Abstract
Polyurethane (PU) is a typical product of the reaction between isocyanate and polyol, whose ratio would greatly influence material properties. In this paper, to investigate the influence of isocyanate on PU thermal stability and flammability, three kinds of rigid polyurethanes (RPUs) with different isocyanate ratio (1.05, 1.1, and 2.0) were manufactured in a laboratory and employed to have a series of TG (thermogravimetry), DSC (differential scanning calorimetry), and cone calorimetry tests. Kissinger’s method was used to calculate the activation energy and judge their stabilities. However, for such a complex degradation which consists of five reactions, it does not make sense by Kissinger method to obtain only two peak active energies. Considering complexity of PU degradation in air, genetic algorithm (GA) was employed to calculate kinetic triplets of five sub-reactions. The effects of isocyanate contents on each sub-reaction stability were obtained and then analyzed. By cone calorimeter testing, we found that great differences in heat release rate data. However, DSC analysis showed a complete opposite changed trend. Such difference is caused by DSC and calorimeter’s sample morphology, the former using grinded polyurethane powders but the latter polyurethane foam block.
Highlights
Polyurethanes (PUs) have been found using in a growing number of applications in building constructions for decades, such as furniture, appliances, and thermal insulation exterior walls, making them the most versatile plastic materials
When this research was begun, large amounts of research have been reported on the mechanism and chemical kinetic of PU degradation, there were, to the knowledge of the authors, few attentions have been paid on the thermal stability study of rigid polyurethanes (RPUs) with different isocyanate index
When we manufactured polyurethane with isocyanate index 1.5, we found that the thermal stability showed few differences with that of isocyanate index 1.1
Summary
Polyurethanes (PUs) have been found using in a growing number of applications in building constructions for decades, such as furniture, appliances, and thermal insulation exterior walls, making them the most versatile plastic materials. Rigid PU (RPU) is one of the most common forms in our life, which is usually used as thermal insulation materials in building construction. The fire disaster that occurred at a high-rising building in Shanghai Jing’an District resulted in more than 120 people dead and injured The investigation of this shocking fire disaster showed that flame caused by RPU in exterior walls could propagate quickly from the ignition point to the whole building. Jiao et al [7] investigated the degradation mechanism of PU in the nitrogen atmosphere, confirming the temperature ranges of escaped isocyanates and polyols. When this research was begun, large amounts of research have been reported on the mechanism and chemical kinetic of PU degradation, there were, to the knowledge of the authors, few attentions have been paid on the thermal stability study of RPU with different isocyanate index. Thermal stability of each step reaction could be compared for different PUs
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