Nondestructive testing of defects in adhesive joints

from HiMedia Laboratories, Mumbai, India. The salts silver nitrate (AgNO3) and tri-sodium
citrate (TS) were obtained from E.Merck, Mumbai, India. Standard cultures of the organisms
were provided by the department of Biotechnology, Govt. Model Science College, Jabalpur,
India. The cellulose based filter paper (Whatman No.42) was received from Sameer Science Lab,
Jabalpur, India. The double distilled water was used throughout the investigations.
2.2.Preparation of grafted filter paper (GFP)
The graft- co polymerization of monomer acrylamide onto filter paper was carried out using
ceric ammonium nitrate as free radical initiator by following the same method as has been
reported previously with cotton fabric as substrate [9].
2.3. Loading of silver nanoparticles into grafted filter paper (GFP)
The silver nanoparticles were loaded into the GFP by using a novel approach, developed
in our laboratory [8]. The GFP was put in AgNO3 solution (15 mg AgNO3 in 40 ml distilled
water) for 12 h, then was taken out and put in tri-sodium citrate solution (20 mg dissolved in 25
ml water) for next 12 h to reduce Ag + ions into silver nanoparticles. The material, so produced,
was allowed to dry. In this way, silver nanoparticles-loaded GFP was prepared.
2.4. Water uptake analysis
Completely dry pre-weighed grafted filter paper was put in 200 ml of distilled water at 30ºC
and then its mass was measured at different time- intervals. The percent mass swelling (% Ms)
was calculated using the following expression [10]
% Ms = Swollen weight –Dry weight / Dry weight x 100 …………(5)
All the experiments (i.e. grafting and water uptake analysis) were done in triplicate and average
values have been produced in the data.
2.4.Characterization of silver nanoparticles loaded paper
The silver nanoparticles were characterized by transmission electron microscopy
(TEM). The TEM images were recorded using a Tecnai F 12 TEM instrument. X-ray
photoelectron spectroscopy(XPS), Model ESCALAB Mg K α (hν = 1253.6 eV) with a resolution
of 1.0 x 10 -4 Pa was used to confirm formation of silver nanoparticles.
Microbial experimentation
For qualitative measurement of microbial activity, the filter paper was cut to make a
circle of 7.4 cm diameter, and the antimicrobial activity was tested using modified agar diffusion
assay (disc test). The plates were examined for possible clear zones after incubation at 37º C for 2
days. The presence of any clear zone that formed on the surface of the filter paper was recorded
as an indication of inhibition against the microbial species.
3. Results and Discussion
Graft copolymerization of vinyl monomers onto cellulose has been studied extensively
[11-15]. However, the substrates used in these studies were native cellulose, cellulose pulp or
cotton linters. In our study, we have used filter paper as a substrate for graft- copolymerization.
Indeed, the mechanism of grafting reaction is more or less the same and may briefly be given as
below: In the presence of an acid used, HNO3 (HA), primary radical species formation occurs as a
result of the action of acid on Ce(IV):
Ce
4+
3+
+ HA → Ce + H + A
+
•
2
…………………. (1)