Phase change material composition

Abstract

The present invention relates to phase change material (PCM) compositions comprising an aqueous solution of a salt hydrate phase change material component, one or more polymers, at least one of which is poly(4-styrenesulfonic acid-co-maleic acid), poly(methyl vinyl ether-alt-maleic acid), or polystyrenesulfonic acid, or mixtures of these polymers. The present invention also relates to methods of making PCM compositions comprising these polymers.

Description

[Technical Field]

[0001] The present invention relates to phase change materials, and more particularly to phase change material compositions that include additives that reduce segregation of the compositions. The present invention also relates to methods for making such phase change compositions. [Background technology]

[0002] Phase change materials (PCMs) exhibit high enthalpies of fusion, with heats of fusion generally much higher than sensible heat. Due to their ability to store and release large amounts of thermal energy as latent heat during their phase transitions, PCMs find use in a wide variety of heating, cooling, and thermal energy storage applications, such as building air conditioning, medical applications, such as heating or cooling biological samples, body cooling in bulky clothing, water heating and cooling, heat pump systems, thermal protection of devices, and many other applications.

[0003] To accommodate the application-specific thermal requirements, the PCM must have a transition temperature within the application's operating temperature range and have good thermal conductivity for efficient heat transfer.

[0004] Salt hydrate PCMs are particularly attractive because they combine high volumetric latent heat storage capacity with good thermal conductivity and sharp melting points. Furthermore, the materials are readily available at relatively low cost.

[0005] However, phase separation, also known as segregation, is one of the major challenges facing the use of salt hydrate PCMs today. During segregation, an insoluble anhydrous precipitate or a precipitate of a different hydrated form with a higher melting point is formed, followed by the formation of the salt hydrate material. This difference in melting temperature induces incongruent melting of the PCM. Once the solution segregates, it loses its phase change ability.

[0006] As the concentration of dissolved salt increases, segregation becomes particularly problematic. This is commonly observed in stoichiometric salt-water compositions. Because the ability of a PCM composition to store and transfer heat is attributable to the salt material and the amount of salt material present in the composition, it is highly desirable to provide salt at high concentrations to enhance the efficiency of the PCM composition. Therefore, segregation must be avoided in concentrated salt compositions.

[0007] To overcome this problem, thickeners are traditionally added to increase the viscosity of the material, thereby slowing the formation of local concentration differences and preventing unwanted crystal precipitation and growth. Increasing viscosity slows the segregation of PCMs; however, it does not completely prevent segregation. As an undesirable side effect, higher viscosity leads to enthalpy losses and impeded heat transfer.

[0008] Recently, polymers without thickening behavior have been used to completely prevent the formation of undesired phases, based on novel mechanistic ideas: in this approach, the formation of nuclei above the critical nucleus size for crystallization is completely prevented, thus avoiding the nucleation of undesired phases, for example.

[0009] For example, WO2014195961A1 (Patent Document 1) discloses the application of this approach to a phase change composition containing sodium acetate trihydrate, which contains an alkali-soluble polymer to inhibit the formation of anhydrous sodium acetate crystals and a nucleation promoter.

[0010] Polymer-based approaches to prevent heterogeneous crystallization have proven promising, and it would therefore be of great interest to find additional specific polymer-containing compositions of salt hydrate PCMs that can be tailored to specific applications. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] WO2014195961A1 Summary of the Invention

[0012] BRIEF DISCLOSURE OF THE INVENTION It is an object of the present invention to provide aqueous salt hydrate PCM compositions with reduced risk of incongruent melting behavior.

[0013] The PCM composition should be homogeneous. The PCM composition should retain its thermodynamic stability when repeatedly heated and cooled.

[0014] It is a further object of the present invention to provide specific polymers that are particularly suitable for preventing crystallization of the anhydrous or differently hydrated salt components of salt hydrate-based PCMs.

[0015] Preferably, a solution to the segregation problem should be applicable to a variety of salt hydrate PCM compositions that may be suitable for different applications.

[0016] Yet another object is to provide an alternative to known salt hydrate PCM compositions that include polymers to prevent heterogeneous crystallization of the salt hydrate PCM.

[0017] According to the invention, one or more of these objects are achieved by the subject matter of the attached claims, in particular by the independent claims. The dependent claims relate to further advantageous embodiments of the invention.

[0018] Specifically, at least one of the above objects is achieved by a phase change material composition comprising a salt hydrate phase change material and one or more polymers, at least one of the polymers having a general formula 1: [ka] General formula 2, [ka] General formula 3 [ka] have or Alternatively, it is a mixture of polymers comprising a polymer having general formula 1, a polymer having general formula 2 and / or a polymer having general formula 3. The PCM composition is provided in an aqueous solution.

[0019] These polymers reduce or prevent the formation of segregates in different salt hydrate PCM compositions.

[0020] The present invention is not particularly limited to the above-mentioned types of salt hydrate PCM. The salt hydrate can be selected depending on the intended application. The melting point of the selected salt hydrate should be within a range suitable for the intended application. The PCM may be, for example, a calcium salt hydrate, a potassium salt hydrate, or a sodium salt hydrate.

[0021] Sodium acetate trihydrate (NaOAc 3H2O), also known as SAT, has a melting point of 58 °C and is a commonly used PCM that is particularly suitable for construction applications and in water heating, cooling, or heat storage systems. The anhydrous form of SAT is known as SA.

[0022] Disodium hydrogen phosphate (DSP), or NaHPO, especially its hydrated form, disodium hydrogen phosphate dodecahydrate (DSPD), is a promising phase change material due to its melting point of approximately 35°C, high phase change enthalpy, low cost, safety, and high compatibility with metals. Nevertheless, at its stoichiometric composition containing approximately 40 wt% salt, DSPD forms disodium hydrogen phosphate heptahydrate (DSPH) above 35°C, resulting in phase segregation. The segregated crystals do not melt under standard cycling conditions. Therefore, DSPD PCM materials no longer undergo phase change. Once this segregated phase forms, the sample can no longer be used as a storage material.

[0023] The compositions of the present invention preferably comprise 20% to 80% by weight, preferably 35% to 55% by weight, for example 45% by weight, of the salt component of the PCM. The salt may be provided in its anhydrous form for the preparation of the composition.

[0024] The inventors have found that polymers of general formula 1, general formula 2, and general formula 3 reduce or completely prevent the formation of anhydrous salt PCM precipitates or different hydrated forms, thereby avoiding segregation of salt hydrate PCM solutions. Thus, the polymers avoid the formation or heterogeneous liquids in aqueous compositions, thereby reducing or preventing the incongruent melting behavior of the compositions.

[0025] The polymer having the general formula 1 is poly(4-styrenesulfonic acid-co-maleic acid) (hereinafter referred to as P4SSA-co-MA or P4SSA). The polymer having the general formula 2 is poly(methyl vinyl ether-alt-maleic acid) (hereinafter referred to as PMVEMA). The polymer having the general formula 3 is polystyrenesulfonic acid or polystyrene sulfonate (hereinafter referred to as PSS).

[0026] Both polymers described herein contain carboxylate groups, which are generally believed to interact with the undesired phase, thereby modifying its crystalline shape and increasing its solubility: the anhydrous phase dissolves faster, so the undesired phase does not precipitate.

[0027] P4SSA-co-MA, i.e., the polymer having general formula 1, and PPS, i.e., the polymer having general formula 3, each further contain sulfonate groups (-SO3R), which are sodium (Na + ) actively binds the hydrated sodium salts. This polymer was observed to be particularly effective in preventing segregation. It is therefore speculated that this polymer may sequester the sodium in the SAT, thereby preventing the SA from forming and precipitating. Therefore, this polymer is expected to similarly prevent the formation of anhydrous precipitates or other hydrated forms of other sodium salt hydrates.

[0028] Similarly, functional groups on the polymer that bind or interact with the cations of the salt hydrate PCM, such as sulfonate groups, can be expected to affect the effectiveness of the polymer in preventing segregation. Thus, we have shown that these polymers with these functional groups can be powerful additives for avoiding the segregation and / or anharmonic behavior of salt hydrate PCMs.

[0029] The P4SSA-co-MA polymer included in the composition of the present invention may have an average MW in the range of 50,000 to 100,000, preferably 70,000 to 80,000, for example 75,000.

[0030] The PMVEMA polymer contained in the composition of the present invention may have an average MW in the range of 180,000 to 260,000, preferably 210,000 to 220,000, for example 216,000.

[0031] The PSS polymer contained in the composition of the present invention may have an average MW in the range of 40,000 to 100,000, preferably 60,000 to 80,000, for example 70,000.

[0032] Polymers of this size are particularly suitable for preventing segregation of the composition and do not significantly interfere with the phase change behavior of the PCM.

[0033] The composition may also include additional polymers known in the art, particularly polymers containing carboxylate groups.

[0034] The one or more polymers are provided in solution in a total amount of 0.5% to 10% by weight of the composition, preferably 1% to 4% by weight. The total amount of polymer in the composition preferably does not exceed 10% by weight, because above this range the solution becomes too viscous. Polymer concentrations below 0.5% by weight may not be sufficient to prevent segregation of the PCM composition, while concentrations above 5% by weight may cause a decrease in the storage capacity of the PCM mixture.

[0035] It may be desirable to adjust the melting point of the PCM composition of the present invention in consideration of a particular application. Adjustment to offset the effect that additives may have on the melting point of the composition may also be advantageous. For this purpose, an agent that modifies the melting point of the PCM may be added to the composition. The agent can lower the melting point of the PCM.

[0036] Preferably, the melting point modifier should be provided at 0.5% to 30% by weight of the composition, preferably 2% to 10% by weight, Concentrations below 0.5% by weight are generally insufficient to cause adequate modification of the melting point.

[0037] In a preferred embodiment, the modifying agent is glycine. Glycine is a melting point depressant. For example, by providing it to a PCM composition containing SAT, it can be made suitable for applications requiring heating or cooling in a temperature range below the inherent melting point of SAT at 58°C. By lowering the melting point of SAT, the composition can be used, for example, in medical applications or other applications requiring thermoregulation at human body temperature.

[0038] In order to avoid supercooling of the liquid phase, a nucleation promoter may be added to the composition.Suitable nucleation promoter may be a compound known in the art, such as disodium hydrogen phosphate (DSP) and its hydrated form, sodium hydroxide (NaOH), titanium dioxide (TiO2) and / or tetrasodium pyrophosphate (TSPP) and its hydrated form.

[0039] When provided in the SAT PCM composition at low concentrations, ie, 0.5% to 15% by weight, DSP acts as a nucleation promoter.

[0040] However, DSP can also be a salt used in its hydrated form and used as a PCM, for example when DSP is provided in aqueous solution at higher concentrations, for example 30% to 40% by weight.

[0041] As part of the present invention, it has been discovered that certain compounds, such as titanium dioxide (TiO), act as efficient nucleation promoters when added to a PCM composition together with a suitable polymer to reduce or prevent the formation of anhydrous PCM precipitates. The TiO can be provided as nanoparticles or in any other form. Different forms of TiO may also be provided in combination.

[0042] Furthermore, it has been observed that particularly good results can be achieved by combining a positively charged agent, particularly TiO2, with a negatively charged polymer. Without wishing to be bound by a particular theory, it is hypothesized that the positively charged agent interacts with or binds to the negatively charged functional groups of the polymer. The polymer can then act as a matrix for the nucleation promoter, thereby supporting uniform distribution of nanoparticles in the composition and enhancing the agent's ability to promote nucleation throughout the PCM.

[0043] The polymers of Formula 1, Formula 2 and Formula 3 are highly negatively charged and are therefore particularly suitable for combination with agents to promote controlled nucleation, such as TiO2.

[0044] The composition may also contain a combination of different nucleation promoters.

[0045] Each nucleation promoter may independently be present at 0.1% to 10% by weight of the composition, preferably at least 0.5% but less than 10%. The total amount of polymer preferably ranges from 0.5% to 10% by weight, preferably from 1% to 5% by weight.

[0046] The present invention also relates to a method of making a salt hydrate phase change material composition comprising at least one polymer of Formula 1, Formula 2 or Formula 3.

[0047] In a first step, a salt hydrate phase change material and at least one polymer having general formula 1, formula 2 and / or general formula 3 are mixed in an aqueous solution.

[0048] The solution is heated above the melting temperature of the PCM material, for example at least 5°C, preferably 5°C to 25°C above the melting temperature of the PCM material.

[0049] During this process, further additives such as melting point modifiers and nucleation promoters may be mixed into the aqueous PCM solution.

[0050] Contrary to what is known in the art, the present invention provides three specific polymers as efficient and versatile anti-segregation additives for salt hydrate PCMs. The present invention further identifies a group of polymers that are particularly effective in preventing segregation of salt hydrate PCMs. [Brief explanation of the drawings]

[0051] Exemplary embodiments of the present invention are disclosed herein and illustrated in the figures: FIG. 1A shows a phase diagram of DSP (Na2HPO4) and water, where the aqueous salt solution concentrations at different temperatures are shown to illustrate the different hydrated forms of DSP. Figure 1B shows the phase diagram of SA, where the concentration of SA in aqueous solution at different temperatures is shown. 2A-2C show the specific enthalpy (dh) of salt hydrate PCM compositions containing different amounts of polymer, where Panel A shows the enthalpy of SAT compositions containing increasing amounts of NaPAA, Panel B shows the enthalpy of SAT compositions containing increasing amounts of PMVEMA, and Panel C shows the enthalpy of SAT compositions containing increasing amounts of P4SSA-co-MA. Figures 3A-3H show three-layer calorimetry of a salt hydrate PCM composition with a polymer, where the enthalpy change during heating (black bars) and cooling (white bars) is shown in the bar graphs (Figures 3B, 3D, 3F, 3H), and the corresponding temperature profile of the PCM composition during heating (solid line) and cooling (dashed line) is shown above the bar graphs (Figures 3A, 3C, 3E, 3G). 3A and 3B show the results of bed calorimetry and specific heat capacity (J / (g K)) for a PCM composition comprising SAT with 3 wt % P4SSA-co-MA. 3C and 3D show the results of bed calorimetry and specific heat capacity (J / (g K)) for a PCM composition containing SAT with 2 wt % PMVEMA. 3E and 3F show the results of bed calorimetry and specific heat capacity (J / (g K)) for a PCM composition containing DSP with 1.5 wt % P4SSA-co-MA and 1 wt % TiO2. Figures 3G and 3H show the results of bed calorimetry and specific heat capacity (J / (g K)) for a PCM composition containing DSP with 1.5 wt% P4SSA-co-MA, 1 wt% TiO2, and 2 wt% crosslinked NaPAA. 4A and 4B show thermal curves of salt hydrate PCM compositions subjected to thermal cycling, where FIG. 4A shows a SAT PCM composition comprising a polymer of the present invention, and FIG. 4B shows a DSP PCM composition comprising a polymer of the present invention. Figure 5A shows the crystallization and segregation behavior of SAT PCM samples containing no polymer inhibitor or either P4SSA-co-MA or PMVEMA polymer inhibitors. Figure 5B shows the crystallization and segregation behavior of DSP PCM samples containing no polymer inhibitor or P4SSA-co-MA, PMVEMA, NaPAA, or PSS polymer inhibitors.

[0052] Examples of embodiments of the present invention The effect of polymers having Formula 1, Formula 2 or Formula 3 on the segregation and crystallization of selected phase change material (PCM) compounds was examined in a series of experiments.

[0053] A PCM according to the present invention may be, for example, disodium hydrogen phosphate (DSP), in particular DSP dodecahydrate. For simplicity, the term DSP as used herein means DSP dodecahydrate unless otherwise specified.

[0054] When heated above 35°C in the absence of a segregation inhibitor, DSP forms DSP heptahydrate, which precipitates, resulting in phase segregation.

[0055] A phase change diagram for DSP is shown in Figure 1A. The stoichiometry at about 40 wt% ± 5 wt% is indicated by line SC.

[0056] The PCM according to the present invention may be a calcium, potassium or sodium salt hydrate, preferably sodium acetate trihydrate (SAT).

[0057] The phase change diagram for SAT is shown in Figure 1B. When provided in its stoichiometric composition, i.e., 61 wt% ± 3 wt% in the PCM composition, SAT forms the anhydrous SA salt above its melting temperature of 58 °C. The temperature range susceptible to segregation is circled in Figure 1B.

[0058] Suitable calcium salt hydrates also include calcium chloride hexahydrate, calcium chloride tetrahydrate, and calcium nitrate tetrahydrate.

[0059] Suitable potassium salt hydrates include dipotassium hydrogen phosphate hexahydrate and potassium fluoride tetrahydrate.

[0060] Suitable sodium salt hydrates include sodium sulfate decahydrate, sodium hydrogen phosphate dodecahydrate, sodium thiosulfate pentahydrate, sodium tetraborate decahydrate, and sodium acetate trihydrate.

[0061] However, the PCM may also be a lithium salt hydrate, such as lithium chlorate trihydrate, a manganese salt hydrate, such as manganese nitrate hexahydrate, a zinc salt hydrate, such as zinc nitrate hexahydrate, or an iron salt hydrate, such as iron(III) chloride hexahydrate.

[0062] The PCM may also include a combination of salt hydrates with similar crystal structures, such as sodium tetraborate decahydrate and sodium sulfate decahydrate. Mixing salts with similar crystal structures can help reduce or prevent supercooling behavior in the PCM.

[0063] Any form of soluble salt hydrate can be used to prepare the salt hydrate PCM compositions. Any type of crystal of these salts can be used to prepare the respective PCM solutions. [Example]

[0064] Experimental results Example 1: Preparation of PCM preparation Sodium acetate trihydrate (SAT) PCM composition For the preparation of the SAT PCM composition, 94 wt % sodium acetate trihydrate (SAT) (CAS no. 6131-90-4) was mixed with poly(4-styrenesulfonic acid- co -maleic acid) (hereafter P4SSA- co -MA or P4SSA) (CAS no. 68037-40-1) at 80 °C and stirred until a clear solution was formed, with no visible anhydrous crystals.

[0065] SAT served as the PCM material, DSP as a nucleation promoter, and P4SSA-co-MA as an inhibitor to prevent the formation of anhydrous SA.

[0066] The temperature of the mixture was then reduced to 70° C. In a subsequent step, 2.5 wt % dibasic sodium phosphate (DSP) (CAS number 7558-79-4) was added to the mixture with continuous stirring at 70° C. until the DSP was uniformly dispersed.

[0067] The melting temperature T of the obtained PCM composition melt The crystallization temperature T crys is between 58℃ and 45℃, and the specific enthalpy of dehydration ΔH dsc was 230 J / g.

[0068] To test the resulting phase change material, it was cooled to room temperature until completely solidified and then cycled between 15°C and 65°C.

[0069] Disodium phosphate (DSP) PCM composition To prepare the DSP PCM composition, 1.42 wt% of the polymer compound, i.e., P4SSA-co-MA, was added to deionized water (provided as a solvent) at 50°C and stirred until completely dissolved. In a subsequent step, titanium dioxide (TiO2) (CAS No. 1317-80-2) (0.95 wt%), NaOH (CAS No. 1310-73-2) (0.95 wt%), and DSP (34.12 wt%) were added to the mixture. The mixture was thoroughly stirred throughout the procedure, and each added component was uniformly dispersed in the aqueous solution before adding the next component. In a further step, cross-linked sodium polyacrylate (cross-linked NaPAA) (CAS No. 9003-04-7) (1.90 wt%) was added to the mixture, which was then stirred for approximately 2 hours to obtain the phase change product PCM35.

[0070] Titanium oxide (TiO2) and sodium hydroxide served as nucleating agents for the DSP salt, and P4SSA-co-MA served as an inhibitor to prevent the formation of the anhydrous salt.

[0071] As part of this study, TiO2 was identified as the most promising nucleating agent for DSP PCMs, either alone or in combination with a cross-linked polymer, such as cross-linked NaPAA.

[0072] The melting temperature T of the obtained PCM composition melt The crystallization temperature T crys is between 58℃ and 45℃, and the specific enthalpy of dehydration ΔH dsc was 230 J / g.

[0073] It was observed that certain nucleating agents, particularly TiO2, when used in DSP compositions tended to form aggregates. By adding cross-linked NaPAA as a gelling agent to the DSP PCM composition, the aggregation could be reduced or completely avoided.

[0074] Without wishing to be bound by any particular theory, it is believed that the crosslinked polymer, and particularly crosslinked NaPAA, increases the porosity of the DSP PCM composition. The crosslinked polymer is believed to provide a pocket structure that facilitates the dispersion and suspension of the nucleating agent suspension.

[0075] It is known that NaPAA itself can prevent or reduce the segregation of some PCMs, such as SAT. However, NaPAA does not inhibit the segregation of DSP PCM compositions, as confirmed in segregation experiments performed without additional inhibitory polymers (see Figure 5B).

[0076] DSP PCM compositions containing PMVEMA or NaPAA as the segregation-inhibiting polymer were prepared according to the same procedure. When NaPAA was used to test its ability to prevent segregation in the DSP PCM composition, no other polymer was added.

[0077] The resulting phase-change material was then cooled to room temperature for testing. The product was subjected to a temperature cycle from 20 to 50°C.

[0078] Example 2: Polymer Content and Heat Storage Capacity – DSC Calorimetry The relationship between enthalpy and temperature determines the heat storage capacity of a PCM. This relationship can be determined experimentally using calorimetry. A high enthalpy indicates a good latent heat storage capacity of the PCM.

[0079] Differential scanning calorimetry (DSC) assays were performed on the polymers of Formula 1, Formula 2 and Formula 3, as well as the aforementioned polymers used to prevent segregation of the PCM.

[0080] DSC is a widely used method in thermal analysis. It can be used to accurately determine the melting temperatures and enthalpies associated with such transformations. The specific heat capacity of a given material can also be measured. These properties are crucial when characterizing PCMs for thermal energy storage applications.

[0081] A phase transition is always associated with a change in the enthalpy of phase change, and the working principle of DSC analysis is based on the determination of this enthalpy. To test PCM compositions containing different polymers for their thermal properties, including their melting temperature and enthalpy of melting, samples are subjected to thermal testing in a DSC.

[0082] The working principle of DSC is that a sample is inserted into the DSC together with a thermally inert reference material, e.g., quartz, and both samples are subjected to a time-linear temperature program in which both increases and decreases in temperature are possible. A DSC3+ calorimeter (Mettler Toledo, Columbus, OH, USA), which, according to the manufacturer, has an enthalpy uncertainty of ±8%, was used for all experiments in this study. In the experiments performed in this study, 5 to 20 ± 0.0005 mg of each sample was subjected to DSC measurement. Both the reference sample and the test sample were subjected to identical thermal profiles in the heating and cooling chambers.

[0083] The sample is measured using two oppositely switched thermocouples, one inserted into the sample being tested and the other into a thermally inert reference. The resulting thermoelectric power is proportional to the heat flow through the sample.

[0084] The enthalpy change of the test sample was determined based on the temperature difference between the test sample and the thermally inactive reference sample using the following energy balance equation:

number

[0085] The enthalpy of phase change is determined by integrating the heat flow over a given time period, during which the material is heated to 2 K. -1 The mixture was heated at a rate of .

[0086] The results of these experiments are summarized in the figures shown in Figures 2A-2C, where the change in enthalpy (J / g) of PCM SAT subjected to increasing amounts of inhibitor polymers NaPAA, PMVEMA, or P4SSA-co-MA was determined.

[0087] NaPAA is known to act as a segregation inhibitor when added to SAT PCM compositions, and this polymer was included as a positive control in the thermal cycling experiments performed with the SAT PCM compositions.

[0088] The diagram shown in Figure 2A represents the sample enthalpy determined from DSC data collected for SAT samples prepared with NaPAA polymer added at 0.5-3 wt%. The enthalpy of the SAT and polymer compositions did not decrease significantly when higher percentages of polymer were added.

[0089] Similar results were obtained when increasing amounts of PMVEMA (shown in Figure 2B) or P4SSA-co-MA (shown in Figure 2C) were added to the SAT samples. In the range measured, higher weight percentages of PMVEMA or P4SSA-co-MA polymer did not significantly affect the enthalpy of the PCM sample composition.

[0090] The results confirm that the excellent heat storage properties of the SAT PCM samples were not altered by the addition of increasing amounts of the tested polymer inhibitor.

[0091] Example 3: PCM materials and heat storage capacity - 3-layer calorimetry Measurement devices for determining the heat storage capacity of PCMs are usually based on small sample sizes (typically between 5 µg and 10 µg) and can be inaccurate if the sample has low thermal conductivity, high heat capacity over a narrow temperature range, or is inhomogeneous.

[0092] Three-layer calorimetry, a method well known in the art, addresses this issue and allows for accurate measurements of larger sample sizes. An added advantage is that three-layer calorimetry is a non-invasive measurement method, allowing the measured sample to be subsequently used in subsequent testing. Therefore, it was selected as a suitable method for determining the heat capacity of various salt hydrate PCM compositions, with and without segregation-inhibiting polymers. The calorimeter was calibrated using materials with known enthalpy distributions.

[0093] To determine the heat storage capacity, the required temperature profile corresponding to the sample PCM composition was programmed into a standard climatic test cabinet inside which a commercially available three-layer calorimeter measuring device (W&A Waerme und Anwendungstechnische Pruefungen) was placed. The SAT PCM composition was cycled between 35°C and 65°C with a DSP A heating rate of 0.3 Kmin. -1 was applied to the samples (which were each provided at 100 g). This large sample reduced the effect of weighing tolerances and allowed for accurate measurement of the salt hydrate PCM containing polymer and nucleating agent.

[0094] The results of these measurements are summarized in Figures 3A-3H.

[0095] In Figures 3A, 3C, 3E, and 3C, the temperature of the cycled sample is shown as a solid line, and the temperature of the surrounding heat transfer medium is shown as a dashed line in these figures.

[0096] The change in enthalpy of the sample during heating (dH) is shown as a black bar in Figures 3B, 3D, 3F, and 3H. The change in enthalpy during cooling (dH) is shown as a white bar in these figures.

[0097] The SAT PCM compositions shown in Figures 3A-3D were cycled from 40°C to 65°C. The DSP compositions shown in Figures 3E-3H were cycled from 22°C to 48°C.

[0098] Calorimetric results for a PCM composition consisting of 95.5 wt% SAT, 3 wt% P4SSA-co-MA, and 1.5 wt% DSP are shown in Figures 3A and 3B. As shown in Figure 3A, the SAT PCM composition containing P4SSA-co-MA melted at approximately 58 °C, as indicated by the long temperature plateau in the thermal sample curve. The sample was further heated to ensure that all SAT crystals melted before the composition cooled. The rapid drop in temperature represents supercooling of the solution, followed by a temperature increase to the crystallization temperature. The close proximity of the melting and crystallization temperatures indicates highly efficient PCM behavior. The efficiency of recrystallization is at least partially due to the absence of segregated material in the sample.

[0099] This is further confirmed by the enthalpy curves during heating and cooling of the composition: the respective enthalpy peaks during heating and cooling are within 2°C of each other, indicating heat storage and release within this narrow temperature range.

[0100] The same experiment was performed with a PCM composition consisting of 96.5 wt% SAT, 2 wt% PMVEMA, and 1.5 wt% DSP, and the results of this experiment are shown in Figures 3C and 3D.

[0101] As can be seen in the graph shown in this figure, the SAT PMVEMA composition also exhibited very good PCM behavior, although the temperature difference between the peaks in the enthalpy curve was slightly larger.

[0102] 3E-3H show the corresponding results for the DSP PCM compositions. In these experiments, the DSP PCM was dissolved at elevated temperatures. The heated compositions were first cooled and then heated to melt the DSP PCM.

[0103] In the tests shown in Figures 3E and 3F, DSP was provided at 38 wt% along with 1.5 wt% P4SSA-co-MA and 1 wt% TiO2 in water.

[0104] Upon cooling the composition from approximately 42°C to 15°C, a supercooling effect was observed (indicated by a rapid drop in sample temperature), followed by a temperature increase to the crystallization temperature of DSP between 30°C and 35°C. Two distinct peaks in the sample temperature were observed. DSP is dimorphic, and each peak is presumed to correspond to one of the two forms of DSP. The polymorphic transition of DSP in this composition is characterized by an intermediate temperature drop at the crystallization plateau of the curve.

[0105] Following crystallization, the DSP PCM was cooled to 15 °C and then exposed to 41 °C. The sample's temperature increased steadily and plateaued at its melting temperature, which was in the same range as its crystallization temperature. As seen in Figure 3F, the sample enthalpy during heating and cooling clearly overlapped, indicating minimal segregation and the suitability of this composition for PCM applications.

[0106] Figures 3G and 3H show heat storage results for a DSP PCM composition containing 38 wt% DSP, 1.5 wt% P4SSA-co-MA, 1 wt% TiO as a primary nucleation promoter, and 2 wt% crosslinked NaPAA as a gelling agent to prevent nucleation promoter aggregation, where the components were mixed in water as the sole solvent.

[0107] The observed behavior of this composition was very similar to the results obtained for the DSP PCM composition shown in Figures 3E and 3F. The addition of a low percentage of crosslinked NaPAA smoothed the polymorphic transition, resulting in a flat crystallization plateau.

[0108] Example 4: Repeated Thermal Cycling To test the durability of the PCM compositions, different compositions were subjected to repeated thermal cycling in the thermal cycling setup described above.

[0109] The samples were subjected to repeated heating and cooling of the surrounding water, and the temperature of the PCM composition was measured continuously throughout these cycles. The results of these experiments are shown in Figures 4A and 4B.

[0110] Figure 4A shows the temperature curves for a SAT PCM sample treated with 3 wt% P4SSA-co-MA and 3 wt% PMVEMA. The sample was cycled between 25°C and 65°C. The left shoulder of each temperature cycle corresponds to the melting plateau, i.e., the relatively constant sample temperature during which the PCM sample absorbs thermal energy and melts. The right shoulder of each temperature cycle corresponds to the crystallization plateau, i.e., the relatively constant sample temperature during which the PCM sample releases thermal energy and crystallizes.

[0111] Figure 4A shows the effect of polymer on the length of the melting plateau, which corresponds to the enthalpy. Samples containing P4SSA exhibit a longer melting plateau than PMVEMA, and consequently a higher melting enthalpy.

[0112] Figure 4B shows the temperature profiles of DSP PCM samples containing 2 wt% P4SSA-co-MA and 2 wt% PSS. The samples were cycled between 20°C and 50°C. The temperature profiles for these compositions were very consistent throughout the cycles.

[0113] Example 5: Segregation behavior For visual examination of the crystallization and segregation behavior of the PCM composition, the sample was packed into a Falcon tube, a transparent container made of a thermally conductive material. The container was then placed in a water bath so that the PCM composition contained in the Falcon tube was completely submerged in water. The temperature of the water contained in the water bath was thermally cycled using a hydraulically connected thermostat. The PCM temperature at the center of the sample was recorded by a thermocouple.

[0114] The segregation behavior of the tested PCM samples was evaluated after one heating / cooling cycle, where the SAT PCM composition was cycled between 25°C and 65°C, and the DSP PCM composition was cycled between 20°C and 50°C.

[0115] Figure 5A shows containers containing SAT PCMs containing either no polymer, 2 wt% P4SSA-co-MA, or 2 wt% PVMEMA. All PCM samples further contained 2 wt% DSP to support nucleation of the PCM material.

[0116] The original SAT sample without polymer was liquid at 60°C and did not solidify at 15°C due to segregation of SA (which is visible as fine precipitates in the sample and indicated by arrows).

[0117] The SAT samples containing either P4SSA-co-MA or PMVEMA were liquid at 60° C. and solid at 15° C. No segregation was detected in these samples.

[0118] Figure 5B shows the segregation behavior of DSP PCM samples with and without segregation-inhibiting polymers, each added at 2 wt% to each sample. The polymers tested were P4SSA-co-MS, PMVEMA, NaPAA, and PSS. The samples did not contain a nucleation promoter.

[0119] The image shows the sample cooled to 15°C after one heating / cooling cycle.

[0120] Segregated DSP material was clearly visible in the DSP composition without polymer as well as in the DSP composition with NaPAA as the inhibitory polymer. The segregated material is indicated by the arrow and is clearly visible in solution.

[0121] This result demonstrates that NaPAA does not act as a segregation inhibitor in the DSP PCM composition. This further supports the hypothesis that NaPAA acts as a gelling agent to prevent aggregation of the nucleation promoter in the DSP PCM composition, and does not itself act as a segregation inhibitor when added to the DSP-PCM composition. This differs from SAT PCM compositions, where NaPAA is known to act as a segregation inhibitor.

[0122] In contrast, the DSP samples containing either P4SSA-co-MS, PMVEMA, or PSS did not contain any segregated material at 15 °C. Because the experiments were performed without a nucleation promoter to induce crystallization, the samples were liquid at this temperature.

[0123] Notably, the DSP PCM sample containing P4SSA-co-MA did not segregate after 40 temperature cycles. For the DSP PCM sample containing PSS, no segregation was detected after 25 cycles. However, when the polymer was omitted, the DSP mixture segregated after 4 or 5 cycles.

[0124] These results demonstrate that the claimed polymers of Formula 1, Formula 2, and Formula 3 are potent segregation inhibitors of various PCMs. The inhibitors have been shown to impart excellent thermodynamic stability to PCM compositions over many temperature cycles, preventing the segregation of salt hydrate PCMs and allowing the PCMs to crystallize and solidify. Thus, the PCM compositions of the present invention are highly efficient and perfectly suited for thermal storage applications. The compositions maintain their efficacy over long periods and during repeated applications.

Claims

1. below: - a salt hydrate phase change material component, one or more polymers, at least one of which is General formula 1 【Chemistry 1】 wherein R is either hydrogen or sodium. Or general formula 2 【Chemistry 2】 Or general formula 3 【Transformation 3】 wherein R is either hydrogen or sodium. the one or more polymers having Alternatively, a mixture of polymers comprising a polymer having general formula 1, a polymer having general formula 2 and / or a polymer having general formula 3, and - water, 1. A phase change material composition comprising:

2. the phase change material a calcium, potassium or sodium salt hydrate, preferably sodium acetate trihydrate, or disodium hydrogen phosphate (DSP), preferably disodium hydrogen phosphate dodecahydrate The composition of claim 1 ,

3. A composition according to claim 1 or 2, wherein the salt within the phase change material is present at a level of from 20% to 80% by weight of the composition, preferably from 35% to 55% by weight.

4. A composition according to any one of claims 1 to 3, wherein the total amount of polymer is preferably present in an amount of from 0.5% to 10% by weight, preferably from 1% to 4% by weight.

5. 5. The composition according to any one of claims 1 to 4, further comprising an agent for modifying the melting point of said phase change material, said agent being preferably present in an amount of 0.5% to 30% by weight, preferably 2% to 10% by weight.

6. The composition of claim 5 wherein the agent is glycine.

7. The composition of any one of claims 1 to 6, further comprising one or more suitable nucleation promoters.

8. 8. The composition of claim 7, wherein the one or more suitable nucleation promoters are independently selected from disodium hydrogen phosphate (DSP) and hydrated forms thereof, tetrasodium pyrophosphate (TSPP) and hydrated forms thereof, and mixtures thereof.

9. At least one of said one or more nucleation promoters, e.g., TiO ２ 9. The composition of claim 7 or 8, wherein the nanoparticles may be at least partially provided as nanoparticles.

10. 10. A composition according to any one of claims 7 to 9, wherein each nucleation promoter is independently present at 0.5% to 10% by weight of the composition, preferably 1% to 5% by weight.

11. Use of a polymer of general formula 1, general formula 2 or general formula 3 to prevent the formation of a non-uniform liquid in a salt hydrate phase change composition.

12. 1. A method for preparing a salt hydrate phase change material composition, comprising mixing an aqueous solution containing a phase change material with at least one polymer having general formula 1, general formula 2 and / or general formula 3, and simultaneously heating the mixture to a temperature at least 80°C, preferably at least 20°C, above the melting temperature of said phase change material.

13. 13. The method of claim 12, wherein at least one nucleation promoter is added to the mixture, preferably provided such that the composition comprises 0.5 wt % to 10 wt % of nucleation promoter in a total amount, or at least one melting temperature modifier is added to the mixture, preferably provided such that the composition comprises 0.5 wt % to 30 wt % of melting temperature modifier in a total amount, or at least one nucleation promoter and at least one melting temperature modifier.

14. 14. A method according to claim 12 or 13, wherein the salt hydrate material is provided in an amount of 20% to 80% by weight, preferably 35% to 55% by weight, for example 45% by weight, in aqueous solution, and the total amount of polymer is provided at 0.5% by weight or more.

15. A device for heat storage or heat transfer comprising a composition according to any one of claims 1 to 10 or a composition obtainable by the method according to any one of claims 12 to 14.

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