(245e) Effect of CO2-Philic Additives and Co-Blow Agents on CO2 Diffusion in Polystyrene Microcellular Foaming

Effect of CO₂-philic
additives and co-blow agents on CO₂ Diffusion in Polystyrene
Microcellular Foaming

Wei Qiang, Dong-dong Hu*, Tao Liu, Ling Zhao*

State Key Laboratory of Chemical Engineering,
East China University of Science and Technology, Shanghai 200237, China

^* Corresponding author.
Tel.: +86 21 64253175; E-mail:
hudd@ecust.edu.cn, zhaoling@ecust.edu.cn

ABSTRACT

The
solubility and diffusivity of gas in polymer matrix play crucial roles in
controlling the CO₂ foaming process and foam structure. The low
solubility and the high diffusion coefficient (D) of CO₂ in
polymers lead to the difficulty of controlling the CO₂ foaming ^[1-3].
In this work, the synergetic effect of molecular weight (Mw) of polydimethylsiloxane
(PDMS) and co-blow agents on the diffusion of supercritical CO₂ into
and out of polystyrene (PS) and foam structures were investigated via DPD
simulations and experiments.

Fig.1 CO₂
diffusion coefficient in PS with PDMS and co-blow agents from DPD simulations and
experiments: the solid dots are the simulation results and the hollow dots are
the experiment results

Fig.2 Desorption curves of CO₂
in PS with PDMS and co-blow agents (the number behind represents the molecular
weight): (a) PS/PDMS (b) PS/PDMS/ethanol (c) PS/PDMS/pentane (d)
PS/PDMS/acetone

The
PDMS with low M_w increased the D of CO₂ in PS,
while the D decreased with the increase of M_w of CO₂-philic
additives. The relation between M_w of PDMS and the D of CO₂
in PS was calculated via DPD simulation, showing a similar variation with
diffusion measurements. From the DPD results, the co-blow agents increased the D
dramatically and the system with acetone showed the highest CO₂
diffusion.

The
desorption test demonstrated the CO₂ desorption rates were smaller
in PS with low Mw PDMS than that in PS with high Mw additives. As for co-blow
agents, ethanol and acetone accelerated the CO₂ desorption rates
while n-pentane lowered the CO₂ desorption rate. However, when the
impregnated with co-blow agents, the desorption rates were larger in PS with
low Mw PDMS than that in PS with high Mw PDMS.

Fig.3 PS foams with additives
and co-blow agents: 1-PS; 2-PS/PDMS2258; 3-PS/PDMS6097; 4-PS/PDMS/16097

The
saturation time of foams was shortened indicated by the DPD simulations as low
Mw PDMS and co-blow agents increased the D of CO₂ in PS. The
cell nucleation was favored as low Mw PDMS increased the solubility of CO₂
in PS. The slow CO₂ desorption rate in PS with low Mw PDMS enabled
higher amount of CO₂ retained in the PS. Hence, PS with low Mw PDMS
foams presented smaller cell size and larger cell density. Moreover, all
co-blow agents had plastication effects on PS, n-pentane slowed the CO₂
desorption and yielded larger cells. PS foamed with low Mw PDMS and acetone
showed bi-modal cell structure due to the strong interactions between low Mw
PDMS and acetone.

REFERENCES

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