Nondestructive testing of defects in adhesive joints

Experimental
Materials
PMMA (876 G) having MI: 6g/10min and density1.19g/cc, obtained from M/S GSFC Ltd., India,
has been used as the base polymer matrix. Cloisite 30B (C30B, CEC of 90 meq / 100g clay), Cloisite
20A(C20A, CEC of 95 meq / 100g clay) and Bentone 109 (B109, CEC of 95 meq / 100g clay)
procured from M/s Southern clay products, Inc. Gonzales, Texas and Elementis UK respectively has
been used as organoclays. Maleic anhydride (MA) in presence of Benzoyl peroxide as initiator has
been used as grafting agent for preparing grafted samples.
Preparation of PMMA Nanocomposites:
PMMA and nanoclays were dried at 65 0 C in vaccum oven for a period of 12hrs prior to processing.
PMMA nanocomposites were fabricated using different weight percentage of nanoclays (1, 3 and 5%)
in Haake Rheocord at 180 0 C , 50 rpm for a mixing time of 30 mins. Finally, these premixes were
brought to room temperature and was injection molded using mini Injection molding machine
(Haake R Minijet 557-2270) (Thermoelectron corporation GMDH, Germany) with a barrel temperature
of 200 0 C and mold temperature of 140 0 C with 700 bar injection pressure
Wide angle-X-Ray Diffraction: (WAXD):
Wide angle X-Ray diffraction (XRD) analysis was carried out using Philips X’Pert MPD (Japan),
which had a graphite monochromator and a Cu Kα radiation source operated at 40kv and 30 mA. The
basal spacing or d001 reflection of the samples was calculated from Bragg’s equation by monitoring
the diffraction angle, 2θ from 2-10 0 .
Transmission Electron Microscopy:
Samples for TEM imaging were sectioned using Lieca Ultracut UCT microtome and TEM of
specimens were carried out using JEOL-1200 EX electron microscope at an accelerating voltage of 80
kV.
Thermal Characterization
The melting, glass transition temperature and thermal stability of virgin PMMA and the
nanocomposite samples have been studied using DSC (Perkin-Elmer Diamond DSC, USA) and TGA
(Perkin –Elmer Pyris-7 TGA, USA), respectively.
Mechanical Properties:
Tensile properties were measured as per ASTM-D 638 with gauge length of 25mm, and crosshead
speed of 5 mm/min by using Universal Testing Machine (LR 100K Lloyds Instruments Ltd. UK).
Tests were carried out taking five specimens for each set at a standard temperature 23+2 0 c and 50+2%
RH.
Dynamic mechanical properties:
The dynamic mechanical behaviour of the samples were carried out at fixed frequency of 1Hz and
heating rate of 10 0 C/min in a temperature range of –150 to 200 0 C using DMTA (NETZSCH DMA
242).
Results & Discussion
Wide angle X-ray diffraction:
The WAXD patterns of PMMA/Na+ MMT, PMMA/C30B, PMMA/B109 and PMMA/C20A
nanocomposites and grafted PMMA-g-MA/C30B and PMMA-g-MA/B109 nanocomposites is
depicted in fig.1. The d001 peak in all the organically modified systems were observed within the range
of 2θ =1 to 10 0 indicating intercalation of PMMA chains with in the clay galleries. Comparison of
diffraction patterns of each nanocomposites systems with respective organoclays, C30B, B109 and
C20A reveals that basal spacing increases from 18.5 A 0 to 39.4 A 0 in PMMA/ C30B, 30.0 A 0 to 35.3
A 0 in PMMA/ B109 and 24.2A 0 to 33 A 0 in PMMA/C20A nanocomposites respectively. However, in
case of PMMA/ Na+ MMT nanocomposites agglomeration and intercalation was observed. Since
there was no evidence of peak intensity within the investigated experimental range. Nevertheless,
broadening of the peak was noticed which is probably due to macroscopic interaction between Na+
MMT & PMMA that might have resulted in dispersion of clay stacks with in the PMMA matrix. As
reported by Sandeep Kumar et al. (9) some level of reduction in the no. of clay platelets per stacks in
the polymer matrix might have resulted between Na+ MMT & PMMA from either the processing
methods used in the fabrication of the nanocomposites or due to favourable interactions between