The effect of macroscopic structures such as pellet size, shape, and orientation on the structure development in the formation of a thermoplastic polyurethane (TPU) foam by supercritical CO₂ foaming was studied. If the same amount of supercritical CO₂ diffused into the polymer, it was found that pellets having a relatively large volume and surface area show the decreasing of cell density and increasing of cell size, consequently, an increase in the expansion ratio of foaming was obtained. The chain orientation resulted in the increase in cell density and decrease in cell size, thereby the foam expansion ratio was reduced. This was understood that the chain orientation might prevent the diffusion of supercritical CO₂ and promotes nucleation at the same time.

펠렛 크기와 모양 그리고 배향과 같은 거시 구조가 초임계 이산화탄소 발포에 의한 열가소성 폴리우레탄(TPU) 발포체 구조 형성에 미치는 영향을 살펴보았다. 초임계 이산화탄소 동일한 양이 고분자로 확산되면 상대적으로 체적과 표면적이 큰 펠렛의 경우, 셀 밀도를 감소시키고 셀 크기를 증가시켜 그 결과, 발포 팽창비가 증가함을 알 수 있었다. 연신에 의한 사슬 배향은 초임계 이산화탄소의 확산을 방해하며 동시에 기핵 형성을 촉진하여 셀 밀도 증가와 셀 크기 감소를 초래하여 발포 팽창비가 감소됨을 확인하였다.

Keywords: supercritical CO₂ forming, thermoplastic polyurethane, foam structure, orientation