Preparation And Properties Of Phenolic Foam Modified By Nano Silica And Lignin

Phenolic foam(PF)is the foam material that is solidified by phenolic resin and a series of additives such as foaming agent,curing agent,surfactant,foam stabilizer,and then the gas produced by the blowing agent owing to the reaction exothermic is dispersed in resin.Thanks to the advantages of low smoke,innocuity,good flame retardancy,no dripping and high carbon residue in combustion,phenolic foam has been widely applied in building energysaving materials,thermal insulation materials for petrochemical industry,structure and interior materials of transportation vehicles and so on.Lignin is a renewable natural biomass resource.It has the advantages of huge reserves,friendly environment,low cost and high added value.It has a chemical structure similar to that of phenol,which reduces the dependence on petroleum chemical raw materials to a certain extent.The synthesis of phenol formaldehyde resin has a more choice on account of a substitute of lignin widely.The surface of the nano silica is rich in hydroxyl groups,which can combine with the large molecules of the phenolic resin to form a network structure,enhancing the mechanical strength of the phenolic resin.At the same time,the nano silica interact with the electron clouds in phenolic resin molecules due to the effect of infiltration caused by size effect in order to improve the stability of phenolic resin.In this paper,tetraethyl orthosilicate(TEOS)was used as the silicon source and phenol as the solvent.The nano silica was synthesized by the sol-gel method.The results of FT-IR show that the hydrolysate contains the characteristic functional groups of silica,which proves that it is silica.XRD showed that silica is amorphous structure;The particle size of the hydrolysate was tested by dynamic light scattering.The results showed that the particle size was between 100 nm~800 nm,reaching the nanometer level.The activity of hydrolysates was analyzed by formaldehyde consumption.From the two levels of free formaldehyde content and mass change,we could see that the activity of nano silicon–phenol system was higher than that of pure phenol,and the optimal hydrolysis time was 1h and the reaction time was 1 h.Nano silica was introduced into phenolic resin through condensation polymerization and intermolecular force,and the properties of nano silica / phenolic resin were tested.The FT-IR analysis showed that the nano silica reacted with the phenolic resin and the Si-O-Si bond was generated.The TG analysis shows that the Si-O-C bonds with larger bonds in the nano silica / phenolic resin have a positive effect on the thermal stability.PR-0.5(nano silica accounted 0.5% for the quality of phenolic resin)> PR-0.7 > PR-0.2 > PR-1 > PR-0.1 > PR-0;The DSC analysis results showed that the peak temperature of PR-0,PR-0.1,PR-0.2,PR-0.5,PR-0.7 and PR-1 were 150.7,155.5,174.4,179.5,170.4 and 168.8 oC.The higher the peak temperature is,the better the stability of the structure is.Therefore,the structural stability of PR-0.5 is the best.The free phenol and free formaldehyde content of phenolic resin analysis showed that free formaldehyde and free phenol content of PR-0 was 6.89% and 7.56%,and the lowest point is at PR-0.5,which was 4.83% and 5.06%;The content of hydroxymethyl content of PR-0,PR-0.1,PR-0.2,PR-0.5,PR-0.7 and PR-1 were 36.3%,37.5%,38.1%,40.8%,39.5% and 38.6%.The results of viscosity analysis of phenolic resin show that the viscosity of the resin increased first and then decreased.The nano silica / lignin based phenolic foam was prepared,and the thermal stability,foam pore uniformity,internal regularity,mechanical strength,toughness,flame retardant properties and combustion properties of modified foam were characterized.The TG analysis results showed that the thermal stability of the foam material at the high temperature stage is LPF-0.5 > LPF-0.7 > LPF-1 > LPF-0.2 > LPF-0.1 > LPF-0;The SEM analysis shows that the foam LPF-0.5 had better uniformity,more compact arrangement,the lower opening rate and regular multiform bubble wall.The XRD analysis showed that the characteristic diffraction peak of silica appeared at 2 theta =22.8 °,and there were many burrs in the peak,indicating that the peak is amorphous structure.The compression strength of LPF-0 is the lowest,which is 0.252 MPa while that of LPF-0.5 is the highest,which is 0.322 MPa,improved by 28%.In addition,the toughness of phenolic foam can be characterized by the integral area under stress-strain curve.The maximum integration value of LPF-0.5 is 2.454 and the minimum value is 2.031 of LPF-0.The pulverization rate of LPF-0 is 19.2%,while that of LPF-0.5 decreases to 14.1%.The flame retardancy and combustion properties of the foam were characterized by a critical oxygen index instrument and a conical calorimeter.The results show that the critical oxygen index of all foams were more than 42.The combustion parameters such as heat release rate(HRR),effective heat combustion(EHC)and total heat release(THR)of LPF-0.5 is 19.14 Kw/m~2,8.14 KJ/Kg and 4.2 Kw/m~2,respectively,which are better than other modified foam.