A Study on Curing Behavior

A Study on Curing Behaviour of Benzoxazines on the Properties of Epoxy Resin

\ of Benzoxazines on the Properties of Epoxy Resin

DEEPAK KUMAR (Reg. No. 11013881)

UNDER THE SUPERVISION OFDr. Gagan Deep,Asst. Professor,

DEPARTMENT OF CHEMISTRYLOVELY PROFESSINAL UNIVERSITY

EPOXY RESINEpoxy resin is defined as a molecule containing more than one epoxide groups. The epoxide group also termed as, oxirane or ethoxyline group.

There are two main categories of epoxy resins, namely the glycidyl epoxy, and non-glycidyl epoxy resins. The glycidyl epoxies are further classified as glycidyl-ether, glycidyl-ester and glycidyl-amine.

INTRODUCTION

Glycidyl-ether epoxies such as, diglycidyl ether of bisphenol-A (DGEBA) and novolac epoxy resins are most commonly used epoxies.

These resins are thermosetting polymers and are used as adhesives, high performance coatings ,potting and encapsulating materials. These resins have excellent electrical properties, low shrinkage, good adhesion to many metals and resistance to moisture, thermal and mechanical shock.

In order to extend the application of epoxy resin as electronic material and in the aerospace industry it is crucial to improve its flame and thermal resistance. Several approaches has been reported in the literature for thermal and flame resistance of the resin. Epoxy-benzoxazine polymer has received increasing attention during recent year in attempts to enhance their thermal properties.

OBJECTIVE AND SIGNIFICANE :-

To study the curing behaviour of benzoxazines on the properties of epoxy resin.

To synthesize novel product with flame retardant, good thermal properties and excellent mechanical properties .

METHODOLOGY :-

Following steps will be used during research work:

Literature survey was done to know the advancement, technology, significance, application and progress in the field till today.

Synthesis of Benzoxazine monomers.

. Systematic Curing of DGEBA with Benzoxazine monomers.

The development of benzoxazine based family of phenolic resins prepared by reacting phenols (Bisphenol-A), primary amines, and formaldehyde has attracted significant attention as show in general reaction sechme :

EXPERIMENTAL

X OH + 4CH2O + 2NH2R

N

OX

R

OHWhere X =

R =

Br

Cl

or or

Benzoxazine

CH3

Cl

or

Benzoxazine monomer of varying structure(as shown below)

O

N

O

NH3C CH3

O

N

O

N

Cl Cl

O

N

O

N

Br Br

O

N

O

N

Cl ClBMCF BPBF

BOTF BPCF

For recording DSC traces at a heating rate of 10oC/ min, TA 2100 thermal analyzer having 910 DSC module was used. About 5 mg of sample was used in each experiment.

The samples were prepared by mixing directly DGEBA with each benzoxazine monomers in the molar 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 digit represents the amount of DGEBA and second digit represents the amount of Benzoxazine monomer.

RESULTS AND DISCUSSION:-

The benzoxazine monomers were viscous liquids of yellow colour and became transparent solid on heating. The color of benzoxazine monomers and DGEBA mixture 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 to asymmetrical C-O-C stretching, symmetrical C-O-C and symmetrical C-N-C respectively. The bands observed around 1599-1680 cm-1

were correspond to the C = C stretching of benzene ring. The figure: 1 shows the FTIR Spectrum of benzoxazine monomer (BPBF).

Figure 1 : FTIR Spectra of BPBF

(b) 1H-NMRThe peaks due to methylene group of (O-CH2-N) and (Ar-CH2-N) of oxazine ring were observed at δ 5.2 and δ 4.2 respectively in the 1H-NMR spectra of all the monomers. The aromatic protons were observed at ~ δ 6.3-7.9. The observation of signal at δ 2.4 in case of monomer BOTF, was due to the methyl group joined to the benzene ring. The proton integrations were consistent with the molecular formula of the monomers. The following figure shows the 1H-NMR spectra of benzoxazine monomers BMCF.

H-NMR spectra of 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 of 10oC/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 BPCF

Resin Designatio

n

Ti

(oC)

Tonset

(oC)

Tp

(oC)

Tf

(oC)∆H

(J/g)

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

Table1.1 :- Results of DSC scans of benzoxazine monomers at a heating rate of 10oC/minute

(b) Curing Studies of Benzoxazines and DGEBA

The Results of DSC scans of benzoxazines in presence of varying amounts of DGEBA are summarized

The blending of benzoxazine monomers with DGEBA in different molar ratio could affect the curing of the cross-linked network.

So different benzoxazines like BPCF, BOTF, BMCF and BPBF were used to investigate curing behaviour of DGEBA and results are shown in following tables:

Resin Designation

Ti

(oC)

Tonset

(oC)

Tp

(oC)

Tf

(oC)∆H

(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 27.9

Table 1.2: Results of DSC scans of DGEBA in the presence of BOTF

Resin Designation

Ti

(oC)

Tonset

(oC)

Tp

(oC)

Tf

(oC)∆H

(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 1.3: Results of DSC scans of DGEBA in the presence of BPCF

Resin Designation

Ti

(oC)

Tonset

(oC)

Tp

(oC)

Tf

(oC)∆H

(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 67.3

Table 1.4: Results of DSC scans of DGEBA in the presence of BMCF

Resin Designation

Ti

(oC)

Tonset

(oC)

Tp

(oC)

Tf

(oC)∆H

(J/g)

DBPBF-31167.6 172.6 212.5 261.5 28.5

DBPBF-11 95.7 99.1 173.5 254.8 54.9

DBPBF-13 74.5 99.5 154.3 254.8 141.2

Table 1.5: Results of DSC scans of DGEBA in the presence of BPBF

The results summarized in tables 1.2-1.5 clearly showed that cross linking reactions were dependent on the structure of benzoxazine monomers and the DGEBA and benzoxazine monomer blend composition. However no definite trend was observed for ΔH values as a function of molar ratios for DGEBA and benzoxazine monomers.

No exothermic transition was seen in the DSC scans of cured polymer, thereby indicating the completion of cross linking reaction. The following trend was observed in the DSC scans of benzoxazine monomers alone: 

BPCF ~ BMCF > BOTF > BPBF

CONCLUSION

Curing behaviour of DGEBA in the presence of different benzoxazine monomers was found to be dependent on the molar ratio of DGEBA and benzoxazine monomers in the DGEBA-benzoxazine polymers. Cure temperature decreased upon the addition of DGEBA to the benzoxazine