A Study on Curing Behaviour of Benzoxazines on the Properties of Epoxy Resin DEEPAK KUMAR (Reg. No. 11013881) UNDER THE SUPERVISION OF Dr. Gagan Deep, Asst. Professor, DEPARTMENT OF CHEMISTRY LOVELY PROFESSINAL UNIVERSITY
INTRODUCTIONEPOXY RESINEpoxy resin is defined as a molecule containingmore than one epoxide groups. The epoxide groupalso termed as, oxirane or ethoxyline group.There are two main categories of epoxy resins,namely the glycidyl epoxy, and non-glycidylepoxy resins. The glycidyl epoxies are furtherclassified as glycidyl-ether, glycidyl-ester andglycidyl-amine.
Glycidyl-ether epoxies such as, diglycidyl ether ofbisphenol-A (DGEBA) and novolac epoxy resins are mostcommonly used epoxies.These resins are thermosetting polymers and are used asadhesives, high performance coatings ,potting andencapsulating materials. These resins have excellentelectrical properties, low shrinkage, good adhesion tomany metals and resistance to moisture, thermal andmechanical shock.
In order to extend the application of epoxyresin as electronic material and in the aerospaceindustry it is crucial to improve its flame andthermal resistance. Several approaches has beenreported in the literature for thermal and flameresistance of the resin. Epoxy-benzoxazinepolymer has received increasing attention duringrecent year in attempts to enhance their thermalproperties.
OBJECTIVE AND SIGNIFICANE :- To study the curing behaviour of benzoxazineson the properties of epoxy resin.To synthesize novel product with flameretardant, good thermal properties and excellentmechanical properties .
METHODOLOGY :-Following steps will be used during research work: Literature survey was done to know theadvancement, technology, significance, applicationand progress in the field till today. Synthesis of Benzoxazine monomers.. Systematic Curing of DGEBA with Benzoxazinemonomers.
EXPERIMENTALThe development of benzoxazine based family ofphenolic resins prepared by reacting phenols(Bisphenol-A), primary amines, and formaldehydehas attracted significant attention as show ingeneral reaction sechme : R N X OH + 4CH2O + 2NH2R X O Benzoxazine Where X = OH R= CH3 or or or Cl Br Cl
Benzoxazine monomer of varying structure(asshown below) O O O O H 3C N N CH3 N N B O TF BPC F Cl Cl O O O O N N N N Cl Cl BM C F BPB F Br Br
For recording DSC traces at a heating rate of 10oC/min, TA 2100 thermal analyzer having 910 DSCmodule was used. About 5 mg of sample was used ineach experiment.The samples were prepared by mixing directlyDGEBA with each benzoxazine monomers in themolar ratio of 1:1, 1:3 and 3:1.These have been designated as DBOTF-01, DBOTF-11, DBOTF-13 and DBOTF-31. The first numeral digitrepresents the amount of DGEBA and second digitrepresents the amount of Benzoxazine monomer.
RESULTS AND DISCUSSION:- The benzoxazine monomers were viscous liquids ofyellow colour and became transparent solid on heating.The color of benzoxazine monomers and DGEBAmixture after heating was orange. Characterization of benzoxazine monomers :-(a) FT-IR The characteristic absorption band due to benzoxazine ring present at 1500 5 cm-1 in the spectra of all the benzoxaine monomer .
The bands observed approx. at 1236 cm-1,1031 cm-1 and 1158 cm-1 are due toasymmetrical C-O-C stretching, symmetricalC-O-C and symmetrical C-N-C respectively.The bands observed around 1599-1680 cm-1were correspond to the C = C stretching ofbenzene ring. The figure: 1 shows the FTIRSpectrum of benzoxazine monomer (BPBF).
(b) 1H-NMRThe peaks due to methylene group of (O-CH2-N) and(Ar-CH2-N) of oxazine ring were observed at δ 5.2and δ 4.2 respectively in the 1H-NMR spectra of allthe monomers. The aromatic protons were observedat ~ δ 6.3-7.9. The observation of signal at δ 2.4 incase of monomer BOTF, was due to the methyl groupjoined to the benzene ring. The proton integrationswere consistent with the molecular formula of themonomers. The following figure shows the 1H-NMRspectra of benzoxazine monomers BMCF.
Curing Studies:- In the DSC scans of all samples of monomers, a broad exothermic transition was observed. These transitions were dependent upon the structure of benzoxazine monomers. the DSC scans of samples of BOTF and BMCF at a heating rate of 10oC/minute.
DSC scans of BOTF at a heating rate of10oC/min
The curing temperatures were higher in case of BPCF as compared to BOTF but Δ H value showed an opposite trend when curing behaviour of BOTF was compared with BPCFTable1.1 :- Results of DSC scans of benzoxazine monomers at a heatingrate of 10oC/minute Resin Ti Tonset Tp Tf ∆H Designatio (oC) (oC) (oC) (oC) (J/g) n BOTF 160.4 176.7 226.1 259.6 64.5 BPCF 185.4 191.8 231.9 298.5 126.5 BMCF 185.4 191.5 228.9 254.4 41.3 BPBF 148.8 152.4 221.4 270.9 150.9
(b) Curing Studies of Benzoxazines and DGEBA The Results of DSC scans of benzoxazines inpresence of varying amounts of DGEBA aresummarized The blending of benzoxazine monomers withDGEBA in different molar ratio could affect thecuring of the cross-linked network. So different benzoxazines likeBPCF, BOTF, BMCF and BPBF were used toinvestigate curing behaviour of DGEBA andresults are shown in following tables:
Table 1.2: Results of DSC scans of DGEBA in the presence ofBOTF Resin Ti Tonset Tp Tf ∆H Designation (oC) (oC) (oC) (oC) (J/g) DBOTF-31 147.8 160.6 202.4 241.9 67.8 DBOTF-11 138.4 157.4 198.6 253.6 70.5 DBOTF-13 115.5 127.4 177.3 205.4 27.9Table 1.3: Results of DSC scans of DGEBA in the presence of BPCF Resin Ti Tonset Tp Tf ∆H Designation (oC) (oC) (oC) (oC) (J/g) DBPCF-31 121.9 175.6 220.5 280.7 125.6 DBPCF-11 147.6 165.7 218.4 265.4 122.5 DBPCF-13 128.9 159.4 202.7 288.4 168.6
Table 1.4: Results of DSC scans of DGEBA in the presence of BMCF Resin Ti Tonset Tp Tf ∆H Designation (oC) (oC) (oC) (oC) (J/g) DBMCF-31 167.6 172.4 213.4 266.9 44.4 DBMCF-11 146.5 166.8 211.4 251.4 83.5 DBMCF-13 151.4 159.4 207.9 277.4 67.3Table 1.5: Results of DSC scans of DGEBA in the presence of BPBF Resin Ti Tonset Tp Tf ∆H Designation (oC) (oC) (oC) (oC) (J/g) 167.6 172.6 212.5 261.5 28.5 DBPBF-31 DBPBF-11 95.7 99.1 173.5 254.8 54.9 DBPBF-13 74.5 99.5 154.3 254.8 141.2
The results summarized in tables 1.2-1.5 clearly showedthat cross linking reactions were dependent on the structureof benzoxazine monomers and the DGEBA and benzoxazinemonomer blend composition. However no definite trendwas observed for ΔH values as a function of molar ratios forDGEBA and benzoxazine monomers. No exothermic transition was seen in the DSC scans ofcured polymer, thereby indicating the completion of crosslinking reaction. The following trend was observed in theDSC scans of benzoxazine monomers alone: BPCF ~ BMCF > BOTF > BPBF
CONCLUSIONCuring behaviour of DGEBA in the presence of differentbenzoxazine monomers was found to be dependent on themolar ratio of DGEBA and benzoxazine monomers in theDGEBA-benzoxazine polymers. Cure temperature decreasedupon the addition of DGEBA to the benzoxazine