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Analytic Methods of Foamed Plastic Insulation Deteriorated by Moisture
Abstract
Foamed plastic insulations installed into buildings are now expected to be long‐lasting materials. However, in recent years, it has been reported that foamed plastic insulations installed in high‐humid environments, such as under waterproof sheets on a rooftop, absorb moisture, and subsequently increase thermal conductivity. This paper studies both moisture absorption and changes in physical properties of foamed plastic insulations after exposure to high humidity and discusses the moisture‐induced deterioration based on the results of several experiments.
A detailed morphometric analysis of one-component polyurethane (PU) expanding foams, with densities of 26 and 28 kg/m3 (‘SUMMER’ and ‘WINTER’ product versions), was conducted to evaluate the topology of the foam cells and to discover processing-to-structure relationships. The microstructural analysis of the heterogeneously distributed pores revealed tight relationships between the foam morphology and the cell topology, depending on the growth rate and local environmental conditions, governed by the properties of the blowing gas used. The most significant morphometric output included the following: open/closed porosity and (heterogeneous) pore distribution, relative density and (homogeneous) strut distribution, and total solid matrix surface and closed pore surface area—at the macroscopic level of the foam. While, at the microscopic level of the cells, the results embraced the following: the size of every detected strut and pore, identified two-dimensional (2D) shapes of the cell faces, and proposed three-dimensional (3D) topologies modelling the PU foam cells. The foam microstructure could be then related with macroscopic features, significant in building applications. Our protocol outlines the common procedures that are currently used for the sample preparation, X-ray scanning, 3D image reconstruction and dataset analysis in the frame of the X-ray computed microtomography (µ-CT) testing of the one-component PU foams, followed by a statistical (multiple Gaussian) analysis and conceptual considerations of the results in comparison with thematic literature.
To clarify the hygrothermal environment of vertical edge insulation methods in moderate and humid climate region, especially in the summer involving the rainy season, temperature and relative humility of 12 houses have been measured. From the measurement results, the temperature variation in the crawl space tends to slide slightly backward compare to the outdoor air. Evaporation from the drying concrete keeps the humidity in the crawl space rather high, especially in the summer just after completion. But it becomes moderate on condition that it passes through the winter. Daily diurnal range of temperature in the crawl space is smaller, and absolute humidity is lower, than the other construction method, that also ensures against condensation proofing.
In order to save energy consumption for air-conditioning of buildings throughout those lifecycle, thermal performance of insulation materials applied in buildings should be kept in required value. On the other hand, there are many factors of ageing of insulation materials such as ambient temperature, vibration and moisture etc. In the previous paper, main factors of thermal performance change were discussed and several experimental results were shown. This paper examines the influences of moisture on thermal performance of various insulations based on three kinds of experiment. In first experiment, the relationship between equilibrium moisture content and thermal conductivity of fiber insulations is obtained. Second experiment is on the influence of gaseous moisture on fiber insulations and the results show that the dimension change of fiber insulations is small even in very humid condition. Third experiment is on the reversibility of thermal conductivity after the internal dew condensation process and the dry process, and the results show that many insulation materials have reversibility except for several plastic insulation foams.
Thermal performance of insulation materials decreases with the passage of time. Such ageing of insulations should be considered in the design stage of buildings to keep insulation performance within the required one throughout the lifecycle of buildings. Firstly, this paper focused various factors that affect performances of insulations. The main factors for fiber insulations are moisture, vibration and microbe. The main factor for plastic insulation foams is ambient temperature that accelerates the diffusion of blowing agent. Secondly, real performances of sold new insulations and scraped old ones were measured and compared the required value by Japanese standard. Performances of some insulations were lower than standard values and performance change was detected. Finally, this paper discussed the influence of vibration on performance for fiber insulations based on the experimental data. The changes of insulation depth and thermal resistances were observed after the vibration test.
The degree of crosslinking of very small amounts of polymer gel, encountered in the characterization of the molecular structure of rubber polymers or of polymers in powder form, cannot be determined satisfactorily by measurement of elasticity or conventional swelling. Therefore a method has been developed which enables us to determine the degree of crosslinking of such polymer systems reliably. This method is based on the measurement of equilibrium swelling by sedimentation in the analytical ultracentrifuge. The degree of swelling can either be used directly as a relative measure of the average degree of crosslinking or as basis for calculating the average degree of polymerization of the molecule chains between two crosslink sites according to the theory of Flory and Rehner. The efficiency of the method is demonstrated by several examples of application (differently crosslinked polybutadienes, gel portions of various polychloroprenes and polyurethane foams).
Accelerated test method for long-term change in thermal resistance of rigid cellular plastics
- Japanese Industrial Standards
Study on Estimation of Venting Ability for the Waterproofing, Summaries of technical papers of annual meeting
- H. Kitayama
Water diffusion into plastic foam(XPS) under temperature cyclic exposure
- M. Hisanaga