Generation of novel microstructures in rapidly foamed polybutylene terephthalate

A novel technology called "Dynamic Decompression and Cooling (DDC) Process" for producing foams from semicrystalline polymers has been developed. In t he present experiment, a solution of polybutylene terephthalate (PBT) melt and blowing liquid (CHCl3) is processed under high pressure and temperature . As the system is decompressed above the boiling point of the solvent, pha se separation occurs; gas bubbles nucleate out from a metastable regime and grow through evaporation of the volatile phase and diffusion of non-conden sable gas. Solidification is achieved by crystallization of the polymer and supercooling of the melt induced by the latent heat of vaporization of the volatile phase. The resulting foams have open, interconnected cell structu res with densities of 10-20% of the original materials. Structural characte rization with DSC, SEM and X-ray diffraction techniques reveals that the DD C foams are semicrystalline with crystallinity of ca. 35% and possess a var iety of micromorphologies as well as crystalline orientations. This structu ral character is believed to modify considerably the mechanical properties of the fabricated DDC foams. (C) 1999 Kluwer Academic Publishers.