Mathematical Property Prediction Models for Flexible Polyurethane Foams—A Comparison between Conventional Slabstock, High Resilience Slabstock and High Resilience Molded Foams

Abstract

Flexible polyurethane foams of all types are a unique group of plastics materials, characterized by the fact that a multitude of different sets of properties can be obtained by varying the levels of a relatively small number of base components in the formulations. This has always made flexible polyurethane foams a highly suitable candidate for correlating these variations in the formulations with the resulting properties in a mathematical way, aimed at predicting these properties as accurately as possible, fine-tuning existing grades and designing new foam grades. Several such models have been reported before, and significant improvements have been achieved in the accuracy of the models and the predictions. This paper extends the models for conventional flexible slabstock beyond the previously reported key properties, namely density, hardness and fatigue, to other properties like elongation, tear strength, tensile strength, set properties and foam exothermic temperature. Some further influencing variables are also included, such as, for example, low TDI indexes and low index stabilizers which lead to rather complex correlations including several interaction terms. A comparison between laboratory foam data and large scale data is also included. The second part of this paper discusses the influences of the specific variables for high resilience slabstock foam on a similar set of properties. Apart from the variables common to both HR and conventional foam, namely water level, TDI index and polymer solids, particular emphasis is put on the effect of diethanolamine, as well on highlighting the inherent differences in hardness between the two types of foam. In the final section of this paper, a mathematical model for high resilience molded foams is presented, using similar predicting variables as for high resilience slabstock foam plus the unique variable of "overpacking," in a standardized molding tool. This paper discusses the use of these models to either calculate properties from formulations or, alternatively, calculate formulations for given sets of properties, as well as mathematical and computer techniques to perform these calculations.