Molecular Structure Design And Performance Of Phenolic Foam Toughened By Flame Retardant Cardanol

Phenolic foams(PFs),as one of the most important thermosetting rigid foam plastics,have been widely employed in a multitude of fields such as electric appliances,petrochemical industry and architecture owing to the flame retardancy.However,most traditional PFs show relatively poor toughness mechanical performance and extremely friability due to their unique molecular structure,which restrict the application scope.Cardanol,which has a natural alkyl phenol with a long flexible aliphatic chain,and like phenol,it can be used to toughen PFs.Because of the long flexible aliphatic chain,the PFs based on cardanol often exhibit poor flammability which blocks their applications in the fire resistance required fields.Based on the unique structure of cardanol,a forestry biological resource,we synthesized a functional cardanol-based toughening agent to replace oil-based toughening agents and used it to modify PFs.Thereby,high-flexibility fatty chain structures were introduced into PF molecules,which improved the toughness and reduced the pulverization ratio of PFs.Meanwhile,via chemical reactions,flame retardant elements such as P and Si were introduced into cardanol molecules,which compensated for the reduction of flame retardant performance and heat insulation due to the introduction of flexible chains.1.9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-(DOPO)containing cardanol based compound(PCD)was prepared from cardanol in combination with DOPO,this PCD was then used to substitute for part of phenol in the preparation of PCD-modified PFs(PPFs).The mechanical properties and flame retardant properties of PPFs were then studied.The findings in this part demonstrated that PCD could be used as a phenol substitute in the synthesis of PFs to overcome their drawbacks of intrinsic brittle and high flammability.The peak of heat release rate(pHRR)and mean heat release rate(mHRR)of PPF containing 4%PCD were 34.01 and 26.07 kW/m~2,which were decreased by 33.43%and 13.42%,respectively,in comparison to those of pristine PF,the compressive and flexural strength were0.264 and 0.271 MPa,which were 79.59%and 20.98%higher than pristine PF.When the PCD substitution amount was 8%,the compressive and flexural strength was maximized to0.268 and 0.354 MPa,which were 82.31%and 58.04%higher than pristine PF,respectively.and the PPF showed similar flame retardant properties as pristine foam.2.Cardanol-basedDOPO-containingpolyurethaneprepolymer(PPUP),a DOPO-containing cardanol polyol(PCP)derivative,were synthesized.Then PFs modified with different contents of PPUP were prepared.Compared with pristine PF,the compressive and flexural strengths of PPUP-modified PFs at 1 phr(parts per hundreds of resin)PPUP were maximized to 0.225 and 0.362 MPa,which are improved by 81.45%and by 94.62%,respectively.The addition of PPUP could improves the flame retardant properties of the PF.This phenomenon might be attributed to the DOPO structure in PFs,which will create PO free radicals acting as scavengers of H and OH during combustion and may create a char residue acting as a barrier for the polymer matrix.The findings in this part demonstrated that PPUP could overcome their drawbacks of intrinsic brittle,while not reducing the flame retardant properties of the PF.3.Cardanol-based siloxane(SAECD),which has silicon groups and reactive epoxy groups,was synthesized.Then,PFs modified with different contents of SAECD were prepared.The flexural strengths of SAECD-modified was 0.390 MPa,which was increased by 38.79%,when the SAECD in resin was 3%and the pulverization ratio was 22.67%,which was reduced by33.66%.The time to ignition(TTI)of the SAECD-modified foam was delayed by 19 s,the pHRR,mHRR,and THR of the SAECD-modified foam were 41.85 kW/m~2?32.89 kW/m~2 and17.27 MJ/m~2,which were decreased by 9.10%,4.11%and 7.55%,respectively.4.Modified PFs were prepared by using epoxidized cardanol(ECD)as a phenol source to partially replace phenol and introducing 1,3-bis(3-aminopropyl)tetramethyldisiloxane(APTMDS).It is indicated during combustion,the enough APTMDS could form a dense heat insulation charcoal layer,which blocks the escape of decomposition products and the combustion of foams,stops the contact between foams and heat/oxygen sources,and decelerates heat release.When the ECD replaced amount of 4%and APTMDS dosage of1.33%,the compressive strength and bending strength of the modified foams were maximized to 0.281 and 0.363 MPa,respectively,which were 91.16%and 62.0%higher than the pristine PF,respectively.When the ECD replaced amount of 4%and APTMDS dosage of 2.67%,the pHRR and mHRR of modified PF were 34.72 and 27.25 kW/m~2,which were decreased by32.04%and 9.50%,respectively,in comparison to those of pristine PF.It is indicated ECD and APTMDS can synergistically toughen the PF.In addition to the toughening ECD,the main chains of phenolic resins also include the compound structures of ECD/APTMDS,APTMDS/phenol,and interweaved formaldehyde,which together improve the toughness of the modified foams.The findings in this part demonstrated that ECD and APTMDS could be used in the synthesis of PFs to overcome their drawbacks of intrinsic brittle and high flammability.