Thermal degradation of natural rubber/ZNO nanocomposites

Nanoparticies have been widely used to enhance the properties of natural rubber (NR). In the present paper a novel nanocomposite was developed by blending nano-ZnO slurry with prevulcanized NR latex, and the thermal degradation process of pure NR and NR/ZnO nanocomposites with different nano-ZnO loading was studied with a Perkin Elemer TGA-7 thermogravimetric analyzer. The thermal degradation parameters of NR/ZnO (2 parts ZnO per hundred dlY rubber) at different heating rates (Bs) were studied. The results show that the thermal degradation of pure NR and NR/ZnO nanocomposites in nitrogen is a one-step reaction. The degradation temperatures of NR/ZnO nanocomposite increase with an increasing B. The peak height (R_p) on the differential thermogravimetric curve increases with the increase of B. The degradation rates are not affected significantly by B, and the average values of thermal degradation rate C_p and C_f are 44.42 % and 81.04 %, respectively. The thermal degradation kinetic parameters are calculated with Ozawa-Flynn-Wall method. The activation energy (E) and the frequency factor (A) vary with ecomposition degree, and can be divided into three phases corresponding to the volatilization of low-molecular-weight materials, the thermal degradation ofNR main chains and the decomposition of residual carbon.

Thermal degradation kinetics and morphology of natural rubber/silica nanocomposites

A novel natural rubber/silica (NR/SiO₂) nanocomposite with a SiO₂ loading of 4 wt% is developed by incorporating latex compounding with self-assembly techniques. The SiO₂ nanoparticles are homogenouslydistributed throughout the NR matrix as spherical nano-clusters with an average size of 75 nm. In comparison with the host NR, the thermal resistance of the nanocomposite is significantly improved. The degradation temperatures (T), reaction activation energy(E), and reaction order (n) of the nanocomposite are markedly higher than those of the pure NR, due to significant retardant effect of the SiO₂ nanoparticles.

Poly (vinyl alcohol) / silica nanocomposites: morphology and thermal degradation kinetics

The morphology of self-assembled poly(vinyl alcohol)/silica (PVA/SiO₂) nanocomposites is investigated with atomic force microscopy (AFM) and transmission electron microscopy (TEM). It is found that the SiO₂ nanoparticles are homogenously distributed throughout the PVA matrix in a form of spherical nano-cluster. The average size of the SiO₂ clusters is below 50 nm at the low contents (SiO₂ ≤ 5 wt%), while particle aggregations are clearly observed and their average size markedly increases to 110 nm when 10 wt% SiO₂ is loaded. The thermogravimetric analysis (TGA) shows that the nanocomposite significantly outperforms the pure PVA in the thermal resistance. By using a multi-heating-rate method, the thermal degradation kinetics of the nanocomposite with a SiO₂ content of 5 wt% is compared to the PVA host. The reaction activation energy (E) of the nanocomposite, similar to the pure PVA, is divided into two main stages corresponding to two degradation steps. However, at a given degradation temperature, the nanocomposite presents much lower reaction velocity constants (k), while its E is 20 kJ/mol higher than that of the PVA host.

Optimization of polymerization conditions and thermal degradation of conducting polypyrrole coated polyester fabrics

PET fabric is coated with conducting polypyrrole (PPy) by oxidative polymerization from an aqueous solution of Py using ferric chloride hexahydrate (FeCl3) as oxidant and p-toluene sulphonate (pTSA) as dopant. The optimum concentrations for Py, FeCl3 and pTSA were found to be 0.11, 0.857 and 0.077 mol/l respectively, which yielded a conductive fabrics with resistivity as low as 72 Ω/sq. PPy fabric gained resistivity less than one order of magnitude when aged for 18 months at room temperature. The stabilizing effect of the dopant pTSA against thermal degradation was demonstrated; the undoped samples reached resistivity of around 40 kΩ, whereas doped samples reached less than 2 kΩ at the same temperature and time.

Thermal degradation kinetics and mechanism of epoxidized natural rubber

Thermal resistance is one of the most dominative properties for polymer materials. Thermal degradation mechanisms of epoxidized natural rubber (ENR) and NR are studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The results show that, the introduction of epoxy groups into the NR molecular main chain leads to a remarkable change in the degradation mechanism. The thermal stability of ENR is worse than that of NR. For the first thermooxidative degradation stage, the thermal decomposition mechanism of ENR is similar to that of NR, which corresponds to a mechanism involving one-dimensional diffusion. For the second stage, the thermal decomposition mechanism of ENR is a three-dimensional diffusion, which is more complex than that of NR. Kinetic analysis showed that activation energy (E?), activation entropy (?H) and activation Gibbs energy (?G) values are all positive, indicating that the thermooxidative degradation process of ENR is non-spontaneous.

Kinetic model of poly(3-hydroxybutyrate) thermal degradation from experimental non-isothermal data

The non-isothermal data given by TG curves for poly(3-hydroxybutyrate) (PHB) were studied in order to obtain a consistent kinetic model that better represents the PHB thermal decomposition. Thus, data obtained from the dynamic TG curves were suitably managed in order to obtain the Arrhenius kinetic parameter E according to the isoconversional F-W-O method. Once the E parameters is found, a suitable logA and kinetic model (f(alpha)) could be calculated. Hence, the kinetic triplet (E +/- SD, logA +/- SD and f(alpha)) obtained for the thermal decomposition of PHB under non-isothermal conditions was E=152 +/- 4 kJ mol(-1), logA=14.1 +/- 0.2 s(-1) for the kinetic model, and the autocatalytic model function was: f(alpha)=alpha(m)(1-alpha)(n)=alpha(0.42)(1-alpha)(0.56).

Thermal degradation of a composite solid propellant examined by DSC - Kinetic study

The thermal decomposition of ammonium perchlorate (AP)/hydroxyl-terminated-polybutadiene (HTPB), the AP/HTPB solid propellant, was studied at different heating rates in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) in non-isothermal conditions. The Arrhenius Parameters were estimated according to the Ozawa method. The calculated activation energy was 134.5 W mol(-1), the pre-exponential factor, A, was 2.04.10(10) min(-1) and the reaction order for the global composite decomposition was estimated in 0.7 by the kinetic Shimadzu software based on the Ozawa method. The Kissinger method for obtaining the activation energy value was also used for comparison. These results are discussed here.

Thermal degradation of geomembranes after exposure to heat

HDPE and PVC geomembranes are sensitive to changes in their properties when in contact with high temperatures. The effects of hot temperature on polymeric geomembranes are assessed by the ASTM D794 and ASTM D5721.This paper brings an analysis of degradation of the Poly Vinyl Chloride (PVC) and High Density Poly Ethylene (HDPE) geomembranes when exposed to conventional and air oven after specific periods.. Mechanical and physical properties were evaluated. OIT tests were also performanced to evaluate the level of oxidation degradation occurred on the HDPE geomembranes. Geomembranes of two thicknesses were tested: 1.0, 2.0 nun (PVC) and 0.8, 2.5 mm, (HDPE). The results obtained show, for example, that after the last period of exposure, the PVC geomembranes (1.0, 2.0 mm) were more rigid and stiffer than fresh samples. The HDPE geomembranes, on the other hand, when exposed to heat presented increases in deformation. OIT tests showed efficient to detect some level of degradation on the HDPE geomembranes.

Nonoxidative thermal degradation kinetic of polyamide 6,6 reinforced with carbon nanotubes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Thermal degradation and lifetime estimation of poly(ether imide)/carbon fiber composites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Thermal degradation of both latex and latex cast films forming membranes: combined TG/FTIR investigation

Latex collected from natural rubber trees forming membranes can be used as biomaterials in several fields being the temperature a key parameter. Thermogravimetry (TG) coupled to Fourier transform infrared spectroscopy (FTIR) is a useful technique to investigate the thermal degradation of both latex and cast films (membranes), wich were obtained from Hevea brasiliensis (RRIM 600 clone) and used without stabilization. The membranes were prepared by casting the latex onto a glass substrate at 65 degrees C for 6 h. The thermal degradation was followed by FTIR spectra acquisition along the process, allowing the identification of the gaseous components evolved upon the thermal treatment. According to TG measurements, the main processes of thermal degradation of the latex and membranes occur at three temperature intervals for both.

Kinetic study of the decompositions involved in the thermal degradation of commercial azodicarbonamide

The transitions and reactions involved in the thermal treatment of several commercial azodicarbonamides (ADC) in an inert atmosphere have been studied by dynamic thermogravimetry analysis (TGA), mass spectrometry and Fourier transform infrared (FTIR) spectroscopy. A pseudo-mechanistic model, involving several competitive and non-competitive reactions, has been suggested and applied to the correlation of the weight loss data. The model applied is capable of accurately representing the different processes involved, and can be of great interest in the understanding and quantification of such phenomena, including the simulation of the instantaneous amount of gases evolved in a foaming process. In addition, a brief discussion on the methodology related to the mathematical modeling of TGA data is presented, taking into account the complex thermal behaviour of the ADC.

Development of a novel pyrolysis-gas chromatography/mass spectrometry method for the analysis of poly(lactic acid) thermal degradation products

Thermal degradation of PLA is a complex process since it comprises many simultaneous reactions. The use of analytical techniques, such as differential scanning calorimetry (DSC) and thermogravimetry (TGA), yields useful information but a more sensitive analytical technique would be necessary to identify and quantify the PLA degradation products. In this work the thermal degradation of PLA at high temperatures was studied by using a pyrolyzer coupled to a gas chromatograph with mass spectrometry detection (Py-GC/MS). Pyrolysis conditions (temperature and time) were optimized in order to obtain an adequate chromatographic separation of the compounds formed during heating. The best resolution of chromatographic peaks was obtained by pyrolyzing the material from room temperature to 600 °C during 0.5 s. These conditions allowed identifying and quantifying the major compounds produced during the PLA thermal degradation in inert atmosphere. The strategy followed to select these operation parameters was by using sequential pyrolysis based on the adaptation of mathematical models. By application of this strategy it was demonstrated that PLA is degraded at high temperatures by following a non-linear behaviour. The application of logistic and Boltzmann models leads to good fittings to the experimental results, despite the Boltzmann model provided the best approach to calculate the time at which 50% of PLA was degraded. In conclusion, the Boltzmann method can be applied as a tool for simulating the PLA thermal degradation.