Biodegradable heat storage microcapsule and manufacturing method thereof

Abstract

To provide a biodegradable heat storage microcapsule which is composed only of an outer shell and a core substance made of a biodegradable material, with a latent heat storage material being the encapsulated core substance unlikely to leak.SOLUTION: A method for producing biodegradable heat storage microcapsules is provided, which uses animal or vegetable oils or fatty acid esters as a core substance and uses biological substances such as proteins and polysaccharides as an outer shell. At that time, the outer shell is cross-linked by biodegradable means and dried by spray drying or the like, thereby making it difficult for the core substance to leak out.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to biodegradable heat storage microcapsules produced using biodegradable biological raw materials, and a method for producing the biodegradable heat storage microcapsules. [Background technology]

[0002] To reduce the burden on the environment, there is a need to reduce the use of fossil fuel-derived energy. At the same time, heat retention technology is attracting attention in a variety of fields. However, conventional heat retention materials have limitations in their performance, and they have not been able to be expected to be effective, especially when used in harsh environments. Thermal energy storage technology is attracting attention as a solution to this problem.

[0003] Heat storage methods include those that utilize sensible heat and latent heat. A known example of sensible heat storage is a sensible heat storage block (Patent Document 1). Sensible heat storage has a wide applicable temperature range, but suffers from the problem of low heat storage density. On the other hand, latent heat storage has a limited applicable temperature range, but can achieve a much higher heat storage density than sensible heat storage. Attention has been focused on the use of phase change materials (PCMs) as raw materials for latent heat storage materials, which can store, absorb, and release energy using latent heat associated with phase changes such as between solid and liquid. Various substances, such as water and hexadecane, are known as PCMs that can be used near room temperature.

[0004] Direct contact is desirable as a means of heat exchange between a PCM and an object to be kept warm or cold from the standpoint of thermal efficiency. However, direct contact is difficult when the PCM and the object interact (through infiltration, dissolution, etc.). Furthermore, PCMs such as alkanes melt and become liquid upon use, which dissipates if used as is. To overcome these drawbacks, heat-storage microcapsules have been proposed, in which the PCM is coated with a polymer or other material. By encapsulating the PCM in tiny capsules, heat-storage microcapsules have the ability to resist changes in the surrounding temperature while avoiding the above-mentioned interactions. Various methods have been developed to fabricate heat-storage microcapsules, including suspension polymerization, in situ polymerization, and interfacial polymerization.

[0005] Applications of heat-storing microcapsules include keeping building materials, textile materials, and other materials warm or cold at a constant temperature despite changes in the ambient temperature (Patent Document 2, Non-Patent Documents 1 and 2). Furthermore, the use of heat-storing microcapsules can reduce temperature changes in the objects being kept warm or cold, thereby contributing to a reduction in energy consumption (Non-Patent Document 3). It is expected that these microcapsules will provide better heat / cold retention than conventional materials, particularly in environments with extreme temperature changes, such as outdoor activities in cold or hot regions.

[0006] Previously, methods for manufacturing heat-storage microcapsules have been proposed, using linear alkanes as the PCM (core material) and urethane resins, urea resins, melamine resins, acrylic resins, polystyrene, etc. as the outer shell (Patent Documents 2-5). This is because alkanes have a wide range of melting points depending on their chain length, and have the advantages of being chemically stable and inexpensive. However, due to their stability, conventional heat-storage microcapsules made from these materials are not biodegradable in the natural environment. As a result, they could contribute to the microplastics problem and are not in line with the SDGs.

[0007] To solve this problem, it would be necessary to produce heat-storing microcapsules using biodegradable materials. However, there is a lack of knowledge about efficient methods for producing biodegradable heat-storing microcapsules and their properties, which is an obstacle to industrial production. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 6-50681 [Patent Document 2] JP 2006-233342 A [Patent Document 3] JP 2016-142056 A [Patent Document 4] JP 2007-137916 A [Patent Document 5] JP 2006-63314 A [Non-patent literature]

[0009] [Non-Patent Document 1] Journal of the Japan Color Materials Association, 92(2), 39-43(2019). [Non-patent document 2] Journal of the Society of Fiber Science and Technology, 66(9), P300-P302(2010). [Non-patent document 3] Architectural Institute of Japan Technical Reports, 23(54), 535-538(2017). Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide biodegradable heat storage microcapsules and a method for producing the biodegradable heat storage microcapsules simply and efficiently. [Means for solving the problem]

[0011] In the present invention, biodegradable heat-storing microcapsules were produced using biologically derived raw materials. In this process, fats and oils were used for the core material (PCM), and proteins and sugars were used for the shell. The effects of the crosslinking agent for the shell and drying conditions on the physical properties of the microcapsules were then investigated. The inventors conducted research to solve the above-mentioned problems and found that heat-storing microcapsules can be produced simply and efficiently using various biodegradable raw materials. The present invention was completed through further research based on these findings. [Effects of the Invention]

[0012] According to the present invention, heat-storing microcapsules can be produced at low cost and with low environmental impact under easy process control using inexpensive and commonly available proteins such as gelatin, sugars such as gum arabic, oils and fats, and crosslinking agents such as glutaraldehyde. [Brief explanation of the drawings]

[0013] [Figure 1] SEM image of biodegradable heat storage microcapsules prepared in Example 1 [Figure 2] DSC analysis results of biodegradable heat storage microcapsules prepared in Example 1 [Figure 3] SEM image of biodegradable heat storage microcapsules prepared in Example 2 DETAILED DESCRIPTION OF THE INVENTION

[0014] The heat storage microcapsules of the present invention are composed of a water-insoluble biodegradable latent heat storage material that stores or releases heat by a phase change of the core material (PCM), and a capsule wall that covers the core material is made of a biodegradable material. Furthermore, any water-insoluble biodegradable latent heat storage material that stores or releases heat by a phase change can be used as the core material without any particular restrictions, and therefore have the same heat storage capacity as conventional heat storage microcapsules. A method for producing the biodegradable heat storage microcapsules of the present invention will now be described in detail.

[0015] The biodegradable heat storage microcapsules and their manufacturing method of the present invention are characterized by comprising a step of forming heat storage microcapsules simply and efficiently by using commonly occurring proteins and sugars as the outer shell, stirring a core substance such as fats and oils or esters under acidic conditions to form a coacervate, and cross-linking the outer shell of the coacervate with a cross-linking agent such as glutaraldehyde.

[0016] In the production method of the present invention, proteins such as gelatin and sugars such as gum arabic can be used as raw materials. The raw materials may be used alone or in a mixed state. In the present invention, the raw materials may be purified, unpurified, or contained in other substances.

[0017] In the present invention, heat storage microcapsules can be produced by mixing an aqueous protein solution, an aqueous sugar solution, fats and oils, etc., adding an appropriate amount of acid to create an acidic condition, and then crosslinking the outer shell with a crosslinking agent. Specifically, an aqueous gelatin solution and an aqueous gum arabic solution are prepared, stirred with fats and oils, and then acidified with hydrochloric acid, after which the outer shell is crosslinked with a crosslinking agent such as glutaraldehyde.

[0018] For the stirring in the production method of the present invention, a known stirrer can be used, or manual stirring is also possible. The processing equipment used in this case is not particularly limited as long as it is chemical-resistant and can withstand stirring, and for example, stainless steel, glass, or plastic containers and stirrers can be used.

[0019] In the production method of the present invention, the concentrations of the protein aqueous solution and the saccharide aqueous solution are not particularly limited, but may be, for example, 1 to 30 wt%. The amount of core material added may be 0.1 to 10 times the total weight of the protein and saccharide shell materials. From the perspective of more efficient production of heat storage microcapsules, the gelatin concentration is preferably 2 to 20 wt%. The gum arabic concentration may be 5 to 20 wt% or more, preferably 10% or more.

[0020] In the manufacturing method of the present invention, a known crosslinking agent can be used. Specific examples include, but are not limited to, aldehydes such as glutaraldehyde. These crosslinking agents can be added alone or in the form of an aqueous solution.

[0021] In the manufacturing method of the present invention, the coacervate can be used as it is as biodegradable heat storage microcapsules. On the other hand, it can be dried to make it easier to handle. Known drying methods can be used. Specifically, stationary drying using an oven or the like, freeze drying, spray drying, and the like can be used, but are not limited to these. The biodegradable heat storage microcapsule powder obtained by drying can be used as it is, or it can be mixed with other substances as necessary.

[0022] Heat storage microcapsules that use latent heat storage materials as core materials have a limited applicable temperature range. When using the biodegradable heat storage microcapsules produced by the present invention, the capsules produced under different conditions can be used alone or in combination. By using a combination, the applicable temperature range, which is a drawback of latent heat storage, can be expanded. [Example]

[0023] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0024] [Example 1] Heat storage microcapsules made of coconut oil, gelatin, and gum arabic A 5 wt% gelatin solution was prepared by adding 13 g of gelatin to 247 mL of water and heating to approximately 40°C. Separately, 13 g of gum arabic was dissolved in 247 mL of water. Next, 2.5 to 40 g of coconut oil was added to 40 to 50 g of gelatin solution. This solution was stirred for 2 minutes using a mixer. An equal weight of gum arabic solution was gradually added to this solution. 0.1 mol / L hydrochloric acid was then gradually added and the pH was adjusted to 4.0 while stirring. After stirring for 30 minutes at room temperature, the solution was cooled to 4°C to obtain a coacervate suspension. A 1% aqueous solution of glutaraldehyde was added to the suspension and stirred overnight at 4°C.

[0025] The suspension obtained by these treatments was frozen at -30°C. The suspension was then freeze-dried using a freeze dryer to obtain heat-storage microcapsules (Figure 1). The heat-storage microcapsules were thermally analyzed by DSC. As a result, heat-storage behavior was observed at all coconut oil blend ratios (Figure 2).

[0026] [Example 2] Heat storage microcapsules containing methyl palmitate as a core material A coacervate suspension was obtained using the same procedure as in Example 1, except that methyl palmitate was used as the core material (PCM) and the amount of this ester was 1 to 4 times the amount of the shell. An aqueous glutaraldehyde solution (5 wt% of the shell material) was added to the suspension and stirred at room temperature for 1 hour. The suspension obtained by this procedure was spray-dried using a spray dryer (inlet temperature 180°C) to obtain powdered heat-storage microcapsules (Figure 3).

[0027] The heat storage microcapsules were subjected to thermal analysis using DSC. As a result, regardless of the methyl palmitate mixing ratio, heat storage behavior due to melting of the core material was observed at around 29°C, and a heat storage density of 40 to 105 J / g was achieved in terms of latent heat of fusion (ΔHm) (Table 1).

[0028] [Table 1]

Claims

1. A heat storage microcapsule comprising a core material made of a latent heat storage material and an outer shell surrounding the core material, wherein the latent heat storage material and the outer shell are both made of materials derived from biodegradable substances.

2. 2. The biodegradable heat storage microcapsule according to claim 1, wherein the outer shell is formed from proteins and polysaccharides by a complex coacervation method, and glutaraldehyde is used as a hardening and cross-linking agent for the wall membrane.

Images