Nondestructive testing of defects in adhesive joints

for packaging owing to their low cost of production, higher tensile strength, gloss and versatility [8].
Therefore, increase in its consumption leads to littering and causes environmental problem. So,
polypropylene was taken as the material for investigation in the present study.
The degradation behaviour of PE using various photoinitiators under natural weathering
condition was investigated [9, 10]. The photodegradation behaviour of polypropylene under natural
weathering conditions using non-toxic transition metal carboxylate as prodegradant has not been
pursued earlier. Iron stearate was taken as the prodegradant for polypropylene and the photodegradability
of polypropylene under natural weathering situations was investigated and the results
are discussed.
Experimental
Materials
Stearic acid, potassium hydroxide, ferric sulphate monohydrate were used as received to
synthesize ferric stearate. Iron salt of stearic acid (MF01) was synthesized by reacting ferric sulphate
monohydrate with the potassium salt of the fatty acid. Polypropylene (Repol Grade H100EY)
obtained from Reliance Industrial Limited, Jamnagar, India was chosen for the present study. The
virgin polypropylene (4Kg) was blended with 0.2% of prepared prodegradant using a blender. The
virgin PP and the prodegradant blended PP were blown into films using an extruder (Film width =
36cm and Film thickness = 60μm).
Methods
The films were naturally weathered on a suitably designed and fabricated outdoor exposure
rack, which was located in the premises of Kamaraj College of Engineering and Technology, S.P.G.C.
Nagar, K.Vellakulam Post - 625 701, Virudhunagar, India. The natural weathering of all PP films was
carried out from December 2006 to March 2007 (winter season) and May 2007 to July 2007 (summer
season). During the course of natural weathering the average temperature, pressure and humidity were
about 34 °C, 748 mmHg and 40 % rel. respectively. The average visible and UV light intensity were
937 x 10 2 LUX and 998 uW/cm 2 respectively. The sampling was done at regular intervals to assess
the changes occurring in the material during the natural weathering. Fourier Transform Infrared
Spectrophotometry (FTIR), Universal Testing Machine (UTM) and Scanning Electron Microscopy
(SEM) were utilized to follow the chemical and physical changes occurring in the material.
Results and Discussion
FTIR Studies
From the FTIR spectra of the weathered PP samples, hydroperoxide, hydroxyl, carbonyl,
lactone, ester, carboxylic acid, vinylidene and crystallinity indices have been calculated. The
characteristic infrared absorption frequencies for the different functional groups are listed in Table 1.
In the present work, the band at 974 cm -1 (CH3- rocking) was chosen as the reference peak, because it
remains unchanged during photodegradation process.
Carbonyl index is the most used parameter to monitor the degree of degradation in polyolefins
[11]. The carbonyl index was calculated as the ratio of the maximum absorbance at 1715 cm -1 to the
absorbance at 974 cm -1 . The carbonyl index value increases with increasing exposure period only after
certain days of exposure, which can be taken as the induction period for degradation. From Fig. 1, it is
clear that PP weathered at winter season starts to degrade after 50 days of exposure whereas for PP
weathered during summer season, the induction period for degradation was found to be 40 days.
Incorporation of the prodegradant (iron stearate, MF01) in PP drastically reduces this induction period.
These results confirm the fact that the added prodegradant plays an important role to induce
photodegradation. Environmental conditions like temperature, UV intensity, visible light intensity,
etc., also play a definite role in the photodegradation behaviour of PP. In general, carbonyl groups