This article presents a review of the kinetic studies on the cure reactions of thermosetting resins. The emphasis is placed on those conducted using the thermal analysis by differential scanning calorimetry. Two important categories of kinetic models are discussed and some existing parameter estimation techniques are presented. A variety of factors affecting the cure reactions, including the formulation of cure and process variables, are discussed. At the end, two different approaches in modeling the chemoviscosity of polymeric reactive systems are presented and some existing chemorheological models developed based on these approaches are briefly reviewed.

Thermoplastic vulcanized (TPV) nanocomposites were prepared in a laboratory mixer using EPDM, polypropylene of different viscosities, maleic anhydride modified polypropylene, an organo‐clay, and a sulfur‐based curing system. Based on the obtained results from X‐ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimeter, and mechanical properties, the microstructure of the prepared nanocomposites was found to be sensitive to the viscosity difference between the two phases and the clay content. X‐ray diffraction and TEM images of the TPV nanocomposites showed that clay was nearly exfoliated and randomly distributed into the polypropylene phase. The SEM photomicrographs of the dynamically vulcanized thermoplastic elastomer samples showed that the rubber particles were dispersed through the polypropylene in form of aggregates and their size increased with the introduction of clay. The nanoscale dimensions of the dispersed clay resulted in a significant improvement of the tensile modulus of the TPV nanocomposite samples, from 20 to 90% depending on clay content and the viscosity ratio of PP/EPDM. In the PP nanocomposites, the clay layers act as nucleating agents, resulting in higher crystallization temperature and reduced degree of crystallinity. Moreover, the oxygen permeability in the TPV nanocomposites was found to be lower than in unfilled but otherwise similar materials. POLYM. ENG. SCI., 47:207–217, 2007. © 2007 Society of Plastics Engineers.

The thermal and rheological properties of two types of metallocene-catalyzed linear low-density PEs (mLL-DPEs) and two LDPEs, as well as their blends, were studied using differential scanning calorimeter (DSC) measurements and rheometry. The DSC results showed that the mLLDPE-1 based on the hexene comonomer is immiscible with both LDPEs in crystalline states, whereas the mLLDPE-2 based on the octene comonomer is miscible with the LDPEs. This suggests that increasing the length of short chains in mLLDPEs can promote the miscibility of mLLDPE/ LDPE blends. The linear viscoelastic properties confirmed the immiscibility of the mLLDPE-1 with the LDPEs in the molten state, and the miscibility of mLL-DPE-2 with LDPEs. In addition, the Palierne [1] emulsion model provided good predictions of the linear viscoelastic data for both miscible and immiscible PE blends. However, as expected, the low-frequency data showed a clear influence of the interfacial tension on the elastic modulus of the blends for the immiscible blends. POLYM. ENG. SCI., 45:1254 -1264, 2005. © 2005 Society of Plastics Engineers

The morphological and rheological properties of thermoplastic elastomer nanocomposites (TPE nanocomposites) were studied using different viscosities of polypropylene (PP) and ethylene‐propylene‐diene monomer (EPDM) rubber content (20, 40, 60 wt%). The components, namely EPDM, PP, Cloisite 15A, and maleic anhydride‐modified PP as compatibilizer, were compounded by a one‐step melt mixing process in a laboratory internal mixer. The structure of the nanocomposites was characterized with X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and rheometry in small amplitude oscillatory shear. The distribution state of the clay between the two phases (PP and EPDM) was found to be dependent on the viscosity ratio of PP to EPDM. In the nanocomposites prepared based on low viscosity PP (LVP) and EPDM, the clay was mostly dispersed into the PP phase and the size of the dispersed rubber particles decreased in comparison with unfilled but otherwise similar blends. However, the dispersed elastomer droplet size in the high viscosity PP (HVP) blends containing 40 and 60% EPDM increased with the introduction of the clay. For TPE nanocomposites, the dependence of the storage modulus (G′) on angular frequency (ω) followed a clear nonterminal behavior. The increase in the storage modulus and the decrease in the terminal zone slope of the elastic modulus curve were found to be larger in the LVP nanocomposite in comparison with the HVP sample. The yield stress of nanoclay‐filled blends prepared with LVP increased more than that of HVP samples. The tensile modulus improved for all nanocomposites but a higher percentage of increase was observed in the case of LVP samples. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

In this paper, the performance of a new in‐line scanning camera system for the study of various bubble instabilities in film blowing extrusion is critically evaluated. Three commercial film‐grade polyethylenes, LmPE, LLDPE and LDPE, were used to generate the bubble instabilities. Reliable and objective criteria for differentiating various bubble instabilities such as draw resonance, helicoidal instability, and frost line height instability are proposed by using the new device. Detailed dynamics of each bubble instability was carefully investigated as a function of time in a broad range of the take‐up ratio (TUR), blow‐up ratio (BUR) and frost line height (FLH). In addition, effects of melt temperature and mass flow rates on dynamics of the bubble instabilities are discussed. It was found that the new system could capture the main characteristics of all bubble instabilities quantitatively. It was also found that magnitude and periodicity of radius variation during draw resonance of LmPE decreased as TUR increased at constant FLH and BUR. This implies that the origin of draw resonance in film blowing seems to be different from that observed in fiber spinning. In the case of helicoidal instability, eccentricity, which defines the deviation of the bubble center from the die center, decreased as TUR increased. However, the bubble could not be stabilized as expected. A graphical quantification approach to determine the stable zone in the bubble stability map is also discussed.

Bubble instabilities observed in film blowing using four different polyolefins are discussed: high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and polypropylene (PP). Special attention is given to the effect of the frost line height on the bubble stability, an effect mostly ignored in the literature. A video-camera system was used to record the bubble shape and oscillations. In general, three forms of instabilities and combinations were observed: (1) axisymmetric periodic variations in the bubble diameter; (2) helical motions of the bubble; and (3) variations in the position of the solidifcation line. The four resins show different stability behaviors. The LDPE has the most stable operating space and the PP is the most unstable one. No correlation was observed between bubble stability and oscillato y shear rheological properties of the resins. Instability is enhanced by increasing take-up ratio, increasing blow-up ratio, and decreasing frost line height. Furthermore, for the LDPE, some operating points were not attainable and multiple steady states were, observed. Our results are in a poor agreement with the predictions Cain and Denn's 1988 analysis.

A combination of the effective medium and the phonon approaches is used to investigate heat conduction in heterogeneous media composed of a homogeneous matrix in which spherical particles of micro and nanosizes are dispersed. In particular, we explore the effect of different types of scattering on the particle-matrix interface, temperature dependence of the effective heat conduction coefficient, and the effect of various degrees of agglomeration of the particles. Predictions calculated explicitly for Si nanoparticles dispersed in Ge matrix agree with available Monte Carlo simulations. Our predictions show that the higher is the temperature the lower is the heat conductivity and the smaller is the influence of the details of the particle-matrix interactions. As for the influence of the agglomeration, we predict both decrease and increase of the heat conduction depending on the degree of the agglomeration.

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