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Synthesis and Properties of Flexible Resorcinol-Formaldehyde Aerogels

Milow, Barbara and Schwan, Marina and Ratke, Lorenz (2013) Synthesis and Properties of Flexible Resorcinol-Formaldehyde Aerogels. Thermosets 2013, 18.-20. Sep. 2013, Berlin.

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Abstract

Organic resorcinol - formaldehyde (RF) aerogels dried under ambient conditions with a large resorcinol (R) to catalyst (C) ratio are usually hard and brittle with strengths about 100 kPa and Young’s-moduli in the range of 1-2 MPa and densities in the range of 0.2 to 0.4 g/cm3. We observe that special conditions of aerogel preparation yield surprisingly flexible aerogels. They can be bent easily (see figure 1), similar to the well-known flexible silica aerogels. They have a low density, a very low elastic modulus of around 70 kPa and are elastically deformable by more than 40% in an almost reversible manner. The procedure of their preparation is simple: The resorcinol is dissolved in deionized water with a very large amount of water (W), close to the gelation limit (molar ratio R/W ≈ 0.008). The R/F molar ratio is fixed at 1:2. The molar ratio R/C is 50:1 usually requiring supercritical drying. The pH is adjusted to be in the range 5.4-5.6. The solution is placed in an oven at 80°C for one week. The gel is washed in acetone and not dried supercritical but in an oven at 80°C. The density of flexible RF-aerogels is about 0.060 g/cm3, a shrinkage is not observed. The thermal conductivity of aerogel is 0.046 W/(mK). The SEM picture in Figure 2 shows the continuous network of particles with sizes of around 1 µm and pores of about 10 µm. The effects of various sol-gel parameters on the flexibility, such as R/W, R/C molar ratios, pH of initial solution, gelation temperature, have been investigated. The aerogels of different densities, microstructures and particle size were obtained by varying the R/W molar ratio. It has been observed that the pH plays a very important role in synthesis of flexible resorcinol-formaldehyde aerogels. The differences between hard and flexible RF aerogels were studied by recording 13C NMR spectra and TGA-FT-IR curves.

Item URL in elib:https://elib.dlr.de/111255/
Document Type:Conference or Workshop Item (Speech, Poster)
Title:Synthesis and Properties of Flexible Resorcinol-Formaldehyde Aerogels
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Milow, Barbarabarbara.milow (at) dlr.dehttps://orcid.org/0000-0002-6350-7728
Schwan, Marinamarina.schwan (at) dlr.deUNSPECIFIED
Ratke, Lorenzlorenz.ratke (at) dlr.dehttps://orcid.org/0000-0003-2487-4717
Date:2013
Refereed publication:No
Open Access:Yes
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:RF-aerogels, sol-gel process, process Parameter, mechanical strength, rigid to flexible
Event Title:Thermosets 2013
Event Location:Berlin
Event Type:international Conference
Event Dates:18.-20. Sep. 2013
Organizer:Frauenhofer Research Institution for Polymeric and Composites PYCO
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Transport
HGF - Program Themes:Terrestrial Vehicles (old)
DLR - Research area:Transport
DLR - Program:V BF - Bodengebundene Fahrzeuge
DLR - Research theme (Project):V - NGC Fahrzeugstruktur (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Materials Research > Aerogele
Deposited By: Milow, Dr. Barbara
Deposited On:28 Feb 2017 07:40
Last Modified:31 Jul 2019 20:08

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