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The kinetics of polyurethane structural foam formation: Foaming and polymerization

AIChE Journal

Rao, Rekha R.; Mondy, L.A.; Long, Kevin N.; Celina, Mathias C.; Wyatt, Nicholas B.; Roberts, Christine C.; Soehnel, Melissa M.; Brunini, Victor B.

Kinetic models have been developed to understand the manufacturing of polymeric foams, which evolve from low viscosity Newtonian liquids, to bubbly liquids, finally producing solid foam. Closed-form kinetics are formulated and parameterized for PMDI-10, a fast curing polyurethane, including polymerization and foaming. PMDI-10 is chemically blown, where water and isocyanate react to form carbon dioxide. The isocyanate reacts with polyol in a competing reaction, producing polymer. Our approach is unique, although it builds on our previous work and the polymerization literature. This kinetic model follows a simplified mathematical formalism that decouples foaming and curing, including an evolving glass transition temperature to represent vitrification. This approach is based on IR, DSC, and volume evolution data, where we observed that the isocyanate is always in excess and does not affect the kinetics. The kinetics are suitable for implementation into a computational fluid dynamics framework, which will be explored in subsequent articles. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2945–2957, 2017.

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TYPE Journal Article YEAR 2017
ScopusOSTIDOI

Modeling Porous PMDI-based Polyurethane Foam Decomposition in Pressurizing Systems

10th U.S. National Combustion Meeting

Scott, Sarah N.; Keedy, Ryan M.; Brunini, Victor B.; Dodd, Amanda B.

Polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. In fire environments, gas pressure from thermal decomposition of polymers can cause mechanical failure of sealed systems. A 3-D finite element conduction-radiation model with porous media flow and a chemistry model was created to investigate the heat transfer and pressurization in such scenarios. Experiments show that the rate of pressurization and the temperature of select thermocouples are dependent on orientation with respect to gravity, indicating buoyancy-driven flow. In this work, the gas velocity is solved by applying the Darcy approximation, and the heat transfer and pressurization are determined by solving the continuity, species, and enthalpy equations in the condensed and gas phases. This work will describe the porous media model, explore material parameters (e.g. phase, permeability, conductivity) for use with PMDI polyurethane, compare predictions to experimental data, and recommend values for material properties. It will use multiple heating rates to validate the data, and show that incorporating gas motion into the model captures the divergent nature of the results in different orientations.

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TYPE Conference Poster YEAR 2017
ScopusOSTI

Mesoscale effective property simulations incorporating conductive binder

Journal of the Electrochemical Society

Trembacki, Bradley T.; Noble, David R.; Brunini, Victor B.; Ferraro, Mark E.; Roberts, Scott A.

Lithium-ion battery electrodes are composed of active material particles, binder, and conductive additives that form an electrolyte-filled porous particle composite. The mesoscale (particle-scale) interplay of electrochemistry, mechanical deformation, and transport through this tortuous multi-component network dictates the performance of a battery at the cell-level. Effective electrode properties connect mesoscale phenomena with computationally feasible battery-scale simulations. We utilize published tomography data to reconstruct a large subsection (1000+ particles) of an NMC333 cathode into a computational mesh and extract electrode-scale effective properties from finite element continuum-scale simulations. We present a novel method to preferentially place a composite binder phase throughout the mesostructure, a necessary approach due difficulty distinguishing between non-active phases in tomographic data. We compare stress generation and effective thermal, electrical, and ionic conductivities across several binder placement approaches. Isotropic lithiation-dependent mechanical swelling of the NMC particles and the consideration of strain-dependent composite binder conductivity significantly impact the resulting effective property trends and stresses generated. Our results suggest that composite binder location significantly affects mesoscale behavior, indicating that a binder coating on active particles is not sufficient and that more accurate approaches should be used when calculating effective properties that will inform battery-scale models in this inherently multi-scale battery simulation challenge.

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TYPE Journal Article YEAR 2017
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Results 26–50 of 77
Results 26–50 of 77