Nondestructive testing of defects in adhesive joints

2.7. Fabrication of curcumin eluting polymer films and its structure
Curcumin loading in EVA grades was achieved by preparing solutions of polymer and
curcumin and cast on glass plates. Cast films were washed with de-ionized water and air-dried. FT-IR
spectra of the curcumin loaded EVA grades were recorded on a Thermo Nicolet 5700 spectrometer
(Thermo Scientific, Germany).
2.8. Contact angle measurement
Contact angle of the films are measured at room temperature (~23 o C) using the sessile drop
method by a video based contact angle measuring device (Data Physics OCA 15 plus, Germany) and
imaging software (SCA 20). Five independent measurements were performed on different region of
the sample surface.
2.9. Curcumin release profile
Samples of 1 cm 2 surface area were cut from the curcumin loaded polymer films and
suspended in 5ml phosphate buffered saline (PBS) at 37 o C and placed in a shaking water bath (Julabo,
SW22, Germany) at 60rpm. At definite time intervals whole quantity of PBS was withdrawn and fresh
PBS was added. Elution kinetics was monitored using UV spectroscopy at a wavelength of 420nm for
a period of 15 days.
3. Results and discussion
3.1. Physico-chemical characterization of Curcumin, EVA grades and Curcumin loaded
EVA
Solubility of EVA grades tends to increase with increase in vinyl acetate content in the
polymer. EVA-40 was found to be soluble in a number of organic solvents such as tetrahydrofuran,
toluene, dichloromethane, cyclohexane, etc. FTIR spectra of EVA, Curcumin and Curcumin-loaded
EVA matrices are shown in the Figure 1. Spectra of EVA shows characteristic absorption peaks at
1735.9 cm -1 due to the stretching vibrations of C = O. A peak in the region 2872 and 2956 cm -1
corresponds to symmetric and asymmetric stretching vibration of C-H bond. A peak was observed in
the region 1143cm-1 corresponding to C-O-C stretch. The spectrum of Curcumin shows characteristic
aromatic absorption peaks in the range 1600.1 to 1504.9 cm -1 . A broad peak in the region from 3223.6
to 3508.6 cm -1 indicates the presence of OH. A feeble peak was observed at 1624.8cm -1 corresponding
to C=O, C-O-C peak was obtained at 1272.7 cm -1 , benzoate trans-CH in CH=CH obtained at 959.2
cm -1 , cis CH in aromatic at 713 cm -1 . The spectra of polymer matrix incorporated with Curcumin
(10wt%) does not exhibit any shift in peaks with respect to the characteristic peaks discussed above.
From these results it is clear that curcumin incorporated in the EVA matrix does not undergo any
reaction or complexation with the matrix.
The storage modulus and tan delta of EVA grades and curcumin loaded EVA are given as a
function of temperature in figure 2. It may be seen that the two grades of EVA, i.e., EVA 12 and EVA
18 have higher modulus compared to EVA 28 and EVA 40. All the EVA grades show glass transition
in the range -15°C to -19°C. EVA 40 shows lower modulus because it has maximum vinyl acetate
content which increases the flexibility of the polymer and hence increased the damping. Incorporation
of Curcumin on to EVA matrices does not alter the characteristic glass transition temperature of the
matrices. However, substantial increase in storage modulus is evident.
Mechanical properties of EVA grades are given in Table 1. Depending upon the vinyl acetate
content and source of EVA grades properties tends to vary. Effect of addition of curcumin in EVA-40
3