Title of Invention	INTERFACIAL POLYMERISATION PROCESS FOR PREPARATION OF PHASE CHANGE MATERIAL CAPSULE
Abstract	The present invention describes process for preparing phase change material (PCM) capsule wherein the PCM is employed for thermoregulatory mechanism such as thermal storage, and thermal regulation. It finds applications in thermo-regulated textile. The PCM capsules of this invention are having better stability to thermal heat, solvent and reduced diffusion rate. More particularly, the capsules of the present invention have high core content and high encapsulation efficiency without compromising/scarifying the wall strength and or wall porosity. The core comprising of organic compounds such as hydrophobic aliphatic alkanes, alcohols, or acids, while the wall consists of natural or synthetic polymer exemplified by but not limited to polyurea, urea formaldehyde, melamine formaldehyde resins. The invention also discloses a process for preparing the PCM capsules. Particularly the capsules are prepared through interfacial polymerization. The monomer preferably used is diisocyanate and diamine along with n-octadecane as core.

Title of Invention

INTERFACIAL POLYMERISATION PROCESS FOR PREPARATION OF PHASE CHANGE MATERIAL CAPSULE

Abstract

The present invention describes process for preparing phase change material (PCM) capsule wherein the PCM is employed for thermoregulatory mechanism such as thermal storage, and thermal regulation. It finds applications in thermo-regulated textile. The PCM capsules of this invention are having better stability to thermal heat, solvent and reduced diffusion rate. More particularly, the capsules of the present invention have high core content and high encapsulation efficiency without compromising/scarifying the wall strength and or wall porosity. The core comprising of organic compounds such as hydrophobic aliphatic alkanes, alcohols, or acids, while the wall consists of natural or synthetic polymer exemplified by but not limited to polyurea, urea formaldehyde, melamine formaldehyde resins. The invention also discloses a process for preparing the PCM capsules. Particularly the capsules are prepared through interfacial polymerization. The monomer preferably used is diisocyanate and diamine along with n-octadecane as core.

Full Text	This invention relates to Interfacial Polymerisation process for Preparation of Phase Change Material Capsule. FIELD OF INVENTION: The invention relates to encapsulated phase change material (PCM) wherein the PCM is employed for thermoregulatory mechanism. Specifically, encapsulated phase change materials (PCMs) of this invention intend to perform functions such as thermal storage, and thermal regulation. It finds applications in thermo-regulated textile. Particularly, the invention relates to a PCM capsule having better stability to thermal heat. Specifically, the capsules of the present invention have better stability for solvent and reduced diffusion rate. More particularly, the capsules of the present invention have high core content and high encapsulation efficiency without compromising/scarifying the wall strength and or wall porosity. The core comprising of organic compounds such as hydrophobic aliphatic alkanes alcohol, or acids while the wall consists of natural or synthetic polymer exemplified by but not limited to polyurea, urea formaldehyde, melamine formaldehyde resins. The invention also discloses a process for preparing the PCM capsules. Particularly the capsules are prepared through in-situ polymerization or interfacial polymerization. The monomers used in the process may be such as amine, alcohol, and diisocynates, melamine-formaldehyde, urea- formaldehyde, melamine-urea-formaldehyde, and urea-resorcinol-formaldehyde. Further, the polymerization process of this invention is cost effective, and efficient as it yields better product. BACKGROUND OF THE INVENTION: Encapsulation is a process of enclosing an active agent in a polymeric shell. The active agent can be in the form of a solid, a liquid, or even a gas, whereas, the wall material can be an organic polymer, hydrocolloid, sugar, wax, fat, metal, or inorganic oxide. The PCM useful for the textile applications are those that change phase from solid to liquid by absorbing large amount of latent heat from the environment and change phase from liquid to solid by releasing the same amount of heat to the environment at a transition temperature close to the body temperature. Suitable PCMs, that satisfy the major requirements of thermoregulation for application in textile clothing, are n-octadecane, n-eicosane and inorganic salts exemplified lithium nitrate tri-hydrate. n-Octadecane is particularly important because its melting temperature is very close to the comfort temperature of the body i.e. around 28-29°C, and it has a high latent heat of fusion of 240 J/g. However, this PCM must be encapsulated using a suitable technique that can provide high wall integrity and stability. This requirement of better wall integrity is unlike other microencapsulation processes used in pharmaceutical products, cosmetics, and textile finishes, where micropores in the wall-membrane are necessary for slow release of drug, perfumes and finishing agents that are present as core. The relevant prior art known to the inventor with regard to the characteristics of the capsule include article that appeared in Colloid and Polymer Science (2002), 280(3), 260-266, titled "Microencapsulation of octadecane as a phase-change material by interfacial polymerization in an emulsion system" by Cho, Jeong-Sook; Kwon, Aehwa; Cho, Chang-Gi. The core content of the PCM capsules as disclosed jn the said paper is 40 to 45%. According to the said paper Microcapsules containing phase-change material for thermal adaptable fiber application were synthesized and characterized. The microcapsules of about 1 urn in diameter were prepared using an interfacial polycondensation method with toluene-2,4-diisocyanate (TDI) and diethylenetriamine (DETA) as monomers in an emulsion system. Octadecane was used as a phase-change material and NP-10, which is nonionic surfactant, was used as an emulsifier. To investigate the reaction ratio of monomers, microcapsules were synthesized with 3 g TDI and 0-4 g DETA. Polyurea microcapsules were formed not only by reaction with TDI and DETA, but also by reaction of TDI with hydrolyzed TDI at the interface. TDI was reacted with DETA in the wt. ratio of 3:1. NP-10 was reacted with TDI to form urethane. According to this paper, the efficiency of octadecane encapsulation increased as the core content decreased. The process reported a maximum core content of 46% with the encapsulation efficiency of 75%. CN1467260 titled Microcapsulated heat absorbing particle describes a microcapsule-type heat absorbing particle able to be sprayed on the surface of object for absorbing a great deal of heat is a (l-l000)-micron particle, which is composed of shell and core. Said shell is a high-molecular polymer chosen from melamine formaldehyde, urea- formaldehyde resin, PU, etc. Said core is a heat-absorbing substance chosen from straight-chain alkane, high-grade alcohol and organic acid. A reference also can be made to Korean Patent No. KR 2002-11266 20020304 titled Preparation of thermostable microcapsules containing phase change materials and articles. According to this patent the method comprises steps of: adding 10 to 50 parts organic phase consisting of 0 to 70% nonpolar organic solvent, 10 to 90% polymerizable monomer phase change materials having alkyl group having 8 to 18 carbon atoms and 10 to 50% compound having two or more isocyanate groups to a solution in which 0.2 to 10 parts surfactant is dissolved into 100 parts water, and emulsifying the mixed solution as agitating the solution and organic phase; and injecting at least one compound selected from diethylenetriamine, ethylenediamine, triethylenetetramine and melamine solution and the compound having two or more isocyanate groups to the emulsified solution in a ratio of 100:20 to 300, and reacting the compounds with emulsified solution so that urea bond is formed. However, the core content and thermal stability is not explicitly mentioned. Further, the procedure does not specify time of addition of the second monomer i.e. diamine or triamines. US 2004121072 Al. In accordance with this patent, the process for encapsulating a core component comprising paraffin compounds that can undergo phase transition, includes the steps of: (A) dissolving first monomers in the core component to form a first solution, the first monomers forming a first polymer; (B) dispersing the first solution into a second aqueous solution to form an emulsion; (C) adding the said emulsion to a third aqueous solution containing a precondensate of melamine-formaldehyde to form an encapsulation mixture characterized in that the first monomers are a polypropylene glycol with an average mol. wt. higher than about 400 and a polyisocyanate soluble in the core component. This patent claims addition of emulsion to the melamine-formaldehyde pre-polymer, maintaining melamine to formaldehyde ratio between 1:1.3 and 1:3, maintaining pH and between 4 and 7. Further, the encapsulation was effected at 70°C. US4876290 Microencapsulation by interfacial polyaddition (1989). This invention does not claim PCM. The invention teaches a process comprising emulsifying a hydrophobic organic liquid which includes an aliphatic diisocyanate and an isocyanurate ring trimer of an aliphatic diisocyanate, in an essentially aqueous liquid containing a protective colloid, a surfactant, or both, wherein the weight ratio of aliphatic diisocyanate/trimer ranges from 0.05/1 to 0.70/1 and the surface tension between the aqueous phase and the hydrophobic organic phase ranges from 0 to 20 mN/m, and then forming microcapsules by interfacially reacting a polyamine with the emulsion which results, thereby constituting polyurea walls of said microcapsules by polyaddition. As can be seen from the above description the information on the characteristics of the PCM capsule is rather scanty. The process for preparing the said capsules uses the melamine formaldehyde ratio in the range of 1:1.3 and 1:3.0. Preparation of prepolymer with lower ratio results in melamine formaldehyde resin of lower molecular weight that influences the condensation of resin on hydrophobic core material. This in turn affects strength of shell wall. Thus, though the existing encapsulation processes may be quite effective each of them suffer from some drawbacks. Particularly, the shell wall becomes more permeable when heated at about 130 C and above especially in dry state, which may be mandatory for fabrics coating in the curing stages. Also, only a limited amount of core content can be encapsulated. The inventors after extensive research have arrived at a solution to this problem. They have found out that when the hexamethylolmelamine prepolymer, prepared using more than 6 times formaldehyde than melamine, is used the condensation rate gets regulated in advantageous manner due to formation of melamine-formaldehyde resin with higher molecular weight. This enables developing shell wall of superior characteristics. Further, the residual formaldehyde can be removed by any known methods to ensure safety of the final products. As herein before disclosed, the novel features of the present invention are: 1. Obtaining the reaction emulsion mixture by preparing emulsion inside the aqueous solution of melamine-formaldehyde pre-polymer. 2. Maintaining the wall material composition at the formaldehyde to melamine (fm) ratio of 6-8. Further this combination gave pre-polymer species having hexamethylol melamine-formaldehyde that on curing gave completely crosslinked stable polymer structure. 3. Regulating temperature profile to properly encapsulate the core material by wall material. 4. Preparing the emulsion at above the melting point of the core, 40°C in case of n-octadecane, and initiating encapsulation at same temperature followed by slowly raising to a temperature of 70°C while slowly bringing down the pH from 7 to 3. 5. Modifying drying and curing conditions to affect the slow but full condensation of melamine and formaldehyde species. The drying was done at 40 °C for 12 hr and final curing was carried out at 100 °C for 11/2 hrs. 6. Significant reduction or Elimination of employing solvent such as cyclohexane in case of polyurea, if desired. 7. Integrating speed of stirring and the manner in which monomer is added. 8. The obtained capsules through above modified processes had a high core content of 70 % and high stability to solvent wash. The capsules were stable >100 °C without any leakage and the process showed high encapsulation efficiency of >80%. It may be pertinent to note that the novel features described herein above are illustrative and should not construe the scope of the invention. SUMMARY OF THE INVENTION: The main object of the present invention is to provide interfacial polymerisation process for preparation of Phase Change Material (PCM) Capsule. The other object is to provide a process for phase change material (PCM) capsule wherein the PCM employed is for thermoregulatory mechanism. Specifically, encapsulated phase change materials (PCMs) of this invention intend to perform functions such as thermal storage, and thermal regulation. Another object is to provide a process for phase change material (PCM) capsule that finds applications in thermo-regulated textile in addition to the applications as herein after described. Yet other object is to provide a process for phase change material (PCM) capsule having better stability to thermal heat. More specifically, the capsules of the present invention have better stability for solvent and reduced diffusion rate. Yet another object is to provide a process for phase change material (PCM) capsule that has high core content and high encapsulation efficiency without compromising/scarifying the wall strength and or wall porosity. The process is simple, cost effective environment and user friendly. The core comprising of organic compounds such as hydrophobic aliphatic alkanes, aliphatic or aromatic polyisocyanate and bulk monomer amines and alcohols, as while the wall consists of natural or synthetic polymer exemplified by but not limited to polyurea, urea formaldehyde, melamine formaldehyde resins. Particularly the capsules are prepared either through interfacial polymerization or in situ polymerization. Further, the polymerization process of this invention is efficient as it yields better product with varied applications. STATEMENT OF INVENTION: Accordingly, the present invention provides interfacial polymerisation process for preparation of Phase Change Material (PCM) Capsule comprising emulsifying hydrophobic aliphatic alkanes having 8 to 25 carbon atoms containing aliphatic or aromatic polyisocyanate, optionally in presence of non polar organic solvent, under stirring in aqueous solution of surfactant optionally containing protective colloid, adding a catalyst selected from dibutyl tin dilaurate, then adding a monomer selected from amine with more than one amino group and/or alcohols with more than one hydroxy group in a phased manner under stirring at 500 to >2000 rpm to initiate interfacial polymerization, reducing the stirring speed to 1800 rpm or lower, and simultaneously increasing the temperature to more than 50 and less than 90°C, adding second installment of monomer to facilitate stronger wall formation with desired diffusion property, isolating, drying and curing capsules in any known manner such as herein described. hydrophobic aliphatic alkanes having 8 to 25 carbon atoms used may be selected from n-octadecane or other alkanes, alcohol, and acids such as Dodecane, Tridecane, Tetradecane,Paraffin, Pentadecane, Hexadecane, Heptadecane, 1-Dodecanol, Octadecane, Nonadecane, Eicosane, 1-Tetradecanol, Heneicosane, n-Octacosane, n-Heptacosane, n-Hexacosane, n-Pentocosane, n-Tetracosane, n-Tricosane, n-Docosane , n-Homeiocosane, or any other organic molecules immiscible with water and inert to encapsulating compounds, preferably n-octadecane. Monomer with more than one amino group may be such as diethylenetriamine (DETA), ethylene diamine (EDA),triethylenetetramine (TETA), and/or hexamethylene diamine (HMDA), Aliphatic or aromatic polyisocyanate used may be such as toluene-2, 4-diisocyanate (TDI), methylene diisocyanate (MDI), or low molecular weight polydiisocynates, preferably TDI. Bulk monomer applied may be diethylenetriamine (DETA), ethylene diamine (EDA), triethylenetetramine (TETA), and/or hexamethylene diamine (HMDA), and/or any polydialcohols. Non polar organic solvent employed may be cyclohexane and surfactant added was anioinic or nonionic such as NP 9.5, Lissopal-N, PVA, Sodium lauryl sulphate. The core to monomer (PCM:TDI) ratio may be in the range of 1.8 to 7.4 preferably 3.7 and PCM to solvent ratio when used may be in the range of 3 to 12 preferably 12. DESCRIPTION OF THE INVENTION: Characteristics of the wall are as follows: Wall composition: melamine-formaldehyde or polyurea Core: organic compounds such as hydrophobic aliphatic alkanes exemplified by n- octadecane or other alkanes, alcohol, and acids such as Dodecane, Tridecane, Tetradecane,Paraffin, Pentadecane, Hexadecane, Heptadecane, 1-Dodecanol, Octadecane, Nonadecane, Eicosane, 1-Tetradecanol, Heneicosane, n-Octacosane, n- Heptacosane, n-Hexacosane, n-Pentocosane, n-Tetracosane, n-Tricosane, n-Docosane , n-Homeiocosane, or any other organic molecules immiscible with water and inert to encapsulating compounds, preferably n-octadecane. Particle size distribution has mean particle size of 3-4 microns. Maximum size is less than 10 microns. Heat storage capacity of about 160 J/g or higher; with nearly no super-cooling Core content: 70% or higher. Wall porosity: Submicron size which allows n-octadecane to diffuse out in liquid bath such as cyclohexane, acetone, or hot water in less than 10% of core content in 10 minutes of washing cycle. The encapsulation may be performed either by interfacial or insitu polymerization as illustrated below: Interfacial polymerization using diisocynate and diamines (polyurea capsules) Microencapsulation of phase change material (PCM) n-octadecane was carried out by interfacial polymerization technique using core and bulk monomers as toluene-2, 4-diisocyanate (TDI) and diethylene triamine (DETA), respectively. The bulk monomer that can be employed may be Diethylenetriamine (DETA), Ethylene Diamine (EDA), Triethylenetetramine (TETA), and Hexamethylene diamine (HMDA) or any di-alcohols and core monomer may be selected from Toluene Diisocyanate (TDI), Methylene Diisocyanate (MDI) and/or low molecular weight polydiisocynates. Cyclohexane was used as the solvent for TDI and n-octadecane, which formed the oil phase. The effect of core to monomer (CM) ratio and PCM to cyclphexane (PC) ratio was found to have profound effect on the core content, encapsulation efficiency, capsule stability. The core content was found to increase with the increasing CM ratio while the encapsulation efficiency continuously decreased with increasing CM ratio. The core content reached a maximum at CM ratio of -3.7. Also the encapsulation efficiency was found to have a strong dependence on PC ratio and a maximum encapsulation efficiency of 97%, along with the core content of 70% was obtained with CM ratio of-3.7 along with the PC ratio of 6. The microcapsules were well shaped, i.e. round and regular, with narrow size distribution at these conditions. The PCM microcapsules were found to be stable to heat treatment at 130°C for 8 hrs. From the initial experiments it was observed that the emulsification stirring speed of more than 2000 rpm was necessary for forming a good emulsion. It was found that the stirring speed should be reduced to allow formation of continuous wall; however, the speed should not be reduced immediately after adding the monomer DETA to prevent capsule agglomeration. Thus it is obvious that the stirring speed & the manner in which monomer is added influences the characteristics of the PCM capsule particularly shell wall properties. It may be worthwhile to mention here that the novelty resides in : 1. Time of reduction of emulsification-speed after the addition of bulk monomer (DETA) was found to have profound effect on formation of stable non-leak wall around the core. 2. Method has been developed to make microcapsules at higher ratios of n-octadecane to solvent (cyclohexane) than reported in the literature/patents 3. Method to formulate microcapsules without adding a solvent in the oil phase. Though a small amount of cyclohexane as solvent (PC value 12) was found to help the microencapsulation process, the microcapsules formed in the absence of cyclohexane also showed high core content with high encapsulation efficiency. The microcapsules produced with the core to monomer ratio of-3.7, PC value of 6 gave the best microcapsules with core content of 70%, and encapsulation efficiency of 97%. The highest core content 71% was obtained with PC ratio of 12 at core to monomer ratio of-3.7. The microcapsules were found to be stable to heat at 130 °C for 8 hrs and hot water wash. The preparation of PCM capsule adopting interfacial polymerization is illustrated below: A calculated amount (Table I) of toluene-2, 4-diisicyanate (TDI) (3 g) was taken in a conical flask. A calculated amount (Table 1) 5ml of cyclohexane (as a solvent) was added to TDI. The TDI-cyclohexane mixture was stirred at 500 rpm on a magnetic stirrer plate. After stirring the mixture for 5min, 15ml of n-octadecane was added to the TDI-cyclohexane mixture and the total mixture was stirred further at 1000 rpm for 5 min on the magnetic stirrer. The above mixture (oil) was added to a 150 ml of aqueous solution of 0.5% NP-9.5 as surfactant in a 250 ml beaker. The oil in water emulsion was formed by stirring the mixture at 2500 rpm using a high shear mechanical stirrer consisting of a mesh plate around blades. The emulsion was stirred for 5min at the room temperature. The dibutyl tin dilaurate was added to the emulsion while stirring was continued. Excess (1.5) g of diethylene triamine (DETA) dissolved in 20 ml of water was added slowly to the above emulsion while being stirred to initiate the interfacial polymerization. The microencapsulation was carried out at 2500 rpm for 5min at the room temperature. Then the microencapsulation speed was reduced to 1800 rpm. Afterwards the temperature of the system was increased to 60 °C and the microencapsulation was continued for additional 45 min. Thereafter, second dose of 1.5 g of DETA dissolved in 20 ml of water was added to the above reaction mixture to increase the concentration of DETA. This helps in further diffusion of the monomer DETA through the capsule wall for continued polymerization. The microcapsules were filtered out after carrying out the microencapsulation for further 45 min at the same conditions. The filtered capsules were washed in distilled water at 60°C to remove the unreacted DETA and other chemicals. The washed capsules were again filtered out and dried at 40°C for 12 h in air oven. (Table removed) Characterization of microcapsules a) Core content The core content of microcapsules (Ca) is defined as the ratio of the heat of fusion (AHm , J/g) of the microcapsules to the heat of fusion (AHpcm , J/g) of the pure PCM (n-octadecane) expressed as a percentage. Ca = (AHm/AHpcm)* 100 The heat of fusion or melting of the microcapsules was determined asing Perkin Elmer DSC 7 attached intra cooler. The samples were scanned at a rate of 10 °C/min under N2 atmosphere. b) Theoretical core content The theoretical core content (Ct) can be expressed as the ratio of the weight of PCM (WPCM) to the combined weight of PCM (WPCM) and monomers (Wm) taken for microencapsulation, expressed as a percentage. Ct = {WPCM/ (WPCM +Wm)}100 c) Encapsulation efficiency The encapsulation efficiency (E) can be defined as the ratio of the actual core content of the microcapsules to the theoretical core content expressed as a percentage. E = (Ca/Ct)100 d) Size and its distribution Aqueous dispersion of microcapsules was placed on a glass slide, dried and studied under Lieca optical microscope. The mean particle size and its distributions were determined by measuring 250 capsules. e) Surface characteristics The above specimen was sputter coated with silver and the morphology of the microcapsules was observed under scanning electron microscope (SEM) Model. f) Stability of microcapsules Heat stability of the microcapsules was evaluated by keeping the microcapsules wrapped in a tissue paper inside an air oven at 130 °C for 8 hrs. The leakage of PCM from microcapsules was qualitatively determined by the amount of stains left by PCM on the tissue paper. For the solvent stability, one gram of microcapsules was washed with 20 ml of cyclohexane at the room temperature for 10 min. The heat of fusion of the solvent washed capsules was determined on DSC as given above and was compared with the heat of fusion of the unwashed capsules. Effect of core to monomer (CM) ratio The values of the actual core content are plotted against the core to monomer ratio (CM ratio) used during encapsulation in Figla&Figlb. For one set of experiments the PC ratio was maintained at one while for another set it was maintained at 3. It can be seen that at a high core to monomer ratio the actual core content is very low while the theoretical core content is at the maximum in both the cases. This suggests that the amount of monomer is not sufficient resulting in improper wall formation for the given amount of core material. The loss of core material is very high at this stage. As the core to monomer ratio is lowered the theoretical core content decreases as expected, whereas the actual core content increased owing to a better wall formation around the cqre. The actual core content decreased after reaching a critical point at the core to monomer ratio of -3.7 indicating core to monomer ratio of 3-4 is sufficient to form stable wall around the core material. Any further increase in monomer content, only adds the dead weight to the microcapsules, resulting in lower core content. On the other hand, the encapsulation efficiency was very high at low core to monomer ratio (Fig2a &Fig2b) because enough TDI is present in oil droplets to form proper polymeric walls. Effect of PCM to Cyclohexane (PC) The cyclohexane along with the PCM is probably used for the better diffusion of core monomer (TDI) to the oil-water interface. However, the amount of cyclohexane necessary for this phenomenon has not investigated till now. It is important to minimize use of cyclohexane in order to maximize the core content. Figure 3 shows the effect of PC ratio on core content of the microcapsules at CM ratio of 3.7. It can be observed from the figure that at low PC ratio the core content is very low at 52.63% while it increases with the decrease in cyclohexane content i.e. increase of PC ratio. It can be inferred that decreasing the solvent (cyclohexane) and increasing the PCM does not affect the wall formation around the core. Thus the use of cyclohexane at the PC ratio of more than 6 is sufficient for the purpose of monomer diffusion. The core content above the PC ratio of 6 remained nearly constant. The plot of encapsulation efficiency against PC ratio is shown in Fig 4. The maximum encapsulation efficiency of 97% was obtained at the PC ratio of 6 while it was low at PC ratio both below and above this value. This would probably be because at low PC ratio, the viscosity of the coil phase (core) is less owing to the presence of more solvent, which may result in poor structural stability of diffusion phase leading to reduced encapsulation efficiency. On the other hand at high PC ratio the viscosity of the oil phase (core) would be so high that the monomer diffusion is less effective leading'to improper wall formation. This may result in loss of core material before encapsulation process is complete and would reduce the encapsulation efficiency. Shape and Size distribution The size distribution of the microcapsules produced using CM ratio of 3.7 and PC ratios of 6 is shown in Fig 5. It can bee seen that most of the capsules clusters are below 10 µm. only a few microcapsules are between 10 to 14 um and none of them is above 14µm. This variation in size appears to be because of the variation in the oil droplets formed during emulsification. The size and its distribution may be further improved by carrying out a better emulsification process. The average capsule size is calculated to be 7.3 µm. The optical micrographs of the microcapsules produced from the core to monomer ratio of ~3.7 with PC ratio of 6 indicate that the capsules are formed even at very low amount of solvent as the monomer diffusing medium. The scanning electron micrographs of the capsules produced using core to monomer ratio of 3 show that the formed capsules are well formed with round shapes. Stability of the capsules Stability to heat The stability of the capsule to heat was tested at 130 °C for 8 h. The capsules were kept inside the oven inside the folded tissue paper. The leakage of the PCM to the tissue paper was tested. All the capsules produced with the modified procedure for microencapsulation are very stable, the capsules did not leak out with the above-mentioned conditions. Whereas the microcapsules produced with the initial experiments i.e. not reducing the emulsification speed after adding DETA, are not stable and the PCM leaked out in the tissue paper. Stability to hot water wash All capsules were washed with hot water at 60°C (well above the melting temperature of the PCM i.e. 30°C) to remove n-octadecane physically entrapped inside the improperly formed microcapsules. All the capsules produced with the modified procedure for microencapsulation are very stable to hot water wash and they retained more than 95 percent of the PCM inside the capsule. Stability to hot cyclohexane washes The capsules produced with CM ratio of 1.8-2.5, PC ratio of 3 (likely to be the strongest due to higher monomer concentration); the capsules produced with core to monomer ratio of-3.7, PC ratio of 6 (likely to be weaker) were tested for solvent stability. The selected capsules were washed with cyclohexane at room temperature in order to study the stability of the microcapsules to solvent wash and the following results were obtained as shown in Table 2. (Table removed) From the above Table2 it can be seen that the capsules produced at core to monomer ratio of 2.5 with PC ratio of 3 shows better stability to solvent wash. While the capsules produced with core to monomer ratio of 5 using PC ratio of 6 shows a poor stability. This might be because at lower CM ratio and lower PC ratio the monomer concentration is more leading to a strong wall (thick layer) formation which provides stability to solvent wash. Application of PCM capsules: 1 Managing the thermal barrier properties of garments, in particular for use in space suits. 2 Outdoor wear thermoregulating garments (parkas, vests, thermals, snowsuits and trousers). 3 Extreme winter clothing materials such as being designed to combat cold, textiles containing PCMs also helps to combat overheating, so overall the effect can be described as thermoregulation. 4 Energy conservation applications such as in maintaining the indoor temperature of buildings. 5 Used in automobiles seating or roofs and side panels to regulate the temperature 6 To preserve the eatables by providing insulation (such as thermal storage applications) 7 Often, active cooling of such electronic components, particularly delicate TR modules, Impatt diodes, data recorders, containers for chemicals and munitions, batteries and the like, is not feasible; and even when it is feasible, it requires continuous high energy cooling. Encapsulated PCM can be incorporated in the heat sinks used for cooling the systems. 8 Cooling body wrap in the emergency treatment of strokes and heart attacks requiring reducing body temperature rapidly. WE CLAIM: 1. Interfacial polymerisation process for preparation of Phase Change Material (PCM) Capsule comprising emulsifying hydrophobic aliphatic alkanes having 8 to 25 carbon atoms containing aliphatic or aromatic polyisocyanate, optionally in presence of non polar organic solvent, under stirring in aqueous solution of ionic or nonionic surfactant optionally containing protective colloid, adding a catalyst selected from dibutyl tin dilaurate, then adding a monomer selected from amine with more than one amino group and/or alcohols with more than one hydroxy group in a phased manner under stirring at 500 to >2000 rpm to initiate interfacial polymerization, reducing the stirring speed to 1800 rpm or lower and simultaneously increasing temperature to more than 50 and less than 90°C, adding second installment of monomer to facilitate wall formation with desired diffusion property, isolating, drying and curing capsules in any known manner such as herein described. 2. A process as claimed in claim 1 wherein the hydrophobic aliphatic alkanes having 8 to 25 carbon atoms used is selected from n-octadecane or other alkanes, alcohol, or acid such as Dodecane, Tridecane, Tetradecane,Paraffin, Pentadecane, Hexadecane, Heptadecane, 1-Dodecanol, Octadecane, Nonadecane, Eicosane, 1-Tetradecanol, Heneicosane, n-Octacosane, n-Heptacosane, n-Hexacosane, n-Pentocosane, n-Tetracosane, n-Tricosane, n-Docosane , n-Homeiocosane, or any other organic molecules immiscible with water and inert to encapsulating compounds, preferably n-octadecane. 3. A process as claimed in claim 1 wherein the monomer with more than one amino group used is selected from diethylenetriamine (DETA), ethylene diamine (EDA),triethylenetetramine (TETA), and/or hexamethylene diamine (HMDA), preferably DETA. 4. A process as claimed in claim 1 wherein aliphatic or aromatic polyisocyanate used is toluene-2, 4-diisocyanate (TDI), methylene diisocyanate (MDI), and/or low molecular weight polydiisocynates, preferably TDI. 5. A process as claimed in claim 1 wherein non polar organic solvent employed is cyclohexane and surfactant added was ionic or nonionic such as NP 9.5, Lissopal-N, PVA, Sodium lauryl sulphate. 6. A process as claimed in claim 1 wherein the core to monomer (PCM:TDI) ratio is in the range of 1.8 to 7.4 preferably -3.7 and PCM to solvent ratio when used is in the range of 3 to 12 preferably 12. 7. Interfacial polymerisation process for preparation of Phase Change Material (PCM) Capsule substantially such as herein described with reference to the drawings.

Full Text

This invention relates to Interfacial Polymerisation process for Preparation of Phase Change Material Capsule.
FIELD OF INVENTION:
The invention relates to encapsulated phase change material (PCM) wherein the PCM is employed for thermoregulatory mechanism. Specifically, encapsulated phase change materials (PCMs) of this invention intend to perform functions such as thermal storage, and thermal regulation. It finds applications in thermo-regulated textile. Particularly, the invention relates to a PCM capsule having better stability to thermal heat. Specifically, the capsules of the present invention have better stability for solvent and reduced diffusion rate. More particularly, the capsules of the present invention have high core content and high encapsulation efficiency without compromising/scarifying the wall strength and or wall porosity. The core comprising of organic compounds such as hydrophobic aliphatic alkanes alcohol, or acids while the wall consists of natural or synthetic polymer exemplified by but not limited to polyurea, urea formaldehyde, melamine formaldehyde resins.
The invention also discloses a process for preparing the PCM capsules. Particularly the capsules are prepared through in-situ polymerization or interfacial polymerization. The monomers used in the process may be such as amine, alcohol, and diisocynates, melamine-formaldehyde, urea- formaldehyde, melamine-urea-formaldehyde, and urea-resorcinol-formaldehyde. Further, the polymerization process of this invention is cost effective, and efficient as it yields better product.
BACKGROUND OF THE INVENTION:
Encapsulation is a process of enclosing an active agent in a polymeric shell. The active agent can be in the form of a solid, a liquid, or even a gas, whereas, the wall material can be an organic polymer, hydrocolloid, sugar, wax, fat, metal, or inorganic oxide. The PCM useful for the textile applications are those that change phase from solid to liquid by absorbing large amount of latent heat from the environment and change phase from liquid to solid by releasing the same amount of heat to the environment at a transition temperature close to the body temperature.
Suitable PCMs, that satisfy the major requirements of thermoregulation for application in textile clothing, are n-octadecane, n-eicosane and inorganic salts exemplified lithium nitrate tri-hydrate. n-Octadecane is particularly important because its melting temperature is very close to the comfort temperature of the body i.e. around 28-29°C, and it has a high latent heat of fusion of 240 J/g. However, this PCM must be encapsulated using a suitable technique that can provide high wall integrity and stability. This requirement of better wall integrity is unlike other microencapsulation processes used in pharmaceutical products, cosmetics, and textile finishes, where micropores in the wall-membrane are necessary for slow release of drug, perfumes and finishing agents that are present as core.
The relevant prior art known to the inventor with regard to the characteristics of the capsule include article that appeared in Colloid and Polymer Science (2002), 280(3), 260-266, titled "Microencapsulation of octadecane as a phase-change material by interfacial polymerization in an emulsion system" by Cho, Jeong-Sook; Kwon, Aehwa; Cho, Chang-Gi. The core content of the PCM capsules as disclosed jn the said paper is 40 to 45%. According to the said paper Microcapsules containing phase-change material for thermal adaptable fiber application were synthesized and characterized. The microcapsules of about 1 urn in diameter were prepared using an interfacial polycondensation method with toluene-2,4-diisocyanate (TDI) and diethylenetriamine (DETA) as monomers in an emulsion system. Octadecane was used as a phase-change material and NP-10, which is nonionic surfactant, was used as an emulsifier. To investigate the reaction ratio of monomers, microcapsules were synthesized with 3 g TDI and 0-4 g DETA. Polyurea microcapsules were formed not only by reaction with TDI and DETA, but also by reaction of TDI with hydrolyzed TDI at the interface. TDI was reacted with DETA in the wt. ratio of 3:1. NP-10 was reacted with TDI to form urethane. According to this paper, the efficiency of octadecane encapsulation increased as the core content decreased. The process reported a maximum core content of 46% with the encapsulation efficiency of 75%.
CN1467260 titled Microcapsulated heat absorbing particle describes a microcapsule-type heat absorbing particle able to be sprayed on the surface of object for absorbing a great deal of heat is a (l-l000)-micron particle, which is composed of shell and core. Said shell is a high-molecular polymer chosen from melamine formaldehyde, urea-
formaldehyde resin, PU, etc. Said core is a heat-absorbing substance chosen from straight-chain alkane, high-grade alcohol and organic acid.
A reference also can be made to Korean Patent No. KR 2002-11266 20020304 titled Preparation of thermostable microcapsules containing phase change materials and articles. According to this patent the method comprises steps of: adding 10 to 50 parts organic phase consisting of 0 to 70% nonpolar organic solvent, 10 to 90% polymerizable monomer phase change materials having alkyl group having 8 to 18 carbon atoms and 10 to 50% compound having two or more isocyanate groups to a solution in which 0.2 to 10 parts surfactant is dissolved into 100 parts water, and emulsifying the mixed solution as agitating the solution and organic phase; and injecting at least one compound selected from diethylenetriamine, ethylenediamine, triethylenetetramine and melamine solution and the compound having two or more isocyanate groups to the emulsified solution in a ratio of 100:20 to 300, and reacting the compounds with emulsified solution so that urea bond is formed.
However, the core content and thermal stability is not explicitly mentioned. Further, the procedure does not specify time of addition of the second monomer i.e. diamine or triamines.
US 2004121072 Al. In accordance with this patent, the process for encapsulating a core component comprising paraffin compounds that can undergo phase transition, includes the steps of: (A) dissolving first monomers in the core component to form a first solution, the first monomers forming a first polymer; (B) dispersing the first solution into a second aqueous solution to form an emulsion; (C) adding the said emulsion to a third aqueous solution containing a precondensate of melamine-formaldehyde to form an encapsulation mixture characterized in that the first monomers are a polypropylene glycol with an average mol. wt. higher than about 400 and a polyisocyanate soluble in the core component. This patent claims addition of emulsion to the melamine-formaldehyde pre-polymer, maintaining melamine to formaldehyde ratio between 1:1.3 and 1:3, maintaining pH and between 4 and 7. Further, the encapsulation was effected at 70°C.
US4876290 Microencapsulation by interfacial polyaddition (1989). This invention does not claim PCM. The invention teaches a process comprising emulsifying a hydrophobic
organic liquid which includes an aliphatic diisocyanate and an isocyanurate ring trimer of an aliphatic diisocyanate, in an essentially aqueous liquid containing a protective colloid, a surfactant, or both, wherein the weight ratio of aliphatic diisocyanate/trimer ranges from 0.05/1 to 0.70/1 and the surface tension between the aqueous phase and the hydrophobic organic phase ranges from 0 to 20 mN/m, and then forming microcapsules by interfacially reacting a polyamine with the emulsion which results, thereby constituting polyurea walls of said microcapsules by polyaddition.
As can be seen from the above description the information on the characteristics of the PCM capsule is rather scanty. The process for preparing the said capsules uses the melamine formaldehyde ratio in the range of 1:1.3 and 1:3.0. Preparation of prepolymer with lower ratio results in melamine formaldehyde resin of lower molecular weight that influences the condensation of resin on hydrophobic core material. This in turn affects strength of shell wall. Thus, though the existing encapsulation processes may be quite effective each of them suffer from some drawbacks. Particularly, the shell wall becomes
more permeable when heated at about 130 C and above especially in dry state, which
may be mandatory for fabrics coating in the curing stages. Also, only a limited amount of core content can be encapsulated.
The inventors after extensive research have arrived at a solution to this problem. They have found out that when the hexamethylolmelamine prepolymer, prepared using more than 6 times formaldehyde than melamine, is used the condensation rate gets regulated in advantageous manner due to formation of melamine-formaldehyde resin with higher molecular weight. This enables developing shell wall of superior characteristics. Further, the residual formaldehyde can be removed by any known methods to ensure safety of the final products.
As herein before disclosed, the novel features of the present invention are:
1. Obtaining the reaction emulsion mixture by preparing emulsion inside the aqueous
solution of melamine-formaldehyde pre-polymer.
2. Maintaining the wall material composition at the formaldehyde to melamine (fm)
ratio of 6-8. Further this combination gave pre-polymer species having hexamethylol
melamine-formaldehyde that on curing gave completely crosslinked stable polymer
structure.
3. Regulating temperature profile to properly encapsulate the core material by wall material.
4. Preparing the emulsion at above the melting point of the core, 40°C in case of n-octadecane, and initiating encapsulation at same temperature followed by slowly raising to a temperature of 70°C while slowly bringing down the pH from 7 to 3.
5. Modifying drying and curing conditions to affect the slow but full condensation of melamine and formaldehyde species. The drying was done at 40 °C for 12 hr and final curing was carried out at 100 °C for 11/2 hrs.
6. Significant reduction or Elimination of employing solvent such as cyclohexane in case of polyurea, if desired.
7. Integrating speed of stirring and the manner in which monomer is added.
8. The obtained capsules through above modified processes had a high core content of 70 % and high stability to solvent wash. The capsules were stable >100 °C without any leakage and the process showed high encapsulation efficiency of >80%.
It may be pertinent to note that the novel features described herein above are illustrative and should not construe the scope of the invention.
SUMMARY OF THE INVENTION:
The main object of the present invention is to provide interfacial polymerisation process
for preparation of Phase Change Material (PCM) Capsule.
The other object is to provide a process for phase change material (PCM) capsule wherein the PCM employed is for thermoregulatory mechanism. Specifically, encapsulated phase change materials (PCMs) of this invention intend to perform functions such as thermal storage, and thermal regulation.
Another object is to provide a process for phase change material (PCM) capsule that
finds
applications in thermo-regulated textile in addition to the applications as herein after
described.
Yet other object is to provide a process for phase change material (PCM) capsule having
better stability to thermal heat. More specifically, the capsules of the present invention have better stability for solvent and reduced diffusion rate.
Yet another object is to provide a process for phase change material (PCM) capsule that has high core content and high encapsulation efficiency without compromising/scarifying the wall strength and or wall porosity.
The process is simple, cost effective environment and user friendly. The core comprising of organic compounds such as hydrophobic aliphatic alkanes, aliphatic or aromatic polyisocyanate and bulk monomer amines and alcohols, as while the wall consists of natural or synthetic polymer exemplified by but not limited to polyurea, urea formaldehyde, melamine formaldehyde resins.
Particularly the capsules are prepared either through interfacial polymerization or in situ polymerization. Further, the polymerization process of this invention is efficient as it yields better product with varied applications.
STATEMENT OF INVENTION:
Accordingly, the present invention provides interfacial polymerisation process for preparation of Phase Change Material (PCM) Capsule comprising emulsifying hydrophobic aliphatic alkanes having 8 to 25 carbon atoms containing aliphatic or aromatic polyisocyanate, optionally in presence of non polar organic solvent, under stirring in aqueous solution of surfactant optionally containing protective colloid, adding a catalyst selected from dibutyl tin dilaurate, then adding a monomer selected from amine with more than one amino group and/or alcohols with more than one hydroxy group in a phased manner under stirring at 500 to >2000 rpm to initiate interfacial polymerization, reducing the stirring speed to 1800 rpm or lower, and simultaneously increasing the temperature to more than 50 and less than 90°C, adding second installment of monomer to facilitate stronger wall formation with desired diffusion property, isolating, drying and curing capsules in any known manner such as herein described.
hydrophobic aliphatic alkanes having 8 to 25 carbon atoms used may be selected from n-octadecane or other alkanes, alcohol, and acids such as Dodecane, Tridecane, Tetradecane,Paraffin, Pentadecane, Hexadecane, Heptadecane, 1-Dodecanol,
Octadecane, Nonadecane, Eicosane, 1-Tetradecanol, Heneicosane, n-Octacosane, n-Heptacosane, n-Hexacosane, n-Pentocosane, n-Tetracosane, n-Tricosane, n-Docosane , n-Homeiocosane, or any other organic molecules immiscible with water and inert to encapsulating compounds, preferably n-octadecane.
Monomer with more than one amino group may be such as diethylenetriamine (DETA),
ethylene diamine (EDA),triethylenetetramine (TETA), and/or hexamethylene diamine
(HMDA),
Aliphatic or aromatic polyisocyanate used may be such as toluene-2, 4-diisocyanate
(TDI), methylene diisocyanate (MDI), or low molecular weight polydiisocynates,
preferably TDI.
Bulk monomer applied may be diethylenetriamine (DETA), ethylene diamine (EDA),
triethylenetetramine (TETA), and/or hexamethylene diamine (HMDA), and/or any
polydialcohols.
Non polar organic solvent employed may be cyclohexane and surfactant added was
anioinic or nonionic such as NP 9.5, Lissopal-N, PVA, Sodium lauryl sulphate.
The core to monomer (PCM:TDI) ratio may be in the range of 1.8 to 7.4 preferably 3.7
and PCM to solvent ratio when used may be in the range of 3 to 12 preferably 12.
DESCRIPTION OF THE INVENTION:
Characteristics of the wall are as follows:
Wall composition: melamine-formaldehyde or polyurea
Core: organic compounds such as hydrophobic aliphatic alkanes exemplified by n-
octadecane or other alkanes, alcohol, and acids such as Dodecane, Tridecane,
Tetradecane,Paraffin, Pentadecane, Hexadecane, Heptadecane, 1-Dodecanol,
Octadecane, Nonadecane, Eicosane, 1-Tetradecanol, Heneicosane, n-Octacosane, n-
Heptacosane, n-Hexacosane, n-Pentocosane, n-Tetracosane, n-Tricosane, n-Docosane ,
n-Homeiocosane, or any other organic molecules immiscible with water and inert to
encapsulating compounds, preferably n-octadecane.
Particle size distribution has mean particle size of 3-4 microns. Maximum size is less
than 10 microns.
Heat storage capacity of about 160 J/g or higher; with nearly no super-cooling
Core content: 70% or higher.
Wall porosity: Submicron size which allows n-octadecane to diffuse out in liquid bath such as cyclohexane, acetone, or hot water in less than 10% of core content in 10 minutes of washing cycle.
The encapsulation may be performed either by interfacial or insitu polymerization as illustrated below:
Interfacial polymerization using diisocynate and diamines (polyurea capsules)
Microencapsulation of phase change material (PCM) n-octadecane was carried out by interfacial polymerization technique using core and bulk monomers as toluene-2, 4-diisocyanate (TDI) and diethylene triamine (DETA), respectively. The bulk monomer that can be employed may be Diethylenetriamine (DETA), Ethylene Diamine (EDA), Triethylenetetramine (TETA), and Hexamethylene diamine (HMDA) or any di-alcohols and core monomer may be selected from Toluene Diisocyanate (TDI), Methylene Diisocyanate (MDI) and/or low molecular weight polydiisocynates. Cyclohexane was used as the solvent for TDI and n-octadecane, which formed the oil phase. The effect of core to monomer (CM) ratio and PCM to cyclphexane (PC) ratio was found to have profound effect on the core content, encapsulation efficiency, capsule stability.
The core content was found to increase with the increasing CM ratio while the encapsulation efficiency continuously decreased with increasing CM ratio. The core content reached a maximum at CM ratio of -3.7. Also the encapsulation efficiency was found to have a strong dependence on PC ratio and a maximum encapsulation efficiency of 97%, along with the core content of 70% was obtained with CM ratio of-3.7 along with the PC ratio of 6. The microcapsules were well shaped, i.e. round and regular, with narrow size distribution at these conditions. The PCM microcapsules were found to be stable to heat treatment at 130°C for 8 hrs.
From the initial experiments it was observed that the emulsification stirring speed of more than 2000 rpm was necessary for forming a good emulsion. It was found that the stirring speed should be reduced to allow formation of continuous wall; however, the speed should not be reduced immediately after adding the monomer DETA to prevent capsule agglomeration.
Thus it is obvious that the stirring speed & the manner in which monomer is added influences the characteristics of the PCM capsule particularly shell wall properties.
It may be worthwhile to mention here that the novelty resides in :
1. Time of reduction of emulsification-speed after the addition of bulk monomer (DETA) was found to have profound effect on formation of stable non-leak wall around the core.
2. Method has been developed to make microcapsules at higher ratios of n-octadecane to solvent (cyclohexane) than reported in the literature/patents
3. Method to formulate microcapsules without adding a solvent in the oil phase.
Though a small amount of cyclohexane as solvent (PC value 12) was found to help the
microencapsulation process, the microcapsules formed in the absence of cyclohexane
also showed high core content with high encapsulation efficiency.
The microcapsules produced with the core to monomer ratio of-3.7, PC value of 6 gave
the best microcapsules with core content of 70%, and encapsulation efficiency of 97%.
The highest core content 71% was obtained with PC ratio of 12 at core to monomer ratio
of-3.7.
The microcapsules were found to be stable to heat at 130 °C for 8 hrs and hot water
wash.
The preparation of PCM capsule adopting interfacial polymerization is illustrated below: A calculated amount (Table I) of toluene-2, 4-diisicyanate (TDI) (3 g) was taken in a conical flask. A calculated amount (Table 1) 5ml of cyclohexane (as a solvent) was added to TDI. The TDI-cyclohexane mixture was stirred at 500 rpm on a magnetic stirrer plate. After stirring the mixture for 5min, 15ml of n-octadecane was added to the TDI-cyclohexane mixture and the total mixture was stirred further at 1000 rpm for 5 min on the magnetic stirrer. The above mixture (oil) was added to a 150 ml of aqueous solution of 0.5% NP-9.5 as surfactant in a 250 ml beaker. The oil in water emulsion was formed by stirring the mixture at 2500 rpm using a high shear mechanical stirrer consisting of a mesh plate around blades. The emulsion was stirred for 5min at the room temperature. The dibutyl tin dilaurate was added to the emulsion while stirring was continued. Excess (1.5) g of diethylene triamine (DETA) dissolved in 20 ml of water was added slowly to the above emulsion while being stirred to initiate the interfacial polymerization. The microencapsulation was carried out at 2500 rpm for 5min at the room temperature. Then the microencapsulation speed was reduced to 1800 rpm. Afterwards the temperature of the system was increased to 60 °C and the microencapsulation was continued for additional 45 min. Thereafter, second dose of 1.5 g of DETA dissolved in 20 ml of water
was added to the above reaction mixture to increase the concentration of DETA. This helps in further diffusion of the monomer DETA through the capsule wall for continued polymerization. The microcapsules were filtered out after carrying out the microencapsulation for further 45 min at the same conditions. The filtered capsules were washed in distilled water at 60°C to remove the unreacted DETA and other chemicals. The washed capsules were again filtered out and dried at 40°C for 12 h in air oven.
(Table removed)
Characterization of microcapsules
a) Core content
The core content of microcapsules (Ca) is defined as the ratio of the heat of fusion (AHm , J/g) of the microcapsules to the heat of fusion (AHpcm , J/g) of the pure PCM (n-octadecane) expressed as a percentage.
Ca = (AHm/AHpcm)* 100 The heat of fusion or melting of the microcapsules was determined asing Perkin Elmer DSC 7 attached intra cooler. The samples were scanned at a rate of 10 °C/min under N2 atmosphere.
b) Theoretical core content
The theoretical core content (Ct) can be expressed as the ratio of the weight of PCM (WPCM) to the combined weight of PCM (WPCM) and monomers (Wm) taken for microencapsulation, expressed as a percentage.
Ct = {WPCM/ (WPCM +Wm)}*100
c) Encapsulation efficiency
The encapsulation efficiency (E) can be defined as the ratio of the actual core content of the microcapsules to the theoretical core content expressed as a percentage.
E = (Ca/Ct)*100
d) Size and its distribution
Aqueous dispersion of microcapsules was placed on a glass slide, dried and studied under Lieca optical microscope. The mean particle size and its distributions were determined by measuring 250 capsules.
e) Surface characteristics
The above specimen was sputter coated with silver and the morphology of the microcapsules was observed under scanning electron microscope (SEM) Model.
f) Stability of microcapsules
Heat stability of the microcapsules was evaluated by keeping the microcapsules wrapped in a tissue paper inside an air oven at 130 °C for 8 hrs. The leakage of PCM from microcapsules was qualitatively determined by the amount of stains left by PCM on the tissue paper.
For the solvent stability, one gram of microcapsules was washed with 20 ml of cyclohexane at the room temperature for 10 min. The heat of fusion of the solvent washed capsules was determined on DSC as given above and was compared with the heat of fusion of the unwashed capsules.
Effect of core to monomer (CM) ratio
The values of the actual core content are plotted against the core to monomer ratio (CM ratio) used during encapsulation in Figla&Figlb. For one set of experiments the PC ratio was maintained at one while for another set it was maintained at 3. It can be seen that at a high core to monomer ratio the actual core content is very low while the theoretical core content is at the maximum in both the cases. This suggests that the amount of monomer is not sufficient resulting in improper wall formation for the given amount of core material. The loss of core material is very high at this stage. As the core to monomer ratio is lowered the theoretical core content decreases as expected, whereas the actual
core content increased owing to a better wall formation around the cqre. The actual core content decreased after reaching a critical point at the core to monomer ratio of -3.7 indicating core to monomer ratio of 3-4 is sufficient to form stable wall around the core material. Any further increase in monomer content, only adds the dead weight to the microcapsules, resulting in lower core content.
On the other hand, the encapsulation efficiency was very high at low core to monomer ratio (Fig2a &Fig2b) because enough TDI is present in oil droplets to form proper polymeric walls.
Effect of PCM to Cyclohexane (PC)
The cyclohexane along with the PCM is probably used for the better diffusion of core monomer (TDI) to the oil-water interface. However, the amount of cyclohexane necessary for this phenomenon has not investigated till now. It is important to minimize use of cyclohexane in order to maximize the core content. Figure 3 shows the effect of PC ratio on core content of the microcapsules at CM ratio of 3.7. It can be observed from the figure that at low PC ratio the core content is very low at 52.63% while it increases with the decrease in cyclohexane content i.e. increase of PC ratio. It can be inferred that decreasing the solvent (cyclohexane) and increasing the PCM does not affect the wall formation around the core. Thus the use of cyclohexane at the PC ratio of more than 6 is sufficient for the purpose of monomer diffusion. The core content above the PC ratio of 6 remained nearly constant.
The plot of encapsulation efficiency against PC ratio is shown in Fig 4. The maximum encapsulation efficiency of 97% was obtained at the PC ratio of 6 while it was low at PC ratio both below and above this value. This would probably be because at low PC ratio, the viscosity of the coil phase (core) is less owing to the presence of more solvent, which may result in poor structural stability of diffusion phase leading to reduced encapsulation efficiency. On the other hand at high PC ratio the viscosity of the oil phase (core) would be so high that the monomer diffusion is less effective leading'to improper wall formation. This may result in loss of core material before encapsulation process is complete and would reduce the encapsulation efficiency.
Shape and Size distribution
The size distribution of the microcapsules produced using CM ratio of 3.7 and PC ratios of 6 is shown in Fig 5. It can bee seen that most of the capsules clusters are below 10 µm. only a few microcapsules are between 10 to 14 um and none of them is above 14µm. This variation in size appears to be because of the variation in the oil droplets formed during emulsification. The size and its distribution may be further improved by carrying out a better emulsification process. The average capsule size is calculated to be 7.3 µm.
The optical micrographs of the microcapsules produced from the core to monomer ratio of ~3.7 with PC ratio of 6 indicate that the capsules are formed even at very low amount of solvent as the monomer diffusing medium. The scanning electron micrographs of the capsules produced using core to monomer ratio of 3 show that the formed capsules are well formed with round shapes. Stability of the capsules Stability to heat
The stability of the capsule to heat was tested at 130 °C for 8 h. The capsules were kept inside the oven inside the folded tissue paper. The leakage of the PCM to the tissue paper was tested. All the capsules produced with the modified procedure for microencapsulation are very stable, the capsules did not leak out with the above-mentioned conditions. Whereas the microcapsules produced with the initial experiments i.e. not reducing the emulsification speed after adding DETA, are not stable and the PCM leaked out in the tissue paper. Stability to hot water wash
All capsules were washed with hot water at 60°C (well above the melting temperature of the PCM i.e. 30°C) to remove n-octadecane physically entrapped inside the improperly formed microcapsules. All the capsules produced with the modified procedure for microencapsulation are very stable to hot water wash and they retained more than 95 percent of the PCM inside the capsule.
Stability to hot cyclohexane washes
The capsules produced with CM ratio of 1.8-2.5, PC ratio of 3 (likely to be the strongest due to higher monomer concentration); the capsules produced with core to monomer ratio of-3.7, PC ratio of 6 (likely to be weaker) were tested for solvent stability. The
selected capsules were washed with cyclohexane at room temperature in order to study the stability of the microcapsules to solvent wash and the following results were obtained as shown in Table 2.
(Table removed)
From the above Table2 it can be seen that the capsules produced at core to monomer ratio of 2.5 with PC ratio of 3 shows better stability to solvent wash. While the capsules produced with core to monomer ratio of 5 using PC ratio of 6 shows a poor stability. This might be because at lower CM ratio and lower PC ratio the monomer concentration is more leading to a strong wall (thick layer) formation which provides stability to solvent wash.
Application of PCM capsules:
1 Managing the thermal barrier properties of garments, in particular for use in space suits.
2 Outdoor wear thermoregulating garments (parkas, vests, thermals, snowsuits and trousers).
3 Extreme winter clothing materials such as being designed to combat cold, textiles containing PCMs also helps to combat overheating, so overall the effect can be described as thermoregulation.
4 Energy conservation applications such as in maintaining the indoor temperature of buildings.
5 Used in automobiles seating or roofs and side panels to regulate the temperature
6 To preserve the eatables by providing insulation (such as thermal storage applications)
7 Often, active cooling of such electronic components, particularly delicate TR modules, Impatt diodes, data recorders, containers for chemicals and munitions, batteries and the like, is not feasible; and even when it is feasible, it requires continuous high energy cooling. Encapsulated PCM can be incorporated in the heat sinks used for cooling the systems.
8 Cooling body wrap in the emergency treatment of strokes and heart attacks requiring reducing body temperature rapidly.

WE CLAIM:
1. Interfacial polymerisation process for preparation of Phase Change Material (PCM) Capsule comprising emulsifying hydrophobic aliphatic alkanes having 8 to 25 carbon atoms containing aliphatic or aromatic polyisocyanate, optionally in presence of non polar organic solvent, under stirring in aqueous solution of ionic or nonionic surfactant optionally containing protective colloid, adding a catalyst selected from dibutyl tin dilaurate, then adding a monomer selected from amine with more than one amino group and/or alcohols with more than one hydroxy group in a phased manner under stirring at 500 to >2000 rpm to initiate interfacial polymerization, reducing the stirring speed to 1800 rpm or lower and simultaneously increasing temperature to more than 50 and less than 90°C, adding second installment of monomer to facilitate wall formation with desired diffusion property, isolating, drying and curing capsules in any known manner such as herein described.
2. A process as claimed in claim 1 wherein the hydrophobic aliphatic alkanes having 8 to 25 carbon atoms used is selected from n-octadecane or other alkanes, alcohol, or acid such as Dodecane, Tridecane, Tetradecane,Paraffin, Pentadecane, Hexadecane, Heptadecane, 1-Dodecanol, Octadecane, Nonadecane, Eicosane, 1-Tetradecanol, Heneicosane, n-Octacosane, n-Heptacosane, n-Hexacosane, n-Pentocosane, n-Tetracosane, n-Tricosane, n-Docosane , n-Homeiocosane, or any other organic molecules immiscible with water and inert to encapsulating compounds, preferably n-octadecane.
3. A process as claimed in claim 1 wherein the monomer with more than one amino group used is selected from diethylenetriamine (DETA), ethylene diamine (EDA),triethylenetetramine (TETA), and/or hexamethylene diamine (HMDA), preferably DETA.
4. A process as claimed in claim 1 wherein aliphatic or aromatic polyisocyanate used is toluene-2, 4-diisocyanate (TDI), methylene diisocyanate (MDI), and/or low molecular weight polydiisocynates, preferably TDI.
5. A process as claimed in claim 1 wherein non polar organic solvent employed is cyclohexane and surfactant added was ionic or nonionic such as NP 9.5, Lissopal-N, PVA, Sodium lauryl sulphate.
6. A process as claimed in claim 1 wherein the core to monomer (PCM:TDI) ratio is
in the range of 1.8 to 7.4 preferably -3.7 and PCM to solvent ratio when used is in the range of 3 to 12 preferably 12.
7. Interfacial polymerisation process for preparation of Phase Change Material
(PCM) Capsule substantially such as herein described with reference to the drawings.

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Patent Number

279775

Indian Patent Application Number

128/DEL/2007

PG Journal Number

05/2017

Publication Date

03-Feb-2017

Grant Date

31-Jan-2017

Date of Filing

22-Jan-2007

Name of Patentee

INDIAN INSTITUTE OF TECHNOLOGY, DELHI

Applicant Address

HAUS KHAS, NEW DELHI-110016

Inventors:

#	Inventor's Name	Inventor's Address
1	PERIYASAMY, S	INDIAN INSTITUTE OF TECHNOLOGY, HAUS KHAS, NEW DELHI 110016
2	AGRAWAL, ASHWINI KUMAR	INDIAN INSTITUTE OF TECHNOLOGY, HAUS KHAS, NEW DELHI 110016
3	JASSAL, MANJEET	INDIAN INSTITUTE OF TECHNOLOGY, HAUS KHAS, NEW DELHI 110016
4	PALANIKKUMARAN, M.	INDIAN INSTITUTE OF TECHNOLOGY, HAUS KHAS, NEW DELHI 110016

PCT International Classification Number

C08G

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA