Flexible Polyisocyanate Based Aerogels
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Flexible Polyisocyanate Based Aerogels
Roxana Trifu1, George Gould1, Shannon White1 1 Aspen Aerogels Inc., 30 Forbes Rd., Northborough, MA 01532, U.S.A.
ABSTRACT Highly flexible, durable aerogels with textile feel were developed at Aspen Aerogels Inc. by sol-gel chemistry and supercritical CO2 solvent extraction. These polyisocyanate-based aerogels reinforced with battings showed little to no brittle fracture with repeated flexing. The crosslinker, the isocyanate content and functionality played an important role on properties such as thermal conductivity, durability and flexural modulus at ambient and cryogenic temperatures. The polyisocyanate aerogels crosslinked with polyamine showed thermal conductivities as low as 18 mW/m-K at ambient pressure and those crosslinked with polyol had low flexural modulus at cryogenic temperatures. Applications of these aerogels in aerospace and diving are presented.
EXPERIMENTAL Preparation Polyisocyanate aerogels were prepared at isocyanate indices over 100 and target densities of 0.04 - 0.10 g/cc. Isocyanate precursors with a functionality ranging from 2 to 3 were used in these preparations. The catalysts were chosen from triazine derivatives (i.e. Polycat 41), quaternary ammonium salts (i.e. DABCO TMR) and tertiary amines. Polyisocyanate aerogels prepared in the absence of another crosslinking reagent are identified as PI. PI-PU aerogels were prepared by crosslinking the isocyanates with polyamines and PI-PUT aerogels were additionally crosslinked with polyols. The isocyanate precursors were dissolved in tetrahydrofuran or acetone and mixed at room temperature with the crosslinkers and catalysts for various amounts of time. The resulting sols were poured in molds over non-woven fibers and left to gel at ambient temperatures. Gelation occurred in 3 minutes to 1 hour. Aging of the fiber reinforced gels in the preparation solvent was carried out for 1-3 days at room temperature or at temperatures up to 45 ºC. The solvent was exchanged several times prior to extraction with supercritical CO2.
Testing methods Fourier Transform Infrared Attenuated total Reflectance (FTIR-ATR) spectroscopy analyses were performed on aerogels, without fiber reinforcement, using a Perkin Elmer Spectrum 100 FTIR over the 4000-600 cm-1 range.
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Thermal conductivity measurements at ambient pressures and temperatures were performed on a FOX300 apparatus manufactured by LaserComp Inc. according to ASTM C518 standard, using a plate temperature difference of 25 ºC. The flexural modulus was measured at ILC Dover using a TA Instruments Q800 Dynamic Mechanical Analyzer. Durability was assessed at ILC Dover by flexing the aerogel materials in a Flex tester, using a Thermal Micrometeoroid Garment “sock” inflated to a pressure of 10 kPa and subjected to 45° flexions/extensions f
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