Polyurethane rigid foams modeling project

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Polyurethanes (PU) foams are extensively, used and they can expand during polymerization if gases or vapors are produced in concert with the polymerization. A common mechanism for gas generation is the chemical reaction between water and isocyanate forming carbon dioxide. For rigid foams, density plays a significant role to determine other physical properties. Accurately predicting density during polyurethane foaming is both important in its own right and as a critical step to ultimately predict other physical properties of foams. A model based on about a dozen fundamental differential equations is used to evaluate and simulate the urethane reactions and physical processes of urethane box foaming. The works of this thesis were performed to advance the understanding of how blowing agents work and to improve the accuracy of heat capacities used in the modeling. Chapter 2 focuses on quantitative modeling of foam density for foams using water and physical blowing agents. The final densities of foams range from 30% to 90% of the densities as projected with full utilization of the blowing agent. The primary sources of inefficient use of blowing agent are loss of the physical blowing during open-air mixing and degassin--basically, physical blowing agents with boiling points between 25 and 80 C will evaporation and experience cell rupture in box foams. This loss of blowing agent would not apply to in-line mixers used for commercial production and should be taken into account with scaling up box or cup foams for commercial processes. In Chapter 3, a group contribution method for the estimation of heat capacities of polyols, isocyanate and DEG/TEG was supplemented to increase accuracy for use with reactants, intermediates, and products during urethane polymerization. Differential Scanning Calorimetry (DSC) was used to measure heat capacities for samples having molecular weights up to about 1100. DSC and literature data were used to obtain the contributions from six groups while five groups of an existing correlation prove