Nondestructive testing of defects in adhesive joints

Experimental:
Materials:
Reagent grades of Diamino Diphenyl Methane, Epichlorohydrin, ethyl alcohol, lithium
hydroxide mono hydrate, sodium hydroxide, toluene, Diamino Diphenyl Sulphone and
Triethylene tetramine were obtained from E-Merck India limited, Mumbai and were used without
further purification.
Synthesis of tetra glycidyl diamino diphenyl methane (TGDDM):
Diamino diphenyl methane, epichlorohydrin and 60 ml of ethyl alcohol were added with
water, and the mixture was stirred at 75° C for 6 hours. Then the reaction mixture was brought to
55° C while 30% NaOH solution added over 5 hours. Excess water and epichlorohydrin were
removed by distillation under reduced pressure (30 mm Hg) . The residue was dissolved in
toluene and washed with water to remove salts and residual caustic.
Curing:
4,4’- diamino diphenyl methane(DDM), 4,4’- diamino diphenyl sulphone(DDS)
and tri ethylene tetramine (TETA) were used as the curing agents, in which each
hydrogen on an amine nitrogen will be reactive and can open one epoxide ring to form a
covalent bond. The correct relative amounts of TGDDM and curing agents were
determined by computing the weight of curing agent that contains one chemical
equivalent of amine hydrogens and matching that with the weight of TGDDM that
contains one chemical equivalent of epoxide groups.
Analytical methods:
Fourier transform infrared spectroscopy:
The FTIR of virgin Tetraglycidyl Diamino Diphenyl Methane was done. the apparatus
used was PERKIN-ELMER make.
Scanning Rate: 16 scans
Resolution: 4 cm -1
Nuclear magnetic resonance spectroscopy (NMR):
The proton ( 1 H) Nuclear Magnetic Resonance spectroscopic study and carbon ( 13 C)
Nuclear Magnetic Resonance spectroscopic study were performed in a Bruker 500 MHz NMR
spectrometer using CDCl3 as the solvent.
Thermo gravimetric analyzer:
The TGA equipment used was TGA Q 50 V 20.5, from TA instruments, where the
temperature range is taken from 20°C to 750°C, at a heating rate of 10°C/min in nitrogen
atmosphere.
Differential scanning calorimetry:
The DSC equipment used was DSC Q 20 V 23.5, from TA instruments, where the
temperature range was taken from 20°C to 300 °C, at a heating rate of 10°C/min, in nitrogen
atmosphere.