J. Serb. Chem. Soc. 63(10) 753-762 (1998)
UDC 664.2:678.7:678.033
JSCS-2582
Original scientific paper
Blends of thermoplastic starch and some
thermoplastic polymers
KATARINA
JEREMIC, BRANKO DUNJIC, JASNA DJONLAGIC and SLOBODAN JOVANOVIC
Faculty of Technology and Metallurgy,
University of Belgrade, P.O . Box 35-03, Karnegijeva 4, YU-11000 Belgrade,
Yugoslavia
(Received 8
April 1998)
Thermoplastic
starch (TPS) was blended in a twin screw mixer with 5 and 10 mass % of
poly(ethylene-co-acrylic acid) (EAA),
poly(ethylene-co-vinyl
acetate) (EVA) or cellulose acetate (CA) in order to improve the TPS
properties. The influence of such low
amounts of
thermoplastic polymer (TPP) on the processability, mechanical properties and
water resistance of TPS was investigated.
The
specimens for mechanical properties determinaiton were conditioned at 45, 67
and 85% relative humidity (RH) before
measurements.
Processability, characterized by viscosity vs. shear rate dependence, was
determined by capillary rheometry. The
obtained
results showed that the TPS blends behaved as pseudoplastic polymers and that
even 10 mass% of EAA or EVA
significantly
decreased the TPS viscosity, whereas addition of the same amount of CA had no
influence on the TPS viscosity.
Tensile
measurements showed that the RH had a much larger influence on the tensile
properties than the addition of the investigated TPP.
Tensile strength and tensile modulus values for TPS and its blends, after
conditioning at 45% RH were an order of magnitude larger
than the values for the corresponding samples kept at 85% RH, whereas
elongation at break values were nearly ten times smaller.
Dynamic mechanical analysis of the TPS and its blends was performed using a
mechanical spectrometer. The specimens
were
subjected to dynamic torsion at a constant frequency in the temperature range
from 30 to 170°C. The glass transition
temperature,
determined from the temperature dependence of tan d, was influenced much more
by relative humidity than by the type
of TPP
used. The swelling of the TPS and the investigated blends was determined
gravimetrically. It was found that the TPS/EAA blends
had the largest water resistance.
Key words: thermoplastic
starch; blends with poly(ethylene-co-acrylic acid), poly(ethylene-co-vinyl
acetate) and cellulose acetate;
capillary
rheometry measurements; tensile properties; dynamic mechanical analysis;
swelling measurements.
J. Serb. Chem.
Soc. 63(10) 763-771 (1998)
UDC 66,063.61:536.4/548.123/
JSCS-2583
Original scientific paper
Phase inversion temperature (PIT) as a
parameter for the selection of an appropriate nonionic emulsifier
S.
GASIC, B. JOVANOVIC* and S. JOVANOVIC*
Institute for Plant Protection and Environment,
Teodora Drajzera 9, YU-11000 Belgrade and
*Faculty
of Technology and Metallurgy, University of Belgrade, YU-11001, P.O.Box 35-03,
Belgrade, Yugoslavia
(Received
17 June 1998)
In this
paper the method of phase inversion temperature (PIT) was applied to the chosen
system of nonionic emulsifiers and oil
phases in
order to find a suitable emulsifier. Two homologous series of nonionic
emulsifiers: nonylphenolpolyglycolethers with 230 ethoxy
units and polyglycolethers of fatty alcohols (C16C18) with 523 ethoxy units
were used as emulsifiers. Compounds of different chemical
structure were used as the oil phase: liquid paraffin, xylene, cyclohexane and
isooctane. The results were presented in
relation
to the corresponding HLB values. The results of the investigations indicated
that the mentioned method applied to certain
series of
nonionic emulsifiers enabled the selection of the group of emulsifiers suitable
for emulsification of a certain oil phase, but does
not give the possibility of finding the optimal one among them. A problem arose
in the visual determination of the PIT when working
with homologues having a higher number of ethoxy units in isooctane as the oil
phase. The temperatures of phase inversion
were too
high to be measured in this way. The opposite problem arose with visual
detection in the case of the system with
homologues
with a low number of ethoxy units in xylene as the oil phase. For these cases
it would be better to use some other way
of
detection. For the lower ethoxylates a linear dependence between the PIT and
the HLB value of the emulsifier was found for all the investigated systems, but placing the
corresponding values into an empirical equation which connects these values,
the expected result was not
obtained.
Key words: choice
of emulsifier, nonionic emulsifiers, phase inversion, temperature.
J. Serb. Chem.
Soc. 63(10) 773-779 (1998)
UDC 661.23:541.124.7:543.42
JSCS-2584
Original scientific paper
Energetics of the ionization and fragmentation
of sulfur-containing molecules studied by electron-impact spectroscopy. I. SO2F2
MIODRAG
B. MILETIC, OLIVERA M. NESKOVIC, MIOMIR V. VELJKOVIC and KIRO F. ZMBOV
Vinca Institute of Nuclear Sciences, Laboratory
for Physical Chemistry, P.O.Box 522, YU-11001 Belgrade, Yugoslavia
(Received
10 April, revised 1 July 1998)
The
positive ions produced by the dissociative ionization on SO2F2 were studied using a
trochoidal electron monochromator as an
electron
gun. The appearance energies of the fragment ions were measured and interpreted
in terms of possible fragmentation
mechanisms.
The results were used to determine the ionization energies and heats of
formation of the observed fragment species.
Key words:
mass spectrometry, electron impact, sulfur-containing molecules.
J.
Serb. Chem. Soc. 63(10) 781-791 (1998)
UDC 546.562' 732''/541.428.49/:547.824/.828
JSCS-2585
Original scientific paper
Carbonato, oxalato and malonato bridged Cu(II)
and Co(II) complexes with an octaazamacrocyclic ligand
ZORAN
M. MIODRAGOVIC, GORDANA VUCKOVIC, SOFIJA P. SOVILJ, DRAGAN D.MANOJLOVIC and
MIJAT J. MALINAR
Faculty of Chemistry, University of Belgrade,
P.O.Box 158, YU-11001 Belgrade, Yugoslavia
(Received 5
May, revised 30 June 1998)
Four new
Cu(II) and Co(II) complexes having an octaazamacrocyclic ligand derived from
cyclam, N,N'N,'',N'''-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane,
with either an m-carbonato, oxalato or malonato as the
additional
ligand were isolated and investigated by elemental analysis, electronic and IR
spectroscopy, as well as molar conductivity, magnetic
and cyclic voltammetry (CV) measurements. Their microbiological activity was
also tested. Binuclear or tetranuclear
structures,
depending on the bridging ligand and metal ion, was proposed.
Key words: Cu(II)
and Co(II) complexes, octaazamacrocycle, m-carboxylato ligands.
J.
Serb. Chem. Soc. 63(10) 793-804 (1998)
UDC 541.13/.138/66.021.3.081/:66.062.612
JSCS-2586
Original scientific paper
Mechanism and kinetics of the electrosorption
of acetate anions on the (111) face of silver
B.
M. JOVIC, D. M. DRAZIC* and V. D. JOVIC**
Institute of Technical Sciences SASA, P.O.Box
745, YU-11001 Belgrade,
*Center
of Electrochemistry ICTM, P.O.Box 815, YU-11001 Belgrade, and
**Center
for Multidisciplinary Studies University of Belgrade, P.O.Box 33, YU-11030
Belgrade, Yugoslavia
(Received
10 July 1998)
The
process of adsorption of acetate anions onto the (111) face of silver has been
investigated by analysis of the cyclic voltammetry and potentiostatic pulse results. It was shown,
by fitting the experimentally recorded q - E dependence, that the adsorption of acetate anions follows Frumkin adsorption
isotherm. The adsorbed structure was found to be less dense than a monolayer
and the process was characterized
by high value of the interaction parameter and the Gibbs energy of adsorption
(f = 10 and DG0ads,q-<0 = 57 kJ mol-1). From the slope of the Ep.a- log (c0) dependence it was
concluded that complete charge transfer between the adsorbed anions and the silver substrated
occurs. It was shown by analysis of the Ep,a - log n dependence in the region of
high sweep rates (n >>
10 V s1) that the
electrosorption process of acetate anions is a complex electrochemical
reaction, taking place through three steps.
The rate-determining step was found to be a third step, the chemical reaction
of CH3COOAg formation.
Key words: (111)
face of silver, acetate anions, complete charge transfer, Frumkin adsorption
isotherm, mechanism and kinetics of
electrosorption.
J.
Serb. Chem. Soc. 63(10) 805-815 (1998)
UDC 547.964.4:543.2
JSCS-2587
Original scientific paper
Determination of insulin-like growth factor-II
in human serum
J.
ANNA NIKOLIC, OLGICA NEDIC and ROMANA MASNIKOSA
INEP-Institute for the Application of Nuclear
Energy, Banatska 31 B, YU-11080 Zemun-Beograd, Yugoslavia
(Received
11 March 1998)
Insulin-like
growth factor-II (IGF-II) is a polypeptide mitogen present at relatively high
concentrations in the human peripheral
circulation.
The aim of the present investigation was to develop a reliable assay system for
determining total IGF-II, for use in studies of
the IGF system. A competitive binding assay was set up using a specific
monoclonal anti-IGF-II antibody and radioactively labelled
recombinant human IGF-II as the tracer. Displacement curves within the IGF-II
concentration range from 0.08 to 5.35 nmol/L were
obtained. Cross reactivity with IGF-I at 50% inhibition of tracer binding was
only 0.4%. Human serum samples were subjected
to
acid-ethanol extraction followed by neutralisation and cryoprecipitation in
order to remove interfering binding proteins before analysis. This was confirmed by the finding
that an excess of IGF-I added at a level below cross reacting concentrations to sequester residual binding proteins did not
affect the values obtained for IGF-II in relation to the standard curve. The
serum concentrations of total
IGF-II determined in three groups of healthy subjects (n = 53) were
similar to those recorded by other authors
and ranged
from 48 to 115 nmol/L. Mean (SD) recovery of IGF-II added to seven sera before
extraction was 102 (7.4)%. Intra-assay
precision
and inter-assay reproducibility were satisfactory. While IGF-II concentrations
in sera stored at 20°C were relatively stable for
several months, it was necessary to assay the extracts within 48 h of
preparation.
Key words: human
serum, IGF-II, radioimmunoassay, acid-ethanol extraction, binding proteins.
J. Serb. Chem.
Soc. 63(10) 817-821 (1998)
UDC 546.863:543.063/.064
JSCS-2588
Original scientific paper
A new kinetic reaction for determination of
ultramicro amounts of Sb(III)
RANGEL
P. IGOV, VIOLETA D. MITIC, TODOR G. PECEV and VESNA P. STANKOV-JOVANOVIC
Department of Chemstry, Faculty of Philosophy,
University of Nis, Cirila i Metodija 2, YU-18000 Nis, Yugoslavia
(Received
17. April, revised 7 July 1998)
A new
reaction is suggested and a new method is elaborated for the determination of
ultramicro amounts of Sb(III) based on its
inhibiting
effect on the oxidation of
s4-bisSn(dimethylamino)phenylCmethylene-2,5-cyclohexadiene-1-ilidenecdimethyl-ammonium chloride (crystal violet, CV) by H2O2. The method
sensitivity is 8×10-8 g/cm3. The relative error
was 6.7-12.8% for Sb(III) concentrations in the
interval 50×10-8 to 10×10-8 g/cm3. The kinetic equation
for this process are given. The influence of some other ions on the reaction rate was tested.
Key words: antimony,
kinetic determination, crystal violet.
J. Serb. Chem.
Soc. 63(10) 823-832 (1998)
UDC 669.017 - 546.46' 621''
JSCS - 2589
Original scientific paper
On the serrated yielding in AlMg6.5 alloy sheet
ENDRE ROMHANJI, MILJANA POPOVIC and VELIMIR
RADMILOVIC
Faculty of Technology and Metallurgy University
of Belgrade, Karnegijeva 4, P.O.Box 494,YU-11001 Belgrade, Yugoslavia
(Received 5
May 1998)
Room
temperature tensile tests were performed on AlMg6.5 alloy sheet, with initial
strain rates of 6.7×10-4 s-1, 6.7×10-3 s-1 and 6.7”102 s1,
after imposing 70% cold rolling reductions, and annealing at 320°C/3h. The
Portevin-Le Chatelier effect is the main mechanism of unstable plastic flow, caused by Mg solute-dislocation
interactions. Although, a comprehensive comparison of the energies of activation, relevant for serrated yielding,
revealed a wide range of values, calculations based on the used strain rates,
retained vacancy concentration
and the Mg solute diffusion coefficient at room temperature, indicate that
serrations are expected to appear
from the
start of plastic deformation. In other words, under the performed test
conditions, the Mg solute atoms are mobile enough for the majority of dislocations to travel in
conjunction with the Mg atmospheres. After deformation at a strain rate of
6.7×10-2 s-1 the "D" type serration observed, as a series of
successive not completely flat stress plateaus, indicates a complex deformation
process, affected by strain
hardening, coused by dislocation reactions and the propagation of a kind of
non-hardening deformation bands.
Key words: AlMg
alloy, serrated yielding, diffusion, activation energy, deformation behaviour.
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