| Awareness and concern about the environment, especially municipal solid waste (MSW), is significant in the U.S. The weight of plastic in MSW generated was about 28.9 million tons and the weight recovered was only 1.65 million tons, 5.7%, in 2005. For MSW in the U.S., plastics are one of the main concerns, occupying about 9 to 12 of the landfills by volume.BiomaxRTM is a biodegradable plastic, one alternative to conventional polymers from an environmental viewpoint. The cost of BiomaxRTM is about Microcellular foam is characterized by cell sizes in the range of 0.1 to 10 mum, and has a cell density in the range of 109-10 15 cell/cm3. The unique features of microcellular foam are fine cell size, high cell density, and use of inorganic blowing agents.BiomaxRTM microcellular foams were successfully developed, yielding closed cell foams. These foams changed from translucent and brownish in the unfoamed Biomax samples to white and opaque, with smooth surfaces.In this study, the effects of foaming temperature and foaming time on size, density, average cell size, cell population density, morphology, tensile strength, percent elongation at break, and tensile modulus of BiomaxRTM microcellular foams were studied. The experimental results for tensile strength and tensile modulus were compared with the simple rule of mixtures and with Moore's empirical square power law, respectively. The results were analyzed using one way ANOVA with 95% confidence interval. With increasing foaming temperature, the polymer chain stiffness decreased, causing the viscosity and surface tension of polymer to decrease (less retarding) so the diffusion rate of CO2 gas from the polymer to the cells was higher, leading to increased cell expansion, increased size of the foam, larger cell sizes, and decreased cell wall thickness and density. With longer foaming time, CO 2 gas had a longer time to diffuse into the cells, so the cells expanded more, leading to larger size, and reduction in density and wall thickness.Tensile strength and modulus decreased with increasing foaming temperature and foaming time. Experimental results for tensile and tensile modulus at different foaming temperatures showed a good fit with the model, and tensile modulus at different foaming times showed a good fit with the model. After one year, foamed samples became slightly stiffer. Tensile strength increased slightly, but percent elongation decreased.The thickness of samples affected the uniformity of the foams. At higher thicknesses, the inside of the foam needed a longer time for gas to diffuse and higher foaming temperature because of the temperature gradient. The outside surface of foams had higher temperature so larger cell sizes than the inside samples. At the same processing conditions, the thicker samples had higher density, smaller cell sizes, and thicker cell walls than did the thinner samples. |
