Modeling of polyurethane foam formation

Behavior Characteristics and Thermal Energy Absorption Mechanism of Physical Blowing Agents in Polyurethane Foaming Process

Polyurethane rigid foam is a widely used insulation material, and the behavior characteristics and heat absorption performance of the blowing agent used in the foaming process are key factors that affect the molding performance of this material. In this work, the behavior characteristics and heat absorption of the polyurethane physical blowing agent in the foaming process were studied; this is something which has not been comprehensively studied before. This study investigated the behavior characteristics of polyurethane physical blowing agents in the same formulation system, including the efficiency, dissolution, and loss rates of the physical blowing agents during the polyurethane foaming process. The research findings indicate that both the physical blowing agent mass efficiency rate and mass dissolution rate are influenced by the vaporization and condensation process of physical blowing agent. For the same type of physical blowing agent, the amount of heat absorbed per unit mass decreases gradually as the quantity of physical blowing agent increases. The relationship between the two shows a pattern of initial rapid decrease followed by a slower decrease. Under the same physical blowing agent content, the higher the heat absorbed per unit mass of physical blowing agent, the lower the internal temperature of the foam when the foam stops expanding. The heat absorbed per unit mass of the physical blowing agents is a key factor affecting the internal temperature of the foam when it stops expanding. From the perspective of heat control of the polyurethane reaction system, the effects of physical blowing agents on the foam quality were ranked in order from good to poor as follows: HFC-245fa, HFC-365mfc, HFCO-1233zd(E), HFO-1336mzzZ, and HCFC-141b.

Changes and Trends-Efficiency of Physical Blowing Agents in Polyurethane Foam Materials

This work developed a novel method for measuring the effective rate of a PBA (physical blowing agent) and solved the problem that the effective rate of a PBA could not be directly measured or calculated in previous studies. The results show that the effectiveness of different PBAs under the same experimental conditions varied widely, from approximately 50% to almost 90%. In this study, the overall average effective rates of the PBAs HFC-245fa, HFO-1336mzzZ, HFC-365mfc, HFCO-1233zd(E), and HCFC-141b are in descending order. In all experimental groups, the relationship between the effective rate of the PBA, rePBA, and the initial mass ratio of the PBA to other blending materials in the polyurethane rigid foam, w, demonstrated a trend of first decreasing and then gradually stabilizing or slightly increasing. This trend is caused by the interaction of PBA molecules among themselves and with other component molecules in the foamed material and the temperature of the foaming system. In general, the influence of system temperature dominated when w was less than 9.05 wt%, and the interaction of PBA molecules among themselves and with other component molecules in the foamed material dominated when w was greater than 9.05 wt%. The effective rate of the PBA is also related to the states of gasification and condensation when they reach equilibrium. The properties of the PBA itself determine the overall efficiency, while the balance between the gasification and condensation processes of the PBA further leads to a regular change in efficiency with respect to w around the overall average level.

Experimental study on thermal effect and gas release laws of coal-polyurethane cooperative spontaneous combustion

This paper presents a research on the kinetics and gas release laws of the cooperative spontaneous combustion of coal-polyurethane binary system by means of thermogravimetric analysis and spontaneous combustion simulation experiments. The coal-polyurethane binary system is more prone than individual samples to combustion. The polyurethane mass fraction has a great influence on the cooperative spontaneous combustion process. As the polyurethane mass fraction rises, the activation energies of oxygen absorption stage and pyrolysis stage decrease. The combustion residues of coal-polyurethane binary system scorches into lumps and the surfaces of the particles become rougher. During spontaneous combustion, the initial release temperatures of the four gases CO₂, CO, C₂H₆ and C₂H₄ drop as the polyurethane mass fraction increases. The gas release amount of them increases with increasing polyurethane mass fraction. And the amount of CH₄ decreases as the polyurethane mass fraction increases. The CO/CO₂ ratio with temperature for different polyurethane mass fraction have the same trends. The results of this study have implications concerning polyurethane materials application and fire protection in coal mine.

Numerical simulation of mold filling water blown polyurethane foams: Effects of sequential pour

Batch molding of polyurethane foams is a widely used processing technique to produce crosslinked cellular structures which form to the shape of the mold. For water-blown polyurethane foams, water is reacted to form gaseous carbon dioxide resulting in a foam which expands to fill the mold completely. Batch molding typically requires an operator to coat the surface of a mold, introducing a significant lag time during the filling stage where significant asymmetric volume change can occur. The purpose of this work is to show, through simulations, that this lag time is significant when predicting flow profiles and part quality. When the mold geometry is complex enough to force bifurcation of the flow, simulations incorporating various filling lag times predicted significantly different locations of knit or weld lines where the flow fronts meet. Current simulation techniques, which assume the filling stage occurs instantaneously, are unable to predict variations in weld line locations. The introduction of a lag time, referred to herein as sequential pour, was achieved through user-defined modules incorporated into Ansys Fluent software.

High Throughput Screening of Rigid Polyisocyanurate Foam Formulations: Quantitative Characterization of Isocyanurate Yield via the Adiabatic Temperature Method

To reduce the time-to-market, a high throughput experimentation (HTE) method has been introduced at Bayer MaterialScience for the rapid development and optimization of polyurethane (PU) foam formulations and for the fast screening of new PU raw materials. The foam processor developed for this purpose allows automated PU foam production on a scale of 0.4 L, which is ten times smaller than the usual lab-scale foam volume. In order to optimize formulations for the increasing polyisocyanurate (PIR) foam market, a rapid in situ method has additionally been developed that is able to quantify isocyanurate concentration and yield. This method, the adiabatic temperature method (ATM), is based on the temperature profile measured within the foam bun in the HTE foam processor.

By comparison with attenuated total reflection (ATR)-FTIR spectra of the cured foams, it is shown that the isocyanurate concentration found in the 0.4 L foams is comparable with that of larger foams typically used in the laboratory (ca. 5 L). This demonstrates that the 0.4 L foams can be used to investigate the trimerization of isocyanates to form isocyanurate.

The suitability of the ATM is demonstrated and verified by ATR-FTIR spectroscopy for the influence of the index on isocyanurate yield and concentration for a pentane blown and a water co-blown PIR formulation. Isocyanurate yield is shown to be negligible at indices close to 100 but increases to an almost constant level at higher indices, the height of which depends on the type of the formulation. A level of approximately 70% has been observed for the physically blown formulations, whereas the water co-blown formulations only reach a level of around 40%.

Due to the successful implementation of the ATM, Bayer MaterialScience is increasingly using high throughput experimentation to optimize PIR recipes and to examine new raw materials and additives for polyisocyanurate foams. This has led to an increase in the efficiency of our polyurethane research and opened up possibilities that were not available to us before.