A new strategy to fabricate polyvinyl alcohol (PVA) foam with low thermal conductivity using PVA-citric acid solution in supercritical carbon dioxide

Polymer foams with low density have a great potential in the field of heat preservation due to good thermal insulation properties. In this work, a new method for the preparation of polyvinyl alcohol (PVA) foam with low density using PVA-citric acid (CA) solution based on supercritical carbon dioxide (scCO2) foaming technology was proposed. This approach introduced abundant water as co-blowing agent and utilized the crosslinking between CA and PVA to regulate the viscosity of solution, thereby the low density PVA foam with stable morphology was prepared. The effects of saturation time, PVA content, CA content, temperature and pressure on PVA foaming behavior were investigated. Meanwhile, the use of water as assistant solvent was explored to increase the co-blowing content and weaken the diffusion of water molecules to CO2 in the PVA-CA solution, which resulted in the successful fabrication of PVA foams with lower density and low thermal conductivity. The results showed that the minimum densities of PVA before and after addition of assistant solvent were 0.070 g/cm3 and 0.047 g/cm3, respectively. Moreover, PVA foam fabricated by the addition of assistant solvent showed the thermal conductivity of 29.68 mW/mK and the compression modulus of 2.21 MPa.