RT info:eu-repo/semantics/masterThesis
T1 A water-free route to porous materials via cryoextraction and supercritical drying
A1 Castedo Hernández, Cecilia
A2 Universidad de Valladolid. Escuela de Ingenierías Industriales
K1 Aerogel
K1 Preparación route
K1 Polvmer
K1 Supercritical drving
K1 2206.10 Polímeros
AB In this study a novel process combining freezing, cryoextraction and supercriticaldrying for producing porous materials is developed. The process consists of threemain steps: first of all, freezing a polymer/DMSO solution at −28 °C to obtain amonolith. Second step is solvent exchange with EtOH at −28 °C to extract DMSOcrystals, obtaining an alcogel at the end of this process. The last part of the processis drying the alcogel with scCO2 at 120 bar and 50 °C for 3 h. The method hasbeen used for the production of polyacrylonitrile (PAN) aerogels, it is demonstratedthat for this material a high quality aerogel is obtained at 5 wt % volumetric shrinkage36.8   6.1 %, porosity is 93.5   0.6 % and 119   18m2 g−1 of specific surfacearea (SSA). In addition to PAN, other polymers such as poly(vinyl alcohol) (PVA)and agar-agar and their combination with PAN are tested. Pure PVA aerogels showthe higgest value of SSA at 7.5 wt % of 107   15m2 g−1. Both combinations resultin a aerogel with worse quality than pure PAN. In particular, porosity and linearshrinkage experimented by PAN/PVA aerogels have a exponential relation withPVA concentration. In addition to standard conditions, liquid nitrogen at −196 °Cis used as a freezing agent obtaining aerogels with lower SSA that lack physical integrity.However, whereas in conventional freezing at −28 °C directional freezing isobserved, more pronounced with the decrease in concentration, for aerogels frozenat −196 °C non-hierarchical pore structures are found.Generally speaking, it has been observed that lower concentrations leave more spacefor DMSO crystals to grow due to looser arrangement of polymer chains. At thesame time, pore walls become thinner making the network weaker leading to highershrinkage.
YR 2021
FD 2021
LK https://uvadoc.uva.es/handle/10324/47143
UL https://uvadoc.uva.es/handle/10324/47143
LA eng
NO Departamento de Ingeniería Química y Tecnología del Medio Ambiente
DS UVaDOC
RD 17-jul-2024