Nanocomposites
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The rheology of polymer nanoclay composites is extremely
sensitive to the clay dispersion, loading and orientation. Polymer layered
silicate nanocomposite melts exhibit a visco-plastic rheology with an
apparent yield stress below which the melt consists of a percolating network
of clay tactoids and above which these tactoids rapidly orient along the flow
direction. The adjoining figure shows the flow alignment of clay tactoids
with increasing shear stress as captured by rheo-XRD measurements using the Cambridge
MultiPass Rheometer. (J. Rheol., 46, 427; Macromolecules , 2001,
34, 3412)
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Stick-slip
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Wall-slip is a phenomenon that limits the productivity of
melt-extrusion processes for highly entangled polymers such as polyethylene.
The stick-slip transition above a critical wall shear stress in extrusion was
modeled by developing a constitutive equation using tube (reptation) theories
to describe the coupled dynamics of bulk chains and of the strongly adsorbed
end-tethered chains under various regimes of wall grafting density. As shown
in the figure the molecular origin of the stick-slip instability is related
to a sudden stretching of tethered chains and their consequent disentangling
from bulk chains above a critical
stress. (J. Rheol., 2002, 46,
1091; Macromolecules, 2001, 34, 852)
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Fingerprinting
We undertake research to help our industrial clients understand
the structure-property relationships in their resins and explain the scientific
reasons for better performance of leading resins in the markets. The figure
shows how the die swell of two blow molding resins is intimately linked to
their MWD. The resin with lower polydispersity exhibits higher transient die
swell due to rapid relaxation.
Product development
We
undertake specific product development activity for our customers. For example, we have developed a PP- glass composite compound having a targeted set of mechanical properties. The adjoining figure
shows the 3-phase morphology of the PP-composite in which the glass fibers have
excellent adhesion to the matrix and the matrix itself consists of uniformly
dispersed fine domains of a polyamide. Several polyester-glass pultruded
profiles were developed using the pilot-scale PULTREX pultrusion facility in
the PPC. The include C-, I-, rod, and notched section profiles for applications
in gratings and ladders.
Advance training programs
We offer our customers tailor-made training programs that are
designed with the aim of providing industrial personnel with a glimpse of the
complex interlinkages between the various life-stages of polymers from
manufacturing to market performance. We also offer modular training programs on
specific specialized topics such as rheology and characterization of polymers
by GPC, involving handson experience with equipment, data generation, analysis and
interpretation.
In-house development
of new equipment:
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A preparative temperature rising elution fractionation equipment
was designed and built at NCL by our group. Reproducibility of the eluted
weight fractions of a ZNLLDPE resin obtained from programmed heating steps
after a slow cooling cycle is shown in the figure. Other equipment that we
plan to build in the near future include rheo-optical setups for measuring
flow birefringence and light scattering during flow.
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