder, centrifuging to obtain a precipitate, and drying to obtain the graft-modified zinc oxide nanoparticles. According to the preparation method, grafting reaction can be carried out without a catalyst and a solvent, and the reaction activity of ZnO is improved by carrying out surface treatment on ZnO, so that the grafting rate is improved. The zinc oxide nanoparticles grafted by the preparation method disclosed by the invention can effectively avoid particle agglomeration, can suspend in a solution for a long time, and can effectively improve the blending effect of the zinc oxide nanoparticles in emulsion polymerization.

Description

Technical Field

[0001] The invention relates to the technical field of zinc oxide surface modification, and in particular to polylactic acid grafted modified zinc oxide nanoparticles and a preparation method thereof. Background Art

[0002] Zinc oxide is a commonly used chemical additive and is used in liquid crystal displays, thin film transistors, light-emitting diodes and other products in the semiconductor field. Zinc oxide particles are very easy to agglomerate and difficult to disperse evenly in the matrix because of their hydroxyl groups, high hydrophilicity and surface energy on the surface.

[0003] The method of grafting polylactic acid onto the surface of particles mostly adopts solution polymerization, in which the surface modification is achieved by grafting the lactide monomer, the catalyst and the modified particles through solution. Since the lactide monomer is used in this process, the polymerization reaction is carried out during the grafting process, making it difficult to control the molecular weight of the surface grafted polylactic acid, and the addition of the catalyst also introduces additional organic reagents. Therefore, it is necessary to achieve controllable synthesis of the grafting process. At the same time, the preparation process of this method requires the addition of organic reagents, which will pollute the environment. The melt grafting method is usually difficult to achieve due to its low reaction activity.

[0004] In order to solve this problem, the surface of ZnO is treated to improve its reaction activity so that the grafting reaction can be carried out without a solvent. The surface of ZnO is treated in an alkaline solution to increase the activity of the hydroxyl groups on the surface of ZnO, thereby improving the reaction activity and achieving the grafting reaction without a solvent and a catalyst. Summary of the invention

[0005] One of the purposes of the present invention is to provide a method for preparing polylactic acid grafted zinc oxide nanoparticles, which can carry out grafting reaction without catalyst and solvent, and improve the reaction activity of ZnO by surface treatment, thereby improving the grafting rate.

[0006] The second object of the present invention is to provide a polylactic acid grafted modified zinc oxide nanoparticles, which can effectively avoid particle agglomeration and can be suspended in a solution for a long time, and can effectively improve its blending effect in polylactic acid.

[0007] The solution adopted by the present invention to achieve one of the purposes is: a method for preparing zinc oxide nanoparticles grafted with polylactic acid, 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: reacting the surface-treated ZnO powder obtained in step 1 with polylactic acid at a certain temperature;

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

[0011] Preferably, in step 1, 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 water solution so that the liquid level is just higher than the powder, the pH is adjusted to 12-14 with a 0.1 mol / L NaOH solution, the reaction is stirred for 2-4 hours, and the surface-treated ZnO powder is obtained after drying.

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

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

[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 solution adopted by the present invention to achieve the second purpose is: a polylactic acid grafted modified zinc oxide nanoparticle is prepared by adopting the 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 a catalyst and a solvent, and the reaction activity of ZnO is improved by surface treatment, thereby increasing the grafting rate.

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

[0024] The preparation method of the invention is simple and easy to implement and can be easily promoted and applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1: Schematic diagram of the appearance structure of zinc oxide particles grafted onto the surface of polylactic acid of the present invention;

[0026] Figure 2 : X-ray diffraction pattern of the microscopic morphology of zinc oxide particles grafted onto the surface of polylactic acid of the present invention;

[0027] Figure 3 : Infrared analysis spectrum of zinc oxide particles grafted onto the surface of polylactic acid of the present invention;

[0028] Figure 4 : Thermogravimetric curve of zinc oxide particles grafted onto the surface of polylactic acid of the present invention;

[0029] Figure 5 : Dynamic light scattering analysis spectrum of zinc oxide particles grafted onto the surface of polylactic acid of the present invention;

[0030] Figure 6 : Scanning electron microscope morphology analysis of the zinc oxide particles grafted onto the surface of polylactic acid of the present invention. DETAILED DESCRIPTION

[0031] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0032] Example 1

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

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

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

[0036] Step 3. After sufficient cooling, pour 50 ml of dichloromethane into the flask, pour out the solution after the powder is dispersed, centrifuge the resulting solution and pour out the supernatant to obtain the lower layer of powder, and dry the powder at 60°C for 24 hours to obtain polylactic acid surface grafted modified zinc oxide particles, which are named g-ZnO-2 (2 hours), g-ZnO-3 (3 hours), and g-ZnO-4 (4 hours) according to the reaction grafting time.

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

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

[0039] The samples prepared in the above embodiments were tested as follows:

[0040] 1. X-ray diffraction pattern:

[0041] The X-ray diffraction pattern of the microscopic morphology of zinc oxide particles grafted onto the surface of polylactic acid is as follows: Figure 2 As shown, X-ray diffraction analysis confirmed that the patterns of polylactic acid surface modified zinc oxide particles g-ZnO-2, g-ZnO-3, and g-ZnO-4 were consistent with those of standard zinc oxide, indicating that polylactic acid surface modification had no effect on the structure of zinc oxide, and the peak intensity would be slightly reduced.

[0042] 2. Infrared analysis spectrum

[0043] The infrared analysis spectrum of zinc oxide particles grafted onto the surface of polylactic acid is as follows: Figure 3 As shown in the figure, the infrared analysis spectrum confirms that the polylactic acid surface modified zinc oxide particles g-ZnO-2, g-ZnO-3, and g-ZnO-4 have a wavelength of 3450 cm -1 There are absorption peaks near the band, which is attributed to OH stretching, at 1586cm -1 The absorption peak in the band is attributed to COO - Antisymmetric expansion, at 1048cm -1 The absorption peak in the band is attributed to the expansion and contraction of CO, while the unmodified ZnO particles do not have the above absorption peak. Combined with the infrared analysis spectrum, it also confirms the successful surface modification of zinc oxide particles.

[0044] 3. Thermogravimetric curve

[0045] The thermogravimetric curve of zinc oxide particles grafted onto the surface of polylactic acid is shown in Figure 4 As shown, zinc oxide particles have high heat resistance. The thermogravimetric analysis shows that the mass loss at 600°C is less than 2%. For zinc oxide particles modified with polylactic acid, the mass loss in the area below 150°C is mainly due to the volatilization of surface crystal water and adsorbed solvent; at 150°C, the surface polylactic acid begins to degrade. The mass loss in the 150-450°C area is mainly due to the decomposition of the surface grafted polylactic acid. The grafting rate of the polylactic acid surface at different grafting times can be calculated according to the following formula 1:

[0046]

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

[0048] Through calculation, it is found that the grafting rate of g-ZnO-3 with a reaction time of 3h is the highest, which is 31.6%. The grafting rate of g-ZnO-4 with a reaction time of 4h is reduced to 28.5%. The grafting rate of g-ZnO-2 with a reaction time of 2h is the lowest, which is 8.7%. The reason may be that the reaction time is too short at 2h, and the polylactic acid grafting effect is poor. At 4h, the reaction time is too long, and the surface grafted polylactic acid will undergo thermal decomposition, thereby reducing the grafting rate. The grafting effect is best at 3h.

[0049] 4. Dynamic Light Scattering

[0050] Dynamic light scattering analysis spectrum of zinc oxide particles grafted onto the surface of polylactic acid Figure 5 As shown, dynamic light scattering confirmed that with the increase of reaction time, the intensity of the peaks of g-ZnO-2, g-ZnO-3, and g-ZnO-4 in the lower size direction gradually increased, and with the increase of reaction time, the width of the peak gradually decreased, which also confirmed that the surface grafting modification of polylactic acid can improve the dispersion of zinc oxide particles, make the particle size distribution more uniform, and reduce the occurrence of agglomeration.

[0051] 5. Scanning electron microscope morphology analysis

[0052] The scanning electron microscopy morphology analysis of zinc oxide particles grafted onto the surface of polylactic acid is shown in Figure 2. Figure 6 As shown in the figure, the successful surface modification of PLA was also confirmed by scanning electron microscopy. There was no PLA deposition on the surface of unmodified zinc oxide. PLA deposition appeared on the surface of zinc oxide particles modified with PLA. There was less PLA on the surface of g-ZnO-2 grafted for 2h, and a large amount of PLA deposition was clearly seen on g-ZnO-3 and g-ZnO-4 grafted for 3h and 4h.

[0053] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A method for preparing polylactic acid grafted zinc oxide nanoparticles, characterized in that: The following steps are involved: 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; Step 2: reacting the surface-treated ZnO powder obtained in step 1 with polylactic acid at a certain temperature; Step 3: After the reaction is completed, the system is fully cooled to room temperature, an organic solvent is added to disperse the powder, and the precipitate is obtained by centrifugation. After drying, the grafted modified zinc oxide nanoparticles are obtained.

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

3. The method for preparing polylactic acid grafted zinc oxide nanoparticles according to claim 1, characterized in that: In the step 1, the pH value is 12-14.

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

5. The method for preparing polylactic acid grafted zinc oxide nanoparticles according to claim 1, characterized in that: In the step 2, the reaction temperature is 160-180° C. and the reaction time is 2-4 hours.

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

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

8. A polylactic acid grafted zinc oxide nanoparticle, characterized in that: The method is prepared according to any one of claims 1 to 7.

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