| Environmental pollution and fossil depletion are two major problems which we are facing in modern society.Therefore,green sustainable development technology has attracted much attention and become one of the hottest research fields.Epoxy resin,as one of the most important thermosetting resins,has been widely used in fields of coatings,adhesives,electronic appliances,automobiles,and aerospace.However,epoxy resin mainly originates from non-renewable petroleum resources,which does not meet the requirements of green and sustainable development.Furthermore,epoxy resin has the defects of flammability and brittleness,which greatly limits its applications.Therefore,it is of great practical significance to develop bio-based flame-retardant and toughened epoxy resin to replace the existing petroleum based one.Aimed to overcome the problems of epoxy resin,such as dependence on petroleum resources,flammability and brittleness,we utilized the unique chemical structure of cardanol to synthesize cardano 1-based flame retardants,cardanol-based epoxy monomers and cardanol-based intrinsic flame retardant epoxy monomers based on molecular design in this thesis.The high-performance cardanol-based epoxy resin with flame retardancy,toughness and heat resistance was further prepared,based on the principle of "nanocomposite" and "synergistic flame-retardant".The main contents of this thesis are summarized as follows:1.A new flame retardant and toughening agent(PTCP)based on cardanol,phosphorus oxychloride and DOPO was synthesized by phenol hydroxyl substitution reaction,epoxidation of side chain double bond and ring opening reaction.A series of flame-retardant and toughening epoxy composites were fabricated by adjusting the PTCP loading.The results of 1H NMR and 31P NMR confirmed the successful synthesis of PTCP.The TGA results showed that the decomposition of PTCP in advance was helpful to the carbonization of epoxy matrix and to protect the polymer from further decomposition.The flame retardancy of the epoxy composite increased with the increase of PTCP content,and the LOI of the EP composite with 30%PTCP was as high as 30.5%.Compared with pure EP,PHRR,THR and av-EHC of the EP composite with 30%PTCP decreased by 50%,27%and 32%,respectively.The enhancement of flame retardancy was mainly due to the increase of char residue,which can effectively inhibit the transfer of volatile combustible gas products,oxygen and heat between the combustion zone and the internal matrix.In addition,compared with pure EP,the impact strength of EP/PTCP-30%composite increased from 14.85 kJ/m2 for EP to 19.14 kJ/m2,indicating that PTCP had a good toughening effect on epoxy system.The toughening mechanism of PTCP was attributed to the flexibility of long carbon chain of cardanol.2.Firstly,a DOPO-derived diamine(BA-DOPO)was synthesized from aniline,DOPO and 4-aminoacetophenone.Then,a phosphorus-containing cardanol-based benzoxazine monomer(CBz)was synthesized from cardanol,BA-DOPO and paraformaldehyde by Mannich reaction.CBz was used as co-curing agent to improve the flame retardancy and toughness of epoxy system.In addition,based on the nanocomposite flame-retardant technology,different contents of CBz were combined with boron doped graphene(BG)in order to further improve the flame-retardant efficiency and thermal stability of epoxy resins.The flame-retardant performance,thermal stability and mechanical property of epoxy/CBz/BG system were compared with those of epoxy/CBz system.The results of FTIR and 1H NMR confirmed the successful synthesis of BA-DOPO and CBz,and the results of XRD,Raman,XPS and TEM manifested the structure and morphology of BG.The results showed that the introduction of CBz into epoxy system can not only endow the composite with excellent flame retardancy,but also improve its glass transition temperature(Tg)and impact strength.Compared with pure epoxy,the PHRR of epoxy composite with 13 wt%CBz and 2 wt%BG decreased by 48%and the impact strength increased by 22%.The comprehensive properties of epoxy/CBz/BG composites were greatly improved owing to the good synergistic effect of CBz and BG:the unique dual functional structure of CBz made it give epoxy resin good flame retardant and improve its toughness simultaneously,while BG had excellent barrier effect and high heat-resistant degradation performance,which could improve the heat-resistant degradation of matrix and inhibit heat and mass transfer to block the exchange of heat and combustibles in the combustion process.Thus,the combination of CBz and BG can significantly improve the flame retardant,thermal and mechanical properties of the epoxy composites.3.In order to reduce the negative effect of low molecular-weight additive-type cardanol-based flame retardant on the mechanical properties and thermal stability of epoxy resin,three kinds of cardanol-based phenolic resin containing phosphorus were synthesized by polymerization.Specifically,the cardanol-formaldehyde resin(CFR)was synthesized by condensation polymerization of cardanol and formaldehyde with ammonia as catalyst,and three phosphorus-containing cardanol-based phenolic flame retardants coded as CF-PO(OPh)2,CF-POPh2 and CF-PPh2 were further synthesized by substitution reaction between CFR with diphenyl phosphoryl chloride,diphenylphosphinic chloride and chlorodiphenylphosphine,respectively.The"structure-property relationship" between these three phosphorus-containing cardanol-based phenolic flame retardants with different phosphorus valence states and their flame retardant epoxy resins was studied,and the phosphorus-containing cardanol-based phenolic flame retardant with the highest flame retardant efficiency was screened out.The results showed that all the three phosphorus-containing cardanol-based phenolic flame retardants had good flame-retardant and toughening effect on epoxy resin,among which CF-PO(OPh)2 exhibited better thermal and flame-retardant properties than CF-POPh2 and CF-PPh2.For EP/CF-PO(OPh)2-10 composite,the char residue at 700℃ under nitrogen was 20%(pure EP was only 13.1%),LOI was as high as 32%,and it can pass UL-94 V-0.The PHRR,THR and FIGRA were 53.8%,13.8%and 67.3%lower than those of pure epoxy,respectively.The impact strength,tensile strength and elongation at break were increased by 30.8%,80.7%and 77.9%,respectively.In order to obtain flame-retardant and toughened bio-based epoxy resins with both low heat release and low smoke release,we combined CF-PO(OPh)2 with a core-shell structure SiO2@MOF hybrid nano-material.The influence of SiO2@MOF on the emission of toxic smoke and gases during the combustion of epoxy resin was studied.The results of flame-retardant test showed that compared with pure epoxy,co-addition of 3 wt%of CF-PO(OPh)2 and 2 wt%SiO2@MOF led to reduction of the PHRR and THR by 27.9%and 20.2%,respectively.It was noteworthy that the tensile strength was increased by 93.5%compared to pure epoxy,which was also better than that of the flame retardant epoxy system with only 5%CF-PO(OPh)2.These results aforementioned demonstrated SiO2@MOF showed good synergistic flame-retardant and mechanical strengthening effect in combination with CF-PO(OPh)2.4.In order to meet the requirements of green and sustainable development and prepare bio-based epoxy resin with thermal stability and mechanical properties,three kinds of cardanol-based phenolic epoxy resins were synthesized from the cardanol formaldehyde resin(CFR)synthesized in the previous chapter,which were used to completely replace the DGEBA epoxy system.(1)The first kind of cardanol-based phenolic glycidyl ether(CFGE)was synthesized from CFR and epichlorohydrin by phenol hydroxyl substitution reaction,with Benzyltriethylammonium chloride and sodium hydroxide as catalysts.(2)The second kind of cardanol-based phenolic epoxy resin(ECF)was synthesized by epoxidation of side chain double bond in CFR,with m-chloroperoxybenzoic acid as oxidant.(3)The third kind of cardanol-based phenolic epoxy resin(ECFGE)was obtained by further epoxidation of side chain double bond in CFGE.These three kinds of cardanol-based phenolic epoxy resins were cured by 4,4-diaminodiphenylmethane(DDM),then the behaviors of the cured products were comparatively studied and compared with commercial DGEBA.The results showed that ECFGE/DDM had higher thermal stability,mechanical properties and lower fire risk than CFGE/DDM and ECF/DDM;however,CFGE/DDM and ECF/DDM showed higher toughness,and the elongation at break increased from 3.08%(DGEBA/DDM)to 12.58%and 32.56%,respectively.The thermal stability of ECFGE/DDM was comparable to that of DGEBA/DDM,and the tensile strength of the former was 16.1%higher than that of the latter.Meanwhile,the PHRR of ECFGE/DDM are 46.0%lower than those of DGEBA/DDM.In addition,CF-PO(OPh)2,which was the most efficient flame retardant selected in Chapter 4,was introduced into ECFGE/DDM system.The ECFGE/DDM with 15 wt%CF-PO(OPh)2 passed UL-94 V-0 classification,and its LOI was increased to 31.0%from 26.0%for ECFGE/DDM system.Compared with ECFGE/DDM system,the PHRR and THR decreased by 48.0%and 21.3%,respectively,while the tensile strength,elongation at break and impact strength increased by 12.77%,130.6%and 18.2%,respectively.5.Based on the molecular design,two kinds of phosphorus-containing cardanol-based epoxy monomers were synthesized:(1)The first kind of phosphorus-containing cardanol-based epoxy monomer(ECF-PO(OPh)2)was synthesized by further epoxidation of side chain double bond in CF-PO(OPh)2,with m-chloroperoxybenzoic acid as oxidant.(2)The second kind of phosphorus-containing cardanol-based epoxy monomer(HECarCP)was prepared from cardanol and hexachlorocyclotriphosphazene with TBAB as phase transfer catalyst,followed by oxidization reaction with m-chloroperoxybenzoic acid as oxidant.The structures of ECF-PO(OPh)2 and HECarCP were characterized by 1H-NMR,31P-NMR,FTIR,epoxy value and GPC.The TGA results showed that the char residue of ECF-PO(OPh)2/DDM and HECarCP/DDM in air was 15.1%and 10.0%,respectively,while that of DGEBA/DDM was only 1.1%.The LOI value of ECF-PO(OPh)2/DDM and HECarCP/DDM was 33.5%and 33.0%,respectively,while that of DGEBA/DDM was only 25.0%.Both the ECF-PO(OPh)2/DDM and HECarCP/DDM could pass the UL-94 V-0 test,whereas the DGEBA/DDM displayed no classification in UL-94 test.Compared to DGEBA/DDM,the PHRR values of ECF-PO(OPh)2/DDM and HECarCP/DDM were declined by 52.1%and 42.2%,and their THR values were also reduced by 29.9%and 7.2%,respectively.In addition,the toughness of ECF-PO(OPh)2/DDM and HECarCP/DDM was significantly higher than that of DGEBA/DDM,and their elongation at break increased to 28.62%and 14.83%,respectively,from 3.14%for DGEBA/DDM. |
