(241h) 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.