Rapid Preparation at Atmospheric Pressure and Gel Phase Analysis of Thermoplastic Phenolic Aerogels with High Specific Strength and Low Shrinkage

This article presents a rapid preparation method of phenolic aerogels using thermoplastic phenolic resin as a raw material under atmospheric pressure, a low temperature and mass fraction of the resin varying from 10 to 30%. The results showed that the initial stage of the aging time of the aerogel with resin mass fraction of 10% (PF-10) was at least 34 h to ensure no neck shrinkage during drying, while that with 30% phenolic content (PF-30) was only 1h. The prepared aerogels had a minimum density of 0.129 g/cm3 and a minimum shrinkage of 0.391%. With the increase of mass fraction of resin, the thermal conductivity of the aerogels decreased first and then increased, and PF-20 had the lowest thermal conductivity, being 0.037 W/(m·K). The effects of resin content on the microstructure were reflected in the pore size of aerogels which decreased from 773 nm for PF-10 to 43.328 nm for PF-30 and the particle size of the phenolic resin which decreased from 194 to 28 nm. The specific surface area increased from 37.707 to 177.231 m2/g, and the number of micropores increased. In terms of mechanical properties, the aerogel with 10% resin mass fraction had a minimum compressive strength of 0.342 MPa and a compressive modulus of 12.811 MPa, showing good elasticity. When the resin content was 30%, the strength and modulus increased to 8.309 and 348.060 MPa respectively. Its specific strength and specific modulus were 16.553 and 693.346 N·m/g, respectively, and the rigidity was greatly increased.