463934 Preparation of Micro and Nanocellular PBT/Ptmg Diblock Copolymer Structure By Using Supercritical CO2 As the Blowing Agent – Effect of Microphase Morphology
Preparation of micro and nanocellular PBT/PTMG diblock copolymer foam by supercritical CO2 foaming ¨C effect of microphase morphology
Solid-state foaming process of segmented block copoly(ether esters) composed of polyoxytertramethylene (PTMG) ¡°soft¡± blocks and poly(butylene terephthalate) (PBT) ¡°hard¡± blocks using supercritical CO2 (scCO2) as the blowing agent was investigated. Plastic foams with nano/micro-scale cellular structures were prepared from PBT/PTMG copolymers. Two kinds of PBT/PTMG copolymers with different block ratio were used to investigate the influence of microphase morphology on foaming behavior. The CO2 dissolved into soft segments (PTMG) and hard segments(PBT) were carefully characterized by using magnetic suspension balance (MSB), meanwhile the gas diffusion coefficient was fitted from the Fick¡¯s diffusion law. The results show that the solubility and diffusivity of CO2 in soft segments (PTMG) is significantly higher than in hard segments(PBT). PBT/PTMG copolymers were foamed in a high-pressure chamber by using scCO2 and the effect of temperature, block ratio, and saturation time on the cell morphology was investigated, respectively. The cell size and location were highly concentered in the dispersed soft segments by using the difference of CO2 solubility and diffusivity between the hard segments and the soft segments. It was found that only soft segments could be foamed in presence of CO2. The average cell diameter of the PBT/PTMG foaming samples were controlled to be 400¨C1800 nm on the preferential condition of block ratio, saturation pressure and foaming temperature. Furthermore, the cellular structure could be highly oriented in one direction by using the foamed soft segment in the microphase morphology as a template for foaming to obtain an alternate lamellar nanocellular structure.
Figure 1. The SEM image of PBT/PTMG foaming sample.
Figure 2. The POM image of highly oriented PBT/PTMG.
Figure 3. The SEM image of highly oriented PBT/PTMG foaming sample with alternate lamellar nanocellular structure.