Partnership for Advancing Technologies in Housing: Microcellular Polymers Processing for Lightweight and Energy Efficient Advanced Panel Systems

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PATH: Microcellular Polymers Processing for Lightweight and Energy Efficient Advanced Panel SystemsAbstractThis award supports a PATH research project to explore the manufacture of thick sheets of microcellular polymers for load-bearing applications such as advanced panel systems for house construction. Microcellular Plastics refer to closed-cell thermoplastic foams with a very large number of very small bubbles. Typically, the cells are of order of 10 micrometers in diameter, and there are 108 or more cells per cubic centimeter (cm3) of the foam. The microcellular polymers offer a number of unique advantages for house construction applications. For example, the microcellular structure can reduce the density, leading to a reduction in the weight of the panels. Lighter panels are more cost effective and promote safety during house construction. In addition, reducing material density leads to conservation of natural resources by only using what is truly needed. Further, the microcellular structure can reduce the thermal conductivity and thus improve the energy efficiency of the panel systems. The basic solid-state microcellular process is a two-stage batch process. In the first stage, the polymer is placed in a pressure vessel with a high-pressure and non-reacting gas. This step is usually conducted at room temperature. Over time, the gas diffuses into the polymer, and attains a uniform concentration throughout the polymer specimen. When the specimen is removed from the pressure vessel and brought to the atmospheric pressure, a "supersaturated" specimen that is thermodynamically unstable due to the excessive gas dissolved into the polymer is produced. In the second stage, the specimen is heated to what is termed the foaming temperature. This step is typically carried out in a heated bath with temperature control. The dissolved gas lowers the glass transition temperature of the polymer and the foaming temperature needs only to be above the glass transition temperature of the gas-polymer system in order for the bubbles to nucleate and grow. Since the polymer is still in a solid state, the foams thus produced are called "solid-state foams" to distinguish them from the conventional foams that are produced in an extruder from a polymer melt. The funded research will explore the feasibility of producing thick microcellular specimens using a number of polymers, including PVC, a common plastic used in building materials today; PET, a polymer considered cost-competitive with PVC; and some of the more recently introduced high-strength polymers such as PEEK and PEI. A number of gases will be explored as a physical blowing agent. These gases include carbon dioxide and nitrogen. The research will advance the state-of-the-art of the emerging microcellular polymers technology by adding the new dimension of load-bearing applications. It will also provide an excellent opportunity for both undergraduate and graduate students to learn and grow in an environment of discovery and scientific understanding.