Xiangmin Han

Nanoscaled reinforcement of polystyrene foams using carbon nanofibers

Carbon nanofibers (CNFs) are used as both the nucleants and the reinforcements for polystyrene (PS) foams in both batch and continuous extrusion processes with CO2 as the blowing agent. The inclusion of CNFs exhibits substantial impact on the morphology and properties of PS foams. The presence of CNFs results in a decrease in the cell size and an increase in the cell density. Macroscopic strength enhancement of PS foams due to the incorporation of CNFs is experimentally observed. These results are qualitatively explained via a series of nanoscaled observations. Through scanning electron microscopy (SEM), the alignment of CNFs and the polymer-sheathing phenomenon are identified. The protective CNF layers around the cell wall and the substantial polymer-fiber interactions resulted in the enhancement of foam strengths. Thermal properties (heat conductivity, infrared transmission, and thermal expansion coefficient) of the PS foams can also be influenced by CNFs. Intensive shear force exerted by the twin-screw extruder broke the fibers in lengths. The impact of the fiber length on the foam structures (cell size and cell density) is also studied.

CO2 Foaming of Polymer Nanocomposite Blends

Nanoparticles are suitable to nucleate small foam cells and simultaneously reinforce the thin foam cell walls. In this paper, it is found that the foam morphology and the physical properties are greatly influenced by the dispersion of nanoclay, the clay surface modification, and the nanocomposite blend morphology. The addition of nanoclay to polystyrene (PS) strongly affects the nucleation of foam bubbles, especially after exfoliation and proper surface modification. CO2 appears to nucleate on the solid clay surface with a CO2-affinitive surface modifier. PS/(PMMA/MHABS) nanocomposite blends composed of polystyrene and poly(methyl methacrylate)/nanoclay exfoliated nanocomposite show an unexpected trend that bubble nucleation inversely correlates with domain size, where the bigger PMMA/MHABS domains are significant in nucleating more bubbles. The total influence volume, formed by the CO2 diffusion from the PMMA/MHABS phase to the PS phase where CO2 concentration decreases from a high value in the former to a low value in the latter, is related to the domain size and determines the nucleation efficiency in the PS phase. The physical properties of PS nanocomposites exhibit unique behaviour in the presence of CO2.