Polymerization of Phenol Formaldehyde in Solvent-Saturated Vapor and Study on the Microstructure and Mechanical Properties of Novolac Aerogel Product

Aerogels consist of low density open-cell foams with large void spaces of nanometer pore size and they are composed of sparsely semi-colloidal nanometer sized particles forming open porous structures. The high porosity and nanometer pores and particles of aerogels have interesting properties such as low thermal conductivity and low sound transmission. The main disadvantages of conventional method for preparation of aerogels are high cost of resorcinol، long preparation time and high cost of supercritical drying device. The previous research showed that sol-gel polymerization lower than temperature of normal boiling point of solvent، and a 50°C difference in temperature between the novolac resin synthesis and the temperature of curing novolac resin is the main reason for long sol-gel polymerization time. A low temperature polymerization is used for prevention of solvent evaporation and foam blowing process. The objectives of this research were to reduce time and cost in the production process of organic aerogels. To reduce the cost of raw materials، the reaction of a low cost commercial novolac resin and HMTA were used for preparation of the gel. To reduce gelation time، the polymerization was performed in an atmosphere of solvent saturated-vapor as a novel method to restrict sol-gel polymerization of curing novolac resin at appropriate temperature. The investigation showed that the polymerization carried out in solvent-saturated vapor did help to reduce polymerization time to 5 h from 5 days duration in conventional reactions without any visible shrinkage under ambient pressure and temperature. Furthermore، the compressive strength increased by one order of magnitude besides other achievements. Aerogels comprise class of low density open-cell foams with large void space، nanometer pore size and they are composed of sparsely semi-colloidal nanometer sized particles forming open porous structures. The high porosity and nanometer pores and particles of aerogels results interesting properties such as low thermal conductivity and low sound propagation speed. The main disadvantages of conventional method for preparation of aerogels are high cost of resorcinol، long preparation time and high cost of supercritical drying device. The previous research showed that sol-gel polymerization lower than temperature of standard boiling point of solvent، also 50 °C differences between appropriate temperatures for curing novolac resin and the performed temperature of curing novolac resin is the main reason for long time of sol-gel polymerization. The low temperature polymerization used for prevention of solvent evaporation and solution blowing. The objectives of this research are reducing time and cost in the production process of organic aerogels. To reduce the cost of raw material، the reaction of low cost commercial novolac resin and HMTA were used for preparation of gel. To reduce gelation time، the polymerization in saturated atmosphere of vaoer of solvent as a novel method for domination of restriction sol-gel polymerization temperature curing novolac resin in appropriate temperature is proposed. The investigation shows that the polymerization in saturated atmosphere of solvent vapor، reducing time of polymerization from 5 days to 5 hours without any observable shrinkage in ambient atmosphere. Furthermore، the compressive strength increased one order and it’s other important achievements of this research.