Rani, Joseph(Wiley InterScience, February 18, 2006)
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Abstract:
In this paper we report the preparation and
dielectric properties of poly o-toluidine:poly vinyl chloride
composites in pellet and film forms. The composites were
prepared using ammonium persulfate initiator and HCl
dopant. The characterization is done by TGA and DSC. The
dielectric properties including dielectric loss, conductivity,
dielectric constant, dielectric heating coefficient, absorption
coefficient, and penetration depth were studied in the
microwave field. An HP8510 vector network analyzer with
rectangular cavity resonator was used for the study. Sbands (2-4 GHz), C band (5-8 GHz), and X band (8-12
GHz) frequencies were used in the microwave field. Comparisons
between the pellet and film forms of composites
were also included. The result shows that the dielectric
properties in the microwave field are dependent on the frequency
and on the method of preparation.
Poly(ethylene terephthalate) (PET) based nanocomposites have been prepared with single walled carbon nanotubes
(SWNTs) through an ultrasound assisted dissolution-evaporation method. Differential scanning calorimetry studies
showed that SWNTs nucleate crystallization in PET at weight fractions as low as 0.3%, as the nanocomposite melt crystallized
during cooling at temperature 24 °C higher than neat PET of identical molecular weight. Isothermal crystallization
studies also revealed that SWNTs significantly accelerate the crystallization process. Mechanical properties of the PETSWNT
nanocomposites improved as compared to neat PET indicating the effective reinforcement provided by nanotubes
in the polymer matrix. Electrical conductivity measurements on the nanocomposite films showed that SWNTs at concentrations
exceeding 1 wt% in the PET matrix result in electrical percolation. Comparison of crystallization, conductivity and
transmission electron microscopy studies revealed that ultrasound assisted dissolution-evaporation method enables more
effective dispersion of SWNTs in the PET matrix as compared to the melt compounding method
A series of short-isora-fiber-reinforced natural
rubber composites were prepared by the incorporation of
fibers of different lengths (6, 10, and 14 mm) at 15 phr loading
and at different concentrations (10, 20, 30, and 40 phr) with a
10 mm fiber length. Mixes were also prepared with 10 mm
long fibers treated with a 5% NaOH solution. The vulcanization
parameters, processability, and stress-strain properties
of these composites were analyzed. Properties such as tensile
strength, tear strength, and tensile modulus were found to be
at maximum for composites containing longitudinally oriented
fibers 10 mm in length. Mixes containing fiber loadings of 30 phr with bonding agent (resorcinol-formaldehyde [RF]
resin) showed mechanical properties superior to all other
composites. Scanning electron microscopy (SEM) studies
were carried out to investigate the fiber surface morphology,
fiber pullout, and fiber-rubber interface. SEM studies showed
that the bonding between the fiber and rubber was improved
with treated fibers and with the use of bonding agent.
A novel method of blending natural rubber with polyvinylchloride in the latex
stage was developed, Dioctyl phthalate (DOP) and Amine terminated natural rubber
(ATNR) were used as plasticisers, for improving the mechanical properties of
these blends. Properties of the latex stage blends were compared with those of
dry blends. Latex stage blends showed superior mechanical properties compared
to the blends prepared in the dry state. The ageing resistance, oil resistance and
processability were found to be improved by latex stage blending.
Isora fibre-reinforced natural rubber (NR) composites were cured at 80, 100, 120 and
150°C using a low temperature curing accelerator system. Composites were also prepared using a
conventional accelerator system and cured at 150°C. The swelling behavior of these composites at
varying fibre loadings was studied in toluene and hexane. Results show that the uptake of solvent
and volume fraction of rubber due to swelling was lower for the low temperature cured vulcanizates
which is an indication of the better fibre/rubber adhesion. The uptake of aromatic solvent was higher
than that of aliphatic solvent, for all the composites. As the fibre content increased, the solvent
uptake decreased, due to the superior solvent resistance of the fibre and good fibre-rubber interactions.
The bonding agent improved the swelling resistance of the composites due to the strong interfacial
adhesion. Due to the improved adhesion between the fibre and rubber, the ratio of the change in
volume fraction of rubber due to swelling to the volume fraction of rubber in the dry sample (V,) was
found to decrease in the presence of bonding agent. At a fixed fibre loading, the alkali treated fibre
composite showed a lower percentage swelling than untreated one for both systems showing superior
rubber-fibre interactions.
A comprehensive overview of reclamation of cured rubber with special emphasis on latex reclamation is depicted in this
paper. The latex industry has expanded over the years to meet the world demands for gloves, condoms, latex thread, etc.
Due to the strict specifications for the products and the unstable nature of the latex as high as 15% of the final latex
products are rejected. As waste latex rubber (WLR) represents a source of high-quality rubber hydrocarbon, it is a
potential candidate for generating reclaimed rubber of superior quality. The role of the different components in the
reclamation recipe is explained and the reaction mechanism and chemistry during reclamation are discussed in detail.
Different types of reclaiming processes are described with special reference to processes, which selectively cleave the cross
links in the vulcanized rubber. The state-of-the-art techniques of reclamation with special attention on latex treatment are
reviewed. An overview of the latest development concerning the fundamental studies in the field of rubber recycling by
means of low-molecular weight compounds is described. A mathematical model description of main-chain and crosslink
scission during devulcanization of a rubber vulcanizate is also given.
Microwave properties of conductive polymers is crucial
because of their wide areas of applications such as coating in reflector
antennas, coating in electronic equipments, firequenry selective .surfaces,
EMI materials, satellite communication links, microchip antennas, and
medical applications. This work involves a comparative study of dielectric
properties of selected conducting polymers such as polyaniline.
poly(3,4-eth),lenedio.syt2iophene), polvthiophene, polvpvrrole. and
pohparaphenylene diazomethine (PPDA) in microwave and DC,fields.
The inicrowave properties such as dielectric constant, dielectric loss.
absorption coefficient, heating coefficient, skin depth, and conductivity in
the microwave frequency (S hand), and DC fields were compared. PEDOT
and polccuiiline were found to exhibit excellent properties in DC
field and microwave frequencies, which make thein potential materials
in many of the alorenientioned applications
Sunil K Narayanankutty(Marcel Dekker , Inc., 2004)
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Abstract:
Blends of styrene butadiene rubber (SBR) with maleic anhydride
grafted whole tire reclaim (MA-g-WTR) have been prepared and the
cure and mechanical properties have been studied with respect to the
reclaim content. The grafting was carried out in the presence of
dicumylperoxide (DCP) in a Brabender Plasticorder at 150'C. The
presence of anhydride group on the WTR was confirmed by infrared
spectrometry (IR) study. The properties were compared with those of
the blends containing unmodified WTR. Though the cure time was marginally higher, the mechanical properties of the blends containing
grafted WTR were better than that of the unmodified blends.
Sunil K Narayanankutty(Taylor & Francis LLC, 2005)
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Abstract:
The thermal degradation of short nylon-6 fiber reinforced acrylonitrile
butadiene rubber (NBR) composites with and without epoxy-based bonding
agent has been studied by thermogravimetric analysis (TGA). It was found that
the onset of degradation shifted from 330.5 to 336.1°C in the presence of short
nylon fiber, the optimum fiber loading being 20 phr. The maximum rate of degradation
of the composites was lower than that of the unfilled rubber compound,
and it decreased with increase in fiber concentration. The presence of epoxy
resin-based bonding agent in the virgin elastomer and the composites improved
the thermal stability. Results of kinetic studies showed that the degradation of
NBR and the short nylon fiber reinforced composites followed first-order
kinetics.
Rani, Joseph(Department of Polymer Science and Rubber Technology, November 8, 2006)
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Abstract:
Copper doped methylene blue sensitized poly(vinyl alcohol) (MBPVA)–acrylamide films were fabricated to improve the
storage life of recorded gratings. The films were fabricated using gravity settling method and the copper chloride
concentration was optimized as 3:18 10 3 mol/l for a dye concentration of 6:2 10 4 mol/l. The gratings recorded on the
optimized film constitution could be stored for months with stable diffraction efficiency (24%) without any chemical or
thermal fixing techniques. The resolution of the material is found to be unaffected with the addition of copper chloride.