Sunil,K Narayanankutty(Taylor & Francis Inc., August 23, 2004)
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Abstract:
The rheological characteristics of short Nylon-6 fiber-reinforced Styrene
Butadiene rubber (SBR) in the presence of epoxy resin-based bonding agent were
studied with respect to the effect of shear rate, fiber concentration , and temperature
on shear viscosity and die swell using a capillary rheonzeter. All the composites
containing bonding agent showed a pseudoplastic nature, which decreased
with increasing temperature. Shear viscosity was increased in the presence of
fibers. The temperature sensitivity of the SBR matrices was reduced on introduction
of fibers. The temperature sensitivity of the melts was found to be lower at
higher shear rates. Die swell was reduced in the presence of fibers. Relative viscosity
of the composites increased with shear rate. In the presence of epoxy resin
bonding agent the temperature sensitivity of the mixes increased. Die swell was
larger in the presence of bonding agent.
Asokan, K; Dr.Ramamohan, T R(Regional Research Laboratory(CSIR), September , 2003)
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Abstract:
We present a novel approach to computing the orientation moments and rheological
properties of a dilute suspension of spheroids in a simple shear flow at arbitrary Peclct
number based on a generalised Langevin equation method. This method differs from
the diffusion equation method which is commonly used to model similar systems in that
the actual equations of motion for the orientations of the individual particles are used
in the computations, instead of a solution of the diffusion equation of the system. It
also differs from the method of 'Brownian dynamics simulations' in that the equations
used for the simulations are deterministic differential equations even in the presence of
noise, and not stochastic differential equations as in Brownian dynamics simulations.
One advantage of the present approach over the Fokker-Planck equation formalism is
that it employs a common strategy that can be applied across a wide range of shear and
diffusion parameters. Also, since deterministic differential equations are easier to simulate
than stochastic differential equations, the Langevin equation method presented in
this work is more efficient and less computationally intensive than Brownian dynamics
simulations.We derive the Langevin equations governing the orientations of the particles in the
suspension and evolve a procedure for obtaining the equation of motion for any orientation
moment. A computational technique is described for simulating the orientation
moments dynamically from a set of time-averaged Langevin equations, which can be
used to obtain the moments when the governing equations are harder to solve analytically.
The results obtained using this method are in good agreement with those available
in the literature.The above computational method is also used to investigate the effect of rotational
Brownian motion on the rheology of the suspension under the action of an external force field. The force field is assumed to be either constant or periodic. In the case of con-
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stant external fields earlier results in the literature are reproduced, while for the case of
periodic forcing certain parametric regimes corresponding to weak Brownian diffusion
are identified where the rheological parameters evolve chaotically and settle onto a low
dimensional attractor. The response of the system to variations in the magnitude and
orientation of the force field and strength of diffusion is also analyzed through numerical
experiments. It is also demonstrated that the aperiodic behaviour exhibited by the
system could not have been picked up by the diffusion equation approach as presently
used in the literature.The main contributions of this work include the preparation of the basic framework
for applying the Langevin method to standard flow problems, quantification of rotary
Brownian effects by using the new method, the paired-moment scheme for computing
the moments and its use in solving an otherwise intractable problem especially in the
limit of small Brownian motion where the problem becomes singular, and a demonstration
of how systems governed by a Fokker-Planck equation can be explored for possible
chaotic behaviour.
Latex waste products contain rubber hydrocarbon of very high
quality, which is only lightly cross linked. Selected wastes such as thread waste
and glove waste were modified into processable materials by a novel economic
process and thermoplastic elastomers were prepared by blending these modified
waste materials with high density polyethylene in various proportions. The
mechanical properties as well as the rheological behaviour of these blends were
evaluated and compared with those of the natural rubber-high density
polyethylene blends.
Latex waste like glove waste was effectively modified using a new reclaiming
agent, thiocarbanilide. This modified waste was blended with linear low-density
polyethylene (LLDPE) to develop a novel thermoplastic elastomer. Both uncrosslinked
and dynamically crosslinked blends were prepared and their properties
were studied. The results were found to be comparable to those of conventional
thermoplastic elastomers.