Observations are reported for oscillatory torsion tests at several temperatures ranging from room temperature to 100 °C on a polymer composite consisting of a polycarbonate matrix reinforced with short glass fibers. Constitutive equations are derived for the linear viscoelastic behavior of the polymer composite, which is treated as an equivalent heterogeneous network of chains bridged by junctions (entanglements and glass fibers). The network is thought of as an ensemble of meso‐regions with arbitrary shapes and sizes. With reference to the concept of cooperative relaxation, the time‐dependent response of an ensemble is associated with the rearrangement of meso‐domains. The rearrangement events occur at random times as meso‐regions are agitated by thermal fluctuations. Stress–strain relations for isothermal deformation of an ensemble of meso‐domains are derived by using the laws of thermodynamics. The governing equations are determined by five adjustable parameters that are found by fitting the experimental data. The effects of temperature and filler content on the material parameters are studied in detail.The shear modulus G GPa versus the content of short glass fibers ν wt.‐%. Symbols: treatment of observations in oscillatory torsion tests at T = 25 (unfilled circles) and T = 100 °C (filled circles). Solid lines: approximation of the experimental data by Equation (27). Curve 1: G0 = 1.05, G1 = 3.83 × 10−2. Curve 2: G0 = 0.91, G1 = 3.65 × 10−2.imageThe shear modulus G GPa versus the content of short glass fibers ν wt.‐%. Symbols: treatment of observations in oscillatory torsion tests at T = 25 (unfilled circles) and T = 100 °C (filled circles). Solid lines: approximation of the experimental data by Equation (27). Curve 1: G0 = 1.05, G1 = 3.83 × 10−2. Curve 2: G0 = 0.91, G1 = 3.65 × 10−2.
Different crystallization kinetic models (Avrami and Tobin) have been applied to study the crystallization kinetics of virgin poly(butylene terephthalate) (PBT) and filled PBT systems under isothermal experimental conditions. The experimental data have been analyzed with a nonlinear, multivariable regression program. The kinetic parameters for the isothermal crystallization have been determined. The analysis results indicate that both models satisfactorily represent the isothermal crystallization kinetics. PBT crystallizes most slowly. The presence of nanoclays or nanofibers, added as fillers, enhances the crystallization rate of PBT composites. An analysis of the kinetic data with the Avrami and Tobin models has shown little change in the crystallization exponent compared with that of virgin PBT. The crystallization rate constant decreases with a rise in the temperature for the two models. This trend has been observed for similar polyester systems reported in the literature. The dispersion of the clay layers in the PBT nanocomposites has been characterized with wide-angle X-ray diffraction and transmission electron microscopy.
Abstract. Different kinetic models like the Avrami, Tobin and Urbanovici-Segal models have been applied for determining the isothermal crystallization kinetics of virgin poly(ethylene terephthalate) (PET) and PET/poly(methyl methacrylate) (PMMA) blends. The different compositions investigated were PET90/PMMA10, PET75/PMMA25 and PET50/PMMA50 [wt/wt%]. The experimental data was fitted using Solver, a non-linear multi-variable regression program and linearization method. The effect of composition variation of PET/PMMA on parameters like crystallization rate constant and crystallization exponent were investigated. Urbanovici-Segal and Avrami models gave the best fit to the experimental data. Tobin model does not seem to fit the experimental data for the systems under investigation. Experimental results indicated that the crystallization rate constant values increased with decreasing temperatures.
The current work seeks to develop a novel polymeric blend containing polycarbonate(PC)/poly(trimethylene‐terephthalate)(PTT)/poly(butylene‐terephthalate)(PBT), (50: 25:25, weight/weight percent). This has been prepared using a single screw extruder. The thermal degradation kinetics of the blend and neat polymers have been investigated by means of a Theromogravimetric analyzer (TGA) machine. Theromogravimetric analysis of the neat polymers and the blend was carried out at 5, 10, 15, and 20°C/min under Nitrogen and air atmosphere. Two analytical models, namely Kissinger and Ozawa were used to estimate the degradation kinetic parameters (Activation energy, E and pre‐exponential factor, A). The neat polymers were found to be more thermally stable under nitrogen than under air. The solid state decomposition was found to follow a phase boundary controlled mechanism. Possibility of transexchange reactions during melt blending was also analyzed using TGA studies. Residual char of blends of different compositions were also used as an indicator to determine possible exchange reactions. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.
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