RAPID MERCURY-FREE PHOTOCHEMICAL MICROENCAPSULATION/NANOENCAPSULATION AT AMBIENT CONDITIONS

Abstract

A method of mercury-free photochemical micro-/nano-encapsulation of an active material is a process for obtaining Micro-/nano-capsules by means of curing by UV LED radiation at ambient or even cold temperatures. A stirrer photo-reactor made from glass or transparent plastics can be used but mixed flow reactor could be also employed. Appropriate mixing is sufficient to expose all droplets, which contain an active material surrounded by curable-shell materials in the emulsion to the LED radiation. Using the optimum light intensities and reactions' times is critical for encapsulating the active material with a high efficiency and producing a high quality micro-/nano-capsules, Solar monochromator device can also be used as long as it generate the same radiation with a narrow/single wavelengths as the LED device. Light emitted diode (LED) is a mercury-free UV radiation source with a long operating life time and an instant ON-Off, it has a high efficiency, a very low cooling requirements and cost-efficient in photochemical encapsulation. It reduces the time of microencapsulation from 6 hours to a less than 5 minutes. It has a significant decrease in manufacturing cost, waste-water, unconverted monomers, and leftover active phase change material (PCM) compared to other methods. Conversion of more than 90% of monomers can be achieved, and encapsulation efficiency can reach 100% at optimum conditions. This is in addition to the ability of this invented technology for encapsulate volatile and heat sensitive active materials at ambient as well as low temperatures. Normal glass or transparent plastics can be used as a reactor material. Only the matched useful wavelength radiation is emitted by LED without having other wavelengths which might have a bad impact on the encapsulation process.

Claims

1. A method for preparing microcapsules or nanocapsules comprising the steps of: (a) preparing an emulsion comprising a discontinuous droplets phase and a continuous phase wherein the discontinuous droplets phase contains (i) at least one active material; (ii) at least one curable material; and (iii) at least one photo-initiator; (b) irradiating the emulsion at ambient temperature for five minutes or less with UV-LED radiation in a transparent plastic or glass tube and continuously mixing the emulsion with a helix stirrer to encapsulate the active material with the curable material and afford the microcapsules or nanocapsules.

2. An LED stirrer photoreactor for microencapsulation or nanoencapsulation of an active material wherein the photoreactor comprises: (a) a transparent tube equipped with a helix stirrer that can be fit inside the tube; and b) at least one LED lamp with adjustable light intensities.

3. The photoreactor of step 2, further comprising a light reflector.

4. The method of claim 1, wherein the emulsion is prepared by a process comprising: (a) adding an active material to a mixture comprising at least one curable material and at least one photo-initiator to form the discontinuous droplets phase; (b) adding a liquid in which both the active material and curable material are immiscible and at least one stabilizer-emulsifier agent to form the continuous phase; and (c) emulsifying the discontinuous droplets phase and the continuous phase using a high shear emulsifier.

5. The method of claim 3, further comprising step (d) wherein the emulsion is subjected to sonication to reduce the droplets' size.

6. The method of claim 5, wherein the size of the droplet is 100 nm.

7. The method of claim 1, wherein the curable material is a mono-functional monomer.

8. The method of claim 4, wherein the continuous phase further comprises surfactant.

9. The method of claim 1, wherein the discontinuous droplets phase further comprises a second mono-functional monomer or a di-, tri-, or poly-functional monomer.

10. The method of claim 1, wherein the irradiation of step (b) is for five minutes.

11. The method of claim 1, wherein the irradiation of step (b) is for less than five minutes.

12. The method of claim 1, wherein the UV-LED radiation is a wavelength of 365 nm and the radiation intensity is between 0 and 12 W/cm.sup.2.

13. The method of claim 1, wherein the UV-LED radiation is a wavelength of 365 nm and the radiation intensity is between 0 and 12 W/cm.sup.2 and the irradiation of step (b) is for five minutes.

14. The method of claim 12, wherein the radiation intensity is 0.6 W/cm.sup.2.

15. The method of claim 1, wherein the active material is an organic phase change material.

16. The method of claim 1, further comprising step (c) wherein the microcapsules or nanocapsules are filtered, washed, and dried.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1. photochemical stirrer reactor for micro- and nano-encapsulation

[0035] FIG. 2. Heat of Fusion of PCM Microcapsules drying at 55° C. for 12 hours and then, after drying at 55° C. for 20 days. Irradiation at 1.2 W/cm.sup.2 for 4 minutes.

[0036] FIG. 3. photochemical thin-film flow reactor for micro- and nano-encapsulation

[0037] FIG. 4: DSC thermogram of pure PT 20

[0038] FIG. 5: DSC measurements of microcapsules treated at 450 W UV intensity for (a) 1 min, (b) 2 min. (c) 5 min, (d) 10 min

[0039] FIG. 6: Thermogravimetric analysis of samples treated at UV intensity of 450 W

[0040] FIG. 7: Weight analysis of PT 20 microcapsules stored at 50° C. over a span of 40 days

[0041] FIG. 8. Influence of Radiation intensity on encapsulation efficiency for 2 minutes reaction time at wavelength of 365 nm.

[0042] FIG. 9. Influence of irradiation time on encapsulation efficiency without using the mixer in the photoreactor at a wavelength of 365 nm and a radiation intensity of 1.2 W/cm.sup.2.

[0043] FIG. 10. Influence of irradiation time on encapsulation efficiency at a wavelength of 365 nm and a radiation intensity of 12 W/cm.sup.2 (maximum light intensity of the LED lamps).

[0044] FIG. 11. Influence of irradiation time on encapsulation efficiency at a wavelength of 365 nm and a radiation intensity of 0.6 W/cm.sup.2.

List of Tables

[0045] Table 2: Chemical recipe of ingredients for emulsion preparation
Table 2. Encapsulation efficiency at decreasing and increasing light intensities for total irradiation of 6 minutes, which is divided into two stages.

REFERENCES

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