Ultra-micro-cellular foaming using super critical CO_2

通过物理发泡过程的目视观察，了解聚合物中气泡的成核和长大行为，开发气泡尺寸小于1微米、气泡密度大于109个/cm2的微孔塑料泡沫塑料技术。应通过增加发泡剂浓度、使释压速率溃烂和/或降低聚合物的表面张力来促进气泡成核，并通过抑制发泡剂从聚合物基质到气泡的传质来降低气泡生长速率。粘度在气泡生长过程中是一个次要因素，但在聚结、气泡稳定和破裂过程中成为一个重要因素。控制发泡过程的温度，精心选择聚合物，制得泡径小于1微米的透明聚烯烃泡沫塑料。然而，由于发泡率低，除非提高发泡率，否则在这个阶段找不到所产生的泡沫塑料的任何适当应用。对聚丙烯/粘土复合纳米复合材料进行了发泡实验。研究了粘土对泡沫成核的影响，并考察了粘土在气泡周围的取向，以提高泡沫塑料的机械强度。

The visual observation of physical foaming processes is conducted to understand the bubble nucleation and bubble growth behavior in polymers and to develop the technique of micro cellular plastic foams, whose bubble size less than 1 micron meter and bubble density is larger than 10^9 bubbles per cm^3.The visual observation elucidates that to make the bubble size smaller. the bubble nucleation should be enhanced by increasing the foaming agent concentration, making pressure release rate fester, and/or reducing the surface tension of the polymer and the bubble growth rate should be reduced by depressing the mass transfer of foaming agents from polymer matrix to bubbles. The viscosity is a less important factor during the bubble growth process but it becomes an important factor in the process of coalescence and bubble stabilization and break-up. Controlling the temperature of the foaming process and carefully selecting the polymer, the transparent foams of polyolefin foams were created, where the bubble size is less than 1-micron meter. However, because of the low foaming rate, any appropriate applications of the created foams were not found at this stage unless the foaming rote is increased. Nano-composites, which is a composite of polypropylene and clay, were foamed. The effect of clay on nucleation was investigated and orientation of clay around the bubble was also investigated in order to make the mechanical strength of the foam higher.