Microcellular plastic

Microcellular plastics, otherwise known as microcellular foam, is a form of manufactured plastic, specially fabricated to contain billions of tiny bubbles less than 50 microns in size (typically from 0.1 to 100 micrometers). This type of plastic is formed by dissolving gas under high pressure into various polymers, relying on 'thermodynamic instability phenomena' to cause the uniform arrangement of the gas bubbles, otherwise known as nucleation. Its main purpose was to reduce material usage while maintaining valuable mechanical properties. The main room for variance in these foams is the gas used to create them; the density of the finished product is determined by the gas used. Depending on the gas used, the density of the foam can lie between 5% and 99% that of the pre-processed plastic. Design parameters, focused more on the final form of the foam and the molding process afterward, include the type of die or mold to be used, as well as the dimensions of the bubbles, or cells, that classify this material as a foam. Since the size of cells is close to the wavelength of light, to the casual observer this foam retains the appearance of a solid light colored plastic. Microcellular plastics, otherwise known as microcellular foam, is a form of manufactured plastic, specially fabricated to contain billions of tiny bubbles less than 50 microns in size (typically from 0.1 to 100 micrometers). This type of plastic is formed by dissolving gas under high pressure into various polymers, relying on 'thermodynamic instability phenomena' to cause the uniform arrangement of the gas bubbles, otherwise known as nucleation. Its main purpose was to reduce material usage while maintaining valuable mechanical properties. The main room for variance in these foams is the gas used to create them; the density of the finished product is determined by the gas used. Depending on the gas used, the density of the foam can lie between 5% and 99% that of the pre-processed plastic. Design parameters, focused more on the final form of the foam and the molding process afterward, include the type of die or mold to be used, as well as the dimensions of the bubbles, or cells, that classify this material as a foam. Since the size of cells is close to the wavelength of light, to the casual observer this foam retains the appearance of a solid light colored plastic. Recent developments at the University of Washington have produced nanocellular foams. These foams are characterized by cell sizes in the 20-100 nanometer range. Also at Indian Institute of Technology Delhi, new technologies are being developed to fabricate high quality microcellular foams. Prior to 1974, traditional foams were created using a method outlined in U.S Patent named Mixing of Molten Plastic and Gas in 1974. By releasing a gas, otherwise known as a chemical or physical blowing agent, over molten plastic, hard plastic was converted into traditional foam. The results of these methods were highly undesirable. Due to the uncontrolled nature of the process, the product was often non-uniform, housing many large voids. In turn, the outcome was a low strength, low density foam, with large cells in the cellular structure. The pitfalls of this method drove the need for a process that could make a similar material with more advantageous mechanical properties. The creation of microcellular foams as we know today was inspired by the production of traditional foams. In 1979, MIT masters students J.E. Martini and F.A Waldman,under the direction of Professor Nam P Suh, are both accredited with the invention of microcellular plastics, or microcellular foams. By doing pressurized extrusion and injection molding, their experimentation led to a method that used significantly less material and a product with 5-30% less voids that were less than 8 microns in size. In terms of mechanical properties, the fracture toughness of the material improved by 400% and the resistance to crack propagation increased by 200%. First, plastic is uniformly saturated with gas at a high pressure. Then, the temperature is increased, causing thermal instability in the plastic. In order to reach a stable state, cell nucleation takes place. During this step, the cells created would be much smaller than that of traditional foams. After this, cell growth, or matrix relaxation would initiate. The novelty of this method was the ability to control the mechanical properties of the product by varying the temperature and pressure inputs. For example, by modifying the pressure, a very thin outside layer could be formed, making the product even stronger. Experimental results found CO2 to be the gas that produced the densest foams. Other gases, such as Argon and Nitrogen produced foams with mechanical properties that were slightly less desirable.