Effect of blowing agent composition and processing parameters on the low temperature foaming of poly(l-lactide/caprolactone) co-polymer by means of supercritical CO2/ethyl lactate binary mixtures

• PLC foams with controlled features have been obtained by solid-state foaming.
• Binary mixtures of scCO2 and EL have been used as blowing agent.
• Foams have been prepared at low operating temperatures (35 and 40 °C).
• Different pressure quench profiles have been used to control foams properties.

The low temperature foaming of poly(l-lactide/caprolactone) (PLC), a semi-crystalline biodegradable co-polymer, by means of supercritical CO2 (scCO2) and ethyl lactate (EL) blowing agent mixtures is reported. EL has been selected as a non-toxic biocompatible plasticizer for PLC to improve its foaming behaviour at low temperature. In particular, the control of the pore structure of PLC foams was achieved by the optimal combination of the EL molar fraction in the blowing agent mixture, studied in the range of 0–0.2%, the operating temperature, selected between 35 and 40 °C, and the depressurization time going from 0.5 to 6 min. The results of this study demonstrate that a small amount of EL enhanced significantly the plasticization power of scCO2 and, depending on the operating conditions selected, allowed for the fabrication of PLC foams with low density and large pores. In particular, we proposed a low temperature and clean approach suitable to prepare PLC foams with densities in the range of 0.21–0.50 g/cm3, mean pore sizes in the range of 20–300 μm and pore densities in the range of 1.6 × 105–4.6 × 108 pore/cm3.

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