Some synergistic effects of antioxidants in natural rubber were investigated considering results obtained by differencial
scanning calorimetry (DSC). Rubber formulations were obtained with mixtures of diaminic(DPPD, IPPD, HPPD) and monoaminic (ADPA,
PBN) stabilizers and evaluated. The samples containing the mixture diamine/ADPA stabilizers showed synergistic effects while,
for those containing diamine/PBN, no effect was observed. Additionally, the diffusion constants determined by use of vulcanized
rubber disks confirmed the molar mass dependence of the stabilizer.
The thermal behavior of chitosan (CS)/natural rubber latex (NRL) blends has been studied by thermogravimetry (TG) and differential
scanning calorimetry (DSC). Decomposition behavior of CS changes with the addition of NRL. The effect of blend composition
on the amount of residue remaining at various temperatures has been studied. Activation energies of degradation have been
calculated using Horowitz-Metzger equation. From the activation energy values, it is found that among the series of the blend
compositions, CS15NRL85 exhibits better thermal stability. DSC studies reveals that the CS/NRL blends are thermodynamically incompatible. This is
evident from the presence of two glass transitions, corresponding to CS and NRL phases in the blend.
Authors:S. Ľalíková, M. Pajtášová, M. Chromčíková, M. Liška, V. Šutinská, M. Olšovský, D. Ondrušová, and S. C. Mojumdar
) spectrometer Tensor 27 in the region 4000–400 cm −1 with a resolution of 4 cm −1 .
Preparation of naturalrubber (NR)/clay composites
Naturalrubber SMR-20 was used as the elastomeric matrix. Carbon black N660 was used as
injection moulding process has been somewhat neglected and the production relied mostly upon experience [ 2 , 7 , 8 ]. Although, naturalrubber (NR) is one of the most widely used rubbers to produce diversified injection-moulded rubber products, the
Authors:R. Simoes, M. Rodriguez-Perez, J. de Saja, and C. Constantino
investigated as a bioactive material for enhancing bone regeneration and vascular prostheses [ 10 , 17 , 18 ].
The naturalrubber latex (NR) obtained from the Hevea brasiliensis trees [ 19 ] is essentially composed by poly cis-1,4-isoprene, besides
Epoxidized natural rubbers (ENRs) with different extents of epoxidation (B) were prepared under various reaction conditions. The effects of the amount of H2O2 and the reaction time on B are discussed. The glass transition temperature Tg, the thermal degradation temperature and the activation energy of thermal degradation of the ENRs increase with B. The results indicate that the thermal stability of the ENRs increases with B.
In view of the lack of precise experimental data in the literature concerning the determination of a definedTg value for natural rubber (NR) and the differences when such data are given, a reference definition ofTg(Vo) is offered and a procedure for obtaining it described in detail.
Authors:C. V. Chaudhari, Y. K. Bhardwaj, and S. Sabharwal
Grafting ofmethyl methacrylate (MMA) on radiation crosslinked natural rubber (NR) film has been investigated by mutual radiation
grafting. The effect of experimental parameters like radiation dose, dose-rate, additives like acids and inorganic salts,
solvents, monomer concentration, cross-linking density of the natural rubber film on the grafting extent has been studied.From
the kinetic studies, a kinetic equation showing almost parabolic and linear dependence of grafting on concentration and dose
rate, respectively, was deduced.Preliminary thermal stability studies of grafted films indicated that grafting of MMA does
not enhance the thermal stability of NR.
Differential Scanning Calorimetry (DSC) is employed to study the changes in enthalpy of natural rubber latex samples when
heated under a controlled temperature program. It is found that the mass normalized areas of the DSC curves between room temperature
and 170 °C for different latex samples are inversely proportional to the dry rubber content (DRC) of the samples, measured
following the weighing and drying method. The changes in total enthalpy of the samples in this temperature range are interpreted
as due to the variations in the quantity of water present in the samples. The measurements have been repeated by diluting
selected samples with known quantities of water, and it is found that the normalized areas of the DSC curves are directly
proportional to the amount of water added to the latex. The method can be used to estimate the DRC of natural rubber latex
accurately. Its advantages and limitations are discussed.
Authors:Eliton Medeiros, Patrini Galiani, Rogerio Moreno, Luiz Mattoso, and José Malmonge
Due to the increasing search for alternative sources of natural rubber (NR) whose properties are similar to Hevea brasiliesis, several sources have been studied in the past few years. Among them, Mangabeira (Hancornia speciosa Gomes), which is native to Amazon rainforest and other regions of Brazil, has a potential as another viable rubber source.
As a continuation of a series of comparative studies between Hancornia and Hevea (clone RRIM 600) these two species by our research team, their thermal behavior was analyzed by thermogravimetry (TG) using
Flynn–Wall–Ozawa’s approach in order to obtain kinetic parameters (reaction order, pre-exponential factor and activation energy)
of the decomposition process. Results indicated that the thermal behavior of NR from Hancornia was comparable to Hevea with some differences observed as follows: reaction order for Hancornia was higher than for Hevea at the beginning of degradation and very close for temperatures over 350 °C; activation energy and pre-exponential factor
had the same trend, i.e., increased with increasing degree of conversion remaining almost constant between 20 and 70% and
then increasing for higher degrees, although Hevea was slightly more thermally stable than Hancornia. These major influences in the degradation process in the early stage are attributed to differences in non-rubber constituents
present in these two species.