WO2011071402A1 - Mortars containing phase change material microcapsules, their preparation process and use - Google Patents

Abstract

The present invention relates to a mortar for use in the interior and exterior coating of construction systems, comprising phase change material (PCM) microcapsules together with a lime binder and other auxiliary materials. The invention also concerns a process for the preparation of these mortars by blending the PCM microcapsules with the binder and other auxiliary products, in a mixing machine. The mortars, according to the invention, are used in the interior and exterior coating of construction systems, in order to save energy.

Description

 DESCRIPTION

"MORTARS CONTAINING MICROCAPSXJLAS OF PHASE CHANGE MATERIALS, PROCESS FOR THEIR PREPARATION AND USE"

Field of the Invention This invention describes the preparation of lime based binder coating mortars and their incorporation with phase change materials (PCM). The incorporation of phase change materials improves the thermal performance of mortars used in the interior and exterior cladding of building systems, thus contributing to the energy saving of the building.

BACKGROUND OF THE INVENTION Energy saving in buildings is becoming increasingly important as a result of rising fuel prices, decreasing reserves of fossil fuels and increasing environmental awareness. One way to contribute to reducing the energy consumption of buildings is to improve their energy efficiency. The use of materials capable of storing latent heat contributes to a reduction in consumption associated with building heating and cooling systems. Some materials have the ability to store latent heat when they change from a solid to a liquid phase (an endothermic reaction taking place), afterwards that heat is released when these materials return to the solid phase (an exothermic reaction). Because of this feature these materials are called PCM (Phase Change Materials). The incorporation of PCM in building cladding mortars allows to control the temperature, reducing the consumption associated with the energy-consuming and pollution-generating HVAC systems. The development of microencapsulation techniques allowed their incorporation into building materials. Energy storage is made from the latent heat of these materials. Latent heat is the energy absorbed or released when a given material changes from solid to liquid or from liquid to solid. For some materials this process can be repeated indefinitely. Paraffins are one of the phase change materials best suited for building system applications because they have a transition temperature of around 22-26 ° C, which is ideal for building applications as it is in the range of comfort (20-25 ° C). Phase change materials have been considered for energy storage for over 30 years. There are examples described in the literature dating from 1975. In recent decades research work has been developed in the area of incorporating PCM in building materials. [1] PCMs have some features that make them particularly interesting for their application in building systems. There are materials for temperature ranges suitable for application in construction, ie their transition temperature is within the thermal comfort zone. The density change in phase transition is very low, and this stability is particularly important when PCM is incorporated into the building material so that its transition does not compromise the mechanical strength of the product. They are chemically stable and compatible with the materials in which they are incorporated (plaster, cement, mortar, etc.). [2]

By incorporating PCM into the materials used to cover buildings' ceilings and walls, it is possible to take advantage of these areas for latent heat storage. Unlike its application on its own plates or structures, in the case of incorporation in building materials, the added cost is mainly that of PCM itself, eliminating the need to use ancillary structures or adapted building systems.

Various methods of incorporating PCM into construction materials and products have been developed, US Patent 5,555,216 describes a technique of incorporating a phase change material (PCM) composite into the hollow cores of a cement brick. A disadvantage of this solution is that PCM is not in contact. with the exterior, as the blocks are covered with finishing materials and wall cladding, thus, it becomes more difficult to exchange heat with the interior air of the rooms. US 4572864 discloses the solution for using PCM in boards finished in different materials (metal, wood or fiber), which can be placed inside buildings. PCM performance depends on the thermal conductivity of the board's finishing materials, which may in some cases greatly decrease the effectiveness of the product.

In the above two examples PCM is not incorporated directly into the building material, US Patent 4,746,240 describes different ways of incorporating PCMs into putties which are used in wall finishing. Although the possibility of using microcapsules is mentioned, in this patent capsules ranging from 500 to 3000 μτη are used. With these dimensions the applied layer must be of high thickness to ensure a good incorporation of the capsules without compromising the quality of the finish. US 4587279 discloses the technique of incorporating PCM into fresh concrete. The development of PCM micro-encapsulation techniques has facilitated the mixing of the material in plaster masses or cement mortars. [3] The invention of US patent 2004/0234738 concerns the incorporation of a PCM microcapsule suspension in plaster mortars. Some disadvantages of this type of applications are mentioned, highlighting the difficulty to obtain a uniform distribution of the microcapsules during the wall application. ES 2298056A1 discloses the production of plasterboard made of a PCM-containing mortar core.

Initially research on PCM development focused mainly on non-organic PCMs, which cannot be directly incorporated into building materials. In the last decade, organic PCMs have been developed, which, although more expensive, have opened the possibility of incorporation into porous building materials. [4]

When comparing organic and inorganic PCMs, one must consider the advantages and disadvantages of each type. In the case of inorganics, the main advantage lies in their high phase shift enthalpy, which ensures greater latent heat storage capacity. However, these materials have some disadvantages, including the possibility of overcooling, which causes the product to cool below solidification temperature without becoming solid. They may also undergo phase separation, have poor thermal stability and may be corrosive. In the case of organic PCMs the main advantage is their high thermal stability, in addition they are non-corrosive and do not suffer from overcooling. But this type of PCM may have some limitations: they have a lower phase transition enthalpy than inorganic ones and some may be flammable.

Some built-in PCM construction products are already on the market, such as the Smartboard ™ product developed by BASF. It is a plaster based product with built-in Micronal capsules for application in the interior lining of buildings. Maxit has developed a commercially available PCM plaster mortar, Maxit Clima. Research has been developed, with some success, in the incorporation of PCM in cement. [5]

As regards the development of PCM-incorporated lime-based mortars, no patents or similar commercial products were found in the searches.

Brief Description of the Figures

Figure 1 represents the PCM particle size distribution curve obtained in a Coulter assay.

Figure 2 is the PCM differential scanning calorimetry for determining the phase transition temperature. Figure 3 represents the performance of the mortar described in Example 1 in the mechanical strength tests. Figure 4 represents the thermal behavior of the mortar of Example 1 with 30% and 50% PCM.

Figure 5 represents the mortar performance described in Example 2 in the mechanical strength tests.

Figure 6 represents the thermal behavior of the mortar of Example 2 with 30% and 50% PCM.

Figure 7 shows the visualization of two samples by scanning electron microscopy. Figure 7a shows a mortar without PCM and Figure 7b represents the same mortar with 30% PCM.

Summary of the Invention

The present invention describes lime-based binder mortars incorporating PCMs which have the ability to accumulate latent heat in order to reduce the energy charge of buildings as well as the process for preparing said mortars and their use in the building. interior and exterior cladding of building systems with the aim of saving energy. Detailed Description of the Invention

The mortars of the present invention use a commercial PCM considered suitable for application to building materials, as their phase transition temperature is within the considered comfort temperature for building interiors (between 20 and 25 ° C). Ç) . [6] Thus, by applying mortar to the interior cladding of a building's rooms, it helps to prevent air cooling in winter by releasing heat trapped by PCMs, and can maintain the coolest room in summer by absorbing heat. heat.

The selected PCM consists of methyl polymethacrylate microcapsules containing a paraffin wax mixture. The product is used in powders with a particle diameter between 2 and 20 μιτι, has a transition temperature of 23 ° C and 110 kj / kg of specific heat (as specified by the supplier).

PCM encapsulation is intended to ensure the integrity of the paraffins by ensuring that they retain their heat storage capacity. The production process results in a suspension of water-dispersed microcapsules which upon spray drying give rise to a fine powder which can be added to porous building materials. Objects of the Invention

It is a first object of the invention to apply mortars for the interior and exterior coating of construction systems comprising phase change material (PCM) microcapsules together with a lime-based binder and other auxiliary materials. The percentage of embedded PCM can range from 5% to 50%. Most preferably this percentage is between 10% and 40%.

Usually the binder consists of air lime or air lime and cement.

The microcapsules of the phase change material are usually between 0.2 and 25 μπι and consist of methyl polymethacrylate containing a mixture of paraffin waxes.

A second object of the invention is a process for preparing the mortars of the present invention by mixing the PCM microcapsules with lime based binder and other auxiliary products in a mixer machine.

A third object of the invention is the use of the mortars of the present invention in the interior and exterior cladding of building systems with the aim of saving energy.

Experimental Part

PCM laboratory tests were performed to confirm these specifications given by the supplier. The Coulter test was performed to determine the particle size distribution of the PCM (Figure 1), and it was found that the largest percentage of particles was between 4 and 15 μηη, with an average size of 6 μιτι.

The supplier-indicated PCM phase transition temperature was compared with the results of a differential scanning calorimetry (Figure 2). This technique provides information on endothermic and exothermic reactions that occur in the material when it is heated and / or cooled. It can be seen from the graph obtained for the differential scanning calorimetry that the phase transition temperature of is between 23 ° C and 25 ° C.

It is concluded from the analysis of particle size distribution and the DSC that the data in the product data sheet is correct.

For the prepared mortars some of their fresh properties were evaluated. Spread value and fresh density were determined to verify your proper workable age. For the evaluation of mechanical resistance to flexion and compression, specimens were tested according to Standard 1015-11 [7]. Some samples were observed by scanning electron microscope (SEM) to analyze their microstructure and the distribution of PCM in the mortar.

In order to study the efficiency of mortars as latent heat storages, ie to evaluate the impact of incorporating PCM in the material, small test cells associated with a measuring system were performed.

This system is divided into three components:

 A programmable climate chamber for predefined temperature and humidity cycles.

 Cells constructed with an insulating material (expanded polystyrene) coated on both sides with a wire plaster, the inner faces are covered with a mortar layer approximately 100 x 100 x 3 mm (width x length x thickness). Each cell has two thermocouples inside, one placed against the wall and one in the central area of the cell.

Data acquisition system, consisting of a data logger with a multi-duplexer connected to a computer that allows the temperature data to be recorded using its own software. Examples

Different lime mortar compositions were prepared and studied, with amounts of PCM ranging from 10 to 50%. The PCM is mixed with the selected mortar taking care to promote good homogenization, then water is added until a scattering test value of 140-150 mm is reached, which ensures adequate workability. Mortars with up to 50% PCM can be prepared without compromising the mechanical strength of the product. By way of example, two possible mortar compositions are provided. Example 1

Mortar C1 contains equal parts (1: 1) of lime and cement binder, and is then added up to 50% (by weight) of the selected PCM. Table 1 summarizes the mortar composition and properties.

PCM is added to the mortar powder, the mixture is homogenized and then the necessary water is added to the previously defined spreading value.

The mixture is kneaded to the consistency of a slurry and applied in accordance with traditional mortar application techniques. Table 1 - Summary of mortar composition and properties

The percentage of water added and the value of fresh mortar density are shown in Table 2.

Table 2 - Fresh characteristics of Cl mortar with PCM

Realizaram-se ensaios de resistência mecânica à flexão e compressão, para avaliar o comportamento da argamassa Cl com 10% a 50% de PCM (Figura 3) Os resultados obtidos demonstram que a adição de

Mechanical flexural and compressive strength tests were performed to evaluate the behavior of Cl mortar with 10% to 50% PCM (Figure 3).

10% to 50% PCM guarantees a mechanical strength of the mortar that enables its use under the same conditions as a traditional mortar. The effectiveness of this mortar as a latent heat storage system and the effect of application of the product on interior walls was evaluated by the test cell assay previously described. The boxes were subjected to heating and cooling cycles between 10 ° C and 40 ° C to simulate the effect of temperature fluctuations between night and day. The results in Figure 4 demonstrate that the presence of PCMs has an impact on the temperature inside the cell. It is noticeable that the temperature rises less in the case with PCM, when the outside temperature rises to 40 ° C, on the other hand, with the temperature decreasing to 10 ° C, it is found that the temperature reduction in this box is smaller. A lower heating and cooling rate is also visible compared to the reference box, which means that temperature variations manifest more slowly in the PCM box. This effect is what enables energy savings in the air conditioning of buildings when mortar is applied in building systems. To ensure that mortar is efficient, it is essential that there is a homogeneous distribution of PCM microcapsules within the mortar. Viewing samples under the scanning electron microscope allows the distribution and integrity of the capsules incorporated into the mortar to be observed (Figure 7). In said Figure 7 two samples are shown, one of the mortar Cl without PCM (Figure 7a) and the other of the same mortar with 30% PCM (Figure 7b). It is visible in the second sample the presence of spherical microcapsules distributed by the material, which demonstrates the good homogenization of the product.

Example 2 Mortar C3 contains equal parts by volume.

(1: 2) lime and sand binder, with up to 50 wt% PCM added. This mortar does not contain any added binders or adjuvants, unlike Cl mortar (Example 1). Thus, the mechanical strength of this composition will be lower starting than in the previous example. Table 3 presents the mortar composition in percentage values.

Table 3 - C3 mortar composition (% by weight)

Lime Sand PCM

 C3 11.2% 58.8% 30.0%

C3 8.1% 41.9% 50% As in the previous example, Table 4 shows the percent water, density and spread value for the 30% and 50% PCM mortar.

Table 4 - Fresh properties of mortar C3

The results of the mechanical flexural strength (Figure 5) allow us to conclude that the addition of PCM helps to improve the mechanical behavior of the mortar unlike other incorporation matrices, such as cement or plaster where mechanical strength decreases. with PCM content, which limits the incorporation capacity of the additive.

 Figure 6 demonstrates the effectiveness of mortar when subjected to heating and cooling cycles in a climate chamber.

References

[1] Zhang Y., Zhou G., Lin K., Zhang Q., Di H., Application of latent heat energy storage in buildings: state-of-the-art and Outlook, Building and Environment, vol. 42, 2007, pp 2197-2209

[2] Zalba B., Marin J., Cabeza L., Mehling H., Review on thermal energy storage with phase change: materials, heat transfer analysis and applications, Applied Thermal

Engineering, vol. 23, 2003, pp 251-283

[3] Hawlader M., Uddin M., Khin M., icroencapsulated phase change materials, Proceedings of 9th APCChE Congress and

CHEMECA 2002, New Zealand, 2002

[4] Athientis A., Liu C., Hawes D., Banu D., Feldman D.,

Investigation of the thermal performance of a passive solar test room with latent heat storage, Building and Environment, vol. 32, 1997, pp 405-410

[5] Cabeza L., Castellon C, Nogues M., Medrano M., Leppers

R., Zubillaga O., Use of microencapsulated PCM in concrete walls for energy savings, Energy and Buildings, vol. 39, 2007, pp 113-119

[6] Ministry of Public Works, Transport and

Communications, Regulation of the thermal behavior characteristics of buildings, Decree Law No. 80/2006 of 4 April 2006

[7] EN 1015-11, Methods of testing for death for masonry -

Part 11 - Determination of flexural and compressive strength of hardened mortar, 1999

Claims

1. Mortars for use in the interior and exterior coating of construction systems, which comprise phase change material (PCM) microcapsules together with a lime-based binder and other auxiliary materials. Mortars according to claim 1, characterized in that the percentage of incorporated PCM ranges from 5% to 50%. Mortars according to claim 2, characterized in that the percentage of incorporated PCM ranges from 10% to 40%. Mortars according to any one of Claims 1 to 3, characterized in that the binder consists of air lime. Mortars according to any one of claims 1 to 3, characterized in that the binder consists of air lime and cement. Mortars according to any one of claims 1 to 5, characterized in that the microcapsules of the phase change material are between 0.2 and 25 μπι. Mortars according to any one of claims 1 to 6, characterized in that the microcapsules consist of methyl polymethacrylate containing a mixture of paraffin waxes. Process for the preparation of mortars of any one of claims 1 to 7, characterized in that the PCM microcapsules are mixed with lime based binder and other auxiliary products in a mixing machine. Use of the mortars of any one of claims 1 to 7, characterized in that said mortars are applied to the interior and exterior coating of building systems in order to save energy.