Influence of Filler Types and Contents on Foaming Structures in ABS Microcellular Foams

The influence of filler types and concentration on the foaming structure was investigated using a batch method to penetrate CO2 in ABS polymer matrix. Vapor grown carbon fiber (VGCF®, averaged diameter = 150 nm), and calcium carbonate (averaged particle diameter = 1.8 μm) were used as fillers and the concentration was changed from 5 to 15 wt %, respectively. Vapor grown carbon fiber or calcium carbonate was compounded with ABS using an extruder and samples were made by hot press method. Foamed samples, whose density reduction showed about 30–40%, were made by controlling preparation conditions.In the case of vapor grown carbon fiber/ABS systems, the average diameter of foaming cell decreased, and the cell density increased as a function of fiber concentration. On the other hand, by the incorporation of calcium carbonate, the diameter increased, and density decreased with higher concentration. The initial nucleation stages of foaming from fillers were carefully observed for fillers having large aspect ratio and particle shape. Based on the evidences from optical microscope observation, the different tendency of cell diameter between the two systems as a function of concentration was discussed.