Nondestructive testing of defects in adhesive joints

Experimental:
The materials used in this study were polypropylene REPOL H034SG obtained from Reliance
Industries (Pvt.) Ltd., maleated polypropylene (PPMA) selected for this work was FUSABOND
M613-05, which contains 0.65 weight % maleic anhydride group. The organoclay, Cloisite20A
provided by Southern Clay Products Inc. Potassium succinate grafted polypropylene ionomer
(KPPSA) was prepared by simultaneous hydrolysis and neutralization of PPMA using methanolic
KOH. All the nanocomposites were prepared by a melt mixing technique using a twin-screw
extruder, DSM Micro 5 having a net barrel capacity of 5 CC with a screw speed of 100 rpm, the
barrel temperature of 190 °C and a residence time of 10 min. Nanocomposites were prepared with
different concentrations of compatibilizer keeping the organoclay concentration at 5 weight %.
For comparison matrix polymer compositions without clay were also prepared. Nanocomposites
were prepared in two different methods. In the first method, the PP, compatibilizer and the
Cloisite 20A were all melt mixed directly in a single step. In the second method, the
compatibilizer was mixed with the organoclay to form a masterbatch in the first step, which was
then mixed with the PP in the second step. Various compositions prepared were coded in such a
way that the number in the code after the compatibilizer name indicates the percentage of the
respective compatibilizer, C for 5% organoclay, and the method of preparation indicated in the
sample code by D for direct mixing and M for masterbatch route. Structure and morphology of all
the nanocomposites prepared was studied using WAXD and TEM. Flexural moduli of the
nanocomposites prepared were studied using INSTRON and the crystallization behavior was
studied using Differential Scanning Calorimetry (DSC).
Results and Discussion:
Prior to evaluation of the new compatibilizer for dispersability of the organoclay in
polypropylene, binary composites containing 95% compatibilizer and 5% C20A was prepared
and characterized with WAXD. The WAXD pattern (figure 1a) of KPPSA/C20A showed no
peak for the organoclay indicating that the organoclay was completely delaminated and exfoliated
in the KPPSA matrix while PPMA/C20A showed a broad low intensity peak at a d-spacing of 38
Å indicating the presence of intercalated tactoids. The above result clearly indicates that the new
compatibilizer, KPPSA containing more polar ionic functional group have better interaction with
the organoclay than PPMA.
The nanocomposites were prepared by varying the concentration of the compatibilizer keeping
the concentration of the organoclay, C20A, at a constant 5-wt %. Two different mixing routes
such as direct mixing and masterbatch route were used to prepare the nanocomposites. The
properties of the nanocomposites obtained were compared with the nanocomposites prepared
using PPMA as compatibilizer under identical conditions. The WAXD patterns for the
nanocomposites prepared were shown in figure1b-d. Nanocomposites prepared with KPPSA and
masterbatch route showed higher d-spacing for the clay as compared the nanocomposites
prepared with PPMA and direct mixing. At higher concentrations of KPPSA no peak for clay was
observed indicating exfoliation. Typical TEM micrographs of the nanocomposites prepared by
masterbatch route with 25% compatibilizer were shown in figure 2. It is clearly evident from the
TEM pictures that the nanocomposites prepared with 25 wt % KPPSA as compatibilizer show
completely exfoliated structures where the clay layers are completely delaminated and dispersed
homogeneously in the polymer matrix while the nanocomposites prepared with 25% PPMA as
compatibilizer showed intercalant clusters of clay layers suggesting intercalated structures.
Crystallization behaviors of various nanocomposites obtained were studied using DSC. Typical
DSC thermogram curves obtained for various nanocomposites, the matrix polymers and the