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Liquid organic foams for formulation optimization : an assessment of foam linear viscoelasticity and its temporal dependence

Kropka, Jamie M.; Celina, Mathias C.; Mondy, L.A.

Liquid foams are viscoelastic liquids, exhibiting a fast relaxation attributed to local bubble motions and a slow response due to structural evolution of the intrinsically unstable system. In this work, these processes are examined in unique organic foams that differ from the typically investigated aqueous systems in two major ways: the organic foams (1) posses a much higher continuous phase viscosity and (2) exhibit a coarsening response that involves coalescence of cells. The transient and dynamic relaxation responses of the organic foams are evaluated and discussed in relation to the response of aqueous foams. The change in the foam response with increasing gas fraction, from that of a Newtonian liquid to one that is strongly viscoelastic, is also presented. In addition, the temporal dependencies of the linear viscoelastic response are assessed in the context of the foam structural evolution. These foams and characterization techniques provide a basis for testing stabilization mechanisms in epoxy-based foams for encapsulation applications.

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TYPE Conference YEAR 2010
OSTI

Experimental-modeling approach for predicting radiation and conduction heat transfer through a uniform, highly-charring foam

20th Annual Conference on Recent Advances in Flame Retardancy of Polymeric Materials 2009

Erickson, Kenneth L.; Celina, Mathias C.; Hogan, Roy E.; Nicolette, Vernon F.; Aubert, James H.

Polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. In fire environments, foams, such as polyurethanes and epoxies, can liquefy and flow during thermal decomposition, and evolved gases can cause pressurization and failure of sealed containers. In systems safety and hazard analyses, heat transfer and thermo-mechanical response in systems involving coupled foam decomposition, liquefaction, flow, and pressurization can be difficult to predict using numerical models. This is particularly true when liquefaction and flow create inhomogeneous "participating media" that behave inconsistently and significantly impact radiant heat transfer to encapsulated objects. To mitigate modeling issues resulting from foam liquefaction and flow, a hybrid polyurethane cyanate ester foam was developed that has mechanical properties similar to currently used polyurethane foams. The hybrid foam behaves predictably, does not liquefy, and forms approximately 50 percent by weight uniform char during decomposition in nitrogen. The char forms predictably and is a relatively uniform "participating medium." Experimental and modeling approaches were developed to predict radiation and conduction heat transfer to encapsulated objects before, during, and after foam decomposition. Model parameters were evaluated from independent small-scale experiments. Largerscale radiant heat transfer experiments involving encapsulated objects were done to provide data for model evaluation. Model predictions were within the variation in experimental results for the major portion of the experiments. © (2009) by BCC Research All rights reserved.

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TYPE Conference YEAR 2009
ScopusOSTI

Hybrid polyurethane cyanate ester foam for fire environments

Conference Proceedings - Fire and Materials 2009, 11th International Conference and Exhibition

Erickson, Kenneth L.; Celina, Mathias C.; Nicolette, Vernon F.; Hogan, Roy E.; Aubert, James H.

Polymer foams are used as encapsulants to provide mechanical, electrical, and thermal isolation for engineered systems. In fire environments, the incident heat flux to a system or structure can cause foams to decompose. Commonly used foams, such as polyurethanes, often liquefy and flow during decomposition, and evolved gases can cause pressurization and ultimately failure of sealed containers. In systems safety and hazard analyses, numerical models are used to predict heat transfer to encapsulated objects or through structures. The thermo-mechanical response of systems involving coupled foam decomposition, liquefaction, and flow can be difficult to predict. Predicting pressurization of sealed systems is particularly challenging. To mitigate the issues caused by liquefaction and flow, hybrid polyurethane cyanate ester foams have been developed that have good adhesion and mechanical properties similar to currently used polyurethane and epoxy foams. The hybrid foam decomposes predictably during decomposition. It forms approximately 50 percent by weight char during decomposition in nitrogen. The foam does not liquefy. The charring nature of the hybrid foam has several advantages with respect to modeling heat transfer and pressurization. Those advantages are illustrated by results from recent radiant heat transfer experiments involving encapsulated objects, as well as results from numerical simulations of those experiments.

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TYPE Conference YEAR 2009
ScopusOSTI
Results 101–125 of 153
Results 101–125 of 153