Experimental methodology for the quality control of extruded polystyrene (XPS) plastic insulation

To support the development of CFC-free plastic foam insulation and establish the design database of the new generations of plastic foams, experimental methodologies for these purposes are required. In this study, two methods have been developed to evaluate the quality of rigid closed-cell cellular plastics. Method one is referred to weighing method. By monitoring the mass changes of the foam slices as time elapse, the thermal aging character of the foam can be obtained by comparing the measurement with the reference mass/time curves. Method two is a modified slicing or scaler aging test, by which the long-term aging of a unfaced heterogenous foam can be predicted. At this stage of study, we put our emphasis mainly on the theoretical analysis. Benchmark tests and primary modelling have shown that a simplified one-dimensional mass transfer model can provide fairly good prediction on the mass changes of foam slices. This evidence forms the basis of the weighing method. The measured mass changes of the extruded polystyrene (XPS) foam slices have suggested that the foam panels are inhomogeneous ones from the view point of gaseous transfer. In viewing the calculations of gaseous transfer within inhomogeneous foams which have different cross-sectional diffusion coefficient distributions, it has been found that there is a representative layer in which the mass transfer process is physically similar to that in the simulated inhomogeneous foam plate. Therefore, it has been recommended that the short-term thermal aging character of this representative foam slice is used to predict the long-term aging of the full-size inhomogeneous foam panel by using the same method as in the normal slice aging test. The overall aging character of a inhomogeneous plastic foam with two relative tight surface layers is much better than the average value of the thin slices selected from the same foam panel. If the foam has only one tight surface, its aging process follows the average value of each thin slice selected from it.