Nondestructive testing of defects in adhesive joints

Sustained release of the above drugs to the affected area may be possible by loading these
drugs into suitable matrices. Ethylene vinyl acetate (EVA) copolymer, a heat processable, flexible
and stable material [7] is commercially available with vinyl acetate (VAc) content varying from 3 to
50%. The properties of EVA vary with VAc content. Vinyl acetate content up to 10% is more
transparent, flexible and tougher than LDPE. Between 15 and 30% VAc content copolymers are soft
and flexible. Compounds with 30–40% VAc are soft, elastic and their strength and adhesion
properties are desirable for coatings and adhesives [8]. Between 40 and 50% VAc content in EVA
produce rubber like properties [8]. In this study curcumin is incorporated in EVA copolymers by
casting method and sustained release of curcumin is evaluated.
2. Experimental
2.1. Materials
Polymer matrices used for this study are: (a) EVA grades of vinyl acetate content 12%
(NOCIL, India), 18% (Aldrich, USA), 28% (NOCIL, India) & 40% (Aldrich, USA). Curcumin (tradenamed
Biocurcumax) was obtained from M/s Arjuna natural extracts Ltd., Aluva, Kerala. Solvents
used in the study were of 99.5% purity and were obtained from s.d. fine chemicals, Mumbai.
2.2. Differential scanning calorimetry
DSC analysis of curcumin was done based on the ASTM E 1356-03 standard using DSC 2920
by TA Instruments Inc., USA. The test was done in nitrogen atmosphere (99.99% N2 and 1 ppm
moisture, 1 ppm O2) using an empty aluminum pan as the reference material. The scan temperature
ranged from -50°C to 200°C at a heating rate of 10°C/min.
2.3. FT-IR analysis
FT-IR spectra of the curcumin were recorded on a Thermo Nicolet 5700 spectrometer with a
diffused reflectance sample holder (Thermo Scientific, Germany).
2.4. Dynamic Mechanical Analysis
Dynamic Mechanical Analysis (DMA) was performed using a Tritec 2000B DMA (Triton
Technology Limited, UK). Storage modulus and damping characteristics of EVA grades and
curcumin loaded matrices were determined as a function of temperature. Temperature scan was done
from (-) 150°C to (+) 100°C at a frequency of 1 Hz. The heating rate used was of 1 o C/min.
2.5. Tensile properties
The tensile properties of EVA grades and curcumin loaded EVA were measured by using an
Instron (model 3345) Universal Testing Machine equipped with a 100N load cell. Dumbbell shaped
test samples were cut from cast films. The samples were conditioned at 23±1°C and at 50% relative
humidity, and the test was performed at a crosshead speed of 100 mm/minute.
2.6. Solubility test
About 0.1 gm of polymer was taken in a 50ml beaker and 10ml solvent was added to it. This
was kept on a hot plate stirrer (Schott Instrument, Germany) and slightly heated along with
continuous stirring to dissolve the polymer.
2