Preparation And Properties Of Foams Based On Modified Phenolic Resins

Phenolic foams were originally used in aviation,aerospace,insulation cabin and other fields.With the maturity of the production process,the increasing performance of phenolic foams and the growing popularity of flame retardant materials,applications of phenolic foams are gradually expanding.In recent years,construction technology has developed rapidly,construction area will reach 60 billion square meters by 2020 in China.Low density,better insulation,flame retardant and other advantages of phenolic foam meet the needs of the construction markets.However,applications of phenolic foams are restricted by some shortcomings such as poor mechanical properties,large dosage of acidic curing agent and high toxicity of phenol and formaldehyde and so on.To solve these problems,the mechanical properties of phenolic foams were improved by introducing flexible polyurethane prepolymers,and the toughening mechanism was studied.Phenolic resins and foams modified with resorcinol were prepared.The introducing of resorcinol was not only improved mechanical properties of phenolic foam but also reduced dosage of curing agent and curing temperature.The lignin-phenol-resorcinol-formaldehyde foams was prepared with lignin of phenolic modification.Polyethylene glycol-phenol-formaldehyde resins(PEG-PF resins)were synthesized in polyethylene glycol system,and PEG-PF resin and foam materials were prepared by using isocyanate as curing agent.It provided experimental basis and theoretical support for the development of polyurethane rigid foam with excellent mechanical properties and flame retardant performance.The main contents and conclusions are as follows:1.Preparation and toughening mechanism of polyurethane prepolymer toughened phenolic resinThe polyurethane prepolymer(PUP)was synthesized by using polypropylene glycol and diphenylmethane diisocyanate as raw materials.The effects of PUP contents on the rheological properties,curing kinetics of modified phenolic resins and on the dynamic thermomechanical properties,mechanical properties and thermal stability of solidification of cured phenolic resins were studied,respectively.And the mechanism of PUP toughening phenolic resin was discussed.The results showed that it was a chemical modification method and the PUP was introduced into structure of phenolic resin by the addition reaction of isocyanate groups and the hydroxymethyl and hydroxyl groups of phenolic resins.With the increase of the amount of PUP,the apparent activation energy of the modified phenolic resin system was gradually increased and the curing process of the resins became slower.The storage modulus and loss factor of phenolic resins modified with PUP increased,and the peak height of the loss peak increased.When the content of PUP was 5 %,the impact strength and bending strength of the cured phenolic resin were 6.92 kJ/m2 and 72.88 MPa,respectively,which increased by 67.1 % and 39.1 % compared with unmodified phenolic resin.2.Study on properties of polyurethane prepolymer modified phenolic foamsPolyurethane prepolymer(PUP)with different isocyanate contents and polyurethane prepolymer(PUPC)using ethylene glycol as chain extender were synthesized with polypropylene glycol and diphenylmethane diisocyanate.The effects of additions,the content of isocyanate of PUP and PUPC addition on the mechanical strength,flame retardant and thermal stability of phenolic foams were studied.The results showed that the mechanical properties of phenolic foams were improved by introducing proper amount of flexible polyurethane prepolymer.Phenolic foams modified with 5 % PUP-3 had better performance and the relative compression strength and relative flexural strength were respectively 3.48 and 5.96 kPa·m3·kg-1,and limited oxygen index(LOI)was 35.3 %,thermal conductivity was 0.054 W·m-1·K-1.The relative compression strength and relative flexural strength of phenolic foams modified with 8 % PUPC-3 were 3.08 and 5.97 kPa·m3·kg-1,respectively,and LOI was 35.9 %.From the relative strength point of view,phenolic foam modified with PUP-3 had better performance than foam modified with PUPC-3,which was because that the high molecular weight and viscosity of PUPC-3 were bad for mixing uniform and foaming.Besides,the crosslinking points were reduced between resol and prepolymers because of low isocyanate contents,which resulted in the relative strength of PUPC-3 modified foam slightly lower than that of PF-PUP-3 foam.3.Preparation and characterization of resorcinol modified phenolic resins and foamsPhenol-resorcinol-formaldehyde resins(PRFRs)with different resorcinol/phenol molar ratio(R/P)and formaldehyde/(phenol+resorcinol)molar ratio(F/(P+R))were prepared using resorcinol,phenol and formaldehyde.And phenol-terminated castor oil-based polyurethane prepolymer(CPUP)was prepared.The effects of R/P and F/(P+R)on physical and chemical properties,chemical structure,rheological and thermal stability of PRFRs and on the mechanical properties,microstructure and flame retardant properties of phenol-resorcinol-formaldehyde foams(PRFFs)were studied,respectively.Meanwhile,the effects of CPUP contents on the mechanical properties,thermal stability,flame retardancy and microstructure of foams were also studied.The results showed that when R/P was 0.09/0.91 and F/(P+R)was 2.0/1.0,the free formaldehyde content,hydroxymethyl content and gel time of PRFR-2 were 0.14 %,34.5 % and 144 s,respectively.Gel point temperature of PRFR-2 was 126 °C,which was lower than that of unmodified phenolic resin.The foam prepared with PRFR-2 had better performance that compression strength,bending strength,and LOI were 180.8 kPa,252.3 kPa and 35.0 %,respectively.It was obviously that the reactivity of phenolic resin and mechanical properties of foams were improved by introducing resorcinol.Besides,the compressive strength,flexural strength and mass loss rate of PRFFs foam modified with 5 % CPUP were 186.2 kPa,329.7 kPa and 17.2 %,respectively.4.Preparation and characterization of lignin-phenol-resorcinol-formaldehyde resin and foam materialsLignin(BR)was first phenolated under alkaline conditions,and the phenolated lignin was used to prepared lignin-phenol-resorcinol-formaldehyde resins(LPRFRs)and lignin-phenol-resorcinol-formaldehyde foams(LPRFFs).The effects of phenolic time on phenol hydroxyl content of lignin and the effects of phenolic time and phenolated lignin contents on the physical and chemical properties of LPRFRs and on the mechanical properties,thermal stability and microstructure of LPRFRs were studied,respectively.When lignin was phenolated for 3.0 h,the phenolic hydroxyl content was 3.36 %,which improved by 15.5 % compared with that of original lignin.And number average molecular weight was 1 730,and weight average molecular weight(Mw)was 2 580.The LPRFRs with 30 % BR phenolated for 3.0 h had low free formaldehyde and free phenol contents and moderate viscosity,which were 0.29 %,2.08 % and 5 800 mPa·s,respectively.The greatest mechanical properties for LPRFFs foams were obtained by replacing with 30 % phenol,and its compressive strength and flexural strength were 181.6 and 261.6 kPa,increased by 41.8 % and 24.3 %,respectively.5.Preparation and characterization of PEG-PF materials under non-acid curing systemPolyethylene glycol-phenol-formaldehyde(PEG-PF)resins with different mass ratio of polyethylene glycol,phenol and formaldehyde(PEG/P/F)were synthesized with polyethylene glycol,phenol and paraformaldehyde.PEG-PF resin and foam materials were prepared with PEG-PF resin and isocyanate.The effects of PEG/P/F on the mechanical properties,thermal stability,glass transition temperature and microstructure of PEG-PF resin materials and on the mechanical properties and flame retardant properties of PEG-PF foam materials were studied.And the reaction mechanism of PEG-PF resin in non-acid curing system was preliminarily explored.The results showed that when PEG/P/F was 60/25.42/14.58,the tensile strength of PEG-PF resin material was 28.08 MPa,which improved by 128 % compared with that of PEG material(FM-1).With the mass fraction of phenol and formaldehyde increasing,the glass transition temperature of PEG-PF resin material was increased until it disappeared.The temperature corresponding to the peak of the loss factor increased and the loss peak became wider.When PEG/P/F was 50/31.77/18.23,the compressive strength and LOI of PEG-PF foam material were 0.259 MPa and 25.9 %,respectively.The PEG-PF resin material and foam materials with better performance were prepared under non-acidic curing system.