Mechanism of interface degradation on thermal performance of composite thermal insulation materials Xu Yanbo, Qian Chunxiang, Chen Chun (Jiangsu Key Laboratory of Civil Engineering Materials, Southeast University, Nanjing 211189), and studied the effects of these specimens on dry and wet cycles and freeze-thaw cycles Thermal conductivity after. By determining the influence factors of the organic thermal insulation component and the matrix, the influence of the interface on the thermal properties of the composite thermal insulation material is indirectly obtained. The experimental results show that when the volume fraction of organic component EPS exceeds 50%, the thermal properties of the composite thermal insulation mortar specimens are significantly degraded. Combined with theoretical analysis, the interface is an important reason for the change of thermal properties of organic-inorganic composite thermal insulation materials. In particular, when the volume fraction of the organic insulating component in the composite exceeds a predetermined value, the interface becomes a key factor leading to deterioration of the thermal properties of the material. Therefore, in the development and application of composite insulation materials, it is necessary to limit the amount of organic thermal insulation components.
For composite insulation materials, the performance of insulation components is a key factor affecting insulation materials. In addition to light weight, heat preservation, heat insulation, sound absorption and other advantages, organic insulation components (such as polystyrene particles) also have unique thermal properties, uniform material properties, can be designed according to requirements, variety and renewable, etc. The advantage of the insulation component in the composite insulation material is that m. The insulation material used for building energy conservation (especially for maintenance structure) will inevitably suffer from external rain, sun exposure and environment during the life of the building. The effect of changes in temperature and humidity. The relationship between the thermal properties of thermal insulation materials and environmental factors is the key to the success of building energy conservation, and has always been valued by researchers and architectural designers. In view of the complexity of the composite insulation material and the variability of the thermal conductivity W/(mK) of the thermal insulation mortar after the dry and wet cycle of the building in the life cycle of the building, the thermal properties of the composite thermal insulation material, especially the long-term thermal performance The research has just started. M. There are two main factors affecting the thermal deterioration process of composite thermal insulation materials: 1 composition of composite materials. In the development process of thermal insulation materials, composite insulation materials with different performance indexes can be developed by selecting the types of thermal insulation components and matrix materials, adjusting the ratio of matrix materials to thermal insulation components. Obviously, there are some differences in the thermal degradation process and mechanism of composites containing different components. 2 environmental factors. The mechanism of the deterioration of the thermal properties of composite insulation materials by different environmental factors is not consistent. Taking the dry-wet cycle as an example, in addition to weakening the various components of the thermal insulation material, it is also necessary to consider the influence of the deformation incompatibility of each component during the dry shrinkage and wet-up process. M. The interface itself is composed of two phases or The number and nature of multiphase materials are closely related to the nature of the two-phase material at the interface, the degree of contact, and the contact process. Even if the material composition is strictly consistent, the number and nature of the interface still have some uncertainty. There are a large number of interfaces in organic-inorganic composite thermal insulation materials. Therefore, the interface factors cannot be ignored when studying the thermal performance degradation mechanism of composite thermal insulation materials.
In this paper, a series of composite thermal insulation mortar specimens with different EPS content were prepared, and the thermal conductivity of the composite thermal insulation mortar after drying and wetting cycles was tested. By determining the influence factors of the organic thermal insulation component and the matrix, the influence of the interface on the thermal properties of the composite thermal insulation material is indirectly obtained.
1 Experiment 40%, 50%, 60%, 70% of 9 composite thermal insulation mortars. The granules having a diameter of about 2. 5 mm are obtained by sieving. In the experiment, the thermal conductivity of the test piece was measured by CD~DR3030A thermal conductivity meter. The dimensions of all test pieces are 300mmx300mmx30mm. Wet and dry cycle test: the test piece is immersed in water for 16h, and then dried in the oven at 70 °C for 8h, which is 1 cycle, 8 cycles is 1 cycle. . The thermal conductivity of the test piece was measured after each cycle of one cycle.
Freeze-thaw cycle experiment: The test piece was immersed in water for 4 h, and then frozen at -15 C for 4 h, which was 1 cycle, and 10 cycles were 1 cycle. The thermal conductivity of the test piece was measured after each cycle of one cycle.
2 Results and discussion 2.1 Thermal conductivity of thermal insulation material after wet and dry cycle The thermal conductivity of composite thermal insulation mortar after dry and wet cycle is shown in Table 1. After 3 cycles of dry and wet cycle, (EPS)=0%, 1%, 10 % of the three test pieces were cracked. The increase in thermal conductivity of each material.
After the dry-wet cycle, the thermal conductivity of the thermal insulation mortar increases. 2.2 The thermal conductivity of the thermal insulation material after the freeze-thaw cycle The thermal conductivity of the composite thermal insulation mortar after freeze-thaw cycles is shown in Table 2. After the freeze-thaw cycle, the thermal conductivity of the thermal insulation material increases. The increase in thermal conductivity of each material.
Table 2 Thermal conductivity of thermal insulation mortar after freeze-thaw cycle W/(mK) initial state increase of thermal conductivity of thermal insulation mortar after freeze-thaw cycle 2.3 Results analysis 2.3.1 Characterization of interfacial action Degradation process of thermal insulation properties of composite thermal insulation materials The change in the coefficient is characterized. When the environmental factors and composition of composite insulation materials are certain, there are three main factors affecting the thermal deterioration: the thermal properties of the matrix, the thermal properties of the insulation components and the interface effects. The influence factor of the unit volume is defined as the influence factor of the A unit volume insulation component is B, and the interface influence factor is C. When the composition is constant, the volume of the matrix material and the insulation component can be obtained, but the volume fraction of the interface It is difficult to get it accurately. Therefore, the interface effect should be considered as a whole. When the influence factors A and B are known, they can be solved
Add the value to establish the equation and find the corresponding parameter value. The result is shown in Table 3. The parameter value is the relationship between C value and p(EPS) after 2 dry and wet cycles. It can be seen that the trend of the curve changes relatively, and when the volume fraction of the organic component exceeds 50%, the C value becomes significantly larger.
2.3.3 Data analysis equations in the freeze-thaw cycle, obtain the parameter values ​​after different cycles (see Table 4), and obtain the parameter values ​​of Table 4 after different freeze-thaw cycles. C-value and organic group after freeze-thaw cycle The influencing factors of the relationship between the volume fractions are not the dominant factors in the middle and low dosage range. The organic component itself has good frost resistance, and the partial substitution matrix can improve the freeze-thaw cycle resistance of the material. In the range of medium and low dosage, the interface has less influence on the freeze-thaw cycle even compared with the interface influence factor corresponding to the dry and wet cycle. The interface itself is a kind of porous material, and the frost heaving effect of the freeze-thaw cycle leads to an increase in the interface and even an open pore, thereby increasing the thermal conductivity. However, since the EPS particles used in the thermal insulation material are a flexible material, the pressure generated by the frost heave can be absorbed to reduce the interface damage, resulting in a smaller calculated C value. The values ​​of C6 and C7 are larger because the organic components self-deposit in the high content range, the pores increase, and although the number of interfaces decreases, the interface properties change, the original pores appear to communicate, and the thermal conductivity increases. At the same time, as the organic component increases, the interfacial properties of the material also change, from the original solid-solid interface portion to the solid-liquid and solid-gas interface, so that the interface has an increased effect on the thermal degradation of the material.
3 Conclusion After the dry-wet cycle and freeze-thaw cycle, the thermal properties of the composite insulation materials have deteriorated. Appropriate addition of organic insulation components helps to improve the material degradation process. However, as the organic thermal insulation component increases, the deterioration process tends to accelerate.
After the dry-wet cycle, the organic component with low water absorption is partially substituted for the matrix, which can improve the dry-wet resistance of the material. However, with the increase of the organic component content, the matrix can not completely enclose the organic component, the material pores increase, the water absorption rate increases, and the resistance to dry-wet cycle decreases. After the freeze-thaw cycle, the organic component has good freeze resistance and flexibility, which can improve the freeze-thaw resistance of the material and counteract the pressure generated by the frost heave, thereby reducing the interface damage. However, the contribution of organic components to the improvement of thermal properties after freeze-thaw cycles of materials is limited.
As the organic thermal insulation component increases, the interface deteriorates the thermal properties of the composite thermal insulation material. This is mainly because as the volume fraction of the organic thermal insulation component increases, the number of interfaces increases, and the interface properties also change, from the original solid-solid interface to the solid-gas interface. The improvement of organic components is not directly proportional to its volume fraction. After a certain value, the improvement effect will be significantly reduced due to the interfacial action. In this paper, the volume fraction of the organic thermal insulation component should not exceed 50%. It can be seen that in the development and application of the thermal insulation material, the amount of the organic thermal insulation component must be limited.
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