Study On Synthesis And Foaming Of Lignin Phenolic Resin

The government paid more attention to energy-saving and emission-reduction in recent years, phenolic foam has drawn plenty of attention because of the excellent properties of flame retardancy, thermal insulation, few smog and innocuity, but the drawbacks of high brittleness and cost impeded its promotion and application. In order to improve the performance and reduce the cost of phenolic foam, in this paper, lignin phenolic resin and foam were prepared with phenol partly replaced by lignin, the effect of different factors on the synthesis and foaming of lignin phenolic resin was researched, the better conditions were obtained, and the pyrolyzation mechanism for lignin phenolic foam was explored. Finally, effect of Cardanol, Polyurethane prepolymer and Polyethylene glycol on properties of lignin phenolic foam was studied. The main conclusions were as follows:(1) Effect of different factors on properties of lignin phenolic resin was studied, when lignin substitution accounted for 30% of phenol, the better synthesis conditions of lignin phenolic resin were as follows: the phenolation time was 40 min, phenolation temperature was 110 ℃, concentrated sulfuric acid content was 3%, polymerization temperature was 85 ℃, polymerization time was 80 min, sodium hydroxide content was 4%, molar ratio of paraformaldehyde to phenol was 1.5 and distilled water content was 25 m L. Lignin phenolic resin synthetised at the better conditions showed good properties such as viscosity and solid content, making it easy to foam rise. Foaming study was conducted using the resin, results showed that the better foaming conditions were as follows: Polysorbate 80 content accounted for 6% of resin, mineral ether 30-60 content was 10%, curing agent content was 16%, temperature was 90℃.(2) Lignin phenolic foam prepared at the better conditions showed good properties, its compression strength and flexural strength were 0.21 MPa and 0.15 MPa, the water absorption was 6.92%, the limited oxygen index was 38.2%, the coefficient of thermal conductivity was 0.030 W/(m·K), it was non-combustible and efficient thermal insulation materials. Microscope pictures showed that foam was uniform and dense, and had good microscopic structure; Thermo Gravimetric Analyzer showed that it had good thermal stability.(3) Thermo Gravimetric curves of lignin phenol foam at different heating rates showed that pyrolysis process contained two stages, residual rate of foam was high and about 50%, lignin phenolic foam had good thermal stability; Analyses of pyrolysis data of foam at different heating rates were as follows: integral type of mechanism function for the first stage was [-ln(1-α)]3, its mechanism was random nucleation and growth, activation energy was 94.5 KJ/mol, pre-exponential factor was 9.55×109; Integral type of mechanism function for the second stage was [-ln(1-α)]4, its mechanism was also random nucleation and growth, activation energy was 65.2 KJ/mol, pre-exponential factor was 1.16×105.(4) Finally, effect of Cardanol, Polyurethane prepolymer and Polyethylene glycol on properties of lignin phenolic foam was studied, the results showed that the better content of Cardanol accounted for 9% of phenol, the better content of Polyurethane prepolymer accounted for 4% of lignin phenolic resin, and the better content of Polyethylene glycol accounted for 6% of lignin phenolic resin; The mechanical properties and water absorption of foam modified with above modifiers were obviously improved at the better content, but the flame retardancy property and thermal stability reduced slightly, thermal insulation property had changed little, modified foam had good micromechanism. Overall, Polyurethane prepolymer was the best one that improved property of lignin phenolic foam, followed by Cardanol, the foam modified with above modifiers showed the better properties in building insulation.