Nondestructive testing of defects in adhesive joints

2. Experimental Details
Polypropylene was obtained from Reliance Industries Ltd, India (REPOL H200F, melt flow index
of 20 g/10min). MWNT were obtained from Nanocyl CA Belgium (NC 3100, L/D=100-1000,
purity=95%) and DMSRDE, Kanpur also subsequently utilized for our study. Various
compositions of PP/MWNT composites using two different types of MWNT were prepared by
melt mixing in a conical twin screw extruder (Micro 5, DSM Research, Netherlands) at optimized
melt mixing condition of 260 0 C with a rotational speed of 200 rpm for 15 min in which MWNT
were varied from 0.5-3 wt%. Melt mixed PP/MWNT samples were dried at 80 0 C under vacuum
over night. PP/MWNT composite were melt-spun using a small scale spinning machine
manufactured by the Bradford University Research Ltd. UK, using a single hole spinneret of 1
mm diameter. The fiber spinning was carried out at 200 0 C with ram speed of 1.4 mm/min. The
take up speed was kept at 20 m/min for all compositions. The melt spun fibers were further drawn
at draw ratio of 8. The mechanical properties of drawn fiber were tested on a Favimat fiber tester
(Textechno) with guage length of 20 mm and at a rate of 20 mm/min for 50 filaments. Raman
spectroscopy was performed using Jobin Yovon (HR 800 micro-Raman) in the scanning range of
200–2000 cm -1 with incident laser excitation wavelength of 514 nm. Scanning electron
microscopic (SEM) analysis was performed with Hitachi S3400, operated at 15 KV. Wide-angle
X-ray diffraction (WAXD) studies were carried out on a Philips X-Pert Pro. The incident X-rays
(λ=1.54 Å) from the Cu-target were monochromatized using a Ni filter.
3. Result and Discussion
3.1 Comparative study of Nanocyl NC 3100 and DMSRDE MWNT
TEM images of MWNT are shown in Figure (1a, 1b) shows a network of entangled MWNT.
DMSRDE produced MWNT are found to be more straight, less coiled and less entangled as
compared to NC 3100. Figure 1c shows the tangential Raman band for two types of MWNT.
Raman peak at ~1347 cm −1 originates from disordered graphitic structure (D-band) and
peak at ~1590 cm −1 originates from crystalline ordered structure of the graphene sheet (Gband);
the intensity ratio, IG/ID provides a measure of crystalline structure in a given MWNT.
The ratio of intensity of G-band and D-band (IG/ID) depict the order structure of MWNT. IG/ID
value of DMSRDE MWNT (1.31) is found higher than NC 3100 MWNT (0.87) which manifests
DMSRDE produced MWNT are more ordered as compared to NC 3100.
3.2 Orientation studies of PP crystal and MWNT along fiber axis
Figure 2a shows the Wide angle X-ray diffraction (WAXD) pattern for PP/MWNT composites
containing 0.5 wt% MWNT. WAXD pattern of the composites show the typical α -form of PP
crystals and exhibits complete absence of the β -crystal form [6, 7]. Quantification of average
orientation of PP crystal plane has been carried out using WAXD by performing azimuthal scan
along the specific (110) PP crystal plane (Representative Figure 2b). The detail procedure of
quantification of crystal plane orientation is given below.
The crystalline orientation of the fibers has been determined quantitatively using Hermans
orientation factor [8] as generalized to a set of three crystallographic axes by Stein [9]. This is
defined as
2
3 < cos φ > −1
f =
2
(1)