Nondestructive testing of defects in adhesive joints

original C30B, C20A increased significantly that probably due to more parallel stacking of the
organoclays in the blend matrix.
Transmission electron microscopy (TEM)
To elucidate the dispersion of clay in the blend nanocomposites in detail, figure-2 illustrates the TEM
micrographs of PTT/m-LLDPE/C20A, PTT/m-LLDPE/B109 and PTT/m-LLDPE/C30B. The dark lines
represent the thickness of individual clay layers or agglomerates. Thick darker lines represent stacked
silicate layers due to clustering or agglomeration. It was observed from the micrographs that clay particles
preferentially resided in the PTT phase rather than m-LLDPE phase. In case C30B blend nanocomposites,
it was found that stacked and intercalated silicate layers are well dispersed within the blend matrix
especially in polar phase due to similar solubility parameter. It was interesting to note that the organoclay
has a strong tendency to be located in the PTT phase and the domain size of dispersed particle effectively
reduced, due to obstacle created by exfoliated clay, as shown in figure: 2(b) and(c). However, a mixed
nanomorphology was obtained in both PTT/m-LLDPE/C20A as well as PTT/m-LLDPE/B109
nanocomposites due to presence of regions of ordered /disordered intercalation.
Mechanical Properties of Polymer Blend and Blend nanocomposites
The mechanical properties of PTT/m-LLDPE blend at variable weight percent (1-5 wt%) of m-LLDPE
are depicted in table-1. It is evident that the tensile & flexural properties of PTT decreases with the
increase in m-LLDPE content. This behavior is probably because m-LLDPE is inherently weak and soft
with elastomeric properties due to linearity in its structure with 5-10% branching. Izod impact strength of
PTT was observed to be 26.80 J/m. Incorporation of m-LLDPE to the tune of 10-30% results in an
increase in the impact properties of PTT matrix in the blends. The blend prepared at PTT: m-LLDPE ratio
of 70:30 exhibits maximum impact strength of 33.76 J/m, which subsequently reduces with the increase
in PTT content to 50-wt%. This indicates that m-LLDPE acts as impact modifier due to presence of
metallocene and butene in its structure, at lower concentrations. The blend prepared at 70:30 ratio of PTT:
m-LLDPE has been optimized based on optimum impact performance and has been considered for
fabrication of blend nanocomposites using various organically modified nanoclays.
The mechanical properties of PTT/m-LLDPE blend nanocomposites at various wt.% of organically
modified is also depicted in table-1. It is evident that a tensile property of blend increases with addition of
5 wt% of C20A, B109 and C30B nanoclays. Tensile strength of blend matrix increases from 37.92 MPa
to 50.86 MPa in PTT/m-LLDPE/C20A, 53.24 MPa in PTT/m-LLDPE/C30B and 51.36 MPa in PTT/m-
LLDPE/B109 blend nanocomposites respectively at 5 wt. % of nanoclay loading, which indicates
stiffening effect of nanoclay layers. A similar linear increase in tensile modulus to the tune of 52.1 % in
C20A, 61.5 % in C30B and 57.4 % in B109 respectively was also obtained as compared with the blend
matrix. According to Via and co-workers [38], the interlayer structure of the organically modified layered
silicate should be optimized to attain maximum configurational freedom of the functionalzing chains
upon layer separation and increase the potential reaction sites at the interlayer surface. In the present
context, the methyl tallow bis-2 hydroxy ethyl quaternary ammonium intercalant in C30B has two –OH
groups in its structure, which might have interacted with the carboxylic group of PTT resulting in
enhanced polar-polar interactions of the silicate layer within PTT phase which further contributes to an
increase in tensile properties. A similar increase in the flexural & impact strength of blend
nanocomposites was also obtained. The mechanical performance of the blend matrix varies in the
following order:
PTT/m-LLDPE/C30B > PTT/m-LLDPE/B109 > PTT/m-LLDPE/C20A >
PTT/m-LLDPE.
This further indicates improved interactions in C30B system as compared with C20A and predominant
role of PTT base matrix.
Dynamic mechanical properties (DMA)
The dynamic storage modulus (E’) versus temperature of PTT, PTT /m-LLDPE blend and blend
nanocomposites are shown in the figure-3. A gradual decrease in E’ with increasing temperature from -
150 to 200 0 C was observed. It was noted that incorporation of m-LLDPE decreased the storage modulus
of PTT matrix due to softening of diluting effect of the soft elastomeric phase. Conversely, addition of