TWI411464B - Microcapsule of phase change materials encapsulated with natural microtubule and their production - Google Patents

Abstract

The present invention is related to microcapsule of phase change materials encapsulated in natural microtubule, comprising phase change material, short cut microtubule and polymer wherein the short cut microtubule is of a fiber section in length of from 0.1mm to 5cm formed by cutting hollow tubular natural fiber; the diameter of the hollow tubular natural fibers is from 0.1-1000 &mgr; m; the phase change material is encapsulated in the short cut microtubule; and the short cut microtubule is encapsulated in the polymer. The microtubule used for microcapsules of phase change material in the present invention is low-priced easily available natural fiber, and has a tubular closed structure in micrometer scale and a large hollowness of the microtubule so that it has a large energy storage density, stable and rapid energy transfer, and thermal and chemical stability and is favorable for long term use. The present invention also provides a process for preparing the aforesaid microcapsule of phase change material.

Description

Microcapsule of natural micro tube embedded phase change material and preparation method thereof

The invention relates to a phase change microcapsule embedded in a natural microtube and a preparation method thereof.

In general, phase change materials (PCM), also known as latent thermal energy storage (LTES), refers to the ability to absorb or release heat when a substance changes phase, and the temperature of the substance itself does not change or A type of material that does not change much. As a energy storage carrier, phase change material has the advantages of high heat storage density, small equipment volume, high thermal efficiency and constant temperature of heat absorption and release, which can effectively improve energy utilization and alleviate energy shortage. At present, it has been widely used in refrigeration and cold storage of refrigerators and air conditioners, automatic constant temperature of intelligent buildings, energy storage and exchange technology in solar energy applications, "peak load shifting" of electric power, waste heat and waste heat. Recycling and daily necessities. Because it is easy to use and does not consume energy, it has great application prospects and a broad market.

From the phase change process of materials, phase change materials are mainly divided into solid-liquid phase changes, solid-solid phase changes, solid-gas phase changes and liquid-gas phase changes, which are accompanied by a large number of phase changes. The presence of gas causes a large change in the volume of the material and is rarely used in practical applications. The solid-liquid phase change is widely used in practical applications due to small volume change, large latent heat, good energy storage, and wide temperature range of phase change. However, since the material has a liquid phase during phase change, it must be sealed with a container to prevent leakage from contaminating the environment, and the container must be inert to the phase change material. This shortcoming greatly limits the practical application of solid-liquid phase change energy storage materials. In recent years, with the development of technology and the requirements of applications, people have tried to shape them to transform into a form-like "solid-solid" phase change, but in fact, solid-liquid phase changes still occur, and solved. The melting problem of phase change materials greatly facilitates practical applications. At present, the methods for shape stabilization of phase change materials mainly include stereotypes and microcapsules.

The stereotyped phase change material is essentially a kind of composite phase change energy storage material, which refers to the phase change material combined with the carrier material to form a phase change material which can maintain a solid shape and has no fluidity in shape, which can replace solid - Solid phase change material. There are two main components of such phase change materials: one is the working material component, that is, the phase change material, and the phase change is used for energy storage and energy release. The working materials include various phase change materials, but more are used. Mainly solid-liquid phase change materials. The second is a carrier material, which functions to maintain the fluidity and processability of the phase change material. Therefore, the melting temperature of the carrier material is required to be higher than the phase change temperature of the phase change material, so that the working material maintains its solid within the phase change range. Shape and material properties. From the recent development of the synthesis of phase-change composite phase change materials, the main preparation methods can be roughly classified into: blending method, grafting method, sintering method, in-situ intercalation method and sol-gel method. However, due to the relatively small physical effect of the shaped phase change material, the material is prone to desorption, leakage and two-phase separation of the solid-liquid phase change material when it is used multiple times.

The microencapsulated phase change material is a composite phase change material having a core-shell structure by coating a surface of a solid-liquid phase change material particle with a polymer film or an inorganic material with a stable performance by using a microcapsule technique. In the phase change process of the microencapsulated phase change material, the core undergoes a solid-liquid phase change, and the polymer film of the outer layer remains solid, so the phase change material is macroscopically solid particles. The chemical preparation methods of phase change microcapsules mainly include in-situ polymerization, interface polymerization, reaction phase separation, interface deposition and complex coacervation. The properties of the shells obtained by different preparation methods are different. With the development of polymer science, microencapsulation technology has gradually matured. Therefore, phase change energy storage microcapsule materials have received extensive attention and research due to their special properties and uses. The heat-absorbing and exothermic heat storage principle of phase-change microcapsules is equivalent to a “heat battery”. The encapsulation of micro-containers transforms phase-change materials into numerous tiny working units, thus greatly expanding the application of phase-change materials. Fields and occasions. An article incorporating phase change microcapsules establishes a microclimate environment around which the melting point of the phase change material is employed, thereby satisfying the requirements for temperature comfort, for example, for warm clothing. The microencapsulated phase change material can well solve the serious problems of melt flow, osmotic migration, phase separation and corrosion during the solid-liquid phase change process. After the shell material is embedded and protected, the phase change material and the external environment are phased. Separation and stabilization, at the same time, the polymer shell material or the modified shell material greatly increases the compatibility of the phase change material with the matrix material, thereby greatly increasing the practicability of the phase change material. However, the insufficient strength of the capsule wall of the microcapsule, the leakage of the phase change material, and the heat resistance have to be improved, especially the high cost, which is an urgent problem to be solved in the industry.

In view of the above, it is an object of the present invention to provide a phase change microcapsule utilizing a chopped natural microtube embedding phase change material and a method of preparing the same.

The phase change microcapsule provided by the invention comprises a phase change material, a chopped micro tube and a polymer; wherein the chopped micro tube is a fiber segment cut into a length of 0.1 mm to 5 cm. The hollow tubular natural fiber has a diameter of 0.1 to 1000 μm, a phase change material is embedded in the chopped microtube, and the chopped microtube is embedded in the polymer.

The natural fibers are, for example but not limited to, selected from the group consisting of kapok fibers, milk grass fibers, loofah fibers, bamboo fibers, diatom fibers, flax fibers, wool, down, and mixtures thereof.

The phase change material may be at least one of the following 1) and 2): 1) a solid-liquid phase change material, 2) a solid-solid phase change material; and the solid-liquid phase change material may be At least one of the following a) and b): a) is an inorganic phase change material, and b) is an organic phase change material; wherein the inorganic phase change material may be a crystalline hydrated salt and/or a molten salt. The crystalline hydrated salt may be any one or any combination of an alkali metal or alkaline earth metal halide, sulfate, phosphate, nitrate, acetate or carbonate, such as, but not limited to, Na ₂ sO ₄ ‧ 10H ₂ O, Na ₂ HPO ₄ ‧12H ₂ O, CaCl ₂ ‧6H ₂ O, SnCl‧6H ₂ O, etc.; the molten salt may be K ₂ WO ₄ and/or K ₂ MoO ₄ or the like.

The organic phase change material is, for example but not limited to, selected from the group consisting of: higher aliphatic hydrocarbons, higher fatty acids, higher fatty acid esters, higher fatty acid salts, higher aliphatic alcohols, aromatic hydrocarbons, aromatic ketones, aromatic guanamines, chlorofluorocarbons, and more. A group consisting of carbonyl carbonate, crystalline polymer, and mixtures thereof.

The higher aliphatic hydrocarbon is usually an aliphatic hydrocarbon having 6 or more carbon atoms, preferably 6 to 36 carbon atoms. Higher fatty acids generally refer to monocarboxylic acids containing C6 to C26.

The higher aliphatic hydrocarbon is any one of the following sixteen substances or any combination thereof: n-octacosane, n-heptadecane, n-hexadecane, n-pentadecane, n. Alkane, n-docosane, n-docosane, n-docosane, n-icosane, n-nonadecane, n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, N-tetradecane and n-tridecane; the crystalline polymer is high density polyethylene, polyvinylidene or crystalline polyvinyl chloride having a density higher than 0.94 g/cm ³ .

The solid-solid phase change material is, for example but not limited to, selected from the group consisting of inorganic salts, polyols, polymer crosslinked resins, and mixtures thereof.

Wherein, the inorganic salt may be Li ₂ SO ₄ and/or KHF ₂ ; the polyol may be any one of the following six substances or any combination thereof: pentaerythritol (PE), 2,2-dihydroxyl Methyl propanol (PG), neopentyl glycol (NPG), 2-amino-2-methyl-1,3-propanediol, trimethylolethane and trishydroxymethylaminomethane; The co-resin is a copolymer of crosslinked polyolefin, crosslinked polyacetal, crosslinked polyolefin and crosslinked polyacetal or a blend of crosslinked polyolefin and crosslinked polyacetal.

The polymer may be any one of the following ten polymers or any copolymer thereof or any blend thereof: urea-formaldehyde resin, melamine-formaldehyde resin, melamine urea-formaldehyde resin, polyurethane, polymethyl Methyl methacrylate, polyethyl methacrylate, phenolic resin, epoxy resin, polyacrylonitrile or cellulose acetate.

The method for preparing microcapsules for cutting short microtubule-embedded phase change materials provided by the invention comprises the following steps:

1) Liquefaction of core material phase change materials

Heating the phase change material to above the melting point or dissolving with a solvent to obtain a liquid phase change material;

2) Fill the chopped natural microtubules with a liquid phase change material

Dispersing the short natural microtubes in the liquid phase change material of step 1), soaking, and absorbing the capillary to fill the natural microtubes with a liquid phase change material;

3) Encapsulation of microencapsulated phase change materials

The microcapsules filled with the phase change material in step 2) are embedded with a polymer to obtain microcapsules of the phase change material.

The method also includes the step of washing away the phase change material adsorbed on the surface of the microcapsule of the resulting phase change material.

The solvent is, for example but not limited to, selected from the group consisting of: deionized water, N,N'-dimethylformamide, N,N'-dimethylacetamide, tetrahydrofuran, dichloromethane, chloroform, ring A group consisting of hexane, methanol, ethanol, acetone, and mixtures thereof.

Compared with the existing microencapsulated phase change material embedding technology, the invention has the following beneficial effects:

1. The embedding tube used in the present invention is a natural micro tube which is cheap and easy to obtain. For example, kapok fiber is a kind of natural fiber with large specific surface area and large hollowness, wherein the emptyness is as high as 80-90%, which is difficult to achieve by existing man-made fibers, so it is more suitable for manufacturing phase change energy storage materials than man-made fibers. It has advantages; and the kapok fiber has good thermal stability, and substantially no thermal degradation occurs at 250 °C. At the same time, kapok fiber has good chemical stability and can be dissolved only in high concentration of strong acid.

2. Using a short natural micro-tube having a microporous structure with a large specific surface area as a supporting material, the liquid organic phase changes the heat storage material or the inorganic phase change heat storage material (above the phase) through the capillary force of the micropores. Under variable temperature conditions, it is sucked into the micropores to form an organic phase change heat storage material, an inorganic phase change heat storage material, or a composite phase change heat storage material composed of organic and inorganic. When the phase change heat storage material undergoes a solid-liquid phase change in the micropores, the liquid phase change heat storage material hardly overflows from the micropores due to the capillary force.

3. Although the capillary action solves the fluidity problem of the solid-liquid phase change material to a certain extent, it is still an "open" package system, so the polymer can be further used to microcapsule the adsorbed phase. Microtubules of varying materials are sealed and capped.

4. Due to the large hollowness of the microtube, the energy storage density is large, the closed structure makes the energy transmission stable, and the extremely fine micron-sized tubular structure makes the heat transfer rapid, the thermal and chemical stability is favorable for long-term use, and the special lipophilic hydrophobic infiltration Performance can be utilized during processing.

5. The microencapsulated phase change material morphology can be better dispersed in the matrix material in the actual technical process. After mixing with the matrix material, the micron-sized encapsulated phase change material size can maintain the appearance of the article unaffected.

Example 1. Preparation of phase change microcapsules embedding paraffin wax with natural kapok fiber tube and embedding with urea-formaldehyde resin

(1) Liquefaction of core material phase change materials

Heating the organic phase change material paraffin to a melting point of 60 ° C or more to obtain a liquid paraffin phase change material;

(2) filling the chopped natural microtubules with a liquid phase change material

1g of natural kapok fiber (short microtubule) with a length of 10-50μm is dispersed in 10mL of the liquid phase change material of step (1), soaked to balance the capillary absorption, and the kapok fiber tube is filled with liquid phase change material. ;

(3) Encapsulation of microencapsulated phase change materials

2 g of urea formaldehyde prepolymer was added dropwise directly to the melt of the natural kapok fiber filled with the phase change material in step (2) (1 g of urea was added to 2 ml of 36% aqueous formaldehyde solution and stirred until completely dissolved, and heated to 60 °C, and kept for 15 minutes), increase the melt temperature to 97~98 ° C, and react for 1 hour. Forming a urea-formaldehyde resin polymer around the kapok fiber to cause phase separation and deposition, so that the microencapsulated phase change material is embedded by the urea-formaldehyde resin;

(4) Purification of microencapsulated phase change materials

The microtubes filled with the phase change material embedded in the urea resin in the step (3) are removed, and then placed in the hot water to wash away the phase change material adsorbed between the tubes, and then dried to form a microcapsule phase change. material.

The DSC curve of the phase change material at the temperature of the loop rise and fall is shown in Fig. 1, and the scanning electron microscope photograph is shown in Fig. 2.

It can be seen from Fig. 1 that the phase change microcapsules have a good energy-recoverable phase change energy storage effect under the temperature of the loop.

It can be seen from Fig. 2 that the encapsulated kapok fiber microtube filled with paraffin is embedded in urea-formaldehyde resin to form an encapsulated phase change material.

Example 2: Preparation of phase change microcapsules embedding pentaerythritol with natural milk grass fibers and embedding with cellulose acetate

(1) Liquefaction of core material phase change materials

Dissolving the organic phase change material pentaerythritol (PE) in a small amount of ethanol to obtain a liquid pentaerythritol (PE) solution phase change material;

(2) filling the chopped natural microtubules with a liquid phase change material

Dispersing 1 g of natural milkweed fiber with a length of 0.5-10 μm in 10 mL of the liquid phase change material of step (1), soaking to balance the capillary absorption, and filling the milk fiber tube with a liquid phase change material;

(3) Encapsulation of microencapsulated phase change materials

The ethanol in the phase change material microcapsules containing the ethanol solvent obtained in the step (2) is volatilized, and the phase change material pentaerythritol (PE) solution is concentrated and solidified, and then immersed in 5 mL of 5% by weight cellulose acetate in methylene chloride. In the solution, the microencapsulated phase change material is embedded in cellulose acetate by an interface deposition reaction;

(4) Purification of microencapsulated phase change materials

The milkweed fiber filled with the phase change material embedded in cellulose acetate in the step (3) is picked up and dried to form a microencapsulated phase change material.

The phase change microcapsules prepared by the method have a good energy storage effect of the loopable phase change at the temperature of the loop, and the encapsulated milkweed fiber microtubule filled with pentaerythritol (PE) is formed by embedding cellulose acetate. A well-dispersible encapsulated phase change material.

Example 3, preparing phase change microcapsules embedded with natural bamboo fiber CaCl ₂ ‧6H ₂ O and embedded with cellulose acetate

(1) Liquefaction of core material phase change materials

Dissolving 1 g of the inorganic phase change material CaCl ₂ ‧6H ₂ O in 10 mL of deionized water to obtain a liquid CaCl ₂ ‧6H ₂ O solution phase change material;

(2) filling the chopped natural microtubules with a liquid phase change material

Dispersing 1 g of natural bamboo fiber having a length of 500-1000 μm in 10 mL of the liquid phase change material of the step (1), soaking to balance the capillary absorption, and filling the bamboo fiber tube with the liquid phase change material;

(3) Encapsulation of microencapsulated phase change materials

Deionized water in the phase change material microcapsules containing deionized water obtained in the step (2) is volatilized, and the phase change material CaCl ₂ ‧6H ₂ O solution is concentrated and solidified, and then immersed in 10 mL of 5% by weight cellulose acetate In the methylene chloride solution, the microencapsulated phase change material is embedded in cellulose acetate by an interface deposition reaction;

(4) Purification of microencapsulated phase change materials

The bamboo fiber filled with the phase change material embedded in cellulose acetate in the step (3) is picked up and dried to form a microencapsulated phase change material.

The phase change microcapsules prepared by the method have good reversible phase change energy storage effect under the loop temperature and the encapsulated bamboo fiber microtubes filled with the inorganic phase change material CaCl ₂ ‧6H ₂ O through the acetate fiber After embedding, a capsule phase change material with better dispersibility is formed.

Example 4, preparing phase change microcapsules embedding pentaerythritol and Li ₂ SO ₄ with natural flax fibers and embedding with polyacrylonitrile

(1) Liquefaction of core material phase change materials

Dissolving 10 g of organic phase change material pentaerythritol (PE) and 10 g of inorganic phase change material Li ₂ SO ₄ in 10 mL of an equal volume mixture of deionized water and alcohol to obtain a liquid organic/inorganic mixed phase change material;

(2) filling the chopped natural microtubules with a liquid phase change material

5g of natural flax fiber having a length of 100-500 μm is dispersed in 10 mL of the liquid phase change material of the step (1), soaked to balance the capillary absorption, and the flax fiber tube is filled with the liquid phase change material;

(3) Encapsulation of microencapsulated phase change materials

Deionized water and alcohol in the phase change material microcapsules containing deionized water and alcohol solvent obtained in the step (2) are volatilized, and the mixed solution of the phase change material pentaerythritol (PE) and Li ₂ SO ₄ is concentrated and solidified and then impregnated. The microencapsulated phase change material is embedded in polyacrylonitrile by using an interfacial deposition reaction in 5 mL of a 5 wt% polyacrylonitrile solution of N,N'-dimethylformamide;

(4) Purification of microencapsulated phase change materials

The flax fiber filled with the phase change material embedded in the polyacrylonitrile in the step (3) is picked up, immersed in deionized water to cure the polyacrylonitrile, and then air-dried.

The phase change microcapsules prepared by the method have a good energy recovery effect of the loopable phase change at the temperature of the loop, and the encapsulated natural flax fiber microtubules filled with the phase change materials pentaerythritol (PE) and Li ₂ SO ₄ . After being embedded in polyacrylonitrile, a capsule phase change material having good dispersibility is formed.

1 is a DSC graph of phase change microcapsules prepared in Example 1 at a loop temperature.

Figure 2 is a scanning electron micrograph of a phase change microcapsule prepared in Example 1, wherein a) a chopped natural kapok fiber tube; b) and c) a paraffin-filled encapsulated kapok fiber microtube; d) a urea resin further The encapsulated paraffin wax is embedded in the kapok fiber tube.

Claims (10)

A phase change material microcapsule comprising a phase change material, a chopped microtube and a polymer; wherein the chopped microtubule is a fiber segment in which a hollow tubular natural fiber is cut into a length of 0.1 mm to 5 cm And the natural fiber is selected from the group consisting of: kapok fiber, milk grass fiber, loofah fiber, bamboo fiber, bamboo fiber, flax fiber, wool, down, and a mixture thereof; the hollow tubular natural fiber has a diameter of 0.1 - 1000 μm; the phase change material is embedded in the chopped microtube; the chopped microtube is embedded with the polymer. The microcapsule of the phase change material of claim 1, wherein the polymer is selected from the group consisting of urea formaldehyde resin, melamine-formaldehyde resin, melamine urea-formaldehyde resin, polyurethane, polymethyl methacrylate, poly A group consisting of ethyl methacrylate, phenolic resin, epoxy resin, polyacrylonitrile, cellulose acetate, any of the above copolymers, and mixtures thereof. The microcapsule of the phase change material of claim 1, wherein the phase change material is at least one of the following 1) and 2): 1) a solid-liquid phase change material, 2) a solid-solid Phase change material. A microcapsule according to the phase change material of claim 3, wherein the solid-liquid phase change material is at least one of the following a) and b): a) an inorganic phase change material, and b) an organic phase a variable material; the inorganic phase change material is a crystalline hydrated salt and/or a molten salt; the organic phase change material is selected from the group consisting of higher aliphatic hydrocarbons and higher fats A group consisting of an acid, a higher fatty acid ester, a salt of a higher fatty acid, a higher aliphatic alcohol, an aromatic hydrocarbon, an aromatic ketone, an aromatic guanamine, a chlorofluorocarbon, a polycarbonyl carbonic acid, a crystalline polymer, and a mixture thereof. A microcapsule according to the phase change material of claim 3, wherein the solid-solid phase change material is selected from the group consisting of inorganic salts, polyols, polymer crosslinked resins, and mixtures thereof. The microcapsule of the phase change material of claim 4, wherein the crystalline hydrated salt is selected from the group consisting of alkali metal halides, alkaline earth metal halides, sulfates, phosphates, nitrates, acetates, carbonates. And a mixture of the mixture; the molten salt is K ₂ WO ₄ and/or K ₂ MoO ₄ ; the higher aliphatic hydrocarbon is selected from the group consisting of n-octacosane, n-heptadecane, and n. Alkane, n-pentadecane, n-tetracosane, n-docosane, n-docosane, n-docosane, n-icosane, n-nonadecane, n-octadecane, positive seventeen a group consisting of alkane, n-hexadecane, n-pentadecane, n-tetradecane, n-tridecane, and combinations thereof; the crystalline polymer is a high density polyethylene having a density higher than 0.94 g/cm ³ , Polyethylene or crystalline polyvinyl chloride. The microcapsule of the phase change material according to claim 5, wherein the inorganic salt in the solid-solid phase change material is Li ₂ SO ₄ and/or KHF ₂ ; the polyol is selected from the group consisting of: pentaerythritol, 2, 2-Dimethylolpropanol, neopentyl glycol, 2-amino-2-methyl-1,3-propanediol, trimethylolethane and trishydroxymethylaminomethane; the polymer crosslinked resin It is a group consisting of a crosslinked polyolefin, a crosslinked polyacetal, a copolymer of a crosslinked polyolefin and a crosslinked polyacetal, a blend of a crosslinked polyolefin and a crosslinked polyacetal, and combinations thereof. A method of preparing a microcapsule of a phase change material according to any one of claims 1 to 7, which comprises the steps of: 1) heating a phase change material above a melting point or dissolving in a solvent to obtain a liquid phase transition 2) Dispersing the chopped microtubes in the liquid phase change material obtained in step 1), soaking, filling the microtubes with liquid phase change material by capillary absorption; 3) embedding the polymer step 2 The chopped microtubules filled with the phase change material are obtained to obtain the microcapsules of the phase change material. The method of claim 8, wherein the method further comprises the step of washing away the phase change material adsorbed on the surface of the microcapsule of the phase change material obtained. The method of claim 8, wherein the solvent is selected from the group consisting of: deionized water, N,N'-dimethylformamide, N,N'-dimethylacetamide, tetrahydrofuran, dichloromethane a group consisting of chloroform, cyclohexane, methanol, ethanol, acetone, and combinations thereof.