Nondestructive testing of defects in adhesive joints

Synthesis and characterization of polypropylene/ionomer/ organoclay
nanocomposites
S. R. Mallikarjuna, N. Ramesh, C. Ramesh and S. Sivaram
Divison of Polymer Science and Engineering, National Chemical Laboratory,
Pune-411 008, Maharashtra, India.
Email: c.ramesh@ncl.res.in
Abstract:
The compatibilization effects provided by ionomer-g-polypropylenes versus those of a maleated
polypropylene, PPMA, for forming polypropylene-based nanocomposites were compared. We
have prepared a novel compatibilizer by grafting ionic functional groups on to the PP and
evaluated its efficiency as compatibilizer in the preparation of PP/clay nanocomposites. The
PP/ionomer/organoclay nanocomposites were prepared by direct melt mixing and by masterbatch
methods and the structure obtained were characterized by WAXD and TEM and were compared
with nanocomposites prepared using PPMA as compatibilizer. Mechanical properties of the
nanocomposites prepared were studied using INSTRON and the crystallization behavior was
studied using Differential Scanning Calorimetry (DSC) and Polarized Optical Microscopy
(POM). Thermal stabilities were characterized using TGA. The dispersion of clay was found to
be dependent on the method of preparation, type of compatibilizer used and the amount of
compatibilizer used. The dispersion of the organoclay was better with the ionomer than PPMA
and the dispersion was better when the nanocomposites were prepared by two step masterbatch
route than the single step direct mixing method. The dispersion of the organoclay improved with
increase in the amount of compatibilizer. The nanocomposites obtained with ionomer as
compatibilizer showed better enhancements in nucleation, thermal properties and mechanical
properties as compared to the nanocomposites obtained using PPMA as compatibilizer.
Introduction:
Polypropylene (PP) is a fast growing thermoplastic and dominating the industrial applications due
to its attractive combination of properties such as low density, high thermal stability, resistance to
corrosion etc. and low cost. There is a strong need to improve their mechanical properties for its
applications in automotive industry 1 . Researchers in the recent decade have shown that
reinforcement with dispersed clay in the polymer matrix enhances the mechanical properties
without much affecting the density of the polymer 2 . Therefore, various research efforts were
made to disperse clay in the PP matrix. However it was very difficult to disperse clay in the PP
matrix, as the polymer was highly non polar and there are no polar groups available to interact
with the clay surface. The usual organo-modification of clay did not sufficiently lower the surface
energy of the clay to interact with PP chains. Unmodified polyolefins lack the intrinsic
thermodynamic affinity with currently available organoclays to form well dispersed
nanocomposites 3 . The surface energy of PP chains was improved by introducing polar
functionalities and used them for the preparation of nanocomposites 4-10 . To improve the surface
energy of semi crystalline polymers in the preparation of nanocomposites, many researchers
introduced ionic groups on to the polymer chains 11-19 . However compatibilizers such as amine and
ammonium functionalized PP had failed to enhance the dispersion of clay in the PP matrix as
compared to maleic anhydride grafted polypropylene via melt mixing 20 .
Therefore in the present work, we have evaluated a novel metallic ionomer of PP as
compatibilizer for preparing PP/organoclay nanocomposite by two different mixing routes. The
properties of the obtained nanocomposites were compared with the nanocomposites, which are
prepared using PPMA as compatibilizer.