Complex
Fluids & Polymer Engineering
Overview
The central theme of work in the group is to understand the links between the microstructure of complex fluids and their fluid and solid-state properties. These links are related to the kinetics and thermodynamics of structure formation on one hand and on the other hand, to the performance of materials and products. While the current work is primarily focused on polymeric materials, future interests include nano-dimensional materials and soft solids.
Mission
& Goals
To add value to our customer's business by providing a fundamental understanding of structure-property relationships for their materials, innovative solutions to problems related to materials processing and performance, and information analysis and continuing education services relevant to their business.
Competencies
Research competency includes quantification of structure flow-property-performance linkages, development of experimental tools for structural characterization including methods, and modeling and simulations of polymer engineering problems. We provide consulting, problem solving, information analysis and continuing education services to the industry. Additional competencies include providing project leadership and management skills for driving industrial sponsored projects, business development and participating in institutional systems planning and processes.
Facilities
The laboratory is equipped with three state-of-the-art rheometers; an ARES (controlled strain rheometer), BOHLIN CVO-50 (controlled stress rheometer) and RHEOVIS 2100 (high shear capillary rheometer). Together these allow for measurement of all material functions of complex fluids under shear flow. The group is currently developing rheo-optical techniques to study stress-birefringence in viscometric and complex flow fields. The group is also building the capability to do POLYFLOW viscoelastic CFD simulations to match rheo-optical data and perform extrusion simulations. The group also uses the pilot scale polymer processing and mechanical testing facilities in the Polymer Processing Centre (PPC) such as the Berstoff ZE-25 twin-screw extruder, Haake Polylab, Arburg injection molding machine, Instron UTM and Ceast Izod impact tester. In the near future our group plans to acquire a Linkam shear cell for scattering & flow visualization and a DSM microcompounder and microinjector.
Glimpses
of current research
Nanocomposites
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)
Stick-slip
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 (repetition) 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)
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
hands on experience with equipment, data generation, analysis and
interpretation.
In-house development of new equipment:
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.
Contact
Dr. Ashish Lele
National Chemical Laboratory ,
Pune 411 008
Email
:lele@cfpe.ncl.res.in
Phone
:+91-20-2589 3300 (extn 2199)
Fax
:+91-20-2589 3041