Nondestructive testing of defects in adhesive joints

Optimization of Various Reaction Parameters
Optimized reaction conditions for getting maximum grafting were: MA (2.21 x 10 -3 mol L -1 );
FAS-H2O2 (molar ratio), 1:4; temperature (ºC), 50; time (min.), 90, and pH, 7.0.
Characterization of Graft Copolymers
FT-IR Spectra of Graft Copolymers
FT-IR spectrum of original flax showed a broad peak at 3422.8 cm -1 which was due to bonded
–OH groups and at 2918.8, 1653.5 and 1058.7 cm -1 arising from –CH2, C-C and C-O stretching,
respectively. However, in case of graft copolymer, an additional peak at 1731.2 cm -1 because of
>C=O group of MA has been observed. This suggests that MA has been graft copolymerized onto
flax fiber through covalent linkages.
Thermal Analysis (TGA/DTA)
The results of TGA have been depicted in Table 1. It is shown that initial decomposition
temperature (IDT) and final decomposition temperature (FDT) of original flax were 279.9 and
489.1 ºC, respectively, whereas, in case of flax-g-poly(MA), IDT and FDT were 313.7 and 478.4
ºC, respectively. Flax-g-poly(MA) showed the higher IDT than flax fiber. The results of TGA
have been supported by DTA studies. DTA of original flax fiber shows the exothermic peaks at
325.3 ºC (13.8 µV) and there has been a continuous exothermic combustion of the sample at
furnace temperature in presence of atmospheric oxygen. This peak shows the disturbance in Hbonded
amorphous region. Another sharp exothermic peak has been observed at 455.3 ºC (38.9
µV), which indicates the complete break down of the crystalline region at this temperature. In
case of flax-g-poly(MA), exothermic peaks at 322.5ºC (24.6 µV) and 380.4ºC (53.1 µV) have
been observed. Thermal stability of flax-g-poly(MA) is not altered very much in comparison to
original flax. This was due to undisturbed crystalline structure of the fiber. Thus, it has been
found that there exists a direct correlation with percentage of grafting and crystallinity.
Scanning Electron Microscopy (SEM)
A clear cut distinction between the scanning electron micrographs (SEM) of original flax and
its graft copolymer reveals that there has been a sufficient deposition of poly(MA) onto flax fiber.
The scans easily verify the fact that cellulosic fibers lying apart in original flax started forming
bundles in the graft copolymers.
Percentage Crystallinity and Crystallinity index of Graft Copolymers
It has been observed that percentage crystallinity and crystallinity index of flax were decreased
a little with grafting (Table 2). There was no comparable difference in the X-ray diffraction
pattern of flax and flax-g-poly(MA). Percentage crystallinity of flax and flax-g-poly(MA) was
3