Preparation And Foaming Of Lignin-modified Phenolic Resin

The preparation of phenolic resin is not complicated and the required cost is not high.It has great potential in industrial production.However,phenolic resin causes the pollution to the environment and the required materials such as phenol are not renewable,so some methods about modification can be used to synthesize materials that meet different needs.Lignin has a certain similarity with phenol in properties and it is easy to obtain and renewable.A part of phenol can be replaced by lignin to synthesize resin.The modified phenolic resin has many advantages such as excellent stability and corrosion resistance.Phenolic foam can be used as insulation material,but the problem of poor toughness hinders further application.By replacing the phenol with lignin to synthesize the modified resin and foaming to obtain the samples,the environment can be improved.In addition,the cost can also be lower.The microwaveassisted method and hydrothermal method were used to degrade lignin and then the phenol was partly replaced by lignin to synthesize resin in the thesis.The resin was foamed to obtain the cellular insulant.The results of the study are as follows:1.Two different degradation methods(microwave-assisted method and hydrothermal method)were used to degrade lignin.The sodium hydroxide was used in the process as catalyst.The effects of substitution rate and reaction conditions on lignin were studied.It shows that phenolic hydroxyl content increases by two methods.Under microwave conditions,when the alkali concentration is 0.2 mol/L,the highest phenol content can reach for 23.16% after reacting for 15 min at the temperature of 170 °C.With hydrothermal method,when the alkali concentration is 0.2 mol/L,the highest phenol content can reach for 23.64% after reacting for 1.5 h at the temperature of 250 °C.2.The hydrothermal method was used to degrade lignin.Sodium hydroxide and sodium thiosulfate were added as additives to explore the effects about concentration of additives and reaction conditions on lignin degradation.The lignin can be degraded better by adding additives and the phenolic content can be increased.When the alkali concentration was 0.2 mol/L and the salt concentration was 0.015 mol/L,the highest phenolic content was 25.96%.Compared with microwave-assisted method,hydrothermal method was more suitable for industrial production because of larger volume injection and lower cost.3.Using lignin as raw material to partially replace phenol,the effects on the tensile strength and other properties of the phenolic resin synthesized with different raw materials were investigated.It showed that the phenolic resin had the highest bonding strength,reaching 2.92 MPa,which was synthesized by using the phenol partially replaced by lignin prepared with additives.The relative curing temperature(ΔT)was reduced by 10 °C.Polymerization and crosslinking are possible at lower temperatures.4.The effects of various conditions on foaming were explored during the foaming process.The amount of curing agent was 20% of the resin mass and the amount of sodium bicarbonate was 1.5% of the resin mass.The amount of active agent was 6%of the resin mass and the amount of diatomite was 10%.The sample obtained had the best effect with curing at 110 ℃.5.The mechanical and flame retardant properties of the foam samples were characterized.All foams met the requirements of compressive strength in the national standard.In terms of flame retardant performance,the oxygen indices of all foams exceeded 32%.All samples were flame retardant materials.