Natural microtubule encapsulated phase-change materials and preparation thereof

Abstract

Microtubule encapsulated microcapsules of a phase-change material and preparation thereof are provided. The microcapsules of a phase-change material consist of a phase-change material, truncated microtubules, and a polymer. The truncated microtubules are formed by truncating hollow tubular natural fibers into fiber segments with a length of 0.1 mm-5 cm. The diameter of the hollow tubular natural fiber is 0.1-1000 μm. The phase-change material is encapsulated in the truncated microtubules and the truncated microtubules are covered with the polymer. The microtubules have high energy storage density due to high hollowness, and can transfer energy stably due to the closed structure, transfer heat rapidly due to the very fine micro-tubular structures, and may be used for a long term in view of the heat and chemical stability.

1 . Microcapsules of a phase-change material, comprising:
 a phase-change material, truncated microtubules, and a polymer;   wherein the truncated microtubules are formed by truncating hollow tubular natural fibers into fiber segments having a length of 0.1 mm-5 cm, and   the hollow tubular natural fibers have a diameter of 0.1-1000 μm; the phase-change material is encapsulated in the truncated microtubules, and the truncated microtubules are encapsulated by the polymer.   
   
   
       2 . The microcapsules of a phase-change material according to  claim 1 , wherein the natural fiber is at least one of the following natural fibers: kapok fiber, milkweed fiber, luffa fiber, bamboo fiber, tex bamboo fiber, flax fiber, wool, and down. 
   
   
       3 . The microcapsules of a phase-change material according to  claim 1 , wherein the polymer is any one of the following polymers or copolymers or blends thereof: urea-formaldehyde resin, melamine-formaldehyde resin, melamine-urea-formaldehyde resin, polyurethane, polymethylmethacrylate, poly(ethyl methacrylate), phenolic resin, epoxy resin, polyacrylonitrile, and cellulose acetate. 
   
   
       4 . The microcapsules of a phase-change material according to  claim 1 , wherein the phase-change material is at least one of 1) a solid-liquid phase-change material and 2) a solid-solid phase-change material;
 the solid-liquid phase-change material is at least one of a) an inorganic phase-change material and b) an organic phase-change material;   the inorganic phase-change material is a crystalline hydrated salt and/or molten salt;   the organic phase-change material is any one of the following materials: higher aliphatic hydrocarbons, higher fatty acids, higher fatty acid esters, salts of higher fatty acids, higher aliphatic alcohols, aromatic hydrocarbons, aromatic ketones, aromatic amides, fluorochloroalkanes, multicarbonyl carbonic acids, and crystalline polymers; and   the solid-solid phase-change material is an inorganic salt, a polyol, or a cross-linked polymer resin.   
   
   
       5 . The microcapsules of a phase-change material according to  claim 4 , wherein the crystalline hydrated salt is selected from: alkali metal halides, alkaline-earth metal halides, sulfates, phosphates, nitrates, acetates, carbonates, and combinations thereof;
 the molten salt is K 2 WO 4  and/or K 2 MoO 4 ;   the inorganic salt is Li 2 SO 4  and/or KHF 2 ;   the higher aliphatic hydrocarbon is selected from: n-octacosane, n-heptacosane, n-hexacosane, n-pentacosane, n-tetracosane, n-tricosane, n-docosane, n-henicosane, n-icosane, n-nonadecane, n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane, n-tridecane, and combinations thereof;   the crystalline polymer is high density polyethylene, polyvinylidene, or crystalline polyvinyl chloride having a density of higher than 0.94 g/cm 3 ;   the polyol is selected from: pentaerythritol, 2,2-bis(hydroxymethyl)propanol, neopentyl glycol, 2-amino-2-methyl-1,3-propanediol, trimethylolethane, and tris(hydroxymethyl)aminomethane; the cross-linked polymer resin is a cross-linked polyolefin, a cross-linked polyacetal, a copolymer of a cross-linked polyolefin and cross-linked polyacetal, a blend of a cross-linked polyolefin and cross-linked polyacetal, and combinations thereof.   
   
   
       6 . A method for preparing the microcapsules of a phase-change material according to one of  claims 1  to  5 , comprising:
 1) heating a phase-change material to above the melting point, or dissolving it with a solvent, so as to obtain a liquid phase-change material;   2) dispersing and immersing truncated microtubules into the liquid phase-change material obtained in Step 1), so as to make the microfibers filled with the liquid phase-change material through capillary absorption; and   3) encapsulating the truncated microtubules filled with the phase-change material obtained in Step 2) with a polymer, so as to obtain the microcapsules of the phase-change material.   
   
   
       7 . The method according to  claim 6 , further comprising washing off the phase-change material adsorbed on the surface of the obtained microcapsules of the phase-change material. 
   
   
       8 . The method according to  claim 6 , wherein the solvent is selected from: deionized water, N,N′-dimethylformamide, N,N′-dimethylacetamide, tetrahydrofurane, methylene chloride, trichloromethane, cyclohexane, methanol, ethanol, acetone, and mixtures thereof.